STUDY ON SITE-SPECIFIC NUTRIENT MANAGEMENT (SSNM) FOR HIGH-YIELDING RICE IN THE MEKONG DELTA

Abstract

The study was conducted in two seasons (Dry and Wet season) at three soil series (alluvial, acid sulfate, and saline-acid sulfate soil) in the Mekong Delta. The results of study showed that: SSNM provided an increase in grain yield about 0.5 t/ha and gave higher benefit than FFP. Fertilizer rate as estimated by SSNM is almost met the requirement of crop, therefore it could save nutrients, especially nitrogen which was applied too high by farmers. SSNM is a simple technique that farmers can be easily applied. FERTILIZER USING IN THE MEKONG DELTA: A REALITY Total amounts of inorganic fertilizers consumption for rice crop in the Mekong Delta area are around 400,000 tones of nitrogen, 180,000 tones of phosphorus, and 120,000 tones of potassium yearly. Most of these are imported and only small quantity is produced in the country (Pham 2005). Fertilizer use efficiency is low due mainly to losses through volatilization, leaching, run off etc. The amount of fertilizer losses is around 1.2-1.3 M tons out of the total fertilizer application (2 M tons) (Nguyen 2002). In fact, fertilizers consumption is varied depending on rice variety, soil condition and farmer practices. Although, there are specified fertilizer recommendations for each soil type but still practice as their ways. Nitrogen fertilizer recommendation for specific rice regions are proposed for areas of Tien and Hau rivers, nitrogen fertilizer dose ranges from 100 to 120 kg N/ha in dry season and 80 to 100 kg N/ha in wet season. In acid sulphate soils such as Long Xuyen quadrangle, West Hau river and Dong Thap Muoi, N-fertilizer recommendation is lower than the area of alluvium soils i.e. 80-100 kg N/ha in dry season and 60 to 80 kg N/ha in wet season. However a small area of the coastal region from Long An to Ca Mau, N-fertilizer recommendation is as low as 30-50 kg N/ha. Actually, farmers in the Mekong Delta prefer to apply nitrogen fertilizer more than recommendation dose. In many cases, they applied nitrogen fertilizer higher in wet than in dry season because they perceive that nitrogen content is lower in wet season than dry season due to shortage of sediment. However, according to many researches, unfavorable weather conditions such as high temperature, low pH value or organic acid toxicity etc. are the main constraints for rice production in this season. Moreover, farmers do not pay much attention on phosphorus and potassium fertilizers resulting in unbalanced nutrient content for wet season crop. Normally, farmers divide fertilizers in to 3 to 4 splits (even 6-7 times) to apply in a crop season. According to many recommendations, nitrogen fertilizer is suggested to apply by 3 times/crop depending upon the crop growth stages. With the longer crop duration (120 days), nitrogen fertilizer is applied at 10-15 day after sowing (DAS), 30-35 DAS and 65-70 DAS. Nowadays, with the short-duration rice genotypes (90-110 days) or the ultra-short genotypes (below 90 days), rates and timing for nitrogen application are also changed. So far, we do not have a suitable fertilizer recommendation for the ultrashort rice genotypes (<90 days). However, recent investigations suggested the time of nitrogen application for the ultra-short rice varieties as: 7-10 DAS, 18-22 DAS and 37-40 DAS (Pham 2005).

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