Corn Yield and Residual Soil Nitrate as Affected by Time and Rate of Nitrogen Application
- W. E. Jokela and
- G. W. Randall
Efficient use of N fertilizer for corn (Zea mays L.) production is important for increasing economic return to the grower and for minimizing the potential impact on water quality. Time and rate of application are important management tools for improving N efficiency. This experiment was conducted for 3 yr on two nonirrigated southern Minnesota soils—a Mt. Carroll silt loam (fine-silty, mixed, mesic Mollic Hapludalf) and a Webster clay loam (fine-loamy, mixed, mesic Typic Haplaquoll)—to evaluate the effect of time and rate of N application on corn yield, N uptake, and residual soil NO−3-N. Nitrogen as (NH4)2SO4 was applied in a factorial arrangement of N rate (low and high) and time of application (at planting (PL), eight-leaf stage (8L), or split evenly between the two times (SP)). A zero N control and a very high N rate at PL were also included. Nitrogen rates were 75, 150, and 225 kg ha−1 on the Mt. Carroll, and 100, 200, and 300 kg ha−1 on the Webster. Grain and total dry matter (DM) yield, and plant uptake of N were increased by N application in five of six site years, in most cases up to the high N rate. Delayed N application (8L or SP vs. PL) resulted in either no effect or a slight decrease in DM and in variable effects on N uptake, depending on the year and location. Residual NO−3-N in the 1.5 m profile ranged from 150 to 400 kg ha−1 for most treatments in the fall but was 50 to 70% lower the following spring. Residual NO−3 in the fall was consistently increased by delayed application of the high N rate from the PL to 8L stage, with most of the increase occurring in the upper 0.6 m of the profile. The decrease in residual NO−3 from fall to spring, attributed in part to leaching beyond the sampled zone, minimized the potential carryover effect for the next year's production and indicated a potential for greater environmental impact where N application was delayed. Dry matter production, N uptake, and residual NO−3-N were affected by unusually dry periods in midsummer of all 3 yr, especially at the Webster site.
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