Model simulation of water and nitrate movement in a level-basin under fertigation treatments

Simulation models, once validated for local conditions, can play an important role in predicting the distribution patterns of yield factors and thus help the farmer with decisions on management practices. Results from a soil water and NO3-N concentration analysis are presented describing their behaviour under irrigation by temporary flooding (level basin). The data was used for validation of Opus model simulation of water movement and nitrate-nitrogen transport through the soil, The study was conducted in an alluvial soil located in the Sorraia River irrigation Project in Southern Portugal. Experimental observations were made in 1993 during the last two from a total of three fertigations conducted in a level basin planted with corn. In each fertigation an average of 85 mm of water and 50 kgha(-1) N was applied. An initial soil sampling described the physical, hydrodynamic and chemical character of the soil profile at the beginning of the experimental season. The saturated hydraulic conductivity was estimated from soil physical characteristics and water profile matching. Later sampling permitted definition of a water and NO3-N distribution pattern along the length of the field and confirmed that the NO3-N fate and transport is highly dependent on the soil water content and its movement. The Opus model was quite satisfactorily validated for the experimental conditions. Spatial variability in the soil physical characteristics was observed, as expected, causing scatter in model predictions, since the soil characteristics were estimated from just one of the seven monitored soil profiles. (C) 1997 Elsevier Science B.V.