Abstract: Several microbiological indicators of soil quality present high sensitivity, but little is known about the influence of topographic factors on them. This work aimed to evaluate variability of biological indicators of soil quality across a hillslope under native forest and the influence of topographic factors on them. Four positions on a hillslope were evaluated. Activity of the enzymes β-glucosidase, acid phosphatase, urease and fluorescein diacetate (FDA) hydrolysis were determined, as well as basal and substrate-induced respiration, and density of microorganisms: total bacteria, total fungi, actinobacteria, phosphate solubilizers, ammonifiers, native rhizobia, free-living N2-fixing bacteria, spores of arbuscular mycorrhizal fungi and percentage of root colonization by arbuscular mycorrhizal fungi. Activity and density of microorganisms were correlated with topographic factors. The relation of these factors to the variations of the evaluated indicators was determined using the random forest algorithm. Microbiological indicators varied according to the hillslope positions. The indicators urease, basal respiration, spore density, mycorrhizal colonization, total bacteria and fungi, phosphate solubilizers, and free-living N2-fixing bacteria detected in JNFB and FAM culture medium did not vary with terrain attributes and were therefore more indicated in cases of topographic variations. This and future studies can help to select the best microbiological indicators for different conditions.

Os aumentos na produção agrícola devem-se ao uso de tecnologias avançadas e expansão de novas fronteiras e ocorrem, em parte, pela substituição das áreas de pastagens e vegetação natural. Algumas dessas áreas estão situadas nas várzeas e, do ponto de vista ambiental, são de extrema importância, pois prestam-se à recarga e manutenção da água de rios e córregos das microbacias. Neste estudo avaliou-se a resistência mecânica à penetração de um Plintossolo Argilúvico sob plantio direto e Cerrado nativo. Em cada área coletaram-se 10 amostras deformadas nas camadas de 0-30 cm e 30-60 cm, para determinação da umidade do solo. A resistência do solo à penetração (RP) foi executada com penetrômetro de impacto, com amostragens aleatórias nas áreas (dez amostras em cada área): 1) Nativas - no topo dos murundus (M) e entre os murundus (EM); 2) Cultivadas - plantio direto implantado há 10 anos (PD10) anos e 15 anos (PD15), em duas épocas: antes do plantio (PD10A e PD15A) e depois do plantio na linha (PD10L e PD15L), e entrelinha (PD10E e PD15E) de plantio, em pontos em cada tratamento. Dos resultados obtidos, observou-se que a RP do solo é influenciada pela posição amostrada. A avaliação da RP mostrou relação com a textura, densidade do solo (Ds), umidade e matéria orgânica do solo. Os valores críticos de Ds e RP são válidos quando comparados aos de áreas de referência próximas, de classe textural e relevo similares. A RP associada a Ds, umidade e textura, é um indicador sensível de alterações da qualidade física do solo, causadas pelo uso. Nas condições deste trabalho, o sistema sob plantio direto não se mostrou eficiente para manter a qualidade física do solo.

Increases in agricultural production are due to the use of advanced technologies and expansion of new frontiers and occur by the substitution of pasture areas and natural vegetation. Some of these areas are located in the floodplains and environmental point of view, are of utmost importance because lend themselves to recharge and maintenance of rivers and streams of water catchments. In this study was evaluated the penetration resistance of Plinthosol Argilúvico under tillage and native savanna. In each area, 10 samples are collected deformed layers 0-30 cm and 30-60 cm to determine soil moisture. The resistance to penetration (RP) was performed with impact penetrometer with random sampling areas (ten samples in each area): 1) Native - on top of the mounds (M) and between the mounds (IN); 2) cultured - tillage implanted 10 years ago (PD10) years and 15 years (PD15), at two times : before planting (PD10A and PD15A) and after planting in the line (PD10L and PD15L), and leading (PD10E and PD15E ) planting in points for each treatment. Results showed that the RP soil is influenced by sampled position. The evaluation of the RP was related to the texture, bulk density (BD), and moisture and soil organic matter. The critical values of Ds and RP are valid when compared to nearby reference areas, textural class and similar relief. The RP associated with Ds, moisture and texture, is a sensitive indicator of changes in soil physical quality caused by use. Under the conditions of this study, the no-tillage system was not efficient to maintain soil physical quality.