Submitted to: World Congress of Soil Science
Publication Type: Proceedings
Publication Acceptance Date: 11/15/2002
Publication Date: 12/31/2002
Citation: STOTT, D.E., GREEN, V.S. SOIL BIOCHEMICAL AND STRUCTURAL CHARACTERISTICS IN NATIVE AND TILLED BRAZILIAN CERRADO SOILS. CD-ROM. BANGKOK, THAILAND: WORLD CONGRESS OF SOIL SCIENCE. 2002. Interpretive Summary:
Technical Abstract: The Brazilian Cerrado is one of the last remaining agricultural frontiers and is undergoing a rapid increase in capital-intensive agricultural development. Soil quality in the Cerrado region is a pressing issue due to the inherent low fertility of these soils. There is limited knowledge on the baseline soil quality of these soils under native vegetation, especially with regard to the biochemical properties, and how the parameters shift under agricultural management. Soil enzymes are involved in nutrient cycling processes and are indicative of the general biological activity of the soil. Enzyme activities are sensitive to soil management and often show signs of soil degradation well before other physical and chemical indicators. Our objective was to survey the baseline soil biochemical indicators of several Cerrado soils. For comparison, we studied the impact of different tillage practices on a dark red Latosol, an important agricultural soil in the region. We hypothesized that soils managed with tillage systems would have lower biological activity than soils under native vegetation, and that among the managed soils, no-till soils would have the highest biological activity and organic C content, but it would be concentrated in the surface layer. Soil samples were obtained from tilled plots along with an area under native vegetation located at the EMBRAPA research facility located at Sete Lagoas, Minas Gerais. Samples were collected in April 1998. Soil was sampled at 3 different depths: 0-5, 5-20, and 20-30 cm, as these were natural horizon breaks in the profile under native vegetation and under no-till management; no visible distinction could be made between the 0-5 and 5-20 cm depths in the tilled systems. The 0-5 cm depth is rich in organic matter; the 5-20 cm depth is the layer where the majority of root growth is taking place; the 20-30 cm depth is just below the primary root zone. Soil samples were gently sieved to pass a 2.0 mm sieve and air-dried. Additionally, soil bulk density was measured at the top of each sampling layer. Five soil enzyme analyses were performed: â-glucosidase, acid phosphatase, and arylsulfatase, arylamidase, and fluorescein diacetate hydrolysis. Physical measurements included antecedent moisture, aggregate stability and surface sealing potential. Initial analyses indicated that as organic C decreased under tillage, biochemical activity also decreased. Benchmark soil quality levels were established for these sites. When managed, the no-till soils maintained the highest activities, followed by the disk harrow system, with the disk plow system having generally lower activities. These results indicate that tillage regimes that are less aggressive maintain higher biological activity than aggressive tillage operations in these tropical Cerrado soils. Soil organic carbon levels followed the same general pattern as the enzymatic activities. At most sites, the increase in biological activity and organic C translated into an increased aggregate stability and a lower tendency to develop a surface seal. In these tropical soils, a no-till management system is likely to be more sustainable due to the influence of soil biological activity in nutrient cycling and aggregate stabilization.