» show abstract Detailed and reliable information on land use systems, as needed for quantitative studies, is scarce and often of low quality. This calls for (guidelines on) data harmonization. Practical concepts to describe and study land use are discussed; the development of the Land Use Database software was instrumental in defining them. Required is that by plot, information on land use purpose(s), on operations and on observations as made by land users is put on record through interviews. To classify land use, three types of classifiers are available: purpose, operation sequence, and context classifiers; using them keeps the possibility to prepare user-defined classification systems open. Detailed land use descriptions augment Land Use Type (LUT) concepts presented by the FAO Guidelines for Land Evaluation. Biophysical LUT requirements emphasized in land evaluation studies are often crop requirements with management requirements predominantly of a socio-economic nature. The FAO guidelines make insufficient use of information on land use operations that are applied to overcome land aspects that limit yields or reduce production. Proposed is a procedure to evaluate practical technology options to remedy limiting conditions. Quantitative production functions are not standard output of land evaluation studies. Use of simulation models for quantitative studies is restricted because presently they can not capture the full dynamics of yield limiting and yield reducing factors and can not consider all management options. Many actual production situations face yield constraints that cause a considerable gap between actual yields and yield levels possible with improved technology. Yield gap studies are essential to identify the biophysical factors and cultural practices that cause the gap. Comparative Performance Analysis (CPA) is an approach to study yield-gaps; it defines quantified yield-gap functions. The key feature of CPA is to relate, after surveying on-farm production situations, differences in land and land use to differences in system performance. CPA complements established land use study methods. The Land Use Database supports it. Three CPA studies are included. The CPA study on rice identifies priority areas for development. It explains 83% of the yield variability across 63 sites. The CPA study on mango was undertaken to remedy the "trial and error" type of management practised in the study area. It identifies the relative importance of selected production factors, i.e. soil-related (30%), management-related (49%), and crop-related (21%). The CPA study on the impacts of land use on the environment evaluated the merits of four erosion indicators. The indicators could function as Land Quality Indicators to reflect soil loss over time. Pre-rills are promising as an indicator. Their occurrence gave the best correlation to management related site conditions. The relation prepared was not map unit specific and suggested that combined positive conditions reduce the formation of pre-rills exponentially.
