Effect of organic mulches and a residual herbicide on soil bioactivity in an apple orchard

Abstract

In New Zealand orchards, weed control is usually achieved with a combination of herbicides and mowing or cultivation. Alternative strategies (e.g., organic mulches) have been called for, on the grounds that persistent herbicides may have undesirable effects on non-target organisms and may leach into the ground water. We compared the effects of sawdust, straw, compost, and wooldust mulches and the residual herbicide terbuthylazine on soil respiration, cellulose degradation activity, and bacterial and fungal biomass in an apple orchard in Hawke's Bay, New Zealand. The control received no residual herbicide or mulch but weeds were checked by paraquat/diquat or glyphosate. Measurements were made over two growing seasons. Terbuthylazine application had no detectable effects on CO2 emission or cellulose degradation activity. Over both seasons, total CO2 emission in the field was increased by compost. In the summer immediately following mulch application, sawdust, and straw mulches suppressed CO2 emission from the soil, but total emission over both seasons was not different from the control. Soil biomass measurements were only taken from the herbicide, sawdust, and wooldust plots and the grass inter-row. In general, bacterial and fungal biomasses in the soil decreased in the order grass > sawdust mulch > residual herbicide > wooldust mulch. Cellulose degradation activity was increased by compost and straw but depressed by wooldust. There was no simple relationship between respiration and cellulose degradation activity across treatments. © 1996 Taylor & Francis Group, LLC.