RESUMO
Identifying seasons sensitive to nutrient losses could help farmers and policymakers to formulate effective nutrient loss reduction strategies. This long-term study monitored water percolation as well as nitrate (NO3 -N) and total phosphorus (TP) leaching from liquid swine manure and chemical fertilizer applied to intact core lysimeters in a sandy loam soil in Manitoba, Canada. Water percolation, NO3 -N, and TP leaching were monitored from 2005 to 2016. Chemical fertilizer showed greater average annual mean water percolation (p = .01), annual flow-weighted mean concentration (FWMC) of NO3 -N (22 mg L-1 ; p < .001), and annual NO3 -N leaching (36 kg N ha-1 ; p = .002) compared with the manure treatment (FWMC NO3 -N, 15 mg L-1 ; NO3 -N leaching load, 22 kg N ha-1 ). Average annual mean TP loss did not differ between treatments (p = .86). Spring (April-June) was the most sensitive season, when >75% of annual percolation, >80% of annual NO3 -N, and >68% of annual TP leaching losses occurred from both manure and chemical fertilizer. Annual NO3 -N and TP leaching increased exponentially with cumulative winter and spring precipitation (control, r2 = .69; manure, r2 = .79; chemical fertilizer, r2 = .63) and decreased with winter and spring air temperatures. The largest spring NO3 -N and TP leaching losses were observed in 2013, which followed the dry year of 2012, indicating the potential for nutrient flushing. The findings emphasize the need for environmentally sound N and P management strategies in cold North American regions underlain by coarse-textured soils, particularly during the spring season.
