Cover Cropping Yields More Substantial Soil Quality Gains Than Composting in Loamy Sand Soil

This post highlights the findings of the following study:

Eric B. Brennan, Veronica Acosta-Martinez. Cover Crops and Compost Influence Soil Enzymes during Six Years of Tillage-Intensive, Organic Vegetable Production. Soil Science Society of America Journal, 2019; 83 (3): 624 DOI: 10.2136/sssaj2017.12.0412

 Take home message:

• ·        There were large differences in soil enzyme activities within organic systems.
• ·        Compost and annual cover crops increased activities of most soil enzymes.
• ·        Activities of most soil enzymes were correlated with microbial biomass.
• ·        Cover crop type did not influence soil enzyme activities.
• The results show the soil health benefits of frequent cover crops in vegetable systems

Background: The presence of carbon in soil provides a food source for microbes which provide nutrients to the crops. A healthy soil ecosystem of microbes, insects, and other life forms aid in water retention and a soil structure that is conducive to plant growth. Tracking changes in the organic matter present in the soil is complicated by the organic matter’s slow rate of change and the intensive tilling that is used to prepare the soil for vegetable farming.

What is being tested? Soil enzymes as indicators of improvements in soil health over an extended period.

Where? Salinas Valley, California. This area is known for high-input, organic vegetable production systems.

Why here? Farmers in this area use extensive amounts of compost to make up for the short breaks between crops.

How? There was a comparison between farming systems that had received varying amounts and types of organic matter that had been created from composting and cover crops.

What did the results show? Annual cover cropping is more beneficial than regular compost, with microbial activity increasing the most in soil that had cover cropping. The soil benefits from cover cropping annually regardless of what plant is being grown.

What does cover cropping mean? A cover crop is a crop of a specific plant that is grown primarily for the benefit of the soil rather than the crop yield. Cover crops are commonly used to suppress weeds, manage soil erosion, help build and improve soil fertility and quality, control diseases and pests, and promote biodiversity. It also reduces the amount of nitrogen that leaches into ground water.

What does this tell us? It brings to discussion the concern about how sustainable both organic and conventional farming techniques are if the cover crops are not generally used. Innovative strategies are needed to make the use of cover cropping easier and thus a viable method of improving soil quality.

Important things to note – These findings are applicable to the loamy sand soil found in the Salinas Valley. Farmers in other areas who may have different types of soil or those that use different fertilizers could experience different results.

Why does this matter? Organic certified farms are required by USDA Organic Standards to provide proof that their cultivation practices maintain or improve the physical, chemical, and biological quality of the soil, along with reducing soil erosion.

Summary. The use of certified organic management techniques alone does not necessarily improve soil health or quality long term, which could complicate matters of compliance with USDA Organic Standards.

Future research. Same testing parameter with different types of soil, such as clay or loam soil. A new study testing the same factors over a shorter period would be helpful.