The productivity of the smallholder farming system in Ghana is under threat due to soil fertility decline. Mineral fertilizer is sparingly being used by smallholder farmers because of prohibitive cost. Grain legumes such as pigeonpea can play a complementary or alternative role as a source of organic fertilizer due to its ability to enhance soil fertility. Despite its importance, the potential of pigeonpea as a soil fertility improvement crop has not been exploited to any appreciable extent and the amount of land cultivated to pigeonpea in Ghana is vey negligible. This paper synthesizes recent studies that have been carried out on pigeonpea in Ghana and discusses the role of pigeonpea cultivation in soil fertility management and its implication for farming system sustainability. The paper shows that recent field studies conducted in both the semi-deciduous forest and the forest/savanna transitional agro-ecological zones of Ghana indicate that pigeonpea/maize rotations can increase maize yield by 75–200%. Barrier to widespread adoption of pigeonpea include land tenure, market, and accessibility to early maturing and high yielding varieties. The paper concludes among other things that in order to promote the cultivation of pigeonpea in Ghana, there is the need to introduce varieties that combine early maturity with high yields and other desirable traits based on farmers preferences.
Agricultural productivity in the smallholder farming systems in Ghana is under threat due to declining soil fertility. In the past, smallholder farmers in Ghana relied on the extended bush fallow system for maintaining the productivity of their farmlands [
Most farmers, especially the smallholder farmers, do not have access to formal credit and therefore cannot afford to buy mineral fertilizers even when it has been demonstrated to be profitable [
In smallholder farming systems in Ghana, legumes can play a complementary or alternative role as source of organic fertilizer. Research in many parts of Sub-Saharan Africa including Ghana has shown that legumes have the potential to sustain soil fertility in smallholder farming systems [
Despite the importance of pigeonpea in terms of nutrition and soil fertility improvement, the crop has not been promoted to any appreciable extent by the national agricultural research and extension system in Ghana. In the forest/savannah transitional zone where the crop is widely cultivated, pigeonpea is considered as women’s crop and therefore minor due to men’s dominion over women in household decision-making process. Furthermore the overemphasis on maize in the current production systems as the major food security and cash crop in the forest/savanna transitional zone has relegated pigeonpea in particular and legumes in general as a minor crop.
However, recent studies in the forest/savannah transitional agroecological zone as well as the semideciduous forest zone of Ghana have demonstrated that when integrated in the cropping system as a form of rotation, pigeonpea has the potential of improving soil fertility. This paper discusses the role of pigeonpea cultivation in soil fertility management and its implication for farming system sustainability and food security.
This paper is largely based on studies that have been conducted in the forest/savannah transitional agro-ecological zone of Ghana between 2002 and 2006 under the framework of Convergence of Science project [
The studies were conducted in the Wenchi Municipal (7° 27 and 8° 30 N, 1° and 2° 36 W) in the forest/savanna transitional agro-ecological zone of Ghana. The relief of Wenchi is gently undulating to flat. The soils, which are mainly Lixisols, are fragile with shallow top soils underlain with compact concretions and impermeable iron pans [
In 2002, we carried out a study under the Convergence of Sciences project to explore farmers’ soil fertility management strategies and their relevant social context [
In addition, two sets of individual interviews with farmers were conducted to collect qualitative and quantitative data. In the first interview, which involved 40 farmers, the selection of farmers was done through stratified sampling. A list of farmers in the community was obtained from the village committee secretary and every tenth name from the list was selected for individual interviewing. The second interview which involved 38 farmers was conducted later to look at the farming characteristics of the various subcommunities in the village using a wealth ranking exercise. For this interview, 6–10 persons were selected from each wealth category within each subcommunity. The individual interviews were semistructured in nature and served both to get more quantitative data on farm size, household composition, and the farming system and to obtain a better qualitative understanding of the soil fertility management strategies and their underlying rationale.
The diagnostic study was followed by farmer participatory on-farm experimentations with three farmer research groups established soon after the diagnostic study to evaluate the agronomic efficacy of the soil fertility management practices being used by the farmers [
In 2008, under the IDRC, funded climate change adaptation in Africa project, farmers evaluated three early maturing and three late maturing pigeonpea varieties obtained from the International Crop Research Institute of the Semi-Arid Tropics (ICRISAT) in India, in a community in Wenchi called Asuoano.
Farmers used several terms to express the fertility status of their soils although the terminology differed from one ethnic group to another. For instance, among the Akans and the Walas, when the soil loses its fertility, the farmers would say the soil is “tired” and therefore must be allowed to “rest” under bush fallow to regain its lost “energy.” Farmers used various indicators such as colour, water holding capacity, and soil texture to assess soil fertility. A black soil was considered fertile while gravelly and sandy soils were considered less fertile. Other indicators used by farmers to express soil fertility included presence of earthworm casts which the farmers call “earth worm faeces,” growth of crops, decline in crop yield and proliferation of certain plant species and weeds. For instance, the presence of weeds like
Farmers pointed out five major factors as being responsible for soil fertility decline in the area as follows: (1) increasing population as a result of migration of people into the area leading to smaller farms, which has resulted in the continuous cropping of the same piece of land over a long period; (2) annual bushfires which destroy vegetation and the population of earthworms that contribute to soil fertility improvement; (3) monocropping of maize without rotating it with any other crop; (4) the rapid increase in the monetary value of land; (5) felling of trees which exposes the land to the direct action of the sun.
Table
The most important food crops and proportion of land allocated to leguminous crops by native and migrant farmers in Asuoano in 2002.
Natives | Migrants | |
---|---|---|
% | ||
Food crop | ||
Maize | 100 | 100 |
Cassava | 100 | 88 |
Yam | 100 | 94 |
Cocoyam | 91 | 19 |
Plantain | 32 | 0 |
| ||
Leguminous crop | ||
Pigeonpea | 50 | 0 |
Groundnut | 20 | 35 |
Cowpea | 10 | 50 |
White kidney bean | 10 | 0 |
Bambara groundnut | 5 | 15 |
Mucuna | 2 | 0 |
Others | 3 | 0 |
Source: [
Among the legumes cultivated by the natives, pigeonpea was grown on a larger scale in comparison with other legumes because of its ability to regenerate soil fertility, its low production cost, its tolerance to pests and diseases, its cash income, and its food value. It was generally grown on less fertile land and land with problematic weeds such as spear grass (
After cropping a piece of land to crops like maize, cassava, and yam for about three to four years, farmers intercropped their food crops with pigeonpea during the last cropping year of the cycle. After harvesting the component crops, farmers allowed the land to remain under pigeonpea for 18–24 months after which the pigeonpea plants were cut down, burnt and the land cropped to maize or yams. The pigeonpea canopy was perceived to protect the soil from the direct action of the sun and therefore prevents the soil from becoming hardened. According to the farmers, pigeonpea forms a canopy after one year and shades out obnoxious weeds by suppressing their growth. The farmers also explained that the leaf litter covers the soil, reduces soil erosion, improves infiltration, prevents heating of the soil, and enhances earthworm activity. Crops grown on the land after pigeonpea, and especially maize, were perceived by the farmers to look greener, grow faster, and yield more. Rotations involving pigeonpea was often regarded by farmers as a long-term soil fertility management strategy. Despites its importance, migrant farmers preferred to use mainly short-term strategies such as mounding and the planting of short duration leguminous crops such as cowpea and groundnut for maintaining soil fertility because of the dynamics surrounding land tenure.
Studies in Wenchi and Kade in the forest/savanna transitional and semideciduous forest zones of Ghana, respectively, indicate the potential of pigeonpea in improving soil fertility and farm profitability (Tables
Effect of crop sequence and N rate on (a) maize grain yield (kg ha−1) and (b) weed biomass (kg ha−1) associated with the maize crop at 8 weeks after planting on researcher-managed plots.
Crop sequence |
N rate (kg ha−1) | Mean | |
---|---|---|---|
O | 60 | ||
Speargrass fallow | 1050 | 2848 | 1949 |
Cassava | 3002 | 2738 | 2870 |
Pigeonpea | 2422 | 2972 | 2697 |
Cowpea-maize-cowpea | 1670 | 2328 | 1999 |
Mucuna-maize-mucuna | 2970 | 4195 | 3582 |
Maize-maize-maize | 1380 | 2128 | 1754 |
| |||
Mean | 2082 | 2868 |
SED: crop sequence (CS) = 318.4; N rate (NR) = 115.3; CS
P < F: CS = 0.001; NR = 0.001; CS
Source [
Crop sequence | N rate (kg ha−1) | Mean | |
---|---|---|---|
O | 60 | ||
Speargrass fallow | 585 | 790 | 686 |
Cassava | 270 | 300 | 285 |
Pigeonpea | 390 | 500 | 445 |
Cowpea-maize-cowpea | 325 | 395 | 360 |
Mucuna-maize-mucuna | 300 | 345 | 323 |
Maize-maize-maize | 240 | 430 | 335 |
| |||
Mean | 351 | 460 |
SED: crop sequence (CS) = 65.9; N rate (NR) = 52.4; CS
P < F: CS = 0.001; NR = 0.05; CS
Source [
Effect of crop sequence on maize grain yield at 12% moisture content.
Crop sequence | Maize grain yield (t ha−1) | |
---|---|---|
2007/2008 | 2008/2009 | |
Pigeonpea | 7.0 | 2.3 |
Ex-Subi | 4.6 | 1.9 |
Boakentemma | 3.5 | 1.4 |
Cowpea-Maize-Cowpea | 3.0 | 1.5 |
Groundnut-Maize-Groundnut | 2.7 | 1.6 |
Maize-Maize-Maize | 2.3 | 1.3 |
LSD at 5% | 1.4 | 0.58 |
Source [
Higher maize yield under legume-maize rotation is expected since legumes are known to fix nitrogen, thereby improving the soil nitrogen economy and enhancing the growth of subsequent crop [
Besides the beneficial effect of pigeonpea on subsequent maize crops as a result of the high N recycling properties of the pigeonpea, the role of other nutrients cannot be ruled out. In some studies, increased soil P availability under pigeonpea was attributed to the efficient solubilisation and uptake of P from bound sources (e.g., Fe-P) by root exudates [
Estimated costs of production, gross revenue, and returns on investment of (a) various crop sequences (b) maize grown after the sequences with N application to the maize and (c) maize grown after the sequences without N application to the maize.
Crop sequence |
|
Total revenue |
Cost of production (US$) ha−1 | Total cost |
Net revenue |
Return on | ||
---|---|---|---|---|---|---|---|---|
Land | Input | Labour | ||||||
(a) Crops in the sequence | ||||||||
1Cassava | 31,000 | 2545.1 | 41.7 | 41.7 | 635.0 | 718.4 | 1826.7 | 254 |
2Pigeonpea | 1,870 | 623.3 | 41.7 | 8.3 | 221.5 | 271.5 | 351.8 | 130 |
3Mucuna-maize-mucuna | 2,016 | 365.1 | 41.7 | 41.7 | 247.4 | 330.8 | 34.3 | 10 |
4Cowpea-maize-cowpea | 2,536* (1,230) | 1079.0 | 41.7 | 106,1 | 475.1 | 622.9 | 456.1 | 73 |
5Maize-maize-maize | 3,287 | 595.2 | 41.7 | 36.1 | 386.1 | 463.8 | 456.1 | 28 |
6Speargrass fallow | 0 | 0 | 41.7 | 0 | 0 | 41.7 | −41.7 | −100 |
| ||||||||
(b) Maize after crop sequence with N application | ||||||||
CS 1 | 2,738 | 495.9 | 13.9 | 104.2 | 190.2 | 308.3 | 187.6 | 61 |
CS 2 | 2,974 | 538.5 | 13.9 | 104.2 | 196.5 | 314.6 | 223.9 | 71 |
CS 3 | 4,194 | 759.4 | 13.9 | 104.2 | 245.9 | 364.0 | 395.4 | 108 |
CS 4 | 2,331 | 422.1 | 13.9 | 104.2 | 177.0 | 295.1 | 127.0 | 43 |
CS 5 | 2,126 | 385.0 | 13.9 | 104.2 | 175.4 | 293.5 | 91.4 | 31 |
CS 6 | 2,848 | 515.7 | 13.9 | 104.2 | 224.4 | 342.5 | 173.3 | 51 |
| ||||||||
(c) Maize after crop sequence without N application | ||||||||
CS 1 | 3,000 | 543.2 | 13.9 | 13.9 | 175.6 | 203.4 | 339.8 | 167 |
CS 2 | 2,423 | 438.8 | 13.9 | 13.9 | 165.5 | 193.3 | 245.5 | 127 |
CS 3 | 2,961 | 537.7 | 13.9 | 13.9 | 209.7 | 237.5 | 300.2 | 126 |
CS 4 | 1,772 | 302.8 | 13.9 | 13.9 | 155.2 | 183.0 | 119.8 | 66 |
CS 5 | 1,380 | 249.9 | 13.9 | 13.9 | 153.0 | 180.7 | 69.1 | 38 |
CS 6 | 1,048 | 189.8 | 13.9 | 13.9 | 173.7 | 200.9 | −11.1 | −6 |
1US$82.1
2US$333.3
3US$181.1
4US$337.5
5US$181.1
6US$0.
*Yield of maize (figure in brackets).
CS 1: cassava; CS 2: Pigeonpea; CS 3: Mucuna-maize-mucuna; CS 4: Cowpea-maize-cowpea; CS 5: Maize-maize-maize; CS 6: Speargrass fallow.
Source: [
Barrier to widespread adoption of pigeonpea include land tenure, market, and availability of early maturing varieties. In the transitional zone of Ghana where the crop is widely cultivated by farmers, migrant farmers prefer cowpea cultivation to pigeonpea cultivation although they acknowledge the superiority of the latter over the former in terms of soil fertility management and the yield of subsequent maize crop (Table
Preferential ranking of different soil fertility management practices by native and migrant farmers in Wenchi.
Management practice | Ranking order* | |||||||
---|---|---|---|---|---|---|---|---|
Natives | Migrants | |||||||
Asuoanoa |
Beposob |
Drobosoc |
Average | Asuoanod |
Beposod |
Drobosoe |
Average | |
(a) Ranking by natives and migrants | ||||||||
Cassava | 1 | 1 | 1 | 1 | 2 | 2 | 1 | 1.7 |
Pigeonpea | 2 | 5 | 2 | 3 | 4 | 4 | 4 | 4 |
Mucuna/Maize/Mucuna | 7 | 6 | 4 | 5.7 | 5 | 6 | 6 | 5.6 |
Groundnut/Maize/Groundnut | 4 | 3 | 3 | 3.3 | 3 | 3 | 3 | 3 |
Cowpea/Maize/Cowpea | 3 | 2 | 5 | 3.3 | 1 | 1 | 2 | 1.3 |
Maize/Maize/Maize | 8 | 7 | 6 | 7 | 7 | 7 | 7 | 7 |
Cowpea/Cowpea/Cowpea | 5 | 4 | 7 | 5.3 | 6 | 5 | 5 | 5.3 |
Bush fallow | 6 | 8 | 8 | 7.3 | 8 | 8 | 8 | 8 |
| ||||||||
(b) Ranking by female and male Bonos | Females |
Males |
||||||
Cassava | 1 | 1 | ||||||
Pigeonpea | 2 | 3 | ||||||
Mucuna/Maize/Mucuna | 5 | 7 | ||||||
Groundnut/Maize/Groundnut | 3 | 4 | ||||||
Cowpea/Maize/Cowpea | 4 | 2 | ||||||
Maize/Maize/Maize | 8 | 8 | ||||||
Cowpea/Cowpea/Cowpea | 7 | 5 | ||||||
Bush fallow | 6 | 6 |
aConsisted of 6 males and 4 females; bConsisted of 4 males and 1 female; cConsisted of 6 females and 1male; dDagarbas; eWalas.
*Each treatment was compared directly against the other until they were ranked from the highest to the lowest with 1 being the highest ranking and 8 being the lowest.
Source: [
Access of farmers to early maturing varieties is also another barrier to widespread adoption of the pigeonpea. Although the late maturing indeterminate pigeonpea varieties have the higher potential to improve soil fertility than the early maturing varieties due to greater biomass production, farmers prefer the early maturing determinate varieties. Criteria farmers used for selecting varieties for planting included maturity, plant height (for ease of harvesting), tolerant to insects, plant architecture (prefer varieties with smaller plant canopy for ease of intercropping with yams), and seed size (bigger seed size is preferred). Amount of biomass and/litter falls and ability to improve soil fertility were not mentioned as criteria although farmers claimed that soil fertility was one of their major production challenges and that pigeonpea was one of the crops they used to improve the fertility of their soils. Although late maturing indeterminate pigeonpea varieties with woody stems are a potential source of fuel wood, farmers did not also include this in their selection criteria. This may be due to the fact that accessibility to fuel wood was not a major constraint in Wenchi.
During focus group discussions in the field, the farmers noted that the late maturing pigeonpea varieties had produced a lot of biomass and had higher litterfalls compared with the early maturing varieties. The farmers observed and commented on the greater litterfall from the late maturing varieties. They further stated that the greater production of biomass and the higher litterfall of the late maturing varieties would lead to better soil fertility improvement compared with the early maturing pigeonpea varieties. Despite their recognition of the soil fertility benefits of the late maturing varieties in improving soil fertility, the farmers did not include this as an important criterion for selecting which pigeonpea varieties to grow (Table
(a) Farmers’ preference ranking and (b) farmers’ criteria for selection of pigeonpea varieties for planting.
(a) Variety | Growth and yield characteristics | Ranking and reasons for the rank | |||||
---|---|---|---|---|---|---|---|
Flowering pattern | Maturity period (days) | 100 grains weight (g) | Yield |
Seed colour | Ranking | Reasons for the rank | |
|
Determinate | 125 | 10.1 | 1.6 | Brownish red | 1 | Early maturing, short plant height, could be planted twice in a year |
|
Determinate | 125 | 10.2 | 1.8 | Brownish red | 2 | Early maturing, short plant height, could be planted twice in a year |
|
Determinate | 125 | 12.1 | 1.1 | white | 3 | Early maturing, short plant height, could be planted twice in a year |
|
Indeterminate | 190 | 10.0 | NA | Brownish red | 4 | Medium maturity, high litter fall |
|
Indeterminate | 196 | 10.2 | NA | Brownish red | 4 | High litter fall |
|
Indeterminate | 195 | 10.1 | NA | Brownish red | 4 | High litter fall |
| |||||||
(b) Criteria | Ranking | ||||||
| |||||||
|
1 | ||||||
|
2 | ||||||
|
3 | ||||||
|
4 | ||||||
|
5 |
NA: not available.
Source: Adjei-Nsiah (unpublished results).
In addition to food uses, pigeonpea has outstanding soil improvement and conservation properties. The growth habit facilitates soil protection, as the canopy continues to expand during the dry season after the component crops in the mixed cropping have been harvested. Living and senesces pigeonpea leaves may offer protective cover for the soil during dry season to prevent the soil from drying out and reduce soil erosion and enhance rain percolation during the rainy season. In farming systems with minimal application of external inputs, management of organic resources plays a major role in maintaining both nutrient availability and soil organic matter [
The paper shows the potential of pigeonpea in improving soil fertility in the smallholder farming systems particularly in a predominantly maize-based farming system as that found in Wenchi, Ghana. We have shown that the potential of pigeonpea in sustaining the productivity of predominantly maize-based farming system is due to its nutrient recycling properties as well as to its role in food security and flexibility in external input use and labour requirement. Soil fertility was apparently not a major criterion during varietal ranking by farmers suggesting that pigeonpea is less likely to be adopted merely on the basis of its capacity to improve soil fertility. Even when there was no strong market demand for pigeonpea, female farmers still integrated pigeonpea in their rotational system. Pigeonpea is largely a women’s crop and therefore the attitude by men as major household decision makers has probably undermined its adoption in a predominantly maize based cropping system in Wenchi. Empowering women to make decision with respect to allocation of production resources may enhance a greater adoption of legumes. As more farmers resort to putting their land under pigeonpea instead of bush fallowing, pigeonpea cultivation could serve as an entry point for farming system sustainability. There is, however, the need to (i) introduce short duration pigeonpea varieties that will fit well in the predominantly mixed cropping systems of smallholder agriculture; (ii) evaluate the nutrient recycling capacities of different pigeonpea genotypes; (iii) develop crop rotation/sequencing and soil management options that can improve and/or sustain the productivity of pigeonpea through integrated soil fertility management (ISFM); (iv) design a range of social arrangements that will encourage investment in soil fertility through integration of pigeonpea in the farming system in a heterogeneous farming community like Wenchi, (v) develop use for pigeonpea in new cooking options and/or value added products.
The author is grateful to the two anonymous reviewers who reviewed an earlier version of this paper. Financial support towards this work provided by the Interdisciplinary Research and Education Fund (INREF) of Wageningen University and Research Centre, and The Netherlands and the Dutch Ministry for International Cooperation (DGIS) is gratefully acknowledged. The author also thanks the International Development Centre for funding the climate change adaption in Africa project through the University of Zimbabwe.