Johansen C.,Agricultural Consultant |
Haque M.E.,Murdoch University |
Bell R.W.,Dhaka International University |
Thierfelder C.,CIMMYT Zimbabwe |
Esdaile R.J.,Agricultural Consultant
Field Crops Research | Year: 2012
Small holder farmers in rainfed agriculture believe that soil tillage is needed to maximize crop yields. However, as cropping intensity, and hence tillage intensity, increases there may be a decline in particular physical, chemical and biological properties of the soil which limit crop yield. This is primarily caused by declining soil organic matter, its oxidation being accelerated by tillage, particularly in warmer climates, and exacerbated by the limited return of above-ground biomass to the soil due to its competing use for other purposes. In large-scale commercial agriculture declining soil quality has been effectively addressed by conservation agriculture-cropping systems based on minimum tillage, crop residue retention and appropriate crop rotations and associations, preferably including legumes. This has required development of minimum tillage planting equipment along with herbicide technology to achieve weed control that is traditionally achieved through tillage. However, a shortage of mechanized options suitable for small holder farmers is creating an impediment to the adoption of conservation agriculture practices that would arrest the decline in soil quality in their fields. In South Asia, two-wheel tractors are replacing animal-drawn ploughing in small holder plots. This speeds the tillage operation and hence the turnaround time between crops, which may increase opportunities for crop intensification, but the problems associated with full tillage remain. Over the previous decade planter attachments to two-wheel tractors have been developed which permit seed and fertilizer placement with minimum to zero tillage in a single-pass. Recent tests have demonstrated that use of these implements can produce crop yields equal to or better than conventional tillage involving hand broadcasting of seed and fertilizer. Further, fuel and labour costs, seed and fertilizer inputs and turnaround time between crops can be reduced. In Africa, the introduction of animal-drawn rippers and direct seeders, originally developed for small-scale farmers in Brazil, is considered as a major breakthrough to small-scale farmer mechanization. It significantly reduces labour required for planting and benefits may be even greater if herbicides can be effectively used for weed control. Nevertheless, movement towards minimum tillage with two-wheel tractor mounted planters and animal-drawn direct seeding equipment is constrained by weed management issues. There are problems of availability and of safe and effective use of herbicides by resource-poor farmers and there is a need to develop more integrated weed management strategies that can be combined with small-scale planters. There is also a need to optimize the performance of small-scale planters to suit farmers' needs in different agro-ecological environments. Tools and concepts are now available to implement conservation agriculture for small holders and thereby increase profitability of their cropping practices and at the same time improve soil quality and sustainability of their livelihoods. However, much more adaptive research and on-farm evaluation is needed across a diverse range of soils, cropping systems and agro-ecological regions to bring conservation agriculture to more small holders. © 2011 Elsevier B.V.
Langyintuo A.S.,Alliance for a Green Revolution in Africa AGRA |
Mwangi W.,CIMMYT Zimbabwe |
Diallo A.O.,CIMMYT Zimbabwe |
MacRobert J.,CIMMYT Kenya |
And 2 more authors.
Food Policy | Year: 2010
Following the liberalization and restructuring of the seed sector, the maize seed industry in eastern and southern Africa has witnessed a proliferation of private seed companies. Whereas the total number of registered maize seed companies in major maize producing countries increased four-fold between 1997 and 2007, the quantity of seed marketed barely doubled suggesting that the seed production and deployment environment is less than perfect.A study involving over 92% of all seed providers in east and southern Africa in 2007 showed that a number bottlenecks affect the entire maize seed value chain. The lack of access to credit constitutes a significant barrier to entry. Until governments and development partners make credit available to seed entrepreneurs directly or through risk sharing arrangements with commercial banks, national seed companies will not grow leaving the seed sector monopolized by the regional and multinational seed companies. In addition, the transfer of genetic materials between public and private sectors should be improved to allow easy access by seed companies to suitable and adapted varieties. To allow for rapid regional spillovers of varieties released in one country to similar agro-ecologies in different countries, the implementation of the harmonized regional seed laws and regulations should be expedited. Finally, the best strategies that increase the adoption of improved maize varieties should be explored and implemented to enhance seed demand. © 2010 Elsevier Ltd.
Mhlanga B.,University of Zimbabwe |
Cheesman S.,CIMMYT Zimbabwe |
Maasdorp B.,University of Zimbabwe |
Muoni T.,University of Zimbabwe |
And 3 more authors.
Crop Protection | Year: 2015
Weed management is a challenge to resource constrained smallholder agricultural production in sub Saharan Africa due to insufficient and inadequate management strategies. When weeds are controlled with herbicides or through rotations under conservation agriculture, shifts in weed spectra are expected, increasing the need to adapt to this new situation. Experiments were conducted at four experimental sites namely the University of Zimbabwe farm (UZ) (clay soil), Domboshava Training Centre (DTC) (sand soil) and two contrasting soil types at Henderson Research Station (HRS sand (s), HRS clay (c)) to investigate the responses of weed communities to crop rotations. The trial was carried out from the 2008-09 to the 2013-14 cropping season. Rotations consisted of maize (Zea mays L.) rotating with a range of green manures, and the control treatment was maize monocropping. Herbicides were only applied in the maize phase at seeding, supplemented by hand weeding whenever weeds were 10cm tall or 10cm in diameter for weeds with a stoloniferous growth habit. Weed count data was collected between 2011 and 2014. Weed density, the Shannon-Weiner index and its components were used to explain weed community responses to rotations. There was a decrease in weed densities over time at all sites with a percentage decrease as high as 92% (i.e. from 357 to 30 weedsm-2) observed in maize-velvet bean (Mucuna pruriens (L.) DC) rotation. At all sites, some maize-green manure rotations were associated with high weed densities and these included maize-black sunnhemp (Crotalaria juncea L.) and maize-cowpea (Vigna unguiculata Walp) rotations. The two weeds Galinsoga parviflora Cav. and Ricardia scabra L. remained abundant throughout the study at all sites with densities reaching above 1000plantsm-2 per season in some plots. Shannon's E' index was highest at HRSs and HRSc sites in the maize-velvet bean rotation and maize-common rattle pod (Crotalaria grahamiana Wight & Arn.) rotations respectively suggesting that in these treatments dominant weeds were reduced in numbers. This suggests that rotations with cover crops such as velvet bean may reduce weed numbers and dominance of problematic weeds over time. This can potentially lead to a less intense weeding schedule, which is more cost effective and affordable for smallholder farmers. © 2014 Elsevier Ltd.