Paulo César de Faccio Carvalho

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.

Atributos físicos do solo e rendimento de soja em sistema plantio direto em integração lavoura-pecuária com diferentes pressões de pastejo

The integration of farming and cattle production activities in no-tillage system areas with winter cover crops can be an income supplement for summer grain farmers. However, many of them are afraid of adopting this integration system, because of possible negative effects of animal treading on soil attributes, mainly of those related to soil compaction. This study was conducted: (1) to determine the alterations in the soil physical attributes promoted by animal treading; (2) to verify if the alterations in soil attributes due to animal treading affect soybean establishment and grain yield. The experiment was carried out with a Rhodic Hapludox (Oxisol), under black oat + ryegrass pasture grazed at different heights (10, 20, 30 and 40 cm) and an ungrazed area. After one cycle of animal treading there were no significant modifications in soil bulk density, porosity and compressibility at different grazing heights. However, soil density and compressibility were higher and the porosity lower in the grazed plots. The soybean population and grain yield were not affected by modifications in the soil physical attributes.

Leaf Traits as Functional Descriptors of the Intensity of Continuous Grazing in Native Grasslands in the South of Brazil

Abstract Plant functional types (PFT) have been used to describe the response of native vegetation to environmental factors (i.e., fertility) and to livestock disturbance, but rarely under conditions of continuous grazing. In this work we investigate whether the long-term response of grassland communities submitted to a gradient of continuous grazing pressure can be described with such an approach. After 15 yr of differentiation of the grazing pressure applied to native grasslands we measured leaf dry-matter content (LDMC) and specific leaf area (SLA) of Poaceae populations of the communities. A grazing pressure gradient was created by levels of daily forage allowance: 4, 8, 12, and 16 kg of dry matter per day per 100 kg of animal live weight, monitored monthly. PFTs were defined by numerical analysis, where an algorithm finds the optimal trait subset based on the agreement between matrices of species × traits, paddocks × grass biomass, and environmental variables (levels of forage allowance and soil characteristics). The results show that it is possible to describe a gradient of grazing pressure by means of LDMC and/or SLA measured only on the Poacea contributing at least 80% of the total Poaceae biomass. Four PFTs were differentiated by these leaf traits. PFTs having low LDMC and high SLA are characteristic of high intensity of use and are made up largely of stoloniferous C4 species typical of rapid resource capture strategies. Conversely, PFTs characterized by high LDMC and low SLA include species that are representative of low grazing pressure. Variations in the aggregate value of traits are due to changes in the species proportions and not to leaf-size adaptation as hypothesized. We conclude than in the absence of a gradient of fertility, plants with strategies of resource capture tend to be more represented under high grazing pressures. This situation results in a loss of functional diversity, but in particular a reduction in forage availability, which is incompatible with high animal production.

Produção animal e de forragem em pastagem nativa submetida a distintas ofertas de forragem

This trial was conducted in natural pasture area of the Agronomic Experimental Station of Universidade Federal do Rio Grande do Sul (Porto Alegre-RS), from 10/25/2000 to 09/13/2001, with the objective of evaluating the treatments: 8%, 12%, 16% of dry matter allowance (DMA) over the year, 8% of DMA at spring and 12% at summer, autumn and winter (8-12%); 12% of DMA at spring and 8% at summer, autumn and winter (12-8%) e 16% of DMA at spring and 12% at summer, autumn and winter (16-12%), using steers on continuous grazing with variable stocking rate. The experimental design used was blocks randomised with two replications. The biggest average daily weight gain over the year (0.466 kg/an/day) was obtained in the increased DMA treatment. This treatment, also, was the only management the animals increased weight at winter. The animal production/ha was smaller in the 16% and 16-12% treatments. The DMA changing over the seasons, as a procedure to manipulate the vegetation structure and composition to increase forage production and average daily weight gain was efficient, and its effect upon the forage and animal production go on all the seasons.

Fluxo de biomassa em pastagem de azevém anual (Lolium multiflorum Lam.) manejada em diferentes alturas

In an italian ryegrass pasture under continuous stocking with sheep, biomass flows were estimated from 2 to 20 October 1999. Treatments corresponded to four different sward heights (5, 10, 15 and 20 cm) maintained by variable stocking. The experimental design was the randomized complete block design with three replicates. The fluxes were defined by morphogenetic and structural variables obtained from measurements performed on marked tillers. During the period in which the intended sward heights were established, significant effects in sward structure resulted in alterations on the biomass fluxes. The growth and intake fluxes showed a quadratic response with maximum values between 10 and 15 cm grazing heights, while the senescence flux increased linearly with sward height. Maximum daily live weight gain and animal yield per hectare were obtained within this interval, indicating this interval being the most appropriate to pasture management. The evaluation period was coincident with the floral induction phase, so the leaf lamina mass was progressively smaller and biomass fluxes showed a negative balance for all treatments.

Variáveis morfogênicas e estruturais de azevém anual (Lolium multiflorum Lam.) manejado em diferentes alturas

Morphogenetic and structural variables were obtained from measurements performed on marked tillers and were quantified during August to October 1999 in a ryegrass pasture grazed by sheep under continuous stocking and variable stocking rate in order to maintain the sward at four different heights (5, 10, 15 and 20 cm). The experimental design was a randomized complete block with three replicates. Fifty marked tillers per experimental unit were assessed and distributed along transects lines. Sward measurements were performed in two periods: the first one, from the start of grazing until the point where the intended grazing heights were established, with no differences among treatments. In the second (after achieving the intended grazing heights), leaf elongation rate, total green leaf lamina length per tiller and leaf size showed a positive response to increasing sward heights, while the time to leaf lamina elongation decreased. The variables leaf appearance rate and leaf life span, tiller population density and number of live leaves per tiller were not affected by treatments.

Ajuste da carga animal em experimentos de pastejo: uma nova proposta

The variation in available forage mass is frequently observed in grazing experiments, conducted with fixed forage allowance. For better forage mass control, a new method is proposed to adjust stocking rate, based on forage mass and forage allowance, dry matter (DM) accumulation rate, herbage intake rate, and forage susceptible to refusal and lost parameters. This method was used in Departamento de Zootecnia, UFSM, in a pearl millet grazing experiment with different nitrogen levels (0, 150, 300, 450 and 600kg ha-1), intending to maintain a forage DM mass close to 2500kg ha-1 during the experimental period. The DM accumulation rate was evaluated every 28 days in grazing exclusion cages. The forage susceptible to be refused, evaluated in fixed quadrats, represented 33 to 57% of forage mass, being dependent on nitrogen levels and stocking rate. The used method was efficient in maintaining the intended forage mass, indicating its potential use in experiments aiming better control of the variables involved in plant-animal interface.

Estoques de carbono orgânico e de nitrogênio no solo em sistema de integração lavoura-pecuária em plantio direto, submetido a intensidades de pastejo

Sistemas de integracao lavoura-pecuaria tem um alto potencial de uso no sul do pais, especialmente em areas de soja sob plantio direto, com especies de cobertura no inverno. A conducao de sistemas de integracao com diferentes intensidades de manejo da pastagem resultara, ao longo do tempo, em estoques de C orgânico (CO) e de N diferenciados, decorrentes do aporte diferenciado de residuos. Este trabalho foi realizado para avaliar a evolucao dos estoques de CO e de N total (NT) e em fracoes fisicas da materia orgânica em solo submetido a diferentes intensidades de pastejo, em plantio direto. O experimento foi iniciado em 2001, em um Latossolo Vermelho distrofico, apos a colheita da soja. Os tratamentos constaram de alturas de manejo da pastagem (aveia-preta + azevem): 10, 20 e 40 cm, com bovinos jovens, e sem pastejo, seguido do cultivo de soja, em delineamento de blocos ao acaso. Amostras de solo foram retiradas no inicio do experimento (maio 2001), apos tres anos (maio de 2004) e apos seis anos (maio de 2007), para a avaliacao dos teores e dos estoques de CO e de NT. Intensidades de pastejo moderadas (20 e 40 cm de altura do pasto) promoveram aumento nos estoques de CO total, CO particulado, NT e N na materia orgânica particulada no solo, semelhante ao plantio direto sem pastejo. Na alta intensidade de pastejo (10 cm), houve reducao no estoque desses elementos, com degradacao da qualidade da materia orgânica.

Carbono orgânico e fósforo microbiano em sistema de integração agricultura-pecuária submetido a diferentes intensidades de pastejo em plantio direto

Integrated crop-livestock systems have attracted more interest in the last few years due to their capacity of improving stability and sustainability of agricultural systems as compared to more specialized production systems. Soil organic carbon content has been used as an indicator of soil sustainability and stability. In this sense, this study aimed to measure the stocks of total organic carbon fractions and phosphorus in the microbial biomass in a Rhodic Hapludox (Oxisol) under integrated crop-livestock system with different grazing intensities in the winter. Soil samples were collected in November 2006 in Sao Miguel das Missoes, state of Rio Grande do Sul, Brazil. The experimental area had been cultivated under no-tillage for 10 years before implementing the integrated system in 2001. The experimental design was completely randomized blocks with three replicates. The treatments consisted of grazing intensities represented by sward heights of 10, 20 and 40 cm during the pasture cycle in winter. This pasture was composed of a black oat (Avena strigosa Schreb) and Italian ryegrass (Lolium multiflorum Lam.) mix, and a control area with no grazing. Total and particulate organic matter (POM) carbon stocks, phosphorus and carbon content in the microbial biomass, as well as microbial biomass activity were evaluated. The total organic stocks carbon were not affected by grazing intensities; however, the stocks of POM carbon were smaller in soils under the highest grazing intensity. The microbial biomass was stimulated at the highest grazing intensity, in which greater root growth was observed. The phosphorus content in the microbial biomass increased linearly with the decrease of the grazing intensity, while an inverse pattern was observed for the microbial biomass. Particulate organic matter carbon was more sensitive to changes in soil organic carbon under the experimental pasture management.

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.