Investigating the Impact of Green Manures and Weed Mat on Soil Biota and Tree Growth in Organic Peach Tree Orchards

In the spring of 2001, organic peach blocks were established at two Western Colorado Research Center sites: Rogers Mesa and Orchard Mesa. These plantings were established to allow multi-disciplinary research, systems comparisons, and demonstration of an organic production system for peaches. The objective of this project is to study the effects of different organic management practices on the soil microbial and faunal communities within peach orchards on the western slope of Colorado. The plots were established with and without weed mat to determine the effect of these treatments on the soil microbial and faunal communities. Secondly, we are examining the effects of two different green manures, alfalfa-grass mix and grass alone, on the soil microbial and faunal communities. This project will allow us to determine if a correlation exists between the applied management practices, soil community structure and functioning, and tree growth and vigor. In order to carry out the objective set forth, we will enumerate numbers of bacteria, fungi, protozoa, nematodes (bacterivorous, fungivorous, omnivorous, predatory, and phytophagous), microarthropods (collembola and mites), and earthworms. Based on the obtained biomass estimates for each organism and published physiology values, we will then use the detrital FOOD WEB model (Hunt et al., 1987) to model nitrogen flow and nitrogen mineralization rates through the decomposer subsystem in each treatment. As these organisms are responsible for the decomposition of organic matter and maintaining normal nutrient cycling, quantifying their numbers and modeling N-flow and Nmineralization rates will allow us to make recommendations as to which green manures will enhance microbial activity, and in turn, nutrient uptake and growth by plants. Additionally, this study will allow us to elucidate the effect of weed mat on the decomposition process, as mediated by soil biota, and its effect on nutrient cycling and uptake by plants. Upon conclusion of this study, we will provide fruit growers with information and recommendations for green manure selection, as well as information concerning the interaction between green manures, weed mat, and the soil biota.