No abstract

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The combination of high aluminium (Al) saturation and severe phosphorus (P) deficiency in sub-surface soil in no-tillage (NT) systems is an obstacle hampering crop yields in Brazil. The introduction of NT without proper soil chemical correction affects crop yields in several parts of the country. The aim of this study was to evaluate the changes in soil chemical properties and response of crops to different application methods of lime and phosphate fertiliser in an Ultisol under NT. The field experiment consisted of combining surface and incorporated liming and P application (without P, surface P and P in the sowing line), plus a treatment with incorporated lime and P. The correction of soil acidity and availability of P at depth was effective with the incorporation of lime and phosphate fertiliser. Five months after lime incorporation, it was possible to increase soybean productivity by more than 40% (from 3.9 to 5.6Mgha−1). The surface application of P and limestone restricts the correction of soil fertility only in the uppermost soil layer evaluated (up to 5cm). The relationship between soybean yield and soil chemical properties in different layers clearly demonstrates that neither the 0–10cm soil layer nor the 0–20cm soil layer is suitable for diagnosing soil fertility and the crop productive potential in NT system with chemical restrictions in subsurface. Further studies are need to establish critical levels of available P and Al saturation for subsurface soil layers in different soil types under no-tillage.

Brazil is one of the largest consumers of pesticides in the world. The high rainfall rate and inadequate soil use and management promote the transfer of these compounds to the aquatic system. The aim of this study was to identify and quantify pesticides present in epilithic biofilms in order to evaluate the effectiveness of this matrix as a bioindicator able to discriminate areas and periods with different inputs of pesticides. Among the 25 pesticides analyzed in the biofilms, 20 compounds were detected. The epilithic biofilms picked up pesticides independent of their polarities, even in the period of lower use. The frequency and median concentration of five herbicides (2,4-D, atrazine, desethyl-atrazine, simazine, nicosulfuron), three fungicides (carbendazim, epoxiconazole, tebuconazole), and one insecticide (imidacloprid) were highest in biofilms sampled in summer crops during the growing period. Biofilms collected in the upper region of the catchment, where genetically modified soybean and corn cultivated in a no-tillage system prevail, the highest frequency and median concentration of three herbicides (2,4-D, thifensulfuron, isoproturon), four fungicides (carbendazim, epoxiconazole, tebuconazole, metconazole), and one insecticide (imidacloprid) were observed. Despite the excessive amounts of pesticides used in the catchment, the median values of all pesticides in the epilithic biofilm were considered low. The lower diversity and concentration of pesticides observed in the autumn/winter season is representative of lower use of pesticides, barriers to pesticide transfer from soil to water, and the biofilm's resilience capacity to decompose pesticides.