Ability for In‐Season Correction of Nitrogen Deficiency in Corn Using Chlorophyll Meters

TLDR

Nitrate‑nitrogen contamination of groundwater is a major concern, especially where groundwater is near the soil surface and irrigated crops require large amounts of fertilizer. The study aimed to use a chlorophyll meter to assess in‑season nitrogen status and correct deficiencies in irrigated corn. Chlorophyll meter readings were converted into a sufficiency index [(as‑needed treatment/well‑fertilized treatment) × 100], and fertilizer was applied when the index fell below 95 %. Maximum yields were achieved when early‑season N kept sufficiency indexes between 90–100 % at V8; if indexes fell below 90 %, in‑season fertilization could not restore maximum yields, though it still increased yields, and the study demonstrated that chlorophyll meter–based corrections can mitigate moderate early N deficiencies, improve N use efficiency, and reduce leaching.

Abstract

Abstract Nitrate‐nitrogen contamination of groundwater continues to be a major concern throughout the USA. These concerns are greatest in areas where groundwater is close to the soil surface and in areas that have irrigated crops with large N fertilizer requirements. Specific objectives of this work were to use the chlorophyll meter to determine in‐season crop N status and to correct in‐season N deficiencies in irrigated corn ( Zea mays L.). Chlorophyll meter readings were used to calculate a sufficiency index [(as‐needed treatment/well‐fertilized treatment) × 100] and in‐season N fertilizer applications were made when index values were below 95%. Using this procedure, maximum yields were attained if early season N levels were adequate to maintain sufficiency indexes between 90 and 100% at the V8 growth stage. However, if the sufficiency index at V8 was below 90%, maximum yields were not achieved with in‐season N fertilizer applications because early season N was below that needed for optimum growth and yield potentials had already been reduced. Even in these causes, N applications did increase yields, but not to the maximum. These results did demonstrate that early N deficiencies could be corrected using chlorophyll meters and the sufficiency index approach when they were not severe. Although the objective was not tested in this study, less N fertilizer may be required when in‐season monitoring is used as the basis for N application. Use of the chlorophyll meter and sufficiency index should also result in greater N use efficiency and less N being available for leaching to the groundwater since these applications are made when N uptake by corn is greatest.