Crop Production and Phosphorus Legacy with Long-Term Phosphorus- and Nitrogen-Based Swine Manure Applications under Corn-Soybean Rotation

The traditional manure management strategy, based on crop N needs, results in accumulation of phosphorus (P) in soil due to the imbalance of N/P ratio between crop requirement and manure supply. This study was conducted from 2004 to 2013 to evaluate the effects of P-based liquid and solid swine manure (LMP and SMP, for P-based liquid and solid swine manure, respectively) application, in comparison with N-based application (LMN and SMN, for N-based liquid and solid swine manure, respectively), on crop yield and soil residual P under corn (Zea mays L.)–soybean (Glycine max L.) rotation in a Brookston clay loam soil of the Lake Erie basin, ON, Canada. Chemical fertilizer P (CFP) and non-P treatments were included as controls (CK). For liquid manure treatments, corn yield for LMN showed a lower annual corn yield (7.82 Mg ha⁻¹) than LMP (9.36 Mg ha⁻¹), and their differences were even statistically significant at p < 0.05 in some cropping years. The annual corn yield of LMP was also higher than those of SMP (7.45 Mg ha⁻¹) and SMN (7.41 Mg ha⁻¹), even the CFP (8.61 Mg ha⁻¹), although the corresponding yield differences were not significant (p < 0.05) in some cropping years. For soybean, the plots with P application produced an average of 0.98 Mg ha⁻¹ greater annual yields than CK. No significant differences were found between CFP and manure treatments. The annual corn yield of SMN was close to that of the CK (7.19 Mg ha⁻¹). The grain P removal (GPR) of SMN (18.6 kg ha⁻¹) for soybean was significantly higher than that of the other treatments. The above-ground-P uptake (AGPU) in SMN, for both corn and soybean, was significantly higher than that of the other five treatments. The soil test P (STP) presented clear stratification, concentrating in the top 30 cm soil depth after 10 years of application. The contents of STP with LMN and SMN increased from 7.1 mg P kg⁻¹ to 12.4 and 45.5 mg P kg⁻¹, respectively. The sum of STP mass (0–30 cm) with LMP (31.6 kg ha⁻¹) was largely identical to that with CFP (30.1 kg ha⁻¹); however, with SMN (173.7 kg ha⁻¹), it was significantly higher than the rest of the treatments. Manure P source availability coefficients were averaged at 1.06 and 1.07 for LMP and SMP, respectively. The addition of phosphorus-based liquid or solid swine manure can overcome the drawback of traditional N-based applications by potentially reducing the adverse impact on water quality while sustaining crop agronomic production.