Jul 23, 2012
Cover crops an important component of healthy soil

Cover crops are grown throughout the world to complement crop needs in the field, while enhancing soil quality.

The use of cover crops spans thousands of years — bell beans during the height of the Roman Empire and lupines in northern Europe were grown to improve sandy soils. In the 1930s, use of cover crops became an intricate part of farming systems in America due to the impact of the Great Dust Bowl, when topsoil was blown away with weeks of high winds in the Central Plains. Responding to these natural disasters, the USDA Soil Conservation Service was established to help farmers implement technologies to reduce soil erosion.

The goal of using cover crops has often been to conserve topsoil. Since the advent of chemical fertilizers, cover crops have not been relied upon much to feed crops. There was increasing dependency on chemical fertilizers to provide macro-nutrients (N, P, K) to crops in the late 1930s. Chemical fertilizers were simpler to apply and provided the crops with quick access to nutrients, but their value stops there.

Cover crops offer multiple benefits for crops and soil, acting as chemical, biological and physical soil amendments. Access to nutrients (macro and micro) is enhanced through cover crops, in addition to beneficial soil microbes and deep roots to improve water filtration. A good example of such a “multipurpose” cover crop is brassica species, including mustard and oil seed radish with roots that penetrate through heavy soil and break up heavy clay soil, making it easier for crop roots to access needed nutrients. Legume roots, such as medium red clover and hairy vetch, are highly effective at enhancing soil fertility via nodules — through a symbiotic partnership formed with bacteria to fix nitrogen and build soil fertility.

Beyond nitrogen, cover crops play a key role in ensuring that a wide range of nutrients is available for healthy crop growth. Vegetables vary in terms of nutrient requirements — for example, cabbage requires more manganese and zinc and broccoli more boron. Adding a micronutrient for each crop’s needs is laborious, and timing is tricky. But enhancing soil organic matter will often improve availability of the micronutrients that are present, thus supporting healthy vegetable crop production. A soil that is rich in beneficial soil microbes will enhance nutrient availability, breaking down organic matter to make nutrients available to crops.

Cover crops help build soil organic matter, particularly when combined with compost or manure. Often, cover crops are selected primarily for aboveground contributions when, in fact, belowground attributes are equally, if not more, valuable to the soil and subsequent crops. The organic inputs from roots provide habitat, an energy source for soil microorganisms and carbon that can be sequestered to build organic matter.

To gain all of these benefits, it is important to find the right window to maximize the benefits of growing a cover crop. One approach is to invest in planting the seed with a seed-drill, to assure good stand establishment and maximize the return on seed purchase and labor.

Selecting the right cover crop depends on what your soil needs and the time of year available to grow a crop. The soil analysis will identify what it will take to produce a healthy and productive crop. This information combined with a cropping plan and basic knowledge of soil physical properties helps identify which cover crops and market crops to grow.

A valuable reference tool that will assist in planning soil testing and steps to improve soil quality is the “MSUE 3144-Building Soil for Organic and Sustainable Farms — Where to Start?“It offers a guide to selecting soil analyses and tables to monitor the soil.

Another Extension bulletin, “MSUE-2896-Cover Crop Choices for Michigan Vegetables,” can assist with the plan. For information on selecting a cover crop and manure management, visit the Midwest Cover Crops website, www.mccc.msu.edu.

By Vicki Morrone, Michigan State University


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