The use of low-rate sprinkler application systems for applying farm dairy effluent to land to reduce contaminant transfers

Abstract

Runoff of farm dairy effluent (FDE) is a major concern in New Zealand water management. To improve handling and applying FDE, this work evaluated the performance of a low-rate (K-line) sprinkler application system compared with that of a travelling irrigator. The volumes of FDE discharged in either mole-pipe drainage or overland flow were monitored at two sites, as were nutrient concentrations and loads (and Escherichia coli (E. coli) at one site). The low-rate sprinkler decreased overland flow losses of applied FDE compared to the travelling irrigator. The relative concentrations of E. coli, total P and ammonium-N (presented as C/C o, the measured concentration in drain flow divided by the concentration in applied effluent) in overland flow at South Otago and mole-pipe drainage at West Otago were also consistently less for the low-rate sprinkler. There were significant and positive correlations between drainage C/C o values and effluent application rate for E. coli, total P and turbidity. Modelling predicted potentially large contamination with E. coli, total P and ammonium-N in mole-pipe drainage with no pond storage when using a travelling irrigator. Modelled loads were considerably less for FDE application to mole-pipe drained land using a low-rate sprinkler. Practical implications are that: (i) effluent pond storage is important for decreasing FDE losses in overland flow and mole-pipe drainage when soils are wet; (ii) a low-rate sprinkler application system requires less pond storage; (iii) a low-rate low-depth management system can decrease mole-pipe drainage discharges of pollutants when soils are wet.