Weed control approach but not fertility source influenced yield and weed populations during grain-based transition to organic production

Abstract

Controlling weed populations and improving soil health while producing high yields are top priorities of organic crop farmers yet are difficult to achieve simultaneously due to the importance of cultivation for weed control. This study examined whether less frequent cultivation for weed control and the application of carbon-rich soil fertility amendments would enable progress toward those goals during the 3-year transition period to organic production. Standard weed control with cultivation was compared to high-frequency cultivation combined with delayed planting. The standard approach produced 7% higher crop yield over the course of a corn (Zea mays L.)–soybean [Glycine max (L.) Merr.]–small grain rotation, likely due in part to earlier corn and soybean planting. In-field weed counts and weed seedbank germination showed weed populations tended to be lower in the high-frequency cultivation treatment, although patterns were crop specific. Weed populations increased over the 3 years in all treatments, suggesting that additional weed control tactics may have been beneficial. Carbon-rich poultry manure had no significant effects on weed populations, soil health, or crop yield compared to an N-rich organic fertilizer. However, crop yields were positively related to soil health indicators, specifically greater soil total carbon and nitrogen and permanganate oxidizable carbon. The standard weed control approach was advantageous during the organic transition period, but the observed increase in weed populations might become problematic in future years of organic production.