Hemmannuella Costa Santos

Frações de fósforo inorgânico do solo e suas correlações com o fósforo quantificado por extratores e pelo milho

The fractionation of inorganic phosphorus (Pi) is important to evaluate in which forms phosphorus is sorbed to soil, because the efficiency of an extractant of available P in soils depends on its capacity to extract each fraction of soil Pi. This study evaluated the contents of Pi fractions in representative soils of the State of Paraiba and their relationship with the chemical and physical characteristics of these soils, as well as the correlation between the Pi fractions and P extracted from soils by maize plants and Mehlich-1, Mehlich-3, Bray-1, and by ion exchange resin extractors. The experiment was conducted in a greenhouse in a randomized block design and tested 12 soils, with and without P application, in three replications. After the application of P doses (75, 88 and 103 mg dm-3) in 3.0 dm-3, soil samples were incubated in polyethylene pots for three weeks with distilled water (50% of total porosity of each soil). Plant-available P was determined by four chemical extractants and the fractionation of Pi performed in sub samples of 0.2 dm-3 per pot. The fractions P-Al and P-Fe were predominant in highly weathered soils and in less weathered soils with lower pH and Ca2+, while P-Ca was preferentially found in alkaline soils with very high Ca2+ contents. Phosphorus extracted by maize plants as well as Mehlich-1, ion exchange resin and Bray-1 were found in P-H2O and P-Al fractions, while P extracted by Mehlich-3 was more correlated with P-Ca fraction. P extracted by Mehlich-1 and Bray-1 was more correlated with P absorbed by plants, while P extracted by Bray-1 was low in soils with high Ca2+ contents and high pH. In general, Mehlich-1 quantified P similar to ion exchange resin, even in Ca2+ -rich soils with high pH values.

Kinetics of phosphorus sorption in soils in the state of Paraíba

The soil P sorption capacity has been studied for many years, but little attention has been paid to the rate of this process, which is relevant in the planning of phosphate fertilization. The purpose of this experiment was to assess kinetics of P sorption in 12 representative soil profiles of the State of Paraiba (Brazil), select the best data fitting among four equations and relate these coefficients to the soil properties. Samples of 12 soils with wide diversity of physical, chemical and mineralogical properties were agitated in a horizontal shaker, with 10 mmo L-1 CaCl2 solution containing 6 and 60 mg L-1 P, for periods of 5, 15, 30, 45, 60, 90, 120, 420, 720, 1,020, and 1,440 min. After each shaking period, the P concentration in the equilibrium solution was measured and three equations were fitted based on the Freundlich equation and one based on the Elovich equation, to determine which soil had the highest sorption rate (kinetics) and which soil properties correlated to this rate. The kinetics of P sorption in soils with high maximum P adsorption capacity (MPAC) was fast for 30 min at the lower initial P concentration (6 mg L-1). No difference was observed between soils at the higher initial P concentration (60 mg L-1). The P adsorption kinetics were positively correlated with clay content, MPAC and the amount of Al extracted with dithionite-citrate-bicarbonate. The data fitted well to Freundlich-based equations equation, whose coefficients can be used to predict P adsorption rates in soils.

Amostragem para avaliação da fertilidade do solo em função da variabilidade de suas características químicas

The aim of this study was to evaluate the variability of chemical attributes of soil, to define the number of single samples required to form a composite sample and to evaluate if the mean fertility values obtained from the composite sample is the same as obtained from the arithmetic mean of single samples. Three series of sampling, each one with 36 samples collected in an Oxisol, were carried out. Samples of the first series were taken 15 m apart from each other, the second one 2.5 m, and the third one 0.42 m. Composite samples were formulated with samples of first series by a homogenous mixture of 4, 8, 14, 20, 28 e 36 single samples, with three replications. The variability of soil chemical attributes did not vary when the area size decreased from 8,100 m2 to 225 m2. Doses of lime and fertilizer may have the same recommendation, independently if soil fertility was evaluated by chemical analysis of a composite sample or obtained from the arithmetic mean of single sampling. At least eight single samples were necessary to compose a representative sample of the area.

Cu e Zn na cultura do sorgo cultivado em três classes de solos: I. Crescimento vegetativo e produção

The micronutrients copper and zinc are important for good vegetative growth and for grain formation in cereals. An experiment was carried out aiming to evaluate the effect of copper and zinc application upon growth attributes of sorghum and upon its grain yield. A randomized block experimental design was used, with a combination of five doses of copper (0, 0.26, 0.90, 1.54 and 1.80 mg kg-1) and five doses of zinc (0, 0.32, 1.1, 1.88 and 2.2 mg kg-1) combined by Box Central Composite design, resulting in nine treatments which were applied in three soil classes (Latosol, Alfisol and Entisol), with three replications. Ninety six days after sowing, growth attributes and sorghum yield were determined. The copper application increased leaf area, stem diameter, panicle length and diameter, dry matter yield and grain yield, however the same results were not observed for zinc application. The foliar concentrations of copper and zinc presented negative interactions between the applied doses. Alfisol was the soil most influenced by nutrient application.

Formas de potássio em solos representativos do Estado da Paraíba

Os solos do Estado da Paraiba apresentam grande diversidade de caracteristicas quimicas, fisicas e mineralogicas, acarretando em variacoes nos teores e formas de K disponiveis no solo. Objetivou-se com este trabalho avaliar os teores de K nao-trocavel, K trocavel e K soluvel em doze solos do Estado da Paraiba, na ausencia e na presenca de fertilizacao potassica, e correlaciona-los com as caracteristicas quimicas, fisicas e mineralogicas desses solos. O estudo constou de 60 tratamentos, sendo 12 solos e cinco doses de K (0; 50; 100; 200 e 300 mg dm-3) na forma de cloreto de potassio, com tres repeticoes. Apos receberem os tratamentos, os solos foram incubados por um periodo de 21 dias, e em seguida, uma sub-amostra de 0,2 dm3 de cada solo foi retirada para determinacao dos teores de K nao-trocavel, K trocavel e K soluvel. Os solos formados sob clima semiarido foram os solos que apresentaram as maiores reservas de K nao-trocavel. Solos com maior proporcao de mica e minerais do tipo 2:1 na fracao argila apresentaram os maiores teores de K nao-trocavel e K trocavel. Independente do grupo de solos, os teores de silte apresentaram correlacao elevada com os teores de K nao-trocavel e de K trocavel. Nos solos mais desenvolvidos, nao foi evidenciada fixacao de K proveniente do fertilizante. Porem, nos solos menos desenvolvidos, a fixacao de K ficou evidenciada pela pequena quantidade de K recuperada pelo extrator acetato de amonio nos solos mais argilosos e, principalmente, naqueles com predominância de minerais do tipo 2:1 e mica.

Cu e Zn na cultura do sorgo cultivado em três classes de solos: II. Composição mineral

The micronutrients copper and zinc have important functions in vegeatable metabolism, but studies about micronutrient needs for sorghum are scarce. Aiming to evaluate the effect of copper and zinc application in nutritional attributes of sorghum an experiment was carried out in a randomized block experimental design with a combination of five doses of copper (0, 0.26, 0.90, 1.54 and 1.80 mg kg-1) and five doses of zinc (0, 0.32, 1.1, 1.88 and 2.2 mg kg-1) combined by Box Central Composite design, resulting in nine treatments, which were applied in three soil classes (Latosol, Alfisol and Entisol), with three replications. Ninety six days after sowing, nutrients contents and accumulation and protein contents were determined. The copper application increased nitrogen, phosphorus, potassium and copper contents and crude protein content in grains, however, the same results were not observed for zinc application. Alfisol was the soil most responsive to the application of nutrients.