ABSTRACT
The interrelationships between climate, soil and plant have in simplified form been combined in the model WATCROS (WATer balance and CROp production Simulation). The evapotranspiration is based on the Penman or the Makkink equation. Plant development is based on temperature sum. Gross and net plant production are predicted from efficiency of absorbed photosynthetic active light and plant respiration, based on crop species, crop mass and temperature.
Of the climatic factors global radiation, air temperature and precipitation, the latter is the variable which changes most with time and space. Therefore it is necessary to record precipitation locally and at ground surface. Critical parameters in the water balance are root growth, effective root depth and soil available water. In crop production the respiration is the most critical parameter.
In Denmark half of the agricultural land is sandy and need irrigation as the root zone capacity for available water is low. About 25% of the sandy soil is under sprinkler irrigation. On an average the actual crop yield is, depending on soil and region, 40 to 55% of the potential yield. Of winter wheat e.g. the potential yield is 10–13 t grain/ha (15% water).
