Introduction

The description of agricultural activities involves a number of different disciplines, so that the representation of an actual agricultural process results from the consideration of different dimensions. The most important among them are the following (see Kostrowicki, 1977; De Walt, 1985; Spedding, 1988):

1. (i) the ‘social’ dimension, represented by features such as population structure, tenure, farming family organisation, farmer attitude to innovation, and so on;

2. (ii) the ‘economic’ dimension, which is related to the enterprise structure, the market structure, the interrelationships between farms and markets, the business policy, and so on;

3. (iii) the ‘biological’ dimension, which concerns technical and productive conditions.

Any type of agricultural process may be conceived as a system, that is, as ‘a group of interacting components, operating together for a common purpose, capable of reacting as a whole to external stimuli: it is not directly affected by its own output and has a specified boundary based on the inclusion of all significant feedbacks’ (Spedding, 1988, p. 18). And for special purposes a subsystem may be identified and extracted from the general system if the subsystem presents a degree of integrity and independence of the whole, and has the same output as the main system. As a result, in any real type of agricultural process, we may distinguish the family farm subsystem, the spatial subsystem of agricultural activities, the agricultural markets subsystem, the production subsystem (describable in terms of major components, different combinations of crop, cultivation method, fertiliser input, sowing date), and so on.