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United States Department of Agriculture

Agricultural Research Service

Title: Optimum nitrogen rate for corn related to hillslope variability in soil water redistribution

Authors
item Schmidt, John
item Hong, Nan - UNIV OF MISSOURI
item FOLMAR, GORDON
item Beegle, Doug - PENN STATE UNIV
item Lin, Henry - PENN STATE UNIV

Submitted to: Potash and Phosphate Institute Guides
Publication Type: Book / Chapter
Publication Acceptance Date: March 8, 2007
Publication Date: September 1, 2007
Citation: Schmidt, J.P., Hong, N., Folmar, G.J., Beegle, D., Lin, H. 2007. Optimum nitrogen rate for corn increases with greater soil water ability. In: Bruulsema, Tom (ed.) Managing Crop Nitrogen for Weather. International Plant Nutrition Institute, Norcross, GA. P. 4.1-4.10.

Interpretive Summary: Improving site-specific N recommendations for corn (Zea mays L.) will depend on an improved understanding of the interactive effects of yield response to N and other independent variables. The objective of this study was to determine in-season soil water content redistribution (dW) for ten locations along a hillslope and to characterize the relationship between dW and the economic optimum N rate (EONR) for corn. 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 and soil profile (0 to 3 ft) water content between 30 June and 25 July (dWj) increased from -0.2 to 4.2 in at these ten locations. A linearly positive relationship between EONR and dWj was the defining relationship in this study (r2=0.92, P less than 0.0001). A “subsurface” wetness index, TWI(sub), derived from a “subsurface” digital elevation map (elevation – soil depth), was also positively related to dWj (r2=0.60, P equal 0.01), suggesting that subsurface water movement was, in part, responsible for the variability in soil profile water content redistribution. Although the causal mechanism responsible for the variability in EONR observed along this hillslope was not identified during this relatively dry growing season, dWj and TWI(sub) were better indicators of EONR than maximum grain yield. Understanding the relationships between these types of independent variables and the yield response to N fertilizer will be essential to improving site-specific N management.

Technical Abstract: Improving site-specific N recommendations for corn (Zea mays L.) will depend on an improved understanding of the interactive effects of yield response to N and other independent variables. The objective of this study was to determine in-season soil water content redistribution (dW) for ten locations along a hillslope and to characterize the relationship between dW and the economic optimum N rate (EONR) for corn. Ten plot locations were selected in 2005 along a 300-m toposequence of a 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. A grain yield response to N fertilizer was observed at nine of 10 locations. The quadratic-plateau response was used to determine EONR for each of the nine responsive 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. The soil profile water content between 30 June and 25 July (dWj) increased from -0.5 to 10.7 cm among these ten locations when rainfall was 12.2 cm. A linearly positive relationship between EONR and dWj (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). A “subsurface” wetness index, TWI(sub), derived from a “subsurface” digital elevation map (elevation – soil depth), was also positively related to dWj (r2=0.60, P equal 0.01), suggesting that subsurface water movement was, in part, responsible for the variability in soil profile water content redistribution. Although the causal mechanism responsible for the variability in EONR observed along this hillslope was not identified during this relatively dry growing season, dWj and TWI(sub) were better indicators of EONR than maximum grain yield. Understanding the relationships between these types of independent variables and the yield response to N fertilizer will be essential to improving site-specific N management.

Last Modified: 9/29/2014
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