Nutritional physiology of the rice plants and productivity decline of irrigated rice systems in the tropics

Abstract

Rice yield declines observed in long-term experiments are associated with N and K deficiencies despite the use of recommended fertilizer rates. Modern rice varieties have an extensive root system, a large N uptake capacity, and produce about 50 kg grain per kg of N uptake. These traits have not changed over the past 30 years. Instead, reduction of soil N and K supply contribute to the observed yield declines, and these deficiencies may result from generic processes associated with management practices common to irrigated lowland rice systems. Most other limiting factors are of more local importance. Negative yield trends can be reversed by increasing the rates of applied nutrients. Maintaining high yields requires nutritional balance and attention to disease-nutrient interactions. Evidence from on-farm studies suggest that these same constraints occur in several rice production domains in the lowland tropics of Asia. Achieving continued increases in rice yields will require field-specific soil and fertilizer management to improve the congruence between nutrient supply and crop demand.