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John Lloyd recently completed his Ph.D. degree
in entomology at The Ohio State University,
Ohio Agricultural Research and Development Center,
in Wooster, and is currently an assistant professor
in the Department of Plant, Soil, and
Entomological Sciences at the University of Idaho in
Moscow, Idaho;
Dan Herms, Ben Stinner, Harry Hoitink, |
Nutrient cycles have been studied thoroughly in forested and agricultural ecosystems (Facelli and Pickett, 1991; Wardle, 1992; Attiwell and Adams, 1993; Mary etal., 1996). In contrast, nutrient cycling has received little attention in ornamental landscapes, and effects of mulch on soil fertility have been largely ignored.
Organic matter, such as leaves and grass clippings, is often collected and removed from ornamental landscapes, which disrupts nutrient cycles, and can increase reliance on inorganic fertilizers. Mulches are used widely to suppress weeds, conserve soil moisture, direct traffic flow, and enhance the beauty of landscapes (Robinson, 1988). Depending on their composition, some mulches may also have substantial effects on soil fertility and plant growth.
Mulches with a high carbon-to-nitrogen (C:N) ratio, such as recycled wood pallets, hardwood bark, straw, and sawdust are thought by some to induce nutrient deficiencies in plants by stimulating microbial growth, which depletes underlying soils of available nutrients. On the other hand, mulches such as composted yard waste and wood or bark blended with composted manure or sewage sludge may increase soil fertility and plant growth because their low C:N ratio resembles high-quality forest litter.
Mulches derived from the bark of mature softwood trees, such as cypress and pine, are quite resistant to decomposition by microbes and thus have little effect on nutrient availability. The key to understanding how different mulches affect soil nutrient availability lies in understanding the role of soil microbes in nutrient cycling, and how they respond to addition of organic matter.