Saturday, 15 July 2006

Improvement of Low Fertility Soils (Oxisols) for High Productivity and Sustainability of Crop-Livestock Systems in Tropical Savannas of Colombia.

Edgar AMEZQUITA1, Idupulapati Rao2, Marco Rondon2, Edmundo Barrios2, Miguel Ayarza Sr.2, Phanor HOYOS1, and Diego Molina3. (1) Centro Internacional de Agricultura Tropical (CIAT), Apartado Aereo 6713, Cali, Colombia, (2) Tropical Soil Biology and Fertility Institute of the International Center for Tropical Agriculture, CIAT, Apartado Aereo 6713, Cali, Colombia, (3) Centro Internacional de Agricultura Tropical - CIAT, A.A. 6713, Cali, Colombia

The neotropical savannas (243 million hectares) in South America are one of the most rapidly expanding agricultural frontiers in the world. Oxisols predominate in the Colombian savannas and cover an area of 17 million hectares. Of this total area, 3.5 million hectares are known as “Altillanura”. Intensification of agricultural production in this agroecosystem requires aluminum tolerant crops, forage germplasm and improvement of soil physical, chemical and biological conditions. Monocropping systems with high levels of inputs and excessive cultivation (disc harrowing) are unsustainable since they cause deterioration of soil properties as well as escalation of pest and disease problems. The soils of this area are characterized by low pH values (4.0-4.8), high Al saturation (>90%), and low levels of nutrients (P, K, Ca and Mg). Additionally these soils are susceptible to degradation when submitted to agriculture and/or livestock production. This is a major edaphic limitation for profitable and sustainable crop-livestock production. Shallow tillage with disk harrow has caused problems of a physical nature, such as: surface sealing and crusting, high bulk density, compaction, low infiltration rates, low rainfall acceptance, high susceptibility to erosion, and high rates of runoff. To overcome these physical and low fertility constraints, the concept of building-up an arable layer is developed and tested. Arable layer is a surface layer of improved soil with minimum physical, chemical and biological constraints, to guarantee higher and stable crop and forage yields that are sustainable over time. The main purpose of building-up an arable layer is to improve and maintain physical and chemical conditions of the soil to favor root growth and thereby enhancing soil biological activity. In this study, we show the results of building-up a productive arable layer in two contrasting soil types (clay-loam and clay sandy loam) during a three-year period. A rigid chisel, for vertical soil preparation was used seeking to accomplish: (1) vertical loosening of the soil to achieve greater infiltration, higher water storage capacity and a more homogeneous distribution of amendments and nutrients with soil depth, and (2) to seek better physical stability of soil through the use of pastures with high root production, to avoid soil repacking and to maintain the favorable conditions for plant growth developed by vertical tillage. After three years of improvement, there were two to five-fold increases in infiltration rates, 13-21% increases in total porosity, 60-80% reductions in soil penetrability, 50-65% decreases in soil strength, and a 10-15% decrease in compaction. As a result of this integrated soil improvement, yields of maize increased from 3.7 t.ha-1 (first year) to 5.4 t.ha-1 (third year). Using this integrated soil management technology it was possible to improve profitability and sustainability of crop-livestock systems in the tropical savannas of Colombian. There is potential to extend this soil management technology to other infertile soils of tropical savannas.

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