Topdressing nitrogen recommendation for early rice

Authors: Lihong Xue Ganghua Li Xia Qin Linzhang Yang Hailin Zhang

Publish Date: 2013/08/08

Volume: 15, Issue: 1, Pages: 95-110

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Abstract

Fertilizing based on soil test and crop nitrogen N demand is the key to optimize yields and minimize fertilizer cost In 2008 a field experiment with different N rates was conducted with early rice near Yingtan City Jiangxi Province in southern China Canopy normalized difference vegetation index NDVI with an active sensor and plant N uptake PNU were collected at key fertilization stages and the sufficiency index SI was calculated as the ratio of underfertilized and wellfertilized NDVI Rice PNU and yield were positively correlated with NDVI and SI at the tillering and panicle initiation stages Canopy SI improved the PNU and yield estimations when the relationship was validated with a different dataset A spectrallydetermined N topdressing model SDNT was established and used in combination with a target yield strategy and splitfertilization scheme An allocation coefficient for plant N requirement to accommodate the potential for high yield and soil N supply was introduced Optimum nitrogen use efficiency NUE at different growth stages was incorporated into the model The model was validated with data from a 2009 plot experiment and three production fields in 2010 The difference of recommended N rate and yield between SDNT and the current yield curve recommendation method was 21 and −07  at high planting density and −24 and −48  at low planting density respectively Compared with farmers’ N management the SDNT strategy resulted in similar or higher yield with reduced N rates higher NUE and higher net profit in both 2009 and 2010 Because canopy NDVI can be obtained while sidedressing N fertilizer in a single field pass the potential of SDNT to accommodate withinfield spatial and temporal variability in N availability should improve N management in rice

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