Appropriate management of agricultural crop residues could result in increases on soil organic carbon (SOC) and help to mitigate gas effect. To distinguish the contributions of SOC and sugarcane (Saccharum spp.) residues to the short-term CO 2 -C loss, we studied the infl uence of several tillage systems: heavy offset disk harrow (HO), chisel plow (CP), rotary tiller (RT), and sugarcane mill tiller (SM) in 2008, and CP, RT, SM, moldboard (MP), and subsoiler (SUB) in 2009, with and without sugarcane residues relative to no-till (NT) in the sugarcane producing region of Brazil. Soil CO 2 -C emissions were measured daily for two weeks after tillage using portable soil respiration systems. Daily CO 2 -C emissions declined after tillage regardless of tillage system. In 2008, total CO 2 -C from SOC and/or residue decomposition was greater for RT and lowest for CP. In 2009, emission was greatest for MP and CP with residues, and smallest for NT. SOC and residue contributed 47 % and 41 %, respectively, to total CO 2 -C emissions. Regarding the estimated emissions from sugarcane residue and SOC decomposition within the measurement period, CO 2 -C factor was similar to sugarcane residue and soil organic carbon decomposition, depending on the tillage system applied. Our approach may defi ne new emission factors that are associated to tillage operations on bare or sugarcane-residue-covered soils to estimate the total carbon loss.Keywords: soil respiration, carbon dioxide, emission after tillage, soil organic carbon IntroductionLosses of soil organic carbon (SOC) due to soil management in agricultural areas have been identifi ed as a factor that accelerates the greenhouse effect, especially by emitting CO 2 in the atmosphere (Eugster et al., 2010). Losses of SOC can be assessed either by directly measuring changes in SOC content or by monitoring soil CO 2 emissions. The latter has the advantage to detect immediate or near-immediate effects of management practices on C loss via emissions. The impact of tillage on the loss of SOC and associated emission factors under different management systems has been studied (Smith et al., 2010;La Scala et al., 2008; La Scala et al., 2009 a,b), and some researchers have used tillage emission factors as bias for estimating soil conversion from conventional to no-till. However, Smith et al. (2010) noted that this conversion can be affected by the depth of tillage, and multiple factors should be developed to reduce estimation errors.Agricultural activities contribute with approximately 20 % to the global greenhouse gas emissions (Lokupitiya and Paustian, 2006). No-till farming combined with the maintenance of crop residues on the soil surface has been identifi ed as an important strategy for sequestering carbon (C) from the atmosphere (Lal, 2007). Tillage induces the loss of C as CO 2 by breaking up soil aggregates and exposing the protected organic matter to microbes. Tillage also incorporates and mixes residues, improving aeration, which can lead to additional C losses by maximizin...

ABSTRACT:The proper management of agricultural crop residues could produce benefits in a warmer, more drought-prone world. Field experiments were conducted in sugarcane production areas in the Southern Brazil to assess the influence of crop residues on the soil surface in short-term CO 2 emissions. The study was carried out over a period of 50 days after establishing 6 plots with and without crop residues applied to the soil surface. The effects of sugarcane residues on CO 2 emissions were immediate; the emissions from residue-covered plots with equivalent densities of 3 (D50) and 6 (D100) t ha -1 (dry mass) were less than those from non-covered plots (D0). Additionally, the covered fields had lower soil temperatures and higher soil moisture for most of the studied days, especially during the periods of drought. Total emissions were as high as 553.62 ± 47.20 g CO 2 m -2 , and as low as 384.69 ± 31.69 g CO 2 m -2 in non-covered (D0) and covered plot with an equivalent density of 3 t ha -1 (D50), respectively. Our results indicate a significant reduction in CO 2 emissions, indicating conservation of soil carbon over the short-term period following the application of sugarcane residues to the soil surface.KEYWORDS: soil respiration, sugarcane management, green harvest. RESÍDUOS DA CULTURA NA EMISSÃO DE CURTO PRAZO DE CO 2 EM ÁREAS PRODUTORAS DE CANA-DE-AÇÚCAR RESUMO:A gestão adequada dos resíduos de culturas agrícolas pode produzir benefícios em um mundo mais quente e mais propenso à seca. Experimentos de campo foram conduzidos em áreas de produção de cana-de-açúcar no Sudeste do Brasil a fim de avaliar a influência dos resíduos de cultura na superfície do solo, em emissões de CO 2 de curto prazo. O estudo foi conduzido por um período de 50 dias após a instalação das 6 parcelas com e sem resíduos de cultura aplicados sobre a superfície do solo. Os efeitos dos resíduos da cana-de-açúcar sobre as emissões de CO 2 foram imediatos; as emissões das parcelas cobertas com restos vegetais de cultura e densidades equivalentes a 3 (D50) e 6 (D100) t ha -1 (massa seca) foram inferiores quando comparadas às parcelas sem cobertura vegetal (D0). Além disso, as parcelas cobertas com restos vegetais tiveram a temperatura do solo mais baixa e a umidade do solo mais elevada para a maioria dos dias de estudo, especialmente durante o período sem chuvas. As emissões totais foram tão elevadas quanto 553,62 ± 47,20 g CO 2 m -2 , e tão baixas quanto 384,69 ± 31,69 g CO 2 m -2 nas parcelas sem cobertura vegetal e com uma densidade equivalente a 3 t ha -1 , respectivamente. Os resultados indicam redução significativa das emissões de CO 2 do solo, indicando a conservação de carbono no solo durante o período de curto prazo após a aplicação de resíduos de cana-de-açúcar na superfície do solo. PALAVRAS-CHAVE:respiração do solo, manejo da cana-de-açúcar, cana crua.

Empiricism in the use of nutrient solutions is frequent. Several times the same nutrient solution is used to grow different species based only on morphological similarities. This practice may lead to nutritional imbalances, affecting not only the production but also the quality of the product due to an accumulation of nitrate. An experiment under hydroponic conditions -the NFT system -was conducted with the aim of evaluating the effect of the concentration of nitrogen in the nutrient solution on the production and on the nutrient and nitrate contents of rocket (Eruca sativa) salad leaves. The experiment was carried out in spring 2003, in a randomized block design and in a 4 × 3 factorial design, with four replicates. Four nitrogen concentrations in the nutrient solution (60.8; 121.6; 182.5; 243.5 mg L -1 ) and three rocket salad cultivars (Cultivada, Folha Larga and Selvática) were evaluated. Cv. Cultivada produced the tallest plants and the highest leaf fresh fitomass, not differing from cv. 'Folha Larga' in the number of leaves, leaf nitrate content, root dry fitomass and root fresh fitomass. An increment in NO 3 -, N, Ca and P and a reduction in Mg, K and S occurred when the concentration of N in the nutrient solution was increased. Cultivation of cv. Cultivada at the concentration of 93 mg L -1 is the most recommended as it provides the highest yield and low nitrate content. Key words: Eruca sativa, Diplotaxis tenuifolia, hydroponic system, cultivar, mineral nutrition TEORES DE NUTRIENTES E PRODUÇÃO DE RÚCULA EM FUNÇÃO DAS CONCENTRAÇÕES DE NITROGÊNIO EM SOLUÇÃO NUTRITIVARESUMO: O empirismo no uso das soluções nutritivas é freqüente. Muitas vezes a mesma solução nutritiva é usada para diferentes espécies baseando-se apenas em semelhanças morfológicas. No entanto esta situação pode proporcionar desequilíbrio nutricional prejudicando tanto a produção quanto a qualidade do produto face o acúmulo de nitrato. Foi conduzido um trabalho em sistema hidropônico -NFT, com o objetivo de avaliar o efeito da concentração de nitrogênio na solução nutritiva na produção, nos teores de nutrientes e de nitrato em folhas de rúcula (Eruca sativa). O trabalho foi conduzido na primavera de 2003. Foram avaliadas quatro concentrações de nitrogênio na solução nutritiva (60,8; 121,6; 182,5; 243,5 mg L -1 ) e três cultivares de rúcula (Cultivada, Folha Larga e Selvática), sob delineamento de blocos ao acaso, fatorial 4 × 3, com quatro repetições. A cv. Cultivada apresentou maior estatura e fitomassa fresca de folhas, não diferindo da 'Folha Larga' quanto a número de folhas, teor de nitrato nas folhas e fitomassa seca e fresca da raiz. Houve incremento de NO 3 -, N, Ca e P e diminuição de Mg, K e S com o aumento da concentração de N na solução nutritiva. O cultivo da cv. Cultivada na concentração de 93 mg L -1 é a mais recomendada em função da maior produtividade e baixo teor de nitrato.

MÉTODOS DE LAVAGEM DE FOLHAS DE MANGUEIRA PULVERIZADAS COM ZINCO