Straw mulching is an effective measure to conserve soil moisture. However, the existence of straw on the soil surface also affects soil temperature, which in turn influences crop growth, especially of winter crops. Five-year field experiments (2000)(2001)(2002)(2003)(2004)(2005) investigated the effects of straw mulching and straw mass on soil temperature, soil evaporation, crop growth and development, yield and water use efficiency (WUE) of winter wheat (Triticum aestivum L.) at Luancheng Station on the North China Plain. Soil is a moderately well-drained loamy soil with a deep profile at the station. Two quantities of mulch were used: 3000 kg ha 21 [less mulching (LM)] and 6000 kg ha 21 [more mulching (MM)], representing half and all of the straw from the previous crop (maize). In the control (CK), the full quantity of mulch was ploughed into the top 20 cm of soil. The results showed that the existence of straw on the soil surface reduced the maximum, but increased the minimum diurnal soil temperature. When soil temperature was decreasing (from November to early February the next year), soil temperature (0-10 cm) under straw mulching was on average 0.3°C higher for LM and 0.58°C higher for MM than that without mulching (CK). During the period when soil temperature increased (from February to early April, the recovery and jointing stages of winter wheat), average daily soil temperature of 0-10 cm was 0.42°C lower for LM and 0.65°C lower for MM than that of CK. With the increase in leaf area index, the effect of mulching on soil temperature gradually disappeared. The lower soil temperature under mulch in spring delayed the development of winter wheat up to 7 days, which on average reduced the final grain yield by 5% for LM and 7% for MM compared with CK over the five seasons. Mulch reduced soil evaporation by 21% under LM and 40% under MM compared with CK, based on daily measuring of microlysimeters. However, because yield was reduced, the overall WUE was not improved by mulch.

With intensifying water shortage, adoption of deficit irrigation strategies is likely to increase around the world. Winter wheat (Triticum aestivum L.) is one of the crops that has successfully been grown with deficit irrigation in the North China Plain. However, irrigating once before winter wheat enters dormancy (simplified as winter irrigation [WI]) is still a popular practice in this region. This study investigated the necessity of this irrigation and its effects on crop performance to provide guidelines for better irrigation management. Field experiments at two sites with up to five irrigation treatments (from rainfed up to three irrigations with or without WI) in a randomized block design with four replications were conducted for two to three winter wheat growing seasons from 2006 to 2009 in the North China Plain. Results showed that with good soil moisture at sowing, winter wheat achieved its maximum grain production with two irrigation applications in dry seasons and one irrigation application in wet seasons, both without WI. Winter irrigation increased evapotranspiration by 20 to 25 mm (0.79 to 0.98 in) and increased drainage from the root zone profile by 20 mm during the long winter dormancy period. With good soil moisture conditions at sowing plus some rainfall, soil moisture before winter wheat enters dormancy would be adequate so WI would have little effect on crop growth. Otherwise, the moisture for the top 50 cm (19.69 in) soil profile might become too dry, which would have a negative affect on winter wheat growth at the recovery stage without WI. However, even under dry conditions, WI didn't increase yield of winter wheat with a postdormancy irrigation in early spring. With the same number of irrigation applications, the ones with WI produced lower water-use efficiency (WUE) values than the ones without WI. Under limited irrigation application, irrigation in early spring after winter dormancy produced greater yield and WUE than that with WI. Applying WI encouraged root growth at the topsoil profile, while withholding WI enhanced root length density in the deep soil layer. The results showed that WI increased evapotranspiration and drainage and reduced WUE. Thus, WI should be replaced by early or late spring irrigation after winter dormancy depending on soil moisture conditions.

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