Reductions in soil water nitrate beneath a perennial grain crop compared to an annual crop rotation on sandy soil

Abstract

Nitrate (NO3--N) leaching into groundwater as a result of high nitrogen (N) fertilizer rates to annual crops presents human health risks and high costs associated with water treatment. Leaching is a particularly serious concern on sandy soils overlying porous bedrock. Intermediate wheatgrass (IWG) [Thinopyrum intermedium (Host.) Barkw. & D.R. Dewey], is a perennial grass that is being bred to produce agronomically and economically viable grain, which is commercially available as Kernza®. Intermediate wheatgrass is a low-input crop has the potential to produce profitable grain and biomass yields while reducing NO3--N leaching on sandy soils compared with common annual row crop rotations in the Upper Midwest. We compared grain yields, biomass yields, soil solution NO3--N concentration, soil extractable NO3--N, soil water content, and root biomass under IWG and a conventionally managed corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] rotation for 3 years on a Verndale sandy loam in Central Minnesota. Mean soil solution NO3--N was 77–96% lower under IWG than the annual crop rotation. Soil water content was greater under annuals compared to IWG early in the growing season, suggesting greater water use by IWG during this time. Interactions between crop treatments and depth were observed for soil water content in Year 3. Root biomass from 0 to 60 cm below the soil surface was five times greater beneath IWG compared to soybean, which may explain differences in soil extractable and solution NO3--N among crops. With irrigation on coarse structured soils, IWG grain yields were 854, 434, and 222 kg ha−1 for Years 1–3 and vegetative biomass averaged 4.65 Mg ha−1 yr−1; comparable to other reports on heavier soils in the region. Annual crop grain yields were consistent with local averages. These results confirm that IWG effectively reduces soil solution NO3--N concentrations even on sandy soils, supporting its potential for broader adoption on land vulnerable to NO3--N leaching.

Age‐related changes in root dynamics of a novel perennial grain crop

“…Standing root stocks were 3-6 and 6-10 times greater in IWG-1 and IWG-2, respectively, compared with spring wheat when averaged across growth period, in line with studies showing that IWG root stocks between 0 and 15 cm were 4-25 times greater in IWG than annual row crop monocultures including soybean and maize (Rakkar et al, 2023Reilly et al, 2022. The larger standing root stocks in IWG were associated with generally greater new root production rates (except between elongation and maturity) compared with wheat, with wheat on average maintaining new root production rates of around 2 g m −3 day −1 in both 2020 and 2021.…”

“…In terms of environmental health, the agronomic practices and physiological traits inherent to perennial crops confer a suite of ecological benefits on agricultural landscapes. When compared to annual crops, the reduced tillage and diminished fertilizer inputs of perennial cropping systems reduce soil nitrate leaching (Jungers et al, 2019;Reilly et al, 2022), enhance nutrient uptake (Sprunger et al, 2018a), and promote the formation of stable soil aggregates (Rakkar et al, 2023;Tiemann & Grandy, 2015). Physiological differences in carbon (C) uptake and partitioning between perennial and annual grains (Woeltjen, 2023) such as greater photosynthetic activity (Jaikumar et al, 2013(Jaikumar et al, , 2016, higher belowground C allocation to roots (Sainju et al, 2017), and extensive root production in perennial grains also contribute to the development of more robust soil microbial communities (Audu et al, 2022;Liang et al, 2012;McKenna et al, 2020;Tiemann & Grandy, 2015) and increase the potential sequestration of atmospheric CO 2 in belowground C pools.…”

Adapting perennial grain and oilseed crops for climate resiliency

“…Utilization of water that is unavailable to annual crops can reduce nutrient losses to surface water and groundwater. Research has shown that intermediate wheatgrass grown for grain can reduce NO 3 leaching to groundwater—thus protecting rural drinking water sources while generating an economic return for farmers (Huddell et al., 2023; Jungers et al., 2019; Reilly et al., 2022). Similarly, Randall and Mulla (2001) showed that subsurface field drainage volume and nitrate N losses were 30–50 times higher beneath annual crops compared with perennial crops.…”

“…Pastures and forage crops are well known for their ecosystem service benefits (e.g., soil health), and have large ranges that encompass many different cropping systems (Aponte et al, 2019;Martin et al, 2020;Teixeira et al, 2021). The perennial grain Kernza is one example of the potential for perennial crops to improve soil quality and water regulation (Audu et al, 2022;Rakkar et al, 2023;Reilly et al, 2022;van der Pol et al, 2022) perennials to provide these ecosystem benefits is one reason they are a powerful climate adaptation tool. Perennials also have a longer growing season than annuals, thus allowing these crops to capture and utilize water that is available outside the typical annual crop growing season (Vico & Brunsell, 2018).…”

“…An opportunity to overcome “chicken or egg” commercialization barriers, expedite scale up of acreage and supply chains, and potentially de‐risk grower adoption of perennial crops lies in strategic landscape deployment where perennials can directly provide ecosystem services. For example, plot‐scale research has shown that Kernza can reduce nitrate leaching to groundwater when grown on various soil types in Minnesota (Reily et al., 2022). Researchers, state public health officials, and the Department of Agriculture initiated a project to financially incentivize the replacement of high nitrogen demanding row crops with Kernza in the state's drinking water supply management areas that were most vulnerable to nitrate leaching.…”