Soil fertility management strategies in irrigated peri-urban agriculture around Jos, Nigeria : an interdisciplinary approach
This thesis examines soil fertility management strategies in dry season irrigated vegetable production (DSIVP) in peri-urban areas of Jos, Nigeria. Farmers have developed a complex strategy of mixing inorganic fertilisers with organic manure and town refuse ash (produced by open burning, and sorting for non-combustible components). The thesis aimed to gain insights into the sustainability (in terms of nutrient supply) of the local agricultural system, acquire an understanding of past and present fertiliser practices and the rationale behind them, provide an appreciation of the role played by urban waste ash and the risks attached to its use, and place the problem of soil fertility in a wider context of farming problems. An inter-disciplinary approach was adopted so the methods used are: chemical analysis of soil and inputs (i.e. refuse ash), questionnaire surveys, semi-structured interviews (with farmers and PADP, JMDB, FUA etc.) and participant observation. The thesis observed that farmers have in-depth, but informal, empirically-derived knowledge about fertiliser application, which explains their past success in soil fertility maintenance. The tremendous increase in DSIVP in the last decade, though, has brought about a scarcity of organic amendments; farmers are increasingly reliant on inorganic fertilisers, probably over-applying them. Although this is not an immediate threat to the stability of the system, it may lead to soil acidification in the near future. Urban waste ash can counteract soil acidification (high pH and base cations), but certain batches can be contaminated by heavy metals, and indeed there is some indication of accumulation in the crops of the study farms. The problem of soil fertility needs to be addressed, however, farmers' short-term concerns (particularly access to credit facilities) need to be solved first. It is imperative that the Nigerian Government should take note of these issues and rapidly take steps to solve them.