FarmLime manual: for small-scale production of agricultural lime

This manual is a concise guide to the small-scale production of agricultural lime. It was developed as part of a research project, ‘Low-cost lime for small-scale farming’ otherwise known as FarmLime (Mitchell, CJ, 2005). The ideal agricultural lime is a ground dolomite or dolomitic limestone with a particle size of 100% <2mm, 60%<400m and up to 50% <150m (Mitchell et al, 1997). It is produced from limestone and/ or dolomite by a three-stage process that involves extraction, crushing and milling to a powder. Agricultural lime is often produced as a co-product in operations that are primarily geared to producing road stone aggregate, quick and hydrated lime, cement and/ or mineral fillers. Dedicated agricultural lime production plants do exist, especially in countries where agriculture is one of the main stays of the national economy such as in sub-Saharan Africa. Agricultural lime is also produced by small-scale mining operations. The quarry site first has to be cleared of vegetation and overlying soil to expose the underlying rock; this can lead to the removal of a large volume of material. The rock is then extracted from the ground, using crow bars, picks and sledgehammers, and transferred to the crushing stage. This involves the use of sledgehammers and club hammers to reduce the rock to pieces smaller than 10mm. The final production stage is carried out using a mill, such as the modified TD Hammer Mill, which produces agricultural lime. The agricultural lime produced should be packaged into 50kg bags. Overall, this style of small-scale production is estimated to cost in the region of US$1.20 to US$1.60 per 50kg of agricultural lime produced. Small-scale production of agricultural lime is considered to be cost-effective for those farmers in districts that have a need for lime and are at least 50 to 100km from the nearest commercial source of agricultural lime.