Volume 29, Number 5, 2005

Water and nutrient availability in the soil at suitable times and in adequate amounts, as related to edaphic and climatic conditions, are undeniably relevant for crop yields. The objective of this work was to evaluate the actual evapotranspiration of an orange plantation, analyze its variability and verify the influence of the soil water loss on crop productivity. The experiment was carried out in Piracicaba County (SP), Brazil, on an Oxisol. The actual evapotranspiration was evaluated by a soil water balance […]

Several laboratory tests were carried out with the objective of evaluating the performance of a numerical model to simulate the unidimensional soil water evaporation process. This model was created based on Richard’s equation linearized in space and by an iterative Newton-Raphson method to solve this unlinearized equation in time. The model considers the vapor flow within the soil profile and its evaporation rate on the surface. Results showed that the model simulated the soil water evaporation process satisfactorily for both […]

Soil micromorphological studies enable a detailed observation of the modifications in soil pore structure and space imposed by cultivation and agricultural machinery traffic. This study tested the hypothesis that compaction caused by machinery affects the form and class distribution of pores in a distinct way and that such alterations can be used as soil quality indicators. The objectives of this study were to evaluate and quantify, through micromorphological studies, the modifications in porosity caused by biological activity (biopores) in a […]

Liming is a common practice to raise soil pH and increase phosphorus (P) bioavailability in tropical regions. However, reports on the effect of liming on P sorption and bioavailability are controversial. The process of phosphorus desorption is more important than P sorption for defining P bioavailability. However few studies on the relationship between soil pH and P desorption are available, and even fewer in the tropical soils. The effects of soil pH on P sorption and desorption in an Ultisol […]

The aim of this study was to evaluate the sorption and desorption of imazaquin in soils with different granulometric, chemical and mineralogical characteristics. Isotherms and kinetics studies were carried out to quantify the hysteresis between sorption and desorption processes. The soils were classified as Rhodic Hapludox (LVdf), Typic Hapludox (LVA) and Typic Quartzipsamment (RQ). The soils were air-dried and passed through a 2 mm mesh sieve, and the chemical, physical and mineralogical properties characterized. The radiolabeled molecule (14C) was imazaquin, an […]

The sorption of herbicides to soil is a process determinant of its dynamics in the environment. For weakly polar compounds such as acetochlor, organic matter represents the main sorbent in soil. The goal of this study was to evaluate the sorption of acetochlor on soil samples, humic acids and humin from an “Argissolo Vermelho distrófico” (PVd-Paleudult) under no-till and conventional tillage systems. Sorption isotherms were carried out at room temperature and the herbicide concentration was determined by high performance liquid […]

The objective of this study was to evaluate the impact of burning native pastures and of cultivating Pinus sp in monoculture in Lages, State of Santa Catarina, Brazil. Total organic carbon (TOC), microbial biomass carbon (MBC), microbial basal respiration (C-CO2), the microbial metabolic quotient (qCO2), and the ratio MBC/TOC were analyzed. Four representative areas of the region with 0.5 ha each were selected: (a) native pasture without burning for at least 50 years (NP); (b) native pasture burnt off every year (NPF); […]

Nitrogen (N) is the mineral nutrient required in largest amounts and is the one that most influence corn yield. With the objective of evaluating the best timing and methods of N fertilizer application on corn in a no-tillage system in a cerrado soil, this experiment was carried out at the Vargem Grande farm in Montividiu County, state of Goiás, Brazil, on a dystrophic Red Latosol (Rhodic distrophic Haplustox) during the 1996/97 crop season. The experimental area had been cultivated with […]

Nitrous Oxide (N2O) plays an important role in the greenhouse effect, owing to its high global warming potential and a long half-life in the atmosphere. A large portion of the natural N2O flux is oceanic and the remaining results mainly from the contribution of microbiological processes (nitrification and denitrification) that occur in tropical soils. The availability of nitrogen (N) for metabolic processes by microorganisms may be an important factor controlling N2O in such soils. The goal of this study was […]

Alleviation of Al rhizotoxicity by Ca and Mg can differ among species and genotypes. Root elongation of soybean [Glycine max (L.) Merr.] line N93-S-179 and cvs. Young and Ransom exposed to varying concentrations of Al, Ca and Mg were compared in two experiments using a vertically split root system. Roots extending from a surface compartment with limed soil grew for 12 days into a subsurface compartment with nutrient solution treatments maintained at pH 4.6 with either 0 or 15 µmol L-1 Al. Calcium and […]