Microbial biomass and soil chemical properties under different land use systems in northeastern Pará

Elessandra Laura Nogueira Lopes,Gladys Ferreira De Souza,José Henrique Cattanio,Maria De Lourdes Pinheiro Ruivo,Antonio Rodrigues Fernandes

doi:10.1590/s0100-06832011000400006

Elessandra Laura Nogueira Lopes, Gladys Ferreira De Souza + Show 3 more

Open Access

https://doi.org/10.1590/s0100-06832011000400006

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Abstract

The increase in agricultural production in the Brazilian Amazon region is mostly a result of the agricultural frontier expansion, into areas previously influenced by humans or of native vegetation. At the same time, burning is still used to clear areas in small-scale agricultural systems, leading to a loss of the soil productive capacity shortly after, forcing the opening of new areas. This study had the objective of evaluating the effect of soil preparation methods that involve plant residue shredding, left on the surface or incorporated to the soil, with or without chemical fertilization, on the soil chemical and biological properties. The experiment was conducted in 1995, in an experimental field of Yellow Latosol (Oxisol) of the Embrapa Amazônia Oriental, northeastern Pará (Brazil). The experiment was arranged in randomized blocks, in a 2x6 factorial design, with two management systems and six treatments evaluated twice. The management systems consisted of rice (Oriza sativa), followed by cowpea (Vigna unguiculata) with manioc (Manihot esculenta). In the first system the crops were planted in two consecutive cycles, followed by a three-year fallow period (natural regrowth); the second system consisted of one cultivation cycle and was left fallow for three years. The following treatments were applied to the secondary forest vegetation: slash and burn, fertilized with NPK (Q+NPK); slash and burn, without fertilizer NPK (Q-NPK); cutting and shredding, leaving the residues on the soil surface, fertilized with NPK (C+NPK); cutting and shredding, leaving residues on the soil surface, without fertilizer (C-NPK); cutting and shredding, with residue incorporation and fertilized with NPK (I+NPK); cutting and shredding, with residue incorporation and without NPK fertilizer (I-NPK). The soil was sampled in the rainier season (April 2006) and in the drier season (September 2006), in the 0-0.1 m layer. From each plot, 10 simple samples were collected in order to generate a composite sample. In the more intensive management system the contents of microbial C (Cmic) and microbial N (Nmic) were higher, while the C (Corg) level was higher in the less intensive system. The treatments with highest Cmic and Nmic levels were those with cutting, shredding and distribution of biomass on the soil surface. Under both management systems, the chemical characteristics were in ranges that classify the soil as little fertile, although P and K (in the rainy season) were higher in the less intensive management system.

Highlights

The need to increase agricultural production in Brazil to meet the growing food demand has resulted, inevitably, in an expansion of the agricultural frontier into anthropic or native forest areas
In the less rainy period, the contents of microbial C (Cmic) content in management system II (MS II) was lower in all treatments except in com adubação NPK (C+NPK) and C-NPK
When treatments were compared within the management systems, the Cmic level in management system I (MS I) in treatment NPK and C+NPK was low, even differing from or even lower than that with burning without NPK in the dry season (Figure 1)

Summary

Introduction

The need to increase agricultural production in Brazil to meet the growing food demand has resulted, inevitably, in an expansion of the agricultural frontier into anthropic or native forest areas. Inappropriate farming practices, such as the use of fire and non-use of conservation techniques has triggered an accelerated degradation of soils in the Amazon. The burning of vegetation as a way of preparing the area for planting has been condemned in view of the nutrient losses, environmental degradation, gradual loss of biodiversity, greenhouse gas emissions into the atmosphere, increased soil erosion, changes in the hydrological and biogeochemical cycle and risks of accidental fires (Ruivo et al, 2007). The absence of management practices to reduce or avoid burning has reduced the period of agricultural exploitation to less than 10 years (Metzger, 2000)

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