Reduced tillage and nitrogen effects on soil water dynamics and maize (Zea maysL.) yield under semi-arid conditions

Soil water and nutrients are critical drivers of crop production for smallholders of southern Africa. A three-year study was conducted to assess the effect of integrating single and double ploughing, ripping and planting basins with nitrogen fertilizer (0, 10 and 20 kg N ha–1) on soil water dynamics and maize (Zea mays L.) yields. The experimental design was factorial with four tillage methods and three nitrogen levels as treatment factors. The study was conducted under semi-arid conditions of Zimbabwe. Tillage methods had similar soil water patterns in the profile and no tillage × N interaction effects were observed on soil water dynamics. Soil water penetrated deeper into the profile under ripper and basin methods than conventionally ploughed treatments. Nitrogen increased maize yields (14–96%) and rainwater-use efficiency (20–92%) regardless of tillage methods and growing season quality. However, more studies are required to explore complementary techniques that can improve rainwater capture and prolong soil water storage, and improve soil fertility

Reduced tillage, mulching and rotational effects on maize (Zea mays L.), cowpea (Vigna unguiculata (Walp) L.) and sorghum (Sorghum bicolor L. (Moench)) yields under semi-arid conditions

Proponents of conservation agriculture (CA) argue that the CA approach offers the greatest opportunity to increase the productivity in smallholder agro-ecosystems. This study was designed to assess (1) first year maize, cowpea and sorghum yield responses to a combination of reduced tillage and mulching and (2) maize yield responses to rotation with cowpea and sorghum in reduced tillage systems. Two conservation tillage methods (ripping and planting basins) combined factorially with seven mulch levels (0, 0.5, 1, 2, 4, 8 and 10 t ha−1) were compared with conventional mouldboard ploughing. The experiment was run for four consecutive growing seasons allowing for a rotation of maize, cowpea, sorghum and maize in some fields used in the study. Crop yields were determined across all tillage and mulch combinations in each year. Tillage system had no significant effect on maize yield while maize grain yield increased with increase in mulch cover in seasons that had below average rainfall. Mulching at 2–4 t ha−1 gave optimum yields in seasons with below average rainfall. Tillage system and mulching had no significant effect on cowpea yield when soil moisture was not limiting. However, the ripper and basin systems had 142 and 102% more cowpea grain than the conventional system in 2006/2007 because of differences in planting dates used in three systems and poor rainfall distribution. The conventional and ripper systems gave 26 and 38% more sorghum grain than the basin system. Rotating maize with cowpea and sorghum resulted in 114, 123 and 9% more grain than first year maize, maize–maize monocrop and maize–cowpea–maize in the conventional system. In the ripper system, maize–cowpea–sorghum–maize rotation gave 98, 153 and 39% more grain than first year maize, maize–maize monocrop and maize–cowpea–maize rotation. In the basin system, maize–cowpea–sorghum–maize rotation gave 274, 240 and 43% more grain than first year maize, maize–maize monocrop and maize–cowpea–maize rotation. However, long term studies under different soil, climatic and socio-economic conditions still need to be conducted to substantiate the observations made in the reported study

Start, end and dry spells of the growing season in semi-arid southern Zimbabwe

Smallholder agriculture in semi-arid Zimbabwe is dependent on the seasonal characteristics of rainfall. The determination of start, end and length of the growing season, and the pattern of dry spells during the season is useful information for planning land preparation and planting activities. This study was designed to assess whether there has been any changes in the start, end and length of growing season and the pattern of 14 and 21 day dry spells during the season. Daily rainfall data were collected from five meteorological stations located in southern Zimbabwe. Results indicated that no significant changes in the start, end and subsequent length of growing season occurred over the past 50–74 years. There was no significant change in the number of wet days per season over the period reviewed. There is a high probability of 14 and 21 day dry spells during the peak rainfall months. The relationship between start and end of growing season is stronger as aridity increases. We conclude that growing seasons have not changed significantly over the past 50–74 years in southern Zimbabwe. As smallholder agriculture continues to be affected by dry spells and droughts, there is scope in exploring rainwater management technologies in rainfed cropping system

Dead level contours and infiltration pits for risk mitigation in smallholder cropping systems of southern Zimbabwe

The persistent droughts, dry spells, and chronic food insecurity in semi-arid areas necessitate the introduction of more robust rainwater harvesting and soil water management technologies. The study reported here was conducted to assess the influence of dead level contours and infiltration pits on in-field soil water dynamics over two growing seasons. A transect consisting of six access tubes, spaced at 5 m interval, was established across each dead level contour with or without an infiltration pit before the onset of the rains. Two access tubes were installed upslope of the contour while four tubes were installed on the downslope side. Dead level contours with infiltration pits captured more rainwater than dead level contours only resulting in more lateral soil water movement. Significant lateral soil water movement was detected at 3 m downslope following rainfall events of 60–70 mm/day. The 0.2–0.6 m soil layer benefited more from the lateral soil water movement at all the farms. Our results suggest that dead level contours have to be constructed at 3–8 m spacing for crops to benefit from the captured rainwater. It is probably worth exploring strip cropping of food and fodder crops on the downslope of the dead level contours and infiltration pits using the current design of these between-field structures. With the advent of in situ rainwater harvesting techniques included in some conservation agriculture practices it will benefit smallholder cropping systems in semi-arid areas if these between-field structures are promoted concurrently with other sustainable land management systems such as conservation agricultur

The influence of conservation tillage methods on soil water regimes in semi-arid southern Zimbabwe

Planting basins and ripper tillage practices are major components of the recently introduced conservation agriculture package that is being extensively promoted for smallholder farming in Zimbabwe. Besides preparing land for crop planting, these two technologies also help in collecting and using rainwater more efficiently in semi-arid areas. The basin tillage is being targeted for households with limited or no access to draught animals while ripping is meant for smallholder farmers with some draught animal power. Trials were established at four farms in Gwanda and Insiza in southern Zimbabwe to determine soil water contributions and runoff water losses from plots under four different tillage treatments. The tillage treatments were hand-dug planting basins, ripping, conventional spring and double ploughing using animal-drawn implements. The initial intention was to measure soil water changes and runoff losses from cropped plots under the four tillage practices. However, due to total crop failure, only soil water and runoff were measured from bare plots between December 2006 and April 2007. Runoff losses were highest under conventional ploughing. Planting basins retained most of the rainwater that fell during each rainfall event. The amount of rainfall received at each farm significantly influenced the volume of runoff water measured. Runoff water volume increased with increase in the amount of rainfall received at each farm. Soil water content was consistently higher under basin tillage than the other three tillage treatments. Significant differences in soil water content were observed across the farms according to soil types from sand to loamy sand. The basin tillage method gives a better control of water losses from the farmers’ fields. The planting basin tillage method has a greater potential for providing soil water to crops than ripper, double and single conventional ploughing practice

Cumulative effects of reduced tillage and mulching on soil properties under semi-arid conditions

Declining soil productivity is one of the greatest challenges facing smallholder agriculture. This study assessed effects of reduced tillage and mulching on soil organic carbon, bulk density, infiltration and maize yield. Treatments consisted of three tillage methods (conventional ploughing, ripping and planting basins) combined factorially with mulch levels (0, 0.5, 1, 2, 4, 8 and 10 t ha−1). The experiment was run for four growing seasons allowing for a rotation of maize, cowpea and sorghum in some of the fields. A new experimental field was opened each year and maintained in subsequent seasons until the end of the experiment. Soil organic carbon increased with time in all tillage systems and more SOC gained in planting basins. Soil bulk density decreased with time in all tillage systems irrespective of mulch quantity applied. Ripping loosened the soil much deeper than the other tillage methods. Total infiltration in all treatments was similar over the four seasons. Soil structural changes resulted in increased unsaturated hydraulic conductivity and sorptivity of the clay loam soil. Maize yield increased with time in all treatments. Long term studies need to be conducted to substantiate the results on soil property and crop yield improvements observed in the reported stud

Effect of minimum tillage and mulching on maize (Zea mays L.) yield and water content of clayey and sandy soils

Rainfed smallholder agriculture in semi-arid areas of southern Africa is subject to numerous constraints. These include low rainfall with high spatial and temporal variability, and significant loss of soil water through evaporation. An experiment was established at Matopos Research Station, Zimbabwe, to determine the effect of mulching and minimum tillage on maize (Zea mays L.) yield and soil water content. The experiment was run for two years at two sites: clay (Matopos Research Station fields) and sand (Lucydale fields) soils, in a 7 × 3 factorial combination of mulch rates (0, 0.5, 1, 2, 4, 8 and 10 t ha−1) and tillage methods (planting basins, ripper tine and conventional plough). Each treatment was replicated three times at each site in a split plot design. Maize residue was applied as mulch before tillage operations. Two maize varieties, a hybrid (SC 403) and an open pollinated variety (ZM 421), were planted. Maize yield and soil water content (0–30 and 30–60 cm depth) were measured under each treatment. On both soil types, neither mulching nor tillage method had a significant effect on maize grain yield. Tillage methods significantly influenced stover production with planting basins giving the highest stover yield (1.1 t ha−1) on sandy soil and conventional ploughing giving 3.6 t ha−1 on clay soil during the first season. The three tillage methods had no significant effect on seasonal soil water content, although planting basins collected more rainwater during the first half of the cropping period. Mulching improved soil water content in both soil types with maximum benefits observed at 4 t ha−1 of mulch. We conclude that, in the short term, minimum tillage on its own, or in combination with mulching, performs as well as the farmers’ traditional practices of overall ploughin