ABSTRACT
In the 1950s, rice (Oryza sativa L.) and wheat (Triticum aestivum L.) accounted for only one third of the grain production in India. This proportion rose to more than 70% by 1989 (Maklin and Rao, 1991). One third of the irrigated rice and half of the irrigated wheat in South Asia come from the rice-wheat cropping system. Rice-wheat systems occupy 24 million ha of cultivated land in the Asian subtropics. In South Asia, the system occupies about 13.5 million ha (10 million in India, 2.2 million in Pakistan, 0.8 million in Bangladesh, and 0.5 million in Nepal), extending across the Indo-Gangetic floodplain into the Himalayan foothills (Ladha et aI., 2000). Rice-wheat systems cover about 32% of the total rice area and 42% of the total wheat area in these four countries, and they account for one quarter to one third of the total rice and wheat production (Hobbs and
Morris, 1996; Huke et aI., 1994a, b; Woodhead et aI., 1994a, b). In the first decade after the introduction of improved rice and wheat varieties, grain production grew rapidly, propelled by increased cropped area as well as by higher yields. More recently, however, the area devoted to rice and wheat has stabilized, and further area expansion seems out of the question-in fact, cropped area may even decline in the years to come (Hobbs et aI., 1998). The need for higher yields has come at a time when evidence is accumulating that growth in rice and wheat yields has started slowing down in the high-potential agricultural areas of northwestern India and Pakistan. There is evidence of declining partial and total factor productivity* (PFP or TFP) (Hobbs and Morris, 1996; Ali and Byerlee, 2000; Murgai, 2000). A diagnostic study of constraints in rice-wheat cropping systems was conducted by CCS Haryana Agricultural University, Hisar, CIMMYT, IRRI, and ICAR and showed that a high population of Phalaris minor-a serious weed of wheat in the rice-wheat cropping system-and a decline in soil productivity were two major constraints of the system (Harrington et aI., 1992). Other causes of decline in the TFP of the rice-wheat cropping system throughout the region included declines and changes in soil organic matter (SOM), a gradual decline in the supply of soil nutrients causing nutrient (macro and micro) imbalances due to inappropriate fertilizer applications, a scarcity of surface and groundwater, and in some places poor water quality (Paroda et al., 1994). At the time of the diagnostic survey conducted in 1991 (Harrington et aI., 1992), scientists at Haryana Agricultural University were gathering evidence that herbicide (e.g., isoproturon) resistance had developed in Phalaris minor, and it was confirmed in 1992-1993 (Malik and Singh, 1993, 1995). These studies provided the scientific community with a framework for setting research priorities (Hobbs, 1994). The resource conservation technology requirements differed in various areas of the IndoGangetic Plains. Herbicide resistance and problems with lowering water tables were major factors in Haryana, India (Malik et aI., 1998). To answer these sustainability issues, work began on no-tillage and bed planting in wheat in collaboration with the Rice-Wheat Consortium for Indo-Gangetic Plains, CIMMYT-Mexico and ACIAR-Australia in 1997.
