Elevation and infiltration in a level basin. II. Impact on soil water and corn yield

The spatial variability of irrigation water recharge and crop yield is affe cted by a number of factors. Soil surface elevation, infiltration and soil water MAD are the most relevant related to level-basin irrigation. Measurem ents of soil water recharge (using a neutron probe) were compared to estima tes based on ring infiltrometers and observations of the opportunity time. Estimates of cumulative infiltration (ECI) were obtained, separating the va riability of infiltration and opportunity time (largely determined by eleva tion). Soil surface elevation was correlated with measured recharge, grain yield and total dry matter. A correlation was found between infiltration an d the measurements of water recharge. While soil surface elevation can be r egarded as a management variable, little can be done to reduce the variabil ity of infiltration. Distribution uniformities from ECI were about 20% high er than those obtained from measurements of water recharge. Seasonal unifor mity was only marginally higher than average uniformity, confirming the low random component of water recharge in level-basin irrigation. Deep percola tion was more intense in areas with low MAD. This finding emphasizes the re levance of characterizing the variability of soil physical properties in su rface irrigation. Extrapolation of the results of this research to field-sc ale irrigation basins should take into account the methodology used: in par ticular, the reduced scale of the experimental level basin.