An Evaluation of five tillage systems for smallholder agriculture in Zimbabwe

Abstract

Soil erosion, both in the form of gully erosion from grazing lands and sheet erosion from arable fields, is widespread in smallholder farming areas in Zimbabwe. A collaborative conservation tillage project between the Department of Agricultural Technical and Extension Services (AGRITEX) and the Deutsche Gesellschaft für Technische Zusammenarbeit (GTZ) GmbH is researching into the sheet erosion problem from cropped land. Launched in 1988, the prime objective of the programme is to assess the soil and water conservation merits and yield potentials of four tillage systems (tied ridging, two ripping techniques, and badza holing-out) as compared to traditional mouldboard ploughing. Research work was conducted on granite-derived sandy soils at two experimental sites, i.e. Domboshawa Training Centre (subhumid natural region) near Harare and Makoholi Experiment Station (semi-arid natural region) near Masvingo. The results achieved over this period of four years suggest, that each of the four  selected treatments has pros and cons over mouldboard ploughing. From a conservation and production point of view, tied ridging appears to be the best tillage technique available only for smallholder farmers under high rainfall conditions. It requires, however, more timely management than mouldboard ploughing with respect to planting (only when ridges are wet) and first weeding (when weeds are still small). It also requires extra labour inputs for cross-tying the ridges and for hoe weeding if the first weeding is not achieved through re-ridging. Mulch ripping, appears to be a sound protection and production technique for dry climatic conditions as the surface residue cover not only protects the soil from being eroded but also facilitates slightly higher topsoil water levels at the beginning of the season as compared to ploughing. However, crop residues for mulching are very  scarce in smallholder farming areas.
Clean ripping requires less net draught energy than ploughing and only a cheap tine.  However, steady-state draught force is as high as for ploughing and the system also does not provide for a weed-free seedbed. Badza holing-out, already practised where draught power is not available, yields at  comparable levels to ploughing in wetter areas and requires hardly any implement input. However, it raises overall labour requirements drastically.  In response to the above, research work into the testing and development of appropriate  mechanization (ridgers, rippers, cultivators) and improved agronomic practices (mixed. relay and/or strip cropping) was initiated.