Judicious use of nitrogen (N) fertilizer in rice requires synchronizing N fertilizer applications with plant needs. Predicting plant N requirement through soil testing has not proven valuable for rice because of dynamic changes in native N supply and difficulty in predicting climatic variables that control soil N mineralization and crop growth. The chlorophyll meter is a simple, portable device that accurately measures leaf N status of rice plants in situ. It could help improve grain yield and N use efficiency (Peng et al 1996, Balasubramanian et al 1999).
The SPAD-guided N technique was evaluated in farmersÕ fields in the new and old Cauvery Delta areas of Tamil Nadu, India, during the 1996-98 wet and dry seasons (DS, kuruvai: June to September; WSI, samba: August to December/January; WS-II, thaladi: October to February). Trials were conducted by TNRRI and SWMRI to compare grain yield and N use efficiency of irrigated transplanted rice under different N management practices. Three N treatmentsÑzero-N control, local N recommendation, and SPAD-guided NÑwere evaluated in the 1996-97 trials. A fourth treatment of SPAD-guided N with a basal application of 20 kg N haÐ1 was included in the 1997-98 trials. Each farm had one replication in the old area and two in the new area.