The influence of dairy factory effluents on soil and plant composition

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Abstract
Effluents from seven dairy factories were analysed for 21 elements. The major elements, calcium, potassium, and phosphorus, had a fivefold range of values in the ashed effluent, while the trace elements differed by up to 1,000-fold. Certain element levels, e.g., copper, could be related to the soils of the area. Irrigation with these effluents raised the exchangeable potassium, sodium, and calcium levels in topsoils and gave high values for available phosphorus. Magnesium levels did not increase in proportion to the other bases. Pastures from 18 areas that had been irrigated with effluents were analysed for 23 elements and compared with those from non-irrigated areas. Of these elements 21 showed the same trends on irrigation for both ryegrass and for white clover. The results for white clover were more significant than those for ryegrass for every element except boron. Irrigation of white clover gave significant increases in the levels of nitrogen, potassium, sulphur, chlorine, and manganese, but gave slight decreases in zinc, copper, boron, and magnesium. The absence of significant gains in the levels of phosphorus in clover and in ryegrass indicated that the supply of nitrogen and potassium exceeded that of phosphorus. These effluents, being rich in nitrogen, could provide a useful fertiliser for zero grazing agriculture.

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