HILLSLOPE VARIABILITY IN CORN RESPONSE TO NITROGEN LINKED TO IN-SEASON SOIL MOISTURE REDISTRIBUTION

Authors: Schmidt, John; HONG, N - UNIV OF MISSOURI; DELLINGER, A - PENN STATE UNIV; BEEGLE, D - PENN STATE UNIV; LIN, H - PENN STATE UNIV

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/23/2006
Publication Date: 1/10/2007
Citation: Schmidt, J.P., Hong, N., Dellinger, A., Beegle, D.B., Lin, H. 2007. Hillslope variability in corn response to nitrogen linked to in-season soil moisture redistribution. Agronomy Journal. 99:229-237.

Interpretive Summary: Corn (Zea mays L.) yield variability within a field or across fields may be unrelated to N supply; yet, site-specific nitrogen (N) management often relies on an extrapolation of general N recommendations that vary depending on yield expectation. The objective of this study was to characterize the spatial variability in economic optimum N rate (EONR) for corn, considering the implications of soil characteristics along a hillslope, such as soil water content, that might affect EONR variability. Yield response to increasing N fertilizer rates (0 to 250 lb per acre) and soil water content throughout the growing season were evaluated at ten locations along a 1000-ft hillslope. The EONR ranged from 40 to 165 lb N per acre (mean = 137 lb N per acre) and was strongly correlated (r2=0.92, P less than 0.0001) to the change in soil profile (0 to 3 ft) water content between 30 June and 25 July (representing the driest and wettest soil conditions early in the growing season). Successful site-specific N management, which has the potential to significantly decrease the amount of excess N applied to cropland, will depend on an evaluation of the spatial variability in EONR and the corresponding causal factors, which may or may not correspond to spatial yield variability.

Technical Abstract: Spatial variability of corn (Zea mays L.) yield within a field is often identified as the primary criterion to justify site-specific N management; yet observed yield variability may be unrelated to N supply, and spatial variability in economic optimum N rate (EONR) is often not considered. The objective of this study was to characterize the spatial variability in EONR for corn, considering the implications of soil characteristics along a hillslope, such as soil water content, that might affect EONR variability. Ten plot locations were selected in 2005 along a 300-m toposequence of a typical production field in central Pennsylvania. At each location, two replications of six N treatments (0, 56, 112, 168, 224, and 280 kg N per ha) were broadcast applied at planting as ammonium nitrate. Soil water content (0-90-cm depth) was recorded approximately weekly at each location between 5 June and 2 September. Grain yield was determined at harvest. Four separate models for the grain yield response to N fertilizer were considered in determining EONR, including: quadratic, linear-plateau, quadratic-plateau, and exponential models. A grain yield response to N fertilizer was observed at nine of 10 locations. The quadratic-plateau response was selected as the most appropriate yield response function for these nine locations and for the field-mean response. The EONR ranged from 47 to 188 kg N per ha among the nine locations, while EONR for the mean response was 137 kg N per ha. At four of nine locations, observed EONR deviated from field-mean EONR by 40 to 50 kg N per ha. The relationship between EONR and the change in soil profile water content (0-90 cm) between 30 June and 25 July (representing the driest and wettest soil conditions early in the growing season) was the defining relationship in this study (r2=0.92, P less than 0.0001). Soil water redistribution during the growing season was implicated in the observed differences in EONR. Successful site-specific N management will depend on an evaluation of the spatial variability in EONR and the corresponding causal factors, which may or may not correspond to spatial yield variability.