Improving Nitrogen Efficiency in Wetland Rice Soils

Keywords: Nitrogen efficiency, Rice production, Ammonia volatilisation, Urea supergranules, Urease inhibition.

Rice is an increasingly important crop, presently feeding over 40% of the world population. In the early sixties large areas in South east Asia, the rice bowl of the world, were experiencing rice deficits. With the introduction of high-yielding rice varieties and the commitment to fertiliser use, the region has gradually become self-sufficient. Total consumption of fertiliser N on rice to date has reached 3 million metric tonnes annually, over 90% of which is urea. The efficiency of fertiliser utilisation is low, ranging from 20% to 40% recovery by the crop, dependent on source, management, and agro-ecological conditions. The poor efficiency is largely due to loss of fertiliser N, primarily volatilisation of ammonia. The loss mechanisms are discussed in some detail. Nitrogen recoveries of 60% are realistically attainable and, if achieved, would obviously result in enormous savings to developing economies and farmers alike.

Several approaches to increase fertiliser N efficiency have been discussed in this paper. Deep placement of urea (by hand or machine) seems the most readily available technique to date. Introduction of this technique will require a policy decision to produce supergranules or the development of suitable equipment for deep placement of prilled urea. An added advantage of this approach is the elimination of run-off losses, of particular importance in monsoonal rainfed rice systems.

More user friendly solutions to the efficiency problem involve the development of slowly soluble N sources, slow-release products (e.g. coatings), or the addition of inhibitors of urease in the urea production process. Only the latter approach appears to have a chance of introduction in the short run, as it does not necessarily require new fertiliser production facilities.

The economic returns on the investment at the national, production, and farm level will ultimately decide the chances of success of these products.

Paul L G Vlek, IFDC, Muscle Shoals, Alabama, USA.

Ian R P Fillery, IFDC, Muscle Shoals, Alabama, USA.

32 Pages, 7 Figures, 9 Tables, 123 references.