Modeling Irrigated Cropping systems with Special Attention to Rice Wheat Sequences and Rice Bed Planting

Abstract

The rice-wheat cropping systems of the Indo-Gangetic Plains (IGP) are of immense importance for food security for south Asia. Over the past 40 years the increase in rice and wheat production has kept pace with population growth due to improved varieties, increased inputs, especially fertilisers, and the expansion of irrigation. However yield stagnation, and possibly yield decline, water scarcity, and water and air pollution are major threats to the sustainability of rice-wheat systems and food security. Therefore the design and implementation of alternative production systems with increased resource use efficiency (especially water) and productivity and reduced adverse environmental impact are urgently required. Bed farming, practised for several decades for crops other than rice in Australia, Mexico and elsewhere, was introduced to the rice-wheat regions of the IGP in the mid 1990s. Farmer experience and research have shown that bed farming offers significant advantages for productivity and resource use efficiency for wheat and other non-rice crops. More recently, attention has focused on the possibility of also growing rice on beds in the IGP and Australia, with the associated potential benefits of permanent bed systems including reduced land preparation costs and turn around times, increased cropping flexibility, and increased productivity of “upland” crops grown in rotation with rice due to improved drainage and soil structure and improved rotations. The radical shift from ponded rice culture on the flat (with or without puddling and transplanting) to intermittently flooded bed layouts affects a host of interacting factors influencing productivity and resource use efficiency of both rice and crops grown in rotation with rice. These factors range from weeds to nutrient availability to pests and diseases to water dynamics to stubble management options. The potential benefits and disadvantages of permanent bed systems need to be quantified under a range of agroecological conditions, and optimum layouts and management systems need to be identified to maximise potential gains. The Australian Centre for International Agricultural Research (ACIAR) is funding a major new project LWR2/2000/89 Permanent beds for rice-wheat and alternative cropping systems in north west India and south east Australia. This is a collaborative project between Punjab Agricultural University, CSIRO Land and Water and NSW Agriculture, with additional support from the International Atomic Energy Agency (IAEA/FAO) for the work in India, and additional support for the work in Australia from the Rural Industries Research and Development Corporation (RIRDC) Rice program, the Grains Research and Development Corporation (GRDC) and Coleambally Irrigation Cooperative Ltd and Murray Irrigation Ltd. The major part of the project comprises field comparison of permanent bed and traditional layouts for rice-based cropping systems in Punjab, India and NSW, Australia, with detailed monitoring, in particular focusing on crop growth and development, water and nitrogen dynamics and balances, and options for stubble management. The project also seeks to further develop and refine models for rice-wheat and alternative systems, and apply them to evaluate permanent bed and traditional layouts for a range of agroecological environments, and to identify options for maximizing resource use efficiency and productivity of rice-wheat cropping systems in India, and rice-based cropping systems in Australia. Therefore an early activity in the project vi was a workshop bringing together a small group of international scientists leading in the development and application of crop models including the modelling of crop sequences and twodimensional approaches. The objectives of the workshop were: 1. to review the state of the art in the modelling irrigated cropping systems (crop sequences as opposed to single crops) and bed geometries (as opposed to “flat” layouts) 2. to workshop conceptualizations of the ways forward in modelling crop sequences and bed layouts, and with particular attention to rice-wheat systems 3. to establish a network of contacts working in these areas to share progress and problems in the future.