Abstract Sugarcane crop conventional tillage has been replaced by deep soil preparation with few studies about its effect on soil quality and sustainability. The aim of this study was to assess structural volumes ina dystrophic Red-Yellow Latosol subjected to conventional tillage (CT) and deep localized soil tillage (DLST) to verify how the microbiological parameters were affected. The study was conducted in a soil derived from the Caiuá Sandstone formation in Brazil. Four trenches were dug for each soil tillage system to describe the cultural profile and evaluate carbon microbial biomass (CMB) and nitrogen (NMB), basal respiration (BR), and metabolic quotient (qCO2). CT profiles exhibited a predominance of cracked soil volumes, medium-sized and large compact clods with some porosity, and continuous volumes with no cracks and of intermediate porosity. DLST profiles were predominantly free-soil volume with no cohesion and porous in appearance, and compact, cohesive volumes with no porosity visible. The highest levels of CMB and NMB were in the cracked soil under CT. Higher microbial activity indicated by BR and qCO2 were in the free powdery soil under DLST. Soil pulverization caused by DLST could cause serious consequences on soil functionality, boosting erosion, and metabolic stress in the microbiota.

RESUMO A aplicação de água residuária de suinocultura (ARS) em solos agrícolas pode gerar impactos na comunidade microbiana do solo, quando realizada em longo prazo. O objetivo deste trabalho foi avaliar possíveis alterações na comunidade bacteriana do solo após oito anos de aplicação contínua de água residuária de suinocultura. As doses de água residuária (0; 100; 200 e 300 m3 ha-1 ), aplicadas desde o início do experimento, foram combinadas com a presença ou a ausência de adubação recomendada. No solo, foram feitas três coletas em cada parcela para a determinação da respiração basal, biomassa microbiana e quociente metabólico, análise de DGGE, correlação entre as condições químicas do solo e a atividade microbiana na comunidade bacteriana do solo. Alterações significativas na estrutura da comunidade microbiana do solo, com a aplicação de água residuária de suinocultura, foram observadas. Doses maiores de ARS (200 e 300 m3 ha-1) influenciaram de forma significativa (p<0,05) e privilegiaram a permanência de alguns grupos específicos de bactérias.

ABSTRACT Swine wastewater (SW) application in agricultural soils may affect its microbial community in a long term. The objective of this study was to evaluate prospective changes in soil bacterial community after eight years continuous application of swine wastewater. The wastewater doses tested were 0; 100; 200 and 300 m3 ha-1, being applied from the beginning of the experiment and with or without recommended fertilization. Three soil samples were taken from each plot for determinations of basal respiration, microbial biomass and metabolic quotient. We also performed DGGE analysis and made a correlation between soil chemical conditions and microbial activity. Microbial community underwent significant structural changes from swine wastewater applications. Higher SW doses (200 and 300 m3 ha-1) influenced significantly (p <0.05) and benefitted certain bacteria groups.