Spatio-temporal dynamics in soil water storage reveals effects of nitrogen inputs on soil water consumption at different growth stages of winter wheat

Abstract Water availability is a major constraint for wheat production in the southeast of the Loess Plateau, China. Plastic mulch exhibits greater potential in rainwater harvesting while nitrogen (N) fertilizer has a strong effect on soil water utilization. Most of annual precipitation in the Loess Plateau occurs in summer. Rainwater retention in summer fallow becomes very important for winter wheat production in the dryland of the Loess Plateau. Straw mulching in summer fallow are commonly used to prevent water evaporation from soil surface and retain rainwater. Recently plastic mulching has also been used. Nitrogen inputs have also a significant impact on soil water utilization and yield production. However, there is little information available for the effects of full coverage of plots with plastic mulch (PM) in summer fallow on soil water storage at sowing and N rates interact with the soil water utilization in winter wheat yield, water use efficiency (WUE) and grain protein concentration (GPC). Therefore, field experiments were conducted in three consecutive years with variable rainfall. The results showed that PM in summer fallow increased soil water storage at sowing by at least 50 mm, and water storage efficiency was the highest (56.5%) in the dry season. Spatio-temporal dynamics in the soil water storage of 0–300 cm depth exhibited a downward movement with crop development. Approximately half of soil water consumption from flowering to maturity was derived from the 200–300 cm soil layers. The optimal N rate with PM increased grain yield by 27% in the wet season, 36% in the normal season, and 41% in the dry season. PM in combination with optimized N could improve WUE only when annual rainfall is equal to or above the yearly average. Furthermore, evapotranspiration is negatively correlated with GPC although the soil water consumption from 200 to 300 cm depth is positively correlated with post-anthesis N uptake. This suggests that the additional N is needed to further increase GPC. In the season with soil water storage of 550–600 mm at sowing, the N rate of 225 kg ha −1 with PM could achieve the highest yield and 13.2% of GPC. In the season with soil water storage of 450–550 mm at sowing, the N rate of 150 kg ha −1 with PM could achieve the highest yield, and 14.3% of GPC. When the season with soil water storage of approximately 400 mm, the N rate of 75 kg ha −1 with PM achieved the highest yield, and 15.0% of GPC. Our results indicate that adjusting N fertilizer inputs based on seasonal variation in summer rainfall could enhance wheat yield and GPC in the southeast region of the Loess Plateau.