Alvaro Pires da Silva

Propriedades físicas de um Latossolo Vermelho distrófico cultivado e sob mata nativa

The understanding and quantification of the impact caused by soil use and management on the physical soil quality are fundamental for the development of sustainable agricultural systems. The objective of this research was to quantify some physical soil properties to evaluate the physical quality of a dystrophic Red Latosol (Rhodic Ferralsol) in the northwest of the State of Parana, Brazil. Undisturbed soil samples were collected from two contiguous areas on an Experimental Farm of the State University of Maringa. One area was cultivated with annual crops under conventional tillage (disk plow and harrowing) and the other under native forest (semidecidual seasonal forest). The evaluated physical soil attributes were soil porosity and bulk density, soil water retention curve, soil resistance curve, and the least limiting water range. Results indicated significantly higher values of bulk density and lower values of soil porosity in the cultivated area. The soil water retention curve was not influenced by the soil use system, but was negatively influenced by bulk density. The soil resistance curve was influenced by the soil use system, evidenced by high values of soil resistance to root penetration under increasing drought in the cultivated soil. The least limiting water range was significantly smaller in the cultivated soil owing to the soil resistance to root penetration and air-filled porosity, which determined the lower and upper limits of soil water availability with bulk density increase. In the soil under native forest, the least limiting water range was equal to the water availability determined by the field capacity and the permanent wilting point. Soil compaction in the cultivated soil induced changes in the soil porous system, which were described by lower values of the least limiting water range than in virgin soil.

Intervalo hídrico ótimo na avaliação de sistemas de pastejo contínuo e rotacionado

Soil physical quality in continuous and short-duration rotational cattle grazing systems was evaluated using the Least Limiting Water Range (LLWR) approach. Soil samples were collected on an experimental site at the Embrapa - Beef Cattle Research Center (Campo Grande, MS, Brazil). The studied soil was a Typic Acrudox. Four sampling sites were selected: two under a short-duration continuous grazing system and two under intensive short-duration rotational grazing system. Thirty soil cores were collected in each site under the continuous grazing system, planted with Brachiaria decumbens cv. Basilisk grass. One of the continuous grazing sites had received biannual fertilization (Cc) while the other had not been fertilized (Cs). Thirty soil cores were also collected in each site under the intensive rotational grazing system, planted with Panicum maximum cv. Tanzania grass. In the intensive rotational grazing system the two sites differed in relation to the post-graze residue level left. In one site (R1) it varied from 2.0 to 2.5 t total dry matter (TDM) ha-1 and in the other R2 it varied from 3.0 to 3.5 t TDM ha-1. The cores were subjected to a soil water suction gradient, and then used for soil bulk density (Db), soil resistance to penetration (SR), volumetric water content (qv), and LLWR determinations. The intensive short-duration rotational grazing system presented the worse physical soil conditions for plant growth, as evaluated by the LLWR. The highest Db and the lowest LLWR were found in R1, which could be a consequence of the heavier stocking rates used on this site.

Quantification of the soil physical quality of a tropical oxisol using the S index

Soil physical quality is fundamental for the sustainability of agro ecosystems. Soil physical quality assessment must be developed using parameters that describe physical behavior. S, a new soil physical parameter has recently been introduced for assessing the soil physical quality. A good soil physical quality has been associated with values of S > 0.035 in soils from temperate climates. However, S has not been evaluated in tropical soils yet. Therefore we tested the hypothesis that S is a reliable soil physical quality indicator of a Typic Hapludox cropped with maize under no-tillage (NT) and conventional tillage (CT). Undisturbed samples were collected from each tillage system in the row and interrow positions. Soil bulk density was determined in the samples and the S parameter was calculated using a pedotransfer function from the same samples. The parameter S was able to differentiate tillage and position with SNT < SCT independent of the row and interrow sampling positions. Higher S values were verified in row position than in the interrow in both tillage systems. With the use of a pedotransfer function it was also possible to establish a negative relationship between S and soil compaction. The results confirmed our hypothesis and suggest that further studies should be carried out to evaluate S in other tropical soils and management systems.

Plant response to mechanical resistance and air-filled porosity of soils under conventional and no-tillage system

Roots may respond to restrictive soil physical conditions and send signals to shoots to control plant growth. Soil mechanical resistance and aeration can be managed to improve the soil physical conditions for plant growth by using different tillage systems. The objective of this study was to quantify the influence of no-tillage and conventional-tillage systems on plant response to soil mechanical resistance and aeration. The study was carried out on a farm, cultivated with corn, with a side-by-side comparison of no-tillage and conventional-tillage systems. Thirty-two paired sampling sites were located along two transects, located one in each treatment. Soil water content, bulk density, and plant growth were measured in each treatment. Based on the soil water and bulk density measurements, the air-filled porosity values were computed for each treatment. Soil water contents and bulk density values were converted to soil mechanical resistance by using the soil resistance curve. Plant growth varied positively with soil air-filled porosity, and negatively with soil mechanical resistance in both tillage systems. However, the decrease rates/increase rates were dependent on the tillage system. The no-tillage system somehow improved the soil physical conditions for the plants, especially when they were more restrictive, allowing them to attain greater values of growth.

Relações entre propriedades físicas e características de solos da região sul do Brasil

Relacoes funcionais entre atributos dos solos podem ser utilizadas para associar certas propriedades fisicas com caracteristicas desses solos. Este trabalho teve como objetivo determinar as relacoes entre algumas propriedades fisicas dos solos, especificamente densidade do solo (Ds), densidade de particulas (Dp) e capacidade de campo (θCC), ponto de murcha permanente (θPMP) e agua disponivel (θAD) e atributos rotineiramente determinados em levantamentos pedologicos. No estudo, foram utilizados 18 perfis representativos dos solos ocorrentes nos estados do Rio Grande do Sul e Santa Catarina, regiao Sul do Brasil. Foram coletadas amostras deformadas e indeformadas nos horizontes A e B para a determinacao de Ds, Dp, θCC, θPMP e θAD, granulometria, materia orgânica, oxidos de ferro e aluminio. As relacoes obtidas (regressoes multiplas) demonstraram que Ds, Dp, θCC, θPMP e θAD foram influenciadas por um numero reduzido de caracteristicas dos solos, especificamente teores de argila, silte e teor de oxidos de ferro e aluminio. Esses resultados preliminares podem servir para nortear o desenvolvimento de funcoes de pedotransferencia para a regiao Sul do Brasil.

Least limiting water range and physical quality of soil under groundcover management systems in citrus

Machinery-based farming operations used for perennial fruit crops often damage soils, particularly if the soil is wet and prone to compaction. We hypothesized that perennial vegetation growing in the interrows of orange orchards can mitigate the soil physical degradation from machinery traffic. The objective of this study was to investigate the effects of different groundcover management systems on the soil physical quality indicators including the least limiting water range (LLWR). An experiment was started in 1993 in a Typic Paleudult to evaluate three groundcover management systems: Bahia grass (Paspalum notatum) with mowing, perennial peanut (Arachis pintoi), and natural regrowth in which weeds were controlled by herbicide. The experimental design was randomized complete block with three replications. In May 2003, 216 undisturbed soil samples were collected at 0-0.15-m depths under and between wheel tracks in the orchard interrows. The soil bulk density, soil organic carbon content, resistance to penetration, soil water retention curve and soil resistance to penetration curve were determined in order to estimate the LLWR. The higher LLWR under wheel tracks in Bahia grass compared to perennial peanut or natural regrowth suggest that a better soil physical quality was achieved with Bahia grass.

Intervalo hídrico ótimo e produtividade de cultivares de soja

The objective of this study was to determine the optimal water interval and its relationship with soybean yield. For this study, an experiment was carried out in Jaboticabal, Sao Paulo State, Brazil, in a Haplustox medium textured soil. The experimental design consisted of a completely randomized with subdivided plots (six compaction levels and four soybean cultivars), with four replications. The soil compaction levels were: T0 = 0, T1* = 1, T1 = 1, T2 = 2, T4 = 4 and T6 = 6 strides of a 11 ton tractor, on the same place, side by side on soil surface. In T1* the compaction occurred when the soil was dry. In December, 2003 the soybean (Glycine max), cultivars IAC Foscarin 31, MG/BR 46 (Conquista), BRS/MG 68 (Vencedora) and IAC 8 - 2 were sown. After sowing, indeformed soil samples were collected in layers of 0.03-0.06, 0.08-0.11, 0.15-0.18 and 0.22-0.25 m for determination of soil water content and resistance to penetration curve and the optimal water content. According to model, the critical soil bulk density (Dsc) for soybean yield varied between cultivars from 1.56 to 1.64 Mg m-3. The soil bulk density at which the yield of soybean cultivars decreased was greater than the Dsc.

Soil resistance to penetration and least limiting water range for soybean yield in a haplustox from Brazil

The objective of this study was determine the resistance to penetration (PR), least limiting water range (LLWR) and critical bulk density (Db-crit) for soybean yield in a medium-textured oxisol (Haplustox). The treatments represented the soil compaction by passing a tractor over the site 0, 1, 2, 4, and 6 times, with 4 replications in a randomized experimental design. Samples were collected from 0.02-0.05, 0.07-0.10 and 0.15-0.18 m depths. Soybean (Glycine max cv. Embrapa 48) was sowed in December 2002. Plant height, number of pods, aerial dry matter, weight of 100 seeds, and the yield in 3.6 m2 plots were recorded. Soybean yield started reduction at the PR of 0.85 MPa and Db of 1.48 Mg m-3. The LLWR was limited in highest part by water content at field capacity (0.01 MPa tension) and in lowest part by water content at PRcrit, achieved the Db-crit to yield at 1.48 Mg m-3.

Improvement of a testing apparatus for dynamometry: procedures for penetrometry and influence of strain rate to quantify the tensile strength of soil aggregates

A resistencia do solo a penetracao (RP) e a resistencia tensil de agregados (RT) sao comumente utilizadas para caracterizar a condicao estrutural de solos agricolas. O objetivo deste trabalho foi avaliar a funcionalidade de uma maquina de ensaio para dinamometria mediante a automatizacao do controle de posicao e da velocidade linear de sua base movel nas medicoes de RP e de RT. O equipamento proposto foi utilizado na determinacao da RP em amostras indeformadas de um Nitossolo Vermelho eutroferrico argiloso sob cultivo de seringueira, considerando duas posicoes de amostragem (linha e entrelinha). Nessas amostras tambem foram determinados o teor de agua e a densidade do solo, cujos dados foram utilizados para o ajuste da curva de resistencia do solo a penetracao (CRP). Os valores de RT foram medidos num Latossolo Vermelho distrofico de textura media (LVd) e num Nitossolo Vermelho distroferrico muito argiloso (NVdf) sob distintos sistemas de uso: LVd, sob culturas anuais e mata nativa, e NVdf, sob culturas anuais e mata com eucaliptos ha mais de 30 anos. Quanto as determinacoes de RT, foram utilizadas duas maquinas de ensaio dinamometrico para aplicar distintas taxas de deformacao: uma de referencia (0,03 mm s-1), ja amplamente empregada em outros trabalhos, e o equipamento proposto (1,55 mm s-1). A CRP apresentou elevado valor de coeficiente de determinacao (R2 > 0,9), independentemente da posicao de amostragem. Os valores medios de RT do LVd e do NVdf obtidos com o equipamento proposto nao diferiram (p > 0,05) daqueles da maquina de ensaio de referencia, independentemente do sistema de uso e da classe textural do solo. Os resultados indicam que a RP e a RT podem ser determinadas mais rapidamente e com elevada acuracia utilizando o procedimento proposto.

Comparação de penetrômetros na avaliação da compactação de latossolos

Diversos penetrometros sao utilizados para avaliar a resistencia do solo a penetracao em sistemas de uso e manejo, no entanto os valores obtidos com os mesmos divergem. O objetivo deste estudo foi comparar os resultados obtidos com tres penetrometros, em tres niveis de compactacao. Utilizou-se de um Latossolo Vermelho distrofico (LVd), textura media, e um Latossolo Vermelho eutroferrico (LVef), textura argilosa, cujas amostras foram coletadas na camada de 0-20 cm e compactadas em camadas, em vasos de 25 cm de diâmetro e 20 cm de altura. Determinou-se a resistencia do solo a penetracao com os penetrometros de impacto, estatico de anel dinamometrico e eletronico de laboratorio. Em solo compactado, o penetrometro de impacto apresentou valores superiores de resistencia a penetracao, comparado aos penetrometros de anel dinamometrico e eletronico, porem todos foram eficientes para caracterizar a compactacao. Os resultados obtidos com os penetrometros de anel dinamometrico e eletronico foram semelhantes.