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

Authors: Osterholz, William; CULMAN, STEVEN - Washington State University; HERMS, CATHERINE - The Ohio State University; DOOHAN, DOUGLAS - The Ohio State University

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/20/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary: Organic agriculture requires a three year transition period prior to full organic production, and organically managed grain production is a potentially beneficial system during the transition period. Grain production during the transition period should control weed populations and also increase or maintain soil health while producing high yields. Less frequent tillage and application of carbon rich fertility amendments could enable progress toward these goals, and this study examined their effects in a field study in Ohio, USA. Less frequent tillage increased grain yield by 7% over a three year crop rotation of corn-soybean-small grain. Less frequent tillage also tended to increase weed populations, a trend that should be closely monitored after the organic transition period is completed. The carbon content of the soil fertility source did not impact weed populations or grain yields, and neither tillage frequency nor fertility source influenced soil health within three years. This study demonstrates the potential benefits of lower tillage intensity, and can be used to improve agronomic outcomes during the transition to organic production.

Technical 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 tillage for weed control. This study examined whether less frequent tillage for weed control and application of carbon-rich soil fertility amendments would enable progress toward those goals during the three-year transition period to organic production. Lower weed control intensity, with fewer tillage passes, was compared to a higher weed control intensity that used additional tillage in a stale seedbed approach. Lower weed control intensity produced 7% higher crop yield over a corn-soybean-small grain rotation. In-field weed counts and weed seedbank germination showed weed populations tended to be greater in the lower weed control intensity treatment, although patterns were crop specific. Weeds increased in number over the three 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, yields were positively related to soil health indicators, specifically greater soil total carbon and nitrogen and permanganate oxidizable carbon. The lower weed control intensity approach was advantageous during the organic transition period, but the increase in weed population might become problematic in future years of organic production.