Soil-coated ultrathin plastic-film mulching and suitable irrigation improve water use efficiency of winter wheat

Abstract: More than 70% of water is used for agriculture, excessive water consumption for conventional winter wheat production is aggravating the groundwater crisis in Hebei Plain. In order to mitigate the water supply and demand conflict, a field experiment was conducted from 2011 to 2014 (October-June) in Shenzhou County, where more than 90% of the agricultural fields are used for the winter wheat-summer maize double-cropping. A randomized block design was employed with six treatments and four replicates, the treatments included: 1) soil-coated ultrathin plastic-film mulching (SUPM) with 75 mm irrigation at jointing stage, 2) SUPM with 75-mm irrigation at heading stage, 3) SUPM with 75 mm irrigation at filling stage, 4) rainfed under SUPM, 5) rainfed, 6) conventional farmers' practice with 225 mm irrigation splitted into three applications (control). The study examined the effects of SUPM with different irrigation management on WUE, yield formation of winter wheat. The fieldwork procedure of SUPM was as follows: the straw of the previous crop was removed, and after base dressing with chemical fertilizer the field was plowed twice, the field surface was leveled, and wheat seeds were sown. The whole plot was mulched using ultrathin 0.004-mm-thick plastic film without separation between adjacent strips of film. The film was tensioned and its surface kept flat without folding, then 1-2 cm of soil was manually placed on it; consequently, the film was completely covered with soil. A wheat plumule could pierce the film and emerge. So relative seamless coverage of field was achieved to control soil water evaporation. After the wheat was harvested, summer maize was manually dibbled without plowing, only 60 mm irrigation applied after sowing during its whole season. The result showed that under SUPM the seedlings and spike number decreased by 8.6%-12.0% and 7.4%-11.7%, respectively, compared with the control, but the 75 mm irrigation at jointing or heading stage ensured the biomass formation and increased grain number per spike and kernel weight. The timely 75 mm irrigation under SUPM promoted the dry matter transfer to grain from vegetative organs, the transfer amount was 37.2%-57.3% higher than the control, and the contribution rate of transfered matter to grain increased by 4.7-10.1 percentage points. Also, the field water consumption decreased by 99.9-118.9 mm, and the water-use efficiency increased by 26.1%-34.5%. Regression analysis showed, under SUPM with 118 mm filed water consumption from jointing to heading, wheat could obtain the most biomass, and with 78 mm from heading to filling could achieve more than 15 fertile spikelets per spike and a higher leaf area index with the value of 5 at filling stage. This was why the wheat whose field water consumption was only 3/4 of the control could achieve an equivalent grain yield to the control. In the study, as wheat growing process and the cropping years continued, the soil water in 2 m soil body tended to decrease, and greater water deficit occurred as the soil layer was closer to the surface. Furthermore, the layer of soil water extracted by the rainfed wheat was deeper than that irrigated. From the second growth season, the continuous soil drought resulted in the yield reduction of the wheat which was irrigated until filling stage, the irrigation at filling stage was unhelpful for yield and increased the field water consumption. As the soil water decreased continuously, it was very necessary that the irrigation was earlier applied to increase yield and WUE. The soil water content at wheat sowing in autumn was significantly higher than that at harvest of previous wheat in summer, decreasing soil water consumption from sowing to jointing was crucial for water-saving of wheat production. SUPM could conserve soil water in autumn and winter，and to supply across seasons for wheat growing in the following spring. Overall, in Hebei Plain SUPM in combination with timely 75 mm irrigation could be considered a new method to decrease the water consumption, improve WUE and maintain grain yield of wheat production effectively.