Communication International Journal of Environment and Bioenergy, 2013, 6(3): 171-176 International Journal of Environment and Bioenergy Journal homepage: www.modernscientificpress.com/journals/ijee.aspx ISSN: 2165-8951 Florida, USA Effect of Drought on the Yields of Different Cowpea Cultivars and Their Response to Time of Planting in Kano State, Nigeria Ahmad R. Sanda 1, Ibrahim M. Maina 2 1 Department of Soil Science, Kebbi State University of Science and Technology, Aliero, P.M.B.1144, Birnin Kebbi, Kebbi State, Nigeria 2 International Institute of Tropical Agriculture, Kano Station, Nigeria * Author to whom correspondence should be addressed; E-Mail: sanda_ahmed@yahoo.com. Article history: Received 8 May 2013, Received in revised form 21 June 2013, Accepted 26 June 2013, Published 5 July 2013. Abstract: A field trial aimed at evaluating the effect of drought on the yield of different cowpea cultivars and their response to time of planting was conducted at the research farm of the International Institute of Tropical Agriculture (IITA) Minjibir, longitude 8 0 37 E and latitude12 0 11 N during the rainy season of 2010. The results shows that in all the parameters measured, which include fodder yield, days to 50% flowering, 95% maturity ratio, and grain yield, and sowing dates, had some significant effect, and it therefore, assumed that drought and terminal stress does not only affect the grain yield, but also the fodder production in all the cultivars tested. Keywords: drought; cowpea; cultivars; legumes; yield; terminal stress. 1. Introduction Cowpea (Vigna unguiculata L. Walp) is an important grain legume in the tropical and subtropical regions of the world. The estimated world cowpea production area is over 14.5 million ha, with an annual production estimated at about 7.64 million tones (FAO, 2000), out of this estimate, West and Central Africa (WECA) account for over 9 million ha, and 3 million tones. West Africa is the key cowpea production zone, mainly in the dry savanna and semi-arid agro-ecological zones. In
172 West Africa, Nigeria and Niger Republics are the major cowpea producers. According to FAO statistics division, 19 January, 2010, Nigeria account for 157184, 150115, 1501115 of cowpea seed/tones in 2006, 2007, and 2008 respectively, while Niger Republic account for 190725, 211786, and 211786 of cowpea seed/tones in the same years respectively. Cowpea is a food legume and of significant economic importance world wide with 24% protein and a high minerals potentials. The relatively high protein content of cowpea makes it an important supplement to the diet of world poorest people (Bressani, 1985), who consumed cereals, roots, and tubers that are high in carbohydrate and low in protein (Lambot, 2002). Cowpea haulms and chaff are used as livestock feeds and also beneficial in maintaining soil fertility (Carsky et al., 2001; Emechebe et al., 1991). Cowpea is extremely resilient crop, and is cultivated under some of the most extreme agricultural conditions in the world. However, despite the plant adaptation to climatic extremes in the arid and semi-arid ecologies, cowpea growth and yield are constrained by a variety of biotic and abiotic factors. Critical among abiotic factors is the increasing incidence of droughts occurrence due to green house effect which in severe cases leads to serious yield reduction or even total crop failure. Where soil moisture is not limiting, indeterminate cowpea produce flowers over a long period leading to more seeds productions, on the contrary, the flowering period is cut short with improper seed maturity. Despite the tremendous efforts of plant breeders in developing improved and drought tolerant varieties, the occurrence of either early and or late season drought negatively affects cowpea growth and yield. However, since the major cowpea producing areas in Nigeria are prone to both early, midseason and terminal drought, an understanding of the different cowpea growth cycles in relation to crop growth period is vital for yield improvement. Therefore, this study is designed to; assess some high yielding but genetically diverse cowpea varieties developed for drought tolerance and their yield response to different sowing dates, and assess the impact terminal drought stress on the productivity of these varieties. 2. Material and Methods The trial was conducted at Minjibir (Longitude 8 0 37 E and Latitude 12 0 11 N) at the International Institute of Tropical Agriculture research farm during the 2010 rainy season (Table 1). The experiment was conducted in a randomized complete block design (RCBD) with five treatments and three replications. The treatments are five cowpea cultivars, two late maturing lines, two medium maturing lines and one early maturing line. The cultivars were planted on three different dates at monthly interval beginning from 8 th July, 8 th August and 8 th September, 2010. The varieties used were IT97K-499-35, IT98K-412-13, IT98K-491-4, IT99K-216-24-2, and IT99K-7-21-2-2. The plots were four rows of 4 m long and a spacing of 0.75 m between ridges making an area of 12 m. All the cultural
173 and agronomic practices involved in cowpea production growth stages; days to 50% flowering, days to 95% maturity, fodder and grain yield respectively. The data collected were subjected to analysis of variance as described by Snedecor and Cochran (1967) for Randomized Complete Block Design (RCBD) using a Genstat Release 7.22 DE 2008 Version. Two way ANOVA was used to compare the difference between the treatment means using the least significant difference (LSD) AT 5%. Table 1. Mean monthly rainfall and maximum and minimum temperature data for Minjibir in 2010 cropping season Month Rainfall(mm) Temperature ( o C) Maximum Minimum May 4.0 36.9 26.9 June 58.6 35.4 26.6 July 361.4 29.2 20.7 August 220.4 29.8 21.7 September 101.0 30.7 21.8 October 16.0 31.9 27.0 November 00.0 31.6 21.5 Total/average 761.4 32.2 26.8 Source: IITA Metrological station Minjibir 3. Results and Discussion 3.1. Effect of Sowing Dates on the Fodder Yield of Some Cowpea Varieties at Minjibir Fodder yield for the five cultivars are given in Table 2. From the result it was observed that cultivar IT97K-499-35 and IT98K-412-13 gave a slight increase in fodder production in August, but significantly dropped in September which could be attributed to the effect of terminal stress and variability of rainfall. IT98K-491-4 produced 1.7 tones of fodder in July, but drastically dropped in August and September. However, there is no significant difference between August and September sowing dates in terms of fodder yield. IT99K-216-24-2 and IT99K-7-21-2-2 produced similar trend of fodder yield, with the yield decreasing accordingly from July to September. However, there is a significant difference between July and September sowing dates. 3.2. Effect of Sowing Dates on Days to 50% Flowering of Some Cowpea Varieties at Minjibir IT98K-412-13, IT98K-491-4, IT99K-216-24-2, and IT99K-7-21-2-2 showed a higher significant difference between July and August sowing dates as shown in Table 3. While IT97K-499-35 which is an early maturing line shows no significant difference between the two sowing dates. The
174 two late lines IT99K-7-21-2-2 and IT99K-216-24-2 shows a wider range in days to 50% flowering between July and August sowing dates. This could be due to response to day length and terminal drought stress which usually occur towards the end of the rainy season. Cowpea tends to flower earlier when it sensed moisture stress and this is one of the characteristics of most early maturing cultivars. Table 2. Effect of sowing dates on the fodder yield of some cowpea varieties at Minjibir Variety Fodder yield (kg/ha) Dates (month) IT97K-499-35 1113 1169 807 1030 IT98K-412-13 2032 2922 1280 2078 IT98K-491-4 1726 780 724 1076 IT99K-216-24-2 3563 3396 835 2598 IT99K-7-21-2-2 2729 2449 1002 2060 Mean 2232 2143 930 1769 LSD 1820.6 1193.3 359.7 658.2 Table 3. Effect of sowing dates on days to 50% of some cowpea varieties at Minjibir Variety Days to 50% flower (%) Date (month) IT97K-499-35 41 40 39 40 IT98K-412-13 48 47 43 49 IT98K-491-4 45 43 42 43 IT99K-216-24-2 74 65 44 61 IT99K-7-21-2-2 64 53 44 54 Mean 54 52 43 49 LSD 1.736 7.54 2.382 2.415 3.3. Effect of Sowing Dates on 95% Maturity of Some Cowpea Varieties at Minjibir Results in Table 4 shows that in all the varieties there is a significant difference between July and September sowing dates on days to 95% maturity. As discussed earlier, terminal stress can be the major factor contributing to these differences. Other factors like day length may be considered especially for the late lines.
175 Table 4. Effect of sowing date on days to 95% maturity of some cowpea varieties at Minjibir Varieties Days to 95% maturity (%) Sowing Dates (month) IT97K-499-35 62 58 57 59 IT98K-412-13 70 70 60 67 IT98K-491-4 65 63 57 61 IT99K-216-24-2 95 94 64 84 IT99K-7-21-2-2 90 81 63 78 Mean 76 73 60 70 LSD 5.446 13.79 1.458 4.445 3.4. Effect of Sowing Dates on Grain Yields of Some Cowpea Varieties at Minjibir Grain yield expressions for the five cultivars as contained in Table 5, shows that IT97K-499-35, IT98K-412-13, IT98K-491-4, and IT99K-7-21-2-2 had the highest significant difference of yield between July and September with a yield decreasing by a month from July through September. This could be attributed to the effect of drought on terminal stress on these cultivars. However, IT99K-216-24-2 produces opposite with a sharp increase of grain yield in August and a slight decrease in September, but much higher than the July sowing date. This explains the characteristics of IT99K-216-24-2 which is a day sensitive, dual purpose, late and drought tolerance. Table 5. Effect of sowing dates on grain yield of some cowpea varieties at Minjibir Variety Grain yield (kg/ha) Sowing Dates (month) IT97K-499-35 1414 1372 1101 1296 IT98K-412-13 2289 1240 1005 1512 IT98K-491-4 2178 1044 1097 1439 IT99K-216-24-2 225 998 918 714 IT99K-7-21-2-2 1313 1006 957 1092 Mean 1484 1132 1015 1210 LSD 896.8 649.2 235 337.7
176 4. Conclusions Drought and terminal stress does not only affect the grain yield of cowpea, but also its fodder production. However, this can be substantially reduced when sowing dates are delayed towards the end of the rainy season. As there is a significant effect on both fodder and grain yields between various sowing dates as shown in this study, timing and manipulation of sowing date can be used to influence these characteristics in this and many other areas with similar conditions. Finally, planting of extra early maturing cowpea cultivars combine with drought tolerance adoptable to an environment can further reduce the risk of yield loss always faced by farmers. References Bressani, R. (1985). Nutritive value of cowpea. In: Cowpea Research Production and Utilization. Singh, S. R., and Rachie, K. O. (eds.), John Wiley and Sons, U.K., pp. 353-359. Carsky, R. J., Singh, B. B., and Oyewole, B. (2001). Contribution of early season cowpea to late season maize in the savanna zone of west Africa. Biol. Agric. Horticul., 18: 303-315. Emechebe, A. M., Singh, B. B., Leleji, O. L., Atokple, I. D. K., and Adu, J. K. (1991). Cowpea-Striga Problems and Research. IAR Cropping Scheme, Institute of Agricultural Research, Ahmadu Bello University Zaria. (Technical Report, 1991 Cropping Season). FAO. (2000). Beans/Cowpea, West Africa Annual Report. FAO. (2010). FAO Statistics Division, 19 th January, 2010. Lambot, C. (2002). Industrial potential of cowpea. In: Challenges and Opportunities for Enhancing Cowpea Production, Fatokun et al., (eds). Proceedings of World Cowpea Conference held at IITA, Ibadan, 4 th -8 th September 2000. Snedecor, G. W., and Cochran, W. G. (1967). Statistical Methods, 6 th ed. Iowa State University, Ames, Iowa, U.S.A.