The study revealed that the crop responded to plant densities as well as phosphorus levels. The biometric characters like number of primary branches per plant (8. 52), pod length (21. 31 cm), pod girth (12. 35 mm), number of pods per plant (37. 02), number of seeds per pod (16. 85), pod weight per plant (10. 93 g) and pod yield per plant (301. 85 g) were higher at lower density plants (37,037 plants/ha) along with 60 kg P2O5/ha. The growth and yield characters like plant height (52. 47 cm), TDM accumulation (3968. 04 kg/ha), days to flowering (34. 73 days), days to first picking (44. 8 days) and pod yield (152. 87 q//ha) were showed better expression in case of high density planting (74,074 plants/ha) along with 60 kg P2O5/ha. The interaction effect of plant densities and phosphorus levels were significant on plant height, total dry matter accumulation and days to flowering, pod length, pod weight per plant, and yield per plant and pod yield /ha. Key words: Growth, yield, plant density, phosphorus level, vegetable cowpea Cowpea plays a substantial role by serving as a grain and vegetable crop mainly for the rural people in the East, West, South and Central parts of Africa (Mortimore et al. 1997). According to FAO (2007), cowpea is produced annually on 11. 2 mha ranking 3rd after common bean (Phaseolus vulgaris L. ) and chickpea (Cicer arietinum L. ) with Africa taking the lead followed by Asia. It is extensively grown in South India particularly in the states of Karnataka and Tamilnadu. Cowpea used at all stages of its growth including as a vegetable (Ofori and Stern, 1986). Vegetable cowpea variety Arka Garima is a bushy type. Pods are thick, light green, long, round, stringless and highly fleshy. Yield potential of Arka Garima is 18 t/ha.
The optimum plant population is an important parameter for increasing the crop productivity and provides the plant with the best environment to express its capacity fully under the given conditions. The optimum plant density with proper geometry and its planting varied with the agro-climatic conditions and growth habit of the plant. Generally, pulses require phosphorus for their growth and nitrogen fixation. It also enhances the nodulation and pod development consequently pod yield. If the phosphate availability from the soil is limited, the growth and nitrogen fixation are affected (Prasad and Sanoria, 1981).
Phosphorus being an essential constituent of cellular proteins and nucleic acids, it encourages the meristematic activity in plants (Black, 1969) and adequate supply of nutrients which might have enhanced the metabolic activity and inturn plant growth. MATERIAL AND METHODS A field experiment was conducted at College of Horticulture, Venkataramannagudem during kharif 2010. The experimental site had red sandy loam with pH 6. 9, EC of 0. 01 dS/m, 0. 34 % organic carbon with 712, 32. 5, 217. 5 kg of N, P2O5 and K2O per ha, respectively. The experiment was laid out in factorial randomized block design with three replications.
There were twelve treatmental combinations comprised of three plant densities (37,037, 55,555 and 74,074 plants/ha) designated as D1, D2 and D3 and four levels of phosphorus (0, 20, 40 and 60 kg P2O5/ha) designated as P0, P1, P2 and P3. The seeds were treated with captan @ 3g/kg seeds before sowing against wilt. The Arka Garima seeds were dibbled on 29-8-2010 at 60 x 45, 60 x 30 and 45 x 30 cm spacings. During the crop period, the total rainfall received was 419. 07 mm. The nitrogen @ 20 kg/ha, potassium @10 kg/ha and phosphorus as per the treatments were applied during the crop period.
The metereological data recorded from planting date to harvest are presented below. Table 1: Monthly mean temperatures, relative humidity and rainfall during the growing season of cowpea (Sep-Nov) in 2010 at Venkataramannagudem, Andhra Pradesh. Month Mean temperature (? C) Mean Relative Rain fall (mm) humidity (%) _____________________________________________________________________ September 28. 99 77. 96 19. 3 October 28. 84 71. 86 46. 00 November 27. 33 75. 14 38. 60 _____________________________________________________________________ A sample of five plants was taken randomly from two central rows in each experimental plot at different intervals. The growth parameters like plant height, number of primary branches, dry matter accumulation, days to flowering and days to first picking were recorded. Similarly the yield and its attributes were recorded.
For estimating total dry matter accumulation, each sample was first air dried and later oven dried at 60? C to constant weight. The sum of dry weights of all plant parts was taken as total dry matter accumulation per plant (g). The data was analyzed by the method of variance outlined by Panse and Sukhatme (1985). RESULTS AND DISCUSSION The results revealed that the effect of plant densities and phosphorus levels on vegetative growth performance and yield were significant. The plant height increased with increasing plant density and decreased number of primary branches per plant at all sampling occasions.
Higher density produced tender and widely spread plants. Significant increase in plant height with high density (74,074 plants/ha) might be due to competition of solar energy coupled with shallow root system. Increased plant density limits the availability of space for plant and hence root configuration affecting the crop growth. Increased plant population increased plant height (Ahmed et al. 2010). The TDM accumulation was higher at a plant density of 74,074 plant/ha. The result might be attributed to optimum use of natural resources, higher uptake of nutrients and more number of plants per unit area.
Beneficial effect of optimum density on total dry matter accumulation has also been reported by Dwivedi et al. (1994) in frenchbean. Though the number of primary branches per plant, pod length, pod girth, number of pods per plant were higher at lower density (37,037 plants/ha), it delayed the maturity. Higher photosynthesis and higher amount of dry matter assimilation due to higher number of leaves and higher availability of nutrients led to vegetative growth at a longer period and as such the reproductive phase was delayed (Honma and Bert, 1977).
The higher pod yield per plant at low plant density (37,037 plants/ha) could be attributed to the significant increase in pod length, pod girth, number of pods per plant, number of seeds per pod and pod weight per plant. These values were significantly lower at higher density (74,074 plants/ha) due to increased competition among the plants for the space, light and nutrients. Increasing population decreased the number of pods per plant. This reduction may be attributed to the interference among branches. The findings are in accord with the previous results reported by Hamad (2004).
The variations in number of pods per plant could be attributed to the variations in number of branches per plant. Hence lower plant densities resulted in maximum number of branches per plant and in turn was responsible for more number of fruiting points. Further, less competition for light, moisture and nutrients associated with wider spacing has an edge in producing more reproductive parts compared to high density plants. The plant growth, yield and its attributes were superior with the application of 60 kg P2O5/ha.
Increase in plant growth might be due to hastened meristematic activity, better root growth and better absorption of nutrients by increased application of P (Philip, 1993). The translocation of photosynthates by the action of P also showed an improvement in various growth parameters (Verma and Saxena, 1995). The infection of Rhizobium bacteria depends on their interception with the root hair. Under adequate phosphate application, nodulation increases due to high bacterial infection on account of properly developed rooting system and increased density of nodule bacteria (Srivastava and Varma, 1985).
Increased nodulation implies greater symbiotic fixation of atmospheric N which also helps in cell division and root extension which might have resulted in vigorous plant growth. Similar results were reported by Joseph and Varma (1994) in chickpea. The phosphorus application @ 60 kg/ha showed a significant influence on days to flowering, days to 50 per cent flowering and days to first picking. Influence of P in hastening maturity is well documented. Phosphorus imparts quicker vegetative growth to the plant and entering into the reproductive phase early.
The same trend of higher levels of P was also noted by Philip (1993) in cowpea and Bahadur and Singh (1990) in garden pea. The increase in yield attributes might be a direct consequence of growth characters. Adequate supply of P is important in laying down the primordia for the reproductive parts of plants. It is also considered important in the formation of pods and seeds. Being a constituent of protoplasm, which may be responsible for increased length of pods, pod weight, number of seeds per pod and inturn pod yield. These results are in conformity with the finding of Sundara et al. 2004) in pea. The interaction effect of application of 60 kg P2O5/ha and higher plant densities (74,074 plants/ha) produced higher pod yield along with rich protein content. The economic returns were more in case of high density as per the results obtained in the present experiment. It is also suggested that a plant density level D3 (74,074 plants/ha) and a phosphorus level of P3 (60 kg P2O5) was most profitable for the cultivation of vegetable cowpea cv. Arka Garima under irrigated conditions in coastal region of Andhra Pradesh. REFERENCES
Ahmed Naim, M. E. and Abdelrhim Jabereldar, A. 2010. Effect of plant density and cultivar on growth and yield of cowpea (Vigna unguiculata L. Walp). Australian Journal of Basic and Applied Sciences, 4: 3148-53. Bahudur, V. and Singh, T. 1990. Yield and growth response of garden pea (Pisum sativum L. ) to nitrogen and phosphorus application. Vegetable Science, 17 : 205-09. Black, C. A. 1969. Soil plant relationships (2nd Ed. ) John Wiley and Sons Inc. New York, pp. 792. Dwivedi, D. K. , Singh, H. , Shahi, K. M. B. and Rai, J. N. 1994.
Response of frenchbean (Phaseolus vulgaris) to population densities and nitrogen levels under mid-upland situation in north-east alluvial plains of Bihar. Indian J. Agron. , 39 : 581-83. FAO (Food and Agriculture Organization). 2007. FAOSTAT http://faostat. fao. org/site/567/default. aspx#ancor. Hamad, M. S. 2004. Effect of planting density on the performance of three cultivars of cowpea. M. Sc. thesis submitted to University of Khartoum, Sudan. Honma, S. and Bert, J. 1977. Growing high density cauliflower. American Vegetable Grower, 25 : 40. Joseph, B. and Varma. 1994.
Response of rainfed chickpea (Cicer arietinum) to jalshakti incorporation and phosphorus and sulphur fertilization. Indian J. Agron. , 39 : 312-14. Mortimore, M. J. , Singh, B. B. , Harris, F. and Blade, S. F. 1997. Cowpea in traditional cropping systems. Advances in Cowpea Research, 8: 99-113. Ofofi, F. and Stern, W. R. 1986. Maize/cowpea intercrops system: Effect of nitrogen fertilizer on productivity and efficiency. Field Crop Research, 14: 247-61. Panse, V. G. and Sukhatame, P. V. 1985. Statistical methods for agricultural workers. ICAR, New Delhi. Philip, A. 1993.
Phosphorus and molybdenum nutrition in cowpea (Vigna unguiculata L. ). M. Sc. (Ag. ) Thesis submitted to the Kerala Agricultural University. Srivastava, S. N. L. and Varma, S. C. 1985. Effect of nitrogen, phosphorus and molybdenum fertilization on growth, nodulation and residual fertility in field pea. Indian J. Agric Res. , 19: 131-37. Sundara, T. H. , Vyakaranahal, B. S. , Shekhargoud, M. , Shishidhara, S. D. and Hosamani, R. M. 2004. Influence of phosphorus and micronutrients on seed yield and quality of pea (Pisum sativum L. ). Seed Research, 32: 214-16. Verma, V. S. and Saxena, K.
K. 1995. Response of Frenchbean (Phaseolus vulgaris) to graded doses of nitrogen, phosphorus and potassium in silty loam soil of central Uttar Pradesh. Indian J. Agron. , 40 : 67-71. Table 2 : Effect of plant densities and phosphorus levels on plant height, number of primary branches per plant and days to flowering of vegetable cowpea cv. Arka Garima. Plant height (cm) (At 60 DAS)No. of primary branches (At 45 DAS)Days to flowering (Days) Plant densitiesPhosphorus levels P0P1P2P3MeanP0P1P2P3MeanP0P1P2P3Mean D145. 6045. 93046. 6748. 8046. 758. 078. 538. 608. 878. 5236. 6736. 0036. 336. 4736. 57 D245. 4047. 4050. 0748. 4047. 828. 008. 338. 138. 338. 2035. 4735. 4035. 3335. 2735. 37 D349. 2052. 6752. 2055. 8052. 477. 477. 808. 078. 077. 8535. 0034. 8034. 6334. 4734. 73 Mean46. 7348. 6749. 6451. 007. 848. 228. 278. 4235. 7135. 4035. 5035. 40 SourceSEm ±CD (P=0. 05)SEm ±CD (P=0. 05)SEm ±CD (P=0. 05) Plant density (D)0. 120. 340. 110. 310. 060. 18 Phosphorus level (P)0. 130. 390. 120. 360. 070. 20 D x P0. 230. 680. 21N. S0. 12NS Table 3 : Effect of plant densities and phosphorus levels on total dry matter accumulation of vegetable cowpea cv. Arka Garima.
Total dry matter accumulation (30 DAS)Total dry matter accumulation (60 DAS)Total dry matter accumulation (90 DAS) Plant densitiesPhosphorus levels P0P1P2P3MeanP0P1P2P3MeanP0P1P2P3Mean D1163. 50169. 03174. 85180. 38171. 941945. 661974. 371954. 932001. 671969. 16 3788. 403798. 773810. 643867. 503816. 33 D2172. 91187. 81189. 64197. 97187. 081965. 171970. 672016. 332014. 281991. 613874. 413885. 983986. 924096. 853961. 04 D3187. 95200. 96211. 37221. 33205. 401951. 191983. 812107. 322094. 432034. 193722. 813865. 744080. 084203. 513968. 04 Mean174. 79185. 93191. 96199. 891954. 001976. 282026. 192036. 793795. 13850. 173959. 214055. 95 SourceSEm ±CD (P=0. 05)SEm ±CD (P=0. 05)SEm ±CD (P=0. 05) Plant density (D)0. 591. 7210. 1029. 637. 6022. 30 Phosphorus level (P)0. 681. 9911. 6634. 218. 7825. 75 D x P1. 173. 4420. 2059. 2615. 2044. 60 Table 4 : Effect of plant densities and phosphorus levels on number of pods per plant, pod weight per plant and pod yield per plant of vegetable cowpea cv. Arka Garima. Pod length (cm)Pod girth (mm)No. of pods per plant Plant densitiesPhosphorus levels P0P1P2P3MeanP0P1P2P3MeanP0P1P2P3Mean D118. 4721. 8021. 8323. 1321. 3111. 8712. 0012. 2713. 2712. 3515. 1316. 4717. 4718. 3316. 5 D218. 5319. 4020. 6720. 5319. 7811. 3313. 1312. 5312. 0012. 2515. 1316. 0717. 0017. 6716. 47 D316. 8017. 1322. 3322. 2719. 6310. 9311. 2712. 0012. 0711. 5715. 1315. 3316. 0716. 9315. 87 Mean17. 6319. 4421. 6121. 9811. 3812. 1312. 2712. 4415. 1315. 9616. 8417. 64 SourceSEm ±CD (P=0. 05)SEm ±CD (P=0. 05)SEm ±CD (P=0. 05) Plant density (D)0. 120. 340. 220. 650. 120. 36 Phosphorus level (P)0. 130. 390. 260. 750. 140. 42 D x P0. 230. 680. 44NS0. 25NS Table 5 : Effect of plant densities and phosphorus levels on number of pods per plant, pod weight per plant and pod yield per plant of vegetable cowpea
