Productivity in subsistence or low-input agriculture depends on the release of nutrients through mineralization of soil organic matter (SOM). For this reason, SOM quantity and quality are two important variables related to the sustainability of subsistence family farming. The objective of this work was to study the interrelationships among soil use, texture and relief, at basin scale, on the concentration of total soil C (Ct) and N (Nt), the oxidizable C fraction with 16.5 mol L-1 KMnO4 (Cox) and the amino-sugars fraction […]

Iron oxides from 22 soil samples (19 from argillic B horizons; one from a plinthic B horizon; one from a cambic horizon and one from a C horizon) were subjected to selective dissolution with sodium dithionite-citrate-bicarbonate at 20 ºC in time intervals of 5 to 3,840 minutes. Mean coherence lengths (MCL), specific surface area (SSA) and iron by aluminum substitution (Al3+-substitution) of goethite and hematite in untreated sub-samples and in selected sub-samples treated during selective dissolution were estimated by X ray diffraction analysis […]

Highly weathered tropical soils present high amount of colloids with variable electrical charge. However, there are few references related to the quantification of such charges, mainly in soils with acric attributes, which represent one of the extremes in the weathering scale. In this study permanent and variable charges were determined in four Oxisols and compared to an Alfisol with predominantly permanent charge. Samples were investigated using the Cs+ adsorption method, which measures the structural permanent charge (so) and is based […]

The objective of this study was to evaluate the long-term effects of soil tillage systems and methods of lime application on biological, physical and chemical attributes of a clayey aluminic Oxisol, and on soybean yield components. The experiment with tillage systems was installed in 1978 in Guarapuava, PR, southern Brazil, and liming methods began to be tested in 1987. The treatments were: conventional tillage (CT) without liming; CT with liming; no-tillage (NT) without liming; NT with surface liming and NT […]

A considerable part of eucalypt plantations in Brazil grows on low-fertility soils for which fertilization techniques and nutrient cycling processes are important to elevate and maintain the forest production. The response of these plantations to nitrogen fertilization has been relatively low, indicating that the soil has been capable of supplying part of the plant demand. Microbial biomass N is considered a readily available fraction, but little is known about the biotic and abiotic factors that affect its dynamics in eucalypt […]

The characterization of several soil phosphorus (P) pools allowed the evaluation of P components not usually monitored in fertilizer soil tests and can help to understand this nutrient’s cycle. The aim of this study was to evaluate the changes in P pools of a Fluventic Eutrochrepts fine clay which had been under long-time sugarcane plantation. In one situation the sugarcane had been cropped for 55 years with and without trash burning prior to harvesting. The other sugarcane plantation, cultivated for 35 years, […]

Crop management systems that favor soil organic matter can improve the available nutrient content for plants and reduce the use of industrial fertilizer. Despite the importance of organic compounds as a P source, little is known about its dynamics in tropical environments. The objective of this study was to identify organic P species present in humic acids by NMR 31P analysis in a fine clay Fluventic Eutrochrepts in Campos dos Goytacazes, in the north of Rio de Janeiro State, Brazil, under […]

The use of mechanistic models based on principles of solute transport may be of great utility to estimate, for example, the impact of eucalypt forest cultivation on the pools and fluxes of nutrient in soils. Among the parameters required by such models are the values of the ion absorption kinetics constants Vmax, Km and Cmin. Thus, the objective of this study was to determine the values of Vmax, Km and Cmin for K, Ca and Mg, as well as to […]

The continuous cultivation of inoculated soybean in the same area can determine the soil colonization with a rhizobia population presenting low nitrogen fixation effectiveness. This fact can be a problem for the establishment of a more effective population. A greenhouse experiment was carried out to evaluate the symbiotic effectiveness and competitiveness of spontaneous mutants isolated from B. japonicum (SEMIA 5079 and SEMIA 5080) and B. elkanii (SEMIA 587 and SEMIA 5019) strains. The soybean biovar BR 16 was inoculated with the same proportion of inoculants […]

The aim of this study was to quantify the contribution of soluble organic-C deposition by rice root system and the CO2 evolution during 64 days in an Oxisol samples treated with glucose, and rice roots collected at different plant growth stages (40, 60, 80, 100, 120 and 140 days after sowing). Thereafter, organic matter was fractionated to evaluate the effect of the addition of a root system on the soil humus composition. It was possible to observe the intense rhizodeposition of organic […]