Long-term organic crop rotation experiments for cereal production - perennial weed control and nitrogen leaching

Summary

In long-term organic crop rotation experiments for cereal production, stubble cultivation to control perennial weeds increased nitrogen leaching compared to catch crops grown after harvest. Stubble cultivation contributed to the control of Elymus repens on a sandy soil, but not to the control of Cirsium arvense on a loamy soil. Manure application had a tendency to decrease E. repens density in one rotation at the sandy soil. Grass-clover green manure decreased C. arvense in the succeeding crops. Despite high infestations of perennial weeds, yields were at the same level with as without stubble cultivation. The results point to an important dilemma in organic farming: should the farmer control perennial weeds in the stubble at the expense of losing nitrogen by leaching? Or should catch crops be grown that preserve nitrogen, but allow E. repens to proliferate?