3298 results

Soil fertility management for sustainable cropping on an oxisol of the central Amazon

M. S. Cravo, T. J. Smyth

01/Dec/1997

Estimates of deforestation in the Brazilian Amazon, primarily for shifting cultivation and pastures, exceed the land area for the State of Rondônia. An experiment was conducted on a Xanthic Hapludox near Manaus, Brazil to establish soil nutrient depletion patterns and fertilizer and lime requirements for continuous cultivation after slash-and-burn clearing. Yield responses to N, P, K, Mg, S, B, Cu, Mn, Zn and lime were evaluated during eight years of cultivation. Seventeen crops were grown during the period from 1981 […]

Geochemical balance of soils derived from basic-ultrabasic rocks under the subtropical climate of Rio Grande do Sul state, southern Brazil

L. F. S. Pinto, N. Kämpf

01/Dec/1997

The mass balance of weathering of soils derived from basic-ultrabasic rocks under the subtropical climate of southern Brazil, the least weathered soils found to date in the Rio Grande do Sul state, showed a higher relative concentration of the mobile elements in the surface horizons than in the subsurface horizons. These features, associated to the soil mineralogy and morphology, indicate the occurrence of erosive-depositional events in a pedogenetically recent past as well as a main contribution from less weathered materials […]

Soil nutrients in two forest types on the coastal plains of Ilha do Mel, Paranaguá, state of Paraná, Brazil

R. M. Britez, A. Santos Filho, C. B. Reissmann, S. M. Silva, S. F. Athayde, R. X. Lima, [...]

01/Dec/1997

The nutrient cycling of two types of vegetation, (a “low forest” – 15 m of height, and a “short forest” – 25 m of height), characteristic of the sandy belts on the Coastal Plains of Ilha do Mel was studied, from June 14th, 1991 to June 12th, 1993. In this first step the soil’s chemical and physical characteristics were studied, in relation to the physical environment and the parent material. The soils were classified as allic/dystrophic podzols, where the B […]

Scaling of semivariograms and the kriging estimation of field-measured properties

S. R. Vieira, P. M. Tillotson, J. W. Biggar, D. R. Nielsen

01/Dec/1997

Two methods were evaluated for scaling a set of semivariograms into a unified function for kriging estimation of field-measured properties. Scaling is performed using sample variances and sills of individual semivariograms as scale factors. Theoretical developments show that kriging weights are independent of the scaling factor which appears simply as a constant multiplying both sides of the kriging equations. The scaling techniques were applied to four sets of semivariograms representing spatial scales of 30 x 30 m to 600 x […]

A new method for the calculation of the mean diameter of soil aggregates

Q. de JONG van LIER, J. A. Albuquerque

01/Dec/1997

When calculating the mean weight-diameter (MWD) or the geometric mean diameter (GMD) of a soil sample, the arithmetic mean diameter (in the case of MWD) or the logarithmic mean (in the case of GMD) of cach class is weighed by the mass of aggregates retained in that class. The use of the arithmetic mean of each class, multiplied by the aggregate mass retained in that class is correct only if a symmetric distribution of aggregate sizes occurs within each class, […]

Sampling strategies for tropical forest nutrient cycling studies: a case study in São Paulo, Brazil

G. Sparovek, O. A. Camargo

01/Dec/1997

The precise sampling of soil, biological or micro climatic attributes in tropical forests, which are characterized by a high diversity of species and complex spatial variability, is a difficult task. We found few basic studies to guide sampling procedures. The objective of this study was to define a sampling strategy and data analysis for some parameters frequently used in nutrient cycling studies, i. e., litter amount, total nutrient amounts in litter and its composition (Ca, Mg, Κ, Ν and P), […]

Phosphorus extractants in Amazonian soils amended with phosphate fertilizers

E. C. Brasil, T. Muraoka

01/Dec/1997

Aiming to evaluate the phosphorus availability in five Amazonian soil samples, amended with different phosphates, a pot trial was carried out under greenhouse conditions at the Centro de Energia Nuclear na Agricultura, Piracicaba (SP,Brazil), from october, 1993 to march, 1994, using the soils: medium texture Yellow Latosol, clayey Yellow Latosol, very clayey Yellow Latosol, clayey Red-Yellow Podzolic and very clayey Red-Yellow Podzolic. Four phosphate sources were applied (triple superphosphate, fine yoorin thermophosphate, granular yoorin thermophosphate and North Caroline rock phosphate) […]

Transfer of nitrogen between plants interconnected by arbuscular mycorrhizal fungi (AMF)

A. F. Cruz, M. A. Martins

01/Dec/1997

This work was undertaken at the State University of North Fluminense (UENF), State of Rio de Janeiro, Brazil, under greenhouse conditions, in the first semester of 1996, to evaluate the role of arbuscular mycorrhizal fungi (AMF) in the process of nitrogen transfer from bean to maize plants using the isotope 15N. Special pots divided in three sections (A, B and C), were constructed and either no barrier and a nylon mesh screen (40 ∝m) (which allowed the AMF hyphae to […]

Mycorrhizae, phosphorus and nitrogen supply on initial growth of “trema” and “fedegoso”

M. E. Paron, J. O. Siqueira, N. Curi

01/Dec/1997

The response of “trema” (Trema micrantha (L) Blum.) and “fedegoso” (Senna macranthera Rich.), both native woody species, to phosphorus (P), nitrogen (N) and inoculation with arbuscular mycorrhizal fungus (AMF) was studied in pots using a low-fertility clayey Dark Red-Latosol (Oxisol) Sample. The study, composed of two experiments, was carried out under greenhouse conditions at the Soil Science Department of Universidade Federal de Lavras, state of Minas Gerais, Brazil, from march 1993 to april 1994. Both species grew poorly in the […]

Extraction of soil water by plants: development and validation of a model

Q. de Jong van Lier, P. L. Libardi

01/Dec/1997

A quantitative model of water movement within the immediate vicinity of an individual root is developed and results of an experiment to validate the model are presented. The model is based on the assumption that the amount of water transpired by a plant in a certain period is replaced by an equal volume entering its root system during the same time. The model is based on the Darcy-Buckingham equation to calculate the soil water matric potential at any distance from […]

1 325 326 327 328 329 330