Variability in Corn Response to N Fertilizer along a 1000-ft Hillslope John Schmidt Nan Hong Adam Dellinger Doug Beegle Henry Lin ARS Missouri Penn State

Background Improving N recommendations for corn Spatial variability in relief, aspect, soil water content Fox observed a relationship in PA between EONR and July precipitation

Field site - 2005 1000 ft horizontal, 30 ft vertical relief Previous crop soybean Soil pH: 5.3 – 5.7 Soil P (M3): 24 – 77 Soil K (M3): 97 – 156

Field site – relief and plot locations

Treatment design Ten locations, 2 blocks each Six N treatments: 0, 50, 100, 150, 200, 250 lb N / acre, applied at planting as NH4NO3 TDR access tubes at each location Soil water content, 5 June – 2 Sept, 0 – 90 cm depth Canopy reflectance, Crop Circle ACS-210 Grain yield at harvest

Rainfall and soil water content

Grain yield response

EONR (Economic Optimum N Rate)

N rec’s as a function of yield goal?

Soil water content

Grain yield related to soil water content

EONR related to soil water content

July 01 sensor information

Summary EONR increased linearly with an increase in soil profile water content, 25 July – 30 June EONR was not correlated to NDVI ratio NDVI 01 July decreased linearly with increasing soil profile water content on 30 June