NITROGEN MANAGEMENT IN RICE USING CHLOROPHYLL METER AND GREENSEEKER OPTICAL SENSOR
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Date
2011
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Punjab Agricultural University, Ludhiana
Abstract
To increase fertilizer nitrogen (N) use efficiency in transplanted irrigated rice (Oryza sativa L.), gadgets like SPAD meter (chlorophyll meter) and GreenSeeker optical sensor can be used to guide application of fertilizer N when it is needed most by the crop. A threshold greenness of the first fully opened leaf from the top needs to be known to decide when to apply a dose of fertilizer N. The GreenSeeker can be employed to manage fertilizer N following an algorithm based on expected yield and response to applied N. Development of yield prediction curves to use optical sensor requires data from experiments conducted over several cultivars, locations and seasons, and thus does not allow using the optical sensor to manage fertilizer N immediately after its procurement. In this study an attempt has been made to use optical sensor following NDVI sufficiency index (ratio of NDVI of the test and over fertilized reference plots) approach which does not require prior calibration. A field experiment was conducted with rice cultivars PR118 and PR120 and 10 treatments to define the SPAD and NDVI sufficiency index thresholds when the crop needs fertilizer N application. It was found that after applying a basal dose of 30 kg N ha-1, application of 30 kg N ha-1 every time when colour of the first fully opened leaf from the top of rice plant was less than the SPAD threshold 40 or 42.5 can lead to production of high yield levels and higher fertilizer N use efficiency. In case of GreenSeeker optical sensor, after applying a basal dose of 30 kg N ha-1 at transplanting of rice and a dose 45 kg N ha-1 at 21 days after transplanting, application of a dose of 30 kg N ha-1 if the NDVI sufficiency index was less than 0.90 resulted in production of grain yield level equivalent to that produced by applying blanket fertilizer dose and fertilizer N use efficiency higher than that observed from the blanket recommendation.