Chlorophyll Meter and Stalk Nitrate Techniques as Complementary Indices for Residual Nitrogen

Abstract

Improved N management techniques are needed to prevent excess N applications while maintaining yields. Environmentally, development of these improved techniques has become critical for crops such as irrigated corn (Zea mays L.), which require large N fertilizer inputs to maximize yield. Our objective was to determine if some current N management techniques could be used to guide and improve future soil sampling strategies that would result in improved N fertilizer recommendations and reduced adverse environmental effects. Chlorophyll meter readings and end-of-season stalk nitrate-N concentrations were taken from an irrigated corn study at Shelton, NE, from 1992 through 1994. Residual soil N samples were collected to a depth of 5 ft after the 1992 and 1993 growing seasons. This study included continuous corn and soybean [Glycine max (L.) Merr.]- corn rotations with four corn hybrids and five N fertilizer rates. Chlorophyll meter readings taken at several growth stages reached a maximum at sufficient N levels for maximum yield and then plateaued. Similarly, end-of-season stalk nitrate-N concentrations exceeded established thresholds (-2000 ppm) above the N fertilizer rate where maximum yields were obtained in both cropping systems. Together, these techniques provided additional criteria to help partition and separate fields into areas with potentially different levels of residual soil N. This information can then be used to guide soil sampling and to develop or improve site specific N fertilizer recommendations which should decrease environmental risk by reducing the amount of nitrate-N available for leaching.