Sometimes, chronic, yield-limiting problems develop in the soils of mature organic systems; such problems are not able to resolved with the same short-term solutions often used for nonorganic production. For example, soils can experience loss of organic matter, poor soil structure, and an increase in pest populations (e.g. plant parasitic nematodes and weeds). Many of such soil quality issues result from frequent tillage. This occurs directly as tillage introduces a burst of oxygen that leads to the loss of organic matter and puts soil aggregates in jeopardy. In a less direct manner, tillage lessens the mycorrhizal fungal abundance, affecting its ability to impact aggregate stability and support the growth of the crop. Perennial weeds can also be spread by tillage, and less than ideal conditions for controlling weeds mechanically increases the soil seed bank, thus increasing annual weed pressure.
Cover cropping appears to offer a means by which organic land can be invigorated by addressing these problems directly. Cover crops are already a critical element in organic production and are often used to fix nitrogen, protect soil, add organic matter, and suppress pests; however, they are not used often enough to have a long-term impact, and their short-term advantages are frequently negated by tillage. Unfortunately, some cover crop species also wind up serving as an alternative host for nematodes.
Last autumn, we began an investigation of a number of cover crop strategies, in the attempt to reinvigorate organic land. The general aim is to take a particular piece of land out of production and introduce a cover crop either to eliminate or reduce yield constraints, or to address soil issues currently present. Both approaches have two things in common: once the first cover crop is introduced, tillage can be eliminated; and, cover crops will be grown so as to maximize the use of the growing season, whether through continuous growth, sequenced growth, or by itself. The initial cover crop will be ended by roller-crimping and the next cover will be no-till planted, where annual species follow other crops.
The strategies used will obviously need to vary by the life cycle of the cover crop (perennial, winter annual, or summer annual), each crop’s inherent properties (cost, ability to suppress pests, productivity, and support of mycorrhizal fungi, for example), and the diversity of the species used in the sequence. Productivity measurements will be taken (i.e. the quantity of biomass produced), along with noting any changes in pest populations and soil quality, and the cost of each will be calculated. From the resulting data, we plan to develop a set of specific recommended actions that can be used to address problems specific to a site. For instance, if a particular soil has a large yearly weed seed bank and poor structure, we will be able to recommend the most cost-effective sequence to address both problems at once. It is our hope that cover crop science will be advanced by this study, with recommendations based on performance that also encapsulate the collective characteristics and synergies between the sequences’ species. At present, we are only able to offer suggestions based on the inferred properties of each individual species, but that may not sufficiently address multiple problems.