Establishment and Nitrogen Management for Maize Rotated with Irrigated Rice on Puddled Soil in the Tropics.

Sustainable intensification of irrigated rice-based cropping systems in the tropics is essential to meet the increasing demand for crop production and to enhance profitability for farmers. Two and even three rice crops are grown each year in intensive continuous rice cropping systems. In some areas of Asia, a rice crop in these systems is being replaced by another crop such as maize (Zea mays L.) in response to limitations in irrigation water and high demand for maize. In other areas, opportunities exist for further intensifying rice monoculture systems through addition of another crop like maize. The conversion from continuous rice to rice-maize cultivation increases soil aeration, which can lead to loss of soil organic matter and increased accumulation and loss of soil nitrate. Experiments were conducted in the Philippines to examine the establishment of maize without tillage immediately after rice grown on puddled or non-puddled soil and to assess alternative practices for N fertilization of maize. The experiments examined scenarios in which maize both replaced a rice crop and was incorporated as an additional crop in the rice-based cropping system. Yields of 8 Mg/ha were attainable for maize grown without tillage following rice grown on flooded clay soil. Maize yields were comparable with conventional and zero tillage. Comparable high maize yield were attainable with two and three times of fertilizer N application. Research demonstrated the potential to intensify irrigated rice-rice cropping with an additional crop of maize. Crop simulation models were used to identify optimized rotations of rice and maize for high productivity and profitability.