Tuesday, 11 July 2006

Plant-Need Based Real Time Nitrogen Management in Rice Grown by Small Farmers in Asia.

Bijay Singh1, Yadvinder Singh1, Meharban Singh1, G.P.S. Sodhi1, J.K. Ladha2, and Vethaiya Balasubramanian3. (1) Department of Soils, Punjab Agricultural University, Ludhiana, Punjab, India, (2) International Rice Research Institute, First Floor, CG Block, National Agriculture Science Centre, DPS Marg, PUSA, New Delhi, India, (3) International Rice Research Institute (IRRI), Los Banos, DAPO Box 7777, Metro Manila, Philippines

Chasing for high yields of rice (Oryza sativa L.), many small farmers in Asia tend to apply fertilizer nitrogen in excess of the requirements. They understand that fertilizer applied at excessive rates costs money, yet they are inclined to manage fertilizer nitrogen to minimize the risk of deficiency, which may lead to excessive fertilizer applications. Synchronization of fertilizer nitrogen application to rice with crop N demand can result in high yields, reduced losses of N, efficient utilization of applied N, avoiding excessive use of fertilizer. Flexibility of farmers in adjusting the timing and amount of fertilizer applied offers great potential to synchronize nitrogen application with the demand of the rice crop. Real-time N management revolves around quick and reliable tools to decide on the time when fertilizer N needs to be applied to the crop. Real-time N management requires the identification of an optimal leaf colour that must be maintained throughout the season to obtain high yields. The Leaf Color Chart (LCC) is a simple innovation enabling farmers to apply nitrogen fertilizer as and when needed by a rice crop. A green colour shade of 4 on the LCC represents greenness that has been found to be a threshold value for rice varieties prevalent in the northwestern India. Rice crops with leaf colour below the threshold greenness shade (LCC 4) suffer from N deficiency and require immediate N fertilizer application to prevent yield losses. In 24 on-farm trials on LCC-based nitrogen management in rice carried out in northwestern India, rice yields were similar to those obtained by applying recommended dose of 120 kg N ha-1 but 27, 35 and 29 kg N ha-1 less fertilizer was used by real-time nitrogen management in 2000, 2001 and 2002, respectively). At some locations, LCC based N management also helped to achieve higher yield with lower input of fertilizer N than the recommended blanket application of fertilizer N. In 107 on-farm experiments on rice conducted in 2002, average yield recorded in LCC based real-time N management and that obtained by following farmer's practice were identical. On average about 40 kg N ha-1 less fertilizer was applied following need-based fertilizer management as compared to the farmer's practice. In 48 on-farm experiments conducted at different locations in northwestern India, LCC-based N management was tested on rice varieties commonly grown by small farmers in northwestern India. Savings of 16 to 43 kg N ha-1 were observed for 7 different rice cultivars by applying N using LCC rather than following the farmer's practice. There was no difference in the yield of rice for any of the varieties. Keeping in view that plant population in transplanted rice varies greatly in farmers' fields; LCC-based N management was tested vis--vis recommended and farmer's practice of applying N at 22 and 33 hills m-2 plant population. Under both situations similar savings in nitrogen fertilizers were obtained as compared to recommended and farmer's practice but with similar yields. These data suggest that LCC is a promising tool to optimize N use. It is effective in avoiding over application of nitrogen fertilizers and can be an eco-friendly tool in the hands of farmers.

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