EFFECT OF FURROW ELEVATION DIFFERENCES ON LEVEL-BASIN PERFORMANCE

The uniformity of the water distribution on level basins is a function of inflow rate, basin length, infiltration characteristics, resistanc e to flow, spatial variability of soils, and, to a large extent, basin microtopography. The leveling precision attainable and the maintenanc e of this precision with various tillage implements are paramount to t he successful use of level basins. Both leveling and tillage inadequac ies were identified in research conducted on level basins in Portugal. The impact of these inadequacies on the performance of level basins, where basin-wide water distribution uniformity (DU) and crop yield (co rn was used in the example) were used as performance indicators, was e stimated by studying a distribution of level furrows with varying bed elevations within a basin, each receiving a different inflow rate depe nding on their relative elevations. The impact of laser-controlled lev eling was illustrated Sor three precision improvement scenarios used t o represent conditions in the United States and Portugal. The resultan t improvement in crop yield in response to improved water distribution for the leveling precision improvement scenarios ranged from 8 (i.e., typical U. S. conditions) to 22 percentage points (i.e., typical Port uguese conditions) which were about one-half to two-thirds the improve ment indicated by water distribution uniformity changes (i.e., 17 and 31 percentage points, respectively), These potential increases in prod uction and the associated income realized, weighted against the cost t o provide and maintain precisely leveled basins, can be used to guide decisions on leveling and the amount of effort to invest in precisely controlled tillage operations, Further, such an analysis can provide a basis for determining changes needed in the application of the techno logy (i.e., precision-controlled leveling and tillage operations) to j ustify its use.