Temporal variability of soil properties under annual and perennial continuous living cover: weather controls and management effects

Authors: KUNDERT, JACOB - University Of Minnesota; JUNGERS, JACOB - University Of Minnesota; Gamble, Joshua; BERGQUIST, GALEN - Natural Resources Conservation Service (NRCS, USDA); GUTKNECHT, JESSICA - University Of Minnesota

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/14/2026
Publication Date: N/A
Citation: N/A

Interpretive Summary: Farmers and researchers use soil biology tests to measure soil health, but we don't know how much these tests naturally vary from year to year. We collected and analyzed soil from the same 64 field locations for five years under two farming systems: diversified annual crops and perennial crops. We found that weather, especially air temperature, strongly affects soil biology measurements each year. This makes it hard to tell if changes in the soil are due to farming practices or just weather. The perennial field saw considerable improvements to soil health over five years, especially in beneficial fungi that help plants get nutrients. However, weather effects on soil tests mean we need better methods to separate weather-driven changes from true soil health improvements due to management.

Technical Abstract: Biological indicators are key to soil health assessment, but their temporal variability remains poorly understood. We collected and analyzed soil annually for five years in two upper midwestern silt loam fields: an annual field under a maize, soybean, wheat, camelina, barley rotation and a perennial field under an alfalfa-Kernza rotation. We analyzed mineralizable carbon (MinC), extracellular enzymes, microbial biomass, microbial lipid indicators, soil organic carbon, and mineral-associated and particulate organic matter. Growing season air temperature was strongly correlated with annual changes in biological properties, including MinC (p < 0.001) and microbial biomass (r = 0.40-0.53, p < 0.05), demonstrating the potential for weather to confound soil health assessment. Temperature sensitivity of MinC was depth-dependent (r = +0.65 – +0.68 at 0-15cm, r = -0.39 – -0.60 at 15-30cm) and incubation-length dependent (p < 0.001 for 1-12d, NS for 21d). The perennial field showed improved soil health: arbuscular mycorrhizal fungi, on average, doubled annually (+100%, p = 0.013) and declined in the annual field (p < 0.001). At 15-30 cm, particulate organic matter and short-term MinC increased by 26-36% annually (p < 0.001) in the perennial field, but remained stable in the annual field. Weather sensitivity of biological indicators challenges soil health assessment protocols, requiring modifications to improve interpretability of results.