The seasonality of nitrate and phosphorus leaching from manure and chemical fertilizer added to a chernozemic soil in Canada.

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.

Influence of climate, topography, and soil type on soil extractable phosphorus in croplands of northern glacial-derived landscapes.

Delineating the relative solubility of soil phosphorus (P) in agricultural landscapes is essential to predicting potential P mobilization in the landscape and can improve nutrient management strategies. This study describes spatial patterns of soil extractable P (easily, moderately, and poorly soluble P) in agricultural landscapes of the Red River basin and the southern Great Lakes region. Surface soils (0-30 cm) and select deeper cores (0-90 cm) were collected from 10 cropped fields ranging in terrain (near-level to hummocky), soil texture (clay to loam), composition (calcareous to noncalcareous), and climate across these differing glacial landscapes. Poorly soluble P dominated (up to 91%) total extractable P in the surface soils at eight sites. No differences in the relative solubilities of soil extractable P with microtopography were apparent in landscapes without defined surface depressions. In contrast, in landscapes with pronounced surface depressions, increased easily soluble P (Sol-P), and decreased soil P sorption capacity were found in soil in wetter, low-slope zones relative to drier upslope locations. The Sol-P pool was most important to soil P retention (up to 28%) within the surface depressions of the Red River basin and at sites with low-carbonate soils in the southern Lake Erie watershed (up to 28%), representing areas at elevated risk of soil P remobilization. This study demonstrates interrelationships among soil extractable P pools, soil development, and soil moisture regimes in agricultural glacial landscapes and provides insight into identifying potential areas for soil P remobilization and associated P availability to crops and runoff.

Contribution of Overland and Tile Flow to Runoff and Nutrient Losses from Vertisols in Manitoba, Canada.

This study quantified the contributions of overland and tile flow to total runoff (sum of overland and tile flow) and nutrient losses in a Vertisolic soil in the Red River valley (Manitoba, Canada), a region with a cold climate where tile drainage is rapidly expanding. Most annual runoff occurred as overland flow (72-89%), during spring snowmelt and large spring and summer storms. Tile drains did not flow in early spring due to frozen ground. Although tiles flowed in late spring and summer (33-100% of event flow), this represented a small volume of annual runoff (10-25%), which is in stark contrast with what has been observed in other tile-drained landscapes. Median daily flow-weighted mean concentrations of soluble reactive P (SRP) and total P (TP) were significantly greater in overland flow than in tile flow ( < 0.001), but the reverse pattern was observed for NO-N ( < 0.001). Overland flow was the primary export pathway for both P and NO-N, accounting for >95% of annual SRP and TP and 50 to 60% of annual NO-N losses. Data suggest that tile drains do not exacerbate P export from Vertisols in the Red River valley because they are decoupled from the surface by soil-ice during snowmelt, which is the primary time for P loss. However, NO-N loading to downstream water bodies may be exacerbated by tiles, particularly during spring and summer storms after fertilizer application.