SOIL PENETRATION RESISTANCE, ROOT-GROWTH AND YIELD OF MAIZE AS INFLUENCED BY TILLAGE SYSTEM ON RIDGES IN MALAWI

Ridge-tillage is a traditional method of seedbed preparation in Malawi and is performed annually by manual operation with a hand hoe. A 3-ye ar field experiment was conducted to evaluate the effects of minimum ( MT) and conventional (CT) ridge-tillage systems on soil strength and m aize (Zea mays L.) growth. Minimum tillage consisted of planting maize on ridges made in the previous year(s) while in CT it was grown on ne w ridges constructed at the beginning of each season. The soil was an Oxic Rhodustalf, Results indicated that a distinct hard and compact la yer had developed below the ridges (about 25 cm depth) In both CT and MT, Soil on ridges of CT had consistently lower penetration resistance than did MT, Bulk density and penetration resistance of soil on the r idges were less under CT than under MT, Penetration resistance in both tillage treatments was strongly related to soil water content, which depended on the amount of rainfall. Consequently, the pattern in chang es of penetration resistance in the soil during the season generally m irrored that of rainfall, The presence of compacted subsurface soil la yers in both treatments and the significantly higher (P less than or e qual to 0.05) penetration resistance in the MT affected root penetrati on and distribution. The MT had significantly lower root length densit y in the 0-20 cm depth and roots were concentrated near the surface co mpared with those of CT, Maize grain yields, however, were not affecte d by the tillage system in the first two seasons of the study but were significantly reduced by MT in the third season. The average grain yi elds over the three seasons were 4812 and 4644 kg ha(-1) for CT and MT , respectively, Use of MT resulted in remarkable reductions of working time and energy requirement for maize production compared with CT. Th is study has shown that maize yields of around 4000 kg ha(-1) can be a chieved by using previous years' ridges under smallholder farmers circ umstances of low resource input.