Conservation tillage for cassava (Manihot esculenta crantz) production in the tropics

Cassava (Manihot esculenta crantz) is often cultivated on tilled plots, traditionally on mounds and ridges with the use of hand hoes or tractor driven implements. These two conditions alter the soil structural parameters and most times increase the vulnerability of soil to erosion or compaction as a result of frequent machine movement under the conventional tillage system. A review of the effects of tillage systems on soil bulk density, total porosity and penetration resistance was conducted to investigate the effectiveness of soil conservation for the optimum production of cassava in the tropics. Tillage treatments under review were: conventional tillage (CT), no-till (NT), minimum tillage (MT) and soil compaction (CP). Our review indicated that the bulk density (BD) in plots under CT was not significantly different (p<0.05) from the value of BD in plots under minimum tillage (MT) within the 0–5cm soil layer, but was highest in soils under compaction due to traffic passes of heavy duty equipment. Soils under no-till were characterized with lowest bulk density within the 0–5cm layer, but gradually increased in BD within the 10–20cm soil layer, which offers the soil some structural stability. However, the difference in bulk densities between plots under NT and CP treatments were highly significant at p<0.05, with CP plots having the highest bulk density within the 0–30cm soil layer. Total porosity was highest in soils under conventional tillage (CT) comparatively with other tillage systems. Organic matter accumulation in NT treatment resulted to higher total porosity compared with other systems except CT at the surface soil (0–5cm) but with reduced porosity at the sub-surface soil. Total porosity was least in plots under traffic passes (compacted plots). Statistically, there were no significant differences in total porosity among plots under conventional tillage with mulch residues, conventional tillage without mulch residues and minimum tillage with mouldboard at the p<0.05. However, plots under minimum tillage without mouldboard had lower total porosity. Penetration resistance was higher in NT plots when compared with plots under CT system, except from compacted plots (CP), which offered highest resistance to penetration. A long term experiment showed that cassava root yield was highest under NT with mulch residues, with or without fertilizer application. The reviewed work further confirmed that cassava can be grown successfully under no-till (NT) to give the optimum growth and yield required of the crop, while conserving the soil physical properties.