Relationship Between Basal Corn Stem Nitrate N Content at V6 Growth Stage and Grain Yield

Public concern about the fate of fertilizer that is not recovered in the harvested portion of crops has intensified interest in efficient methods to manage N fertilization. In 1986, six sites across Iowa with a wide range of physical and environmental conditions were selected to determine the relationship between NO3‐N content of basal corn stems and grain yield and to establish preliminary critical concentration levels of NO3‐N required to obtain various levels of maximum yield. Preplant fertilizer, in increments of 25 to 40 lb/acre with maximum rates of 160 to 200 lb/acre was applied to produce a range of stem NO3‐N contents. Two‐inch segments of corn stem immediately above the soil surface were collected from 10 plants per plot when the plants were in the V6 growth stage and analyzed for NO3‐N. Grain yield and stem NO3‐N content were highly correlated (R values from 0.80 to 0.93) at sites that were responsive to N fertilizer. A direct and an indirect method of establishing critical levels of stem NO3‐N content for various levels of relative yield were compared and produced similar results. Soil parent material seemed to significantly affect the critical levels of stem NO3‐N required for various levels of relative yield. Critical levels of stem NO3‐N for maximum yield were determined to be 0.90% and 1.78% (dry‐weight basis) for corn grown on loess and glacial till soils, respectively.