Abstract

GONZALEZ-TORRES, Anselmo et al. SPAD-502 Calibration to Evaluate Nitrogen Requirements in Forage Corn. Terra Latinoam [online]. 2009, vol.27, n.4, pp.303-309. ISSN 2395-8030.

In this study SPAD equipment was calibrated to evaluate the relationship between nitrogen sufficiency index (NSI) and corn forage yield and to generate preliminary regression equations to estimate the nitrogen (N) requirement of silage corn. Increasing N rates were evaluated in a sandy clay loam soil during 2007 and 2008. SPAD readings were taken before every irrigation event and the NSI was estimated. Regression analyses were computed between relative yield (RY) and NSI against N rate + residual soil N (N_f+s). Dry matter yield followed a quadratic equation as a function of N_f+s. According to the quadratic equation, the N rate + residual soil N to achieve 95% of the maximum relative yield was 325 kg ha^-1. SPAD readings were related to dry matter yield. Values of r² for the relationship between N rate and NSI varied from 0.78 to 0.99. However, when NSI data measured at the first sampling date in both years were combined, the r² was 0.692, and the equation was: NSI = -2 x 10^-6 (N_f+s)² + 0.0012 (N_f+s) + 0.77. More studies are required to calibrate the SPAD in order to recommend it for commercial purposes in silage corn.

Keywords : N sufficiency index; foliar N; soil residual N.

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