Saturday, 15 July 2006

Nebraska Soil Fertility Project Revisits Corn Recommendations under High Yield Environments.

Charles Shapiro1, Achim Dobermann2, Richard Ferguson2, Gary Hergert1, David Tarkalson3, Daniel Walters2, and Charles Wortmann2. (1) Univ of Nebraska, 57905 855 Road, Haskell Agricultural Laboratory, Concord, NE 68728, (2) Dept of Agronomy and Horticulture, 279 Plant Science, Univ of Nebraska, Lincoln, NE 68583, (3) West Central Research and Extension Center, 461 W University Dr., North Platte, NE 69101

Maize (Zea mays) was grown in 34 environments across Nebraska's varied ecozones over three years. Nine treatments were the same at these sites, with N rates differing by previous crop which was either maize, soybeans (Glycine max) or drybeans (Phaseolus vulgaris). The hypothesis tested is that the University of Nebraska nutrient recommendation procedures produce maximum economic yield given historical fertilizer and maize prices. Hybrids used range in maturity from 1280 to 1590 GDDs (base T of 10 degrees C) and were chosen to be adapted to the areas grown. For the nitrogen, phosphorus, and potassium exclusion treatments, maize yield averaged 10.6, 14.0, and 14.5 Mg ha-1, respectively, with an average maximum yield of 15.1 Mg ha-1. Maize following maize averaged 14.4 Mg ha-1 with 180 kg ha-1 applied nitrogen compared to maize following soybean that averaged 14.0 Mg ha-1 with 120 kg ha-1 applied nitrogen. Fitted N response curves had optimum N rates 73 and 86 percent of recommendations for maize following maize and maize following soybean, respectively. Optimum rates were calculated at current nitrogen and maize prices ($0.30/lb N and $2.00/bu maize). When prices were closer to long range prices ($0.20/lb N and $2.00/bu maize) the optimum rates were 91 and 104 percent of recommended rates, respectively. Soil test P values ranged from 5 to over 80 mg kg-1, but yields were not consistently increased by fertilizer P application at low soil test P levels. Soil K levels were all higher than the critical level established in Nebraska and none of the sites had significant K responses.

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