Productivity Potentials of the Global Land Resource for Cropping and Grazing

The chapter gives an overview of global land potentials, crop yields and their limiting factors, and of methods to evaluate the productivity potential of land. Maintaining the capacity of the global land resource to produce plant biomass which can be used for humans is one of the most challenging issues of the 21st century. We need methodologies to observe and control the status of the potential productivity of agricultural and other lands. Methods of overall soil quality assessment which include the most significant factors and indicators relevant to soil productivity potentials can be useful tools for monitoring and managing the global soil resource sustainably. The aim was to find a common basis for soil productivity evaluation, as required by a global community of land users to allow achievement of high productivity in the context of a sustainable multifunctional use of landscapes. Results showed that soil types or reference groups in most existing soil classifications are largely defined on pedogenetic criteria and provide insufficient information to assess soil functionality. Traditional specific soil and land evaluation schemes already exist at national levels. They are based on different concepts of soil fertility or quality, local soil properties and the types of land use and management that prevail in the region or country. Their soil data inputs differ, ratings are not transferable and not applicable in transnational studies. At a transnational level, methods like agro-ecological zoning or ecosystem and crop models provide reliable assessments of land productivity potentials. Such methods are not intended for a field scale application to detect main soil constraints or to derive soil management recommendations in situ. A comparative analysis of several soil and land evaluation methods revealed the usefulness of indicator-based approaches applicable reliably, simply and consistently over different scales, from field level to large regions (aided by soil maps). Basic soil survey methods, including visual tactile soil structure assessment, are useful diagnostic tools for the recognition of productivity limiting soil attributes and estimation of indicator values. We advocate a straightforward indicator-based soil functional assessment system supplementing the current WRB (2006) classification or the coming Universal Soil Classification. It operates as a useful tool for monitoring, planning and management decisions based on soil quality (SQ) by detecting properties and limitation of soils for cropping and grazing and by providing estimates of attainable crop yields over different scales. The Muencheberg Soil Quality Rating (M-SQR), described in a chapter of Part II, has the potential to serve as a global reference assessment method of soil productivity potentials consistently over different scales. It combines visual methods of soil assessment (methods of soil survey, visual assessment of soil structure) with climate data in expert-based evaluation, classification and ranking schemes. M-SQR has been successfully tested in most agricultural regions worldwide. It provides concrete results about soil quality but also a frame for further research towards sustainable agricultural practices.