Feasibility and Acceptability

(based on Degrande and Duguma 2000; Kanmegne and Degrande 2002)

Between 1994 and 1998, periodic surveys were conducted with experimenting farmers to document their assessment of rotational hedgerow intercropping, to determine the problems they were having with management and to monitor modifications introduced (Degrande and Duguma 2000). In 1995/1996, a survey of 44 households involved in testing the technology was undertaken. The study provided baseline data on socio-economic conditions of trial households and revealed key characteristics that are likely to influence adoption of rotational hedgerow intercropping (Degrande and Duguma 2000).

Rotational hedgerow intercropping is a labour-intensive technology and is unlikely to be adopted where labour is a limiting factor. Monitoring of on-farm trials showed that the first pruning, approximately 4 weeks after planting was carried out in 80 % of the tree plots, however it was often done too late. On the other hand, the second pruning was neglected in 67 % of the cases. Farmers said that they were very busy with crop weeding at that time and many thought that tree coppices could not harm the crops anymore. Fifty-seven percent of the respondents explicitly complained about time required for tree cutting.

The incentive to adopt hedgerow intercropping for the purpose of erosion control in the study villages appears to be low. Survey results suggest that farmers do not consider erosion in the study area as a major problem. Seventy-five percent indicated that less than 1/4 of their fields are on steep slopes whereas only 4 % reported that more than 3/4 of their fields are on steep slopes (steep, as defined by each farmer).

According to Carter (1995a; 1995b), hedgerow intercropping is more likely to be adopted in areas with high land pressure. In the study area however, 64 % of households reported that they have enough land to meet the needs of the family. Seventy-three percent indicated that it is still possible to get more land in the village, provided one has the means to buy or rent. Only 16 % reported that they had no possibility of acquiring additional land. However, there is evidence that forest land is becoming scarce, especially near Yaoundé. Only 2 out of 44 households had cleared land from the forest after 1990, whereas 66 % reported that the last time they had cleared forest land was before 1980. The average fallow period in Yaoundé area is estimated at 4 years (IITA 1996).

By-products are known to be an additional incentive for farmers to adopt tree fallows. In spite of evidence that firewood is still abundant in the study area, 67 % of the trial farmers said that they collect firewood from the pruned hedgerows. Furthermore, the production of stakes for yam and tomatoes is well appreciated by experimenting farmers. Eighty percent of them used wood from hedges for staking whereas it was mentioned as the main benefit by 47 % of respondents.

Feedback to Research

In the conventional hedgerow system (tested from 1988 to 1993), trees were planted in rows with distances of 4 m between rows and 0.25 m within rows. A year later, hedgerow trees were cut back at 0.5 m above ground level and the tree prunings were incorporated in the soil as mulch (Kang and Wilson 1987). These management options were observed to have several shortcomings (IRA/ICRAF 1996), including:

(1) Poor hedgerow tree growth, thus low biomass yield due to premature cut back (only 1 year after planting) and too frequent pruning (two to three times per cropping cycle);

(2) High labour demand and low flexibility in time of tree pruning. The resprouts of trees pruned at 0.5 m rapidly overshadow adjacent crops, causing yield suppression. To avoid this, farmers need to prune hedgerow trees as soon as resprouts start hindering crop growth. Research results recommend pruning of hedgerow trees respectively before planting (during land preparation), 4 weeks (during first crop weeding) and 8 weeks (during second crop weeding) after planting.

(3) Low impact on weed control and nutrient cycling due to absence of a tree fallow phase. Fast growing trees, such as calliandra and leucaena, planted in rows of 4 m close canopy after 1 year of fallow, allowing to shade out weeds efficiently.

To address the above problems, the management of the conventional hedgerow system was modified in 1993. Some of the modifications were greatly inspired by observations in farmers’ fields and informal discussions with pilot farmers. The modifications deal with aspects of pruning height and frequency, cropping intensity and combination of crops, residue management, and agroforestry tree species used (Kanmegne and Degrande 2002).

a) Pruning Height and Frequency

Recommended pruning height was initially at 0.50 m above ground level; hedges were pruned three times during each cropping phase: before crop planting, then 4 and 8 weeks later. The plots were cropped twice a year, resulting in 6 prunings per year. Farmers complained that they lacked appropriate tools to prune trees well. They also reported that respecting the pruning height of 0.50 m took too much time compared to the traditional system where slashing is done at ground level. With these remarks, it was suggested to prune hedges at ground level (or 0.05 m). All interviewed farmers appreciated the change in cutting height, which also reduced pruning frequency. Subsequent surveys showed that the first pruning - approximately 4 weeks after planting - was carried out in 80 % of the farms, but the second pruning - about 8 weeks after planting - was done only in 33 % of the farms. Farmers considered hedgerow regrowth not to be harmful to the adjacent maize crop at that stage because the maize had already reached a height, allowing it to compete with hedgerow tree resprouts. This was considered as an added advantage of pruning at ground level.

Tree establishment: calliandra is planted

alongside maize After harvest of maize, calliandra is left to grow for about 2 years

During the fallow period, beehives are placed in the calliandra tree plot

After the fallow phase, calliandra is cut back

b) Cropping Intensity and Crop Combination

While during on-station and in researcher-designed/researcher-managed (type I) on-farm trials maize was the sole test crop, most of the farmers preferred associating groundnut and cassava with maize. This mixture of crops affected the management of hedgerows considerably. First, unlike maize (harvested after 3 months), cassava is a crop that takes between 6 and 18 months to mature, depending on the variety used. Second, cassava is harvested progressively over time. In fact, since storage of harvested tubers in the humid tropics is difficult, farmers prefer “storage in the soil” and harvest cassava tubers when need arises. Thirdly, after cassava harvest, farmers usually allow the plot to enter a fallow phase of at least one year before a new crop is planted. This is because cassava exhausts soil nutrients quickly. As a result of associating cassava, hedgerow plots were thus entering a fallow phase, allowing leguminous trees to grow. Consequently, initial alley cropping or hedgerow intercropping shifted to a rotational tree fallow (Annex 3). This rotational tree fallow system favoured recycling of nutrients with the possibility of obtaining higher crop yields. The majority of farmers using this technology (93 %) mentioned an improvement in soil fertility whereas 71 % reported increased yield in the tree plots compared to the control plot. The fact that during the fallow phase hedgerow trees were allowed to grow longer also offered opportunities to obtain by-products of the trees, such as stakes, fuelwood and honey, mentioned by 67 % of interviewed farmers.

After having observed these added benefits of introducing a fallow phase, rotational tree fallow was now recommended to farmers, independently of the kind of crops planted in the alleys.

c) Residue Management

In the original design of hedgerow intercropping, the leafy materials of the prunings were applied as mulch while the wood was removed from the plots. With the introduction of a fallow phase, however, wood biomass increased considerably because the trees were now allowed to grow longer. Leucaena wood biomass for example increased from 4.5 t ha-1 _to

10.1 t ha-1 _{and with gliricidia from 1.9 t ha}-1 _{to 3.4 t ha}-1 _{after two years of fallow. This}

increase in tree biomass makes management of the residues a time-consuming and labour- intensive activity, in addition to the fact that a lot of nutrients contained in the wood are exported from the field. Farmers modified residue management in rotational tree fallows after having observed what happened in a tree plot that was incidentally burnt. The best branches were removed and used as stakes (mentioned by 80 % of interviewed farmers) or taken home for use as fuelwood in the kitchen (67 %), whereas the remaining wood was burnt in the field. In this type of burning, also referred to as ‘spot burning’, tree leaves are removed from the branches and woody residues are piled in the middle of the alley, where they are burnt. During land preparation, ash is spread over the alley and incorporated in the soil together with the mulch. The fact that leaves are separated from the branches avoids burning of leaves, so that they can rather decompose. Nevertheless, 60 % of farmers admitted that some leafy material is usually burnt. Spot burning is reported to increase phosphate and cation levels of the surface soil through addition of ash. It cleans the land of great masses of residues, reduces weed seeds in the soil and increases soil pH (Kang and Saggapongse 1980, Tonye et al. 1997).

d) Agroforestry Species

Leucaena leucocephala and Gliricidia sepium were initially introduced as best suited agroforestry species for the humid forest zone of Cameroon (Tonye et al. 1994). After experimenting a number of years, farmers complained that leucaena was too invasive and that the biomass yield of gliricidia stands decreased significantly over the years. In response, researchers introduced Calliandra calothyrsus, which was previously screened on-station. This species produces few seeds, so is not invasive, and performs as well as leucaena for soil fertility restoration in the humid lowlands of Cameroon (Duguma and Tonye 1994; Duguma et al. 1994; Duguma 1995; Duguma and Mollet 1995). Calliandra also has the added advantage of providing fodder and producing flowers throughout the year, making it an excellent melliferous plant (Duguma and Mollet 1997). With increasing interest of farmers in Cameroon for bee farming, calliandra was the most suitable tree species and farmers shifted from gliricidia and leucaena to calliandra fallow.

With this added flexibility in technology design, a growing interest from farmers to plant hedgerows was observed between 1996 and 1998. The total number of farmers with hedgerows increased from 57 in 1996 to 236 in 1998, whereas more NGOs and farmer associations were asking for tree seeds. Eighty-six percent of experimenting farmers said to be satisfied with the technology and 42 % spontaneously expanded their tree plot. The increased spread of tree fallows in the humid lowlands of Cameroon was mainly due to efforts from NGOs, which actively promoted the technology by distributing tree seeds to interested farmers and providing them with technical assistance.