Vineyard Soils: Biology

Mark Chien, Penn State University

The soil food web is relatively new to the viticulture lexicon. It refers to the great diversity of biological life that exists in the soil medium. This myriad of organisms is often present in astonishing numbers and range in size from the tiniest single-celled bacteria to small vertebrates and everything in between such as algae, fungi, protozoa, arthropods, nematodes, earthworms, insects, and more. Each of these organisms has its own important function in the web and all are food for each other. Actinomycetes help to decompose organic matter. Fungi and bacteria create compounds that help to bind soil particles. Nematodes are involved in nutrient cycling. Soil arthropods help to shred dead plant materials, greatly enhancing decomposition. Earthworms mix and aggregate soil particles and stimulate microbial activity.

Only recently has much been done to develop an understanding on how this complex world impacts plant life and how it might influence wine quality. There are laboratories that will analyze soil for types and amounts of key organisms and make recommendations for treatment. Most of the evidence for any benefit from applying food web products is anecdotal. Grape growers should be attentive to this underground world and employ practices that enhance and preserve the food web. Reducing chemical inputs, aerating soils, reducing soil compaction, improving soil drainage, and adding compost when needed are all practices that can contribute to the sustainability of the subterranean life. Some of the organisms that live in the soil, such as pathogenic nematodes (vectors for grape viruses), grape phylloxera, grape root borer and various bacteria and fungi, may be harmful to vines. These should all be evaluated and treated before planting.