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

Marton (Argillic Perched-gley Pallic, Typic Endoaqualf), Ohakune (Typic Ort hic Allophanic, Typic Hapludand), and Westmere (Mottled Mafic Melanic, Moll ic Hapludalf) soils with differing structural vulnerability were compared a t matched sites under different land uses. Topsoil samples (0-10 cm) from i ndigenous 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, d espite their differing mineralogy. However, the biological properties of re spiration, microbial C, and mineralisable N were generally significantly lo wer under arable cropping and pine plantations compared with pastures and i ndigenous forest. Within each soil type, land use caused significant but va rying effects on soil properties. There was considerable decline in the phy sical condition of the Ohakune topsoil under arable cropping despite the ve ry low vulnerability rating. The findings suggest that the degradative pres sures caused by cropping for carrots on Ohakune soil were considerably grea ter than those of cereal cropping on Marton and Westmere soils. Deteriorati ng soil physical structure is likely to be the main limitation to continued arable cropping on Marton and Ohakune soils.