A study of the pattern of sulphur responses shown by dryland lucerne on some brown-grey earths

Field trials showing apparently anomalous lack of response to sulphur topdressing of dryland lucerne on brown-grey earths in the Maniototo basin, Central Otago, were followed up by soil studies. Soil analyses showed the presence of sulphate in the deeper layers (2 to 4 ft) of the non-responsive soils, but no such accumulations were present in the responsive soils. Sulphur concentrations in lucerne from the non-responsive soils were normal (0.19% S or greater), but lucerne from the responsive soils had lower sulphur levels (0.15 to 0.17% S). Conditions leading to the presence of sulphate in the subsoils are discussed and two situations are recognised: (a) the older brown-grey earths have accumulations of sulphate-bearing salts in the subsoil, often below the claypan; and (b) the lower horizons of the younger brown-grey earths are continually replenished with sulphate which is present in low concentrations in the ground water. The significance of the results in relation to fertiliser recommendations for dryland lucerne on brown-grey earths is discussed.