Modification of the RZWQM2-P model to simulate labile and total phosphorus in an irrigated and manure-amended cropland soil

With the expansion of the dairy industry, phosphorus (P)-enriched dairy manure has increasingly been used to replace chemical fertilizer to meet crop nutrient demand. This practice could lead to excessive total P accu-mulation in the soil and increase the risk of P pollution in the environment. The newly-developed RZWQM2-P model uses the soil P pool structure from the EPIC model, which is not sensitive to total soil P. Therefore, we modified the P module in RZWQM2-P to improve its capability in simulating total soil P. We subsequently assessed the ability of the modified model to simulate labile soil P, total soil P, plant P uptake, and crop yield using a dataset collected from an irrigated field treated with dairy manure and inorganic fertilizer at eight rates under a repeating wheat-potato-barley-sugar beet rotation. The results suggested that the modified RZWQM2-P model satisfactorily simulated field-measured annual total soil P, plant P uptake, and crop yield. Labile soil P was simulated less accurately, but the results were acceptable as the model responded well to P treatments. We simulated the long-term soil P dynamics under three P-application scenarios. Long-term simulation results showed that it took 14 years for the labile soil P level to return to the initial level after eight years of manure-P applications at a rate of 65.5 kg P/ha year -1. The modified RZWQM2-P model can be used to simulate total soil P and labile soil P contents and to assess P management practices in irrigated cropland amended with manure.

Automated summary

With the expansion of the dairy industry, the use of phosphorus-enriched dairy manure as a replacement for chemical fertilizer has increased. However, this practice can lead to excessive accumulation of total phosphorus in the soil and increase the risk of environmental phosphorus pollution. To improve the simulation of total soil phosphorus, the P module in the RZWQM2-P model was modified using the soil P pool structure from the EPIC model. The modified model showed satisfactory simulation results for labile soil P, total soil P, plant P uptake, and crop yield.