Comparison of uniform and variable rare phosphorus and nitrogen fertilizer application
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Answer:
Variable rate fertilizer application has the potential to improve fertilizer use efficiency, increase economic returns, and reduce environmental impacts. This study was designed to examine differences in yield and economic returns between uniform and variable rate fertilizer applications. During the 1997 and 1998 growing seasons, a variable rate applicator, capable of varying two liquid fertilizers simultaneously, was used to evaluate three fertility strategies: conventional uniform N, uniform N and P, and variable rate N and P. The three treatments were assigned in six blocks within three 14-ha grain sorghum fields (two blocks in each field) in a randomized complete block design. Thirty-six soil samples were taken in a staggered systematic grid from each field, and levels of soil nutrients were determined. Application rate maps for the variable rate N and P treatment were generated based on a fixed yield goal and site-specific soil N and P levels across the experimental plots, while application rates for the uniform N and P treatment were calculated from the same yield goal and average soil N and P levels for all three fields.