OPCE-STR.vp Acta Bot. Croat. 69 (2), 291–297, 2010 CODEN: ABCRA 25 ISSN 0365–0588 Growth and yield response of cowpea (Vigna unguiculata L. Walp.) to soils from different fallow physiognomies in the rainforest zone of Nigeria SAMSON O. OKE*, DAMILOLA L. EYITAYO Department of Botany, Obfemi Awolowo University, Ile-Ife, Nigeria A study was conducted to evaluate the response of cowpea (Vigna unguiculata) seedlings to soil collected from four fallows of different physiognomy. Seedlings of cowpea were grown from seeds on soil samples collected from the four different fallow statuses (Panicum maximum-dominated fallow soil, Chromolaena odorata-dominated fallow soil, Tithonia spp.-dominated fallow soil and bush fallow soil that contains many herbaceous plant species) in plastic containers each having fifteen replicates. Among the growth char- acteristics assessed the number of nodules and stem dry weight being the most influenced. Panicum maximum-dominated fallow soil with greater organic matter content produced the most desirable growth characteristics during the growing period and at harvest. The results were used to deduce the best type of fallow soil for cowpea cultivation. Key words: Growth, yield, fallow soil, Vigna unguiculata, physiognomy, rainforest, Nigeria Introduction Cowpea (Vigna unguiculata L. Walp.) is a legume grown under rain-fed conditions in the tropics (SANGAKKARA 1998). Although it occupies a smaller proportion of the crop area than cereals, it contributes significantly to household food security in West and Central Af- rica. Compared with many other crops, the cowpea has received little attention from plant breeders and a large efforts need to be made to break the yield barriers. If cowpea produc- tion is to keep pace with other crops, especially cereals, its yield potential must be im- proved. In Nigeria, 80% of the cowpea production is mainly from the savanna zone of the coun- try (FAO 1999). A wide range of seed yields have been recorded for cowpeas but they are generally low. Among the factors responsible for the low yields are low soil fertility, as most tropical soils are deficient in essential nutrients particularly nitrogen and phosphorus (JONES and WILD 1975). Traditionally, soil fertility in West Africa has been maintained ACTA BOT. CROAT. 69 (2), 2010 291 * Corresponding author: soke@oauife.edu.ng U:\ACTA BOTANICA\Acta-Botan 2-10\279 Oke.vp 13. listopad 2010 12:28:07 Color profile: Disabled Composite 150 lpi at 45 degrees through fallow. In Nigeria intensive cropping is gradually replacing the traditional shifting cultivation that is associated with long fallow and low crop yields are among the results of this practice. The steady decline in food production due to reduced length of fallow on land has prompted farmers to improve soils with different materials (organic and inorganic) in order to enhance plant growth and increase yield. There is limited documentation on the effect of status of soil of different fallow physi- ognomies on cowpea growth and yield in Nigeria. Such information would be useful and important in agricultural extension delivery to farmers for increased crop productivity and poverty alleviation. An attempt to find out the growth and yield responses of cowpea to soils from different fallow status in the rainforest zone inform this study. Since fallows not only improve subsequent crop performance but also restore soil fertility and organic matter content over the long term, this experiment seeks to evaluate the effects of four fallow soils of different physiognomies on the growth characteristics and yield of the cowpea (Vigna unguiculata var. IFE BROWN) in the Ile-Ife area of southwestern Nigeria. Materials and methods Four fallow plots of different physiognomies were selected within the same area at Obafemi Awolowo University, Ile-Ife, southwestern Nigeria. These sites had to be in close proximity to one another to satisfy the conditions of the chronosequence approach of the study. Topsoil from the four fallow plots of different physiognomies (a Panicum maximum -dominated fallow plot, a Chromolaena odorata -dominated fallow plot, a fallow plot that contains many herbaceous plant species (mixed) and a Tithonia spp -dominated fallow plot) that are common in Ile-Ife area of southwestern Nigeria were collected. The soil was air dried and loosened before being put in 20cm wide plastic containers with holes at the bottom to facilitate effective drainage. The four soil types were analyzed for pH; particle size distribution, organic matter con- tent, sodium, potassium, calcium, magnesium and nitrogen contents. The soil particle size distribution was determined by Bouyoucos hydrometer and the pH electrometrically. Or- ganic matter was determined by the chromic acid digestion method (BLACK 1965), the ex- changeable cations and nitrogen by the semi-micro Kjeldahl method (TEL and RAO 1982). Pure lines of cowpea seeds (Ife brown variety) were collected from the International In- stitute for Tropical Agriculture (I.I.T.A) Ibadan. The seeds were planted in each soil type in May 2008 and seedlings were established in each soil type at densities of 1, 2, and 3 per 5 litre pot. Each density had fifteen replicates, watering was with tap water every two days in the morning and in the evening to field capacity to give the best soil moistures regime for growth, thus there was no competition for water. When the seedlings were nursed to full and equal establishment in the pots, measure- ment of some growth parameters such as leaf length, leaf breadth, leaf area, leaf number, shoot height were taken weekly. At harvest in August 2008 ten weeks after planting, the plants were removed and seedling mean dry matter yield (leaves, stems, roots, total), pod numbers and nodule numbers were measured after oven drying at 80 °C. The effects of soils from different fallow on the seedlings growth characteristics were determined using analy- sis of variance (ANOVA) with the aid of the software SAS Release 8.1. Significant means were separated by Duncan’s multiple range test at the 5% probability level. 292 ACTA BOT. CROAT. 69 (2), 2010 OKE S. O., EYITAYO D. L. U:\ACTA BOTANICA\Acta-Botan 2-10\279 Oke.vp 11. listopad 2010 15:44:20 Color profile: Disabled Composite 150 lpi at 45 degrees Results Physical and chemical properties of soil A chemical and mechanical analysis of the soils prior to cropping with cowpea is shown in table 1. The Panicum maximum -dominated fallow soil was found to have higher organic matter, organic carbon, pH and greater percentage of exchangeable cations than other fal- low soils. The Tithonia spp -dominated fallow soil had higher nitrogen and phosphorus content, while Chromolaena odorata -dominated fallow soil had intermediate values for most of the soil properties determined. Growth characteristics The cowpea seedlings in Panicum maximum -dominated fallow soil had better growth characteristics such as greener leaves, higher number of leaves, bigger leaves, bigger stems, leaf area, shoot height and greater canopy than seedlings from other fallow soils. The cowpea seedlings growing in the Chromolaena odorata -dominated fallow soil were observed to have the slowest growth rate, the smallest number of leaves, the lowest leaf area, shoot height and the least canopy while the seedlings from the other two fallow soils had intermediate values (Figs. 1, 2, 3). The analysis of variance for the seedling growth pa- rameters that were measured during the growing period revealed that the soils from the dif- ferent fallows had a significant influence on leaf area (p<0.05). Vigna unguiculata seedlings had the highest mean stem dry weight per plant in Panicum maximum -dominated fallow soil, the lowest in Chromolaena odorata -domi- nated fallow soil and intermediate values in the other two fallow soils (Tab. 2). The fallow soil types significantly affected the mean stem dry weight (P £ 0.05). Vigna unguiculata seedlings had the highest mean root dry weight in mixed fallow soil, the least in Chromo- laena odorata -dominated fallow soil and intermediate values in Panicum maximum and Tithonia spp fallow soils. The fallow soil types had no significant effects on the mean root dry weight.Vigna unguiculata seedlings had the highest mean leaf dry weight in Panicum maximum -dominated fallow soil, the least in Chromolaena odorata -dominated fallow soil and intermediate values in the other two fallow soils. The fallow soils had significant ef- fects on the mean leaf dry weight (p £ 0.05). Vigna unguiculata seedlings had the highest mean dry weight of pods in Tithonia spp fallow soil, the lowest in Chromolaena odorata -dominated fallow soil and intermediate values in the other two fallow soils. The fallow soils had significant effects on the mean dry weight of pods (p £ 0.05). Vigna unguiculata seedlings had the highest mean number of pods in Panicum maximum -dominated fallow soil, the lowest in Chromolaena odorata -dominated fallow soil and intermediate values in the other two fallow soils. The fallow soil types had significant effects on the mean number of pods (p £ 0.05). Vigna unguiculata seedlings had the highest mean total biomass in Tithonia spp fallow soil, the lowest in Chromolaena odorata fallow soil and intermediate values in Panicum maximum and mixed fallow soils. The fallow soil types had a significant effect on the mean total biomass (p £ 0.05).Vigna unguiculata seedlings had the highest mean number of nod- ules in Panicum maximum -dominated fallow soil, the lowest in Chomoleana odorata -dominated fallow soil and intermediate values in the two other fallow soils. The fallow ACTA BOT. CROAT. 69 (2), 2010 293 GROWTH AND YIELD OF VIGNA UNGUICULATA IN THE RAINFOREST U:\ACTA BOTANICA\Acta-Botan 2-10\279 Oke.vp 11. listopad 2010 15:44:20 Color profile: Disabled Composite 150 lpi at 45 degrees 294 A C T A B O T .C R O A T .69 (2),2010 O K E S .O .,E Y IT A Y O D .L . Tab. 1. The chemical and mechanical analyses of the fallow soils prior to cropping with cowpea. Fallow soil sample % sand % silt % clay % O.C % O.M Phosphorus mg kg–1 % K % Ca % Na Total N PH Electrical conductivity Panicum 54 18 28 4.24 7.3 8.47 0.55 7.0 3.17 1.5 7.8 H2O 7.5 CaCI2 0.37 Chromokena 62 14 24 2.21 3.8 6.64 0.21 3.4 2.26 0.8 6.6 H2O 6.2 CaCI2 0.27 Mixed 36 26 38 3.66 6.3 7.13 1.03 6.2 3.04 1.3 6.9 H2O 6.6 CaCI2 0.55 Tithonia 72 14 14 2.04 3.5 9.86 0.36 5.1 2.48 2.48 8.1 H2O 7.6 CaCI2 0.30 Tab. 2. Some growth characteristics and yield of seedlings of the cowpea (Vigna unguiculata) grown in the four different fallow soil types at harvest. Fallow soil types Stem dry weight Root dry weight Leaf dry weight Pod dry weight Pod number Total dry weight No of Root nodules Leaf number Leaf area Panicum dominated 1.41a 0.70ab 3.95a 2.81b 4.62a 8.26ab 15.24a 24.01a 35.49a Tithonia dominated 1.31a 0.81ab 3.52b 3.67a 4.17ab 9.31a 15.12a 16.86b 31.85a Chromolaena dominated 0.62b 0.59b 1.30c 1.48c 2.92b 4.04c 10.33b 17.23b 23.75b Mixed 1.00c 1.10a 2.53b 2.13bc 3.51ab 6.77b 12.37b 18.47b 28.83ab Mean within the same column and with the same letter are not significantly different according to DMRT U : \ A C T A B O T A N I C A \ A c t a - B o t a n 2 - 1 0 \ 2 7 9 O k e . v p 1 1 . l i s t o p a d 2 0 1 0 1 5 : 4 4 : 2 0 C o l o r p r o f i l e : D i s a b l e d C o m p o s i t e 1 5 0 l p i a t 4 5 d e g r e e s ACTA BOT. CROAT. 69 (2), 2010 295 GROWTH AND YIELD OF VIGNA UNGUICULATA IN THE RAINFOREST 0 5 10 15 20 25 30 35 40 45 50 Panicum Chromolaena Mixed Tithonia Fallow Types L e a f N u m b e r WAP1 WAP2 WAP3 WAP4 WAP5 WAP6 WAP7 WAP8 WAP9 WAP10 Fig. 1. Response of cowpea leaf number to various fallow soil types (WAP1–WAP10) during the growing period 0 5 10 15 20 25 30 35 40 Panicum Chromolaena Mixed Tithonia Fallow Types M e a n L e a f A re a (c m ) 2 WAP1 WAP2 WAP3 WAP4 WAP5 WAP6 WAP7 WAP8 WAP9 WAP10 Fig. 2. Response of cowpea leaf area to various fallow soil types (WAP1–WAP10) during the growing period. 0 10 20 30 40 50 60 70 Panicum Chromolaena Mixed Tithonia Fallow Types M e a n S h o o t H e ig h t (c m ) WAP1 WAP2 WAP3 WAP4 WAP5 WAP6 WAP7 WAP8 WAP9 WAP10 Fig. 3. Response of cowpea shoot height to various fallow soil types (WAP1–WAP10) during the growing period. U:\ACTA BOTANICA\Acta-Botan 2-10\279 Oke.vp 11. listopad 2010 15:44:20 Color profile: Disabled Composite 150 lpi at 45 degrees soil type had significant effects on the mean number of nodules (p £ 0.05). Vigna unguiculata seedlings had the highest mean number of leaves in Panicum maximum fallow soil, the lowest in Chromolaena odorata fallow soil and intermediate values in mixed and Tithonia spp. fallow soils. The fallow soil types had significant effects on the mean number of leaves (p £ 0.05). Discussion The study set out to highlight the response of the growth characteristics of cowpea (Vigna unguiculata) seedlings to soils from different fallow physiognomy. The analysis carried out on the performance of cowpea in relation to number of leaves, shoot height, leaf area and total biomass at harvest, showed a significantly higher value in Panicum maxi- mum -dominated fallow soil than in the other fallow soils. The result showed clearly that fallow soil types are important factors in the cultivation of the cowpea. The rapid growth rate observed in Panicum maximum fallow soil may be due to its rich- ness in organic matter content, organic carbon content and in exchangeable cations. The binding influence of Panicum maximum roots on the soil is considered to be responsible for the ability of the grass to effectively check erosion (AMUSAN and OKE 2000). As a result the enriched soil will be able to retain its nutrients due to its better ability to check soil erosion. Enriched soils through proper management of organic amendments such as crop residues and manure can increase the yield of cowpea. Cowpea seedlings (Vigna unguiculata) grow- ing in Panicum maximum -dominated fallow soil were observed to have the highest number of leaves and leaf area and so when considering growing cowpea as a fodder or vegetable, Panicum maximum fallow soil is highly recommended. Comparison of the biomass of different parts of cowpea seedlings indicated that leaves had the highest yield. This could be attributable to the fact that the leaf is the site of food manufacture through photosynthesis and hence is expected to have a greater biomass accu- mulation compared to the stem and root. HEUVELINK (1995) while monitoring the growth, development and yield of a tomato crop found that in all experiments the ratio between leaf and stem dry weight was 7:3 and that this ratio did not change with crop development. The highest yield of pod biomass obtained at harvest in the Tithonia spp -dominated fallow soil which was due to its high phosphorus content and is in agreement with the observations of ISRAEL (1987) that cowpea has a high phosphorus requirement. The highest number of pods produced was observed in the Panicum maximum fallow soil because it had the highest number of root nodules which can fix atmosphere nitrogen and hence contribute signifi- cantly, towards the nitrogen nutrition of cowpea. Similar results were obtained by AWO- NAIKE (1991). In this study, it was observed that soils from different fallows had significant effects on the leaf number, leaf area, shoot height, pod number, stem dry weight, leaf dry weight, root dry weight and pod dry weight of cowpea. It was interesting to note that Panicum maximum fallow soil had the best growth characteristics and highest yield of biomass. There were significant lower values for almost all the growth parameters examined in Chromolaena odorata -dominated fallow soil. It is often suggested that, as a short fallow species, Chromolaena odorata has serious adverse effects on agricultural productivity and on the weed composition and subsequent food crops (MCFAYDEN and SKARRATT 1996). 296 ACTA BOT. CROAT. 69 (2), 2010 OKE S. O., EYITAYO D. L. U:\ACTA BOTANICA\Acta-Botan 2-10\279 Oke.vp 11. listopad 2010 15:44:20 Color profile: Disabled Composite 150 lpi at 45 degrees In conclusion, we suggest that farmers who are interested in cultivating cowpea, fallow lands dominated by Chromolaena odorata should as much as possible be avoided, as cow- pea growth is adversely affected on such fallow soil, while fallow lands dominated by Panicum maximum is highly recommended for farmers who are interested in vegetative growth as such fallow soils tend to have greater organic matter content, organic carbon con- tent and exchangeable cations, which favour cowpea (Vigna unguiculata) seedling growth. Farmers who are interested in yield of pods are recommended to grow their cowpea in Tithonia spp -dominated fallow soil. References AMUSAN, A. A., OKE, S. O., 2000: Effect of different fallow plant species on regeneration of degraded Ultisols in Southwestern Nigeria. Annals of Agricultural Sciences 2, 53–59. AWONAIKE, K. O., 1991: Nitrogen assimilation and distribution in field grown cowpea at various growth stages. Agronomy Journal 55, 81–85. BLACK, C. A., 1965: Methods of soil analysis I. A. S. A. Monogram, Madison. FAO, 1999: Production yearbook, FAO, Rome. HEUVELINK, E., 1995: Growth, development and yield of a tomato crop. Scientia Horti- culturae 61, 77–79. ISRAEL, D. W., 1987: Investigation of the role of phosphorus in symbiotic dinitrogen fixation. Plant Physiology 84, 835–840. JONES, M. I., WILD A., 1975: Soils of West African savanna. The maintenance and im- provement of their fertility. Commonwealth Bureau of the Soils Technical Communi- cation of the Harpenden, U.K. Commonwealth Agricultural Bureau (CAB), Farnham Royal, UK. 55, 246. MCFAYDEN, R. C., SKARRATT B., 1996: Potential distribution of Chromolaena odorata (siam weed) in Australia, Africa and Oceania. Agriculture Ecosystem and Environment 59, 89–96. SANGAKKARA,U. R., 1998: Growth and yields of cowpea (Vigna unguiculata (L.) Walp) as influenced by seed characters, soil moisture and season of planting. Journal of Agron- omy and Crop Science 180, 137–142. TEL, D. A., RAO P. V., 1982: Automated and semi-automated methods of soil and plant analysis. Manual Series 7. International Institute for Tropical Agriculture, Ibadan, Ni- geria. ACTA BOT. CROAT. 69 (2), 2010 297 GROWTH AND YIELD OF VIGNA UNGUICULATA IN THE RAINFOREST U:\ACTA BOTANICA\Acta-Botan 2-10\279 Oke.vp 11. listopad 2010 15:44:20 Color profile: Disabled Composite 150 lpi at 45 degrees