Soil Health After 19 Years Under Organic and Conventional Agriculture and Restored Prairie Grassland.

The Glenlea long-term study, located in Manitoba was established in 1992 to compare organic, conventional, no-input and restored prairie grass land management practices. Two 4-yr rotations exist under all agriculture management practices: annual-grain and forage-grain. The objective of the present study was to evaluate the effect of conventional, organic, and no-input agricultural management on soil health using restored grassland prairie as a biological benchmark for soil health. Microbial biomass carbon, microbial metabolic quotient (qCO₂), microbial biomass phosphorus, and microbial nitrous oxide quotient (qN₂O) were measured to evaluate soil health. Microbial biomass carbon, microbial biomass phosphorus, qCO₂, and qN₂O were measured five times from May-October in 2010 under the Triticum aestivum (L.) (wheat) year in both rotations. Seasonal variation was significant for all measurements. Across all sample dates, MBC and activity were higher in the forage-grain (MBC= 1613 µg-MBC/g-dry soil; qCO₂= 0.75 mg CO₂-C /g-dry soil/hr) rotation compared to the annual (MBC= 1124 µg-MBC/g-dry soil; qCO₂= 0.60 mg CO₂-C /g-dry soil/hr). The forage-grain organic system (1718 µg-MBC/g-dry soil) had the highest MBC compared to its conventional (1476 µg-MBC/g-dry soil) counterpart and behaved most similarly to the restored grassland prairie (MBC= 1668 µg-MBC/g-dry soil; qCO₂= 1.46 mg CO₂-C /g-dry soil/hr). Effects of rotation were significant (P<0.0001) for MBC, MBP, CO₂-C, qCO₂, N₂O, and qN₂O suggesting rotation has a strong influence on soil microbial characteristics. The rotation and management interaction was statistically significant for MBC, CO_2, and N₂O indicating that management effects microbial abundance and activity differently under annual rotations compared to rotations that include perennials, but does not affect the ratio of MBC to gas emissions. Rotation and fertility management practices, such as organic systems that include perennials, mimic natural systems like prairies and have the greatest capacity to sustain soil microbial life.