PS 20-22 - Residue and fertility management considerations for annual forage polycultures

Abstract: Regenerative agriculture practices are becoming more prevalent as producers seek to improve soil quality and store carbon. One of the key principles of regenerative agriculture is to increase crop biodiversity, which can be achieved through the inclusion of diverse annual mixtures (also known as polycultures or polycrops) in a crop rotation. These mixtures may be grown as a cover crop or used as forage for livestock. In this experiment, our objectives were to determine the effect of annual polyculture residue and fertility (nitrogen) management on forage production, soil health, and system productivity. Three diverse annual forage mixtures were grown in a research trial in 2018 near Swift Current, Saskatchewan, including a “balanced mix” (two cereals, two legumes, two brassicas), “nitrogen fixing mix” (three legumes), and “weed control mix” (one cereal, one legume, three brassicas). Crops were grown under three N fertilizer rates (0, 60, and 120 lbs/ac actual N), and at harvest three different residue amounts were left behind (0, 50, and 100%). To determine the effects of these treatments on subsequent crop growth, wheat was seeded over all plots in 2019, followed by peas in 2020.



We found that forage production was significantly different between the seeded mixtures in 2018, and the balanced mix produced the highest biomass. In 2019, spring soil nitrate-N and wheat yield was significantly greater under the treatments that received more fertilizer and had more residue left behind in 2018, but there was no effect based on the previous crop. However, following the wheat harvest, impacts of the 2018 crop were observed as the plots previously seeded to the N fixing mix had higher soil moisture, higher N, nitrate-N, total C and organic C. The amount of residue left in 2018 also significantly impacted nitrate-N and total C in fall 2019. In 2020, pea yield was impacted by the 2018 seeded crop, as pea yield was lowest on the N-fixing plots, indicating concerns with seeding legumes too soon after a polyculture that includes a high proportion of legumes. In fall 2020, following the pea crop, no soil factors were significant, suggesting that nutrient dynamics following a forage polyculture might be short-lived in a semi-arid system, or that longer time is needed to see complete breakdown of crop residues. In conclusion, crop mixture, fertilizer, and residue all impacted subsequent crop and soil conditions, indicating these are important management considerations for farmers adopting regenerative agriculture practices.