Effect of deep storage water irrigation amount on the phosphorus utilization of winter wheat and loss risk down to deep soil

Objective Deep storage water irrigation before rain season is an efficient utilization way of rainwater and flood resources in central Shanxi province. As the potential risks of nutrient leaching, and reduced fertilizer utilization efficiency due to large irrigation water volume, we studied the effect of storage water irrigation volumes on wheat P utilization, apparent P balance, and leaching risks down to deep soil.

Methods A field experiment on wheat was conducted in the Baojixia Irrigation Area of the Guanzhong Plain (Caoxinzhuang Farm, Yangling Demonstration Zone),.with winter wheat cultivar "Xiaoyan 22" as the test material. The treated storage irrigation water volumes were 0, 80, 120, 140, 160, and 180 cm, denoted as CK, D80, D120, D140, D160, and D180, respectively. The biomass and P contents in various organs of winter wheat were analyzed for the calculation of wheat phosphorus uptake, phosphorus fertilizer utilization efficiency, and apparent P surplus. The available phosphorus content in 0−200 cm soil layers were measured for the assessment of P leaching down to deep soil.

Result Compared with CK, D80, D120, D140, D160, and D180 water storage irrigation increased winter wheat yield by 8.85%, 24.71%, 30.99%, 17.91%, and 9.90%, respectively. The phosphorus accumulation at maturity stage grains increased by 37.55%, 20.91%, 46.34%, 38.09%, 28.23%, and 22.11%, respectively. The phosphorus absorption efficiency of wheat plants increased by 10.10%, 12.47%, 10.25%, 7.59%, 5.95%, 12.46%, and the phosphorus apparent surplus decreased by 13.82%, 17.05%, 14.02%, and 10.39%, 8.13%, and 17.05%, respectively.With the increase of water storage irrigation volume, the P accumulation in wheat showed a trend of first increasing and then decreasing, reaching the highest at D120; The apparent P surplus reached lowest (79.83 kg/hm²) at D120, which was significantly lower than at D160 and D180 treatments. Within volume of 80−140 cm, the storage water irrigation promoted pre-anthesis P export and post-anthesis P assimilation, and the resulted available P in 0−200 cm soil layer during the mature period was lower than the environmental threshold for leaching (39.9 mg/kg), indicating a lower risk of available phosphorus leaching; When the storage water irrigation volume was greater than 140 cm, the wheat P absorption significantly decreased, and the pre-anthesis P export decreased, and the soil available P showed obvious downward migration trend, with a significant increased P surplus.

Conclusions Appropriate storage water irrigation volume significantly improves the efficiency of wheat phosphorus absorption and utilization, and controls the soil available phosphorus content within threshold of P leaching, and reduces phosphorus surplus in soil. The suitable irrigation volume for water storage is not more than 140 cm in the Northwest area.