OBSERVATIONS ON THE BIOLOGY OF ORGANIC ORCHARD SOILS

Abstract

Three studies were used to evaluate the biology of organic orchard soils. The work focused on the three phases of organic systems: development, dynamic equilibrium and senescence. The first study consisted of a comparative analysis of the vertical distribution of nematodes, ciliates, flagellates, amoebae and endomycorrhizae associated with four pairs of mature organic and conventional cherry orchards. The second study investigated the dynamics of nematode community structure associated with transitioning a corn-soybean site into a certified organic apple orchard. In the third study, the soil biology of the new organic apple orchard was compared with the soil biology of an organic vegetable site that had been certified for 20 years, a neighboring conventional corn-soybean field with similar soil physical characteristics, and an old field secondary succession site at the Michigan State University, Kellogg Biological Station, Long Term Ecological Research project. Absolute population densities of bacterial feeding nematodes, ciliates, flagellates, amoebae and endomycorrhizae were significantly higher in the O-horizon in all eight cherry orchards, compared with the population densities at 0-15 or 15-30 cm soil depth. The O-horizon of organic orchards had significantly higher absolute population densities of flagellates and total soil-borne organisms compared with soil from the conventional orchards. In general, soil biological diversity was greater in the organic orchards than in the conventional orchards. During the apple orchard organic transition process, the relative population density of herbivorous nematodes declined. The data indicate that the soil biology of the new organic apple orchard took seven years to reach a state of dynamic equilibrium.