Regulatory effects of mulching in fallow period and phosphorus fertilization on soil reservoir of dryland wheat

To explore the effects of water-osmotic plastic film mulching in fallow period and phosphorus fertilization on soil water storage and movement, grain yield and water use efficiency of dryland wheat, field trial was conducted in Wenxi County, Shanxi Province. A split plot design was used in the trial and the mulching condition assigned to the main plot and the phosphorus fertilization rate assigned to the sub-plot. The experiment included three phosphorus fertilization levels during wheat growth period, which were 75 kg(P₂O₅)·hm^-2, 112.5 kg(P₂O₅)·hm^-2 and 150 kg(P₂O₅)·hm^-2. Two mulching conditions were set up for each fertilization treatment - water-osmotic plastic film mulching and no mulching in fallow period. Each mulching-fertilization treatment replicated three times. The results showed significant increase in soil water storage in the 0-100 cm layer under mulching treatment from sowing stage to booting stage. The soil water storage increased 38-41 mm at sowing stage compared with no mulching treatment. Increased phosphorus fertilization rate enhanced soil water storage from wintering stage to booting stage, it especially obvious for the 40-100 cm soil layer at elongation stage. Water-osmotic plastic film mulching in fallow period promoted decrement of soil water and its percentage of that of the whole growth period from sowing stage to elongation stage, and inhibited soil water decrement from elongation stage to anthesis stage. Increasing phosphorus fertilization rate significantly enhanced soil water decrement and its percentage of that of the whole growth period from elongation stage to anthesis stage. The decrement of soil water in 80-100 cm layer also increased significantly from anthesis stage to maturity stage with the increased phosphorus fertilization rate. Under mulching treatment, wheat yield increased 1 452 kg·hm^-2, water use efficiency improved by 16%, compared with those of the no mulching treatment. With the increasing of phosphorus fertilization rate, both yield and water use efficiency improved significantly. Under the combination of mulching and phosphorus fertilization, the decrement of soil water in 60-100 cm layer from elongation stage to anthesis stage and that in 80-100 cm layer from anthesis stage to maturity stage significantly correlated with wheat yield. These results suggested that mulching in fallow period in dryland be beneficial for water storage and conservation of rainfall in fallow period, which made it possible for wheat to use the rainfall in fallow period in spring and summer. Mulching in fallow period was also helpful for wheat to absorb soil moisture in early and middle growth periods. Increasing phosphorus fertilization improved wheat absorbing soil moisture in deep layer in later growth period. Mulching in fallow period combined with 150 kg(P₂O₅)·hm^-2 phosphorus fertilization in dryland wheat improved soil water retention capacity, increased wheat production and efficiency.