Nitrogen dynamics in forestry and grassland soils in the Amazon region - A review

The main economical land use in the Amazon since the 1970s has been as cattle pastures, which are largely the result of widespread deforestation. Estimates indicate that approximately 120,000 km(2) of pastures show some degree of degradation, which will require the opening up of new areas of forest. The authors' conclusions are as follows: (1) The quality of organic matter in the forage grasses modifies N cycling in relation to that originally present in forest soils. (2) In cases where N availability in the soil is not limited to the soil microbiological processes, other soil parameters, such as humidity, start to control N2O fluxes to the atmosphere. (3) Tillage and fertilization induce higher nitrate availability in the short term, but this could be synchronized with plant uptake, which would lead to fewer losses from leaching, plus soil denitrification rates would also decrease and would not support N loss in gaseous form. Any degraded pasture recovery strategy that affects available soil N content will also indirectly influence atmospheric N2O flux. When N availability is not a limitation to soil biological processes, water content changes and other soil properties become important N2O flux controllers. (4) If these conditions are acknowledged, there can be a higher level of sustainability and more effective development of the system and productivity can be achieved.