Quantifying the sensitivity of soil organic matter decomposition (SOM) to global warming is critical for predict future impacts of climate change on soil organic carbon stocks (SOC) and soil respiration, especially in semi‐arid regions such as north‐eastern Brazil, where SOC stocks are naturally small. In this study, the responses of the labile and recalcitrant carbon components and soil respiration dynamics were evaluated in three different soil types and land use systems (native vegetation, cropland and pasture) of the Brazilian semi‐arid region, when submitted to temperature increase. After 169 days of incubation, the results showed that an increase of 5°C generated an average increase in CO2 emission of 12.0%, but which could reach 28.1%. Overall, the labile carbon (LC) in areas of native vegetation showed greater sensitivity to temperature than in cropland areas. It was also observed that recalcitrant carbon (RC) was more sensitive to warming than LC. Our results indicate that Brazil's semi‐arid region presents a substantial vulnerability to global warming, and that the sensitivity of RC and of LC in areas of native vegetation to warming can enhance SOC losses, contributing to positive feedback on climate change, and compromising the productive systems of the region. However, further studies evaluating other types of soil and texture and management systems should be carried out to consolidate the results obtained and to improve the understanding about SOM decomposition in the Brazilian semi‐arid region.

Preparing regional development strategies for the Amazon Basin is a vexing task for policymakers, in part because3 For a broad assessment of forestry and land use policy in Brazil, see Lele et al, 2000. 4 We leave aside the issue of the potential endogeneity of soil quality, i.e., the possibility that farmers with a particular set of characteristics (say, high levels of capitalization) seek out better soils, as this lies beyond the scope of the LP model at present.

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The sugarcane (Saccharum spp. L.) mechanical harvesting system leaves a large amount of straw mulch on the soil surface. The straw mulch may affect soil conditions, root regrowth, and sugarcane yield. Thus, this study assessed the response of sugarcane root system growth and stalk yield to different rates of straw removal. An experiment was conducted in a Rhodic Kandiudox with sand clay loam texture to test the impact of four rates of straw removal: no removal (18.9 Mg ha−1 of dry mass); moderate removal (8.7 Mg ha−1); high removal (4.2 Mg ha−1) and total removal on sugarcane root system and stalk yield. Higher concentrations of roots (60%) were found in the first 40 cm of soil. Moderate straw removal resulted in higher root mass (3.6 Mg ha−1) and stalk production (23 Mg ha−1 of dry mass). However, no straw removal reduced root mass by <40% (2099 kg ha−1) and reduced stalk yield by >20% (105 Mg ha−1). Through regression analysis, it was estimated that retaining between 8.5 and 13 Mg ha−1 of straw resulted in the highest root mass and stalk yield. Managing straw removal to retain a moderate amount enables producers to sustain suitable soil conditions for sugarcane root growth and stalk production while providing straw for industrial use.

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This study quantifies phenolic and flavonoid compounds and evaluates the antioxidant activity by the DPPH (2,2-diphenyl-1-picrylhydrazyl) method, also identifying some secondary metabolites of R. sativus under organic fertilization and water stress. For this, a greenhouse experiment was carried out with the preparation of plant extracts (leaves and roots), quantification of phenolic and flavonoid compounds, analysis of antioxidant activity, and phytochemical screening. Different classes of secondary metabolites (catechins, steroids, saponins, among others) were identified. The DPPH method showed that the leaf extract has higher DPPH radical scavenging activity. The leaf extract had a high content of phenolic compounds, especially in treatments without water stress, either with organic fertilization (1925.59 mg GAE/g extract) or with mineral fertilization (2058.47 mg GAE/g extract). For root extracts, R. sativus developed under water stress and organic fertilization showed higher phenolic content (1383.24 mg GAE/g extract). Regarding flavonoid content, the root extract that showed the highest concentration corresponded to the treatment under water stress and without fertilization (82.1 mg QE/g extract). Therefore, radish was shown to be rich in bioactive compounds and with antioxidant potential in both its leaves and roots.

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RESUMO -Com o objetivo de avaliar o efeito de fosfatos naturais no cultivo irrigado de melão orgânico, foram conduzidos dois ensaios em Petrolina-PE, sendo um em Argissolo Amarelo (PA) e outro num Argissolo Acinzentado (PAC). Foram avaliados os seguintes tratamentos: 1-testemunha (sem P); 2-50 kg ha -1 de P 2 O 5 na forma de superfosfato triplo (ST); 3-100 kg ha -1 de P 2 O 5 na forma de ST; 4-150 kg ha -1 de P 2 O 5 na forma de ST; 5-100 kg ha -1 de P 2 O 5 na forma de termofosfato; 6-100 kg ha -1 de P 2 O 5 na forma de fosfato natural de Gafsa, e 7-100 kg ha -1 de P 2 O 5 na forma de fosfato natural Fosbahia. O melão apresentou resposta semelhante às doses de P nos dois solos, cujas produtividades máximas de 26,00 t ha -1 e 25,46 t ha -1 foram obtidas com 107,6 kg ha -1 e 118,6 kg ha -1 de P 2 O 5 no PA e PAC, respectivamente. A eficiência do termofosfato, fosfato de Gafsa e Fosbahia em relação ao ST assumiu a sequência de 86,2%, 77,1% e 71,9% no PA e 101,5%, 72,3% e 67,3% no PAC, demonstrando que o termofosfato é a fonte de fósforo mais indicada para ser usada no cultivo orgânico do melão. São necessários 843,12 kg de termofosfato para produzir 25.000 kg ha -1 de melão, o que representa 3,4% do custo de produção. Termos para indexação: Cucumis melo, dose de fósforo, eficiência de fosfato, fertilização, irrigação, análise econômica. NATURAL PHOSPHATE AS PHOSPHORUS SOURCE FOR ORGANIC MELON CROPPINGABSTRACT -Aiming to evaluate the efficiency of natural phosphates in melon organic cropping under irrigation, two experiments were carried out in Petrolina-PE, one in a Yellow Argisol (PA) and other in a Grey Argisol (PAC). The evaluated treatments were: 1 -without P, 2 -50 kg ha -1 of P 2 O 5 as triple super phosphate (TS), 3 -100 kg ha -1 of P 2 O 5 as TS, 4 -150 kg ha -1 of P 2 O 5 as TS, 5 -100 kg ha -1 of P 2 O 5 as thermo phosphate, 6 -100 kg ha -1 of P 2 O 5 as natural phosphate of Gafsa and 7 -100 kg ha -1 of P 2 O 5 as natural phosphate Fosbahia. The melon crop showed similar responses to the P application in both soils, whose maximum productivities of 26.00 t ha -1 and 25.46 t ha -1 were obtained with 107.6 kg ha -1 and 118.6 kg ha -1 of P 2 O 5 in PA and PAC, respectively. The efficiency of thermo phosphate, phosphate of Gafsa and Fosbahia in relation to TS assumed the sequence of 86.2%, 77.1% and 71.9% in PA and 101.5%, 72.3% and 67.3% in PAC. These results suggest that thermo phosphate is the most appropriated phosphate source to be used in the melon organic cropping. It is necessary 843.12 kg of thermo phosphate to produce 25 t ha -1 of melon fruit that represent 3.4% of the production cost.