Soil quality indicators may have different seasonal trends during the year. The hypothesis of this study was that sowing maize and marandu palisadegrass with the presence of grazing animals might cause short-term changes in soil indicator responses. We compared four intercropping techniques: ICLS-1: maize plus marandu palisadegrass sown simultaneously, without herbicide; ICLS-2: maize plus marandu palisadegrass sown simultaneously, with herbicide; ICLS-3: maize plus marandu palisadegrass in lagged sowing (i.e., marandu palisadegrass sown 20 days after maize sowing); ICLS-4: maize plus marandu palisadegrass sown simultaneously (palisadegrass on the rows and inter-rows, with herbicide). Two control treatments in monoculture (i.e., grass and maize monocultures) represented the conventional systems. The soil was sampled three times over a one-year period, for the evaluation of carbon and nitrogen fractions as affected by seasonal variability. Results indicated that ICLS-1 and ICLS-4 enhanced soil quality more quickly during the seasonal variation.The ICLS-2 negatively affected microbial biomass (22%), resulting in reduced labile carbon (43%), carbon management index (33%), and potentially mineralizable nitrogen (20%). Labile carbon and the carbon management index were more sensitive and efficient indicators for verifying soil quality changes in the short-term. Results indicated that there is large variability in these soil indicators during the annual cycle, and further studies are needed to verify the effects of the tested systems on different soil nitrogen fractions and how they affect available nitrogen in the short-term. However, potentially mineralizable nitrogen can provide positive insights for short-term changes in the soil.

Cover crops and N fertilization strongly impact the forms of soil organic C and N and their availability, which change the responses of plants to N fertilization and soil organic C accumulation. Our study objectives were to evaluate the effects of cover crops and N doses on soil total and soluble C and N contents, N fractions, and potentially available N in a long-term no-till experiment. The experiment was conducted in a randomized block design with split plots and four replicates. The main treatments were cover crops species, jack bean, lablab bean, millet, velvet bean, and fallow cultivated prior to maize. Secondary treatments included two doses of mineral N (0 and 120 kg ha−1). Soil samples were collected at depths of 0–5, 5–10, 10–20, and 20–40 cm, which were analyzed for total and water-soluble C and N contents, N fractions (acid hydrolysis method), and potentially available N (hot KCl solution and direct steam distillation methods). Cover crop velvet bean resulted in the highest soil organic carbon levels, and cover crop millet plus fertilization resulted in the highest levels of soil total N. The amino sugar was the largest N fraction, which decreased by 8% with N fertilization. The soluble C and N content strongly correlated with total and available N content. The changes in soil N were influenced by cover crop species and fertilization and the interactions of both, so the combination of fertilization regime and cover crops must be chosen with care. Additionally, legumes are a good source of plant and soil N in systems with low input of N via fertilizer; however, the combination of N fertilizer with legumes can reduce soil N reserves, leading to its long-term depletion.

No abstract

In last years, the damage caused to the environment due to anthropic activities have become a worldwide concern. The carbon dioxide (CO2) is one of the main greenhouse gases because the increase of its concentration in the atmosphere has intensified to global warming. Therefore, to study the CO2 amounts emitted to the atmosphere has been even more important, especially in agricultural areas in Brazil. This study aimed to determine the spatial variability of soil CO2 emissions (FCO2), soil temperature (Ts) and soil moisture (Ms) in soybean and sugarcane cultivation areas in the Cerrado region in Mato Grosso do Sul. The FCO2 and Ts registration were done using a portable flow chamber and temperature sensor of the LI-8100 system. The Ms was evaluated using TDR portable system. The studies were conducted in the years of 2013, in soybean cultivation, and in 2014, in the sugarcane cultivation, during the crop growth early stages, using grids which contain 89 and 102 sampling points, respectively, spanning 1 ha area in both experiments. The spatial variability variables were characterised by geostatistics: mathematical models adjustments to the experimental variograms and spatial pattern maps construction through ordinary kriging technique. The sTe sH variables did not show significant correlations with FCO2. Despite the years of conducting the experiments, the soybean cultivation presented the higher average values of soil CO2 emission equal 2.11 µmol m-2 s-1 and higher variation in range of the spatial dependency between 8.41 and 27 m when compared to sugarcane culture, with a FCO2 average of 1.71 µmol m-2 s-1 and variation in the ranges of spatial dependency between 15.3 and 27.3 m.