Planted forests occupy more than 6.5 million ha in Brazil, where harvest and logging operations are performed with increasingly heavier machinery, increasing the risk of soil compaction. Soil compaction can be avoided if soil load bearing capacity is not exceeded, what makes it important to assess both the soil strength and the impact of different operations. The aim of this study was to evaluate the load bearing capacity of some coarse textured soils (two Hapludult and one Haplorthod) in two soil horizons (BA and B), from northeastern Brazil; and to assess the impact of harvest and logging operations performed with harvester and forwarder. Although the Haplorthod presented higher load bearing capacity in both the BA horizon (for the whole moisture range) and the B horizon (for higher water contents), it suffered the greatest soil compaction. Traffic with the harvester resulted in soil compaction in both the BA and the B horizons, but the increase in bulk density was higher on the later, reaching 18.7% in the Haplorthod. The forwarder traffic intensity and the presence of plant residue cover significantly affected the occurrence of soil compaction. In the BA horizon, the increase in soil bulk density for different forwarder traffic intensities was 3 passes ~ 6 passes < 12 passes ~ 16 passes. The increase in bulk density was higher in the Haplorthod, reaching 32% after 16 forwarder passes over bare soil. Significant linear regressions were obtained from the number of forwarder passes and the increase in bulk density. Index terms:Harvester; forwarder; precompression stress; soil load bearing capacity. RESUMOAs florestas plantadas ocupam mais de 6,5 milhões de ha no Brasil, nas quais as operações de colheita e baldeio são realizadas com maquinário cada vez mais robusto, o que aumenta o risco de compactação do solo. A compactação do solo pode ser evitada se a sua capacidade de suporte de carga não for excedida, o que torna importante a avaliação tanto da resistência mecânica do solo quanto o impacto de diferentes operações. O objetivo deste estudo foi avaliar a capacidade de suporte de carga de solos de textura grosseira (dois Hapludult e um Haplorthod) em dois horizontes (BA e B) do Nordeste do Brasil; além de avaliar o impacto das operações de colheita e baldeio de madeira realizadas com harvester e forwarder. Apesar de o Haplorthod ter apresentado a maior capacidade de suporte de carga no horizonte BA (para toda a faixa de umidade) e no horizonte B (para maiores umidades) ele foi a classe de solo que apresentou maior compactação. O tráfego com o harvester resultou em compactação tanto no horizonte BA quanto no B, mas o aumento da densidade do solo foi maior no último, chegando a 18,7% no Haplorthod. A intensidade de tráfego do forwarder e a presença de resíduos de plantas na superfície do solo afetaram significativamente a ocorrência de compactação do solo. No horizonte BA, o aumento da densidade do solo em decorrência da intensidade de tráfego do forwarder foi de 3 passadas ~ 6 passadas < 12 passadas ~ 1...

Eucalyptus forests play a major role in the world economy, providing raw materials for different purposes. In planted forests, harvest operations performed by heavy machinery may cause severe soil compaction. This study aimed to evaluate the impact of a full‐tree harvesting system in planted eucalyptus forests from Northeastern Brazil. Different soils were evaluated (two Hapludults and one Haplorthod) in two horizons (BA and Bt). We tested different equipment, namely feller buncher, skidder (with traffic intensities of 3, 6, 12 and 16 passes), flail (at different ground‐contact points), grapple saw and loader. The soil physical attributes reflected not only the impact of equipment traffic but also the intrinsic differences between the soils. Bulk density (ranging from 1.36 to 1.80 t m−3 after trafficking) related well to soil class and horizon. Precompression stress (ranging from 203 to 430 kPa) and degree of compaction (76%–94%) following trafficking were well correlated, while increase in bulk density (reaching a maximum of 20%) related more strongly to soil moisture. A contingency table was constructed with the number of compacted samples and further examined by correspondence analysis. Compaction varied according to soil, horizon and equipment, indicating that machine–soil interactions are very specific and demand detailed research under different conditions. The Haplorthod experienced the greatest amount of compaction, whereas the Hapludult‐2 was more resistant (60% and 25% of compacted samples, respectively). The grapple saw and the skidder at higher traffic intensities (12 and 16 passes) exerted the highest mechanical impacts (81% and 67% of compacted samples, respectively).

Research on rainfall and annual daily maximum discharge rates is essential to support decisions during the design of hydraulic structures. This study tested the adequacy of probability functions to predict the probable rainfall and discharge rates of the Aiuruoca River Basin in Minas Gerais State in Brazil. This basin is very important as starting point of the Rio Grande Basin that eventually discharges into the Parana River in the southern region of Brazil at the border with Argentina. It was found that the log-normal two parameters probability function provided the best fit to historical monthly rainfall series. For example, in the month of January, there is a 75% probability that 201 mm of rainfall will occur. This is the month with the highest volume of rainfall in the region. On another hand, for flow rate, the best fit was provided by the log-normal distribution with three parameters.

Most of Brazilian agricultural land is occupied by pastures, which often show some degree of degradation. Grazing is usually associated to damages on soil structure because of soil compaction. The aim of this work was to evaluate short term changes on soil physical quality following different pasture renovation methods, including fertilization (FERT), conventional soil tillage (TILL) and two crop-livestock system (no-till and conventional tillage, respectively COTI and CONT), on a very clayey Red Latosol (Ustox), also comparing these to the original pasture and a nearby forest fragment. Bulk density and macroporosity were significantly different on the pasture sites (averaging 1.12 g cm -3 and 0.16 cm 3 cm -3 respectively) from that under the forest fragment (respectively 0.87 g cm -3 and 0.34 cm 3 cm -3 ); however, significant differences between the renovation methods and the original pasture were not observed. The load bearing capacity model (LBCM), which relates decrease on soil precompression stress (σ p ) with increase on water content (U), obtained for the original pasture, ORIG (σ p = 10 ), with the former being more resistant to compaction. When the ordinate pairs (U, σ p ) obtained from soil cores collected on the different renovation methods experimental plots were plotted on the LBCM from ORIG, an increase on soil strength could be noticed, but with small differences between renovation methods. This was because of higher stocking rates on FERT and TILL and corn harvest for silage production on COTI and CONT. Tillage failed to improve soil physical quality even on the short turn (only one growing season) and should be disregarded as a renovation method for pastures on initial stages of degradation, while soil fertility is the main limitation.Key words: load bearing capacity, precompression stress, soil compaction Alterações na qualidade física do solo no curto prazo após diferentes métodos de renovação de pastagens em um Latossolo Vermelho argiloso oxídico RESUMOAs pastagens ocupam a maior porção das terras agrícolas do Brasil e frequentemente apresentam algum grau de degradação. O pastejo animal geralmente está associado a danos à estrutura do solo, devido à compactação. O objetivo deste trabalho foi avaliar as mudanças no curto prazo na qualidade física de um Latossolo Vermelho muito argiloso, após diferentes métodos de renovação de pastagens, incluindo adubação (FERT), preparo convencional (TILL) e interação lavoura-pecuária (com preparo convencional do solo e em plantio direto, COTI e CONT respectivamente), comparando estes à pastagem original e a um fragmento de mata próximo. A densidade do solo e a macroporosidade nas áreas de pastagem (respectivamente 1,12 g cme 0,16 cm 3 cm -3 ) foram significativamente diferentes em comparação ao solo sob mata (respectivamente 0,87 g.cm -3 e 0,34); contudo, diferenças significativas entre os métodos de renovação e a pastagem original não foram observadas. O modelo de capacidade de suporte de carga (MCSC), que relaciona o decréscimo na pressão de pré-c...

The knowledge of rainfall distribution and behavior at certain area is indispensable at irrigation systems design and management, as well rainfall tracking regarding soil conservation aspects. Thus the objective of this research was the comparison and statistical adequacy of probability distribution models applied to probable rainfall studies, to determine which probability model is more appropriate to distinct seasons (monthly, fortnightly and decendial) and to estimate probable rainfall for different probability levels on Lambari region, South of Minas Gerais state, Brazil. Log-normal at 3 parameters and Gamma were the most adequate for monthly and decendial periods, for fortnight periods Gamma was the most adequate, with annual average values of monthly, fortnightly and decendial rainfall to 75% probability level of 82.4, 72.1, and 42.4 mm, respectively.