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Title: COMPARISONS OF UNIFORM AND VARIABLE RATE NITROGEN AND PHOSPHOROUS FERTILIZER APPLICATIONS FOR GRAIN SORGHUM

Author
item YANG, CHENGHAI - TX A&M UNIV EXPT STATION
item Everitt, James
item Bradford, Joe

Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/16/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: Variable rate fertilization has the potential to improve fertilizer use efficiency, increase economic returns, and reduce environmental impacts. While a significant number of producers are interested in the site-specific management concept, only a relatively small number of producers have actually implemented it because reliable, user-friendly equipment is not yet readily available and they are uncertain if this technology will increase their profits. This two-year study was designed to evaluate differences in grain sorghum yield and economic returns between uniform and variable rate fertilizer strategies using a variable rate fertilizer applicator. 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. The experiment was conducted across three grain sorghum fields. Yield monitor data indicated that the variable treatment resulted in significantly higher yields than the unifor treatments for both years (400 kg/ha higher in 1997 and 338 kg/ha higher in 1998). A simple economic analysis showed that the variable rate treatment had positive relative economic returns over the uniform nitrogen and phosphorus treatment ($27/ha in 1997 and $23/ha in 1998). However, additional costs associated with variable rate application may have significantly reduced the benefits. Nevertheless, this research demonstrated that variable rate fertilization could increase yield and reduce yield variability and has the potential to improve economic returns.

Technical Abstract: 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. Yield monitor data indicated that the variable rate treatment resulted in significantly higher yields than the uniform N and P treatment for both years (400 kg/ha higher in 1997 and 338 kg/ha higher in 1998). Moreover, coefficients of variation of yield monitor data for the variable rate treatment were smaller than those for the two uniform rate treatments. A simple economic analysis showed that the variable rate treatment had positive relative economic returns over the uniform N and P treatment ($27/ha in 1997 and $23/ha in 1998).