Effect of tied riding and mulch ripping on water conservation in Maize production on sandveld soils

Abstract

Soil water measurements taken weekly at 6 depth levels over a period of 26 months  (October 1991 to November 1993) in a sandveld soil in the subhumid north of Zimbab-  we revealed tillage treatment to have a significant effect (P < 0.05) on soil water levels during the second half of the dry season (May-September) and for the first two months  of the rainfall-growing season (October-April). During this period, soil water levels in  the top 750 mm of the soil profile, the rooting depth for maize in this soil, was significantly higher on the mouldboard ploughing treatment. Thereafter (December-April), the effect of tillage treatment on water content within the same zone was not statistically significant, except for the severe drought in February and March 1992. During this mid-season drought period, soil water levels in the top 450 mm of the ridged treatment were 30-40% lower than those recorded in ploughed soil; and slightly higher than the ploughed soil in the top 150 mm on the mulched treatment.  Parallel studies involving non-weighing lysimeters indicated that tied ridges experience more deep percolation of water than ploughed soil, in particular if heavy rainfall occurs early in the growing season when the maize plants are still small and the water-collecting crossties are of adequate height. In 1992-93, more internal leaching  of applied fertilizer nutrients occurred from ridged than from ploughed soil. In contrast, however, surface runoff from ploughed field plots was always significantly  higher than from tied ridged and mulch ripped plots.  Maize (Zea mays L.) yields at the site under investigation were significantly higher on  the tied ridged treatment; except for the 1991-92 drought season when differences in  treatment yields were statistically insignificant. The higher biomass production on tied  ridged field plots was mainly due to increased root depth and root length density, and  the prevention of waterlogging in above-average rainfall years.