Shading and intercropping with buffelgrass pasture affect soil biological properties in the Brazilian semi-arid region

Abstract

The objective of this work was to evaluate the changes caused by shading and intercropping with a legume (Clitoria ternatea L.) in a grass (Cenchrus ciliaris L.) pasture on the microbiological and biochemical attributes of the soil. Microbial biomass carbon (MB-C), soil respiration, the activities of soil enzymes (β‑glucosidase, acid phosphatase and urease) and total soil fungal and bacterial were evaluated. Soil samples were collected at four periods: before intercropping (BI), at 120, 165 and 210 days of cultivation and under four shading levels 0 (full sun), 26, 39 and 55%. Before intercropping (BI), shading affected biological and biochemical parameters by increasing the MB-C but reducing soil respiration, resulting in a reduction of qCO2. There was an increase in MB-C and β‑glucosidase in the intercropping treatment and 39% shading, while under monoculture an increment in MB-C was reached only under 55% shading at 120 days of cultivation. The highest CO2 fluxes by soil respiration were observed in the intercropping areas and in the shaded areas at 0, 26 and 39% at 120 days of cultivation. The intercropping system and the higher levels of shading reduced the qCO2 at all sampling time. The highest soil urease activity occurred in the intercropping areas and in full sunlight, regardless of the sampling time, while acid phosphatase presented greater activity in the intercropped areas at 165 days of cultivation. From the multivariate analysis, it was possible to verify that the effects of intercropping are evident at 165 days of cultivation with the formation of two distinct groups and an increase in the biological quality in the intercropped areas. For qPCR it was verified that only shading affected the amounts of total soil fungi and bacteria; the use of shading reduced the amount of fungi only at 120 days, while for bacteria, the use of 26% shading in the BI period and full sun at 165 days increased the amount of bacteria. This variation of shading effect over time on the amount of fungi and bacteria may indicate changes in the composition of fungal and bacterial species. It is concluded that shading and intercropping with C. ternatea into C. ciliaris pasture promotes improvements in soil quality indicators under semi-arid conditions.