Fallow replacement and alternative nitrogen management for reducing nitrate leaching in a semiarid region

Abstract

Nitrate (NO 3 -) leaching into groundwater is a growing global concern for health, environmental, and economic reasons, yet little is known about the effects of agricultural management practices on the magnitude of leaching, especially in dryland semiarid regions. Groundwater nitrate-nitrogen (nitrate-N) concentrations above the drinking water standard of 10 mg L -1 are common in the Judith River Watershed (JRW) of semiarid central Montana. A 2-year study conducted on commercial farms in the JRW compared nitrate leaching rates across three alternative management practices (AMP: pea, controlled release urea, split application of N) and three grower standard practices (GSP: summer fallow, conventional urea, single application of urea). Crop biomass and soil were collected at ten sampling locations on each side of a management interface separating each AMP from its corresponding GSP. A nitrogen (N) mass balance approach was used to estimate the amount of nitrate leached annually. In 2013, less nitrate leached the year after the pea AMP (18 ± 2.5 kg N ha -1 ) than the year after the fallow GSP (54 ± 3.6 kg N ha -1 ), whereas the two AMP fertilizer treatments had no effect on nitrate leaching compared to GSPs. In 2014, leaching rates did not differ between each AMP and its corresponding GSP. The results suggest that replacing fallow with pea has the greatest potential to reduce nitrate leaching. Future leaching research should likely focus on practices that decrease deep percolation, such as fallow replacement with annual or perennial crops, more than on N fertilizer practices.

The road less traveled: Assessing the impacts of farmer and stakeholder participation in groundwater nitrate pollution research

“…This growth in area (and anecdotal feedback from our PRAG members) suggests that those already planting annual legumes in 2012 greatly increased the amount of area devoted to annual legumes over the threeyear period. As noted above, data from our on-farm plots did not demonstrate consistent benefits from split application methods or slow-release N products, but instead identified the use of alternatives to fallowing having the most potential to reduce NO 3 leaching while maintaining farm profitability (John et al 2017). In this sense, some, but not all, of the changes in producers' behavior in the watershed were consistent with our project's results and communication messages.…”

“…Perhaps fortuitously, our on-farm field observations and model results led to the conclusion that changes in crop rotations (especially the use of fallow under no-till conditions, combined with periods of heavy rainfall and deep soil moisture movement) were probably at least as important as commercial fertilizer applications in explaining rates of NO 3 leaching (John et al 2017;Sigler et al 2018). At a minimum, the fact that fertilizer (alone) was not identified as the main culprit opened up opportunities for farmers to let down their guard and engage in conversations about how their overall farming systems were impacting local environmental conditions.…”

“…Participatory Research Approach. The research presented below was part of a larger USDA-funded project (fall of 2011 to summer of 2015) to better understand and develop effective responses to the problem of rising NO 3 concentrations in groundwater wells in the JRW (John et al 2017;Miller 2013;Sigler et al 2018). A primary goal of the project was to empower local farmers and community leaders by giving them important roles in the design and implementation of the scientific research and fieldwork components of the effort.…”

“…The project team also monitored water movement and extensively sampled soils and crops on the study farms, and sampled surface and groundwater across the watershed (John 2015;John et al 2017;Miller 2013;Sigler et al 2018). Although we saw potential for all three practices to have beneficial impacts, our field trials (and materials included in our publicity and outreach efforts) demonstrated relatively modest impacts for two fertilizer BMPs (split application in the spring, and slow-release forms of N), but found that planting annual legumes (like pea) in lieu of fallowing showed the greatest promise for both reducing NO 3 leaching and sustaining farm income (John et al 2017). Analysis of water composition and NO 3 abundance in soil, groundwater, and surface water samples informed quantitative models of NO 3 leaching losses at the landscape scale, and supported the observation that replacing fallow fields with a crop has strong potential to reduce NO 3 leaching (Sigler et al 2018).…”

New perennial grains in African smallholder agriculture from a farming systems perspective. A review

“…3 On-farm adoption and experiences of perennial grains: preliminary insights from around the world The rationale for a transition towards perennial grains has at this point been thoroughly documented and discussed, and will not be extensively covered here. Above all, perennial grains are being developed as a way to mitigate (or even reverse) the negative environmental impacts of agriculture; problems such as soil erosion, nutrient leaching, eutrophication, salinization, water logging, and high energy intensity are often named (Bell et al 2008;Finlayson et al 2010;John et al 2017;Zhang et al 2017;Crews et al 2016). Many of the ecological benefits of perennials can be attributed to their extensive root systems which, together with greatly reduced soil disturbance, help build up soil organic matter, stabilize soils, and improve nutrient uptake (Crews and Rumsey 2017;Larkin et al 2014).…”