Management impacts on soil organic matter of tropical soils.

Increased soil organic matter (SOM) improves the cation exchange capacity of tropical weathered soils, and liming is required to achieve high yields in these soils. Despite a decrease in SOM in the short term, liming may increase SOM with time by improving cation chemical bonds with soil colloids. Soil C may also be increased in high dry matter input cropping systems. We evaluated C changes in a Typic Rhodudalf as affected by four production systems with increasing residue inputs, with or without limestone or silicate. Soil use intensification by increasing the number of species in rotation as well as acidity remediation resulted in higher plant residue production. Introducing a green manure or a second crop in the system increased plant residue by 89% over fallow, but when a forage crop was used, plant residues more than doubled. Soil acidity amelioration increased plant residue deposition by 21% over the control. The introduction of a forage crop increased labile SOM and C contents in the particulate fraction, and lime or silicate application led to increases in the more stable SOM fraction. High amounts of plant residues (>70 Mg ha?1 in 5 yr) are effective in raising soil labile C, but the alleviation of soil acidity results in increased soil stable C irrespective of crop rotations in tropical weathered soils, and in this case plant residue deposition can be lower. Lime and silicate are equally effective in alleviating soil acidity and increasing soil C, probably due to the formation of cation bridges with soil colloids

Balanço de potássio no sistema plantio direto em razão da adubação potássica na sucessão milheto-soja.

Trabalho publicado também nos Resumos do CONGRESSO BRASILEIRO DE SOJA, 6., 2012, Cuiabá

Silt as K source for crops in tropical soils.

The original soil exchangeable potassium (K) concentrations are at or above critical levels in many Brazilian Cerrado (savanna) soils. Hence, many cropped areas have been fertilized with low K rates, below crop requirements, but yields have not decreased as expected. In these areas, topsoil exchangeable K analyses have shown no decrease, or even some increase. The aim of this study was to evaluate exchangeable and non-exchangeable K forms in soils under different uses and managements in the Vale do Araguaia region of Mato Grosso state, Brazil. Soil samples were taken from 91 sites at depths of 0-20 cm and 20-40 cm, in areas under grain crops, pasture and native vegetation (Cerrado or forest). Silt content ranged from 12 to 175 g kg-1 and clay from 90 to 595 g kg-1, and the predominant clays were kaolinite, hematite, goethite and gibbsite. Under pasture, the soils had high levels of exchangeable K in the 0-20 cm layer and high levels of non-exchangeable K from 20 to 40 cm. This can be a result of the absorption of non-exchangeable K by grasses, the main cultivated species, by recycling K to the exchangeable fraction in the topsoil. There was a positive relationship between silt and non-exchangeable K contents. Ratios of exchangeable to non-exchangeable K were over 3 in soils with silt above 70 g kg-1, in which non-exchangeable K was over 100 mg dm-3. Cover crops growing in soils rich in silt take up non-exchangeable K and exchangeable K from deeper layers, which is recycled to the soil as exchangeable K upon plant residue mineralization, which may have been responsible for the maintenance or increase in exchangeable K levels in the 0-20 cm layer in areas where low K rates have been used for grain production

Densidade de plantas na cultura da soja

Two field experiments were led to study the effects of plant population, fertilizer level and planting time upon soybean (Glycine max (L.) Merrill, cv. UFV-1) yields and yield components. In the first experiment the soybean was grown on a Dark-Red Latosol (clay), fertilized with 100, 200, 300 and 400 kg/ha of the 0-33-12 formula, utilizing the populations of 10, 20, 30 and 40 plants per meter of row. In the second experiment, carried out on a "Latosol Roxo" (clay), soybean was planted in November and December, with populations of 8, 16, 24, 32 and 40 plants per meter of row. The results showed that the increase in plant population caused a lower production per plant, as function of the lower pod number per plant. The fertilization levels did not influence the grain production significantly or the yield components.Foram conduzidos dois ensaios de campo como objetivo de estudar os efeitos de densidades de semeadura, níveis de adubação e épocas de semeadura na cultura da soja (Glycine max (L.) Merrill cv. UFV-1). No primeiro ensaio, instalado em solo classificado como Latossolo Vermelho-Escuro orto, foram estudados os efeitos das densidades iniciais de 10, 20, 30 e 40 plantas por metro e das adubações com 100, 200, 300 e 400 kg/ha da fórmula 0-33-12. No segundo ensaio, conduzido em Latossolo Roxo Distrófico, foram estudados os efeitos de duas épocas de semeadura (novembro e dezembro), e cinco densidades de plantas na linha (8, 16, 24, 32 e 40 plantas/m). Os resultados demonstraram que ocorreu menor produção por planta, em função de menor produção de vagens, à medida que a densidade foi aumentada. Os níveis de adubação empregados não afetaram significativamente a produção, nem seus componentes

Effect of the soil Ca/Mg, Ca/K and Mg/K ratios on sweet sorghum production

Foi conduzido um ensaio em casa de vegetação, em vasos com capacidade para 25 litros de terra, com o objetivo de estudar a resposta do sorgo sacarino (Sorghum bicolor) ao magnésio na presença e ausência de calagem e de adubação potássica. Amostras de terra foram tomadas na época da emergência das plantas, onde foi determinado o efeito de quatro doses de Mg na forma de sulfato, duas de potássio na forma de cloreto e duas de cálcio na forma de calcário calcítico sobre as relações Ca/Mg, Ca/K e Mg/K do solo. Na época do emborrachamento foram colhidas folhas para a diagnose foliar, e ao final do ciclo foram analisadas as produções de colmos e de grãos. Os resultados obtidos demonstraram que com teores de Mg no solo variando de 0,15 a 0,52 meq/100 cm3 não houve resposta do sorgo sacarino em termos de produção de colmos, mas quando a relação Mg/K no solo foi menor que 0,6 ou a relação Ca/K no solo foi menor que 7,4, houve prejuízo na produtividade, em função das menores absorções de Mg e Ca, respectivamente. Não houve efeito da relação Ca/Mg sobre a produção de sorgo sacarino. Com relação à produção de grãos, houve resposta ao Mg apenas em um dos solos na ausência de potássio.A experiment was carried out in greenhouse conditions, in pots containing 25l of soil, to study the sorghum (Sorghum bicolor) response to magnesium with and without liming and potassium fertilization. Soil samples were taken at plant emergence and analysis of K, Ca and Mg were performed to determine the effect of four Mg doses as sulphate, two potassium doses as chloride and two calcium doses as calcite limestone upon the soil Ca/Mg, Ca/K and Mg/K ratios. At boot stage sorghum leaves were sampled for foliar diagnosis, and at harvest stalk and grain yields were evaluated. The results didn't show any difference in sorghum stalk yields when the magnesium level in the soil ranged from 0,15 to 0,52 meq/cm3, but when the Mg/K and Ca/K ratios in the soil were lower than 0.6 and 7.4 respectively, there was a decrease in sweet sorghum stalk yields, as a function of the lower Mg and Ca uptake. There was not any effect of the Ca/Mg ratio on sorghum yields. There was an increase in grain yields due to Mg application only in the absence of potassium in one of the soils