Land quality indicators of sustainable land management across scales

Existing definitions of "soil quality" and "sustainable land management" are analysed to derive a procedure for defining land quality (LQ) indicators of sustainable land management. Land--rather than soil qualities are considered to reflect the impact of the climate on soil behaviour. LQ is different for different types of land use and attention is arbitrarily confined here to agriculture. Simulation modelling of crop growth and solute fluxes is used to define LQ as the ratio between a conditioned crop yield and potential yield x 100. The actual agro-ecological condition and its potential, both expressed by LQ for a given piece of land, is considered here as independent input into broader landuse discussions which tend to be dominated by socioeconomic and political considerations. Agro-ecological considerations should not be held hostage to actual socio-economic and political considerations which may change in the near future while the LQ has a much more permanent character. The proposed LQ reflects yields, risks of production as simulations are made for many years, and soil and water quality associated with the production process. The latter are expressed here in an exploratory manner for seven tropical soils and in more detail for Dutch conditions in terms of the probability that groundwater is polluted with nitrates, reflecting the most dominant current LQ problem. The proposed procedure requires the selection of acceptable production and pollution risks by the user before a LQ value can be obtained. Existing definitions implicitly emphasise the field and farm level. However, LQ is also important at the regional and higher level which, so far, has received little attention. Then, again, an agro-ecological approach is suggested when defining the LQ as input into the planning process, emphasising not only an independent assessment of the potential for agricultural production, but also of nature conservation.