G. S. A. Castro

Produção, decomposição e ciclagem de nutrientes em resíduos de crotalária e milheto, cultivados solteiros e consorciados

The objective of this work was to evaluate the biomass production and the rates of decomposition and macronutrient and silicon release on crop residues of sunnhemp (Crotalaria juncea) and pearl millet (Pennisetum glaucum), in monocropped and intercropped systems. A randomized complete block design was used, with four replicates in a factorial arrangement consisting of three cover crops - pearl millet, sunnhemp, and these species intercropped - and six sampling times - 0, 18, 32, 46, 74, and 91 days after management (DAM). Pearl millet produces a greater amount of dry matter and accumulates more N, P, K, Mg, S, C, and Si, whereas sunnhemp accumulates more Ca. Pearl millet phytomass has the highest rates of decomposition and nutrient release. These rates are higher between 0 and 18 DAM. Over the time, the C/N, C/P and C/S ratios increase, and the C/Si ratio, as well as the decomposition rate, decreases. Potassium is the most rapidly released nutrient, and silicon has the lowest release rate.

Aplicação foliar de ácido silícico estabilizado na soja, feijão e amendoim

A aplicacao de silicio (Si) e benefica as plantas. Porem, existem duvidas sobre a eficiencia do seu fornecimento via foliar. Objetivou-se com este trabalho avaliar o efeito da aplicacao de Si via foliar, na forma de acido silicico estabilizado (fonte recem-desenvolvida), na nutricao e na produtividade das culturas da soja, feijao e amendoim. O delineamento experimental para cada cultura foi em blocos casualizados, com quatorze repeticoes. Os tratamentos foram: controle (sem aplicacao de Si) e aplicacao de Si via foliar, na dose de 2 L ha-1 do produto Silamol® (0,8% de Si soluvel como um concentrado estabilizado de acido silicico). A dose de Si foi parcelada em quatro aplicacoes. A aplicacao via foliar elevou os teores de Si, proporcionando aumento do numero de vagens e da produtividade de graos das tres culturas. O incremento foi da ordem de 14; 15 e 9,6%, respectivamente, para as culturas da soja, feijao e amendoim.

Effects of surface application of dolomitic limestone and calcium-magnesium silicate on soybean and maize in rotation with green manure in a tropical region

Although lime is currently the material most frequently used to ameliorate soil acidity in Brazil, silicate could efficiently replace this source because of its greater solubility and its greater silicon content, which are beneficial for plant development. This study aimed to evaluate the effects of superficial lime and silicate application on soil chemical attributes as well as on soybean and maize nutrition and grain yields when these crops are grown in rotation with green manure. The experimental design was a complete randomized block with sixteen replicates. Plots were treated with one of two materials for acidity correction (dolomitic lime and calcium/magnesium silicate) or with no soil correction, as a control. Silicate corrected soil acidity and increased exchangeable base levels in soil at greater depths faster than does liming. The application of both acidity-correcting materials increased N, Ca and Mg leaf concentrations, and all yield components and grain yield in soybean; but in maize, just silicate also increased N and Si when compared with lime, whereas both acidity-correcting increased just two yield components: grains per ear and mass of 100 grains, resulting in highest grain yield. The application of both acidity-correcting materials increased dry matter production of green manures, but for pigeon pea the silicate provided the best result in this dry-winter region.

Surface application of limestone and calcium-magnesium silicate in a tropical no-tillage system

Although lime is currently the most commonly applied material for soil acidity correction in Brazil, calcium-magnesium silicate application may efficiently replace this source due to its higher solubility and silicon supply, which is beneficial for plant development. This study aimed to evaluate the efficiency of surface liming and silicate application on soil chemical attributes as well as soybean and maize nutrition, yield components, and grain yield. The experiment was conducted in a Rhodic Hapludox in Botucatu-SP, Brazil. The randomized complete block design contained 16 replications. Treatments consisted of two materials for soil acidity correction (dolomitic lime, calcium/magnesium silicate), applied on October 2006 to raise base saturation up to 70%, and a control, with no acidity correction. Soybean and maize were sown in 2006/2007 and 2007/2008, respectively. After 18 months Ca-Mg silicate corrected soil acidity up to 0.60 m, and increased exchangeable base levels up to 0.40 m. Silicate increased silicon concentrations in plant tissues in both crops as well as phosphorus in soybean. The application of both sources increased calcium and magnesium concentrations as well as yield components and yield grains of soybean and maize. Soil acidity correction improved the efficiency of fertilizers applied for grain production.

Surface lime and silicate application and crop production system effects on physical characteristics of a Brazilian Oxisol.

This work aimed to evaluate the effects of crop rotations and soil acidity amelioration on soil physical properties of an Oxisol (Rhodic Ferralsol or Red Ferrosol in the Australian Soil Classification) from October 2006 to September 2011 in Botucatu, SP, Brazil. Treatments consisted of four soybean (Glycine max)?maize (Zea mays)?rice (Oryza sativa) rotations that differed in their off-season crop, either a signal grass (Urochloa ruziziensis) forage crop, a second crop, a cover crop, or fallow. Two acid-neutralising materials, dolomitic lime (effective calcium carbonate equivalent (ECCE) = 90%) and calcium-magnesium silicate (ECCE = 80%), were surface applied to raise the soil?s base saturation to 70%. Selected soil physical characteristics were evaluated at three depths (0?0.1, 0.1?0.2, and 0.2?0.4 m). In the top 0.1 m, soil bulk density was lowest (P < 0.05) and macroporosity and aggregate stability index were greatest (P < 0.05) in the forage crop compared with all other production systems. Also, bulk density was lower (P < 0.05) and macroporosity was greater (P < 0.05) in the acid-neutralising-amended than the unamended control soil. In the 0.1?0.2-m interval, mean weight diameter and mean geometric diameter were greater (P < 0.05) in the forage crop compared with all other production systems. All soil properties evaluated in this study in the 0.2?0.4-m interval were unaffected by production system or soil amendment after five complete cropping cycles. Results of this study demonstrated that certain soil physical properties can be improved in a no-tillage soybean?maize?rice rotation using a forage crop in the off-season and with the addition of acid-neutralising soil amendments. Any soil and crop management practices that improve soil physical properties will likely contribute to sustaining long-term soil and crop productivity in areas with highly weathered, organic matter-depleted, acidic Oxisols.