VOLUME 7 NUMBER 2 (July to December 2014)

by Virginia C. Cuevas*¹, Joey I. Orajay², and Cirilo A. Lagman, Jr.³

¹Institute of Biological Sciences, CAS, UPLB, College, Laguna, Philippines
²Crop Protection Cluster, CA, UPLB, College, Laguna, Philippines
³Department of Soil Science, BSU, La Trinidad, Benguet, Philippines

A rice paddy field experiment was conducted during the 2012 dry season in Brgy. Cabiten, Mankayan, Benguet to test the efficacy of rice straw compost amendment in reducing available Cu in soil and observe its effect on rice yield. Three treatments in randomized complete block design were made with four replicates each: T₀ - no compost added, T₁ - compost applied at 16 kg m^-2 and T₂ - compost applied at 32 kg m^-2. Mineral fertilizer was applied in all treatments. The subject of the study was the cold-tolerant rice variety, C18. Compost application significantly increased mean grain yield by 23.0% compared to control. The mean grain yield with treatment T₀ was 246 kg m^-2, with T₁ was 320 kg m^-2 and with T₂ was 325 kg m^-2. The available mean soil Cu was significantly reduced from 281 ppm in the control to 25 ppm with T₁ and 15 ppm with T₂. The mean soil pH after harvest also significantly improved to pH 5.66 with T₀, to 5.95 with T₁ and to 6.12 with T₂. There was a significant correlation of the Cu contents in the soil and in rice roots with T₀ having the highest content in both soil and roots, decreasing with T₁ and lowest with T₂. Mean Cu contents in straws were very low at 3 to 5 ppm, and were not significantly higher Cu (260 ppm with T₁, 155 ppm with T₁ and 26 ppm with T₂) than the straws. The results of this field study demonstrate that the use of rice-straw compost is a good remediation strategy for reducing soil Cu toxicity to the normal limit of 30 ppm, and for improving rice yield.