The Relationship Between Cultural Practices and Arbuscular Mycorrhizal (AM) Activity in Orchards Under Different Management Systems

Abstract

It has been demonstrated that soil disturbance, excessive fertilization and the use of some agrochemicals affect the survival and function of arbuscular mycorrhizal (AM) fungi. To clarify the effect of different cultural practices on mycorrhizal activity in orchards, spore population dynamics, soil and plant mineral content and mycorrhizal infection were surveyed monthly from May to October, 2000 in kiwifruit, Japanese chestnut, Iyo tangor, satsuma mandarin, Japanese persimmon, apple, peach, Japanese plum and grape plantings, subjected to different management regimes. In intensively managed orchards, levels of major elements in the soil were generally high, owing to periodic fertilization ; consequently, the content of these elements in the leaves was within the recommended range for normal growth and function. High levels of AM infection were maintained throughout the season in the apple orchard that received no fertilizer or fungicide. The infection levels on roots of kiwifruit vines decreased in July and August after three fungicide sprays in June ; it also decreased in Iyo tangor in July following four fungicide applications in May and June. These orchards had no under-story cover plants. However, the infection level of peach trees under sod culture remained relatively high even after five fungicide sprays from May through August. Thus, population density of AM spores in the soils seems to be low in the clean cultivated orchards, subjected to frequent fungicide sprays, whereas it was high under sod culture. We conclude that excessive fertilization, frequent fungicide sprays and clean culture have an adverse effect on AM spore populations and tree infection in orchards.