An 11-Year Agronomic, Economic, and Phosphorus Loss Potential Evaluation of Legacy Phosphorus Utilization in a Clay Loam Soil of the Lake Erie Basin
Zhang, T., Wang, Y., Tan, C.S., Welacky, T. (2020). An 11-Year Agronomic, Economic, and Phosphorus Loss Potential Evaluation of Legacy Phosphorus Utilization in a Clay Loam Soil of the Lake Erie Basin. Frontiers in Earth Science, [online] 8 http://dx.doi.org/10.3389/feart.2020.00115
Plain language summary
Phosphorus is an essential nutrient required for crop production and has been continuously applied to agricultural soils in chemical fertilizers and animal manures for many decades. Phosphorus application often exceeds plant requirements, resulting in accumulation in soils (i.e., legacy phosphorus). There are tremendous amount of legacy phosphorus in Ontario soils, as well as in soils across the country and many parts of the world. This legacy phosphorus moves with surface and tile drainage water flows into water resources, streams, rivers and lakes, and can cause environmental damage in the form of eutrophication of surface waters. On the other hand, our previous studies proved that legacy phosphorus can be reusable by crops the following years. Legacy phosphorus in soils is thus a double-sided sward. Also considering phosphorus reserves a non-renewable and finite resource, effective yet sustainable nutrient management strategies for legacy phosphorus in soils must be studied. Accordingly, this paper assessed the efficacy of utilizing legacy phosphorus in soil, while halting phosphorus addition, over an 11-year span in the lake Erie basin. The results of this study demonstrated that in studied soils, utilizing legacy phosphorus while halting phosphorus addition resulted in identical crop yields as compared to continuous chemical phosphorus addition. Because crop yields were largely similar between legacy phosphorus and continuous phosphorus addition strategies, utilizing only legacy phosphorus increased net farming income due to savings on phosphorus application and materials. Additionally, soil phosphorus losses to water resources decreased when phosphorus application was halted. It can be recommended that utilizing legacy phosphorus is a beneficial management practice to achieve both agronomic and economic goals in an environmentally sustainable manner.
Legacy phosphorus (P) in agricultural soils has become a predominate source contributing to P loadings to Lake Erie since the mid-90s. The use of legacy P in soils can be an ultimate and effective way to mitigate the risk of agricultural P loss and to circumvent potential P rock reserve shortage, while sustaining crop production. A field experiment was conducted to assess the impacts of P draw-down (PDD) (i.e., use of legacy P in soils) on crop yields, P uptake and removal, and soil test P (Olsen P, an agronomic P calibration and environmental soil P risk indicator in the region) under a corn–soybean rotation in a clay loam soil of the Lake Erie Basin, southwestern Ontario, Canada, from 2008 to 2018. Corn and soybean grain yields with PDD were identical to those with continuous P addition (CPA), averaged at 7.7 Mg ha–1 for corn and 3.7 Mg ha–1 for soybean, over 11 years. Similarly, no significant differences in crop P uptake and removal were found between PDD and CPA. Compared to CPA, PDD increased net farming income by Canadian dollar (CAD) 104–125 ha–1 year–1 (i.e., USD 78.5–94.4 ha–1 year–1), with savings on P fertilizer materials and associated application costs. Soil P loss risks with PDD reduced, as indicated by soil test P that, in the top layer (0–15 cm), decreased linearly with crop production year at 3.27 mg P kg–1 year–1 or 16.2 mg P kg–1 per 100 kg crop P removal per hectare, while in the lower soil layers, 15–90 cm, it remained unchanged. In comparison, CPA of 50 kg P ha–1 sustained soil test P in the entire soil profile, 0–90 cm, over the 11-year period. PDD can be a beneficial management practice utilizing legacy P in soils to achieve both agronomic and economic goals in an environmentally sustainable manner.