STRUCTURAL VULNERABILITY OF NEW-ZEALAND SOILS

Some New Zealand soils withstand intensive cultivation and support con tinuing high production and yet maintain essential soil physical quali ties of infiltration, aggregation, and aeration. In other soils, essen tial soil qualities deteriorate rapidly under the impact of even moder ately intensive management practices. Our objective was to estimate th e inherent susceptibility of New Zealand soils to physical degradation by focusing on structural vulnerability. We took a deductive approach by reviewing the available information on the structural stability an d physical degradation of New Zealand soils. We identified 4 soil attr ibutes that are well represented in the national soils database and ar e most likely to control structural vulnerability: (i) stabilising sho rt-range-order oxy-hydroxides of aluminium and iron as estimated by ph osphate retention, (ii) total organic carbon content, (iii) clay conte nt, and (iv) wetness. The 4 attributes were standardised and transform ed and a simple structural vulnerability index (SV) was devised. We de termined SV for all mineral soils in the national soils database. The results provide a ranking of soil groups according to their structural vulnerability. We concluded that the index may be used as a first app roximation rating of the structural vulnerability of New Zealand soils to aid resource management.