Applied Geography (1987), 7, 89-91

Nutrient cycling and land use management: an introduction

Martin Kent

Department of Geographical Sciences, Plymouth Polytechnic, Drake Circus, Plymouth, Devon, PL4 8AA, UK

and David Gilbertson

Department of Archaeology and Prehistory, University of Sheffield, Sheffield, SI 0 2 TN, UK

Introduction

The aim of this short series of papers is to summarize and explore some developments in the study of nutrient cycling in relation to land use management. Traditional discussion of ecosystems in biogeography and ecology has emphasized the balanced or steady state of nutrient cycles in most natural and semi-natural environments (Tivy 1982; Odum 1983; Pears 1985; Thompson et al. 1986). The disruption caused to these cycles by man’s activities through numerous different forms of land use, particularly agriculture and forestry, are now widely documented (e.g. Briggs and Courtney 1985). Until recently, much of this discussion has been largely descriptive in nature. However, present trends indicate that various aspects of the modified and simplified nutrient cycles resulting from land use activity are now receiving close attention and research on the applied aspects of nutrient cycling, and its implications for manage- ment practice in agriculture and forestry, is assuming ever-increasing importance (Frissel 1977, 1978; Lee et al. 1983; Lowrance et al. 1984).

The concept of the agro-ecosystem is now widely recognized (Odum 1984) and a journal of that title has been published since 1974, with a symposium on Cycling of Mineral Nutrients in Agricultural Ecosystems presented in 1977 (Frissel 1977). The highly modified and simplified nutrient cycles which characterize such ecosystems may now be seen as being of equal, if not greater, significance for research than those of natural and semi-natural systems for which nutrient cycles were quantified under the International Biological Programme in the 1960s and 1970s (Leith and Whittaker 1975). A number of existing research projects into nutrient cycling under various land use regimes in different world biomes is now underway within the Man and the Bio- sphere programme (Giacomini 1978; Batisse 1980).

The theme volume

The first paper of this volume (Tivy 1987) serves as an introduction to concepts of nutrient cycling in agro-ecosystems. Major inputs to the system are examined, together with the efficiency of nutrient use under agricultural systems of differing intensities. The openness or potential for gain and loss from the cycles within agri- cultural ecosystems are stressed.

Foster et al. (1987), in the second contribution, demonstrate one of the most important approaches to research into nutrient cycling, namely the lake-watershed

0143.6228/87/020089-03 $03.00 0 1987 Butterworth & Co (Publishers) Ltd

90 Nutrient cycling und land use management

model. Following the pioneering work of Likens et al. (1977) on the ecosystem- watershed idea, the study of small-scale catchments within hydrology and geo- morphology is now commonplace (Gregory and Walling 1973; Burt and Walling 1984; Trudgill 1986), but in such studies a greater emphasis has generally been placed on hydrological, solute and weathering processes than on nutrient cycling and its ecological implications. Nevertheless, a significant body of research on nutrient cycling and land use is now emerging using the ecosystem-watershed model (Gower 1980; Likens 1981; 1985). In this volume, Foster et ul. show how the paired catch- ment framework can be used to study both the effects of atmospheric pollution on nutrient cycling and the intensification of land use in agricultural ecosystems.

The other two papers, by Proctor (1987) and Charlton (1987) examine problems of nutrient cycling and land use management in the humid tropics. Studies of nutrient cycling in tropical forest ecosystems have reached a stage of synthesis only within the past few years and the contribution by Proctor is complementary to other develop- ments, notably the publication by Jordan (1985). Proctor’s paper stresses both the paucity of data on nutrient cycling within tropical rainforest ecosystems and the methodological difficulties involved in gathering such data. The problems of research within undisturbed forests are great enough, without introducing the complexities of man’s interference and modification. Many existing concepts concerning tropical nutrient cycling may be challenged and he concludes that much more research on natural systems in the tropics is required, before we can establish really effective long-term management within man-modified systems.

Finally, as Odum (1984) emphasized, it is almost impossible to discuss nutrient cycling and agricultural systems in the tropics without a detailed consideration of social, economic and cultural factors. In the final paper, Charlton (1987) deals with the problems of sustainable agricultural systems in the humid tropics, with particular reference to the conservation of nutrients. First, he reviews different approaches to land use management which maintain nutrient cycles and potentially may increase output for small-scale farms. Secondly, the practical difficulties in terms of the possible contribution of the indigenous farmer to sustainable tropical agricultural development is discussed. Lastly, he demonstrates how the achievement of ecological goals in terms of balanced nutrient cycling among other ecological considerations may only be achieved through a great number of socioeconomic controls and limita- tions.

Taken together, these papers show how applied geographers have a valuable role to play in both unravelling the complexities of nutrient cycling in modified ecosystems and in providing information for long-term management. The next decade should see a substantial increase in research output in this direction from the whole range of world ecosystems. It is clear, however, that although research by applied physical geographers may provide answers, practical implementation involves increased appreciation of the links between human and physical geography and the socio- economic, cultural and political dimensions of resource management.

References

Batisse, M. (1980) The relevance of MAB. Environmental Conservution 7, 179-184. Briggs, D. J. and Courtney, F. M. (1985) Agricultureandenvironment: thephysiculgeogruphy

of temperate ngricultural systems. London: Longman. Burt, T. P. and Walling, D. E. (eds) (1985) Cutchrnent experimenfs in fluvial hydrology.

Norwich: GeoBooks.

Martin Kent and David Gilbertson 9 1

Charlton, C. A. (1987) Problems and prospects for sustainable agricultural systems in the humid tropics. Applied Geography 7, 153-174.

Foster, I. D. L., Dearing, J. A., Charlesworth, S. M. and Kelly, L. A. (1987) Paired lake catchment studies: a framework for investigating chemical fluxes in small drainage basins. Applied Geography 7, 115 - 133.

Frissel, M. J. (ed.) (1977) Cycling of mineral nutrients in agricultural ecosystems. Agro- Ecosystems 4, l-354.

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(Revised manuscript received 2 September 1986)