Corte e trituração da capoeira no preparo de área para o estabelecimento e desempenho de pastagens em Igarapé-Açu, estado do Pará

Abstract

In the Eastern Amazon, the traditional land preparation procedure for planting crops and pasture is the slash-and-burn of vegetation. Besides being fast and cheep, slash-andburn procedure prepares the land for planting, but allows large lost of nutrients by the processes of volatilization, leaching and soil erosion. The slash-and-trituration of vegetation procedure, that does not need the use of fire, has the advantage of conserving and enriching the soil by the effect of organic matter. This study evaluated the slash-and-trituration method as an alternative to the slash-and-burn for land preparation in the establishment and performance of pasture in Igarapé-Açu, state of Pará. The Chapter 1 (Slash-and-trituration of capoeira in land preparation for pasture establishment and performance in Igarapé-Açu, state of Pará) is about the contextualization of the following study. In Chapter 2 (Evaluation of forage grasses and legumes established with slash-and-trituration of capoeira in Igarapé-Açu, state of Pará), 20 forage grasses and legumes were evaluated objecting to select forage species to be established with slash-and-trituration of capoeira. It was used a split-split plot completely randomized design, with three replications. The forage species were allocated in the plot, the fertilization in the split and the harvest in the split-plot plots. In Chapter 3 (Slashand-trituration versus slash-and-burn of capoeira in land preparation for planting in IgarapéAçu, state of Pará: Establishment and utilization of pasture) and in Chapter 4 (Slash-andtrituration versus slash-and-burn of capoeira in land preparation for planting in Igarapé-Açu, state of Pará: Pasture quality and weight gain of bovines), those two practices of land preparation were compared in the performance of pasture and in animal production. In the Chapters 3 and 4, the practices were implanted on two main plots of a 12-year capoeira. In the slash-and-burn main plot, the vegetation was slashed manually and, after three weeks, was burn, whereas in that of slash-and-trituration, the vegetation was triturated and spread over the land by a AHWI FM 600 machine. It was used a randomized block experimental design, with three replications and two pasture types: BQ = Brachiaria brizantha cv. Marandu + B. humidicola cv. Quicuio-da-amazônia, and BQA = B. brizantha cv. Marandu + B. humidicola cv. Quicuio-da-amazônia + Arachis pintoi cv. Amarillo. Three groups of steers grazed the experimental units, one group the three replications of BQ pasture and two groups the six replication of BQA pasture, in a rotational grazing system, with 18 days of grazing period and 36 days of rest, under a stock rate range of 1.2 to 2.2 animal unit per hectare. The pasture was evaluated each 36 days and the animal weighted each 54 days. In Chapter 2, the more promising forage species were: Grasses - Pennisetum purpureum cv. Napier, Panicum maximum BRA 6645, P. purpureum cv. Cameron, P. maximum cv. Mombaça e Brachiaria humidicola cv. Quicuio-da-amazônia (seedlings), and Legumes - Leucaena leucocephala BRA 002236, L. leucocephala BRA 002336 and Arachis pintoi cv. Amarillo. Regarding the Chapters 3 and 4, in establishment phase, advantage of the slash-and-trituration over the slash-and-burn was in increasing the soil cover what reduce the weed infestation, and probably, in soil conservation. In the utilization phase, the advantage was in improving the fertility, microbial carbon and humidity of the soil, possibly due to the effect of organic matter. The reduction of weed growth, favored the increasing of forage mass and the decreasing the bare ground. Also, the slash-and-trituration increased the nutritional level of pasture by the same effects in the soil. However, this practice only improved the weight gain per animal in the dry season of the first year of pasture utilization, and the total weight gain, in the two first years. However, the adoption potential of slash-and-trituration practice in the animal production systems of the region will depend on an economic evaluation. It is concluded that the slash-and-trituration practice can substitute satisfactorily the slash-andburn in the animal production in Igarapé-Açu – PA. As an environmentally sound practice xv which requires large investments in equipments, its dissemination among local producers will depend on public polices that stimulate it and compensate their environmental services.