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-year field experiment was conducted to evaluate the effects of minimum (MT) and conventional (CT) ridge-tillage systems on soil strength and maize (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 new ridges constructed at the beginning of each season. The soil was an Oxic Rhodustalf, Results indicated that a distinct hard and compact layer 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 ridges 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 changes of penetration resistance in the soil during the season generally mirrored that of rainfall, The presence of compacted subsurface soil layers in both treatments and the significantly higher (P less than or equal to 0.05) penetration resistance in the MT affected root penetration and distribution. The MT had significantly lower root length density in the 0-20 cm depth and roots were concentrated near the surface compared with those of CT, Maize grain yields, however, were not affected 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 yields 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. This study has shown that maize yields of around 4000 kg ha(-1) can be achieved by using previous years' ridges under smallholder farmers circumstances of low resource input.