**4. Cover cropping and improved short-season fallow with leguminous cover crop**

The practice of planting certain crops to cover the cultivated area of fallow land thereby pro‐ viding protection for the purpose of reducing erosion by rain drop splash and surface runoff and weed growth is referred to as cover cropping. Where necessary, cover crops are cut down or killed by weedicides so that the seasonal crops can be planted in the mulch.

Improved short fallow is the planting of leguminous cover crops consciously with the objec‐ tive of protecting the soil surface and fixing nitrogen as part of the crop fallow. The system is practiced where land is limited and farmers rely on little or no external soil enhancing ma‐ terials to improve the soil fertility status. Examples of cover crops*: Mucuna pruriens, Dolicus lablab Canavalia ensiformis.* Sometimes edible cover crops such as the creeping types of cow‐ pea are used.

Improved fallow systems using e.g. *Mucuna puriens* are promoted by different projects in Ghana. So far, the system seems to be adopted only by some farmers in certain areas (Quan‐ sah et al., 1998). Benefits observed by the farmers may vary and include increased soil mois‐ ture, weed suppression and residual yield effects on maize. Leguminous fallows have been used in northern Ghana to accumulate N from biological N fixation (BNF), smother weeds, and improve soil physical properties (Fosu et al., 2004). Leguminous cover crop systems ap‐ parently were more extensively tested than tree fallow systems in the country. Demand for arable land in many parts of the country has increased in recent years in response to increas‐ ing human population. This situation is gradually moving the emphasis from resting fallow to continuous and intensive cropping. However, some farmers in southern Ghana can still fallow their lands up to two years or two seasons. Leguminous cover crops such as *Callopo‐ gonium, Dolichos, Mucuna* and *Cannavalia* species are the main cover crops used during this short fallow. In the north, farm lands to undergo short term fallow of about two years were planted to either *Mucuna* or *Callopogonium* and left for these number of years. In the third year the residue was either ploughed in or if it was dry, the crop was planted directly into the mulch. This system was found to increase maize yields in both on-station and on-farm trials (Kombiok et al, 1995) as seen in Table 1. The highest mean yield of maize was obtained when residue was left but maize planted in it and this could be due to the micro-climate cre‐ ated by the residue on the surface and the decay of some of the residue to make N available to the crop.

**Treatments**

2WAP. Weeks after planting

Source: Kombiok and Clottey 2003

weeding of *Mucuna* vines at certain intervals.

ideal cover crop to use in mixed-cropping systems.

**5. Cropping systems**

Control 6 WAP 8 WAP 10 WAP

mucuna

**Maize grain yield (kg ha-1)1 1996 1997 1998**

Enhancing Soil Fertility for Cereal Crop Production Through Biological Practices and the Integration of Organic...

1180 b 1620 a 1110 b 1530 a 1050 d 1850 a 1650 b 1250 c

7

http://dx.doi.org/10.5772/53414

1800 a 1500 b 1130 c 1100 c

1For a factor. means followed by a similar letter in a column are not significant at 5% level of significance

**Table 2.** Maize grain yield as affected by time of interplanting mucuna in maize and after two years of continuous

In some cases where weed infestation is high, farmers still have to do one weeding. After establishment, the *Mucuna* survives the short dry period during July–August and later forms a thick biomass that peaks in mid-November. This biomass canopy then covers the soil until it starts to decompose in the dry season in December– January. *Mucuna* seeds are then harvested and stored for later use. Unlike the late-maturing *Mucuna* variety, planting the medium- to early-maturing mottled variety is done at the onset of the minor season (Loos et al. 2001). Clearing and at least one initial weeding may be necessary for successful establishment. Once established, the biomass covers the soil surface and dies back naturally with the onset of the dry season. This means that no other food crop can be planted on the land that has an improved *Mucuna* fallow. After the improved fallow, farmers plant any oth‐ er crop such as maize, yam, cassava or plantain. Incorporating *Mucuna* into the local crop‐ ping systems by intercropping *Mucuna* with plantain during the first season can be very economical. Such a system reduces the overall demand for labour, as it requires only spot

In places where rice cultivation is significant, farmers have developed and adapted *Mucuna*– rice rotations. Here, farmers cultivate rice in the major season and follow it with *Mucuna* in the minor season to suppress weeds and improve the fertility of the soil. *Canavalia ensiformis* did not attract the same attention as *Mucuna* because it was less vigorous in growth and did not suppress weeds as well as *Mucuna*. The less aggressive nature of *Canavalia* made it an

A cropping system may be defined as a community of plants which is managed by a farm unit to achieve various human goals (FAO, 1995). In this particular case the cropping system

is to achieve an enhanced soil fertility status for increased crop production.


**Table 1.** Maize Yield (kg/ha) under 4 different Management Practices after 2 years of *Callopogonium* fallow and three rates of nitrogen fertilizer at Nyankpala

In the wetter southern parts of the country, *Cannavalia or Mucuna* is planted as a minor-sea‐ son fallow, from August to March. In the next major season beginning in April, farmers plant their crops (maize, yam, cassava or any other crop) through the mulch without burn‐ ing. Weed control in the crops is by the hoe in northern Ghana and cutlass in southern Gha‐ na when necessary. Where rainfall during the major season is not reliable, farmers plant the cover crop in April, and plant the food crop in the minor season (August–September). A synthesis of results of trials of a *Mucuna* fallow system by Carsky et al. (2001) suggested that in simultaneous intercropping systems, the yield of maize associated with *Mucuna* is de‐ creased dramatically as the Mucuna smothers the maize. However, maize yield reduction from relay intercropping of Mucuna at 40 to 50 days after maize planting is only about 5%.

Similarly, in a 2-yr study on a typical plinthic Planleustalf in the savanna zone of Ghana, Kombiok and Clottey (2003) found that maize grain yields obtained after two years of inter‐ planting *Mucuna* was highest at 6 weeks after planting followed by 8 weeks after planting and the least was obtained from 10 weeks after planting (Table 2). It was also found that N was highest in the plot with *Mucuna* planted 6 and 8 weeks after maize compared to 10 weeks and the bush fallow treatments due to the amount of biomass produced by the cover crop. They concluded that the highest yields of maize from relay cropping of *Mucuna* at 6 weeks after maize was due to the beneficial effects of the decay of the higher *Mucuna* bio‐ mass produced in that treatment in the previous years. It is clear that if *Mucuna* does not accumulate substantial biomass, then it will not accumulate sufficient N as well as suppress weeds. They however recommended the pruning of Mucuna as a management strategy to ensure it does not smother the maize crop in association with the cover crop.

Enhancing Soil Fertility for Cereal Crop Production Through Biological Practices and the Integration of Organic... http://dx.doi.org/10.5772/53414 7


1For a factor. means followed by a similar letter in a column are not significant at 5% level of significance

2WAP. Weeks after planting

when residue was left but maize planted in it and this could be due to the micro-climate cre‐ ated by the residue on the surface and the decay of some of the residue to make N available

**Table 1.** Maize Yield (kg/ha) under 4 different Management Practices after 2 years of *Callopogonium* fallow and three

In the wetter southern parts of the country, *Cannavalia or Mucuna* is planted as a minor-sea‐ son fallow, from August to March. In the next major season beginning in April, farmers plant their crops (maize, yam, cassava or any other crop) through the mulch without burn‐ ing. Weed control in the crops is by the hoe in northern Ghana and cutlass in southern Gha‐ na when necessary. Where rainfall during the major season is not reliable, farmers plant the cover crop in April, and plant the food crop in the minor season (August–September). A synthesis of results of trials of a *Mucuna* fallow system by Carsky et al. (2001) suggested that in simultaneous intercropping systems, the yield of maize associated with *Mucuna* is de‐ creased dramatically as the Mucuna smothers the maize. However, maize yield reduction from relay intercropping of Mucuna at 40 to 50 days after maize planting is only about 5%.

Similarly, in a 2-yr study on a typical plinthic Planleustalf in the savanna zone of Ghana, Kombiok and Clottey (2003) found that maize grain yields obtained after two years of inter‐ planting *Mucuna* was highest at 6 weeks after planting followed by 8 weeks after planting and the least was obtained from 10 weeks after planting (Table 2). It was also found that N was highest in the plot with *Mucuna* planted 6 and 8 weeks after maize compared to 10 weeks and the bush fallow treatments due to the amount of biomass produced by the cover crop. They concluded that the highest yields of maize from relay cropping of *Mucuna* at 6 weeks after maize was due to the beneficial effects of the decay of the higher *Mucuna* bio‐ mass produced in that treatment in the previous years. It is clear that if *Mucuna* does not accumulate substantial biomass, then it will not accumulate sufficient N as well as suppress weeds. They however recommended the pruning of Mucuna as a management strategy to

ensure it does not smother the maize crop in association with the cover crop.

**Treatment 0 N kg/ha 40 N kg/ha Mean**

to the crop.

6 Soil Fertility

Mean

1-Residue not removed /No till 2-Residue removed/No till 3-Residue worked in by hoeing 4-Residue removed/hoeing

Source: Kombiok et al 1995

rates of nitrogen fertilizer at Nyankpala

Source: Kombiok and Clottey 2003

**Table 2.** Maize grain yield as affected by time of interplanting mucuna in maize and after two years of continuous mucuna

In some cases where weed infestation is high, farmers still have to do one weeding. After establishment, the *Mucuna* survives the short dry period during July–August and later forms a thick biomass that peaks in mid-November. This biomass canopy then covers the soil until it starts to decompose in the dry season in December– January. *Mucuna* seeds are then harvested and stored for later use. Unlike the late-maturing *Mucuna* variety, planting the medium- to early-maturing mottled variety is done at the onset of the minor season (Loos et al. 2001). Clearing and at least one initial weeding may be necessary for successful establishment. Once established, the biomass covers the soil surface and dies back naturally with the onset of the dry season. This means that no other food crop can be planted on the land that has an improved *Mucuna* fallow. After the improved fallow, farmers plant any oth‐ er crop such as maize, yam, cassava or plantain. Incorporating *Mucuna* into the local crop‐ ping systems by intercropping *Mucuna* with plantain during the first season can be very economical. Such a system reduces the overall demand for labour, as it requires only spot weeding of *Mucuna* vines at certain intervals.

In places where rice cultivation is significant, farmers have developed and adapted *Mucuna*– rice rotations. Here, farmers cultivate rice in the major season and follow it with *Mucuna* in the minor season to suppress weeds and improve the fertility of the soil. *Canavalia ensiformis* did not attract the same attention as *Mucuna* because it was less vigorous in growth and did not suppress weeds as well as *Mucuna*. The less aggressive nature of *Canavalia* made it an ideal cover crop to use in mixed-cropping systems.
