Volume 23, Number 2, 1999

The objective of this paper was to study the effect of eight soil tillage systems on the aggregation status of an Albaqualf at a depth of 0-10 cm using the following parameters: distribution of water stable aggregates in different size classes and mean weight diameter aggregates. The field experiment was carried out at the “Empresa Brasileira de Pesquisa Agropecuária – Centro de Pesquisa Agropecuária de Clima Temperado” (EMBRAPA-CPACT) experimental station, in Pelotas (RS) in 1985. After ten years, the soil […]

Soil compaction is a common problem that affects several soil properties and plant growth. In order to assess the effects of soil strength expressed by its mechanical resistance on roots, a growth chamber experiment was conducted at the Universidade Federal do Rio Grande do Sul, Porto Alegre, in 1994, during 35 days (530 GDD, 0ºC base temperature) on a typical Paleudult soil. Treatments, using pots arranged in a completely randomized design, consisted of soil compactions that resulted in resistances of […]

To test the performance of a numeric model in prediction of water content (θ) and tension (|ψm|) in time and space, data were chosen from the literature on two porous materials with different hydraulic properties: a marine sand (quatzipsamment) of Tottori, Japan and a sandy phase Red-Yellow Latosol (Haplustox) of Piracicaba, SP. The results led to the following conclusions: (a) in both porous materials studied, the behaviour of the model was highly significant, with the profiles of humidity aligning satisfactorily […]

Using the compressibility test, the effect of soil management and moisture content on the preconsolidation pressure (σp) of three soils, a Red-Yellow Latosol (LV), a Dusk Red Latosol (LR) and a Dark-Red Latosol (LE) under annual crop, natural forest and pasture, was studied in the area of Lavras (MG) at two depths (0-0.03 and 0.27-0.30 m). For each condition, five undisturbed soil samples and a disturbed one were collected, with three replications. The undisturbed soil samples with different soil moisture […]

High phosphate adsorption in oxidic tropical soils changes the charge balance on the surface of particles and can increase dispersion. Consequently, it can affect pore size distribution, aggregate stability and susceptibility to compaction. In order to measure the effect of phosphate sorption on compression curves and consistence limits, a Dark-Red Latosol (LE) (very fine, allitic, isothermic Typic Hapludox) and a Cambisol (C) (very fine, isothermic Oxic Distropept) were sampled at 0-3 and 27-30 cm depth, at Campos da Mantiqueira, Minas […]

Different soil boron fractions were evaluated from 29 superficial (0-20 cm) soil samples in Ceará, Brazil. Relationships were established between soil fractions and soil properties and soluble boron, which has been used as an index of boron availability to the plants. Fractional boron analyses of the soils were carried out following a sequential procedure. The following determinations were carried out: the water soluble boron (B-Sol), the not specifically adsorbed boron (B-NEsAd), the boron associated to manganese oxide (B-OxMn), the boron […]

In order to evaluate the saline tolerance of Rhizobium loti strains (NFB 494 and SEMIA 6069) on Leucaena leucocephala-cv K8, an experiment was carried out using a Red-Yellow Podzolic, submitted to different levels of soil salinity (C.E. = 1.5; 6.6; 10.1; 12.8 e 14.4 mS cm-1). For comparative purposes, a non-inoculated treatment was added with and without mineral fertilization (200 mg kg-1 soil of N as NH4NO3). The experimental design was a complete randomized block, arranged in a 5 x […]

The C and N mineralization potential of 20 soils from Pernambuco, Brazil (10 from the humid area and 10 from the semi-arid) was determined in a greenhouse experiment, conducted from January to October 1987. Samples of 50 g from 0-20 and 20-40 cm depth layers were incubated. The released C-CO2 and the accumulated mineral N (NO3– and NH4+) were periodically measured during 20 and 4 weeks, respectively. The mineralized amounts varied much among soils. In spite of this they were […]

This work was carried out to evaluate the alterations in organic-C, microbial-C and in the activities of the enzymes cellulase and amylase in soil samples of a Rhodustalf collected in the summer at 0-10, 10-20 and 20-30 cm depths, under natural forest (NF), 20 (P20) and 25 (P25) year old pastures and 10 year old cotton cultivation. Organic-C and microbial-C contents and the amylase and cellulase activities were very similar in NF, P20 and P25. Reduction of 18% in organic-C […]

A field experiment was carried out on a clay-sand-loamy Red-Yellow Latosol (Typic Acrustox) in Planaltina, Federal District, Brazil, during the cropping seasons of 1995/96, 1996/97 and 1997/98, to compare the effect of three methods of copper application (soil, foliar spray and seed treatment) on soybean (cv. Doko RC) grain yield and to determine the soil and leaf critical levels of that nutrient. There were no significant differences among the treatments in the first crop, probably due to a dry spell […]