Targeted subfield switchgrass integration could improve the farm economy, water quality, and bioenergy feedstock production

Abstract

Progress on reducing nutrient loss from annual croplands has been hampered by perceived conflicts between short-term profitability and long-term stewardship, but these may be overcome through strategic integration of perennial crops. Perennial biomass crops like switchgrass can mitigate nitrate-nitrogen (NO 3 -N) leaching, address bioenergy feedstock targets, and -as a lower-cost management alternative to annual crops (i.e., corn, soybeans) -may also improve farm profitability. We analyzed publicly available environmental, agronomic, and economic data with two integrated models: a subfield agroecosystem management model, Landscape Environmental Assessment Framework (LEAF), and a process-based biogeochemical model, DeNitrification-DeComposition (DNDC). We constructed a factorial combination of profitability and NO 3 -N leaching thresholds and simulated targeted switchgrass integration into corn/soybean cropland in the agricultural state of Iowa, USA. For each combination, we modeled (i) area converted to switchgrass, (ii) switchgrass biomass production, and (iii) NO 3 -N leaching reduction. We spatially analyzed two scenarios: converting to switchgrass corn/soybean cropland losing >US$ 100 ha À1 and leaching >50 kg ha À1 ('conservative' scenario) or losing >US$ 0 ha À1 and leaching >20 kg ha À1 ('nutrient reduction' scenario). Compared to baseline, the 'conservative' scenario resulted in 12% of cropland converted to switchgrass, which produced 11 million Mg of biomass and reduced leached NO 3 -N 18% statewide. The 'nutrient reduction' scenario converted 37% of cropland to switchgrass, producing 34 million Mg biomass and reducing leached NO 3 -N 38% statewide. The opportunity to meet joint goals was greatest within watersheds with undulating topography and lower corn/soybean productivity. Our approach bridges the scales at which NO 3 -N loss and profitability are usually considered, and is informed by both mechanistic and empirical understanding. Though approximated, our analysis supports development of farm-level tools that can identify locations where both farm profitability and water quality improvement can be achieved through the strategic integration of perennial vegetation.

Where can switchgrass production be more profitable than corn and soybean? An integrated subfield assessment in Iowa, USA

“…In a previous modeling study, Brandes et al. () showed that nitrate leaching could be reduced by 18% in Iowa if 12% of corn/soybean cropland was converted to switchgrass. Our analysis revealed that three counties in Iowa could reach this percentage of switchgrass cover, while simultaneously increasing total producer benefit by millions of dollars, when converting all corn/soybean cropland areas with breakeven switchgrass yields of up to 10.08 Mg ha −1 , assuming all land is owned and medium switchgrass price (Fig.…”

Black walnut alley cropping is economically competitive with row crops in the MidwestUSA

“…For example, policymakers could set a target AC adoption rate and then use the high‐resolution analysis to identify the ideal land to meet this goal (Brandes et al. ).…”

“…identifies environmentally sensitive areas (SooHoo et al 2017, Brandes et al 2018 or the current extent of existing agroforestry practices (Herder et al 2017) could further hone the identification of target regions for MSR alternatives.…”

“…However, recent studies suggest that there are strong economic opportunities for land‐use alternatives across existing MSR land (Brandes et al. , ). We combine publically available data on black walnut soil suitability, timber prices, crop productivity, cash rents, and land cover to (1) evaluate where PF and AC can be economically competitive with MSR without monetization of any environmental benefits or direct government assistance; and (2) determine if the resulting PF and AC target regions coincide with marginal MSR land.…”

“…1. Maps of spatial input variables to the model: (a) 2016 Cropland Data Layer (CDL; USDA NASS 2016a), (b) National Commodity Crop Productivity Index (NCCPI; Dobos et al 2012), and (c) Black Walnut Suitability Index (BWSI; Wallace and Young 2008). studies suggest that there are strong economic opportunities for land-use alternatives across existing MSR land (Brandes et al 2016(Brandes et al , 2018. We combine publically available data on black walnut soil suitability, timber prices, crop productivity, cash rents, and land cover to (1) evaluate where PF and AC can be economically competitive with MSR without monetization of any environmental benefits or direct government assistance; and (2) determine if the resulting PF and AC target regions coincide with marginal MSR land.…”