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Articles by D. Zhou
Total Records ( 2 ) for D. Zhou
  J. L. Schroder , H. Zhang , D. Zhou , N. Basta , W. R. Raun , M. E. Payton and A. Zazulak
  The USEPA Part 503 rule did not directly specify the amount of sludge-borne P that can be applied but allowed application rates based on the recommended N requirement of a crop. Monitoring of long-term application of biosolids is important to protect both soil and water quality. Biosolids and ammonium nitrate were annually applied for 13 yr to winter wheat at six plant available N (PAN) rates: 0, 45, 90, 180, 269, 536 kg N ha–1 yr–1. Biosolids application did not increase soil pH but increased levels of total C, total N, NH4–N, NO3–N, and electrical conductivity (EC). Soil concentrations of Cd, Cu, Pb, Mo, and Zn were greater in biosolid-treated plots but were <24% of their respective cumulative pollutant loading rates. Application of biosolids increased plant micronutrient B, Cu, Fe, and Zn concentrations. The addition of biosolids to the Norge soil (fine-silty, mixed, active, thermic Udic Paleustoll) increased Mehlich 3 plant available P (M3P) and water soluble P (WSP) and these P levels were well correlated with biosolids application rate. Application of biosolids at rates of >=2 times the recommended agronomic rate of 90 kg PAN ha–1 resulted in M3P concentrations that exceeded an environmental threshold of 200 mg kg–1 established by the USDA-NRCS for the land application of manures in Oklahoma non-nutrient limited watersheds. Significant relationships were found between the ammonium oxalate P saturation index (PSIox) and M3P as well as between PSIox and WSP. It appears the repeated long-term application of biosolids above the N agronomic rate should be avoided and application should be based on other criteria such as an agronomic P threshold, an environmental P threshold, or a P site index.
  Y. Wang , Y. He , H. Zhang , J. Schroder , C. Li and D. Zhou
  Phosphate mobilization by organic acids has been shown to be soil type dependent and controlled by the soil`s intrinsic P status. The objective of this study was to evaluate the capacity and mechanisms of three organic acids in the mobilization of phosphate from an upland clay loam Ultisol that had received different long-term fertilizer treatments. Soil samples were incubated at 25 ± 1°C and 40% moisture content for 3 wk with citric, tartaric, or oxalic acid at 1.0 mmol kg–1 of soil. Soil pH, inorganic P fractions, and plant-available P (Olsen P) were analyzed after incubation. The results indicated that Olsen P and the loosely bound P extracted with 1.0 mol L–1 NH4Cl (NH4Cl-P) were significantly increased by the treatment of the three organic acids, and Fe phosphate (Fe-P), occluded phosphate (Oc-P), and Ca phosphate (Ca-P) were mobilized and released to various degrees as well. The order of increased mobilization of P by the organic acids was citric acid > tartaric acid > oxalic acid. These three organic acids have the potential to increase the availability of P in soil but need to be evaluated at the field scale.
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