|Yost, Matt -|
|Coulter, Jeff -|
Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: January 26, 2012
Publication Date: February 15, 2012
Citation: Yost, M., Russelle, M.P., Coulter, J. 2012. Improving N credit predictions to reduce soil residual nitrate. In: Southern Minnesota Nutrient Efficiency Coalition Grant, 2011 Participant's Reports. p. 15-21. Technical Abstract: The potential to increase farm profitability and reduce nitrate leaching in Minnesota are huge if the alfalfa N credit was better understood and applied to first-year corn. If the N credit (150 lb/N/ac) were applied to the nearly 250,000 acres of corn following alfalfa in Minnesota each year, 19,000 tons of N fertilizer ($17 million at $0.45 lb/N) could be spared and water contamination would be greatly reduced. When growers apply too much N to corn, it decreases profit, wastes resources, and increases the risk of nitrate leaching. However, not applying enough N can sometimes reduce yield and profit. Experiments were conducted on 6 farms with no-till corn after alfalfa and on 10 farms with manure applied during alfalfa termination in order to determine: i) whether adjustments should be made to the alfalfa N credit to account for no-till or manure application, ii) the accuracy of the presidedress nitrate test (PSNT) in identifying fields that would be responsive to N fertilization, and iii) whether fertilizer rates were adequate according to the basal stalk nitrate test (BSNT). At six no-till farms, fertilizer N was not required to maximize grain or silage yield, which confirmed that alfalfa N credits to first-year corn for good stands of alfalfa do not need to be altered for no-till corn. Manure application to good stands of alfalfa during fall alfalfa termination had no effect on corn grain yield. However, across five farms where silage yield was measured, manure increased silage yield by 1.4 tons/ac. At two farms with excess precipitation, grain yield increased by 30 bu/ac when 160 lb/N/ac was applied. However, manure (>100 lb total N/ac) did not increase grain yield across these two farms and even reduced yield by 10 bu/ac. Fertilizer and manure N are often not needed to maximize grain yield of first-year corn following alfalfa. Sidedress N applications at these two farms were twice as efficient in increasing grain yield as N applied at planting. The PSNT successfully identified responsive and non-responsive fields 40% of the time, whereas the BSNT success rate was 67% suggesting that growers should be cautious when applying these tests in corn following alfalfa.