Influência do manejo agrícola e do clima sobre alguns atributos biológicos do solo

Abstract

Soil fungi groups may favor increasing in the plant absorption of nutrients. These are known as arbuscular mycorrhizal fungi (AMF) and are distributed in most of the agricultural and natural systems, in mutualistic association with plant roots. The symbiosis associated to the mineralization of soil organic matter, overly influences the plant nutrition. The understanding of alterations occurring in the carbon of the soil microbial biomass (Cmic) and in the activity of this biomass, when different vegetable coverings are used, may offer conditions for choosing the best management strategies to favor the maintenance of organic matter in the soil. This study had two objectives, the first to determine the active portion and the dynamics of AMF, related to the effect seasonal changes and soil management practices on these fungi. The studied soils were under organic cultivation of vegetables and fruit trees (Capítulo I). The second objective was to determine alterations in the carbon of the microbial biomass (Cmic), and loss to atmosphere in the form of CO2, as a function of seasonality and management of green mass of perennial herbaceous legumes, in a Red-Yellow Argissolo (Ultisol) (Chapter II). In the chapter I, the data showed that all vegetables and fruit trees were colonized by FMA, in the dry and rainy seasons. Twenty-seven AMF species were identified in the field. Glomus macrocarpum, Glomus etunicatum, Acaulospora mellea and Entrophosphora colombiana prevailed in the rizosfera of vegetables and fruit trees and showed to be more adapted on organic cultivation system. G. macrocarpum showed larger occurrence frequency (FO), and it was found in all crops roots. The highest richness of species occurred on banana's rizosfera. In the greenhouse experiment eighteen species of AMF were recovered in the vases. The sorghum was used as a trap crop. Acaulospora mellea, Glomus claroideum, Glomus etunicatum and Glomus macrocarpum multiplied in higher intensity in the vases and presented a fast infection of the sorghum roots. Therefore, these species should be considered in inoculation programs. The sweet potato cultivation (BD2) showed higher AMF esporulation during the dry period. The seasonality and soil management resulted in differentiated effects in the mycorrhizal colonization and population of AMF spores. These were more evident on cultivation BD2. In the chapter II, the results showed that Arachis pintoi coverage induced higher Cmic in the soil, in relation to the Pueraria phaseoloides and Macroptilium atropurpureum, especially in the dry season. This legume contributed to increase of organic carbon (CO) during the rainy season, mainly when the residues were maintained as soil coverage. Losses of carbon through microbial respiration (RM), as the microbial biomass activity, evaluated from the qCO2, occurred in higher intensity in the rainy season, even when the soil covering were maintained. Probably, due to the stimuli of microbial metabolism, when there was a high energetic offer.