Osmar Conte

Managing grazing animals to achieve nutrient cycling and soil improvement in no-till integrated systems

Crop-livestock systems are regaining their importance as an alternative to unsustainable intensive farming systems. Loss of biodiversity, nutrient pollution and habitat fragmentation are a few of many concerns recently reported with modern agriculture. Integrating crops and pastures in no-till systems can result in better environmental services, since conservation agriculture is improved by system diversity, paths of nutrient flux, and other processes common in nature. The presence of large herbivores can positively modify nutrient pathways and soil aggregation, increasing soil quality. Despite the low diversity involved, the integration of crops and pastures enhances nature’s biomimicry and allows attainment of a higher system organization level. This paper illustrates these benefits focusing on the use of grazing animals integrated with crops under no-tillage systems characteristic of southern Brazil.

Evolução de atributos físicos de solo em sistema de integração lavoura-pecuária

The objective of this work was to assess the effect of sward height and successive grazing cycles over soil physical attributes in an integrated crop-livestock system. The experiment was established in 2001, in the Planalto Medio region, RS, Brazil, in a Rhodic Hapludox (Oxisol), with annual ryegrass (Lolium multiflorum) intercropped with black oat (Avena strigosa), under continuous grazing, during the winter, and single cropped soybean (Glycine max) during the summer. The treatments consisted of different grazing intensities, determined by sward height (10, 20, 30, and 40 cm), and a no-grazing area was used as a control. Soil bulk density and soil porosity were evaluated at the end of the grazing and soybean cycles, as well as soil resistance to mechanic penetration and aggregate stability in the seventh year of the experiment. No significant differences were found on soil bulk density and soil porosity after seven years under crop-livestock integration. Soil resistance to penetration is higher on the superficial layer after the grazing cycle. Soil aggregation increases in grazing areas, regardless of grazing intensities.

Demanda de tração em haste sulcadora na integração lavoura-pecuária com diferentes pressões de pastejo e sua relação com o estado de compactação do solo

An experiment was carried out with crop and cattle rotation in an Oxisoil, in Tupancireta - RS, which aimed to evaluate the draft effort in fertilizer direct drillings used in direct seeding, working at different depths and intensities of fields under different grazing pressures. Grazing pressure effects on soil compactness were also assessed. The main treatments were grazing maintaining 0.10, 0.20, 0.30, 0.40 m pasture (Lolium multiflorum + Avena strigosa) without grazing, height (adjusting the number of cows on the plots) and two working depths of fertilizer shanks: 0.12 m and 0.15 m. Root dry matter in the superficial layer (0.0 - 0.12 m) was increased when higher grazing pressures were used. Soil resistance to a penetrometer showed increased values at higher grazing pressures; it was detected until 0.12 m depth. Draft requirement of fertilizer shanks increased from 1,900 to 4,300 N (120%) when the working depth changed from 0.12 m to 0.15 m condition. Draft demand by fertilizer shanks was higher on soils under higher pressures as well, but the absolute values showed that only treatments with remaining heights of 0.10 and 0.20 m were different from those found without grazing systems. Soil resistance to penetrometer and power demand by fertilizer shanks was closely related.

Sistemas de preparo de solo: alterações na estrutura do solo e rendimento das culturas

A introducao e intensificacao no uso do sistema de semeadura direta no Brasil nas ultimas decadas desenharam um novo cenario na agricultura brasileira, aumentando a preocupacao com as caracteristicas fisicas dos solos. O objetivo deste trabalho foi avaliar a implicacao que diferentes sistemas de preparo de solo impoem sobre algumas caracteristicas fisicas de um Argissolo Vermelho inicialmente sob uso com campo natural. Cinco metodos de preparo de solo foram ensaiados: semeadura direta (SD), escarificacao (E), semeadura direta com escarificacao a cada dois anos (SDE2), escarificacao com escarificador munido de rolo destorroador (ER) e escarificacao seguida de gradagem (EG). Foram avaliados: densidade do solo, macroporosidade, microporosidade e porosidade total, resistencia mecânica do solo a penetracao, infiltracao de agua no solo e rendimento das culturas. Os valores de densidade do solo, resistencia mecânica do solo a penetracao e microporosidade aumentaram em detrimento da diminuicao da macroporosidade. A densidade do solo foi menor nos sistemas de preparo com maior grau de mobilizacao do solo, sendo os maiores valores observados para o sistema SD e os menores para o sistema EG. A taxa de infiltracao de agua apresentou-se maior no sistema ER, seguido pelos sistemas EG, SD e SDE2, ao passo que o rendimento das culturas foi maior nos sistemas com menor mobilizacao de solo.

Força de tração e mobilização do solo por hastes sulcadoras de semadoras-adubadoras

No tillage implies keeping the soil surface covered with crops or crop residues, which might influence planter performance. Using fixed shanks as furrow openers to place fertiliser is an alternative to minimize compaction, as it mobilizes the soil in the sowing line. The aim of this research was to evaluate the effect of different amounts of winter cover crop residues evenly distributed on the soil, the effect of the shanks working depth and quantity of planter lines on power demand, cross sectional furrow area and total volume of soil mobilized in the lines and corresponding wheel slippage in distrophic red Argisol. During winter, black oats and black oats plus turnip were used as cover crops before maize and beans, respectively. Increasing the working depth showed an increase in power demand, as measured directly at the shanks (three lines for maize and five for beans). There was also an effect of residue, increasing power demand on the shanks, but only measurable with the planter operating with three lines in maize sowing. Soil mobilization in the sowing lines was influenced by the amount of residues, the working depths of shank and the quantity of planter lines. Wheel slippage was higher with larger amounts of soil cover residues and when power demand was higher.

Densidade, agregação e frações de carbono de um Argissolo sob pastagem natural submetida a níveis de ofertas de forragem por longo tempo

The adjustment of animal quantity according to the herbage allowance is fundamental to the sustainability of natural pastures. The management of herbage allowance, besides affecting the plant species that compose the pasture, can also compromise soil properties, such as density and aggregation. This study aimed to evaluate the soil bulk density, weighted mean diameter of soil aggregates and carbon fractions under natural pasture, under varying grazing intensities for 22 years, represented by herbage allowance levels of 4, 8, 12, and 16 kg dry matter per 100 kg animal weight. Two ungrazed areas were included as references. Changes in soil properties were found, related to the grazing intensity. These changes occurred mainly in the soil surface layer (0-10 cm), where soil density increased with decreasing herbage allowance. The behavior of the weighted mean diameter of soil aggregates and the root mass in the layer 0 - 10 cm were inversely proportional to the herbage allowance. The carbon storage index indicated that under forage supplies of 12 % the soil C stock increased compared to the control, but decreased at other allowance rates. The index of carbon management shows that the highest herbage allowance (12 and 16 %) improved the system quality of natural pasture, while at the lowest allowance rate (4 %) the system lost quality and sustainability, as demonstrated by the substantial reduction of this index.

Produtividade de soja e milho após coberturas de inverno e descompactação mecânica do solo

The objective of this work was to evaluate the effect of soil winter covers and soil mechanical loosening on soybean and corn yield, in no-tillage system. Two experiments were carried oud in Rio Grande do Sul state, Brazil, in a compacted Argissolo Vermelho (Haplic Acrisol), in the 2005/2006 and 2006/2007 crop seasons. The first experiment was carried out in a complete block design, with a split plot arrangement. The treatments were two theoretical working depths of a driller chisel-type furrow opener (0.06 and 0.12 m, split plot), and three soil winter covers (main plot): fallow, black oat (Avena strigosa), and black oat+common vetch (Vicia sativa). In 2006, the soil cover black oat+common vetch was replaced by oilseed radish (Raphanus sativus). In the second experiment, in a complete block design, the soil was chiseled and treatments consisted of black oat or oilseed radish as winter cover crops. Cover crops reduced soil superficial (0-0,06 m) compaction compared to fallow and, in the 2005/2006-crop season, under low water availability, provided higher soybean and corn yields. In the 2006/2007-crop season, when water availability was higher, the same did not happen. Increasing working depths of the chisel-type furrow opener did not affect soybean or corn yields. Soil chiseling reduced soybean and corn yields in comparison to the continuous no-tillage system.

Capacidade de suporte e compressibilidade de um argissolo, influenciadas pelo tráfego e por plantas de cobertura de inverno

One of the most effective practices in preventing soil compaction is to apply stresses below the bearing capacity of the soil, often estimated by the pre-compression stress (σp). To evaluate the effects of cover crops and tractor traffic on σp and compression index (CI), a field experiment was initiated in 2002 on sandy clay loam Paleudult, in Southern Brazil (Rio Grande do Sul State). Treatments under no-tillage involved winter fallow and two winter cover crops (black oats and black oats + vetch, which was substituted in 2006 by oilseed radish - Raphanus sativus L.) in the plots and two traffic conditions (with and without wheel-tractor traffic) in the subplots. Undisturbed soil cores were sampled in June and November 2006 to determine soil physical properties as well as σp and CI by uniaxial compression tests in an oedometer. Before oedometer tests, soil cores were equilibrated at different water tensions. Regardless of time and traffic conditions, winter fallow showed the highest σp value and the lowest CI value at 0.03-0.06 m. As the soil became drier, differences in σp between winter fallow and cover crops were reduced. In five years, seven wheel-tractor passages increased σp only in the surface layer (0.03-0.06 m), without altering CI. The use of cover crops and absence of traffic reduced the soil bearing capacity and increased soil susceptibility to compaction due to the reduction in soil bulk density and increase of macropores.

Resistência mecânica do solo e força de tração em hastes sulcadoras de semeadoras-adubadoras em sistema de integração lavoura-pecuária

A integracao lavoura-pecuaria, realizada mediante a implantacao de pastagens no inverno e a semeadura de milho ou soja no verao, constitui-se numa alternativa para a diversificacao de atividades e ampliacao dos lucros. Animais em pastejo, principalmente em areas agricolas manejadas sob semeadura direta, podem resultar na compactacao adicional do solo, diagnosticada geralmente pelo aumento de resistencia do solo a penetracao (RP). Com o objetivo de avaliar a correlacao entre RP e forca de tracao (FT) medida em hastes sulcadoras de semeadoras-adubadoras, nos anos de 2004 e 2005, foi conduzido um experimento em Sao Miguel das Missoes - RS, em Latossolo Vermelho (0.540 kg kg-1 de argila). Os tratamentos consistiram em quatro intensidades de pastejo, que resultaram em alturas de pastagem de 10; 20; 30 e 40 cm, e de testemunha sem pastejo, organizados em DBC, com tres repeticoes. Avaliou-se a RP, no final do periodo de pastejo, e na semeadura da soja, obteve-se a FT exigida nas hastes sulcadoras de semeadoras-adubadoras. A RP e a FT aumentaram com o incremento na intensidade de pastejo. A correlacao entre essas variaveis foi significativa, comprovando que e possivel avaliar o estado de compactacao do solo por meio da medicao da FT requerida pelas hastes sulcadoras de semeadoras-adubadoras.

Demanda de tração, mobilização de solo na linha de semeadura e rendimento da soja, em plantio direto

The objective of this work was to evaluate the relationship between the draft power (FT) in the fertilizer furrow-opener and the volume of mobilized soil in the sowing line as affected by the amount of residues, tractor traffic and furrow‑opening working depth, and its influence on soybean agronomic performance. Treatments consisted of six residue dosages (DR), two fertilizer furrow‑opener working depths (PT) and two soil traffic conditions - with and without tractor traffic - carried out in a randomized block design, in a split‑split‑plot scheme. The treatments were applied with or without irrigation under no-tillage on a Rhodic Paleudult soil. The different PT and tractor traffic conditions influenced FT significantly. Regardless of the irrigation conditions, DR treatments did not affect soybean grain yield and shoot dry matter weight. In the absence of irrigation, soybean productivity increased by 180 kg ha -1 when PT was changed from 0,064 to 0,10 m, which indicates fertilizer furrow-opener at greater depths as a viable practice to decrease the effects of drought on crop.