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

Objectives Deep storage water irrigation before rain season is an efficient utilization way of rainwater and flood resources in central Shaanxi 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.

Results Compared with CK, treatment D80, D120, D140, D160, and D180 increased winter wheat yield by 8.85%, 24.71%, 30.99%, 17.91%, and 9.90%, increased the grain P accumulation at maturity stage by 37.55%, 46.34%, 38.09%, 28.23%, and 22.11%, enhanced phosphorus absorption efficiency of wheat plants by 10.10%, 12.47%, 10.25%, 7.59%, 5.95%, and decreased phosphorus apparent surplus by 13.82%, 17.05%, 14.02%, 10.39%, and 8.13%, 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 value at D120. And the apparent P surplus showed a trend of declining first and then rising, the lowest P surplus (78.83 kg/hm²) was recorded at D120, which was significantly lower than that at D160 and D180 treatments. Compared with D160 and D180, D120 treatment was more conducive to pre flowering phosphorus transport and post flowering phosphorus assimilation in wheat. D80 treatment showed lower phosphorus transport before flowering compared to D120 wheat, but showed a compensatory effect on phosphorus accumulation after flowering. Although D140 treatment reduced phosphorus accumulation after flowering, it achieved balance by increasing phosphorus transport before flowering. It was worth noting that there was no significant differences in plant and grain phosphorus accumulation between D80, D120, and D140 treatments. In addition, due to the fact that the available phosphorus content in the 20−100 cm soil layer was much lower than the environmental threshold for phosphorus leaching in the area (39.9 mg/kg), the high level of phosphorus surplus did not cause phosphorus leaching when the water storage water irrigation amounts was less than 140 cm, however, it did when the water storage depth was greater than 160 cm.

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 80–140 cm in the Northwest area.