No abstract

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 × 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.

No abstract

International audienc

Fertilizer nitrogen (N) is one of the major inputs in rice-wheat production systems in South Asia. As fertilizer N has generally been managed following blanket recommendations consisting of two or three split applications of preset rates of the total amount of N, improvement in N use efficiency could not be achieved beyond a limit. Feeding crop N needs is the most appropriate fertilizer N management strategy to further improve N use efficiency. Since plant growth reflects the total N supply from all sources, plant N status at any given time should be a better indicator of the N availability. The chlorophyll meter and leaf colour chart have emerged as diagnostic tools which can indirectly estimate crop N status of the growing crops and help define time and quantity of in-season fertilizer N top dressings in rice and wheat. Supplemental fertilizer N applications are thus synchronized with the N needs of crop. The chlorophyll meter may not be owned by South Asian farmers individually, but it can be made available to farmers through village cooperatives, extension specialists, and crop consultants. Leaf colour chart, a simple and cost-effective device has already penetrated into South Asian farming and increasing numbers of farmers are finding it helpful in efficiently managing N fertilizers. This paper reviews the results of investigations carried out using these diagnostic tools in managing need based N applications in rice and wheat in South Asia.