Carbon and nitrogen stocks in soil under castor bean in the semi-arid Caatinga of Brazil

Grande parte da produção brasileira de mamona encontra-se no Nordeste, como opção de cultura para a região semiárida no bioma Caatinga. O objetivo deste estudo foi avaliar as alterações nos estoques de C e N devido à mudança de uso do solo de vegetação natural para o cultivo de mamona no bioma Caatinga. Este trabalho foi realizado na Fazenda Floresta, no município de Irecê, no centro-norte baiano. O clima da região é do tipo BSwh (Köppen) - clima semiárido de altitude. O solo foi classificado em Latossolo Vermelho de textura argilosa. As situações avaliadas foram: três áreas cultivadas com mamona com diferentes tempos de implantação: (i) com 10 anos, (ii) com 20 anos e (iii) com 50 anos; e uma área de referência (vegetação nativa de Caatinga) contígua às situações avaliadas. Os estoques de C e N foram determinados em amostras de solo coletadas em cinco minitrincheiras, nas camadas de 0-5, 5-10, 10-20 e 20-30 cm. Os resultados mostraram que o constante aporte de resíduos vegetais na Caatinga promoveu a manutenção dos estoques de C (90 Mg ha-1) e N (10 Mg ha-1) para a camada de 0-30 cm. A mudança de uso da terra para o cultivo da mamona ocasiona redução em aproximadamente 50 % nos estoques de C e N do solo em relação à vegetação nativa nos primeiros 10 anos de implantação da cultura. A meia-vida da matéria orgânica do solo (MOS) calculada para essa situação na região do semiárido foi de 4,7 anos. O fator de emissão de C do solo, devido à mudança de uso da terra após 20 anos, conforme proposto pelo método do IPCC (2006), foi de 2,47 Mg C ano-1. Por meio do conjunto dos resultados, observa-se a fragilidade do solo do bioma Caatinga no que se refere à perda de MOS devido à mudança de uso da terra

EMISSÕES DE GASES DE EFEITO ESTUFA NA PRODUÇÃO DE MAMONA E DE SEUS SUBPRODUTOS

The largest production of castor bean ( Ricinus communis L .) focuses on Bahia savanna, where the change of land use to their cultivation has been considered a strategy of degraded areas recovery. However, changes in the native soil can arise environmental impacts as greenhouse gases (GHG) emissions. We have assumed that higher GHG emissions come from a change of land use for castor bean cultivation and their sub - products contribute to GHG emissions. The objective of this study was to make the inventory of the emission of GHG resulting from the castor bean cultivation and their sub - products. It was done a study in the municipality of Irecê - BA and were evaluated: changes in carbon (C) soil stocks in cultivated areas with castor bean and Lo- cal native forest; a number of senescent leaves and the biomass produced epigeal; GHG emissions from the sub - products of castor bean. The results showed that the sum of senescent leaves and epigeal biomass obtained by castor bean pruning is more than 1.6 Mg ha - 1 ano - 1 and the castor bean residues used in this soil presented N 2 O emissions close to 600 μg m - 2 . The emissions from the use of castor oil biodiesel represented less than 10% of the emissions. The change in land use handled high emissions of greenhouse gases, accounting for 87% of the total in CO 2 eq. Compared to emissions estimated for sugarcane ethanol, castor biodiesel showed emissions 32% lower

New rhizobial strains for velvet bean (Stizolobium aterrimum) evaluated under greenhouse and field conditions

ABSTRACT The selection of efficient rhizobia for the inoculation of velvet bean may increase the use of this plant as green manure, maximizing the addition of nitrogen (N) to the crop. This study aimed to select rhizobia that nodulate velvet bean more efficiently than do strains currently recommended and for the potential of rhizobia to compose an inoculant. A greenhouse experiment evaluated 39 strains using non-sterile soil and was followed by a field experiment with the five most effective strains under field conditions on a dystrocohesive Yellow Argisol. Both experiments included non-inoculated and inoculated treatments with currently recommended strains and N-fertilized controls. Nodules, root and shoot dry mass, shoot N concentration and accumulation and relative efficiency were evaluated. The N dose corresponding to the shoot dry mass increase of the inoculated plants was also estimated. Under field conditions, the plants inoculated with the strains T2.19A and T1.17M had a shoot N concentration similar to that from the application of 80 kg ha-1 N, and the N concentration was significantly higher that of the other treatments; additionally, the N accumulation was significantly higher than that of the control (112 and 104% for the two strains, respectively), the recommended strain mixture inoculation (99 and 91%, respectively) and the mineral N application (58 and 52%, respectively). Inoculation with T2.19A and T1.17M presented promising results, showing the potential of these strains for recommendation and inoculation of velvet bean

Evaluation methods used for phosphate-solubilizing bacteria

Phosphorus solubilizers naturally acidify rhizospheric soil and increase phosphorus availability; therefore, their evaluation may help to reduce phosphorus fertilizer use. This work aimed to evaluate the different selection methods and select inorganic phosphorus-solubilizing bacteria as potential plant-growth promoters. Bacterial isolates obtained from sugarcane roots and soil were tested using solid growth media containing bicalcium phosphate and Irecê Apatite ground rock phosphate as phosphorus sources. Seven isolates with high (3), moderate (3) and low solubilization indices (1) and the Pseudomonas fluorescens R-243 strain were tested in two liquid growth media, followed by the pH and soluble P in the solution. The same isolates, in the absence of inoculation, were tested in Leonard jars with two high- and low-solubility sources using cowpea as a test species. Forty-four days after planting aboveground dry mass, the phosphorus content and total aboveground phosphorus and substratum phosphorus contents were evaluated. The growth media affected phosphorus solubilization by the bacteria. Evaluation of liquid media was the most reliable method for analyzing bicalcic phosphorus solubilization by the bacteria not linked to pH reduction. Isolates UAGC 17, 19 and 65 should be better studied because they were the best solubilizers in culture media; however, they did not demonstrate the same efficiency when inoculated on cowpea.Keywords: Solubilization, phosphate, P-solubilizing-microorganism

Silvopastoral systems drive the nitrogen-cycling bacterial community in soil

ABSTRACT Intercropping tree legumes with forage grasses in a silvopastoral system can avoid pasture degradation benefiting the soil. In such a system, nitrogen (N) is supplied by symbiosis between legumes and bacteria. However, the pasture quality determines the action of free-living nitrogen-fixing bacteria, which possess nifH genes, which encode nitrogenase enzyme. Ammonium-oxidizing bacteria (AOB), involved in the nitrification step, can be evaluated by specific regions of the 16S rRNA corresponding to AOB. Thus, we investigated the influence of the introduction of tree legumes into a silvopastoral system on the community structure and abundance of total bacteria, diazotrophic bacteria and ammonium-oxidizing bacteria by DGGE (denaturing gradient gel electrophoresis) and real-time qPCR (quantitative PCR). The experiment involved nine plots of one hectare each, planted with sabia (Mimosa caesalpinifolia), a Gliricidia species (Gliricidia sepium), and a Brachiaria species (Brachiaria decumbens) in a randomized block design, forming three treatments: I-Brachiaria intercropped with sabia; II-Brachiaria intercropped with Gliricidia and III-Brachiaria only, with three replicates. The structures of the total bacterial and ammonium-oxidizing bacterial communities were influenced by tree legume introduction, possibly through modification of the soil chemical attributes. The copy numbers of total bacteria, ammonium-oxidizing bacteria and diazotrophic bacteria were higher in soils planted with legumes, which provided better conditions for microbial growth compared to planting with the Brachiaria species alone. Silvopastoral management with tree legumes improves the biological quality of soil, favouring the bacterial community linked to N-cycling

Coffee waste as an eco-friendly and low-cost alternative for biochar production impacts on sandy soil chemical attributes and microbial gene abundance

International audienceBiochar is a material produced by the pyrolysis of agro-industrial waste, which has become one of the most promising management tools to improve soil quality. The aim was to determine the effects of incorporating biochar from different coffee wastes in sandy soil, cropped with maize, on soil chemical and microbial attributes. The experiment followed a factorial design 2 × 3 + 1 with two types of biochar, including coffee ground (CG) or coffee husk (CH) in 3 doses (4, 8, and 16 t·ha-1) and a control fertilized solely with bovine manure (3 t·ha-1). The variables analyzed were soil organic carbon, chemical attributes, microbial biomass (C, N and P), soil basal respiration and microbial gene abundance (16S rRNA, 18S rRNA and nifH gene). Most chemical attributes were strongly increased by CH application, while CG at 8 t·ha-1 increased the soil C:N ratio (3.5 times), P (2.1 times) and K+ (7.9 times) and at 4 t·ha-1 increased the C content, microbial biomass C and N (3, 2.1 and 1.6 times, respectively). The application of CG biochar at 16 t·ha-1 showed trend to increase the abundance of bacteria, fungi and diazotrophic genes (11, 10 and 2%, respectively). Contribution of both coffee biochar types, but mainly CH, was more effective than the soil that received organic manure alone. Biochar from coffee wastes is a promising tool to improve sandy soil quality