Relationships between Corn Yields and Soil Nitrate in Late Spring
- G. D. Binford,
- A. M. Blackmer and
- M. E. Cerrato
Recent studies have shown good correlations between corn (Zea mays L.) yields and concentrations of NO3 in the surface 30-cm layer of soil in late spring. Here we report additional correlations and evaluate the benefits of sampling to 60 cm instead of to 30 cm only. The study involved 45 site-years (1346 plot-years) of data collected in 1987, 1988, and 1989 in Iowa. Weather conditions were dryer than normal, with a severe drought occurring in 1988. Each site-year included seven to 10 rates of N applied before planting. Samples representing the surface 0- to 30-cm and the 30- to 60-cm layers of soils were collected when corn plants were 15 to 30 cm tall. Nitrate concentrations in these soil layers were correlated with grain yields. The deeper sampling slightly improved the correlations between grain yields and soil NO3 concentrations, but the advantage was probably not great enough to justify the costs of the deeper sampling. The critical concentration of NO3 was 23 to 26 mg N kg−1 in the surface 30-cm layer of soil and 16 to 19 mg N kg−1 in the surface 60-cm layer of soil. Overall, the results support the idea that a soil test based on concentrations of NO3 in the surface 30-cm layer of soil when corn plants are 15 to 30 cm tall has great promise for improving N management during corn production.
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