Structural vulnerability of New Zealand soils

Abstract

Some New Zealand soils withstand intensive cultivation and support continuing high production and yet maintain essential soil physical qualities of infiltration, aggregation, and aeration. In other soils, essential soil qualities deteriorate rapidly under the impact of even moderately intensive management practices. Our objective was to estimate the 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 and physical degradation of New Zealand soils. We identified 4 soil attributes that are well represented in the national soils database and are most likely to control structural vulnerability: (i) stabilising short-range-order oxy-hydroxides of aluminium and iron as estimated by phosphate retention, (ii) total organic carbon content, (iii) clay content, and (iv) wetness. The 4 attributes were standardised and transformed and a simple structural vulnerability index (SV) was devised. We determined 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 approximation rating of the structural vulnerability of New Zealand soils to aid resource management.