Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/15/2006
Publication Date: 9/27/2006
Citation: Jaynes, D.B., Colvin, T.S. 2006. Corn yield and nitrate loss in subsurface drainage from mid-season N fertilizer application. Agronomy Journal. 98:1479-1487. Interpretive Summary: High nitrate concentrations in the Nation’s surface waters is a recurring environmental and public health problem and the source of much of the nitrate is from agricultural use of nitrogen (N) fertilizers. Thus, there is much interest in developing farming practices that reduce off-site effects of fertilizer use while maintaining the economic viability of crop production. Mid-season application of N fertilizer has been proposed as an economical method of applying N to a corn crop that will reduce nitrate occurrence off site. In this study, we measured crop yield and loss of nitrate in tile drainage from a production field when applying half of the N fertilizer at mid-season. We showed that the mid-season application could increase corn yields and gain back much of the yield potential of the crop, but often gave less yield than if the same amount of N was applied in a single application when the corn plant had emerged from the soil. Mid-season application also increased losses of nitrate in tile drainage and thus is not a promising environmental practice. These findings will be of use to soil fertility and environmental experts, farmers, and crop consultants.
Technical Abstract: Whether in response to remotely sensed plant N status or as a rescue treatment when previously applied N has been lost to denitrification or leaching, there is growing interest in applying N to corn at mid-season. While the yield benefits of this practice are variable, little information is available as to the impacts of mid-season N application on water quality. We compared grain yields and NO3 losses in drainage water as a result of applying N either once at emergence or equally split between emergence and mid-season. Nitrogen treatments consisted of 199 (H), 138 (M), and 69 (L) kg ha**-1 applied post-emergence and 69 kg ha**-1 applied post-emergence and again at mid-season (R). Grain yield for corn and soybean, grown in a 2-yr rotation, and drainage water NO3 concentrations were measured on replicated tile-drained plots within a producer’s field from 2000 through 2004. Mid-season application of additional N (R treatment) increased corn yield every year from 0.9 to 2.5 Mg ha**-1 compared to the L N treatment. However, in only one of three years (2000) did the mid-season application increase yield compared to the equivalent total N rate applied in the spring (M treatment). The yield advantages in 2000 may have been due in part to disease preferentially infesting the higher N treatments. There was no carry over N-treatment effect on soybean yields. Nitrate concentrations in tile drainage were consistently greater (0.3 – 2.5 mg L**-1) for the R treatment than the M treatment and significantly greater when averaged over all years. Residual soil NO3 at the end of the year also indicated that some of the mid-season N application was not taken up by the crop and was available for leaching. Thus, mid-season N application may be beneficial for recovering some of the potential yield in corn, but the practice did not benefit water quality compared to a single application at emergence in this study.