The effects of alternation and duration of temperature levels on the germination of dormant and nondormant seed of tall fescue (Festuca arundinacea Schreb ‘Fawn’) were evaluated. Dormancy induction and temperature preconditioning of dormant seed were also studied. Dormancy was greater in seed matured at 15 C compared to that matured at 26.6 C. The expression of dormancy was also more pronounced at a higher germination temperature (26.6 C). Temperature preconditioning of dorma nt fescue seed was important in relieving dormancy; germination response was essentially confined to imbibing temperatures of ≥ 15 C. Preconditioning time was important and 48 days at 1 C, 24 or 48 days at 5 C, and 24 days at 10 C gave near maximum germination response. Germination of dormant and nondormant seed was influenced differentially by level and alternation of temperature and by the amplitude of temperature fluctuation. For nondormant seed, constant temperature at 20 to 25 C was optimum. For dormant seed, alternating temperatures were more favorable, and the optimum regime was 8 hours at 20 to 25 C and 16 hours at 10 to 13 C with the range of response to temperature being more restricted than for nondormant seed. Germination response of dormant seed diminished as the time period at the higher temperature increased. The germination responses of dormant seed observed in this study indicate that at least two physiological phenomena may be involved. The thennogradient response could be a combination of the effects of temperature on the germination processes, per se, and on the metabolic and/or physical processes involved in dormancy. In nondormant seed, only the rate and extent of germination was affected by the temperature regime.

Polygonum pensylvanicum and Abutilon theophrasti, components of old—field communities in central Illinois were grown on a controlled soil moisture gradient to determine whether they exhibit different response centers. Germination response of a constant number of seeds per six moisture resource states, height, biomass, and reproductive response of initially constant numbers of plants per state were monitored. States, ranging from saturation down to 13.61 ± 5.53% moisture, are numbered in order of increasing drought. Maximum height of Polygonum occurred in states 4 and 5, and of Abutilon in 4, 5, 6. Vegetative and reproductive biomass maxima of Polygonum and Abutilon occurred in states 5 and 6, respectively. Abutilon reproduced only in states 5 and 6 where it overtopped the Polygonum canopy, while Polygonum reproduced in all states. Polygonum performance declined sharply in state 6. Thus, Polygonum and Abutilon response centers are displaced toward the wetter and drier ranges of the gradient, respectively. On a within—community level, Abutilon reproduces in less mesic resource states where Polygonum canopy height is reduced. In general, Abutilon reproduction may occur throughout the gradient when the Polygonum canopy opens. The performance of these species is strongly influenced by both physical and biotic conditions. Previously investigated adaptations, including drought resistance and rooting patterns in space and time, appear to underlie divergence along the moisture gradient. The response patterns found here are broad and exhibit considerable overlap as expected in fugitive strategies. The patterns of divergence shown on point and gradient scales in this and our previous work reflect a related complex of adaptations and strongly suggest that competitive divergence occurs in early successional communities.

IntroductionMechanization in West Africa has been of limited importance and influence for farming and manual labour is the dominant power input. At present only about 0.07 kW per ha is applied, while at least about 0.37 kW is desirable to obtain high yield levels.In this mechanization study a review is given of the inter-relationships of socioeconomic and agro-ecological factors with agricultural development and with agricultural mechanization in particular and of the different forms of and policies on mechanization (Chapter 2). Some model studies on mechanization are reported, which indicate the importance and constraints of soil tillage and weed control for most mechanization levels. The model study on vegetables also indicated the importance of different land preparation practices on yields (Chapter 3). Soil tillage studies were therefore carried out, with the emphasis on rice (Chapter 4). These studies were conducted in several places along a typical toposequence, from purely upland (rainfed) conditions to irrigated conditions. The weed growth effects of different tillage practices are reviewed and the results with manual and mechanical weed control practices in rice are indicated (Chapter 5).Principles of mechanization and mechanization stategyMechanization has obvious advantages, but can also have disadvantages. The most important advantages are: increased land and labour productivity, increased yields, higher profits, reduced costs, reduction of drudgery and reduced losses (2.3). The most important constraints are related to socioeconomic and technical factors (2.3). Socio-economical problems are also the most prohibiting to the introduction of new technology (2.4).Four levels of mechanization can be distinguished: manual labour, animal draught, small-scale mechanization based on small tractors and large-scale mechanization based on standard four-wheel tractors (2.5). Manual labour is cheap, but offers serious limitations for increased area under cropping and for increasing cropping intensities (2.5.2). Animal draught cannot be applied in the humid parts of West Africa, because of Trypanosomiasis ; in the savannah areas it is locally available and relatively cheap, while it can help increase the area under cropping (2.5.3). Two-wheel tractors have not found any significant application in West Africa; they can offer serious ergonomical disadvantages, while the costs per hp and per ha are high. It is argued that small four-wheel tractors should be pursued instead (2.5.4.3). So far mechanical power in Africa has come almost exclusively from standard four-wheel tractors. Their application has had considerable impact in some instances, while in other cases they have been failures, due to inadequate planning, management and support and because other necessary conditions were not met (2.5.4.4).Four mechanization 'philosophies' are reviewed (2.6).Intermediate, or sometimes called appropriate, technology is a term used to describe a technology which is compatible with the prevailing socio-economic and technical local conditions and most advocates also argue that this type of technology should be designed in such a way, that it can be made locally from locally available materials (2.6.2).Selective mechanization, sometimes indicated as partial mechanization, emphasizes that mechanization should only be applied under those conditions or situations and during those stages in the production-marketing process, where labour is the limiting factor (2.6.3).Tractor hiring services have been the main means by which mechanical power until now has been applied in West Africa; they are based on standard four-wheel tractors. These hiring services are usually started as Government operated units and it is argued that these should be handed over to private individuals as soon as possible (2.6.4).Large-scale farming with large-scale equipment has been exercised by various Governments in West Africa and its performance has been mostly negative, due to socio-economic and agro-ecological, as well as technical, restrictions. It is argued that intensification, rather than developing new largescale projects, is a more secure and faster way of increasing food production (2.6.5).Some aspects of the agro-ecology and the socio-economics are reviewed (2.7). It is emphasized that soils and crops have to be selected well before mechanization is applied. The mechanization potentialities are indicated to be best for hydromorphic: areas and for rice (2.7.2), and it is argued that irrigation developments will stimulate mechanization most.Cost calculations for the different levels of mechanization are made and they indicate that, although the costs per hour are lower for two-wheel tractors, the costs per hp and per hectare (for soil tillage) are lower for standard four-wheel tractors (2.7.3.1).The importance of the ergonomical aspects (2.7.3.2.), as well as of the social acceptability of new technology is indicated (2.7.3.3).The effect of mechanization on employment is reviewed (2.8). It is argued that mechanization undoubtedly can create unemployment or increased underemployment under certain conditions, but that the introduction of irrigation and the new seed-fertilizer technology coupled with a selective introduction of mechanization increases rather than reduces labour requirements. So far, mechanization in West Africa has not shown any serious labour displacing effects.In the general discussion (2.9) it is argued that for West African conditions private tractor hiring units could possibly be the best solution for the short and medium term basis, to get mechanization developments started. In this way mechanization will be introduced selectively, since the farmers decide for which operations they want the mechanization services applied.Intermediate technology may start slowly as the technical capabilities and the socio-economic acceptability of the new technology develop in the rural areas and it can be visualized that on a medium and long term basis this type of technology will supplement the basic (mainly soil tillage) operations, as carried out by the standard four-wheel tractors of the hiring services. The scope for twowheel tractors seems limited, although their application in hydromorphic valleys with rice or in market gardening seems to be feasible. It is argued that small four-wheel tractors instead could possibly find easier application and acceptance.It is concluded that farming in West Africa will mainly depend, for many years to come, on manual labour and that mechanization will become increasingly important, as soon as a 'Green Revolution' is set in motion.Model studies on mechanization systemsTwo model studies are reported. The first study concentrated on rice and made use of available data on time and labour requirements for the various operations in the production process for different levels of mechanization (3.2). The second study was a field study with vegetables, in which all inputs were recorded and yields were measured (3.3).The main purpose of the model studies was to determine which operations in the production process are most limiting to an increased area under cropping for different mechanization levels, while an additional objective in the second study was to investigate the effects of different mechanization levels on yields and profitability.The rice mechanization study indicated that, although transplanting and harvesting and threshing can offer restrictions, in general soil tillage and weed control are the major limiting factors for all steps in mechanization development; these two operations claim between 40 and 60% of the total labour requirements.The field study with vegetables, where two mechanization levels were applied, also indicated that soil tillage and weed control were major bottlenecks, in the manual system soil tillage and weeding were equally limiting, taking together as an average about 54% of the total input hours, while in the tractor system weed control was far more limiting than soil tillage, taking on average about 29% of the total labour requirements, about 25% of which for weeding. This study demonstrated the effects of different land preparation practices, inherent to the two mechanization systems, on yields; while most crops reacted positively to the tractor tillage (about 15 - 20 cm deep), some crops reacted favourably to the shallow manual hoeing (about 4-6 cm deep). In general, this field study indicated that growing vegetables under the tractor system resulted in higher yields, lower production costs and higher net income per manhour of labour input than under the manual system.Soil tillageSoil tillage and weed control are studied in more detail in this mechanization study, because they are usually the major limiting factors in the crop production process, because most mechanized inputs in West African agriculture have so far been in land preparation, and because soil tillage studies and recommendations can have considerable effects on the desirable level and type of mechanization (4.1).Soil tillage studies were carried out in several places along a typical toposequence, which consists of three major soil groups: the plateau soils (well-drained), the lower slope soils (well-drained) and the valley soils (poorly-drained).Well-drained soilsTwo experiments were conducted on the plateau soils, a five-year long experiment on Egbeda soil, which was newly-cleared (4.4.3.2), and a one-year experiment on Iwo soil, which had been cleared for one year (4.4.3.3).On the plateau soils zero or minimum tillage techniques may be feasible if enough crop residues are available. Without crop residues these techniques perform poorly. Deep tillage practices are not to be recommended, as they turn up gravel and expose the bare soil, which can result in surface crusting and poor germination. Deep tillage practices may, however, appear to be fair treatments during the first few years after clearing. Shallow tillage techniques yielded highest in the experiments for rice and maize and can also protect the soil well against erosion, if enough crop residues are available and if they are mixed in the surface layer (4.4.3.2.1).The bulk density showed a considerable increase over a five-year period, and the pore volume decreased accordingly (4.4.3.2.2). Mulching had a positive effect on quantitative root growth, and deep tillage practices resulted in reduced root growth for rice and maize in the 0-10 cm layer, while zero tillage showed a reduced root growth in the 10-20 cm layer for rice. In general, shallow tillage techniques resulted in more quantitative root growth than the other tillage practices (4.4.3.2.2). Soil moisture, which had become a limiting factor because of the increased bulk density, was highest following shallow tillage; zero tillage resulted in the lowest soil moisture, while deep tillage conserved soil moisture best, resulting in less wilting during dry periods. Mulching increased soil moisture and the water- holding capacity (4.4.3.2.4 and 4.4.3.2.5). Deep tillage resulted in a reduced number of plants and delayed maturity (4.4.3.2.6). Mulching increased the infiltration rates, and infiltration was highest for zero tillage, followed by deep tillage and shallow tillage (4.4.3.2.7). The most important soil chemical changes were a reduction in pH and available P (4.4.3.2.8).Differences in nutrient uptake by the plants for the different treatments could not be detected (4.4.3.2.9).On the lower slope soils a two-year experiment was conducted on Iregun soil, which had one crop of maize after land-clearing before the experiment was started (4.4.4.2). As compaction already occurs under natural forest conditions, zero tillage rechniques will not perform well. Bulk densities following ploughing (20 cm deep) were considerably lower than following zero and shallow tillage, especially in the 10-20 cm layer (4.4.4.2.2), and root growth was much better following ploughing (4.4.4.2.3). Ploughing showed a higher soil moisture (4.4.4.2.4) and a higher water-holding capacity than zero and shallow tillage (4.4.4.2.5). Plant growth was significantly higher following ploughing (4.4.4.2.6). Infiltration rates were highest following ploughing (4.4.4.2.7). Chemical changes in comparison to the natural conditions could not be measured, although the pH and the available P appeared to have decreased (4.4.4.2.8). Plant tissue analysis did not indicate any difference between the tillage treatments (4.4.4.2.9).The effect of mulching on soil physical characteristics was less clear on the lower slope soil compared to the plateau soil; mulching did not appear to have an effect on soil chemical properties of both soils.Poorly-drained soilsOn the poorly-drained soils without water control soil tillage to a reasonable depth (about 15 cm) resulted in higher yields than zero tillage during the wet season, while during the dry season zero tillage yielded higher, although the yield levels then were much lower (4.5.2.1). Mulching in general had a negative rather than a positive effect on yields. Good water management proved to be the most important factor for high yields (4.5.2.3). On poorly-drained soils with water control three series of experiments were conducted.The first, comparing wet and dry tillage on newly developed paddy lands, showed that wet tillage results in significantly higher yields than dry tillage on the light, sandy loam soils where the creation of a plough-pan, which can be done most quickly through wet tillage practices, is important to reduce leaching losses (4.5.3.4). A description of the layer stratification in puddled soil is given (4.5.3.4.3).The second series of experiments dealt with the timing of wet land preparation in relation to different amounts of rice straw to be incorporated (4.5.3.5). These experiments did not indicate any significant effect of different tillage times or of increased amounts of incorporated rice straw, although there were some indications that primary tillage at about two weeks before sowing or transplanting seemed to offer minimum risks (4.5.3.5. 1).The third series studied different wet tillage practices on sandy, loamy and clayey soil types (4.5.3.6). Zero tillage techniques, which hardly create a ploughpan, resulted in lower yields, especially on the lighter soils. Intensive puddling or ploughing and harrowing during the first crops after land development, created the desired plough-pan most quickly and resulted in the highest yields, while during the subsequent crops less intensive tillage practices yielded equally high as intensive tillage. The % increase due to nitrogen application was highest for the lightest soil and also highest for zero tillage (4.5.3.6. 1). These results show the importance of tillage-nitrogen interactions, especially with zero tillage techniques. IWeed controlTillage effects on weed growth were studied and showed that deep tillage treatments resulted in less weed growth than shallow tillage techniques, while zero tillage resulted in the most quantitative weed growth (5.4.1). Tillage at the end of the wet season did not reduce the amount of weeds grown compared to the conventional tillage at the beginning of the wet season, although there was a marked change in the weed species grown following these two treatments (5.4.1).On poorly-drained soils, good water control and intensive puddling or ploughing with harrowing were most effective in reducing the weed growth (5.4.2).Manual and mechanical weeding practices were compared under upland conditions with rice (5.5.1) and indicated that manual weeding is very effective, but requires a lot of time, and that mechanical inter-row weeding is not very effective. Also in combination with manual weeding, mechanical weeding did not result in reduced labour requirements, compared to manual weeding alone, while the yields were reduced.A model experiment with inter-, intra-row and complete weeding treatments indicated the same results and it was concluded, therefore, that mechanical weeding methods are of little or no use with upland rice.Chemical weed control methods, either alone or in combination with manual weeding, yielded highest, while the labour requirements were fairly low.ConclusionMechanization of West African agriculture is only at a starting point, but its importance will increase considerably, if and when the prevailing subsistence farming becomes commercialized agriculture.Soil tillage and weed control are the main limiting factors in the production process of most crops.Soil tillage requirements vary for different soil types and can have an effect on the desired level and type of mechanization.Weed control is a serious problem and alternative methods to manual weeding are needed.

<em>Introduction</em>Mechanization in West Africa has been of limited importance and influence for farming and manual labour is the dominant power input. At present only about 0.07 kW per ha is applied, while at least about 0.37 kW is desirable to obtain high yield levels.In this mechanization study a review is given of the inter-relationships of socioeconomic and agro-ecological factors with agricultural development and with agricultural mechanization in particular and of the different forms of and policies on mechanization (Chapter 2). Some model studies on mechanization are reported, which indicate the importance and constraints of soil tillage and weed control for most mechanization levels. The model study on vegetables also indicated the importance of different land preparation practices on yields (Chapter 3). Soil tillage studies were therefore carried out, with the emphasis on rice (Chapter 4). These studies were conducted in several places along a typical toposequence, from purely upland (rainfed) conditions to irrigated conditions. The weed growth effects of different tillage practices are reviewed and the results with manual and mechanical weed control practices in rice are indicated (Chapter 5).<em>Principles of mechanization and mechanization stategy</em>Mechanization has obvious advantages, but can also have disadvantages. The most important advantages are: increased land and labour productivity, increased yields, higher profits, reduced costs, reduction of drudgery and reduced losses (2.3). The most important constraints are related to socioeconomic and technical factors (2.3). Socio-economical problems are also the most prohibiting to the introduction of new technology (2.4).Four levels of mechanization can be distinguished: manual labour, animal draught, small-scale mechanization based on small tractors and large-scale mechanization based on standard four-wheel tractors (2.5). Manual labour is cheap, but offers serious limitations for increased area under cropping and for increasing cropping intensities (2.5.2). Animal draught cannot be applied in the humid parts of West Africa, because of <em>Trypanosomiasis</em> ; <em></em> in the savannah areas it is locally available and relatively cheap, while it can help increase the area under cropping (2.5.3). Two-wheel tractors have not found any significant application in West Africa; they can offer serious ergonomical disadvantages, while the costs per hp and per ha are high. It is argued that small four-wheel tractors should be pursued instead (2.5.4.3). So far mechanical power in Africa has come almost exclusively from standard four-wheel tractors. Their application has had considerable impact in some instances, while in other cases they have been failures, due to inadequate planning, management and support and because other necessary conditions were not met (2.5.4.4).Four mechanization 'philosophies' are reviewed (2.6).Intermediate, or sometimes called appropriate, technology is a term used to describe a technology which is compatible with the prevailing socio-economic and technical local conditions and most advocates also argue that this type of technology should be designed in such a way, that it can be made locally from locally available materials (2.6.2).Selective mechanization, sometimes indicated as partial mechanization, emphasizes that mechanization should only be applied under those conditions or situations and during those stages in the production-marketing process, where labour is the limiting factor (2.6.3).Tractor hiring services have been the main means by which mechanical power until now has been applied in West Africa; they are based on standard four-wheel tractors. These hiring services are usually started as Government operated units and it is argued that these should be handed over to private individuals as soon as possible (2.6.4).Large-scale farming with large-scale equipment has been exercised by various Governments in West Africa and its performance has been mostly negative, due to socio-economic and agro-ecological, as well as technical, restrictions. It is argued that intensification, rather than developing new largescale projects, is a more secure and faster way of increasing food production (2.6.5).Some aspects of the agro-ecology and the socio-economics are reviewed (2.7). It is emphasized that soils and crops have to be selected well before mechanization is applied. The mechanization potentialities are indicated to be best for hydromorphic: areas and for rice (2.7.2), and it is argued that irrigation developments will stimulate mechanization most.Cost calculations for the different levels of mechanization are made and they indicate that, although the costs per hour are lower for two-wheel tractors, the costs per hp and per hectare (for soil tillage) are lower for standard four-wheel tractors (2.7.3.1).The importance of the ergonomical aspects (2.7.3.2.), as well as of the social acceptability of new technology is indicated (2.7.3.3).The effect of mechanization on employment is reviewed (2.8). It is argued that mechanization undoubtedly can create unemployment or increased underemployment under certain conditions, but that the introduction of irrigation and the new seed-fertilizer technology coupled with a selective introduction of mechanization increases rather than reduces labour requirements. So far, mechanization in West Africa has not shown any serious labour displacing effects.In the general discussion (2.9) it is argued that for West African conditions private tractor hiring units could possibly be the best solution for the short and medium term basis, to get mechanization developments started. In this way mechanization will be introduced selectively, since the farmers decide for which operations they want the mechanization services applied.Intermediate technology may start slowly as the technical capabilities and the socio-economic acceptability of the new technology develop in the rural areas and it can be visualized that on a medium and long term basis this type of technology will supplement the basic (mainly soil tillage) operations, as carried out by the standard four-wheel tractors of the hiring services. The scope for twowheel tractors seems limited, although their application in hydromorphic valleys with rice or in market gardening seems to be feasible. It is argued that small four-wheel tractors instead could possibly find easier application and acceptance.It is concluded that farming in West Africa will mainly depend, for many years to come, on manual labour and that mechanization will become increasingly important, as soon as a 'Green Revolution' is set in motion.<em>Model studies on mechanization systems</em>Two model studies are reported. The first study concentrated on rice and made use of available data on time and labour requirements for the various operations in the production process for different levels of mechanization (3.2). The second study was a field study with vegetables, in which all inputs were recorded and yields were measured (3.3).The main purpose of the model studies was to determine which operations in the production process are most limiting to an increased area under cropping for different mechanization levels, while an additional objective in the second study was to investigate the effects of different mechanization levels on yields and profitability.The rice mechanization study indicated that, although transplanting and harvesting and threshing can offer restrictions, in general soil tillage and weed control are the major limiting factors for all steps in mechanization development; these two operations claim between 40 and 60% of the total labour requirements.The field study with vegetables, where two mechanization levels were applied, also indicated that soil tillage and weed control were major bottlenecks, in the manual system soil tillage and weeding were equally limiting, taking together as an average about 54% of the total input hours, while in the tractor system weed control was far more limiting than soil tillage, taking on average about 29% of the total labour requirements, about 25% of which for weeding. This study demonstrated the effects of different land preparation practices, inherent to the two mechanization systems, on yields; while most crops reacted positively to the tractor tillage (about 15 - 20 cm deep), some crops reacted favourably to the shallow manual hoeing (about 4-6 cm deep). In general, this field study indicated that growing vegetables under the tractor system resulted in higher yields, lower production costs and higher net income per manhour of labour input than under the manual system.<em>Soil tillage</em>Soil tillage and weed control are studied in more detail in this mechanization study, because they are usually the major limiting factors in the crop production process, because most mechanized inputs in West African agriculture have so far been in land preparation, and because soil tillage studies and recommendations can have considerable effects on the desirable level and type of mechanization (4.1).Soil tillage studies were carried out in several places along a typical toposequence, which consists of three major soil groups: the plateau soils (well-drained), the lower slope soils (well-drained) and the valley soils (poorly-drained).<font size="+1">Well-drained soils</font>Two experiments were conducted on the plateau soils, a five-year long experiment on Egbeda soil, which was newly-cleared (4.4.3.2), and a one-year experiment on Iwo soil, which had been cleared for one year (4.4.3.3).On the plateau soils zero or minimum tillage techniques may be feasible if enough crop residues are available. Without crop residues these techniques perform poorly. Deep tillage practices are not to be recommended, as they turn up gravel and expose the bare soil, which can result in surface crusting and poor germination. Deep tillage practices may, however, appear to be fair treatments during the first few years after clearing. Shallow tillage techniques yielded highest in the experiments for rice and maize and can also protect the soil well against erosion, if enough crop residues are available and if they are mixed in the surface layer (4.4.3.2.1).The bulk density showed a considerable increase over a five-year period, and the pore volume decreased accordingly (4.4.3.2.2). Mulching had a positive effect on quantitative root growth, and deep tillage practices resulted in reduced root growth for rice and maize in the 0-10 cm layer, while zero tillage showed a reduced root growth in the 10-20 cm layer for rice. In general, shallow tillage techniques resulted in more quantitative root growth than the other tillage practices (4.4.3.2.2). Soil moisture, which had become a limiting factor because of the increased bulk density, was highest following shallow tillage; zero tillage resulted in the lowest soil moisture, while deep tillage conserved soil moisture best, resulting in less wilting during dry periods. Mulching increased soil moisture and the water- holding capacity (4.4.3.2.4 and 4.4.3.2.5). Deep tillage resulted in a reduced number of plants and delayed maturity (4.4.3.2.6). Mulching increased the infiltration rates, and infiltration was highest for zero tillage, followed by deep tillage and shallow tillage (4.4.3.2.7). The most important soil chemical changes were a reduction in pH and available P (4.4.3.2.8).Differences in nutrient uptake by the plants for the different treatments could not be detected (4.4.3.2.9).On the lower slope soils a two-year experiment was conducted on Iregun soil, which had one crop of maize after land-clearing before the experiment was started (4.4.4.2). As compaction already occurs under natural forest conditions, zero tillage rechniques will not perform well. Bulk densities following ploughing (20 cm deep) were considerably lower than following zero and shallow tillage, especially in the 10-20 cm layer (4.4.4.2.2), and root growth was much better following ploughing (4.4.4.2.3). Ploughing showed a higher soil moisture (4.4.4.2.4) and a higher water-holding capacity than zero and shallow tillage (4.4.4.2.5). Plant growth was significantly higher following ploughing (4.4.4.2.6). Infiltration rates were highest following ploughing (4.4.4.2.7). Chemical changes in comparison to the natural conditions could not be measured, although the pH and the available P appeared to have decreased (4.4.4.2.8). Plant tissue analysis did not indicate any difference between the tillage treatments (4.4.4.2.9).The effect of mulching on soil physical characteristics was less clear on the lower slope soil compared to the plateau soil; mulching did not appear to have an effect on soil chemical properties of both soils.<font size="+1">Poorly-drained soils</font>On the poorly-drained soils without water control soil tillage to a reasonable depth (about 15 cm) resulted in higher yields than zero tillage during the wet season, while during the dry season zero tillage yielded higher, although the yield levels then were much lower (4.5.2.1). Mulching in general had a negative rather than a positive effect on yields. Good water management proved to be the most important factor for high yields (4.5.2.3). On poorly-drained soils with water control three series of experiments were conducted.The first, comparing wet and dry tillage on newly developed paddy lands, showed that wet tillage results in significantly higher yields than dry tillage on the light, sandy loam soils where the creation of a plough-pan, which can be done most quickly through wet tillage practices, is important to reduce leaching losses (4.5.3.4). A description of the layer stratification in puddled soil is given (4.5.3.4.3).The second series of experiments dealt with the timing of wet land preparation in relation to different amounts of rice straw to be incorporated (4.5.3.5). These experiments did not indicate any significant effect of different tillage times or of increased amounts of incorporated rice straw, although there were some indications that primary tillage at about two weeks before sowing or transplanting seemed to offer minimum risks (4.5.3.5. 1).The third series studied different wet tillage practices on sandy, loamy and clayey soil types (4.5.3.6). Zero tillage techniques, which hardly create a ploughpan, resulted in lower yields, especially on the lighter soils. Intensive puddling or ploughing and harrowing during the first crops after land development, created the desired plough-pan most quickly and resulted in the highest yields, while during the subsequent crops less intensive tillage practices yielded equally high as intensive tillage. The % increase due to nitrogen application was highest for the lightest soil and also highest for zero tillage (4.5.3.6. 1). These results show the importance of tillage-nitrogen interactions, especially with zero tillage techniques. I<em>Weed control</em>Tillage effects on weed growth were studied and showed that deep tillage treatments resulted in less weed growth than shallow tillage techniques, while zero tillage resulted in the most quantitative weed growth (5.4.1). Tillage at the end of the wet season did not reduce the amount of weeds grown compared to the conventional tillage at the beginning of the wet season, although there was a marked change in the weed species grown following these two treatments (5.4.1).On poorly-drained soils, good water control and intensive puddling or ploughing with harrowing were most effective in reducing the weed growth (5.4.2).Manual and mechanical weeding practices were compared under upland conditions with rice (5.5.1) and indicated that manual weeding is very effective, but requires a lot of time, and that mechanical inter-row weeding is not very effective. Also in combination with manual weeding, mechanical weeding did not result in reduced labour requirements, compared to manual weeding alone, while the yields were reduced.A model experiment with inter-, intra-row and complete weeding treatments indicated the same results and it was concluded, therefore, that mechanical weeding methods are of little or no use with upland rice.Chemical weed control methods, either alone or in combination with manual weeding, yielded highest, while the labour requirements were fairly low.<em>Conclusion</em>Mechanization of West African agriculture is only at a starting point, but its importance will increase considerably, if and when the prevailing subsistence farming becomes commercialized agriculture.Soil tillage and weed control are the main limiting factors in the production process of most crops.Soil tillage requirements vary for different soil types and can have an effect on the desired level and type of mechanization.Weed control is a serious problem and alternative methods to manual weeding are needed.