Future land utilization and management for sustainable crop production

Soil cultivation caused a great change in the ecological state, from a situation with the soil surface protected by vegetation to a situation with bare soil exposed to climatic forces during part of the year. Annual crops require annual soil cultivation, and the increased mineralization of organic matter and the loss of soil productivity by erosion, leaching and other degradation processes remain a problem for sustainable food production. The challenge for the future is to manage the agricultural landscape in units which are catchments. These units would contain intensively drained and cultivated areas, permanent vegetation zones, as well as natural and constructed wetlands working as condensors and self-purifying units. The management would be differentiated according to a land suitability approach with intensity of use based on productivity and requirements for maintenance of environmental quality.     

Simulation of flow patterns and ion-exchange in soil percolation experiments

An increased understanding of ion-exchange processes in raw-humus was obtained by simulations using quantitative mathematical models. The work is based on a series of percolation experiments with a water flow of about 1 mm min^?1 through raw-humus samples of 4 cm thickness. For the input solutions consisting of 10^?3 N H₂SO₄, HNO₃, HCl and NaCl the results indicate that cation-exchange reactions are the most important processes for the chemical composition of the run-off. Since a large part of the water flows quickly through the soil, both the water residence time and the ion-exchange kinetics must be taken into account. As a basis for the chemical model, a hydrologic sub-model reproducing the residence time distribution of the flow in the soil is used. Considering the ions H⁺, M⁺ (monovalent metal ions) and M²⁺ (divalent metal ions), four different chemical models were tried but only one of them gave satisfactory agreement with the experimental results. This model has 5 independent parameters and consists of first and second order chemical processes.