Jim Walworth

Interests

Teaching

Soil Science, Soil Fertility, Plant Nutrition

Research

Nutrient Management, Soil Fertility, Pecans, Turf grass, Vegetables, Salinity, Soil Management

Courses

Scholarly Contributions

Chapters

• Faber, B., Walworth, J. L., Giraud, D. D., & Silva, D. (2017). Soil and Fertilizer Management. In California Master Gardener Handbook, Second Edition(pp 37-82). Richmond, CA: University of California Agriculture and Natural Resources.
• Farrell-Poe, K. L., Walworth, J. L., & Pabedinskas, V. (2016). Backyard Composting. In Arizona Master Gardener Manual(p. 11). Arizona Cooperative Extension.
• Pabedinskas, V., Walworth, J. L., & Farrell-Poe, K. L. (2016). Backyard Composting. In Arizona Master Gardener Manual(p. 11). Arizona Cooperative Extension.
• Walworth, J. L., Nunez-Moreno, H., & Pond, A. (2015). Soil Zinc Fertilization in One-Year-Old Potted 'Wichita' Pecan Trees in Alkaline Soil. In International Symposium on Pecans and Other Carya in Indigenous and Managed Systems. International Society for Horticultural Science. doi:10.17660/ActaHortic.2015.1070.8

Journals/Publications

• Wang, Y., Heerema, R. J., Walworth, J. L., Dungan, B., Van Leeuwen, D., & Holguin, F. O. (2020). Nutraceutical Properties of Pecan Kernels Are Affected by Soil Zinc Fertilizer Application. HortScience, 55(12), 2001-2007. doi:https://doi.org/10.21273/HORTSCI15314-20
• Walworth, J. L., Comeau, M. J., Sherman, J. D., Potter, M. T., VanLeeuwen, D., & Heerema, R. J. (2016). Leaf Photosynthesis of Immature 'Wichita' pecan trees is Improved by Soil-Application of Zinc-EDTA (20%). American Society for Horticultural Science, 35.
• Heerema, R. J., VanLeeuwen, D., Potter, M. T., Sherman, J. D., Comeau, M. J., & Walworth, J. L. (2016). Leaf Photosynthesis of Immature 'Wichita' pecan trees is Improved by Soil-Application of Zinc-EDTA (20%). American Society for Horticultural Science, 142(1), pp. 27-35.
• Heerema, R. J., VanLeeuwen, D., Potter, M. T., Sherman, J. D., Comeau, M. J., & Walworth, J. L. (2016). Leaf Photosynthesis of Immature 'Wichita' pecan trees is Improved by Soil-Application of Zinc-EDTA. American Society for Horticultural Science, 35.
• Pessarakli, M., Pessarakli, M., Breshears, D. D., Breshears, D. D., Walworth, J. L., Walworth, J. L., Field, J. P., Field, J. P., Law, D. J., & Law, D. J. (2017). Candidate halophytic grasses for addressing land degradation: Shoot responses of Sporobolus airoides and Paspalum vagenitum to weekly increasing NaCl concentration. Arid Land Research and Management, 31(2), 169-181.
• Walworth, J. L., Comeau, M. J., & Heerema, R. J. (2017). Soil-Applied ZnEDTA: Vegetative Growth, Nut Production and Nutrient Acquisition of Immature Pecan Trees Grown in an Alkaline, Calcareous Soil. HortScience, 52(2), 301-305.
• Walworth, J. L., Comeau, M. J., Sherman, J. D., Potter, M. T., VanLeeuwen, D., & Heerema, R. J. (2017). Leaf Photosynthesis of Immature 'Wichita' pecan trees is Improved by Soil-Application of Zinc-EDTA (20%). American Society for Horticultural Science, 142(1), pp. 27-35.
• Hafsteinsdottir, E. G., Rocavert, A. L., Camenzuli, D., Walworth, J. L., & Gore, D. B. (2015). Chemical immobilization of metals and metalloids by phosphates. Applied Geochemistry, 59, 47-62.
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  Remediation of metal contaminated media using orthophosphate fixation forms insoluble and non-bioavailable salts from metal and phosphate sources. The main focus has been on fixation of Pb, where the formation of pyromorphite, the most insoluble lead phosphate, has shown the great potential of this remediation technique. Other metals (Ba, Cd, Co, Cu, Eu, Ni, U, Zn) also have potential for effective fixation by orthophosphate. We review the applicability of the treatment across wider environmental conditions, particularly in surface soil, its use with elements other than Pb, product stability and efficiency with mixed contaminants.
• Walworth, J. L., Harvey, P., & Snape, I. (2013). Low Temperature Soil Petroleum Hydrocarbon Degradation at Various Oxygen Levels. Cold Regions Science and Technology, 96, 117-121.
• Walworth, J., Harvey, P., & Snape, I. (2013). Low temperature soil petroleum hydrocarbon degradation at various oxygen levels. Cold Regions Science and Technology, 96, 117-121.
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  Abstract: A laboratory incubation study was conducted on a petroleum-contaminated soil from Macquarie Island in sub-Antarctic Australia to develop a target O2 level for bioventing. The soil was amended with NH4NO3 (175mg Nkg-1 soil) and 14C-hexadecane (250mgkg-1 soil) and placed in sealed respirometry chambers. The headspaces in the chambers were adjusted to 0, 1, 2.6, 5.2, 10.5, and 20.9% O2. Each chamber was connected to an NaOH CO2 trap and to an O2 feed line (except the 0% O2 chambers were connected to an N2 feed line). Chambers were supplied with O2 in response to pressure drop resulting from CO2 trapping. Soils were incubated at 6°C for 12weeks. O2 consumption and petroleum degradation were maximized in chambers with 10.4% O2. There was a slight decline in both O2 consumption and petroleum degradation at 20.9% O2. As O2 concentrations declined below 10.4% O2 both O2 consumption and petroleum degradation declined markedly. 14C collected in the CO2 traps did not follow this pattern, but was greater in the 1% O2 chambers than in 2.6 or 5.2% O2 chambers. Nitrogen remaining at the conclusion of the study indicated that nitrate was completely consumed in the 0, 1, 2.6, and 5.2% O2 chambers. nC17:pristane and nC18:phytane ratios in the soil at the conclusion of the incubation were significantly lower in the 10.4% O2 chambers than in those with 20.9% O2, and more petroleum hydrocarbons were consumed in the 10.4% chambers. Preferential degradation of pristane and phytane in the presence of limited O2 may be the result of denitrification, evidenced by lower residual nitrate levels in the 10.4 than the 20.9% O2 environment. Ten percent O2 is suggested as a target for O2 enhanced bioremediation. © 2013.
• Núñez-Moreno, H., Walworth, J. L., & Pond, A. P. (2012). Field identification and characterization of manganese toxicity in 'Western Schley' pecan trees. Acta Horticulturae, 938, 291-298.
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  Abstract: Adult 'Western Schley' pecan trees with delayed budbreak and dieback of current year's shoots during and immediately following budbreak were observed in a pecan orchard located in Cochise County in Southeast Arizona. Soil and leaf tissue analyses indicated that this condition was a result of Mn toxicity. Leaf and soil were sampled from trees with varying degrees of toxicity symptoms during the period from 2004 to 2007. In the spring of 2008 twenty trees with different grades of delayed budbreak were classified as unaffected, moderately affected, and severely affected according to the intensity of the disorder to determine leaf Mn concentration and content, leaf area, leaf weight, shoot growth, fruiting shoot percentage, and fruits per cluster corresponding to these conditions. Severely affected trees had higher leaflet Mn concentration (4034 ± 1482 ppm) as compared with unaffected trees (1620 ± 646 ppm). Fruiting shoot percentage was reduced from 86 ± 8.4 % in unaffected trees to 7 ± 6.2% in severely affected trees. Shoot growth and leaf area were also influenced. Severity of the disorder increased as soil pH decreased (down to 5.26) and diethylene triamine pentaacetic acid (DTPA) extractable Mn increased (up to 42 ppm). By midsummer, leaf size and weight were similar in severely affected and unaffected trees. Chlorophyll index was not affected by the intensity of the disorder. During budbreak, trees with leaf Mn less than 1620 ± 646 ppm had a normal growth and reproductive characteristics. Trees with leaf Mn concentrations higher than 2782 ± 1203 ppm in May had reduced shoot growth (reduced from 13 ± 4.2 to 2 ± 0.8 cm) and the percentage of shoots with fruit was reduced from 86 ± 8.4 to 7 ± 6.2.
• , H., Walworth, J., & Pond, A. (2011). Field Identification and Characterization of Manganese Toxicity in Western Schley Pecan Trees. Acta Horticulturae (ISHS), 938, 291-298.
• , J., Walworth, J., Brown, P., & Kopec, D. (2011). Deficit Irrigation of Seashore Paspalum and Bermudagrass. Agronomy Journal, 103, 1567-1577.
• McLain, J., Rock, C., Lohse, K., & Walworth, J. (2011). False Positive Identification of E. coli in Treated Municipal Wastewater and Wastewater-Irrigated Soils. Canadian Journal of Microbiology, 57(10), 775-784.
• Mclain, J. E., Rock, C. M., Lohse, K., & Walworth, J. (2011). False-positive identification of escherichia coli in treated municipal wastewater and wastewaterirrigated soils. Canadian Journal of Microbiology, 57(10), 775-784.
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  PMID: 21936679;Abstract: The increasing use of treated wastewater for irrigation heightens the importance of accurate monitoring of water quality. Chromogenic media, because they are easy to use and provide rapid results, are often used for detection of Escherichia coli in environmental samples, but unique levels of organic and inorganic compounds alter the chemistry of treated wastewater, potentially hindering the accurate performance of chromogenic media. We used MI agar and molecular confirmatory methods to assess false-positive identification of E. coli in treated wastewater samples collected from municipal utilities, an irrigation holding pond, irrigated soils, and in samples collected from storm flows destined for groundwater recharge. False-positive rates in storm flows (4.0%) agreed closely with USEPA technical literature but were higher in samples from the pond, soils, and treatment facilities (33.3%, 38.0%, and 48.8%, respectively). Sequencing of false-positive isolates confirmed that most were, like E. coli, of the family Enterobacteriaceae, and many of the false-positive isolates were reported to produce the b-D-glucuronidase enzyme targeted by MI agar. False-positive identification rates were inversely related to air temperature, suggesting that seasonal variations in water quality influence E. coli identification. Knowledge of factors contributing to failure of chromogenic media will lead to manufacturer enhancements in media quality and performance and will ultimately increase the accuracy of future water quality monitoring programs.
• Artiola, J. F., & Walworth, J. L. (2009). Irrigation water quality effects on soil carbon fractionation and organic carbon dissolution and leaching in a semiarid calcareous soil. Soil Science, 174(7), 365-371.
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  Abstract: Irrigation water quality and soil organic matter content influence crop yields and soil properties such as salinity and soil particle aggregation. We used laboratory column and batch studies and soil carbon fractionation to study potential organic carbon (OC) losses from a Typic Torrifluvent with 0.79% total OC and 4.7% inorganic carbon ([IC] as carbonates). About 4% of the total OC fraction was determined to be water-soluble OC (SOC). Under saturated flow, a significant amount of SOC (20%-35%) was lost from this soil (Pima clay loam) with just two pore volumes of irrigation water. Sodium- and sulfate-rich waters and rainwater were up to twice as effective at releasing SOC as waters dominated by calcium and chloride ions. Not all OC losses can be attributed to well-known soil particle dispersive effects of sodium and rainwater. Soluble OC losses were also highly correlated to the progressive dissolution of the soil IC fraction. Water quality has a measurable impact on OC and IC losses from OC-poor carbonate-rich soils. Changes in irrigation water quality may increase OC leaching from the plow layer and favor increased denitrification and potentially carbon sequestration in and below the root zone of irrigated semiarid soils. © 2009 Lippincott Williams & Wilkins.
• Núñez-Moreno, H., Walworth, J. L., & Pond, A. P. (2009). Manure and soil zinc application to 'Wichita' pecan trees growing under alkaline conditions. HortScience, 44(6), 1741-1745.
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  Abstract: The effect of cattle manure or combined manure and zinc (Zn) application on Zn uptake, mineral composition, and yield and nut quality in pecan trees [Carya illinoinensis (Wangenh.) C. Koch] was evaluated. In 2006, treatments evaluated were: manure (12 ton/ha; M), manure plus Zn (12 ton/ha plus 129 kg Zn/ha as ZnSO4; MZ), and an untreated control. During 2007, two more treatments were added with doubled manure and Zn rates. New treatments were manure 2× (24 ton/ha; M2) and manure 2× plus Zn 2× (24 ton/ha plus 258 kg Zn as ZnSO4; M2Z2). Manure was broadcast on the soil in a 2.5-m wide band 2 m from the trunk. Zinc sulfate was broadcast over the manure, and then manure and Zn were disked into the top 10 cm of soil. In 2008, in five of nine sampling dates, significant treatment effects were detected on leaf Zn concentrations. On all of the dates, M2Z2 had the highest foliar Zn levels. During the Summer 2008 (17 July) foliar Zn in M2Z2, treatment reached 66 μg·g-1; the control treatment level was 45 μg·g-1. Nut yields were higher in treatments receiving manure, with or without Zn in the first year, and highest in the untreated control the second year. No differences were observed in trunk growth, leaf area, leaf weight, or nut growth. Kernel percentages were over 61.4 in the 3 years of study in all treatments. Largest differences among treatments in nut size were found in 2007; nut weight in the control treatment was 7.5 g per nut and in M was 8.0 g per nut. Nut weight was smaller during 2008 when nut yield was high, and the untreated control nuts were smaller than those from treated trees. The manure and manure plus Zn treatments increased foliar Zn levels in pecan trees after 3 years of annual applications. In 2008, significant differences in leaflet Zn concentration among treatments were detected with M2Z2 having the highest concentrations.
• Núñez-Moreno, H., Walworth, J. L., Pond, A. P., & Kilby, M. W. (2009). Soil zinc fertilization of 'Wichita' pecan trees growing under alkaline soil conditions. HortScience, 44(6), 1736-1740.
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  Abstract: The effect of soil banding zinc sulfate and zinc (Zn)-EDTA was evaluated over a period of 4 years on established 'Wichita' pecans [Carya illinoinensis (Wangenh.) K. Koch] growing in alkaline, calcareous soil. Treatments evaluated were ZnSO4 applied at 74 kg Zn/ha and Zn-EDTA at 19 kg Zn/ha. These materials were applied just once on 23 Mar. 2005. Fertilizers were injected in two bands placed 1.2 m from either side of the trunk of the tree and 18 cm deep. Treatments were replicated four times in a randomized complete block design. Data collected included foliar Zn concentrations throughout the season, midseason foliar nutrient concentrations, leaflet growth, nut yield, and nut quality. Significant differences in foliar Zn levels were found 1 month after application of Zn-EDTA. Differences also were noted during the next 3 years on ≈ 25% of the sampling dates. Yields of in-shell pecans averaged 2800 kg·ha-1 during the 3 years of harvest but were unaffected by treatments. Nut quality also was unaffected. Nut kernel percentage was very high, ranging from 61.2% to 63.6% during the study. Growth, measured as leaflet area and trunk cross-sectional area, was unaffected by Zn application. Chlorophyll index ranged from 47.5 to 48.0 in 2007 and from 44.7 to 45.4 in 2008 and was unaffected by applied treatments. Zn-EDTA increased Zn uptake slightly by 'Wichita' pecan trees in alkaline, calcareous conditions during 3 years after one soil band injection. Ongoing research on potted pecan trees (with the same soil used in the present study) suggests that Zn-EDTA can very effectively increase Zn uptake if placed in close proximity to the tree roots. Additional research is needed to refine application and placement methods in these types of soils to produce a more effective and consistent response.
• Al-Ismaily, S. S., & Walworth, J. L. (2008). Effects of osmotic and matric potentials on nitrogen mineralization in unamended and manure-amended soils. Soil Science, 173(3), 203-213.
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  Abstract: Application of manure is used to increase the N and C status of arid and semiarid agricultural soils. Organic N contained in animal manures must be mineralized before crop use, a process which is affected by soil water status either by the direct influence of soil moisture and/or salt interactions on the N dynamics. The objectives of this work were: i) to examine the influences of soil osmotic and matric water potentials on N mineralization, ii) to determine the extent of N mineralization over a range of total soil water potentials, and iii) to study the effect of manure addition on N dynamics in an agricultural desert soil. Gila fine sandy loam soil was treated with varying amounts of water, sodium chloride, and composted dairy manure and incubated at a depth of 20 cm in Ziploc® bags. Inorganic N, soil moisture content, and total soil water potential were measured for 14 weeks. N mineralization was maximal at total soil water potentials of -2.3 to -0.35 MPa and decreased rapidly as potentials declined below -5.5 MPa. Regression analysis indicated that matric potential had twice the inhibitory affect on N mineralization compared with osmotic potential. Manure addition resulted in net N immobilization especially during the early part of the study. Net N immobilization also occurred in unamended soil, but this generally lasted only a few weeks. Immobilization was prolonged in soils with lower water potentials. Net N mineralization in the manure-amended soils was higher than in the unamended soils when soil moisture content was at field capacity. © 2008 Lippincott Williams & Wilkins, Inc.
• Field, J. P., Farrell-Poe, K., & Walworth, J. L. (2007). Comparative treatment effectiveness of conventional trench and seepage pit systems. Water Environment Research, 79(3), 310-319.
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  PMID: 17469663;Abstract: On-site wastewater treatment systems can be a potential source of groundwater contamination in regions throughout the United States and other parts of the world. Here, we evaluate four conventional trench systems and four seepage pit systems to determine the relative effectiveness of these systems for the treatment of septic tank effluent in medium- to coarse-textured arid and semiarid soils. Soil borings were advanced up to twice the depth of the trenches (4 m) and seepage pits (15 m) at two horizontal distances (30 cm and 1.5 m) from the sidewalls of the systems. Soil samples were analyzed for various biological and chemical parameters, including Escherichia coli, total coliform, pH, total organic carbon, total dissolved solids, total nitrogen, ammonium-nitrogen, and nitrate-nitrogen. Most soil parameters investigated approached background levels more rapidly near the trenches than the seepage pits, as sampling distance increased both vertically and horizontally from the sidewalls of the systems.
• Rayner, J. L., Snape, I., Walworth, J. L., Harvey, P. M., & Ferguson, S. H. (2007). Petroleum-hydrocarbon contamination and remediation by microbioventing at sub-Antarctic Macquarie Island. Cold Regions Science and Technology, 48(2 SPEC. ISS.), 139-153.
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  Abstract: Natural attenuation of petroleum hydrocarbons in polar and subpolar soils is limited by low nutrients, low temperatures, and water availability. This study investigated three sites contaminated with diesel fuel and the use of aeration to remediate one of the sites at sub-Antarctic Macquarie Island. These sites were of differing ages and had different soil-water regimes. The most recent spill (New Main Power House) occurred in 2002 and resulted in ∼ 180 metric tons of highly-contaminated (∼ 7000 mg kg- 1), moderately-drained, sandy soil. An older site (< 1994; Old Main Power House) comprised ∼ 100 metric tons of moderately-contaminated (∼ 2800 mg kg- 1) water-saturated peaty soil. A third spill (< 1994; Fuel Farm) contained approximately 600 metric tons of low- to moderately-contaminated (∼ 800 mg kg- 1) sandy soil. Using a hydrocarbon distribution model (NAPLANAL) we determined that non-aqueous phase liquid droplets start to form in these soils at concentrations 50-1000 mg kg- 1 mostly depending on organic carbon fraction. An in-field treatability evaluation with an air sparge port to increase oxygen concentration in the soils proved unsuccessful because the shallow water table and thin soil cover led to channel development. However, an easily-installed 'microbioventing' system, comprising many small air injecting rods, successfully aerated a wide area of soil. Field estimates of biodegradation rates under unamended aerobic conditions were ∼ 10-20 mg kg- 1 d- 1. When considered with results from a nutrient optimisation respiration experiment [Walworth, J., Pond, A., Snape, I., Rayner, J.L. and Harvey, P.M., 2007-this issue. Nitrogen requirements for maximizing petroleum bioremediation in a sub-Antarctic soil. Cold Regions Science and Technology, In Press.], we conclude that in situ bioremediation for these sites should treat the soil to a target concentration of ∼ 200 mg kg- 1 in approximately 1-2 years of continual operation at ambient temperatures. This simple methodology could have useful application in the summer treatment of other waterlogged tundra soils. © 2007.
• Walecka-Hutchison, C. M., & Walworth, J. L. (2007). Evaluating the effects of gross nitrogen mineralization, immobilization, and nitrification on nitrogen fertilizer availability in soil experimentally contaminated with diesel. Biodegradation, 18(2), 133-144.
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  PMID: 16897581;Abstract: Sandy clay loam soil was contaminated with 5000 mg kg-1 diesel, and amended with nitrogen (15.98 atom% 15N) at 0, 250, 500, and 1000 mg kg-1 to determine gross rates of nitrogen transformations during diesel biodegradation at varying soil water potentials. The observed water potential values were -0.20, -0.47, -0.85, and -1.50 MPa in the 0, 250, 500, and 1000 mg kg-1 nitrogen treatments respectively. Highest microbial respiration occurred in the lowest nitrogen treatment suggesting an inhibitory osmotic effect from higher rates of nitrogen application. Microbial respiration rates of 185, 169, 131, and 116 mg O2 kg-1 soil day -1 were observed in the 250, 500, control and 1000 mg kg-1 nitrogen treatments, respectively. Gross nitrification was inversely related to water potential with rates of 0.2, 0.04, and 0.004 mg N kg-1 soil day-1 in the 250, 500, and 1000 mg kg-1 nitrogen treatments, respectively. Reduction in water potential did not inhibit gross nitrogen immobilization or mineralization, with respective immobilization rates of 2.2, 1.8, and 1.8 mg N kg-1 soil day-1, and mineralization rates of 0.5, 0.3, and 0.3 mg N kg-1 soil day -1 in the 1000, 500, and 250 mg kg-1 nitrogen treatments, respectively. Based on nitrogen transformation rates, the duration of fertilizer contribution to the inorganic nitrogen pool was estimated at 0.9, 1.9, and 3.2 years in the 250, 500, and 1000 mg kg-1 nitrogen treatments, respectively. The estimation was conservative as ammonium fixation, gross nitrogen immobilization, and nitrification were considered losses of fertilizer with only gross mineralization of organic nitrogen contributing to the most active portion of the nitrogen pool. © 2006 Springer Science+Business Media, Inc.
• Walworth, J., Field, J. P., Farrell-Poe, K. L., & Walworth, J. L. (2007). Comparative treatment effectiveness of conventional trench and seepage pit systems. Water environment research : a research publication of the Water Environment Federation, 79(3).
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  On-site wastewater treatment systems can be a potential source of groundwater contamination in regions throughout the United States and other parts of the world. Here, we evaluate four conventional trench systems and four seepage pit systems to determine the relative effectiveness of these systems for the treatment of septic tank effluent in medium- to coarse-textured arid and semiarid soils. Soil borings were advanced up to twice the depth of the trenches (4 m) and seepage pits (15 m) at two horizontal distances (30 cm and 1.5 m) from the sidewalls of the systems. Soil samples were analyzed for various biological and chemical parameters, including Escherichia coli, total coliform, pH, total organic carbon, total dissolved solids, total nitrogen, ammonium-nitrogen, and nitrate-nitrogen. Most soil parameters investigated approached background levels more rapidly near the trenches than the seepage pits, as sampling distance increased both vertically and horizontally from the sidewalls of the systems.
• Walworth, J., Pond, A., Snape, I., Rayner, J., Ferguson, S., & Harvey, P. (2007). Nitrogen requirements for maximizing petroleum bioremediation in a sub-Antarctic soil. Cold Regions Science and Technology, 48(2 SPEC. ISS.), 84-91.
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  Abstract: Many contaminated cold region soils are deficient in nitrogen, and addition of the proper amount of this nutrient can increase the biodegradation rate. However, it has been demonstrated that excess nitrogen can depress the rate of microbial activity and petroleum degradation in contaminated soils due to osmotic soil water potential depression. This study was undertaken to optimize nutrient amendments in a sub-Antarctic soil. Soil collected from a petroleum-contaminated site on Macquarie Island, Australia, located in the sub-Antarctic, contained approximately 5250 mg kg- 1 of hydrocarbons and 20.9% H2O. Inorganic nitrogen levels prior to fertilization were < 1.0 mg kg- 1 of NO3-N and 1.3 mg kg- 1 of NH4-N. Inorganic nitrogen, in the form of NH4Cl, was added at rates of 0, 125, 250, 375, 500, and 625 mg nitrogen kg- 1 of dry soil. On a soil water basis (NH2O-calculated by dividing inorganic soil nitrogen by the soil water content), applied plus native N levels were 6, 604, 1202, 1800, 2399, and 2997 mg nitrogen kg- 1 of soil water for these treatments. The soil was incubated at 6 °C. O2 consumption was monitored for approximately 4 months. Maximum O2 uptake was observed with the 125 and 250 mg nitrogen kg- 1 of soil application rates. Respiration in the 625 mg kg- 1 treatment was slightly lower than that in the untreated soil, although they were not statistically different. Respiration was maximized when NH2O was 604 mg nitrogen kg- 1 H2O, and was depressed when it reached 1800 mg N kg- 1 H2O. Residual soil petroleum following incubation was least in soil amended with 125 mg N kg- 1 (NH2O = 604) and was greater in unfertilized soils or in soils receiving 250 mg N kg- 1 or more (NH2O ≥ 1202). Thus, the rate of bioremediation was maximized when NH2O was maintained below 1200 mg N kg- 1 soil H2O. Whereas previous studies have indicated that bioremediation in polar and sub-polar region soils are inhibited by nitrogen amendments above 2500 mg N kg- 1 H2O, results from this study indicated inhibition at a lower level of 1200 mg N kg- 1 H2O. © 2006 Elsevier B.V. All rights reserved.
• Walworth, J., Walecka-Hutchison, C. M., & Walworth, J. L. (2007). Evaluating the effects of gross nitrogen mineralization, immobilization, and nitrification on nitrogen fertilizer availability in soil experimentally contaminated with diesel. Biodegradation, 18(2).
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  Sandy clay loam soil was contaminated with 5000 mg kg(-1) diesel, and amended with nitrogen (15.98 atom% (15)N) at 0, 250, 500, and 1000 mg kg(-1) to determine gross rates of nitrogen transformations during diesel biodegradation at varying soil water potentials. The observed water potential values were -0.20, -0.47, -0.85, and -1.50 MPa in the 0, 250, 500, and 1000 mg kg(-1) nitrogen treatments respectively. Highest microbial respiration occurred in the lowest nitrogen treatment suggesting an inhibitory osmotic effect from higher rates of nitrogen application. Microbial respiration rates of 185, 169, 131, and 116 mg O(2) kg(-1) soil day(-1) were observed in the 250, 500, control and 1000 mg kg(-1) nitrogen treatments, respectively. Gross nitrification was inversely related to water potential with rates of 0.2, 0.04, and 0.004 mg N kg(-1) soil day(-1) in the 250, 500, and 1000 mg kg(-1) nitrogen treatments, respectively. Reduction in water potential did not inhibit gross nitrogen immobilization or mineralization, with respective immobilization rates of 2.2, 1.8, and 1.8 mg N kg(-1) soil day(-1), and mineralization rates of 0.5, 0.3, and 0.3 mg N kg(-1) soil day(-1) in the 1000, 500, and 250 mg kg(-1) nitrogen treatments, respectively. Based on nitrogen transformation rates, the duration of fertilizer contribution to the inorganic nitrogen pool was estimated at 0.9, 1.9, and 3.2 years in the 250, 500, and 1000 mg kg(-1) nitrogen treatments, respectively. The estimation was conservative as ammonium fixation, gross nitrogen immobilization, and nitrification were considered losses of fertilizer with only gross mineralization of organic nitrogen contributing to the most active portion of the nitrogen pool.
• Pond, A. P., Walworth, J. L., Kilby, M. W., Gibson, R. D., Call, R. E., & Núñez, H. (2006). Leaf nutrient levels for pecans. HortScience, 41(5), 1339-1341.
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  Abstract: Measurement of nutrients in leaf tissue is a practical method of monitoring the nutritional status of perennial crops such as pecan (Carya illinoinensis, Wang. C. Koch). Accurate interpretations require known standard concentrations for the crop and region. To determine standard concentrations for pecans, focusing on those grown in the desert southwest, we conducted a survey of 135 'Western Schley' pecan trees in Arizona for 2 years. Leaf nutrient concentrations and yield were collected for each tree. Leaf nutrient concentrations from the highest yielding trees (50th yield percentile) were used to calculate a mean and CV for each nutrient. Results were compared with data from New Mexico, Georgia, and Sonora, Mexico. Relatively large differences were noted in mean K, Ca, B, Cu, Fe, Mn, and Zn levels. Nutrient interpretation ranges were calculated based on Arizona population statistics using the balance index method.
• Walecka-Hutchison, C. M., & Walworth, J. L. (2006). Assessment of C:N ratios and water potential for nitrogen optimization in diesel bioremediation. Bioremediation Journal, 10(1-2), 25-35.
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  Abstract: Sandy clay loam soil contaminated with 5000, 10,000 or 20,000 mg/kg of diesel fuel no. 2 was amended with 0 (ambient nitrogen only), 250, 500, or 1000 mg/kg nitrogen (NH 4Cl) to evaluate the role of C:N ratios and soil water potential on diesel biodegradation efficacy. The soil was incubated at 25°C for 41 days and microbial O 2 consumption measured respirometrically. Highest microbial respiration was observed in the 250 mg N/kg soil treatments regardless of diesel concentration. Higher levels of nitrogen fertilization decreased soil water potential and resulted in an extended lag phase and reduced respiration. Application of 1000 mg/kg nitrogen reduced maximum respiration by 20% to 52% depending on contaminant levels. Optimal C:N ratios among those tested were 17:1, 34:1, and 68:1 for the three diesel concentrations, respectively, and were dependent on contaminant concentration. Nitrogen fertilization on the basis of soil pore water nitrogen (mg N/kg soil H 2O) is independent of hydrocarbon concentration but takes into account soil moisture content. This method accounts for both the nutritional and osmotic aspects of nitrogen fertilization. In the soil studied the best nitrogen augmentation corresponded to a soil pore water nitrogen level of 1950 mg N/kg H 2O at all diesel concentrations. © 2007 Taylor and Francis Group, LLC.
• Walworth, J. L., Pond, A. P., Sower, G. J., & Kilby, M. W. (2006). Fall-applied foliar zinc for pecans. HortScience, 41(1), 275-276.
• Jia, X., Larson, D. L., Zimmt, W. S., & Walworth, J. L. (2005). Nitrate pollution control in different soils by electrokinetic technology. Transactions of the American Society of Agricultural Engineers, 48(4), 1343-1352.
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  Abstract: Previous studies found that a small DC electrical current could attract onions to the anode in sandy soil, even with solute flow towards the cathode. Laboratory experiments were conducted in a vertical, partially saturated column with different soils to determine if nitrate transport could similarly be controlled using electrokinetic (EK) technology. Nitrate concentration, pH value, electrical potential difference, and soil water content were measured for three soils at selected times at different distances from the anode. Constant electrical current was applied to the system for 9 h, and measurements continued for a total of 48 h. The results demonstrated that nitrate can be strongly retained near the anode against gravity in sandy soil with an 80 mA (0.5 mA/cm2) current input. When the percentage of clay in the soil was increased, the EK effect on ion movement decreased; the transport of both ions and water were inhibited by fine clay particles. The loamy soil showed a slight increase in nitrate concentration near the anode, but the clayey soil showed no change. An increase in pH near the cathode was seen in all soils. Water content for sandy soil was higher at the bottom of the column and lower at the top of the column, but for loam and clay soils, the lowest water content was found above the cathode near the bottom of the column. Electrical potential difference between the two electrodes showed that the sandy soil required the highest electrical potential difference to obtain the desired current level; loamy and clayey soils required less. For sandy soil, the highest potential difference was found near the top of the column, but for loam and clay soils, the highest electrical potential difference was measured near the bottom, next to the cathode, suggesting that these locations were the critical zones limiting electrical ion transport. © 2005 American Society of Agricultural Engineers.
• Walecka-Hutchison, C., & Walworth, J. L. (2005). Quantification of in-situ trichloroethene dilution versus biodegradation using a novel chloride concentration technique. Environmental Chemistry: Green Chemistry and Pollutants in Ecosystems, 317-328.
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  Abstract: The objective of this study was to evaluate the effectiveness of in-situ trichloroethene (TCE) bioremediation, and to determine whether the observed decrease in TCE concentrations was attributable to biological degradation versus abiotic processes. An enhanced in-situ TCE bioremediation project in which groundwater amended with microbe stimulating compounds was injected into the contaminated subsurface was analyzed. Dilution, attributed to mixing between the injected clean and contaminated waters, was calculated using a modified groundwater mixing equation and chloride concentrations of the waters at various times in the study. Over the course of the trial, spatially averaged TCE concentrations within the aquifer decreased by 41%. The chloride calculations suggested that a 29% reduction may be attributable to dilution, and that only a 12% decrease in concentrations may be attributable to biological degradation. © 2005 Springer-Verlag Berlin Heidelberg.
• Jia, X., Larson, D. L., Zimmt, W. S., & Walworth, J. L. (2004). Nitrate pollution control in different soils by electrokinetic. ASAE Annual International Meeting 2004, 1635-1651.
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  Abstract: Laboratory experiments were conducted to determine if nitrate transport in soils can be controlled using electrokinetic (EK) technology. Nitrate concentration, pH, electrical potential and soil water content were measured in soil column tests with three soils at different distances from the anode and at desired times. Constant electrical current was applied to the system for 9 hrs and continued for a total of 48 hrs. The results showed that in sandy soils nitrate can be strongly retained near the anode, even against gravity and drainage effects. When the percentage of clay in the soil was increased, the EK effect was decreased; due to the increase of fine clay particles both the transports of ions and the water were inhibited. The loam soil showed slight increase of nitrate concentration near the anode, but the clay soil showed no change. An increase of pH near the cathode was seen in all soils. Water content measurement showed that in sandy soil, water content was higher at the bottom and lower at the top, but for loam and clay soil, the lowest water content was at the layer just above the cathode. The electrical potential required to obtain constant amperage was 97.23 V in sandy soil, 18.24 V in loamy soil and 14.22 V in clayey soil. For sandy soil, the highest potential fraction was found near the top of the column in the system, but for loam and clay soil, the highest potential portion was near the bottom, next to the cathode, suggesting that these locations were the critical zones limiting the ion transport.
• Thompson, T. L., White, S. A., Walworth, J., & Sower, G. J. (2003). Fertigation frequency for subsurface drip-irrigated broccoli. Soil Science Society of America Journal, 67(3), 910-918.
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  Abstract: Subsurface-drip irrigation and fertigation with fluid N fertilizer sources offers substantial flexibility for N fertilizer management. Fertigation events can be scheduled as often as irrigation, up to several times per day. However, because of system or management constraints very frequent fertigation may not be possible or desirable for some growers. Optimum fertigation interval for subsurface drip-irrigated crops has not been well researched. A 3-yr field experiment was conducted on a sandy loam soil in southern Arizona with subsurface drip-irrigated broccoli (Brassica olearacea L. Italica) to i) determine the effects of N rate and fertigation frequency on crop yield, quality, and crop N status, and ii) estimate a N balance. Broccoli was planted in two rows per raised bed 1.02 m apart, with one drip line buried 0.15 to 0.20 m deep within each bed. The experiment included factorial combinations of two N rates and four fertigation frequencies (intervals of 1, 7, 14, and 28 d). Broccoli marketable yield and quality were responsive to N rate, but not to increased fertigation frequency. During one of three seasons, fertigation frequency significantly (P ≥ 0.05) affected crop N uptake, but there was no trend of increasing N uptake with increasing fertigation frequency. Unaccounted fertilizer N and apparent N use efficiency (ANUE) were calculated for two seasons. Unaccounted fertilizer N averaged 20 and 75 kg ha-1 and ANUE 90 and 81% with 250 and 350 kg N ha-1 applied, respectively. Neither was significantly affected by fertigation frequency. We conclude, therefore, that for broccoli production with subsurface-drip irrigation on sandy loam or finer soils, fertigation can be applied as infrequently as monthly, without compromising crop yield or quality, or causing excessive N losses.
• Walworth, J. L., Woolard, C. R., & Harris, K. C. (2003). Nutrient amendments for contaminated peri-glacial soils: Use of cod bone meal as a controlled release nutrient source. Cold Regions Science and Technology, 37(2), 81-88.
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  Abstract: The lack of available nutrients, particularly nitrogen, often limits the rate of microbial petroleum hydrocarbon degradation in contaminated cold region soils. Microbial activity in many peri-glacial soils responds to addition of nitrogen, although excess levels can inhibit biodegradation by decreasing soil water potentials. Aqueous soluble inorganic fertilizer quickly partitions into soil water, increasing the salt concentration, and imposing an osmotic potential. Strategies that can be used to avoid microbial inhibition include the use of controlled release fertilizers. We studied the use of an organic fertilizer, cod bone meal, as a nutrient source for bioremediation. Nitrogen mineralization from cod bone meal was greater at 20 °C (first-order reaction rate constant k=0.0206 d-1) than at 10 °C (k =0.0154 d-1) and greater at pH 6.5 and 7.5 (k=0.0208 and 0.0189 d-1, respectively) than at pH 5.5 (k=0.0143 d-1). Net O2 consumption from diesel fuel degradation in a contaminated soil was greatly increased by addition of nitrogen and phosphorus in the form of diammonium phosphate (DAP) or cod bone meal relative to unfertilized soil. Cod bone meal fertilized soils had greater net O2 consumption than DAP fertilized soils. However, residual soil hydrocarbon analyses indicated no difference in petroleum loss between the two nutrient sources. © 2003 Elsevier Science B.V. All rights reserved.
• Walworth, J. L., & Carling, D. E. (2002). Tuber initiation and development in irrigated and non-irrigated potatoes. American Journal of Potato Research, 79(6), 387-395.
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  Abstract: Tuber initiation and development are processes basic to potato production and are particularly critical in areas with short growing seasons. It is important to know how and to what extent management decisions affect these processes in order to maximize the yield of marketable tubers. A two-year field study, conducted in southcentral Alaska, examined top growth, tuber initiation, and tuber development in eight potato cultivars grown with and without irrigation. Plants of the cultivars Allagash Russet, Bake-King, Green Mountain, Kennebec, Lemhi Russet, Russet Burbank, Shepody, and Superior were harvested weekly throughout the growing season, and top dry weight, numbers of tubers, and individual tuber fresh weights were recorded. Top dry weight was reduced by moisture stress shortly after emergence in 1993, and about one month following emergence in 1994, when early-season soil moisture was greater. The weight of tubers was similarly affected within approximately 5 wk of emergence in 1993 and 6 weeks in 1994. Tuber weight at harvest was increased two- to three-fold by irrigation in all cultivars. The number of tubers each plant set was affected by irrigation in most, but not all, cultivars. Some varieties (Lemhi Russet in 1994, Allagash Russet both years) set more tubers than were maintained through the growing season. Tuber remnants found during sample collection indicated that tuber reabsorption had occurred. Irrigated Green Mountain had more than one tuber initiation period during the season, whereas other varieties such as Shepody maintained a relatively constant number of tubers following initial tuber set. Tuber size distribution at the end of the growing season showed that larger tubers were favored by irrigation.
• Walworth, J., Braddock, J., & Woolard, C. (2001). Nutrient and temperature interactions in bioremediation of cryic soils. Cold Regions Science and Technology, 32(2-3), 85-91.
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  Abstract: Low temperatures and lack of available nutrients often limit the rate of microbial petroleum hydrocarbon degradation in contaminated cryic soils. Proper management of both these parameters may increase microbial respiration in such soils. Interactions between nutrient level and temperature could impact management decisions for both factors, but these interactions have not previously been adequately described. Petroleum-contaminated soils from two Alaskan sites were studied in separate laboratory experiments. Nutrients and incubation temperatures were independently varied so interactions between the two could be studied. Soil from a gravel pad near Barrow, AK responded positively to temperatures increasing from 5°C to 20°C, and to addition of 50 or 100 mg/kg of supplemental nitrogen. Soil from Ft. Wainwright, AK responded positively as temperatures were increased from 1°C to 21°C, but microbial respiration decreased when temperatures were raised to 41°C. Microbial activity increased when 100 or 200 mg/kg of supplemental nitrogen was applied. In both soils, there were positive interactions between soil temperature response and addition of nitrogen fertilizer. Microbial response to soil warming was accentuated by proper nitrogen management, and response to fertilizer application was greatest when soil was warmed. © 2001 Elsevier Science B.V. All rights reserved.
• Braddock, J. F., Walworth, J. L., & McCarthy, K. A. (1999). Biodegradation of Aliphatic vs. Aromatic Hydrocarbons in fertilized arctic soils. Bioremediation Journal, 3(2), 105-116.
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  Abstract: The objectives of this study were to (1) test a simple bioremediation treatment strategy in the Arctic and (2) examine the effect of fertilization on the degradation of aliphatic and aromatic hydrocarbons. The site is a coarse sand pad that once supported fuel storage tanks. Concentrations of diesel-range organics at the beginning of the study (July 1996) ranged from 250 to 860 mg/kg soil. Replicate field plots treated with fertilizer yielded final concentrations of 0, 50, 100, or 200 mg N/kg soil. Soil samples were collected three times during the thaw season and analyzed for physical and chemical properties, microbial populations and activities, and concentrations of semivolatile hydrocarbons. Soil pH and soil-water potentials declined as a result of fertilizer application. Addition of fertilizer significantly increased soil respiration potentials, but not the populations of microorganisms measured. Fertilizer addition also resulted in ~50% loss of measured aliphatic and aromatic hydrocarbons in surface and subsurface soils. For fertilized plots, hydrocarbon loss was not related to the amount of fertilizer added. Losses of aliphatic hydrocarbons were attributed to biotic processes, whereas losses of aromatic hydrocarbons likely were a result of both biotic and abiotic processes. © 1999, CRC Press LLC.
• Walworth, J., & Chaobal, V. (1999). Nutrient and temperature interactions in bioremediation of petroleum-contaminated cryic soil. Battelle Memorial Institute International In Situ and On-Site Bioreclamation Symposium Proceedings, 5, 3/-.
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  Abstract: A factorial study was performed using a sandy, petroleum-contaminated subsoil from Fort Wainwright, Alaska, to examine the effect of temperature, moisture content, nutrient levels, and diesel range organic (DRO) concentration on microbial activity at a cold climate bioremediation site. In soils with 500 mg/kg of DRO, soil heating and nutrient addition slightly increased biodegradation rates, implying a substrate limitation. With 8100 mg/kg of DRO, soil warming increased the microbial activity, suggesting that low soil temperature was the main factor limiting biodegradation rates at this site. Maximum microbial activity was achieved at ~ 21°C, with little or no additional increase at 31°C. Heating the soil to 41°C decreased biodegradation rates. Addition of nitrogen and phosphorus to soil heated at > 1°C increased biodegradation. Soil nitrogen concentration was the more essential factor in maximizing biodegradation rates.
• Braddock, J. F., Ruth, M. L., Catterall, P. H., Walworth, J. L., & Mccarthy, K. A. (1997). Enhancement and inhibition of microbial activity in hydrocarbon- contaminated arctic soils: Implications for nutrient-amended bioremediation. Environmental Science and Technology, 31(7), 2078-2084.
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  Abstract: Bioremediation is being used or proposed as a treatment option at many hydrocarbon-contaminated sites. One such site is a former bulk-fuel storage facility near Barrow, AK, where contamination persists after approximately 380 m3 of JP-5 was spilled in 1970. The soil at the site is primarily coarse sand with low organic carbon (
• Walworth, J. L., Woolard, C. R., Braddock, J. F., & Reynolds, C. M. (1997). Enhancement and inhibition of soil petroleum biodegradation through the use of fertilizer nitrogen: An approach to determining optimum levels. Soil and Sediment Contamination, 6(5), 465-480.
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  Abstract: Laboratory studies were conducted to evaluate the relationship between soil water content and microbial response to soil nitrogen (N) in petroleum-contaminated soils. Various levels of N were added to a sand, a sandy loam, and a silt loam. Measurements of the extent of biodegradation in each soil (petroleum loss or CO2 production) indicated that biodegradation was related to soil N expressed as a function of soil water (mg N/kg soil H2O or mg N/l) better than N expressed as a function of soil dry matter (mg N/kg soil). A loamy sand was treated with four levels of N (0, 250, 500, 750 mg N/kg soil) and incubated at three water contents (5.0, 7.5, and 10.0% on a dry soil weight basis). Soil water potential and O2 consumption were best related to N expressed on the basis of soil water. It is concluded that expressing N in units of mg N/kg soil H2O (easily obtained by dividing [mg N/kg dry soil] by [soil moisture content]) can be used to determine fertilization rates for bioremediation processes. On this basis, an optimum N level of approximately 2000 mg N/kg H2O is tentatively identified for the range of soils and conditions tested. © 1997 by AEHS.
• Walworth, J. L., & Reynolds, C. M. (1995). Bioremediation of a petroleum-contaminated cryic soil: Effects of phosphorus, nitrogen, and temperature. Journal of Soil Contamination, 4(3), 299-310.
• Gavlak, R. G., Campbell, W. L., Walworth, J. L., Johnson, C. L., Muniz, J. E., & Tindall, T. A. (1993). Nitrogen fertilization of irrigated Russet potatoes in southcentral Alaska. American Potato Journal, 70(8), 571-578.
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  Abstract: Allagash Russet, BelRus, Frontier Russet, HiLite Russet, Russet Norkotah and Russet Burbank were evaluated with preplant N fertilizer levels of 0, 67, 134, 201, and 201 kg N/ha in a split application on a Knik silt loam in 1990 and 1991 near Palmer, Alaska. BelRus and Russet Norkotah yielded less marketable tubers than the other cultivars and Russet Burbank performed well under warm, dry 1990 conditions and poorly when conditions were cool and wet (1991). Allagash, HiLite and Frontier Russets were consistent producers with marketable tuber yields averaging 35.4, 32.3, and 32.2 t/ha, respectively. Marketable tuber yield was maximized with approximately 175 kg total N/ha (residual soil plus applied) and approached 43 t/ha in 1990. Splitting the N application had no significant effect on tuber yield. Newly released russets appear promising for commercial Alaska producers. © 1993 Springer.
• Walworth, J. L., & Muniz, J. E. (1993). A compendium of tissue nutrient concentrations for field-grown potatoes. American Potato Journal, 70(8), 579-597.
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  Abstract: Current literature was reviewed to evaluate relationships between potato tissue nutrient concentrations and yield. Primary sources (those based on original research) were emphasized to prevent duplicate information. Data were rejected if stage of growth and plant part were not specifically defined. Data that met these criteria were separated by plant part, stage of growth, and nutrient form (soluble versus total nutrient). The information was then compiled to illustrate the range of reported values for each nutrient, stage of growth, and plant part. Values are presented for deficient, low, sufficient, high, and toxic levels of nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, boron, chlorine, copper, iron, manganese, and zinc. © 1993 Springer.
• Walworth, J. L. (1992). Soil drying and rewetting, or freezing and thawing, affects soil solution composition. Soil Science Society of America Journal, 56(2), 433-437.
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  Abstract: A laboratory study was conducted on samples of Bt horizons of three Hapludults to determine the effects of time of extraction and reextraction freezing and thawing, or drying, rewetting, and incubating. The relationship between electrical conductivity (EC) and ionic strength (I) also was studied. Significant changes in soil solution composition were found as centrifugation solution extractions. Also EC can provide a good estimate of I of soil solutions. Soil solution composition was substantially altered by preextraction drying-rewetting or freezing-thawing. Neither of the methods studied here provide a good means of storing soil samples prior to soil solution extraction. -from Author
• Walworth, J. L., Gavlak, R. G., & Panciera, M. T. (1992). Mehlich 3 extractant for determination of available B, Cu, Fe, Mn, and Zn in cryic Alaskan soils. Canadian Journal of Soil Science, 72(4), 517-526.
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  Abstract: Mehlich 3 extractable B, Cu, Fe, Mn and Zn, DTPA-TEA extractable Cu, Fe, Mn and Zn, and hot water extractable B were measured on three soils from factorial experiments with variable rates of B, Cu, Mn and Zn, and from two B rate and liming studies. Neither Mehlich 3 nor DTPA-TEA extractant predicted plant-available Cu or Fe. The inclusion of soil pH and organic matter slightly improved estimates of available B, Mn and Zn. Mehlich 3 extractable Fe was poorly related to DTPA-TEA extractable Fe. Copper extracted with Mehlich 3 was related to that extracted with DTPA-TEA; the inclusion of soil pH improved the relationship. Mehlich 3 extractable Mn and Zn were closely related to DTPA-TEA extractable levels. The correlation between Mehlich 3 and hot water B was significantly improved by including soil organic matter content. -from Authors
• Walworth, J. L., & Sumner, M. E. (1990). Alfalfa response to lime, phosphorus, potassium, magnesium, and molybdenum on acid ultisols. Fertilizer Research, 24(3), 167-172.
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  Abstract: Alfalfa (Medicago sativa L.) is a high protein forage, cultivated widely in young, fertile soils. There is considerable potential for alfalfa production in areas with acidic, highly weathered soils, but few field studies on fertility requirements under these conditions have been published. Two field trials were conducted on ultisols to study the effects of lime, P, K, Mg and Mo on alfalfa growth and tissue composition. A trial with three rates of calcitic lime (0, 2400, and 3800 kg ha-1) and P (0, 25, and 50 kg ha-1) and two rates each of K (20 and 200 kg ha-1 the first year, 250 and 500 kg ha-1 in subsequent years), Mg (36 and 106 kg ha-1) and Mo (0 and 0.25 kg ha-1) was conducted on an Appling coarse sandy loam (Typic Hapludult). Another factorial experiment with three levels each of lime (0, 2000, and 4,000 kg ha-1), P (0, 100, and 200 kg ha-1), and K (0, 150, 300 kg ha-1) was conducted on a Davidson sandy clay loam (Rhodic Paleudult). Application of lime or P resulted in increased dry matter (DM) production at both locations. Liming also raised plant tissue N concentration. Addition of Mo had no effect on DM production or on foliar composition. Addition of K depressed soil Mg, plant tissue Mg, and plant Mg uptake at both locations. On the Davidson soil DM increased when K was applied, but on the Appling soil K increased DM production only where Mg was also added. Addition of Mg decreased K uptake and depressed DM production unless K was also added. The observed antagonism between K and Mg is of importance for alfalfa production in highly weathered soils. Successful alfalfa production in these soils is unlikely unless attention is paid to the balance between these two nutrients. Raising soil pH increased foliar N concentration affecting forage quality as well as DM production. © 1990 Kluwer Academic Publishers.
• Walworth, J. L., Letzsch, W. S., & Sumner, M. E. (1986). Use of boundary lines in establishing diagnostic norms.. Soil Science Society of America Journal, 50(1), 123-128.
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  Abstract: Whether utilizing a critical value or a nutrient balance system such as the Diagnosis and Recommendation Integrated System for interpreting plant tissue composition, determination of accurate optima is of paramount importance. Two procedures for determining such optima, one using the mean of a high yielding population, the second establishing yield maxima at all nutrient values (the boundary line approach) were contrasted. -from Authors

Proceedings Publications

• Walworth, J. L. (2017, September 7-8, 2017). Recent Advancements in Micronutrient Management in Pecans. In Proceedings of the Simposio Internacional de Nogal Pecanero.
• Heerema, R., & Walworth, J. L. (2015, August). Soil-Applied Zinc-EDTA: Photosynthesis in ‘Wichita’ Pecan Grown on an Alkaline and Calcareous Soil. In 29th International Horticulture Congress, Acta Horticulturae.
• Walworth, J. L. (2015, August). Soil-Applied Zinc-EDTA: Growth and Nutrient Acquisition of Non-bearing Pecan Grown on an Alkaline and Calcareous Soil. In 29th International Horticulture Congress, Acta Horticulturae.
• Walworth, J. L. (2015, September). Interpretation of Soil and Leaf Analysis for Diagnosing Salinity Problems. In Simposio Internacional de Nogal Pecanero.
• Walworth, J. L., & Heerema, R. (2015, March). Soil Application of Zinc to Pecans in Calcareous Soils. In Western Nutrient Management Conference, 72-78.
• Walworth, J. (2011, September). Yield and Nut Quality of Hedge Pruned Pecans in Arizona. In XII Simposio Internacional de Nogal Pecanero.
• Walworth, J. L. (2011, September). Yield and Nut Quality of Hedge Pruned Pecans in Arizona. In XII Simposio Internacional de Nogal Pecanero, 29-30.

Presentations

• Walworth, J. L. (2013, August). Identifying and Managing Problem Soils for Improved Urban Landscape Health. SHADE Conference. Phoenix, AZ: SHADE.
• Walworth, J. L. (2013, December). Soil Testing and Interpretation. Master Farmer Program. Phoenix, AZ.
• Walworth, J. L. (2013, February). Hedge Pruning Pecan Trees: The Arizona Experience. First South African Pecan Conference. Hartswater, SA.
• Walworth, J. L. (2013, February). Importance of Soil Preparation and Chemical Corrections. First South African Pecan Conference. Hartswater, SA.
• Walworth, J. L. (2013, January). Characteristics of Desert Soils. Desert Turfgrass shortcourse. Tucson, AZ: UA.
• Walworth, J. L. (2013, January). Managing Soils for Turfgrass. Desert Turfgrass shortcourse. Tucson, AZ: UA.
• Walworth, J. L. (2013, January). Salts, pH, and Other Soil Considerations. Soil short course. Chinle, AZ.
• Walworth, J. L. (2013, January). Soil Fertility and Turfgrass Nutrition. Desert Turfgrass shortcourse. Tucson, AZ: UA.
• Walworth, J. L. (2013, January). Using Plant Analysis to Diagnose Nutrient Needs in Alfalfa. Yuma Agricultural Conference. Yuma, AZ.
• Walworth, J. L. (2013, June). Zinc Management in Calcareous Aridisols. Western Soil Science Society meeting. Tucson: Western Soil Science Society.
• Walworth, J. L. (2013, March). Nutrient Management in Pecans. Western Nutrient Management Conference. Reno, NV: WERA-103.
• Walworth, J. L. (2013, March). Trends in the South African Pecan Industry. Western Pecan Growers Association annual conference.
• Walworth, J. L. (2013, May). Measuring Soil Characteristics and Fertility. Desert Horticulture Conference. Tucson, AZ;.
• Walworth, J. L. (2013, May). Nutrient Management. Community Gardens. Tucson, AZ.
• Walworth, J. L. (2013, May). Phosphorus Utilization in Desert Soils. Desert Agriculture Conference. Casa Grande, AZ;.
• Walworth, J. L. (2013, October). Soil Salinity Management. New Mexico Pecan Growers Field Day. Las Cruces, NM.
• Walworth, J. L. (2013, September). Can I Quit Spraying Zinc?. Arizona Pecan Growers Association annual conference. Tucson: Arizona Pecan Growers Association.
• Walworth, J. L. (2012, April). Nutritional Requirements for Bioremediation. 8th International Conference on Contaminant in Freezing Ground. Obergurgl, Austria.
• Walworth, J. L. (2011, March). Microbes: The Good, the Bad, the Ugly. Western Pecan Growers Association annual meeting. Las Cruces, NM: Western Pecan Growers Association.
• Walworth, J. L. (2011, March). Soil Applied Zinc. Western Pecan Growers Association annual meeting. Las Cruces, NM: Western Pecan Growers Association.
• Walworth, J. L. (2011, September). Yield and Nut Quality of Hedge Pruned Pecans in Arizona. XII Simposio Internacional de Nogal Pecanero. Hermosillo, Sonora.

Poster Presentations

• Killebrew, A., Papuga, S. A., Brown, P. W., Walworth, J. L., & Pope, A. J. (2016, Spring). Quantifying pecan water use in southern Arizona: a two-year study. UA Earth Week Student Symposium.
• Killebrew, A., Papuga, S. A., Brown, P. W., & Walworth, J. L. (2015, Spring). On quantifying pecan water use in Arizona: knowledge about phenological activity can help inform management decisions. UA Earth Week Student Symposium.
• McCune, J., & Walworth, J. L. (2015, April). Nitrogen and Phosphorus Response in Pecan. UA Earth Week Student Symposium.
• Walworth, J. L. (2011, March). Effectiveness of Soil-Applied Zinc for Pecans. Western Nutrient Management Conference. Reno, NV.

Other Teaching Materials

• Walworth, J. L., & Flynn, R. (2016. Unavailability of Water in Saline Soils. New Mexico State University.
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  Animated presentation to educate on soil sodium, soil salinity, and plant relationships.
• Walworth, J. L., & Flynn, R. (2016. Understanding the Sodium Adsorption Ratio (SAR). New Mexico State University.
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  An animated presentation designed to provide the basics of soil salinity, sodicity, and structure; a video of the impact of gypsum on water flow in soils; and a video lecture on soil salinity.
• Walworth, J. L., Flynn, R., & Davenport, J. (2016. The Olsen Test for Phosphorus. New Mexico State University.
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  An animation explaining choice of extractants for measuring plant-available soil phosphorus.

Others

• Brown, H., Walworth, J. L., & Mpanga, I. (2020, 08). Zeolite Application in Crop Production: Importance to Soil Nutrient, Water, Health, and Environmental Pollution Management. University of Arizona Cooperative Extension bulletin.
• Walworth, J. L., & Heerema, R. (2019, January). Zinc Management in Arid Region Pecan Orchards. Arizona Cooperative Extension. https://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1789-2019_0.pdf
• Miller, R., Sutitarnnontr, P., Tuller, M., Walworth, J. L., & Jones, S. B. (2015, March). Impact of Manure Incorporation on Greenhouse Gas Emissions in Semi-Arid Regions. eXtension: http://www.extension.org/pages/72838/. http://www.extension.org/pages/72838/
• Walworth, J. (2013, Fall). Manure in the Home Garden. University of Arizona Cooperative Extension publication.
• Walworth, J. (2013, Fall). Nitrogen in Soil and the Environment. University of Arizona Cooperative Extension publication.
• Walworth, J. (2013, Fall). Recognizing and Treating Iron Deficiency in the Home Yard. University of Arizona Cooperative Extension publication.
• Walworth, J. (2012, Fall). Using Gypsum and other Calcium Amendments in Southwestern Soils. University of Arizona Cooperative Extension publication AZ1413.
• Banuelos, J., Walworth, J., Brown, P., & Kopec, D. (2011, Fall). Deficit Irrigation of Seashore Paspalum and Bermudagrass. Golf Course Management. http://digitalgcm.gcsaa.org
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  Volume 79, Issue 10, pgs 98-104
• Guangyao, W., Loper, S. J., Ottman, M. J., & Walworth, J. L. (2011, September). Pre-plant Soil Testing for Small Grains. Arizona Cooperative Extension Bulletin..
• Walworth, J. (2010, Fall). Gypsum and Other Calcium Sources. United States Golf Association, Green Section Record.
• Walworth, J. (2010, Fall). Using Gypsum and other Calcium Amendments in Southwestern Soils. Arizona Cooperative Extension publication.
• Walworth, J. L. (2011, September). Leaf Sampling Guide with Interpretation and Evaluation for Arizona Pecan Orchards. Arizona Cooperative Extension Bulletin AZ1410.
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  Revision of existing publication
• Walworth, J. L. (2011, September). Salinity Management and Soil Amendments for Southwestern Pecan Orchards. Arizona Cooperative Extension Bulletin AZ1411.
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  Revision of existing publication
• Walworth, J. L. (2011, September). Soil Sampling and Analysis. Arizona Cooperative Extension publication AZ1412.
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  Revision of existing publication.
• Walworth, J. L. (2011, September). The Roles of Sodium and Salts. Arizona Cooperative Extension publication AZ1414..
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  Revision of existing publication.
• Guangyao, S., Loper, S., Ottman, M., & Walworth, J. (2010, Fall). Pre-plant Soil Testing for Small Grains. University of Arizona Agricultural Experiment Station Bulletin.
• Walworth, J. (2010, Fall). Salinity Management and Soil Amendments for Southwestern Pecan Orchards. Arizona Cooperative Extension Bulletin.
• Walworth, J. (2010, Fall). Soil Structure: The Roles of Sodium and Salts. Arizona Cooperative Extension.
• Walworth, J. L. (2010, Fall). AZDRIP, The University of Arizona Subsurface Drip Irrigation Demonstration and Research Project. http://cals.arizona.edu/crops/irrigation/azdrip/azdripindex.html
• Walworth, J. L. (2010, Fall). Soil Fertility. http://ag.arizona.edu/swes/soil_fertility/
• Walworth, J. L. (2010, Fall). Soil Sampling and Analysis. Arizona Cooperative Extension publication.
• Walworth, J., Pond, A., & Kilby, M. (2010, Fall). Leaf Sampling Guide with Interpretation and Evaluation for Arizona Pecan Orchards.. Arizona Cooperative Extension Bulletin.