Quantity and Quality Variations in Subsurface Drainage

ABSTRACT FIFTEEN parallel drains, spaced at 37 m and servicing an overlying area of 180,000 m2, were monitored for quality and quantity evaluation of subsurface drainage. Of interest were spatial and temporal variations in drainage and whether such variations were induced by changes in water management. Spring wheat was grown in 1979, winter wheat in 1980, and alfalfa in 1981. Irrigation methods included flooding and sprinkling. In the first two years TDS vs. EC, TDS vs. Na, and TDS vs. CI were statistically significant in simple regression tests. Mean annual values of all drains combined showed significant differences between 1979 and 1980 in the case of concentrations of CO3, turbidity, TSS, and Kjedlahl-N. Only TSS and Kjeldahl-N were significantly different for loading rates. Spatial variations were very pronounced; each parameter produced a different spatial pattern for annual mean values. Data from 1981 were used to demonstrate temporal variability. Management effects could not be separated from natural effects of the soil.