Conceptual methodologies in agro-environmental systems

When continuous measurement of relevant above- and below-ground environment al factors is made, and the dynamics of crop growth and phenology is follow ed, it is shown that small-plot agronomic experimentation can provide infor mation vital to the development and testing of simulation models. Such mode ls for crops of maize (Zen mays) and the legume cowpea (Vigna unguiculata), grown as sole crops and in an intercrop system, were used to simulate yiel d at two separate sites in the main savanna farming zones in Ghana, West Af rica. Simulation was carried out for these three cropping systems using 20 years of historical rainfall data for the two sites, investigating the effe ct on yield of management options which included time of planting, rate of nitrogen fertilizer application, and crop planting density. The yield results of this series of simulations were then subject to two di fferent types of analysis in order to assist the evaluation of agricultural options for the nation. The first analysis was an economic evaluation base d on gross margins, but using the stochastic-dominance technique to rank th e profitability of the alternative cropping and management systems. The second, more general methodology employed was multi-criteria analysis ( MCA). This analysis covered economic returns and their variability, the amo unt and quality of residue returned to the soil, and the aerial cover provi ded by the crop. Other factors which could affect the sustainability of pro duction in the long term, but which could only be evaluated qualitatively, were also included in the analysis, as allowed in MCA methodology. The MCA was then carried out for three scenarios in which different weightings were given to economic outcomes and to factors which are believed to encourage ecological sustainability. These scenarios allow recognition of different p riorities which might be given by traditional subsistence farmers as compar ed to commercial producers. Outcomes of this broad analysis of development alternatives provided scient ific support for the traditional Ghanaian practice of grain/legume intercro pping which is also widespread in the tropics. The suite of methodologies i llustrated by the case study appears to be suitable for the evaluation of a lternative farming systems at the scale of a small nation such as Ghana. (C ) 2001 Elsevier Science B.V. All rights reserved.