Performance of soil condition indicators across taxonomic groups and land uses

Information on soil conditions in New Zealand is needed to assess soil quality at a national scale. We tested a standard set of 16 primary indicators at 29 sites (0-10 cm depth) across nine soil great groups with matched examples of indigenous forest, plantation forest, pastures, and crops. Soils under indigenous forest were acidic (pH 5.55.7), low in Olsen P (5-14 mu g cm(-3)), with high microbial C (814-1228 mu g. cm(-3)), respiration (1.1-1.4 mu g C cm(-3) h(-1)), total C (31.8-52.9 mg cm(-3)), macroporosity (9.6-11.7% v/v), and total available water (29.2-31.5% v/v). Plantation forest soils had generally similar characteristics. Pasture soils were less acidic (pH 5.3-6.9) than forest soils, but with more available P (5.5-43.0 mu g cm(-3)), higher total C (30.7-141.5 mg cm-3), total N (2.7-9.0 mg cm(-3)), and mineralizable N (68-175 mu g cm(-3)). The physical condition was similar to forest soils. Cropped soil had low total C (20-34 mg cm(-3)), microbial C (160-956 mu g cm(-3)), respiration (0.29-1.33 mu g C cm(-3) h(-1)), and total available water (6.7-30.1% v/v), but high pH (5.8-7.2), Olsen P (11.2-199 mu g cm-3), and hulk density (0.96-1.3 g cm(-3)). Principal component analysis identified outlier sites and grouped land uses independently of soil great groups. Some indicators were less useful because of high variability (unsaturated hydraulic conductivity), correlation to other indicators (microbial C) or interpretation difficulties (respiration). Overall, the standardized approach provided useful information about soil conditions on a national scale.