Soil health indicator responses to three years of cover crop and crop rotation in a northern semi-arid region, the Canadian prairies

Abstract

Increasing crop diversity via cover cropping is considered a powerful strategy to improve soil health; thus, a better understanding of the impacts on soil is crucial. In northern semi-arid regions, cover cropping can be agronomically challenging due to growing condition limitations, and the paucity of cover crop data only exacerbates this challenge. Still, farmers are interested in adopting cover crops to reach their soil health goals. Our study addressed this gap by 1) comparing rotations with versus without cover crops; and 2) comparing different rotational treatments of perennial alfalfa, two-year ‘short’ rotations, to four-year ‘long’ rotations with and without cover crops. After three years, soil health indicators were measured at four sites across the Canadian prairies, including wet aggregate stability (WAS), soil pH, electronic conductivity (EC), evolved soil CO2, soil active C, soil organic carbon (SOC), total carbon (C), N2O production, inorganic N, soil protein, potential mineralized N (PMN), and total N. During a dry period which limited cover crop growth, the cover crops had limited impact on soil health indicators, except for a reduction in spring soil nitrate-N levels at two of the four sites. Surprisingly, the crop phase of the rotation had more differences on soil health indicators than the inclusion of cover crops, but the inconsistency of the changes made it difficult to draw clear patterns. Most notably, soil health indicators (and especially soil CO2) responded to crop rotation treatment. The perennial treatment produced 4.57–8.74 µg g-1 24 hr-1; whereas other rotation treatments respired 25–28%, 44–45%, 22–28%, and 35–36% less CO2. Overall, early indicators of soil health change tended to be related to dynamics of soil inorganic N cycling and CO2 evolution. Our results suggest that a longer-term period of cover cropping and greater biomass accumulation will be needed to substantially impact soil health in this semi-arid environment. Implementing more ‘perennialized’ crop rotations will benefit the early indicators of soil health change in a short timeframe.