Atributos de solo sob revegetação no semiárido brasileiro e extração de elementos pelas plantas

Abstract

The search for alternatives for the recovery of degraded soils is constant. The restoration of its attributes is essential for the maintenance of ecosystem services. The objective of this work was to evaluate the influence of revegetation on physical, chemical and biological attributes of a degraded soil in the Brazilian Northeast semiarid, in the dry and rainy seasons; as well as to analyze the associated microbiota and the extraction of chemical elements by different plant species. For that, an experiment was installed in the field, in November of 2013. The experimental area was fenced and divided into four blocks, with eight treatments: 1) control (without plant cultivation); 2) Atriplex plants; 3) Sabiá plants; 4) Leucaena plants; 5) Neem plants; 6) Atriplex and Sabiá consortium; 7) Atriplex and Neem consortium; 8) Atriplex and Leucaena consortium. Two evaluations were performed in the experiment, the first at the end of dry period (November/2015), 24 months after transplanting, and the second at the end of rainy season (May/2016) at 30 months. The samples were collected in three layers, 0-10, 10-30 and 30-60 cm, being carried out the physical characterization, by granulometric composition and particle density, and analyzed physical attributes (water dispersed clay - WDC, flocculation degree, soil density and saturated hydraulic conductivity - Ksat) and chemical attributes (pH in water, exchangeable cations, cation exchange capacity - CEC, total organic carbon - TOC, total nitrogen - N, C/N ratio, pH and electrical conductivity of the saturation paste, and soluble cations). The biological attributes were evaluated in the superficial layer, being rhizospheric pH, basal respiration of the soil - BRS, carbon of the microbial biomass - CMB, metabolic quotient - qCO2 and microbial quotient - qMIC. The presence of arbuscular mycorrhizal fungi (AMF) was also evaluated through glomerospores density, mycorrhizal colonization and glomalin quantification. The structure of the soil microbial community was analyzed by the fatty acid methyl ester (FAMEs) technique. In the rainy season, the plants were collected for analysis of Na, K, Ca, Mg, Cl, P and N in the plant tissue. The results of this work indicate that the plant species were efficient in improving attributes of degraded soil due to the reduction in WDC content and increase in flocculation degree, as well as decrease in soil density and increase in saturated water hydraulic conductivity (Ksat). Plant species also increased soil TOC and CMB. In the rainy season, BRS and qCO2 were lower in the cultivated area, compared to the control area. In general, the FMA spore density and mycorrhizal colonization were higher in the cultivated area. It confirmed the formation of mycorrhizal association in Atriplex nummularia (Chenopodiaceae), with rates higher than 50%. The rainy season and both crops, isolated or consortium, positively influenced diverse attributes of the soil. Regarding the extraction of sodium and chloride, the isolated or intercropping culture did not influence the phytoextractor potential of Atriplex. Atriplex consortium with Neem was more efficient at extracting K, Ca, Mg, P and N.