Estimating plant-available nitrogen release from manures, composts, and crop residues Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/4t64gq41z

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  • In order to properly utilize organic amendments as nitrogen sources, reliable methods to estimate plant-available nitrogen (PAN) are needed. The objectives of this study were to (1) evaluate the use of crop and soil responses in fertilizer N equivalence (FNE) calculations, (2) examine the relationships between the C/N ratio, total N concentration, and inorganic N concentration of organic amendments and PAN, (3) evaluate the use of early-season soil N tests as indicators of PAN, and (4) examine the ability of the computer model DECOMPOSITION to predict PAN from a wide variety of organic amendments under laboratory and field conditions. In the field, four levels of urea fertilizer and a total of 15 different organic amendments were applied to sweet corn (Zea mays L.) in 2002 and 2003. The FNE values for amendments were determined by fitting crop N uptake, crop N uptake + post-harvest soil inorganic N, fresh weight ear yield, and chlorophyll meter data to urea-N response curves. In the laboratory, a total of 22 different organic amendments were evaluated for CO2 evolution and N mineralization in a 70 d incubation. Amendments were incorporated into soil from field locations in Oregon and Washington in 2002 and 2003. DECOMPOSITION was run using decomposition kinetics obtained in the laboratory and climatic data for either laboratory conditions or actual field conditions. While FNE values were similar using the different responses, crop N uptake + post-harvest soil inorganic N had the best predictive value. While initial amendment characteristics were strongly correlated to PAN in this study, the relationships held for only certain ranges. Pre-plant inorganic soil N tests and the pre-sidedress nitrate test (PSNT) were also strongly correlated to PAN and treatments with PSNT values below 17 mg N kg⁻¹ all responded to early-season supplemental urea. Actual and modeled PAN estimates had a close linear relationship in both the laboratory (r² = 0.74) and field experiment (r² = 0.78) with slopes not significantly different than unity. The model did, however, consistently over-predict PAN in the laboratory and field for materials with inorganic N concentration greater than 4.5 g kg⁻¹. This study demonstrated that FNE calculations based on different crop and soil responses were closely related in sweet corn cropping systems. Organic amendment analyses and early-season N testing were also shown to be valuable tools in estimating N availability from organic amendments. Additionally, the model DECOMPOSITION was found to be a good predictor of PAN for a variety of amendments under climatic and soil conditions different from those used to develop the model.
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