ABSTRACT. We tested the hypothesis that the increase in soil stiffness, induced by variations in bulk density and water content at the tire-soil contact interface, causes a reduction in the contact area. For this, we examined the contact area from different tire-ground contact scenarios and compared the measurements and simulations using a contact area description model. Front and rear tractor tires were used for the measurement of the contact area under tilled soil, sugarcane field, unpaved road, and paved ground scenarios, which induced different bulk densities and water content levels. The results revealed that soil stiffness reduced the tire-soil contact area. The tire-soil contact area increased as the water content increased and the bulk density was reduced. For the front tractor tire, the theoretical contact area was similar to the values found for tilled soil, but there was a large difference between the measurements (2,200 cm2, for the tilled soil) and the theoretical estimates (3,100 cm2) for the rear tractor tire (likely induced by tire dimensions). Our results suggest that increases in soil stiffness reduce the tire-soil contact area. The higher the soil bulk density and the lower the soil moisture, the lower the contact area. The results also revealed that the tire tractor tread might reduce the contact at the hard surface, making the shape of the contact area more geometrically irregular and different from those predicted by models using regular geometry (e.g., cycles, ellipses, or rectangles). This study suggests that two-body (soil and tire) contact models for deformable surfaces should be used in future tire-soil contact models of agricultural field vehicles. ABSTRACT tiresoil interface this tireground model road levels 2,200 2200 2 200 (2,20 cm2 cm 3,100 3100 3 100 (3,10 likely dimensions. dimensions . dimensions) moisture surface e.g., eg e g (e.g. cycles ellipses rectangles. rectangles rectangles) twobody two body vehicles 2,20 220 20 (2,2 3,10 310 10 (3,1 e.g. (e.g 2,2 22 (2, 3,1 31 1 (3, e.g 2, (2 3, (3 (

ABSTRACT Reduced stability and structural resilience expose sandy soils to physical degradation under intensive production systems. This study aimed to evaluate the influence of different cover crops (CC) under no-tillage system (NTS) cotton cropping, grown either individually or in combination, on the soil physical quality (SPQ) of a sandy loam Oxisol (Latossolo) in southeastern Brazil. To quantify the effects of CC on soil physical quality indicators, an experiment in randomized blocks design was implemented with the treatments: CC1: single cultivation of Ruzi grass; CC2: Intercropping of Pearl Millet + Ruzigrass; CC3: Intercropping of Pearl Millet + Velvet bean; CCMixture: Intercropping of Ruzi grass, Pearl Millet and Velvet bean; and Control: maintenance of spontaneous plants. Undisturbed samples were taken from layers 0.00-0.10, 0.10-0.20, 0.20-0.40 and 0.40-0.60 m, in which were determined the soil bulk density (Bd), total porosity (TP), available water (AW), soil penetration resistance (PR) and the least limiting water range (LLWR). According to the multivariate analyses, the CC2 treatment resulted in better SPQ compared to the other treatments. The LLWR, air-filled porosity (θAFP), and AW were responsible for differentiating the CC2 treatment compared to the other treatments evaluated. Regardless of treatments, values of Bd> 1.75 Mg m-3 result in loss of SPQ due to the significant increase in PR and decreases in AW and LLWR. In the CC3 and Control, there was a physical impediment caused by the increase in Bd in the 0.10-0.20 m layer, which could result in the confinement of cotton roots to the surface, making them more susceptible to water stress. Soil PR reached values greater than 2.5 MPa for water contents lower than the θPWP in most treatments. In treatment CC3, for water contents equivalent to the θPWP, the PR did not exceed 6 MPa, while for the other treatments, the PR reached values greater than 10 MPa. Only the PR was influenced using CC. Soil moisture is considered crucial to maintain PR below impeding values, determining the control of the physical quality of this sandy soil. systems (CC notillage no tillage NTS (NTS cropping combination (SPQ Latossolo (Latossolo Brazil indicators CC1 grass Ruzigrass bean CCMixture Control plants 0.000.10, 000010 0.00 0.10, 0 00 0.00-0.10 0.100.20, 010020 0.10 0.20, 20 0.200.40 020040 0.20 0.40 40 0.20-0.4 0.400.60 040060 0.60 60 0.40-0.6 Bd, , (Bd) TP, TP (TP) AW, (AW) (PR LLWR . (LLWR) analyses airfilled air filled θAFP, θAFP (θAFP) evaluated 175 1 75 1.7 m3 3 m- 0.100.20 0.10-0.2 layer surface stress 25 2 5 2. 000 0.000.10 00001 0.0 010 0.00-0.1 100 01002 0.1 020 200 0.200.4 02004 0.2 040 0.4 4 0.20-0. 400 0.400.6 04006 060 0.6 0.40-0. (Bd (TP (AW (LLWR (θAFP 17 7 1. 0.100.2 0.10-0. 0.000.1 0000 0. 01 0.00-0. 0100 02 0.200. 0200 04 0.20-0 0.400. 0400 06 0.40-0 0.100. 0.10-0 0.000. 0.00-0 0.200 0.20- 0.400 0.40- 0.100 0.10- 0.000 0.00-

Resumo: O objetivo deste trabalho foi determinar a acurácia em medidas do potencial mátrico da água no solo (ψm) por tensiômetros de punção com cápsulas arredondadas ou pontiagudas, instalados com ou sem “lama de solo”, e comparar o desempenho destes tensiômetros com o de tensiômetros com manômetros de mercúrio. O experimento foi conduzido em Argissolo Vermelho-Amarelo distrófico, em delineamento experimental de blocos ao acaso, em arranjo fatorial, com cinco repetições. Tensiômetros de punção com cápsulas arredondadas, instalados com “lama de solo”, apresentam maior acurácia nas determinações do ψm em uma faixa mais ampla de medidas, assemelhando-se aos tensiômetros com manômetros de mercúrio com o secamento do solo.

Abstract: The objective of this work was to determine the measurement accuracy of the soil water matric potential (ψm) by puncture tensiometers with either rounded or pointed porous cups, installed with or without “soil mud”, and to compare the performance of these tensiometers with that of tensiometers equipped with mercury manometers. The experiment was conducted in a Ultisol, in a randomized complete block design, in a factorial arrangement with five replicates. Puncture tensiometers with rounded porous cups, installed with “soil mud”, present more elevated accuracy for ψm determination in a wider measurement range, resembling tensiometers equipped with mercury manometers in drying soil.

ABSTRACT There are many methods for determining precompression stress (σp), whose value is affected by the slope of the soil compression curve. This study was designed to evaluate the hypothesis that for a certain compression curve all methods used to determine σp present the same value and accuracy. The aim of this study was to compare the accuracy and the relationship among seven of these methods by computational simulation of soil compression curves under nine scenarios. The following methods were used: Casagrande, Pacheco Silva, intersection of the initial void ratio with the virgin compression line (VCLzero), and the regression methods based on 2 (reg1), 3 (reg2), 4 (reg3), and 5 (reg4) points for modeling the elastic curve. Under each scenario, created by combining the swelling and the compression indices, 1,000 compression curves were computationally simulated via the Monte Carlo method. Subsequently, 95 % percentile confidence intervals were built using the 1,000 estimates of σp from each method under each scenario. Most of the differences among the methods were detected under scenarios consisting of high swelling and low compression indices. In general, Casagrande, Pacheco Silva, and reg4 were strongly correlated and presented the highest values of σp, as well as similar variability. The latter two can be considered as alternatives to the standard method of Casagrande, except for Pacheco Silva when the curve has a low compression index (≤0.2) and from medium to high swelling index (≥0.025), for which differences (p<0.05) were detected.

O penetrômetro é o instrumento usualmente indicado para avaliação da resistência mecânica do solo à penetração (RMP). O objetivo deste trabalho foi comparar o desempenho de dois penetrômetros: um eletrônico e outro de impacto, na avaliação da RMP. O trabalho foi realizado na Fazenda Experimental Chã-de-Jardim, Centro de Ciências Agrárias, da Universidade Federal da Paraíba (CCA/UFPB), Areia-PB, em área de Latossolo Amarelo de dimensão 35 × 35 m. Os penetrômetros utilizados foram: um de impacto, modelo IAA/Planalsucar-Stolf, e um digital, Falker, modelo PenetroLOG - PLG 1020, com aptidão eletrônica para aquisição de dados em quatro profundidades. Dentro da área, 40 pontos foram amostrados, seguindo duas direções: Norte, para o penetrômetro eletrônico, e Sul, para o de impacto, com os pontos de coleta de cada penetrômetro espaçados em 0,1 m. Os dados foram analisados segundo o modelo de análise de variância de um experimento em delineamento inteiramente casualizado. Os penetrômetros de impacto e Falker apresentaram médias de 1,75 MPa, sendo, portanto, semelhantes na avaliação da RMP em todas as profundidades analisadas, sugerindo que ambos modelos testados podem ser utilizados para solos com características texturais semelhantes as do solo deste estudo.

The penetrometer is an instrument usually suitable for evaluating the penetration resistance of soil (PR). This study aimed to compare the performance of an electronic penetrometer and an impact penetrometer on the evaluation of the PR. The experiment was carried out at the experimental farm Chã-de-Jardim, CCA/UFPB, Areia - PB, in an area of Yellow Latossoil measuring 35 × 35 m. The impact penetrometer evaluated was an IAA/Planalsucar-Stolf and the digital penetrometer Falker PenetroLOG - PLG 1020, with electronic capability for data acquisition in 4 depths. Within the area, 40 points were sampled following two directions, North for the electronic penetrometer and South for the impact penetrometer, with the sample points of each penetrometer spaced 0.1 m apart. Data were analyzed following the analysis of variance of a completely randomized design. Both penetrometers showed means of 1.75 MPa, being similar on the evaluation of PR for all analyzed depths, suggesting that both devices can be used for soils with textural characteristics similar to those of this study.

O objetivo deste trabalho foi avaliar a existência de camadas compactadas, em três diferentes classes texturais de solos. O estudo foi desenvolvido em áreas, sob cultivo de cana-de-açúcar, da Fazenda Guanabara, localizada no município de Nova Olímpia, Mato Grosso, Brasil. Para coleta dos dados, foi utilizado um penetrômetro de impacto, modelo IAA/Planalsucar, para avaliação da resistência à penetração (RP), em três diferentes classes texturais (Areia Franca, Franco - Argilo- Arenosa e Muito Argilosa). O solo de classe textural franco-argilo-arenosa apresentou os maiores valores de resistência à penetração, entre as três classes. As classes texturais franco-arenosa e muito argilosa comportaram-se de forma semelhante, em todas as camadas. Houve semelhança na resistência à penetração das três classes texturais na camada 0,3-0,4 m.

The purpose of this study was to evaluate the existence of compacted layers in three different textural classes located in production areas of sugarcane. The study was conducted in production areas of sugarcane at Fazenda Guanabara, located at municipality of New Olympia, Mato Grosso state, Brazil. Data collection was conducted using an impact penetrometer, model IAA/Planalsucar, evaluating the penetration resistance in three different texture (Loam Sandy, Sandy Clay Loam and Clay). Loam Sandy and Clay textures showed the highest penetration resistance. Loam Sandy and Clay textures behaved very similarly in all layers. There were similar values of penetration resistance of the three classes in 0.3-0.4 m layer.