Anthony Young

Is there Really Spare Land? A Critique of Estimates of Available Cultivable Land in Developing Countries

Five assessments covering less-developed countries have identified a ‘land balance’, available for future cultivation, using the approach of inventory and difference: assessment of the area cultivable, and subtraction of the area presently cultivated. All arrive at a balance of 1600–1900u2009Mha, about twice the present cultivated area. The supposed existence of this spare land is widely quoted in forecasts of capacity to meet the food requirements for future population increase. It is argued here that these estimates greatly exaggerate the land available, by over-estimating cultivable land, under-estimating present cultivation, and failing to take sufficient account of other essential uses for land. Personal observation suggests that the true remaining balance of cultivable land is very much smaller, in some regions virtually zero. An order-of-magnitude estimate reaches the conclusion that in a representative area with an estimated ‘land balance’ of 50%, the realistic area is some 3–25% of the cultivable land. This speculation could be tested by directly attempting to find such land in areas where it is supposed to exist. The impression given by current estimates, that a reserve of spare land exists, is misleading to world leaders and policy-makers.

Recent advances in the survey and evaluation of land resources

The term ’land’ is used in this review in the sense implied by a widely-used method of resource survey, the land systems approach; by the title of an organization to which reference is made, the Land Resources Division; and in which it is defined as a technical term by the Food and Agriculture Organization of the United Nations. The latter is that land comprises the whole of the physical environment, including climate, landforms, hydrology, soils and vegetation, to the extent that these factors influence potential for rural land use (FAO, 1976). Land is thus a much wider concept than soil. It involves resources for agriculture sensu lato, including arable use, tree crops and pasture resources for livestock production, together with forestry, water catchments and ’non-productive’ types of rural land use such as recreation, tourism and wildlife conservation. Land resources have long been of interest to geographers, as an aspect of human activity in which environment-man relationships are most clearly displayed. Renewed interest has been directed towards such resources in the

The nature and management of the poorer tropical latosols

The latosols, or ‘red and yellow’ soils of the tropics, encompass a wide range of properties and fertility. The poorer types occupy large areas both in the rain forest and in savanna climatic zones. The various systems of shifting cultivation traditionally practised are now inadequate with regard to increasing population densities, and management should be based on fertilizer application at moderate levels together with methods of maintaining organic matter and hence soil structure.

Book Review: The physical chemistry and mineralogy of soils.The physical chemistry and mineralogy of soils. Vol. II: Soils in place. C Edmund Marshall. Pp. xiii+313. John Wiley, New York, London, etc. 1978. £17.50.

Solute movement In the soli-root system. P H Nye and P B Tinker. Pp xiv+342. Studies in Ecology Volume 4. Blackweils, Oxford. 1977. £12·80. This book must be welcomed as an important addition to the literature for it breaks new ground in attempting a rigorous analysis of the factors determining the movement of nutrient ions from the soil to the plant root. It is no fault of the authors that, though a pleasure to read, it is also a disappointment. In spite of the very large endeavour that has gone into the study of the movement of ions in soils, thereis a long way to go towards understanding and being able to predict nutrient up-take by plants. As the authors say at the end of the book, the treatment of the topics is necessarily incomplete, and progress is impeded by the inaccuracy of soil physical measurements; the natural heterogeneity of soils; and the difficulty of predicting root development and properties. They could well have added further difficulties associated with the biological factors that influence nutrients in the vicinity of the root, and after entry to the root, and the structural changes that occur in soils; present knowledge of the soil-root interface is still rudimentary. However, the authors have brought together in a coherent form a wealth of information on water and nutrient movement in the soil, and provided a framework within which further work may more fruitfully be conducted. The book will be essential reading for all those interested in advancing an understanding of plant nutrition. D J GREENLAND