**5.2. Crop rotation and intercropping**

**5.1. Multiple cropping**

8 Soil Fertility

Fisher (1979) and Willey (1979).

Source: Kombiok et al 2005

piece of land in the next cropping season.

It is the growing of different arable crops and /or other crops on a given piece of land at the same time. The aim is to increase the productivity from the land while providing protection of the soil from erosion. Growing more than one crop at the same time also cushions the farmer against total crop failure as adverse growing conditions might not affect the different crops equally-*sequential cropping* (growing two or more crops on the same piece of land with‐ in the same year or season but planting one after harvesting the other) or *intercropping* which is the growing of two or more crops on the same piece of land at the same time (Abalu, 1977). The existence of multiple cropping especially intercropping system involving mostly cereals and legumes among the small scale farmers of West Africa has long since been iden‐ tified (Norman, 1975) and studied by many workers including Andrews and Kassam (1976),

Some of the reasons advanced for the persistence of this system of cropping have been pre‐ cautions against uncertainty and instability of income and unstable soil fertility maintenance (Abalu, 1977). In most of the intercropping trials implemented in the sub-region the results of the crop yields showed that there have been agronomic advantages in the practice since the Land Equivalent ration (LER) is always more than one (1). In addition to the agronomic advantage in terms of yield associated with intercropping systems, a substantial amount of

**Cropping System Maize grain Cowpea grain %N fixed**

Sole 2734 2400 1401 1153 40.47 62.42

Inter 1069 1731 954 544 30.20 34.74

Intra - 1938 - 473 - 28.72

SE 124 111 52 28 6.08 10.89

LSD (0.05) 398 355 166 91 NS NS

**Table 3.** Grain yields (kg ha-1) of maize and cowpea and percent N fixed as affected cropping Systems 2000 and 2001

It was found that more than 50% N was fixed by the component cowpea in maize cowpea mixture. This is very beneficial to the farmers since the cereal crop component of the system will benefit from this N fixed if the legume matures earlier than the cereal. Secondly, there will also be a residual N left in the soil for use by any subsequent crop grown on the same

**2000 2001 2000 2001 2000 2001**

N is also fixed by the leguminous component of the system (Table 3).

Cereal production in Ghana, especially northern Ghana is limited by low levels of nitrogen in the soil. Strategies such as intercropping/mixed cropping and crop rotations involving ce‐ reals and legumes have been adopted to raise crop yields as they fix substantial amounts of atmospheric N, can provide large amounts of N-rich biomass. Legumes grown as a food crop or live mulch (cover crop) can be successfully rotated with a crop which produces high biomass or intercropped with tree species (e.g. alley cropping) in order to provide N, en‐ hance organic matter content and agroforestry. The amount of N returned from legume ro‐ tations depends on whether the legume is harvested for seed, used for forage, or incorporated as a green manure.

Crop rotation entails the growing of different crops in a well defined sequence on the same piece of land- Changing the type of crops grown in the field each season or year. Eg; a field could be planted to maize in the major season as in the south of Ghana and after harvesting, the same field is planted to cowpea in the minor season of the year. In the savanna region this will be done yearly since there is only one rainy season/cropping season in a year.

Crop rotation forms a central pillar of CA, and many approaches highlight the use of cereal– legume rotations. Rotations allow crops with different rooting patterns to use the soil se‐ quentially, reduce pests and diseases harmful to crops and sustain the productivity of the cropping system. The most widely grown legumes in the farming systems of Ghana are the grain legumes; groundnut, cowpea and soybean. These crops have the advantage over other legumes in that they provide a direct economic yield for food or for sale. Yet unless there is a ready market for the grain, farmers tend to grow grain legumes on only a small proportion of their land, and certainly not sufficient to provide a rotation across the farm. Analyses in northern Ghana, where farmers indicated their normal rotation is cereal/legume, showed that the actual area sown to the legume was often less than 30% of the farm area. Further investigation indicated that crop rotations tended to be practiced more on the fertile 'home‐ fields' than on the poorer outfields.

The yield response of cereal crop following a legume can be substantial. In Ghana, the grain yield of sorghum crop following groundnut averaged 30-40% higher than the yield of con‐ tinuous sorghum (Schmidt and Frey, 1992; Buah, 2004). Horst and Härdter (1994) showed large maize yields in northern Ghana following cowpea. In all the cases, crop residue was not removed from the field after harvest. Nonetheless, crop residues are often removed from the field at harvest so they do not provide the mulch cover wanted for CA. Various field experiments have shown that crop rotation of maize with various legumes was beneficial for maize production and that maize following groundnut often had the greatest yields when compared with maize following other legumes (Härdter, 1989; Horst and Härdter, 1994; Schmidt and Frey, 1992). Cotton-maize rotation is the most common rotation system in the northern part of Ghana. Cotton, even though not a legume, its production is accompanied by the application of inputs such as fertilizers and chemicals. Maize is therefore planted af‐ ter cotton to take advantage of the residual fertilizers applied in the previous year. Farmers have reported increases in maize yields in the north by several tons per hectare as a result of cultivating maize after cotton in a rotation system. In southern Ghana where there are two cropping seasons, maize is planted in the major season (April-June) and an edible legume such as cowpea or a cover crop (*Mucuna*) is planted in the minor season.

farm experiments have been found to be higher than the yields from the traditional slash and burn method of farming, it has not been easy to convince farmers to adopt the practice holistical‐ ly. Generally the adoption of CA by farmers in Ghana is therefore low and those who are said to have adopted CA may either be practicing one or two of the principles of CA such as no-till, notill with intercropping but not all the three principles of the practice. Comparatively, climatic and weather conditions in the southern part of the country favour the adoption of some of these principles. For example, the rainfall system in the south is bi-modal with only a dry period of less than three months. This allows the growth and development of vegetation all year round and therefore not prone to bush fires. The decay of these vegetative matter when killed by weedicide,

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On the other hand, the northern part of Ghana has only one rainy season which commences in late May and ends in early November with a dry period of about five months which is characterized by the Hamattan winds. During the dry season, the vegetative matter is dried up and therefore prone to bush fires. The occurrence of bush fires either accidentally or in‐ tentionally, clears up all the dry vegetative cover exposing the soil to the Harmattan winds in the dry season and the running water during the rainy season which robs the soil of its nutrients. It is therefore not surprising to know that farmers in the northern part of the coun‐ try consider any technology that conserves soil and water such as soil bunding as a CA tech‐ nology. Table 4 shows the results of a survey that was carried out to identify technologies related to CA practiced by farmers in the northern part of Ghana. Comparatively, among the districts covered, East Mamprusi recorded a higher percentage of farmers practicing some of these technologies than Lawra or Bawku which according to Ekekpi and Kombiok (2008)

**Technology East Mamprusi (%) Lawra (%) Bawku (%)** Contour bunding 19 47 19 Crop rotation/intercropping 60 3 4 Agro-forestry 3 16 3 Manure/refuse application 22 16 19 Minimum tillage 3 0 0 Crop residue management 31 3 2 Composting/application 50 63 50 Organic farming 0 0 0 Animal traction 4 22 20 Rotation kraaling 3 0 0 Bush fallow 3 0 0

will go a long way to enrich the soil with its nutrients.

could be indicative of better extension services in that district.

**Table 4.** Percentage of farmer respondents on CA technologies in the savanna zone

Number of respondents = 32 Source: Ekekpi and Kombiok, 2008

A legume as a candidate crop in intercrop systems is again being encouraged because of the same reason as above. In the northern part of Ghana where the soils are low in both organic matter and essential nutrients, farmers intercrop cereals with legumes. The most common intercropping systems in this area are maize/cowpea, millet/cowpea, and maize/soybean. In some cases, both in the north and south of Ghana cover crops such as *Mucuna or Callopogoni‐ um* is planted in maize at the latter part of its growth cycle (6 weeks after planting maize). In southern Ghana, maize is harvested earlier and the cover crop (*Mucuna*) is left to grow into the minor season (August to March) until the next major season (April to August). In the northern savanna zone however, the cover crop dries when the rains end in October and the residue forms mulch protecting the soil. The incorporation of the residue in the soil after two years of cropping increased both the soil nitrogen and maize grain yield significantly (Kombiok Clottey, 2003).

One approach that has proved to be inherently attractive to farmers and is standard practice in most parts of northern Ghana is intercropping maize or sorghum with the grain legume cowpea or groundnut. If cowpea is sown between maize rows, the plant population and yield of maize can be maintained, whilst reaping the advantage of yield from the cowpea harvest. There is high labour requirement in the practice of intercropping because more than one crop is being planted at a time. So, labour is required for planting the component crops and for the careful control of weeds in the system. Insecticides are needed for the control of insect pests on the legume component either being rotated or intercropped.

Pigeon pea is an ideal legume for intercropping with cereals. Its slow initial growth affords little competition with the cereal for light or water, and it continues growing into the dry season after the maize crop has been harvested. The leaves that fall from pigeon pea before harvest provide a mulch and can add as much as 90 kg N/ha to the soil that then mineralizes relatively slowly during the subsequent season, releasing N for the next maize crop (Adu-Gyamfi et al., 2007). Thus a substantial rotational benefit, although not a perfect soil cover, can be achieved for the next season.
