Agronomic management practices in dryland wheat result in variations in precipitation use efficiency due to their differential impacts on the steps in the precipitation use process

Yield loss due to low precipitation use efficiency (PUE) occurs frequently in dryland crop production. PUE is determined by a complicated process of precipitation use in farmland, which includes several sequential steps: precipitation infiltrates into the soil, the infiltrated precipitation is stored in soil, the soil-stored precipitation is consumed through transpiration or evaporation, transpired precipitation is used to produce dry-matter, and finally dry-matter is re-allocated to grains. These steps can be quantified by six ratios: precipitation infiltration ratio (SW/SWe; SW, total available water; SWe, available soil water storage at the end of a specific period), precipitation storage ratio (SWe/P; P, effective precipitation), precipitation consumption ratio (ET/SW; ET, evapotranspiration), ratio of crop transpiration to evapotranspiration (T/ET; T, crop transpiration), transpiration efficiency (B/T; B, the increment of shoot biomass) and harvest index (Y/B; Y, grain yield). The final efficiency is then calculated as: PUE=SWeP×SWSWe×ETSW×TET×BT×YB. Quantifying each of those ratios is crucial for the planning and execution of PUE improvements and for optimizing the corresponding agronomic practices in a specific agricultural system. In this study, those ratios were quantified and evaluated under four integrated agronomic management systems. Our study revealed that PUE and wheat yield were significantly increased by 8–31% under manure (MIS) or biochar (BIS) integrated systems compared to either conventional farmers' (CF) or high N (HN) integrated systems. In the infiltration and storage steps, MIS and BIS resulted in lower SWe/P but higher SW/SWe compared with CF and HN. Regarding the consumption step, the annual ET/SW under MIS and BIS did not increase due to the higher ET after regreening and the lower ET before regreening compared with CF or HN. The T/ET was significantly higher under MIS and BIS than under CF or HN. In the last two steps, transpiration efficiency and harvest index were less strongly affected by the agronomic management system, although both values varied considerably across the different experimental years. Therefore, attempts to achieve higher PUE and yields in rainfed wheat through agronomic management should focus on increasing the T/ET and SW/SWe, while maintaining ET/SW throughout the year and keeping SWe/P relatively low at harvest time.