Nitrogen deep-placement technologies for productivity, profitability, and environmental quality of rainfed lowland rice systems

The recovery of applied nitrogen by rice is low due to several loss processes operating in the ricefields. Split application of fertilizer suggested for increasing nitrogen-use efficiency is often not practical in rainfed lowland rice due to adverse soil–water situations. Hence, the entire required amount of N has to be applied in one single application when the water regime is favorable. A single broadcast application, however, increases N loss. Deep placement of urea supergranules (USG) has been proven to improve N fertilizer efficiency. The placement technology is best suited to conditions where the predominant N loss mechanism is ammonia volatilization rather than leaching or denitrification. Deep placement of USG thus has greater benefit over surface split application on soils with moderate to heavy texture, low permeability and percolation rate, and high cation exchange capacity and pH. Environments and management factors conducive to high ammonia volatilization potential would benefit most from deep-placement technology. Improved N recovery and efficiency of USG has been well-documented for lowland rice, but its market availability and methods to achieve placement pose problems. The technology has very limited adoption because USG is not commercially available or manufactured in most countries, and labor requirement is high with hand placement. Manual application creates more difficulties in handling the granules, besides taking 36–42 more hours per hectare, than 2 split broadcast applications of prilled urea. Applicators developed so far have not worked satisfactorily under standing water conditions and in direct-seeded rice conditions due to hardness of the soil. Hence, it is necessary to develop a suitable applicator to overcome these difficulties. Alternatively, for direct-seeded rice, N-fertilizers can be subsoil-banded near seedrows. The placement technology, if adopted by the farmers of the potential lowland areas in eastern India, is expected to give an additional production of 5.6 million tons of rice.