Influence of the covered bean, Phaseolus vulgaris L., production system on the chemical, physical and biological properties of A[n]disols
Slash mulch systems are fundamental to covered common bean (' Phaseolus vulgaris') production throughout tropical America. The aims of this study were to evaluate the effects of management on properties of Andisolic soils in farmland areas in which covered bean crops have been planted together with coffee for several years; to assess bean response to Arbuscular Mycorrhyzal Fungi (AMF) inoculations; to study if P additions decrease AMF infection; and to study the effect of rock phosphate additions on soil nutrients, root distribution and plant growth. The comparison of soils under shaded coffee and covered beans showed remarkably similar characteristics despite the fact that bean production occurred on steeper slopes on which erosional losses should be expected to result in poorer soil quality. There was no response in beans growth to plant residue additions, even if they contained levels of P higher than the critical value for mineralization. 'Glomus manihotis ' inoculation increased plant response to P addition, independent of the source and doses of P used. At the field site all the studied plants were infected with AMF indicating the prevalence of the symbioses in covered bean growing in Andisols. In spite of the addition of rock phosphate, P levels at the field plots were low and did not inhibit mycorrhizal infection. Throughout the different bean development stages, most of the root system was growing at the soil mulch interface. The concentration of roots in this zone would give the beans an advantage for obtaining nutrients released from the mulch.