Carbon and nitrogen availability in an alfisol sandy loam soil as influenced by rice straw quality
2002
Pangga, G.V. (Philippines Univ. Los Banos, College, Laguna (Philippines) Farming Systems and Soil Resources Inst.) Blair, G.J.
Plant residues that remain in the field after harvest contribute to a large portion of the organic matter of the soil. These are vital resources for the conservation of soil productivity. Residues replace the organic matter used up during production and also are important sources of nutrients. The different characteristics of these crop residues affect the decomposition rate and the release of the available nutrient elements. The availability of carbon and nitrogen in the soil was studied after straws of different rice varieties (Soc Nau, IR-67962, IR-30) were added to a sandy loam soil with low fertility. The effects of flooding, fertilization and variety of incorporated straw on the availability of carbon and nitrogen in the soil were examined at different growth stages of the rice plant. Release of nutrient from the straw was dependent on the quality of the straw after it has been mixed with the soil. A high quality straw is characterized by high nitrogen and low carbon content or low C:N ratio and high amount of digestible organic matter and low amount of lignin ( a complex chemical component which can make straw woody). The usual flooding practice decrease the amount of available total carbon and nitrogen in the soil. The straw residue with high nitrogen level and low carbon:nitrogen ratio increased the availability of these nutrient elements. `Soc Nau' had better quality straw than `IR-67962' and `IR-30'. Application of high rates of fertilizers likewise increased the availability of nitrogen ions. There are more carbon and nitrogen available to the rice plant at active tillering stage than at later stages of plant growth. This study revealed that crop residues of high quality and cultural practices like fertilization result in more available nitrogen and carbon released to the soil
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