Use of a Chlorophyll Meter at the Early Dent Stage of Corn to Evaluate Nitrogen Sufficiency

Abstract

A late‐season chlorophyll meter test for corn (Zea mays L.) could provide growers with a convenient evaluation of that year's N management program, along with information useful for N fertilizer rate decisions in subsequent growing seasons. Chlorophyll meter (SPAD 502) readings were taken late in the growing season on corn ear leaves in replicated plots of 357 N treatments from 93 N‐response experiments conducted in Pennsylvania. At sites not affected by severe late‐season drought or disease, chlorophyll meter readings taken at the 1/4 milk line stage separated N‐deficient from N‐sufficient treatments with 93% accuracy using a critical level of 52.0 SPAD units. If meter readings were normalized at each site by comparison with a site‐specific high‐N reference reading, chlorophyll meter readings of ear leaves made from the late milk to the middent stage of corn could separate N‐deficient from N‐sufficient treatments with 92% accuracy using a relative SPAD reading critical level of 0.93. For treatments with meter readings below the critical level, relative grain yields and the additional N that would have been needed for economic optimum grain yield were correlated with chlorophyll meter test values. For treatments with a meter reading above 52.0 SPAD units, the amount of excess N that may have been applied could not be accurately predicted. For corn tested at the 1/4 milk line stage, we suggest an N‐sufficiency range of 52.0 to 56.0 SPAD units, above which there is a 70% probability of an excess of >50 kg N ha−1 having been applied.

Airborne Hyperspectral Images and Ground-Level Optical Sensors As Assessment Tools for Maize Nitrogen Fertilization

“…The purpose was to determine whether readings from the former, which are usually represented in airborne imagery, were correlated with traditional measurements of nutritional N status at flowering, that is, in husk leaves [6].…”

“…A procedure previously used to test the ability of handheld Chl meters as tools for N fertilizer recommendation was adapted to test the accuracy of the actual indices [2,6]. The N yield response curve was obtained by fitting a linear-plateau model to the observed data using the non-linear regression procedure of PASW Statistics Software ® .…”

“…Chlorophyll estimation based on the difference between either the transmittance or the reflectance of two wavelengths has been conducted with leaf clip and tractor-mounted equipment. This technique has been applied to various crops and demonstrated its potential for N fertilizer recommendations; as a result, it is currently used at a commercial level [2,5,6]. Nevertheless, limitations have been reported: readings can be affected by water stress or nutrient deficiencies other than N [5], by non-uniform leaf Chl distribution [7] or by the time of the day when readings are taken [4].…”

Quantitative sidedress nitrogen recommendations for potatoes based upon crop nutritional indices

“…Being one of the first and most interesting, this uses plant N concentration and crop N uptake as N nutritional indices in winter wheat. This, was followed by Singh (1993) in potato with petiole nitrate content and by Piekielek et al (1995), Heckman et al (1996) and most recently by Scharf (2001) on corn using, respectively, chlorophyll-SPAD readings, the pre-sidedress soil nitrate test and total N in whole plants and chlorophyll-SPAD readings. Their methodological basis consisted in establishing a relationship between the level of crop or soil N indicators and optimal sidedress N rates, for well-defined sampling dates.…”

SPAD Values and Nitrogen Nutrition Index for the Evaluation of Rice Nitrogen Status

“…Hawkins et al (2007) used RSPAD values to determine N application rates for corn. Coefficients of determination ranging from 0.57 to 0.99 have been reported between relative grain yield (ratio of grain yield to the highest yield) and RSPAD values in corn (Piekielek et al, 1995;Waskom et al, 1996;Scharf et al, 2006).…”