Effects of fertiliser application on nutrient status and organic matter content of hill soils

Abstract

Effects of two fertiliser treatments on soil characteristics were measured during 1972–87, within 10 grazed permanent‐pasture “farmlets”, on steep hill country in southern Hawke's Bay, New Zealand. The low fertiliser (LF) treatment received 125 kg ha‐1 superphosphate p.a., and the high fertiliser (HF) an average 625 kg ha‐1 p.a. for 5 years then 375 kg ha‐1 p.a. subsequently. Ground limestone was applied to HF in 1975 and 1979. Grazing pressure was the same across treatments. Soil fertility decreased with increasing slope of measurement site, and aspect had a less marked effect. Phosphorus initially accumulated mainly in inorganic forms, with organic P accumulating at a slower rate similar to that for organic S. Olsen P status reflected P application regime, although the responsiveness was lower than anticipated. Soil pH in the non‐limed LF treatment increased slightly over time, probably as a consequence of the decline in soil organic C. Soil total N (0–75 mm depth) remained constant in LF, but increased by 19 kg ha‐1 yr‐1 in HF soils. Soil carbon decreased in LF and HF by 200 kg C ha‐1 yr‐1 This suggests that soil organic matter may be decreasing in some New Zealand pastoral environments.