Yield and phosphorus transformations in a rice-wheat system with crop residue and phosphorus management
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Phosphorous deficiency limits productivity of rice (Oryza sativa L.)-wheat (Triticum aestivum L.) systems in the Indo-Gangetic Plains. Deterioration of soil and air quality due to straw burning is also a concern. Field experiments were conducted to determine the effects of straw and P management strategies on yield, P balance, and P transformations in soil in a rice-wheat system. Four treatments composed of different combinations of rice and wheat straw removal, burning, and incorporation were the main plots. Subplot treatments were P fertilization to wheat or to both rice and wheat and a no-P control. Wheat yield was similar where straw was burned in situ or removed. Incorporation of straw increased the wheat yield in Year 4. Significant straw x P management interactions, observed after 4 yr, suggested that residues can enhance yield under limited P supply situations. Application of 26 kg P ha(-1) to wheat increased grain yield by 6 to 15% compared with no P. Rice yield did not respond to incorporation of residues or P fertilization. The P balance was negative with removal or burning of rice straw, but when both wheat and rice straw were incorporated, the balance was positive at the recommended P level (26 kg P ha-1 to wheat only). Changes in total soil P suggested that the two crops remove significant P from below 15 cm. Incorporation of residues increased soil Olsen, inorganic, and organic P; reduced P sorption; and increased P release. Data show that continuous incorporation of residues substituted for 13 kg inorganic P ha(-1) yr(-1) and improved system yield.
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