Topsoil characteristics of three contrasting New Zealand soils under four long-term land uses

Marton (Argillic Perched-gley Pallic, Typic Endoaqualf), Ohakune (Typic Orthic Allophanic, Typic Hapludand), and Westmere (Mottled Mafic Melanic, Mollic Hapludalf) soils with differing structural vulnerability were compared at matched sites under different land uses. Topsoil samples (0-10 cm) from indigenous forest (>50 yr), permanent pasture (>50 yr), pine plantation (>20 yr), or arable cropping (>13 yr) sites were characterised using a range of 17 chemical, physical, and biological properties. Land-use effects masked overall differences in the physical and chemical properties of the soils, despite their differing mineralogy. However, the biological properties of respiration, microbial C, and mineralisable N were generally significantly lower under arable cropping and pine plantations compared with pastures and indigenous forest. Within each soil type, land use caused significant but varying effects on soil properties. There was A00014 Received 9 March 2000; accepted 11 August 2000 considerable decline in the physical condition of the Ohakune topsoil under arable cropping despite the very low vulnerability rating. The findings suggest that the degradative pressures caused by cropping for carrots on Ohakune soil were considerably greater than those of cereal cropping on Marton and Westmere soils. Deteriorating soil physical structure is likely to be the main limitation to continued arable cropping on Marton and Ohakune soils.