Management practices and soil nitrogen dynamics in a lowland rice-maize cropping system

The option to grow maize in the dry season can be made available to farmers in lowland areas traditionally planted to continuous rice because of the potential to raise productivity and income. However, there are soil-related concerns associated with a system characterized by alternate wetting and drying within and between seasons that must be further understood. These include soil N dynamics, with potential N losses in the dry season-wet season transition (DWT). Management practices for the rice-maize system, such as zero tillage, N fertilizer management, and residue management, may also affect this dynamics. Two researcher-manager field experiments were conducted during the 2008 and 2009 dry seasons (DS) at IRRI experimental station and in a farmer's field in San Benito, Victoria, Laguna to assess yield performance of maize and rice crops in clayey lowland soil under different tillage methods and nutrient and residue management, to assess soil water status during maize cropping under zero and full tillage, to analyze soil N dynamics during DWT between maize and rice cropping, and to evaluate the financial benefits from the rice-maize system. Yields were comparable between full and zero tillage regardless of nutrient and residue management. In farmers' field, the maize yield obtained was consistently high in both years. Soil water monitoring during maize cropping showed a benefit from zero tillage and crop residue retention with higher soil water at crop establishment and early in the growing season. Soil N dynamics, that involved the relation between soil water and soil inorganic N and the transformations that result, were highlighted during DWT especially if prolonged. Estimating the total soil N losses during the period between harvest of dry season maize and establishment of wet season rice must consider variation in levels due to nitrification-denitrification and leaching processes in response to drying and wetting cycles with rainfall episodes within this period. This research shows that farmers in lowland rice areas have an option to increase productivity and income with the rice-maize cropping system, especially when water is insufficient for a dry season rice crop. However, in years with high rainfall growing maize is also not favored in a lowland environment where the clay soil will not permit sufficient drainage of soil water. Thus, the farmer may opt to plant other upland crops better adapted to a wetter environment than maize. Zero tillage has potential in a rice-maize system, but there is still a need to test and improve this technology to address constraints specific to lowland areas with heavy clay soils. The design of farm implements that will enable good crop establishment after rice in lowland clay soil, the physical condition of which is affected by soil water content, should be considered. Fertilizer nutrient management and residue management are practices that can also be encouraged in a rice-maize system because of their potential short and long-term benefits to the soil and environment.