Modelling spatial extension of vegetable land use in urban farms

Increasing vegetable production to meet the growing urban demand is essential in developing countries. This article proposes a new model to analyse farm land use for market gardening in tropical urban agriculture and to evaluate the capacity of farmers to increase their vegetable surface area. It is based on a decision model simulating crop sequences and crop location initially validated for temperate arable and vegetable productions. In this study, the leafy vegetables land use model (LYLU) was first adapted to suit the specificities of urban leafy vegetable production: short crop cycles; wide crop diversity; instability of the cultivated area during a season, in our case due to flood recession; manual labour and close relationships with retailers. The output variables of the model were then compared to observations collected on an 11 farms sample. The model estimates the surface area for each leafy vegetable, depending on plant species requirements, farm resources and relations with retailers. This is the first model that simulates the spatial and temporal variation of the farm land and the exploitable surface areas over the cropping season depending on the dynamics of water availability and labour force. In some cases, up to half of the surface remained uncultivated because of slow fields' drainage at the end of the rainy season and/or lack of water in the wells in the dry season. Moreover, the available labour force on farm and the way vegetables were sold greatly affected the intercrop period, which in turn contributed to reducing the cultivated area. Finally the model was used to quantify farmers' room for manoeuvre in order to increase their vegetable cultivation area. Opportunities to overcome them were discussed both at farm and territorial levels. This is an innovative approach that could be useful to face the growing urban demand in developing as well as in Western countries.