Effect of compost application on the soil microflora

Compost is used in agriculture as a fertiliser or to improve the physical structure of the soil. In addition, compost amended soil has been found to be suppressive against plant diseases caused by nematodes, bacteria, or soil-borne fungi in various cropping systems (Hoitink and Fahy, 1986; Ringer, 1998). However, the opposite, an increase of disease incidence due to a compost application, has also been demonstrated (Tuitert et al., 1998). Several reasons for these inconsistent results can be given. There are many types of compost, i.e. they differ in composition of organic materials and in maturity. In addition, the method and time of the compost application is important for the final effect in the field. Application of organic material just before planting the crop can even stimulate pathogens. Up to now, it is still difficult to predict the beneficial effect of compost products in plant pathosystems. To understand the influence of compost applications on soil suppressiveness, the microflora in soil before and after compost application has to be studied in more detail.