Cover Crop Strategies for Organic Reinvigoration
May 17, 2015
Soils in mature organic systems may develop chronic, yield limiting problems that can’t be addressed with the short-term fixes available for nonorganic production. Examples include poor soil structure, loss of organic matter and the build-up of pest populations, most notably weeds and plant parasitic nematodes. Frequent tillage is responsible for many of the soil quality issues. Directly, tillage jeopardizes soil aggregates and introduces a pulse of oxygen leading to organic matter loss. Indirectly, it reduces mycorrhizal fungal abundance, limiting their ability to contribute to aggregate stability as well as support crop growth. Tillage can also spread perennial weeds while suboptimal conditions for mechanical weed control increases annual weed pressure by increasing the soil seed bank.
Cover crops may offer a solution for reinvigorating organic land by directly addressing these issues. They are already an integral component of organic production and are frequently used to protect soil, fix nitrogen, suppress pests and add organic matter, but are used too infrequently to produce long-term effects and short-term gains are often negated by tillage. Some species also serve as an alternate host for nematodes.
Last fall we initiated a trial to investigate several cover crop strategies to reinvigorate organic land. The overall idea is to remove land from production and practice intensive cover-cropping to address soil issues to eliminate or reduce yield constraints. The strategies have two features in common: cover crops will be grown continuously, alone or in sequence to maximize use of the growing season; and once the first cover crop is established, tillage is eliminated. Where annual species follow others, the first cover crop will be terminated by roller-crimping and the next cover no-till planted.
The strategies vary by cover crop life cycle (summer annual, winter annual and perennial), diversity of species used in the sequence, their inherent properties such productivity, ability to suppress pests or support mycorrhizal fungi and cost. We will take measurements of productivity (how much biomass is produced), changes in soil quality and pest populations and will determine the cost of each. From the results, we hope to develop a set of specific recommendations which can be used to address site specific problems. For example, if soil has poor structure and a large annual weed seed bank, the most cost effective sequence which best addresses these two problems would be recommended. Potentially, this represents a great advancement in cover crop science because recommendations are performance based and will capture the collective attributes and synergies between the species in the sequence. Currently, we can only offer recommendations based on the purported properties of individual species which may or may not address multiple problems.