CSIRO PUBLISHING www.publish.csiro.au/journals/ajsr Australian Journal of Soil Research, 2005, 43, 623–628 Rice growth and post-rice mungbean in relation to two puddling intensities under glasshouse conditions G. Kirchhof A,B and H. B. So A A The University of Queensland, School of Land and Food Sciences, Brisbane, Qld 4072, Australia. B Corresponding author. Email: g.kirchhof1@uq.edu.au Abstract. The effect of soil puddling on growth of lowland rice (Oryza sativa) and post-rice mungbean (Vigna radiata) was investigated using mini rice beds under controlled glasshouse conditions. Each mini rice bed was approximately 1 m 3 in size. Three different soil types were used: a well-drained, permeable loam; a hardsetting, structurally unstable silty loam; and a medium clay. Rice yields were reduced by low puddling compared with high puddling intensity on the loam but not affected on the heavier textured soils (silty loam and clay). Yield of mungbean was reduced on highly puddle, structurally unstable soil, indicating that puddling should be reduced on structurally unstable soils. Under glasshouse condition where crop establishment was not a limiting factor and plant available water in 0.65 m of soil was 100 mm, mungbean yields of >1 t/ha were achieved. However, under conditions where subsoil water reserves were depleted for the production of vegetative biomass during initial optimal growing condition, grain yield remained well below 1 t/ha. Additional keywords: rice, mungbean, tillage, soil puddling, soil structure, dryland. Introduction The total global area of rainfed lowland rice (Oryza sativa) was 40.5 million ha in 1992 (IRRI 1993), which is 18% of the global rice supply. Most of these areas are located in Asia: 36% in south Asia, 43% in south-east Asia, and 27% in east Asia (IRRI 1993). In these areas rice is grown during the wet season on bunded fields. Soil preparation for rice traditionally requires soil puddling. It assists in weed control, facilitates transplanting, and reduces water loss through a decrease in water percolation rates, and therefore flooded conditions can be maintained for at least part of the rice cropping season. Irrigation is limited and generally not available during and after the rice crop. Rice fields are often left fallow due to the lack of water for an upland crop in the dry season following rice. However, soil water contents are generally high after rice harvest following several months of inundated conditions. Usage of soil water stored in the profile should be sufficient to grow a moderate upland crop, provided crop establishment is adequate and roots can access the subsoil water store. Potential crops in rice rotations are pulses, e.g. soybean (Glycine max), mungbean (Vigna radiata), or groundnut (Arachis hypogaea), wheat (Triticum aestivum), and maize (Zea mays). Maize is generally grown at the end of the dry season and harvested before rice planting. In The Philippines, mungbean contributed 35% of the net return in a rice–mungbean–fallow system, although mungbean yields were as low as 0.33t/ha following a rice crop of 4.1 t/ha (IRRI 1994). Under experimental conditions, mungbean yields of >2 t/ha were achieved without irrigation (IRRI 1985). Yields were mainly affected by rooting depth. Yield increases for mungbean of 100 kg/ha were observed for additional exploitable soil depth ranging from 0.07 to 0.13 m (IRRI 1985, 1986, 1988). Poor soil physical conditions are the major limiting factor for successful upland cropping following rice. Soil puddling degrades soil structure and leads to reduced infiltration rates. Although macropores as elongated transmission pores are decreased, the total porosity of puddled soils is generally increased due to an increase in small pores (Pagliai and Painuli 1988; Sharma and Bhagat 1993). The strength of puddled soil increases rapidly during drying (Cook et al. 1995). This is important for seed germination and crop establishment. If seeds are sown too late after rice harvest, soil strength may be too high, resulting in poor crop establishment and shallow root systems with subsequent early onset of water stress leading to poor yields or crop losses. If seeds are sown too early after rice harvest, anaerobic conditions may reduce crop establishment and decrease yield potential (IRRI 1987). A potential strategy to minimise soil structural degradation in rice-based cropping systems is a reduction in soil puddling (So and Woodhead 1987). Although beneficial effects from reduced puddling may increase post-rice legume yields, it may also increase water use, increase © CSIRO 2005 10.1071/SR04067 0004-9573/05/050623