Jane A. Elliott

Global change pressures on soils from land use and management

Soils are subject to varying degrees of direct or indirect human disturbance, constituting a major global change driver. Factoring out natural from direct and indirect human influence is not always straightforward, but some human activities have clear impacts. These include land-use change, land management and land degradation (erosion, compaction, sealing and salinization). The intensity of land use also exerts a great impact on soils, and soils are also subject to indirect impacts arising from human activity, such as acid deposition (sulphur and nitrogen) and heavy metal pollution. In this critical review, we report the state-of-the-art understanding of these global change pressures on soils, identify knowledge gaps and research challenges and highlight actions and policies to minimize adverse environmental impacts arising from these global change drivers. Soils are central to considerations of what constitutes sustainable intensification. Therefore, ensuring that vulnerable and high environmental value soils are considered when protecting important habitats and ecosystems, will help to reduce the pressure on land from global change drivers. To ensure that soils are protected as part of wider environmental efforts, a global soil resilience programme should be considered, to monitor, recover or sustain soil fertility and function, and to enhance the ecosystem services provided by soils. Soils cannot, and should not, be considered in isolation of the ecosystems that they underpin and vice versa. The role of soils in supporting ecosystems and natural capital needs greater recognition. The lasting legacy of the International Year of Soils in 2015 should be to put soils at the centre of policy supporting environmental protection and sustainable development.

Conventional and conservation tillage: influence on seasonal runoff, sediment, and nutrient losses in the Canadian Prairies.

Conservation tillage has been widely promoted to reduce sediment and nutrient transport from agricultural fields. However, the effect of conservation tillage on sediment and nutrient export in snowmelt-dominated climates is not well known. Therefore, a long-term paired watershed study was used to compare sediment and nutrient losses from a conventional and a conservation tillage watershed in the Northern Great Plains region of western Canada. During the treatment period, dissolved nutrient concentrations were typically greater during spring snowmelt than during summer rainfall events, whereas concentrations of sediment and particulate nutrients were greatest during rainfall events. However, because total runoff was dominated by snowmelt, most sediment and nutrient export occurred during snowmelt. Overall, conservation tillage reduced the export of sediment in runoff water by 65%. Similarly, concentrations and export of nitrogen were reduced by 41 and 68%, respectively, relative to conventional tillage. After conversion to conservation tillage, concentrations and exports of phosphorus (P) increased by 42 and 12%, respectively, with soluble P accounting for the majority of the exported P, especially during snowmelt. Our results suggest that management practices designed to improve water quality by reducing sediment and sediment-bound nutrient export from agricultural fields and watersheds can be less effective in cold, dry regions where nutrient export is primarily snowmelt driven and in the dissolved form. In these situations, it may be more appropriate to implement management practices that reduce the accumulation of nutrients in crop residues and the surface soil.

The effects of multiple beneficial management practices on hydrology and nutrient losses in a small watershed in the Canadian prairies.

Most beneficial management practices (BMPs) recommended for reducing nutrient losses from agricultural land have been established and tested in temperate and humid regions. Previous studies on the effects of these BMPs in cold-climate regions, especially at the small watershed scale, are rare. In this study, runoff and water quality were monitored from 1999 to 2008 at the outlets of two subwatersheds in the South Tobacco Creek watershed in Manitoba, Canada. Five BMPs-a holding pond below a beef cattle overwintering feedlot, riparian zone and grassed waterway management, grazing restriction, perennial forage conversion, and nutrient management-were implemented in one of these two subwatersheds beginning in 2005. We determined that >80% of the N and P in runoff at the outlets of the two subwatersheds were lost in dissolved forms, ≈ 50% during snowmelt events and ≈ 33% during rainfall events. When all snowmelt- and rainfall-induced runoff events were considered, the five BMPs collectively decreased total N (TN) and total P (TP) exports in runoff at the treatment subwatershed outlet by 41 and 38%, respectively. The corresponding reductions in flow-weighted mean concentrations (FWMCs) were 43% for TN and 32% for TP. In most cases, similar reductions in exports and FWMCs were measured for both dissolved and particulate forms of N and P, and during both rainfall and snowmelt-induced runoff events. Indirect assessment suggests that retention of nutrients in the holding pond could account for as much as 63 and 57%, respectively, of the BMP-induced reductions in TN and TP exports at the treatment subwatershed outlet. The nutrient management BMP was estimated to have reduced N and P inputs on land by 36 and 59%, respectively, in part due to the lower rates of nutrient application to fields converted from annual crop to perennial forage. Overall, even though the proportional contributions of individual BMPs were not directly measured in this study, the collective reduction of nutrient losses from the five BMPs was substantial.

Critical Factors Affecting Field-Scale Losses of Nitrogen and Phosphorus in Spring Snowmelt Runoff in the Canadian Prairies

A long-term, field-scale study in southern Manitoba, Canada, was used to identify the critical factors controlling yearly transport of nitrogen (N) and phosphorus (P) by snowmelt runoff. Flow monitoring and water sampling for total and dissolved N and P were performed at the edge of field. The flow-weighted mean concentrations and loads of N and P for the early (the first half of yearly total volume of snowmelt runoff), late (the second half of yearly total volume of snowmelt runoff), and yearly snowmelt runoff were calculated as response variables. A data set of management practices, weather variables, and hydrologic variables was generated and used as predictor variables. Partial least squares regression analysis indicated that critical factors affecting the water chemistry of snowmelt runoff depended on the water quality variable and stage of runoff. Management practices within each year, such as nitrogen application rate, number of tillage passes, and residue burial ratio, were critical factors for flow-weighted mean concentration of N, but not for P concentration or nutrient loads. However, the most important factors controlling nutrient concentrations and loads were those related to the volume of runoff, including snow water equivalent, flow rate, and runoff duration. The critical factors identified for field-scale yearly snowmelt losses provide the basis for modeling of nutrient losses in southern Manitoba and potentially throughout areas with similar climate in the northern Great Plains region, and will aid in the design of effective practices to reduce agricultural nonpoint nutrient pollution in downstream waters.

Transport of lincomycin to surface and ground water from manure-amended cropland.

Livestock manure containing antimicrobials becomes a possible source of these compounds to surface and ground waters when applied to cropland as a nutrient source. The potential for transport of the veterinary antimicrobial lincomycin to surface waters via surface runoff and to leach to ground water was assessed by monitoring manure-amended soil, simulated rainfall runoff, snowmelt runoff, and ground water over a 2-yr period in Saskatchewan, Canada, after fall application of liquid swine manure to cropland. Liquid chromatography tandem mass spectrometry was used to quantify lincomycin in all matrix extracts. Initial concentrations in soil (46.3-117 mug kg(-1)) were not significantly different (p > 0.05) for manure application rates ranging from 60,000 to 95,000 L ha(-1) and had decreased to nondetectable levels by mid-summer the following year. After fall manure application, lincomycin was present in all simulated rainfall runoff (0.07-2.7 mug L(-1)) and all snowmelt runoff (0.038-3.2 mug L(-1)) samples. Concentrations in snowmelt runoff were not significantly different from those in simulated rainfall runoff the previous fall. On average, lincomycin concentrations in ephemeral wetlands dissipated by 50% after 31 d. Concentrations of lincomycin in ground water were generally <0.005 mug L(-1). This study demonstrates that the management practice of using livestock manure from confined animal feeding operations as a plant nutrient source on cropland may result in antimicrobial transport to surface and ground waters.

Influence of Tillage System on Water Quality and Quantity in Prairie Pothole Wetlands

Since zero tillage (ZT) requires more herbicide and fertilizer use than conventional tillage (CT) and may improve water infiltration into soil, the system may negatively impact prairie pothole wetlands. In this paper, the hydrology and water quality of pothole wetlands in zero tillage and conventional tillage systems were compared by monitoring three wetlands (ZT-1, ZT-2 and CT) from 1995 to 1997, and during a runoff-producing summer storm in 1998. Wetland water levels were recorded during snowmelt runoff and throughout the unfrozen period. Water samples from the wetlands were analyzed for total P, ortho P, NO2-NO3, NH3 and a suite of commonly-used herbicides. In each year of the study, similar snow accumulations generated more runoff per unit area from the ZT basins than the CT basin. Water levels were similar in the three wetlands in the spring of 1995, but by 1997 the water depths were less in the ZT wetlands than in the CT wetland. Despite greater fertilizer use in the ZT basins, we did not observe a consistent effect of tillage system on available N and P in the surface soil. Phosphorus concentrations were generally higher in the ZT than the CT wetlands during snowmelt but there was no consistent effect of tillage on NO2-NO3 or NH3 concentrations in the wetlands. The herbicides found in all three wetlands included those that were applied during the study and some that were not. At least one herbicide was detected in trace amounts in approximately 75% of samples from the wetlands.

Leaching of three sulfonylurea herbicides during sprinkler irrigation.

Sulfonylurea herbicides are widely applied on the Canadian prairies to control weeds in a variety of crops. Several sulfonylurea herbicides are mobile in soil, and there is concern about their possible movement to ground water. This study was performed to assess the susceptibility of three sulfonylurea herbicides commonly used in prairie crop production to leach under a worst-case scenario. Thifensulfuron-methyl, tribenuron-methyl, and rimsulfuron were applied to a 9-ha tile-drained field, and then approximately 300 mm of irrigation water were applied over a 2-wk period using a center pivot. The commencement of tile-drain flow corresponded to the rise of the water table above tile-drain depth, and peak flow rates corresponded to the greatest depths of ground water above the tile drains. The volume of irrigation water intercepted by the tile drains in each quadrant was determined by site hydrology and represented <10% of the irrigation water applied. Concentrations of thifensulfuron-methyl, tribenuron-methyl, and rimsulfuron in the tile-drain effluent ranged (analysis by liquid chromatography/tandem mass spectrometry) from 2.0 to 248 ng L(-1), not detected (nd) to 55 ng L(-1), and nd to 497 ng L(-1), respectively. Total herbicide transport from the root zone in each quadrant was estimated at <0.5% of the amount of each sulfonylurea herbicide applied. Thifensulfuron-methyl was the only herbicide detected in ground water, with concentrations ranging from 1.2 to 2.5 ng L(-1). With the frequency and amount of rainfall typically encountered in the prairie region of Canada, detectable concentrations (>1 ng L(-1)) of these sulfonylurea herbicides in ground water would be unlikely.

Nutrient and sediment losses in snowmelt runoff from perennial forage and annual cropland in the canadian prairies.

An 8-yr field-scale study, 2005 to 2012, investigated effects of agricultural land use on nutrient and sediment losses during snowmelt runoff from four treatment fields in southern Manitoba. In 2005, two fields with a long-term history of annual crop (AC) production were planted to perennial forage (PF), while two other fields were left in AC production. In 2009, the AC fields were converted to PF, while the PF fields were returned to AC. Runoff flow rates were monitored at the lower edge of the fields, and nutrient concentrations of runoff water were determined. The effects of AC and PF on selected variables were similar for the spatial (between-fields) and temporal (within-field) comparisons. The flow-weighted mean concentrations (FWMCs) and loads of particulate N, P, and sediment were not affected by treatment. Soil test N and the FWMC and load of NO (NO + NO) were significantly greater in the AC treatment, but the FWMC and load of NH were greater in the PF treatment. Loads of total dissolved N (TDN) and total N (TN) were not affected by treatment, although the concentrations of TDN and TN were greater in the AC treatment. The PF treatment significantly increased FWMCs and loads of total dissolved P (TDP) and total P (TP). On an annual snowmelt runoff basis, the PF treatment increased the FWMC of TDP by 53% and TP by 52% and increased the load of TDP by 221% and TP by 160% compared with the AC treatment. The greater P and NH losses in the PF treatment were attributed mainly to nutrient release from forage residue due to freezing.

Conversion of Conservation Tillage to Rotational Tillage to Reduce Phosphorus Losses during Snowmelt Runoff in the Canadian Prairies.

In a preceding study, converting conventional tillage (ConvT) to conservation tillage (ConsT) was reported to decrease nitrogen (N) but to increase phosphorus (P) losses during snowmelt runoff. A field-scale study was conducted from 2004 to 2012 to determine if conversion of ConsT to rotational tillage (RotaT), where conservation tillage was interrupted by a fall tillage pass every other year, could effectively reduce P losses compared with ConsT. The RotaT study was conducted on long-term paired watersheds established in 1993. The ConvT field in the pair has remained under ConvT practice since 1993, whereas tillage was minimized on the ConsT field from 1997 until 2007. In fall 2007, RotaT was introduced to the ConsT field, and heavy-duty cultivator passes were conducted in the late fall of years 2007, 2009, and 2011. Runoff volume and nutrient content were monitored at the edge of the two fields, and soil and crop residue samples were taken in each field. Greater soil Olsen P and more P released from crop residue are likely the reasons for the increased P losses in the ConsT treatment (2004-2007) relative to the ConvT treatment (2004-2007). Analysis of covariance indicated that, compared with ConsT (2004-2007), RotaT (2008-2012) increased the concentrations of dissolved organic carbon (DOC) by 62%, total dissolved N (TDN) by 190%, and total N (TN) by 272% and increased the loads of DOC by 34%, TDN by 34%, and TN by 60%. However, RotaT (2008-2012) decreased soil test P in surface soil, P released from crop residue, and duration of runoff compared with ConsT (2004-2007) and thus decreased the concentrations of total dissolved P (TDP) by 46% and total P (TP) by 38% and decreased the loads of TDP by 56% and TP by 42%. In the Canadian Prairies, where P is a major environmental concern compared with N, RotaT was demonstrated to be an effective practice to reduce P losses compared with ConsT.

Assessing Effects of Small Dams on Stream Flow and Water Quality in an Agricultural Watershed

Small dams and associated reservoirs have notable effects on soil and water dynamics in prairie streams. In this study, we developed a simulation module of small dams in the soil and water assessment tool (SWAT) to evaluate their long-term effects on stream flow and water quality at a watershed scale. To overcome the challenges in characterizing small storage and short retention time in small reservoir routing, concepts of equivalent reservoir storage and equivalent reservoir discharge are applied by which the average daily storage and daily discharge of the small reservoirs are calculated. Accordingly, the sediment deposition and nutrient abatement within the reservoir are computed using available SWAT routines. The effects of small dams in reduction of daily peak flow, sediment, and nutrient loads at the watershed outlet are obtained by summing the effects of all small dams within the watershed considering both reservoir and channel processes. The model is applied to the 74.6-km(2) South Tobacco Creek watershed located in Southern Manitoba of Canada. A total of 26 small dams exist in the watershed with surface area ranging from 0.002 to 0.492 km(2) and storage capacity from 3,380 to 642,000 m(3). The simulation results show that the combined effect of these small dams can reduce daily peak flow by 0-14% at the watershed outlet depending on climate and initial reservoir storage conditions. The estimated average annual sediment, total nitrogen and total phosphorus reductions at the watershed outlet are about 4.51, 3.59, and 2.96%, respectively. However, the on-site effects of individual small dams are much higher depending on its size, location, shape, drainage area, and land use compositions in the contribution area. The simulation results also show that snowmelt-flooding events have higher reduction amounts but lower relative reduction rates compared to rainfall storm events and the back-flood small dams have greater impact on sediment, nitrogen, and phosphorous abatement followed by multipurpose small dams and dry dams in the study watershed