Soil health response to cropping systems in semi-arid Montana

Abstract

Traditional cropping systems in the northern Great Plains (NGP) were dominated by cereal-fallow rotations until the 1970s, resulting in increased soil erosion, decreased soil organic matter (SOM) accumulation, and declines in soil biological activity. Recent shifts toward continuous and more diverse no-till crop production attempt to increase sustainability, diversify economic opportunities, and keep up with the growing food demand without converting more land into agriculture. With a two-year study, I explored the effects of crop types in diverse, no-till, crop sequences on soil health in dryland and irrigated systems on one farm in semi-arid Montana, using biological indicators of potentially mineralizable nitrogen (PMN), soil enzyme activity (beta- glucosaminidase, beta-glucosidase, arylsulfatase, and acid and alkaline phosphatases), and permanganate oxidizable carbon (POxC), a measure of labile carbon. Crop sequences included four crop types -- cereals, oilseeds, legumes, and root crops. Root crops, namely sugar beet, drove soil responses in PMN, evident by increased plant-available N in soils following sugar beet. Soil enzyme activity, an indicator of nutrient cycling capacity, was strongly correlated with SOM, but did not follow a pattern based on crop type. Labile carbon changed in soils between years but did not respond consistently to crops. This research also explored the soil health gap by comparing soil health in cultivated systems to nearby grasslands. In a paired-site comparison on two farms in Montana, biological health indicators were 45% lower, on average, in cultivated soils compared to adjacent uncultivated soils. This difference was consistent with lower SOM averages, offering a simple assessment to quantify the maximum attainable soil health capacity within a specific agroecosystem. Soil acidification, a growing concern for producers across the NGP, contributed to 42% lower soil enzyme activity, based on four enzymes, compared to adjacent neutral pH cultivated soils. Enzyme activity was the only soil health parameter that was lower in acid soils compared to neutral pH soils, demonstrating the sensitivity of soil enzymes. Overall, these results indicate that biological soil health indicators are sensitive to changes in crop production, changing yearly, and provide farmers with the opportunity to fine- tune their management practices to meet their soil health goals.