17. Conservation Farming in
Semi-Arid Lands Abstract In order to promote appropriate land and crop management systems to meet the growing population in Kenya’s semi-arid region, there is need to improve on the existing local practices rather than introducing new ones, developed elsewhere. Foreign or high resource based technologies rarely considers the technical, social and economic constraints faced by resource poor farmers. Over generation,
Mbeere farmers have cultivated their land by use of different approaches, though locally
developed but relatively satisfying in performance. Despite these, there is need to
improve on the management approaches and enrich these with options that would overcome the
economic and bio-physical constraints. Eight land management practices that conform to the
principles of conservation tillage were identified in semi-arid Mbeere District of Kenya.
Four tillage practices have been evaluated against the flat conventional tillage. Inherent
soil fertility, soil texture and rainfall amount and distribution affect the influence of
the tillage practice on crop yield. Introduction Semi-arid lands
(SAL) of eastern Kenya are dominantly under rainfed crop production which is mainly
composed of low resourced farmers. The region is also characterized by frequent drought
phenomenon, inherently low soil fertility and poorly distributed bi-modal rainfall
patterns. The dominant farming system is purely sorghum-millet and extensive livestock
system. The crop production is on subsistence level, while livestock is the main source of
cash income. Indigenous knowledge is important and used widely to utilize the local
resources available. The government‘s effort towards practical adaptation and wide
promotion of the locally available knowledge to enhance land productivity has received
least priority. Due to socio-economic and environmental constraints the more conventional
conservation tillage practices, have not been adopted. New approaches to promote
conservation tillage are believed to be economically and environmentally sustainable in
the farming system. These approaches, divers in type and form, have in common to dependent
on the positive interaction with the desired crop and planting patterns and other
competing farm enterprises. For a long time conservation tillage has been promoted in large scale mechanized farms and in situations where farm labour has become scarce and expensive. Changing from conventional tillage approach to conservation tillage in mechanized farms was largely due to problems of deterioration of soil structure due to excessive cultivation, and compaction below surface due to regular plowing at same depth. Due to rapidly increasing population and increasing pressure on land demand for more reliable crop production from marginal areas, previously considered low agricultural potential, is becoming obvious. As such promising conservation measures need to be addressed urgently. The inappropriate tillage practices and continued soil exposure to spells of rain do reduce aggregate stability and cohesion of the soil mars and thereby leading to formation of a seal and crust on drying and subsequent increase in soil loss. Conservation tillage practices therefore favours maintenance of stable aggregates thereby maintaining high infiltration rates, leading to both environmental and productivity benefits. These benefits include less soil erosion, less water pollution, increased organic matter in the soil, lower labour costs, less time required per crop, and in some cases the possibility of an additional crop per year. In small scale farms
of SAL, farmers are very conservation conscious yet little has been developed to improve
upon their indigenous crop production constraint evasion strategies. Widescale promotion
of conservation tillage concepts may have to contain other locally sustainable tillage
perceptions but keeping to the primary goal of conservation tillage. Mbeere District The following identified forms of conservation tillage practices were found in the SAL of Mbeere district. The information is based on farmer participatory appraisals and research evaluations in the area. Location and Agroecology Mbeere District, Kenya is typical of undulating uplands found on the South-east of footslopes of Mount Kenya with complex long slopes (upto 100m), dissected by valleys. The rainfall is low and unreliable, falling in two distinct season, one (shorter and less reliable) from March to May and the other (longer and more reliable) from October to January. The mean annual rainfall is 765mm, of which 40% (323mm) falls in the first season and 60% (442mm) falls in the second (Okoba et al., 1997). Rainfall is intense and frequently exceeds the infiltration capacity of the soil and can cause soil crusting, runoff and soil erosion (Kiome, 1992; Gibberd, 1993). The temperatures are relatively high (31°C) and humidity is low with average evaporation (2020 mm) exceeding annual precipitation (Okoba et al., 1997; Gibberd, 1993). The classification of soils range from chromic Cambisols to rhodic Ferralsols and Luvisols with varying degree of stoniness, rockness and soil depth (van de Weg & Mbuvi, 1975; Njoroge & Gicheru, 1995). The low and erratic rainfall leads to regular periods of moisture stress affecting common food crops, especially maize and beans. More traditional crops such as sorghum, pearl millet, cowpeas and pigeon peas are less vulnerable to the effects of drought. However, production of these crops is highly depended on the bio-physical condition of the soil, most common degradation in the area is as a result of the effects of sealing and crusting. 95 percent of the district lies within and between agroecological zone 3 to 5 (Jaetzold, R. & Schmidt, H., 1983) and at altitude ranging from 800 to 1100 m a.s.l. Livestock which forms the main source of cash, for most of the household demands and input to other farm enterprises, is extensively managed. The grazing system is greatly still communal, though with increasing population and the changing land tenure, livestock numbers are on decrease and intensive livestock management is getting appreciated. Forms and practices of conservation tillage The following set of evolutionary land management practices and cropping patterns have been perceived over time and space to have sustained land productivity, without compromising conservation of the environment. The described management are specific to a larger proportion of Mbeere District (Siakago and Gachoka Divisions). Slash and Muro The Mbeere people started cultivation nine generations ago, they were otherwise basically pastoralists and hunters. Grazing was generally in low lands and getting most of their food from the neighbouring higher lands (Kirinyaga district). Shifting cultivation was used, where 4 to 6 seasons period on one field before shifting was adequate. 3 acres per household was sufficient to provide food as soil fertility was high. Land preparation involved cutting of bush using traditional axe and burning, leaving selective tree species for other services (medicinal and building). Digging sticks (muro) were used to make planting holes. All crops were simultaneously grown, with no distinct row arrangement. As population increased the per capita available land declined and even became inaccessible. Farmers, however, continued to practice shifting cultivation system though very cautiously. Due to short rotational cycle most targeted fields did not have old bushes. These fields were cleared during the long dry inter-seasonal breaks (June to September), which ensured drying of cleared shrubs/crop stovers, and were burnt just before rains. Planting would be through seed broadcasting in ash-covered field. Weeding would follow using a traditional „muro" or spear-like tool. Yields gained from a single reliable October rains would be enough for a household all year around. As land productivity started declining as realized through reduced crop yields, a new strategy was born by leaving cleared residues in situ, without burning. Then, early planting using muro, after the onset of the rains would follow. Weeding was undertaken by use both muro and manual weed pulling. Fields were relatively small but crop yields could just meet family demand. During weeding there would be minimal soil surface disturbance. Late Planting and use of Draft Animal Power (DAP) or Muro Under this practice, land clearing is not done, since the field is under continuous cultivation. Due to the surface hardening of soils (long exposure to the sun and reduced organic matter content) the planting and land tilling is delayed until the onset of rain. After a long dry spell, the weeds from the previous crops will wither and/or grazed by cattle in situ. At the onset of the rains the farmers plant behind the plow and weeding is done with the use of DAP. The crop planted may be of either pure or inter-crop type. The inter-crop takes a form of alternating strips, each strip of a different seed type. In some cases, it has been observed that the major crop for the season takes a higher ratio of the field (4:1). In this case, the widest strip, made of several rows of the priority crop, will be alternated by minor crop (narrower strip). Sometimes narrower strips could be left fallow but in case planting is done, a cover crop sown by use of a muro still ensures least surface disturbance. By using DAP in planting, the seed is placed more deeper than when using a muro. Ridging and Plow-planting This system of tillage is common with well resourced farmers, especially those who own bulls and mouldboard plows or cash to hire the plow and/or animals. The tillage type is common in the planting of pure crop stands and solves the problem of labour shortage during the beginning of the planting season. The most common and suitable land preparation operation is plow-planting. This is done after the first storm, at least to avoid forcing the weak animals to break hard soil after a long dry spell. In a reliable season, using this approach, late planting would still ensure a good harvest, minimal weed emergency and retain all the rain water insitu in the cropped area. But in unreliable season, early land preparation and hence early planting (before onset of rainfall) need to be undertaken to avoid a crop failure. Block cropping This approach employs both cropping pattern and tillage strategies for sustainable land productivity. The field is cropped with divers crop types but normally in pure stands arranged in blocks. Planting is carried out through seed broadcasting. The initial land preparation may take two forms. Firstly, slashing of the previous crop stalks/weeds (which are left to dry in situ) or burning could be considered, if the previous crop noted incidences of pest attack. The seeds are later broadcasted and covered by soil by using DAP, preferably during the first rain storms. The second approach is by, firstly, broadcasting the seed in the field, still with previous season’s weeds/crop stalks, and then plow by using DAP. The latter operation is undertaken after the onset of the rains. The land preparation would basically depend on the resource level of individual farmer. Several blocks of legume varieties and cereals are planted and rotated between one another on seasonal or annual basis. It is perceived that this approach, demands less labour input during planting, weeding, pest control and harvesting. The planting could be through staggered sowing using a muro or plow-planting behind the plow, along the contour in each block. Plant density tends to be high, hence low weed emergency but low crop yields achieved. In most cases, the crop could either be the local two-season sorghum or cowpeas varieties or drought resistant bean and maize cultivars, depending on the season. Farmers who practice this system of cultivation and crop arrangement pattern, have observed that, the crop yields are significantly better than fields under continuous tillage. This approach is viable in view of the reducing land sizes and short fallow periods in a shifting system. Stover incorporation and mulching This practice is common across all other tillage practices in the area. The crop stovers are left in the field after harvesting. Maize and cowpeas stovers are the only types that are sometimes carried from the fields to the cattle boma, especially those grown nearby the homestead. Sometimes animals are allowed in the field to graze the materials. The short crop stables left behind standing are incorporated in the soil during tilling and/or weeding, these stovers could otherwise have remained on the surface. Conventional mulching is not very common, and among those who practice it, the mulch does not cover the whole field uniformly. Mulching is commonly practiced in kitchen gardens. Wide scale mulching is probably restrained by labour time and availability of sufficient materials. Farmers appreciate the incorporation of stovers and mulching for better crop growth as a result of better moisture storage and improved nutrient availability. Sources of mulch are generally from sorghum, millet and other leguminous crops. Planting pits This form of tillage
is not only common in fruit growing but also to food crops. Pit sizes vary in depth,
diameter and spacing but are determined by the tools available to a particular farmer.
Adapted dimensions are 0.15m depth by 0.8m diameter and spaced at 0.2m. These measurements
are different from what is illustrated by Critchley (1992). Those farmers questioned in
the district feel that wider spaced pits is a waste of land. Planting is done on the
shoulders/risers of the pits. The crops could be a mixture of both cereals and legumes.
Once made, the pits can last for two to three seasons (1-1.5 years). Tied furrows Unlike the conventional furrowing by oxen plows, farmers have adopted tying of the furrows at distances ranging from 2-5m, depending on slope, available equipment and accuracy of contouring. The average dimensions are 0.45m distance between ridges by 0.15m as ridge height. Furrow and ridge making is by done by using DAP but in subsequent seasons, the furrows are subjected to minimal disturbance i.e. pulling out the weeds in the furrow where the planting is done. The ridges are covered by stovers and pulled out weeds, this is to ensure that moisture is adequately stored and released nutrients are beneficial to the plant. This tillage practice can last between two to three seasons, depending on soil texture and free rooting depth. Research evaluation Studies in the SAL have shown improvements in soil hydraulic properties under conservation tillage, although the existence of certain interactive effects between these hydraulic characteristics and seasonal weather patterns have yielded negative effects (Okwach et al 1990). In general where improvements in hydraulic properties have been reported, the effects were: a reduction in runoff and soil losses; an increase in crop water storage; and in some instances an increase in deep storage beneath the root zone. Application of crop residues as mulch under a minimum cultivated fields similarly reported improvements in hydraulic properties, significant reduction in bulk density of the soil, and insured yields in poor rain seasons (Black, 1973; Okoba and Twomlow, 1997-unpublished). Kilewe and Mbuvi (1987a), by application of maize stover mulch at the rate of 3t/ha, reported significant reduction in runoff and soil loss, leading to conclusion that mulch application was the best conservation practice, were it not for competition from livestock for fodder, in the region. Other findings in similar conditions found reduction in rainfall detachment, improved entrainment, reduced sediment concentration in runoff, reduced amount of coarser sediment fractions in the eroded sediment and reduction in total N loss. (Palis et al, 1990; Okwach, 1988). Recent studies of farmer-based practices are hereby present to demonstrate the added value to the principles of conservation tillage as understood in this region. Due to other factors, reported results may greatly differ from perceived benefits and vary from site to site. The negative yields indicate that a conventional flat tillage at the site performed better than the conservation tillage practice. However, soil fertility, soil type and rainfall amount and distribution may negate the effect of the tillage. Typical examples are the cases of, Kairungu with tied ridge and furrow during the wet season when with and without fertilizer and the tied and not tied ridge and furrows of Machanga-b, without fertilizer. Planting pits and mulching generally showed an express superiority over the flat tillage. Results are given in two set of seasons i.e. dry season, when rainfall was less than 300 mm and wet when rainfall was more than 300 mm. Maize was the test crop in all the trials. Table 1 shows extra yields obtained over the control management. Table
1: Extra maize grain yields over the
control under various conservation tillage practices (After KARI’s Katumani and Embu
centres).
Note:* = fertilized; ** = Manured 5t/ha *** = no fertility added; nd= no data available. Dry season stands for the March rains while the wet season is for the November rains. Machanga-a and Machanga-b are information provided by Okoba and Twomlow (1997) and Kiome and Stocking (1993) respectively from Machanga site, with different soil texture classes. Table 2: SWOT Analysis of conservation tillage practices
Farmer perceptions Table 2 shows the
perceived strengths, weaknesses, opportunities and threats (SWOT) of conservation tillage
known to farmers in the study region. Conclusion Generally, in view
of the prevailing demographic pressure, economic and environmental constraints, the
evaluated practices are effective in reduction of runoff, ensure better germination in all
seasons, better yields in comparison to flat tillage practices. Better result impact is
during dry April season and highest impact is felt on cereals since they have higher
moisture demand. Farmer-based adaptive research need to be initiated for more options of
conservation tillage practices that are environmentally safe and economically viable
within the farming system. Acknowledgment We sincerely wish to
express our appreciation to FARMESA, for providing the travel opportunity to attend this
workshop, our employers: Director KARI and Head of National Soil conservation Branch in
the Ministry of Agriculture and Livestock Development and Marketing for allowing us share
this information with other stakeholders. We are very thankful to our colleagues who
assisted with survey data or provided the evaluation data on conservation tillage within
their research domain, specifically we mention Dr. Itabari and Dr. Okwach (of
KARI-Katumani Dryland Research Centre), Dr. R.M. Kiome (AD-SWM, KARI Hqt) and David Mellis
(formerly of KARI-RRC, Embu). Any misquote or error in the paper is our responsibility.
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Po Box 80, Siakoago, Kenya. |
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