Water use patterns and agronomic performance for some cropping systems with and without fallow crops in a semi-arid environment of northwest China

Winter wheat (Triticum aestivum L.) monoculture, characterized by a 2-3 mon th summer fallow (from the wheat harvest in early July to sowing in late Se ptember), not only lowers the overall precipitation-use efficiency because of the large amount of water evaporated from the bare soil during the fallo w period but also has a high risk of the erosive action of rainstorms. To d evelop effective cropping systems as alternatives for farmers, thirty-two 3 -year crop rotation systems with and without fallow crops were established and their water use pattern, agronomic performance and soil conservation ch aracteristics were evaluated in a semi-arid region of northwest China. Comp ared with wheat monoculture, the 16 rotations without fallow crops produced more grain yield and greater water-use efficiency. Among the 16 rotations with fallow crops, seven patterns were significantly greater in grain yield and five patterns were significantly higher in water-use efficiency than w heat monoculture. Cropping systems showed a marked increase in evapotranspi ration when fallow crops were added to the rotation largely because of bett er utilization of seasonal precipitation. On average, the 16 rotations with fallow crops utilized 17 and 27% more precipitation than the 16 rotations without fallow crops and wheat monoculture. The use of the fallow crops did not greatly influence the quantity of water stored in the soil for use by the subsequent wheat crop because their growth depends only on growing-seas on precipitation. From a perspective of soil conservation and productivity improvement, it appears highly viable to cultivate winter wheat followed by a 2-3 month fallow crop in 1 year and a summer crop cultivation in the nex t. This system allows the soil to be covered during both easily-eroded rain y periods but lies bare 6 months every 2 years. As most of this 6-month per iod is winter, not only is soil evaporation reduced but also the danger of erosion is low. (C) 2000 Elsevier Science B.V. All rights reserved.