Changes in paddy soils under transition to water-saving and diversified cropping systems

Abstract

Most rice (Oryza sativa L.) is produced on soils with a prolonged period of submergence. Soil submergence has helped sustain the productivity of continuous rice production systems. It helps maintain soil organic matter (SOM), favors input of N through biological nitrogen fixation, and enhances availability of soil P to rice. Rice will increasingly be produced within political and economic environments of less supply of irrigation water and more income opportunities from alternative crops. This will lead to changes in water management, rice cultivation practices, and cropping patterns resulting in reduced soil submergence and increased duration of soil aeration. Soil aeration alters soil biogeochemical processes, which can lead to loss of SOM, reduced supply of plant-available N and P, and reduced zinc and iron availability on high-pH soils. Soil aeration favors the formation of nitrate, which can be lost via denitrification upon soil submergence for rice cultivation. Soil drying and wetting favor increased emission of nitrous oxide and reduced emission of methane. The productivity of paddy soils, which has been sustained with ample water resources, must in the future be sustained with management interventions that more effectively use water and provide enhanced crop diversification and income generation.