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

Abstract

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 accumulation 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.