|Karlen, Douglas - Doug|
Submitted to: Iowa Academy of Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/11/1998
Publication Date: N/A
Citation: N/A Interpretive Summary: Good nitrogen management practices are needed to help producers be profitable and to protect the environment. Traditional soil and plant measurements are helpful to ensure that excess nitrogen is not applied, but they can be very time consuming and expensive, especially in developing countries. New technologies that use leaf and canopy characteristics to measure the nitrogen status of plants may be useful for improving nitrogen management. The research reported in this paper was conducted in central Iowa and tested the usefulness of chlorophyll meters to sense the nitrogen status of corn plants grown with different fertilizer rates, sources, and times of application. Tillage and crop rotation effects were also evaluated. The results show that the chlorophyll meter could successfully be used to detect the nitrogen status of the corn plants and could thus be useful for helping to improve fertilizer nitrogen management practices. We conclude that to effectively use this tool, measurements should be taken when corn plants have from nine to twelve leaves. The hand-held instrument should be calibrated for different hybrids, soils, and past management practices by establishing a low nitrogen (0 to 50 pounds N per acre) and a high nitrogen (>225 pounds N per acre) treatment in a small area of each field. If readings throughout the field are similar to the high-nitrogen strip, no additional fertilizer will be needed. Readings that are similar to those in the low-nitrogen strip will need more fertilizer nitrogen for optimum growth and yield.
Technical Abstract: Environmentally sound nitrogen (N) management is necessary to simultaneously achieve high crop yields and protect surface and groundwater quality. We evaluated a hand-held chlorophyll meter as a diagnostic tool for improving N management for corn (Zea mays L.). Five N fertilizer rates (0, 67, 134, 201, and 280 kg N ha**-1) were evaluated in one study, and in a second study, the meter was used to evaluate the N status of corn plants grown under varying tillage (chisel plow vs. no-till), crop rotation (continuous corn vs. corn-soybean [Glycine max (L.) Merr.]), and N management treatments. Meter readings were taken at several plant growth stages in both studies and correlated with plant N concentrations and grain yield. The chlorophyll meter readings identified differences between low and high fertilizer N rates. Correlations between grain yield and meter readings at all growth stages were highly significant. The chlorophyll meter identified differences attributed to tillage, N fertilizer management, and crop rotation. We recommend taking measurements between plant growth stages V9 and V12, and conclude that the chlorophyll meter can be a very effective tool for evaluating effects of various N fertilizer management practices.