Submitted to: Terra Latinoamerica
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/29/2009
Publication Date: 11/23/2009
Citation: Torres, A., Viramontes, U., Delgado, J.A., Hernandez, G., Cueto-Wong, J., Gil, A., Rangel, P. 2009. Chlorophyll Meter SPAD-502 Calibration to Evaluate Nitrogen Requirements in Forage Corn. Terra Latinoamerica. 27:303-309. Interpretive Summary: In areas where milk and forage are produced, it is common to apply manure with chemical fertilizers, causing higher fertilization costs and contamination risks because of the nitrogen (N) losses to the environment. Although more studies are required to calibrate the SPAD and recommend it for commercial purposes in silage corn, this research suggests that there is strong potential to use these new techniques and tools to improve the management of N so N use efficiencies could be increased. Specifically, these tools could potentially be used to synchronize the application of N with N uptake so that N losses to the environment are reduced.
Technical Abstract: In this study SPAD equipment was calibrated with the objective to evaluate the relationship between the nitrogen sufficiency index (NSI) and the corn forage yield, as well as to generate preliminary regression equations to estimate the N requirements of silage corn. Increasing N rates were evaluated in a sandy clay loam soil during 2007 and 2008. SPAD measurements were taken before every irrigation event and the NSI was estimated. Regression analyses were computed between relative yield and NSI against N rate. Dry matter yield follows a quadratic equation as a function of N rate. 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 units were related to the 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 0.69, and the equation was: NSI = -2E-6X2 + 0.0012X + 0.77, where X is the N rate + residual soil N. More studies are required to calibrate the SPAD and recommend it for commercial purposes in silage corn.