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Abstract
This case study examines the effects of 6 years of farm dairy effluent (FDE) irrigation on the upper 40 cm of a Greytown silt loam, Wairarapa, New Zealand. Physical and chemical soil properties were measured, i.e., particle size distribution, porosity, dry bulk density, field‐saturated hydraulic conductivity, total carbon, total Kjeldahl nitrogen, pH, total and Olsen phosphorus, cation exchange capacity, and concentrations of exchangeable cations (K+, Na+, Ca2+, Mg2+). While the concentrations of total carbon and total Kjeldahl nitrogen were generally low at all depths, the application of effluent has caused a significant increase in their concentrations in the upper 10 cm of the profile. The concentration of exchangeable cations has been similarly increased in the upper 10 cm of the profile. The soil has very low phosphorus retention, however effluent application has increased both total and Olsen phosphorus to 40 cm depth. Most of the changes in soil properties have led us to believe that current application rates and pasture production can be maintained and that FDE application has improved the soil's long‐term fertility or “soil quality”, especially in the upper 10 cm of the profile. However, there is no evidence to suggest that current application rates are sustainable in terms of other environmental effects (e.g., nitrate leaching).
