Contrary to the popular paradigm it is not always the smaller, poorer farmer who is threatened by lack of nutrients. This study confirms earlier conclusions (Lekasi et al, 1998) that the small, mixed farm featuring a dairy enterprise has a significant nutrient supply available to use to improve soil fertility. As such, in intensifying agricultural production systems, the presence of livestock, in this case cattle, are regarded by rural communities in densely populated areas as a fundamental factor determining the viability of agricultural-based livelihoods.
Manure-compost quality has a profound influence upon crop yields not just in the season of application but up to one year later. The quality of manure-compost can be influenced by simple no- or low-cost changes in animal and excreta management.
Animal management, feeds and feeding practices have significant impact on the quality of excreta. However improvements attained through feeding can be lost during manure storage particularly where nutrients are excreted in urine and inadequate urine storage mechanisms are in place.
Urine may not necessarily be most effectively used as an addition to the manure heap but perhaps, instead, applied directly to actively growing crops.
In line with the DFID Development Strategy for Kenya (DFID, 1998) the project described in this book has successfully demonstrated that mixed farming can actually deliver greater and sustained land productivity whilst, at the same time, protecting the natural resource base. The fact that `best practice' for sustainable agriculture involves close integration of livestock with crops, and probably has done for centuries, is essential to bear in mind at a time when livestock are currently considered a global scourge on the environment. It is true that environmental threats exist where intensive rearing methods have become de-linked from crop production as in the case of industrial animal production systems and that these rearing methods, often operating on subsidised inputs, also serve to undermine the viability of smallholder livestock production. However, the research described above demonstrates that it is possible for small-scale farmers to sustainably intensify production in the face of both environmental and economic challenges. The techniques demonstrated for better manure management conserve a greater proportion of nutrients for subsequent uptake by crops and do so at minimal extra cost to the producer. It may well be that the contribution this research makes to enhancing the competitiveness of the smallholder sector in Central Kenya is increased where improved manure management can be linked to cultivation of higher value horticultural crops.
Potential manure application rates are greatest on the smallest farms because of higher livestock densities. This finding contrasts with those of Smaling et al (1992) who conclude that manure application is insufficient to sustain crop production in high potential Kisii District of Kenya. The estimates in this report support observations of Kagwanja (1996) for Embu District that the smaller farms do actually apply considerable quantities of manure on a regular basis. There is a still a need, highlighted by Lekasi et al (1998), to measure manure accumulation and application rates on the smallest (poorest) farms in high potential farming areas of Kenya.
The survey described in Section 2 documented the wide range of organic materials that are available at the farm level and it was observed that they are generally used in combination in different proportions either as bedding or deliberate additions in the heaps. Some of these materials are mixed with animal excreta when they are still fresh (green), as is the case with napier grass feed refusals and hedge and tree prunings. Others are mixed when dry as is the case with most crop residues such as bean trash, maize stover and fallen leaves from avocado and mango trees. Quantification of the nutrient cycling capability of these different forms of organic materials would assist in formulating the kind of composting strategy that could be applied in order to optimise nutrient retention when combined with animal excreta. This quantification would also clarify, whether any pre-treatment would be necessary before mixing, as is the case with maize stover where it may be necessary to break open the stalks to allow absorption of urine.
The composting strategy experiments reported here have shown that including urine when manure is composted with limited amounts of organic material does not necessarily contribute significantly to the conservation of N, and including urine with faeces only may conserve N but leads to a poor quality manure. This suggests that direct application of urine to the field may be a possible way of utilising urinary nutrients. However, further investigation may be necessary in order to ascertain the long term effects the urine would have on soil chemical, physical and biological characteristics associated with crop production. For instance, urine has been shown to increase the soil pH, available P and ammonium levels in the top 10-15 cm of soil in semi-arid West Africa and increased millet yield production (Powell et al, 1998).
A substantial amount of research has been conducted on crop residues with respect to nutrient mineralisation and crop production (Woomer & Swift, 1994). Information from such trials may be useful and can be extrapolated to give an indication of the potential of feed refusals in recycling nutrients if directly returned to the soil without prior composting. In comparison, information on the capability of urine to recycle nutrients without passing through the manure heap in intensive farming systems of the Kenya Highlands is scarce.
A more radical alternative to conserve urinary N during collection and composting would be to use inorganic chemicals, such as calcium and potassium salts of sulphuric and phosphoric acids, gypsum, calcium carbonate, rock phosphate and thiosulphate, that would minimise nutrient losses (Beckwith & Parsons, 1980; MacKenzie & Tomar, 1987; Stevens et al, 1989; Frost et al, 1990; Al-Kanani et al, 1992; Sallade & Sims, 1992). Such methods have been used in developed countries where slurries are widely used. A similar approach could be adapted and modified appropriately for the systems in Kenya but would require thorough investigation prior to implementation. However, this may not be a popular choice bearing in mind that additives may not be readily available, may be expensive, and handling of chemicals may require specialised technical knowledge. This approach would also require that the inorganic chemicals chosen do not interfere with desirable soil characteristic that promote crop productivity.
With cattle manure having originated mostly from fodder, both manure and fodder possess many similar chemical characteristics and may be expected to react similarly in soil. However, unlike fresh plant materials, manure applied to crops results from digestive, respirative and degradative processes inside the gastro-intestinal tract and in the compost heap. The loss of many soluble and volatile components renders it more stable than fresh uncomposted plant materials (Kemppainnen, 1989).
Criteria for predicting quality of organic resources is currently based on a decision tree for assessing quality of organic materials mostly of plant origin developed by the Tropical Soil Biology and Fertility Programme (TSBF, 1998). However, cattle manure does not seem to conform to outcomes predicted by the TSBF decision tree since manure is a low quality organic resource and yet it promotes crop performance to an extent similar to high quality resources of plant origin. This decision tree groups organic materials of lower N content than 2% as low quality and this happens to be the category that most livestock manures fall into. Therefore, this observation calls for the development of different criteria for predicting manure quality based on chemical characteristics unique to manures that can be linked to nutrient mineralisation and crop performance. Some simple physical parameters, which are easily discernible, do show significant relationships to some manure chemical characteristics.
There appears to be scope for the further development of decision tools for manure-compost quality. Further work is required to refine/qualify the physical parameter categories, to apply these to more specific sub-types of manure-compost, and to correlate these with chemical characteristics such as lignin and polyphenol concentrations that are better linked to crop response than even C:N ratio.
Time of manure application is important in determining crop performance, depending on the type of manure available at hand. Manures that are not well composted may perform better if applied well before sowing because decomposition can progress in the soil. But this choice may be useful only where soil fauna may allow storage of manure in the soil without damaging it before the crops are planted. Also, different crops may exhibit highest nutrient demands at different times of manure nutrient mineralisation. Therefore, a good understanding of manure nutrient mineralisation patterns could be used as a guide on deciding the time of application.
Once the farmer has decided that it is time the manure is applied in the field, then the next major concern would be the best method of application. Farmers normally prefer either hole or furrow application for most crops, not because they think the nutrients are better utilised but because it makes it easier to cover the manure when covering the seed. The danger with this kind application method is that if the manure compost was not mature, then the seed may be damaged or the seedling growth may be suppressed. In fact, yield suppression has been reported in Kandara and Gatuanyaga (Delve, 1998; Kimani, 1999) due to application of fresh manures that had not composted properly. When such manures are applied in the soil, composting continues which encourages nutrient immobilisation at the early stages of seed germination when the seedlings are most vulnerable.
The rate of manure application and how often manure should be applied to a field should really be based on the type and demands of the crop under consideration. However, the choice of farmers to apply for example, one or two handful per hole or continuously over a distance of the furrow complicates the issue of the actual amount that is applied and available to be utilised by the crop. Applying two handfuls rather than one handful means that the farmer is doubling the rate of nutrient application. This would only be useful if the manure is, once again, well composted, otherwise the choice of the higher rate would lead to higher nutrient immobilisation and hence greater competition between the crops and the microbes leading to depressed yields than with manure applied at a lower rate, especially in the immediate season after application.
The choice of whether manure should be incorporated or surface mulched also lies in compost maturity, which is normally reflected in the physical characteristics of the manure. Cattle manure composts that are not mature would normally contain organic materials that would sometimes be too big to be easily incorporated in the soil and the best choice of application method for this type manure would be surface mulching. On the other hand, it is also possible to have manure composts that are not mature but can easily be incorporated into the soil. In such circumstances, the best choice would be broadcasting over a large area so that, as the composting progresses, immobilisation takes places more evenly in the plot rather than just within the vicinity of the plants and hence minimise competition. This way, as the plants grow the roots will be able to reach out for nutrients over a wider area as mineralisation begins later in the season.
The research suggests that despite reduction in farm size units can remain viable both economically and environmentally as long as diversification into integrated crop/dairy production is possible. Obviously a crucial factor to successful diversification is sustained access to cattle feed. For the smallest farms that depend to a large extent upon common property forage resources to feed dairy cattle this is anticipated to become problematic as public- or waste-land from which forage is currently obtained is increasingly privatised. Where forage supply to small farms can no longer meet the requirements of large ruminants the question remains as to what livestock options remain that can guarantee the environmental sustainability of small-scale farming. Changing the livestock portfolio on a small farm from `forage-demanding' cattle to small ruminants and/or mono-gastric species will obviously have implications for the quantity of manure available to support continuous cropping. However, there is currently considerable uncertainty about (1) the dynamics in livestock populations on the smallest holdings, (2) whether these farms are already employing alternative strategies to cope with shortfalls in organic inputs and (3) what technical and economic interventions may be required to support access by poor farmers to organic matter be it through livestock or some other means.
As economic structural adjustments in Kenya result in the reduction of public-sector extension activities promotion of methods to improve the use of organic matter in the smallholder sector relies more heavily upon the NGO sector. At the same time the Government of Kenya is seeking to promote the involvement of the private sector in smallholder agriculture as an important step in the Poverty Reduction Strategy Plan. NGOs can be effective in promotion of improved farming practices but tend, due to financial limitations, to be localised in impact. For more widespread effect of knowledge transfer it is vital, therefore, that the rapidly proliferating private sector be encouraged to disseminate information.
Improved manure management as well as better use of organic matter as a soil ameliorant would not be a natural focus of advertising campaigns run nationally by fertiliser companies. Whilst it is well known that organic and inorganic fertilisers can be managed to interact synergistically in the soil, incentives over and above providing greater farmer satisfaction may be required to encourage the private sector to adopt more of a `farming-best-practice' stance in their dissemination activities. Determination of the policy and institutional settings most conducive to broadening the objectives of private sector advertising has yet to be systematically carried out. This research needs to be conducted in conjunction with efforts to seek alternative information transfer pathways in the public (education) and civil society (e.g. religious groups) sectors to ensure an unbiased and reliable flow of knowledge to end users.
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