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Field microplot estimates of soil N mineralization for manured and non-manured soils

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  • Credits for available N from past manure applications are often used in nutrient management planning. However, it is difficult to verify the accuracy of these credits. The major objective of this study was to estimate long-term effects of manure application on soil N mineralization. Specific objectives were to: 1) estimate the quantity and timing of N mineralized in manured vs. non-manured soils via an field microplot incubation method, 2) to compare N mineralized in the microplots to N mineralized in an adjacent field soil, and 3) to apply our research findings to a predictive N mineralization model. We collected soils (0-8 in depth) from sites with and without a history of manure application. Soils were incubated at a single field site in 2 inch i.d. x 8 in. long open-ended PVC microplots. A nylon bag containing ion exchange resins was placed in the bottom of each microplot to capture leached NO3- and NH4+. Microplots were installed in April, and harvested 1-2 times per month through October. Cumulative N mineralization data for each soil was fit to a sigmoid function. We then used a linear fit between cumulative net N mineralized and degree days to determine a “mineralization rate constant” for each soil. In both years, the maximum mineralization rates of 0.4 to 1.9 lb/acre per day occurred in July, corresponding to maximum soil temperatures. Over the two year study, cumulative net N mineralization per season averaged 85 ppm for three manured soils and 63 ppm per season for three non-manured soils. For the 8-inch depth measured, this amounted to an average of 152 lb N/acre for manured soils vs. 114 lb/acre for non-manured soils. Seasonal net N mineralized for the Puyallup soil in the incubation microplots (35 to 53 ppm) was similar to that measured for adjacent Puyallup soil in the field. This suggests that the microplot incubation procedure gave values that are realistic for field conditions. The mineralization rate constants developed by this study show promise in making our data transferable to other soil temperature conditions, or to portions of a growing season. However, much work remains to be done before this technique is implemented for routine use for nitrogen management.
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  • Sullivan, D.M., A.I. Bary, C.G. Cogger and E.A. Myhre. 1999. Field microplot estimates of soil N mineralization for manured and non-manured soils. Western Nutrient Management Conference. Salt Lake City, UT. 4-5 Mar. 1999. Potash & Phosphate Institute. Manhattan, KS
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  • Salt Lake City, UT, USA
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  • Washington Dept of Ecology, Centennial Clean Water Fund
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