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In the Chhattisgarh plains in the agroclimatic region of central India (Figure 1), farms may be characterized by one of the following: unbunded lathyritic soils, bunded rice fields (rainfed), bunded rice fields (irrigated), unbunded black soils, or rice bunds. Under these five farming situations, different crop sequences have been in vogue. New crops and crop sequences are recommended by the Agricultural University from time to time based on experimental results.
In the unbunded black soils, farmers usually plant small millets and pigeon pea. However, based on experimental results, the University has recommended soybean followed by chickpea crop sequence under rainfed conditions during monsoon and post-monsoon (winter) seasons, respectively. In the two to three years since that recommendation, the area under soybeans has increased from 3,000 ha to more than 70,000 ha. Experimental results have shown that the evapotranspiration (ET) rate of the soybean crop during peak vegetative and reproductive stages is very high, ranging between 5 mm and 6 mm per day. In view of this, soybeans have been recommended only for heavy soils. Even in black soils with high retention capacity, water stress conditions do occur during dry spells in the monsoon season. After the withdrawal of monsoon rains in September, soybeans sometimes face acute water shortage during the end of reproductive and maturity stages.