Site-Specific Fertilizer Nitrogen Management Using Optical Sensor in Irrigated Wheat in the Northwestern India

An optical sensor-based fertilizer nitrogen (N) management strategy that relies on visible and near-infrared spectral response from plant canopies was evaluated for irrigated wheat in the northwestern India. GreenSeeker™ optical sensor-guided fertilizer N dose, computed from an estimate of potential yield and response index, takes into account both the temporal and field-to-field variabilities and is applied only once after measuring in-season spectral response from the crop canopy. Seven field experiments were conducted in four wheat seasons to decide whether to apply the optical sensor-guided fertilizer N dose at 2nd or 3rd irrigation stage and to work out the appropriate N management before applying it. Robust relationships between in-season sensor-based estimates of yield and actual wheat yields were observed both at 2nd (R 2 = 0.64) and 3rd (R 2 = 0.86) irrigation stages of the crop. GreenSeeker-based fertilizer N management resulted in high yield levels and high N-use efficiency. Application of 30 kg N ha−1 at planting and 45 kg N ha−1 at 1st irrigation was found to be the appropriate N management before applying the GreenSeeker-guided dose at 2nd irrigation stage. Grain yields obtained by following sensor-guided N management were at par with those observed with the blanket recommendation of 120 kg N ha−1, but with greater recovery efficiency (by 6.7–16.2%) and agronomic efficiency [by 4.7–9.4 kg grain (kg N applied)−1]. The major outcome of this study was that applying a moderate amount of fertilizer N at planting and enough fertilizer N to meet the high N demand during the period between crown root initiation stage and maximum tillering stage before applying a sensor-guided fertilizer N dose at 2nd irrigation stage results not only in high yields but also in high fertilizer N-use efficiency in irrigated wheat.