Leaching losses of major nutrients from a mole-drained soil under pasture

The concentrations of chloride (Cl⁻), sulphate (SO₄²⁻), nitrate (NO₃⁻), potassium (K⁺), magnesium (Mg²⁺), calcium (Ca²⁺), and sodium (Na⁺) in mole-tile drainage and the quantity of drainage from two 0.125 ha paddocks were measured over 2 years. The soil, a Typic Fragiaqualf, was under pasture periodically grazed by sheep. In the autumn of both years, potassium chloride (KC1) was applied to both paddocks and sulphur (S) as either superphosphate or elemental S, supplying equal amounts of S, was also applied. Cl⁻was the dominant anion in the drainage, with losses totalling c. 100 kg/ha per yr. The leaching loss of SO₄²⁻was c. 13 kg S/ha per yr from the paddock fertilised with superphosphate compared with 3 kg/ha per yr from the elemental S-fertilised paddock. Less than 20 kg N/ha per yr was leached which is less than other workers have found under cattle-grazed pasture. Losses of K⁺were less than 11 kg/ha per yr but losses of Na⁺of up to 65 kg/ha per yr were found. Losses of Ca²⁺and Mg²⁺were of the order of 40 and 10 kg/ha per yr, respectively. There was a close agreement between the moles of charge of inorganic anions and cations in the drainage water.