Canopy Indices: a Model to Estimate the Nitrogen Rate for Barley and Wheat

WYNGAARD, NICOLÁS; SAINZ ROZAS, HERNÁN R.; QUEIROLO, IGNACIO; REUSSI CALVO, NAHUEL I.; PRYSTUPA, PABLO

Journal of Soil Science and Plant Nutrition

Springer Nature

Año: 2020 vol. 20 p. 2419 - 2430

0718-9508

The objectives were tocalibrate the Soil Plant Analysis Development (SPAD) and Green Seeker (GS) astools to determine the differential of the economic optimum nitrogen rate(dEONR) at different growth stages of barley and to evaluate if a single SPAD orGS calibration model can be used for two cereal crops: barley and spring wheat.Fourteen field experiments were conducted (2016?2018)evaluating five N rates. Relative canopy indices were determined using aSPAD-502 (rSPAD) and a GS sensor (rNDVI) at Z24, Z31, and Z39 growth stages.The relationship between sensor indices and dEONR was evaluated by fitting quadratic-plateau(QP) regression models. Data from a previous study was used to evaluate if aunique QP model could predict dEONR from canopy indices for barley and wheat.Statistically  significant QP models weredetermined for rSPAD and rNDVI at all evaluated growth stages. The sensitivityof these models was greater for rSPAD (0.0006 on average) than for rNDVI(0.0004 on average). A single QP model was developed to predict dEONR fromrSPAD at Z31 and Z39 barley growth stages (R2 = 0.68). Also, a unique model was developed to predictdEONR from rSPAD at Z31 and Z39, but not only for barley but also for wheat (R2 = 0.64). A single model could be used to determinevariable in-season N rates for barley and wheat, increasing the N useefficiency and limiting possible negative economic and environmental impacts offertilization over the agroecosystems.