Ecological Intensification of Organic Grain Systems in the Midwest: Impacts on Biological Soil Health, Nutrient Availability, and Crop Yields

Organic grain production is a rapidly growing sector in the Midwest, yet it continues to face challenges in sustaining soil health, managing nutrients efficiently, and maintaining consistent yields. While organic farming systems avoid synthetic inputs, they often rely on frequent tillage and simple crop rotations, which can degrade soil structure and limit long-term sustainability. Ecological intensification, which incorporates practices such as extended cover cropping, reduced tillage, and microbial seed inoculation, may improve soil health and biologically regulated nutrient cycling, thereby supporting crop productivity. This study aimed to evaluate the effects of ecological intensification practices on biological soil health indicators, soil nutrient availability, crop nutrient uptake, and crop yields in organic grain production systems in the Midwest. By analyzing key soil health and agronomic parameters, this research aimed to provide empirical insights into the effectiveness of ecological intensification in improving soil function and supporting organic crop production.

Field trials were conducted in two study sites in Indiana and Wisconsin over the 2023 and 2024 growing seasons. Two management systems were compared within corn-soybean-small grain organic rotations: a Standard Organic system, which included frequent tillage, limited cover crop growth, which was terminate before the crop was planted and no microbial inoculation, and an Eco-Intensive Organic system, which featured reduced tillage, extended cover crop growth it was terminated after the crops were planted with a roller crimper and rhizobia seed inoculation. Soil samples were collected at two depths (0–15 cm and 15–30 cm) during the early, mid, and late growing seasons to assess soil moisture, soil organic matter content, soil microbial biomass and other biological soil health indicators, as well as the availability of inorganic nitrogen (N) in the soil. Crop leaf N content was also measured at reproductive stages to evaluate crop nutrient uptake, and final crop yields (soybean in 2023 and corn in 2024) were recorded at harvest. Statistical analyses were conducted using mixed linear models to evaluate the effects of treatment system, depth, location, and sampling time on soil and crop parameters.

The results revealed that ecological intensification had varying effects on soil moisture, biological soil health indicators, and the availability of inorganic N. In 2023, a relatively dry year, the Eco-Intensive Organic system exhibited significantly greater soil moisture content in the mid and late seasons, particularly at the 0–15 cm depth, likely due to reduced tillage and extended cover crop growth and residue retention. However, the effects of ecological intensification on biological soil health indicators, including soil microbial biomass carbon (C) and N (SMBC and SMBN), autoclaved-citrate extractable soil protein (ACE protein), and permanganate oxidizable C (POXC), were insignificant in both years. The variation in these parameters was driven by location, depth, and temporal patterns rather than differences in organic management. In contrast, the availability of inorganic N (soil nitrate content), responded strongly to treatment system, with significantly higher nitrate levels in the Standard Organic system than in the Eco-Intensive Organic system in both years. This pattern was likely due to increased mineralization resulting from tillage, providing greater immediate nutrient availability for plant uptake. Soil organic matter levels did not show significant treatment system effects, indicating that longer-term implementation may be required to detect meaningful changes. These findings suggest that while ecological intensification may enhance water retention and biodiversity, it does not result in significant immediate biological soil health benefits and requires N availability that influence crop performance and yields.

Similar to soil nitrate content, crop leaf tissue N content was lower in the Eco-Intensive Organic system than in the Standard Organic system in both years, indicating lower crop nutrient uptake, likely due to reduced inorganic N availability in the soil. Crop yields were generally lower in the Eco-Intensive Organic system than in the Standard Organic system, except for corn yield in Wisconsin in 2024. These findings highlight a key challenge of ecological intensification—reduced immediate soil nutrient availability and crop nutrient uptake may potentially affect yields, particularly in the early years of implementation.

Overall, this study provides critical insights into the trade-offs associated with ecological intensification in organic grain production. While ecological intensification may reduce soil disturbance and promote soil health and moisture retention, its effects on nutrient availability could impact organic crop yields. These findings suggest that organic farmers adopting ecological intensification practices should consider complementary nutrient management approaches, such as incorporating additional organic amendments, to ensure adequate N availability for their crops. Future research should focus on long-term monitoring of these systems to better understand the effects of ecological intensification on soil nutrient cycling, crop performance, and sustainability over multiple growing seasons.