Soil fertility assessment and mapping of irrigated rice areas in Isabela [Philippines]
2010
Results of soil analysis on 4,430 samples showed that all areas were deficient in N, with % OM [organic matter] ranging from 0.1 to 3.6. Using the Table of Fertilizer Recommendations formulated by the Bureau of Soil and Water Management [BSWM], the recommended amount of N fertilizer is 60-120 kg for hybrid rice and 40-80 kg for inbred rice varieties. A total of 109,706.44 ha or 96.49% were P deficient, with P content ranging from 0 to 30 ppm. These soils required 20-60 kg P/ha. Compared with the 2003-2005 fertility assessment results, the P deficient areas increased by 9.49%. K deficient soils were mapped in 107,479.06 ha or 94.53%. These areas had K contents of 0-150 ppm, requiring 30-60 kg K/ha. The extent of deficiency increased by 19.05% compared with the 2003-2005 assessment results. Zn deficient soils were plotted in 78,601.26 ha or 69.13% of the total area which was 8.43% lower than the 2003-2005 results. Zn deficient soils contained 0-1.15 ppm Zn, requiring 10-20 kg Zn sulfate per hectare. The decline in Zn deficient areas was a result of the Zn sulfate intervention provided by DA [Department of Agriculture, Quezon City, Philippines].
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