Abstract:The main factors that limit wheat productivity on the northwestern Loess Plateau in China are drought, low temperature in spring, and the seasonal rainfall dynamics, which do not meet the water requirements of wheat. Efficient conservation of rainwater in the soil, and its utilization in the wheat-growing period, are the most important means of increasing wheat yield in this region. Whole-field plastic and soil mulching (i.e., the whole soil surface in a field is first mulched with plastic, on top of which a soil layer about 1 cm thick is spread), which is commonly used for high-planting-density crops on the Loess Plateau, could significantly improve rainfall use efficiency and crop productivity. However, no systematic analysis of the productivity increment and environmental effects of this technique has been undertaken previously. Spring wheat (Triticum aestivum cv. Lunchun 27) was selected as the test material for a field experiment conducted from 2011 to 2013 to study the effects of whole-field plastic and soil mulching on soil temperature, soil moisture, water use efficiency and wheat yield. The three treatments applied were 1) whole-field plastic and soil mulching and bunch seeding (FMS), 2) whole-field plastic mulching and bunch seeding (FM), and 3) soil uncovered and bunch seeding (CK). The seasonal soil water content, soil temperature, and wheat yield were recorded and the rainwater fallow efficiency, evapotranspiration, and water use efficiency were calculated. The FMS treatment increased average soil temperature in the 0-25 cm soil profile by 1.4-3.5℃ compared with CK at the seedling stage, and reduced the surface ground temperature by 5.3-6.4℃ and 3.1-4.3℃ compared with FM and CK, respectively, at 14:00 from the booting stage to the filling stage. Both FMS and FM treatments improved soil water storage in the 0-200 cm soil profile by 33.1 mm and 29.3 mm, respectively, compared with CK before the jointing stage. Water storage was lower at deeper soil depths (100-200 cm) in FMS and FM compared with CK. At the maturing stage, the soil water storage in the 100-200 cm soil profile of the FMS treatment decreased by 44.4-69.6 mm compared with before the seeding stage, which was 8.4-145.5% higher than that of CK. However, the soil water of the FMS treatment was recharged by 77-127 mm in the fallow period, which was 4.5-40.9% and 12.8-109.5% higher than that of FM and CK, respectively. The rainwater fallow efficiency of FMS was 30.5-52.6%, which exceeded that of CK and FM by 12.8-109.5% and 4.5-40.9%, respectively. Based on the regulatory effect of soil thermal-moisture status and crop water use, the wheat yield and water use efficiency of FMS were 1750-3180 kg/hm2 and 5.5-11.5 kg hm-2 mm-1, respectively, which were 40-220% and 27-239% higher than those of CK. The increased extent of yield and water use efficiency were higher in a dry year than that in a wet year. Consequently, FMS ameliorated soil thermal-moisture status, optimized wheat water use, and increased wheat water use efficiency and yield. Rainwater fallow efficiency was significantly higher in FMS, so the soil water consumed in the wheat-growing period was recharged completely in the fallow period, which is important for maintenance of the inter-annual soil water balance.
