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Short communication: Palm bunch ash effects on growth of cowpea and the characteristics of a Ghanaian soil E.Y. SAFO, A.B. ANKOMAH and J. BRANDFORD-ARTHUR Department of Crop Science, University of Science and Technology, Kumasi, Ghana (West Africa) (Received 22 January, 1996; accepted 15 February, 1997)
Code Number: CS97037
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ABSTRACT A pot experiment was conducted in a roofless planthouse to study the effect of application of oil palm [Elaeis guineensis] bunch ash (PBA) to an acid soil, on dry matter (DM) yield of cowpea [Vigna unguiculata (L.) Walp.], tissue nutrient content and soil characteristics. Air-dry PBA was applied to cowpea in Ofin soil (loamy sand, Aquic ustifluvent) at 0.0, 0.42, 0.83, 1.67, 2.50, 3.33 and 4.17g kg^-1 soil. Plants were harvested 41 days after planting (DAP), and shoot and root DM yields were measured. Whole plant tops were analysed for N, P, K, Ca, and Mg. Shoot DM yields increased with increase in PBA application from 5.6 to 30.3 g plant^-1, and root DM from 0.9 to 3.3 g plant^-1. Similarly, cowpea tissue K increased from 1.2 to 10.6% and P from 0.09 to 0.51%. Palm bunch ash application had no significant effect on tissue Ca and Mg. Soil analysis after harvest showed that PBA application increased soil pH from 4.7 to 7.2, available P from 0.7 to 5.3 mg kg^-1 soil, exchangeable Ca^2+ from 0.52 to 2.17 cmol kg^-1 soil, and exchangeable K^+ from 0.05 to 1.3 cmol kg^-1 soil. However, soil total N decreased from 2.8 to 0.7 g kg^-1, and soil exchangeable Mg^2+ from 0.76 to 0.10 cmol kg^-1 under PBA treatments. It was concluded that PBA can be utilised as a fertilizer on acid soils of Ghana. Key Words: Acid soil, Elaeis guineensis, palm bunch ash, Vigna unguiculata RESUME Une experimentation en pots a ete realisee dans une maison de plantes ciel ouvert. Le but de cette recherche etait d'etudier l'effet de l'application des cendres du regime de palmier a huile [Elaeis guineensis] (ACP) sur un sol acide, le rendement en matiere seche (MS) du niebe [Vigna unguiculata (L.) Walp.], la teneur en elements mineraux nutritifs des tissus et les proprietes du sol. Le PBA seche a l'air a ete appliqueau niebe dans le sol d'ofin (sablo-angileux, Aquic ustifluvent) 0,0, 0,42, 0,83, 1,67, 2,50, 3,33 et 4,17 g/kg sol. Les plantes ont ete recoltees 41 jours apres le semis (JAS). La production des tiges et des racines a ete ensuite mesuree. Toutes les parties aeriennes des plantes ont fait l'objet d'analyses chimiques. Celles-ci ont porte sur les elements suivants: N, P, K, Ca et Mg. Les productions de la matiere seche (MS) des tiges augmentaient avec l'accroissement de l'application de PBA de 5,6 a 30,3 g/plante. Par contre, les productions de la matiere seche (MS) des racines augmentaient avec l'application PBA de 0,9 a 3,3 g/plante. De la meme facon, la concentration de K contenu dans les tissus augmentait de 1,2 a 10,6% et celle de P de 0,09 a 0,51%. L'application des cendres des regimes du palmier a huile n'a pas eu d'effet significatif sur le Ca et le Mg contenus dans les tissus. L'analyse du sol apres la recolte des plantes a montre que l'application de PBA augmentait a la fois le pH du sol de 4,7 a 7,2, le P assimilable de 0,7 a 5,3 mg/kg sol, le Ca^2+ echangeable de 0,52 a 2,17 cmol/kg sol, et le K^+ echangeable de 0,05 a 1,3 cmol/kg sol. Cependant, le N total du sol a diminue de 2,8 a 0,7 g/kg, et le Mg^2+ echangeable du sol de 0,76 a 0,10 cmol/kg pendant les traitements PBA. Il ressort donc de cette etude que le PBA peut tre utilise comme engrais azote sur les sols acides du Ghana. Mots Cles: Sol acidique, Elaeis guineensis, cendres des regime de palmier a huile, Vigna unguiculata INTRODUCTION Among the three primary agricultural inputs (seed, water and fertilizer) in a rain-fed farming system, fertilizer is the largest investment made by both the individual farmer and the Ghanaian government. In Ghana commercial fertilizers are imported and are very expensive. In situations of limited financial resources, attention should be focussed on locally available materials with the potential of being used as fertilizer. Indeed, awareness of the benefits of applying agricultural and agro-industrial residues on crop production is increasing (Ahenkorah and Halm, 1976; Toh et al., 1983). Oil palm bunch refuse is one of such local residues. It is available in raw composted or bunch ash form. On the basis of cost, convenience and ease of application, palm bunch refuse is generally used in the form obtained from the incineration of empty oil palm bunch waste. Palm bunch ash (PBA) is very hygroscopic, extremely basic (pH 10-12) and contains 25-34% K, 3.6-5.5% Ca, 1.6-3.6% Mg, 0.5-1.7% P, and approximately 0.1% N (Arokiasamy, 1967; Toh et al., 1983). In view of such properties and in line with Ghana's search for locally available materials that can effectively serve as fertilizer, this work studied the effects of PBA on the growth of cowpea and on the chemical characteristics of an acid soil. MATERIALS AND METHODS A pot experiment was conducted in a roofless planthouse at the University of Science and Technology, Kumasi, Ghana (1 degree 36' W and 06 degrees 43' N). Natural daylight, mean temperature and mean humidity for the day/night were 12 hr, 30/22 C and 60/95% RH, respectively. The soil used was from the surface 0-18 cm of the Ofin series, an Aquic Ustifluvent with loamy sand texture, pH(H2O) 4.8, total N content of 0.18%, available P (Bray P1) of 2.0 mg kg^-1 soil, and exchangeable Ca^2+, Mg^2+, and K^+ of 1.68, 1.79 and 0.064 cmol kg^-1 soil, respectively. Palm bunch ash, obtained from the Ghana Oil Palm Development Company at Kwae in the Eastern Region of the country, was sieved through 1 mm diameter openings. The PBA had a pH 10.6 and contained 32% moisture, 26% K, 6.8% Ca, 5.8% Mg and 4.0% P. Oven-dry PBA was applied at 0.0, 0.42, 0.83, 1.67, 2.50, 3.33 and 4.17 g kg^-1 soil. Treatments were replicated three times in a completely randomised design. Large wooden pots were each filled to capacity with 12 kg soil, and watered to 20% by weight which was the water-holding capacity. Four seeds of cowpea [Vigna unguiculata (L.) Walp., cv. IT 82E-32] were sown per pot, at a depth of 4 cm. At planting the appropriate amount of ash was applied in a ring about 5 cm from the seed and about 8 cm below the soil surface. Plants were thinned to one per pot, ten days after planting (DAP). Plants received natural rainfall but were watered whenever necessary. Pre-flowering insect pests were controlled with Ripcord 2.5 EC insecticide (Cypermethrin) at a concentration of 10 ml per litre of water. Plants were harvested 41 days after planting (DAP) at flowering by cutting at soil level. Roots were removed from the soil, washed and air-dried. Tops and roots were oven-dried at 70 C for 72 hr and weighed. The plant tops were ground and 0.5 g samples ashed at 450 C overnight. The ash was dissolved in 10 ml of 2M HCl and filtered (No 42 Whatman paper). Total K, P, Ca and Mg in the filtrate were measured. Total P was measured by the volorimetric (Phospho-vanadomolybdate, yellow complex) method (Hesse, 1971), K^+ by flame photometry, and Ca and Mg by the EDTA titrimetry (Lanyon and Heald, 1982). At the end of the experiment, the soil in each pot was mixed and sampled for chemical analysis. The samples were analysed for pH, total N, exchangeable K^+, Ca^2+ and Mg^2+, and available P. Soil total N was determined by the macro-Kjeldahl method. Soil available P was extracted by Bray P1 method (Bray and Kurtz, 1945) and measured by the stannous chloride-molybdate blue method (Dickman and Bray, 1940). Exchangeable cations were extracted with 1.0 M neutral ammonium acetate solution, and K^+, Ca^2+ and Mg^2+ in solution were measured as described previously for plant tissue analysis. Soil pH was measured at a soil: water ratio of 1: 2.5 Analysis of variance and the Duncan's multiple range test were performed to determine the significance of differences among treatment effects at the 0.05 level of probability (SAS, 1991). RESULTS AND DISCUSSION Cowpea plants not treated with PBA shed their basal leaves, an indication of P deficiency (Effah-Bafi, personal communication). Dry matter yield of control plants was low (Table 1) apparently as a result of high acidity and low fertility of the soil. According to Robson and Lonragan (1970), high soil acidity depresses growth of annual legumes by affecting plant nutrition, promoting Al toxicity, suppressing rhizobial survival and multiplication, and supporting the nodulation process and the symbiotic N2-fixation. The poor nutrient status of the unamended soil was also evidenced by the low level of soil exchangeable K^+ (0.064 cmol kg^-1 soil) compared with the level generally considered adequate for most field crops (including cowpea) in loamy sands (0.22 cmol kg^-1 of soil) (Doll and Lucas, 1973). Palm bunch ash application significantly (P<0.05) increased shoot and root DM yields (Table 1), and also increased plant height, number of leaves and branches, and stem thickness (data not presented). The good growth of the plants treated with PBA in this study might have resulted from the improvement of the pH and general fertility of the soil by application of the PBA. Palm bunch ash significantly (P<0.05) increased cowpea tissue K from 1.2 to 10.6% and tissue P from 0.09 to 0.51%. A tissue P concentration of 0.27% at a PBA application of 0.83g kg^-1 soil (1,860 kg PBA ha^-1) is comparable to the sufficiency level of P in soybean (Ankomah and Osei-Kofi, 1992) and groundnut at early pegging (Small and Ohlrogge, 1973). Heavy application of K or a high K/Mg ratio in the soil can lead to a low Mg concentration in plants (Doll and Hossner, 1964; Mengel and Kirkby, 1980; Haby et al., 1990). However, in our study, high levels of K^+ in the tissue and high ratios of K/Mg in soil, resulting from heavy applications of PBA, had no adverse effect on the Mg concentration of cowpea tissue and plant growth (Tables 1 - 3). In fact, the cowpea tissue Mg levels tended to increase with increase in PBA application. This finding agrees with Ologunde and Sorensen1982) suggestion that as long as the absolute amounts of K and Mg in a sand culture were adequate to meet plant demands, the K/Mg ratio could vary widely (1-25) without causing any adverse effect on plant matter production. The lack of adverse effect of high levels of tissue K and the high K/Mg ratios in soil on Mg concentration of cowpea tissue could also be explained by the improvement of soil pH with PBA application. Uptake of Mg is, especially, very sensitive to pH and shows, with most plant species, a strong positive response to increased pH of the soil (Jones and Haghiri, 1963; Hesse, 1971). Soil analysis after harvest indicated that PBA application significantly increased soil pH, available P and exchangeable K^+ and Mg^2+, but decreased soil total N and exchangeable Mg^2+ (Table 3). Soil pH increased from 4.7 to 7.2 over the range of PBA application. Teoh et al. (1986) reported that equal rates of limestone and PBA application produced essentially the same increase in topsoil pH, indicating that PBA may be as effective as limestone in ameliorating acidity in poorly buffered soils. The decrease in soil total N with PBA application could be attributed to greater supply of the other nutrients that caused increased growth. It is possible that the amount of N fixed by the cowpea was inadequate for the increase in growth. This observation supports the assertion that some legumes can deplete soil N if symbiotically supplied N is inadequate (Mulongoy, 1985). The decrease in soil exchangeable Mg with increase in PBA application (Table 3) could be attributed to an apparent enhanced uptake of soil Mg in order to offset the increasing imbalance in the K/Mg ratio in the plant. The plant had to draw on native soil Mg probably because the Mg content of the PBA was inadequate to meet the Mg needs of the plant. This means that Mg fertilisation would be required if a second cowpea crop was to be grown on the soil that received PBA. This would be especially so at and above a PBA application rate of 0.83 g kg^-1 of soil, where residual soil exchangeable Mg was 0.40 cmol kg^-1 and lower, which is below the adequacy range (0.42-0.83 cmol kg^-1 soil) reported by Doll and Lucas (1973) and Haby et al.(1990). The K/Mg ratio in soil is very important. Very wide residual ratios might depress uptake of Mg by the succeeding crop. Although it is reported that K/Mg ratio could vary widely (1-25) without causing any adverse effect on plant growth as long as the absolute amounts of K and Mg in the growth medium are adequate (Ologunde and Sorensen, 1982), it has been recommended for field crops that the K/Mg ratio be not greater than 1.5 (Doll and Lucas, 1973) or 2.0 (Batey, 1967) on equivalent basis. According to Batey (1967), soils with low Mg availability (<100 mg kg^-1) and a pH of <5.4, or a K/Mg ratio >4 were likely to be deficient. He suggested maintenance of a K/Mg ratio of <2 in the soil by balancing soil K and fertilizer K application with dressings of kieserite (MgSO4.H2O) or other Mg-containing fertilizers to avoid Mg deficiency. In view of the potentially large depletion of soil Mg resulting from PBA application, it is suggested that lower rates of PBA be applied in combination with dolomite, where kieserite is unavailable or unaffordable, to ensure proper K and Mg nutrition of cowpea on acid soils inherently low in these elements. CONCLUSION Oil palm bunch ash has a great potential for ameliorating soil acidity as well as supplying plant nutrients, especially K. Heavy applications of PBA result in high residual soil K and low residual soil Mg, leading to wide soil K/Mg ratios. It is suggested that lower rates of PBA be applied in combination with dolomite, or with kieserite where available and affordable, to ensure proper K and Mg nutrition of cowpea and other plants on acid soils that are low in these plant nutrients. More research is needed on the use of oil palm bunch ash as a nutrient source for increasing yields of crops, especially the high-K demanding ones such as the root crops, on acid soils. ACKNOWLEDGEMENT We thank the Ghana Oil Palm Development Company at Kwae, Ghana, for supplying the PBA, and the technical staff of the Soils Laboratory of the Department of Crop Science, University of Science and Technology, Kumasi, Ghana, for the analytical services. REFERENCES Ahenkorah, Y. and Halm, B.J. 1976. Potting media for growing cocoa seedlings. Ghana Journal of Agricultural Science 9:207-210. Ankomah, A.B. and Osei-Kofi, V. 1992. External and internal critical phosphorus requirements of soybean [Glycine max L. Merrill] in three Ghanaian soils. Tropical Agriculture (Trinidad) 69:315-318. Arokiasamy, M. 1967. Investigation on the best method of using the oil palm bunch waste as a fertilizer. Commun. (Agron.) Chemara Res. 7:1-7. Batey, T. 1967. The ratio of K to Mg in the soil in relation to plant growth. In: Soil Potassium and Magnesium. Technical Bulletin No. 14, pp. 143-146. Her Majesty Stationery Office, London. Bray, R.H. and Kurtz, L.T. 1945. Determination of total, organic and available forms of phosphate in soil. Soil Science 59:39-45. Dickman, S.R. and Bray, R.H. 1940. Colorimetric determination of phosphate. Ind. Eng. Chem. Anal. Ed. 12:665-668. Doll, E.C. and Hossner, L.R. 1964. Magnesium deficiency as related to liming and potassium levels in acid sandy podzols. International Congress of Soil Science Transactions 8th (Bucharest, Romania) IV:907-912. Haby, V.A., Russelle, M.P. and Skogley, Earl O. 1990. Testing soils for potassium, calcium, and magnesium. In: Soil Testing and Plant Analysis (3rd Ed.). Westernman, R.L. (Ed.), pp. 181-227. Soil Science Society of America Inc. Madison, Wisconsin, USA. Hesse, P.R. 1971. A Textbook of Soil Chemical Analysis. Chemical Publishing Co., Inc., New York. 255-300 pp. Jones, J.B. and Haghiri, F. 1963. Magnesium deficiency in Columbian County soils. Ohio Agricultural Experiment Station Circular No. 116. Lanyon, L.E. and Heald, W.R. 1982. Magnesium, calcium, strontium, and barium. In: Methods of Soil Analysis Part 2, Chemical and Mineralogical Properties, Second Edition. Page, A.L., Miller, R.H. and Keeney, D.R. (Eds.), pp. 247-262. Soil Science Society of America Inc., Madison, Wisconsin, USA. Mengel, K. and Kirkby, E.A. 1980. Potassium in crop production. Advances in Agronomy 33:59-110. Mulongoy, K. 1985. Nitrogen- fixing symbiosis and tropical ecosystems. In: Cowpea Research, Production and Utilization. Singh, S.R. and Rachie, K.O. (Eds.), pp. 307-315. John Wiley and Sons Ltd. Chichester, UK. Olugunde, O.O. and Sorensen. 1982. Influence of concentrations of K and Mg in nutrient solu-tions on sorghum. Agronomy Journal 74:41-46. Robson, A.D. and Lonragan, J.F. 1970. Nodulation and growth of Medicago truncatula on acid soils. Effect of calcium carbonate and inoculation level on the nodulation of Medicago truncatula on a moderately acid soil. Australian Journal of Agricultural Research 21:427-434. SAS Institute. 1991. SAS useruide: Statistics. SAS Institute, Cary, NC, USA. Small Jn, H.G. and Ohlrogge, A.J. 1973. Plant analysis as an aid in fertilizing soybean and peanuts. In: Soil Testing and Analysis. Walsh, L.M. and Beaton, J.D. (Eds.), pp. 315-327. Soil Science Society of America Inc. Madison, Wisconsin, USA. Teoh, C.H., Chang, A.K. and Chong, C.F. 1986. Fertilizer and soil amelioration trials on inland coastal soils in Malaysia. In: Cocoa and Coconut: Progress and Outlook. Pushparajah, E. and Chew, P.S. (Eds.), pp. 467-487. Kuala Lumpur Incorporated Society of Planters. Kuala Lumpur, Malaysia. Toh, P.Y., Poon, Y.C. and Yeow, K.H. 1983. Bunch ash as a nutrient source in oil palms. In: National Workshop on Oil Palm By-Product Utilization. pp. 135-139. Penyelidikan Minyak Kelapa Sawit Malaysia Kuala Lumpur, Malaysia. Copyright 1997 The African Crop Science Society The following images related to this document are available:Line drawing images[cs97037c.gif] [cs97037b.gif] [cs97037a.gif] |
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