Diagnóstico da ocorrência de micro-organismos simbiontes em áreas sob processo de desertificação no município de Irauçuba, Ceará

Abstract

The soil degradation resulting from non-conservative practices can cause irreparable damage to chemical and biological properties of the soil of semiarid regions in northeastern Brazil. The objective of this research was to evaluate the soil chemical attributes, the population density of rhizobia and its symbiotic fixing efficiency of the atmospheric nitrogen in cowpea (Vigna unguiculata (L.) Walp.) in addition to density of arbuscular mycorrhizal fungi and the basal soil respiration in four areas of exclusion and overgrazing located in the municipality of Irauçuba-CE. Four areas of animal exclusion and overgrazing (adjacent to the exclusion areas) were chosen, with soil samples being collected in the 0 to 20 cm to analyze the chemical attributes pH, Electric Conductivity (EC), Carbon (C),Nitrogen (N), Organic Matter (OM), and assimilable Phosphorus (P) and biological attributes (arbuscular mycorrhizal fungi spores density, rhizobia density and effectiveness and basal soil respiration. The experiments were conducted under greenhouse conditions and, for the atmospheric symbiotic nitrogen fixation performance tests, native strains were isolated from the four areas and a completely randomized design, with four replications, was adopted. In area 1 were used nine treatments and four replications, with a control with the addition of mineral nitrogen (+N-R) and another with mineral nitrogen omission and no inoculation C(-N-R); in area 3 were used eight treatments and four replications, with a control with the addition of mineral nitrogen (+N-R) and with mineral nitrogen omission and no inoculation C(-N-R); in area 4 the test consisted of six treatments and four replications, with a control with the addition of mineral nitrogen (+N-R) and with mineral nitrogen omission and no inoculation C(-N-R); in area 5 the test were used four treatments and four replications and a control with the addition of mineral nitrogen (+N-R) and another with mineral nitrogen omission and no inoculation C(-N-R). The different treatment numbers of the four areas were established according to the total number of isolated and authenticated strains of each study area. The current soil management practices employed in the areas of exclusion of animals (fallow) favored the presence of propagules of arbuscular mycorrhizal fungi in the soil due to the preservation of vegetation and conservation of topsoil. Native rhizobia strains isolated and tested from Areas 1 and 5 established symbiosis with the cowpea and demonstrated a fixing efficiency of N 2 reasonable and can be used in future field trials. More studies on the chemical and biological properties of soils Irauçuba-CE should be performed so that we can find alternatives for reducing the negative effects of the degradation process observed in the areas under study.