Global Theme on Agroecosystems
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Global Theme on Agroecosystems
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The Potential for Conservation Tillage Practices to Improve Smallholder Maize Production in Zimbabwe
(Paper prepared for presentation at I World Congress on Conservation Agriculture Madrid, 1-5 October 2001 )
Summary A series of on-station trials was conducted to assess the performance of a range of draught animal powered minimum tillage implements available in Zimbabwe for crop establishment and mechanical weeding. The draught power requirements, field efficiencies, depth of work and soil and yield responses are reported. Although two season's work involving six designs of ripper tine revealed significant differences in measures of draught power performance, the lack of significant differences in yield response for the ox-drawn equipment indicates that the criteria for the selection of rippers at the farm household level would lie more on the durability of the implement and its price, rather than its geometry. However, it is clear that tine tillage systems do not give adequate weed control and need to be combined with other crop husbandry practices to control weeds, such as winter ploughing, post emergent ridging to smother weeds, or the introduction of herbicide technologies. Key words: Conservation, tillage, draught animals, and yield, Zimbabwe
Introduction Conventional annual ploughing using an ox-drawn mouldboard plough is the commonest tillage practice for smallholder farmers in Zimbabwe and was first introduced in the 1920s (Alvord, 1926). Most farmers use the mouldboard plough to do spring ploughing after the first rains, whilst a few better resourced households do both winter and spring ploughing. However, annual conventional ploughing is considered an intensive technique and is associated with soil degradation, high draught force requirement and loss of crop productivity (Vogel, 1994). For these reasons, some regard plough use as unsustainable (Elwell, 1991), mainly because of the serious erosion that can be caused, yet it still has to be accepted as the farmers' traditional practice. The increasing effort towards sustainability has stimulated the need to explore alternative tillage techniques, for example conservation tillage. It is estimated that less than 1% of smallholder farmers practice conservation tillage techniques (Nyagumbo, 1998) and this proportion will not increase significantly until the benefits can be clearly demonstrated to the farmers and are fully evaluated. The work reported here for the 2000/2001 season is part of a series of on-station field trials to assess the performance of a range of draught animal powered implements available in Zimbabwe for crop establishment and mechanical weeding. This paper concentrates on the draught power characteristics and yield responses to a variety of animal drawn minimum tillage implements that have been developed with the smallholder farmer in mind. The implications for transfer to the on-farm situation are discussed.
Materials and Methods Site LocationField experiments were conducted at Domboshawa Training Center, Mashonaland East in northern Zimbabwe during the 2000/2001 cropping seasons. The soils are deep coarse-grained granitic sands (82% sand, 13% silt, 5% clay) with a plant available water capacity of less than 12% by volume, which means that crops grown on these soils are prone to drought, as any excess water quickly drains below the plant rooting zone (Vogel, 1994). These are typical soils that are found in most smallholder farming areas of Zimbabwe. Dependent on the availability and condition of draught animals and implements, they are normally cultivated annually to a depth of 80 to180 mm (Koza et al. , 2000).
Implements and experimental design The experiment involved six designs of ripper tine - the BSP Ripper (BSPR), the Zimplow Ripper (ZR), the Magoye Ripper (MR), the Palabana Sub-soiler (PS), the Contil Knife Ripper (CTK) and the Contil Single Donkey Toolbar Ripper (CTB) and two ploughs. The ploughs were the standard plough (V8) and the BSP Light-weight plough (BSPP). The trials were laid out in a randomized split-plot design with primary land preparation as the main plot factor and with crop establishment techniques using the ripper tines or ploughs as the split plot factors replicated four times. Four tillage strips for each primary land preparation treatment (winter ploughed or no-till) were each 8m wide by 195 m long. In each strip there were eight 8 m wide by 20 m long split plots, making a total of 64 split plots on the whole trial field. A 5-m discard area (headland) was left at the end of each plot to facilitate turning. The crop establishment methods under investigation were A) the farmer practice of third furrow planting (TFP) - dropping seed into the V8 plough furrow to be subsequently covered by the next pass of the V8 plough, B) planting into a rip line created by a range of commercially available ripper tines mounted on a standard plough beam and C) open plough furrow planting - seed planted into furrows opened with a single pass of a the BSPP plough at the desired inter-row spacing, and subsequently covered with a hand hoe. Two or four oxen provided the draught power for all operations, including the ploughing, with the exception of the single donkey drawn CTB. The maize hybrid SC513 test crop was planted at 0.9 m row spacing and thinned to an in-row spacing of 0.3 m after crop emergence. The crop was top-dressed with 56 kg/ha N (150 kg Ammonium Nitrate) in split application at 6 and 10 weeks after planting. No basal fertilizer was applied, in accordance with smallholder farmer practice. All plots were uniformly hand-weeded two and six weeks after emergence.
Data Collection At crop establishment, the depths and widths of soil disturbance for each ripper tine were taken (four measurements per plot), as were draught forces (eight measurements per run for a total of 8 runs per plot). Effective working time per run, turning time and total time spent on each plot were measured, from which work rates and draught power characteristics were calculated. Maize plant population was recorded following thinning and repeated at harvest when a total crop dry biomass, grain yield at 12% moisture content, and the number of barren plants were also determined. Estimates of weed biomass cover were made on a whole plot basis after the first weeding. Data was analyzed by conventional ANOVA for the design and comparisons of means by t-test at the 0.05 level of probability.
Results Typical seasonal rainfall (October/November to March) at Domboshawa ranges between 400 and 1150 mm, with a ten-year average of 803 mm (1989 to 1999). The 2000/2001 season was wetter than average, 1342 mm, with February (501 mm) and March (327 mm) accounting for 62% of the annual total, which severely restricted post planting field operations. Figure 1 summarizes the maize grain yield response to implements used for crop establishment and the incremental yield increases due to tillage (winter ploughing). Although there was no significant interaction between tillage and implements, the incremental yield increases due to winter ploughing resulted in significant yield increases for the CKR, CTB and PS implements,
doubling or even trebling yield responses, compared to no-till plots. Overall, winter ploughing increased maize yields by 900 kg ha -1 and is attributed to the significant ( P<0.001 ) reduction weed density on the ploughed plots.
The field experiment reported has been repeated over two seasons at Domboshawa and on a heavy red clay loam soil with very similar patterns of observation. The results have consistently revealed significant differences in draught power characteristics for the six designs of ripper tine and clearly show that planting into a rip line is much faster than the traditional practice of TFP, typically 4 to 5 hours per ha using a ripper tine, compared to 13 to 15 hours per ha for TFP. The use of a reduced tillage system would, therefore enable a farm household to save time over the critical planting period after the first rains. However, it is clear that tine tillage systems alone do not give adequate weed control and need to be combined with other crop husbandry practices to control weeds, such as post emergent ridging to smother weeds, the introduction of herbicides technologies, or as in this work winter ploughing. Although the weed data is not reported here, no till plots had significantly ( P<0.023 ) higher weed densities, and lower yields than winter ploughed plots. The responses observed for tine tillage following overall winter ploughing are not new and have been observed both here in Zimbabwe (Shumba, 1984) and in Burkina Faso (Twomlow and O'Neill, 1994). However, the overall lack of significant differences in yield response for the ox-drawn equipment indicates that the criteria for the selection of rippers at the farm household level would lie more on the durability of the implement and its price, rather than its geometry.
Acknowledgements The work reported here is part of a research project (R7352) funded by the UK Department for International Development (DFID) and the Government of Zimbabwe (GoZ). However, neither DFID nor GoZ can accept responsibility for any of the information or views expressed . References Alvord E.1926 . The Great Hunger: the story of how an African chieftaincy improved its farming methods under European guidance. Native Affairs Department Annual Report . Elwell H A.1991 . A need for low-input sustainable farming. Zimbabwe Science News 24 . pp 311-335 Koza T, Ellis-Jones J, O'Neill D, Twomlow S.2000 . Enhancing the use of draught animal power by smallholder farmers in Zimbabwe. In Optimizing DAP for cropping . pp.5-13. Report IDG/00/22, Silsoe Research Institute, UK. Nyagumbo I.1998 . Experiences with conservation tillage practices in southern and eastern Africa: a regional perspective. In: Conservation tillage for sustainable agriculture , pp. 73-86. Eds J Benites et al . Proceedings Part II of an International Workshop, Harare, 22-27 June 1998. GTZ, Eschborn, Germany. Shumba, E M.1984 . Reduced tillage in the communal areas. Zimbabwe Agricultural Journal 81 . pp 235-239 Twomlow, S J and O'Neill, D H.1994 . A dry season tillage system for compacting and crusting soils in Burkina Faso. In: 'Sealing, Crusting and Hardsetting Soils: Productivity and Conservation', pp 497-502 Eds H B So et al. Australian Society of Soil Science Inc. Brisbane, Australia. Vogel H.1994 . Conservation tillage in Zimbabwe - Evaluation of several techniques for the development of sustainable crop production systems in smallholder farming. African Studies Series, A 11 . Geographica Bernensia, Bern., pp150
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