Effects of plant density of tepary beans [Phaseolus acutifolius] on growth and seed yield

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1 African Journal of Applied Agricultural Sciences and Technologies [Online] Published by African-American Institute 2[1]: Edje and Dlamini, 215 Submitted 28 March, 215 Accepted May 12, 215 Published 25 May, 215 Effects of plant density of tepary beans [Phaseolus acutifolius] on growth and seed yield O. T. Edje and E. Dlamini Crop Production Department, Faculty of Agriculture and Consumer Science University of Swaziland. T ABSTRACT epary beans [Phaseolus acutifolius], known locally as insambasamba, literally meaning abundance, many seeds, is a grain legume crop well adapted to semi-arid regions of Swaziland. It is popular among small-scale farmers for its taste and fast cooking qualities. Despite its popularity, there is very little information about its agronomic practices for increased production, especially plant population densities, hence this experiment was conducted. A field trial was conducted at Malkerns Research Station during the 211/212 cropping season. The treatments consisted of four plant densities: 5,, 1,, 2, and 4, plants/ha. The inter-row spacing was 5 cm in all treatments, but intra-row spacings were 4, 2, 1 and 5 cm, for the respective plant densities. The design of the experiment was randomised complete block and the treatments were replicated five times. All plots received 3 kg/ha of a compound fertiliser [2-3-2 (22)) at planting. Data collected included: plant height, leaf area index, number of braches/plant, pod length, number of pods/plant, 1-seed mass [g], seed yield [g/plant] and seed yield [kg/ha]. Results showed that seedling emergence was highest where the intra-row spacing was lowest. Leaf area index increased with time after planting and was highest at the highest plant density [4, plants/ha]. There was an inverse relationship between plant density and the number of primary branches/plant, being 46.1, 42.3, 38.1 and 3.3 branches/plant at the plant densities of 5,, 1,, 2, and 4, plants/ha, respectively. Plant density had significant [P<.5] effect on the number of pods/plant. It was 9.1, 84.3, 79.1 and 75.2 pods/plant at 5,, 1,, 2, and 4, plants/ha, respectively. Seed mass [g/plant] for 5,, 1,, 2, and 4, plants/ha were 23.3, 2.1, 14.6 and 1.1, respectively. The inverse was true for seed yield [kg/ha], being 644, 1167, 1383 and 1867 kg/ha for 5,, 1,, 2, and 4, plants/ha, respectively. It is concluded that increasing plant density increased ground cover, leaf area index, reduced the number of branches/plant, reduced seed yield/plant but increased seed yield [kg/ha] significantly [P <.1]. Despite the high cost of seed with increase in seed rate, the increase in ground cover, weed suppression, moisture retention associated with high plant density should not be ignored. Thus increase in seed rate could one strategy of adapting to climate change and mainstreaming climate-smart agriculture into crop production. It is recommended that tepary beans be grown at a plant population of 2, to 4, plants/ha. The experiment should be repeated for validation. Key words: Inter-row spacing, Intra-row spacing, Phaseolus acutifolius, Plant density, Tepary beans. INTRODUCTION AND LITERATURE REVIEW Tepary beans [Phaseolus acutifolius], known locally as insambasamba, literally meaning abundance, many seeds, is a grain legume crop well adapted to semi-arid regions of Swaziland. It is popular among small-scale farmers for its taste and fast cooking qualities. Despite its popularity, there is very little information about its agronomic practices for increased production and productivity, especially plant population densities. Corresponding Author: O. T. Edje, Crop Production Department, Faculty of Agriculture and Consumer Sciences, University of Swaziland: todoedje@yahoo.com

2 African Journal of Applied Agricultural Sciences and Technologies [Online] The manipulation of plant density in order to maintain a balance between crop performance and production factors, such as genetic potential, soil moisture, soil nutrients, light and space has long been recognised as accepted crop husbandry practices [Edje, 214]. Makama [211] conducted an experiment on the effects of plant density on the yield of tepary bean. The plant densities ranged from 56,25 to 225, plants/ha and seed yields increased with increase in plant density, presumably due to the fact that most grain legumes exhibit plasticity [Donald, 1963]. MATERIALS AND METHODS Experimental site A field experiment was conducted at the Malkerns Research Station during the 211/212 cropping season. Malkerns Research Station is m above sea level, latitude S and longitude E. The site has an annual mean rainfall of 8-1 mm; and temperature ranging from 7.3 C to 26.6 C. The soil type is classified as Mset soil series, dark clay, loam to sandy loam soil. Treatments and experimental design The experiment consisted of four plant densities [5,, 1,, 2, and 4, plants/ha]. These plant densities [Table 1] were achieved by planting at an intra-row spacings of 4, 2, 2 and 5 cm, respectively with an inter-row spacing of 5 for all plant densities. The experimental design was randomised block design. Table 1. Treatment code and treatment description Treatment code Intra-row spacing [cm] Plant densities [plants/ha] 1 5 4, 2 1 2, 3 2 1, 4 4 5, Plot size Each plot was 5 m long and 2.5 m wide, with inter-row spacing of 5 cm. There was 1 m path between replicates. Net plot was one row, 4 m long Fertiliser and planting All plots received 3 kg/ha of a compound fertiliser [2-3-2(22)]. It was banded along seed rows and covered before planting. There was no additional fertiliser as side dressing after the basal application of the compound fertiliser. The reason is that tepary bean is short-seasoned and similar grain legume crops have not benefited from additional nitrogen application under rain-fed condition, as is the case with maize and other cereal crops. However, under irrigation, additional nitrogen can be applied. Seeds were planted according to the intra-row spacings in shown in Table 1. Planting was done on 26 November, 211. Data collection Data colleted included: emergence count, plant height, leaf area, leaf area index, number of branches/plant, pod length, number of pods/plant, mass of 1 seeds [g], seed yield [g/plant] and seed yield kg/ha]. A seedling was regarded as emerged when the seedling was in the hook stage. Plant height from the distance from the ground level to the tip of the growing point. Ten plants were used for plant height determination. Leaf area was calculated after the method of Edje and Ossom [29]. The number of leaves/plant was determined from 1 plants. Only fully unrolled leaves were counted. Leaf area index [LAI] was leaf area, one side only, was the leaf area divided by land area. The number of branches/plant, were primary branches only and was determined from ten plants. Pod length was from ten pods. The mass [g] of 1 seeds was the mass after oven drying for 48 hours at 1 C Seed yield [kg/ha] was expressed at 1.% moisture content. 15

3 African Journal of Applied Agricultural Sciences and Technologies [Online] RESULTS AND DISCUSSION Seedling emergence and ground cover Emergence count was most rapid at the highest plant density and least rapid at the lowest plant density. This may be attributed to mutual assistance by seedlings. At the highest plant density [intra-row spacing of 5 cm], the epigeal characteristics of the emergence might have resulted in even low vigour seedlings emerging because the more vigourous seedlings pushed up soil thereby enhancing their emergence. Similar observations have been made by Edje et al., [23] and Edje [214]. Ground cover increased with increase in plant density. While seed cost increases with increase in seed rate without corresponding increase in seed yield, the side benefits of high seed rate should not be ignored. For example, farmers in Bukoba, Kagera Region, Tanzania, are know to use as much as about four times the recommended for beans when the legume is intercropped with banana [Musa spp.] such that about two weeks after seedling emergence, there is complete ground cover. The reason for the high plant density is for weed control. In other words, farmers invest money in seeds as a means of weed control. Similar observations have noted in parts of Ethiopia, where nomadic farmers use high plant density as a means of weed control; here farmers are investing resources in seeds as herbicides [weed killer]. Blackshaw et al. [1999] reported that narrow row spacing [high plant density] of Phaseolus beans resulted in greater weed suppression than wider row spacing. With climate change and associated adverse effects, increasing plant population could be one strategy of adaptation to climate change. In addition to weed suppression, which reduces reliance on chemicals for weed control, whose manufacture produces greenhouse gases, rapid attainment of ground cover could reduce moisture loss and increase soil health.. Plant height and pod clearance As would be expected, plant height increased with time after planting Figure 1]. At eight weeks after planting, plant height was highest [6.8 cm ] at the 4, plants/ha and lowest [41.3 cm] at the plant density of 5, plants/ha. The differences were significant at P <.5. Lodging increased with increase in plant density. However, the differences were not significant. The lower the plant density, the lower the pod clearance and vice versa. This would suggest that in mechanical harvesting, low plant density is not recommended as this will result in yield loss because some pods will be too low for mechanical harvesting. Also seed yield could be low with low density as some of the pods would be resulting on the ground or rather close to the ground to allow bacterial and fungal growth on the pods and in seeds. Number of leaves/plant The number of leaves/plant increased significantly [P <.5] with increase in plant density [Figure 2] and with time after planting [Figure 2]. Leaf development was gradual between four and six weeks after planting. Thereafter, it was rapid. The large number of leaves/plant with increase in plant density would be expected to provide ground cover, reduce rainfall drop impact on the soil, reduce soil and water erosion, increase moisture retention and improve soil health.. Leaf area index Leaf area index increased with time after planting [Figure 3]. Leaf area indices at 1 weeks after planting for the 4,; 2,, 1, and 5, plant/ha were 3.5, 2.8, 2.9 and 2.6, respectively. The differences were significant at P <.1. However, Makama [211] reported that LAI in tepary bean experiment decreased as plant density decreased. Number of branches/plant The number of branches/plant was significant [P <.5] at 4, 6, 8 and 1 weeks after planting [Figure 4]. There was inverse relationship between plant density and the number of branches/plant. The lower the plant density, the higher the number of branches/plant. For example, the number of branches/plant at 4,; 2,, 1, and 5, plants/ha were 3.1, 38.2, 42.1 and 46.3, respectively. The lower the plant density, the shorter the inter-node length. 16

4 Plant height [cm] African Journal of Applied Agricultural Sciences and Technologies [Online] In this experiment, seed yield was not determined for main stem and branches separately. One of the reasons for yield differences between climbing beans [Type IV] and dwarf beans [Type I] has been attributed to differences in the number of nodes. Climbing beans have more nodes [points of pod attachment, sink site for yield container] than dwarf beans. Consequently, plants with larger branch number would be expected to have higher yields per plant. And as will be seen later, this was the case in this experiment Time [Weeks after planting] Figure 1. Plant height of tepary beans at four densities at 2, 4, 6 and 8 weeks after planting 17

5 Leaf area index No. leaves/plant African Journal of Applied Agricultural Sciences and Technologies [Online] Time [Weeks after planting] 5, 1, 2, 4, Figure 2. Number of leaves/plant of tepary beans at four densities at 8 and 1 weeks after planting Time [Weeks after planting] Figure 3. Leaf area index of tepary beans at four densities at 4, 6, 8 and 1 weeks after planting 18

6 No. branches/plant] African Journal of Applied Agricultural Sciences and Technologies [Online] Time [Weeks after planting] Figure 4. Number of branches/plant of tepary beans at four densities at 4, 6, 8 and 1 weeks after planting Yield components Data for pod length, number of pods/plant, shelling percentage and 1-seed mass [g] are presented in Table 2. Plant density had no significant effect on pod length. The number of pods/plant increased with reduction in plant density. However, an eight-fold increase in plant density [from 5, to 4, plants/ha] caused only 16.5% reduction in the number of pods/plant. Seeds mass [g/1 seeds] increased with reduction in plant density. Similar results have been reported by Shirtliffe et al. [22]. They found that increasing seed rate from 2 to 1 seeds/m 2 resulted in a decline of only 2.9% in a 1-seed mass, a difference that was not probably of agronomic nor economic significance. The higher the plant density, the lower the shelling percentage, a trend similar to that of density-number of pods/plant relationship. Similar trend was observed with 1-seed mass [g]. The correlation coefficient [r] between number of pods/plant and pod length was.641. Table 2. Plant density, pod length, number of pods/plant, shelling % and mass of 1 seeds [g] of tepary beans at four plant densities. Plant densities [plants/ha] Pod length [cm] Number of Shelling % Mass [g] of 1 seeds pods/plant] 4, , , , LSD [.5] Yield [g/plant and kg/ha] Seed yield [g/plant] increased with reduction in plant density, being 23.3, 2.1, 14.6 and 1.1 g/plant at the 4,, 2,; 1, and 5, plants/ha, respectively [Figure 5]. Seed yield [kg/ha] increased significantly [P <.1] with increase in plant density, being 1867, 1383, 1167 and 644 kg/ha for the 4,; 2,; 1, and 5, 19

7 Seed yield [kg/ha] Seed mass [g/plant] African Journal of Applied Agricultural Sciences and Technologies [Online] plants/ha, respectively [Figure 4]. Similar results have been reported by Shirtliffe et al. [22], Blackshaw et al. [1999], Njoka et al [25], Pawar et al. [27], Moniruzzaman et al. [29], and Abubakar [28] The inverse was true for seed yield [g/plant] The inverse relationship between seed yield [kg/ha] and seed yield g/plant] may be explained on the basis of inter- and intra-plant competition as explained by Donald [1963]. At low plant density, inter-plant competition is low early in the season and several pods are set. But with high population scenario, intra-plant competition is high to severe early in the growth of the plant and only a few pods are set. Although the number of pods/plant and seed yield/plant is high, the number of plants at the low plant density are two few to compensate in the loss of stand, hence low seed yield [kg/ha]. An eight-fold increase in plant density caused only about three-fold [2.9 times] increase in seed yield [kg/ha]. This is due to the fact that tepary beans, like most other grain legume crops, exhibit plasticity. That is they are able to compensate for loss stand by increasing yield components. The ability of pulse crops to compensate for loss stand,, without reducing seed yield significantly, does not suggest that seed rates should be reduced to cut back on seed cost. Reducing seed rate because of compensatory attribute of grain legume crops could be reduce seed rate too low as to reduce crop yield significantly. As was stated earlier, solid or near solid planting could be encouraged as a means of addressing the adverse effects associated with climate change and climate variability , 2, 1, 5, Plant densities [plants/ha] Seed yield [kg/ha] Seed mass [g/plant] Figure 5. Seed mass [g/plant] and seed yield [kg/ha] of tepary beans at four densities. 11

8 African Journal of Applied Agricultural Sciences and Technologies [Online] CONCLUSION The following conclusions emerge from the experiment: [1] increasing plant density increased ground cover and leaf area index, [2] additional plant population reduced the number of branches/plant, reduced seed yield/plant, and [3] increasing plant density increased seed yield [kg/ha] significantly [P <.1] being 644, 1167, 1383 and 1867 kg/ha for plant densities at 5,, 1,, 2, and 4, plants/ha, respectively. RECOMMENDATION It is recommended that tepary beans be planted at 4, plants/ha with inter-and intra-row spacings of 5 cm and 5 cm, respectively. While the high seed rate would increase seed cost and thereby reduce profit, the benefits of increased soil cover, increased soil moisture retention, weed suppression and improvement of soil health resulting from increased soil biomass, should not be ignored. LITERATURE CITED Abubaker, S. [28]. Effect of plant density on flowering date, yield and quality attribute of bush beans [Phaseolus vulgaris L.] under cnter pivot irrigation system. American Journal of Agricultural and Biological Sciences 3[4]: Blackshaw, R. E., Muendel, H. H. and Saindon, G. [1999]. Canopy architecture, row spacing and plant density effects on yield of dry beans [Phaseolus vulgaris] in the absence and presence of hairy nightshade [Solanum sarrachoides]. Canadian of Plant Science 79[4] Donald, C. M. [1963]. Competition among crop and pasture plant species. Advances in Agronomy 15: Edje, O. T. and Bhekizizwe, D. M. [214]. Conservation agriculture: 1. Effects of legume crop species on ground cover, weeds, litter fall and maize yield in Swaziland. Paper presented at Fourth RUFORUM Biennial Conference Maputo, Mozambique, July 214 Edje, O. T. [214]. Response of bambara groundnuts [Vigna unguiculata (L.) Verd] to inter-row spacing in Swaziland African Journal of Applied Agricultural Sciences and Technologies 1[2]: Edje, O. T., Mavimbela, E. K. and Sesay, A. [23]. Response of bambara groundnuts [Vigna unguiculata (L.) Verdc] to plant density.. Proceedings of the international bambara groundnut symposium. Botawana College of Agriculture, Gabarone, Botawana, 8-12 August, 23. Makama, S. D. [211]. Effects of plant density on the growth and yield of a local bean variety insambasamba. Unpublished Final Year Research Report, Faculty of Agriculture, University of Swaziland. Luyengo Campus, Luyengo, Swaziland. Moniruzzaman, M., Halim, G. M. A. and Firoz, Z. A. [29]. Performance of French beans as influenced by plant density and nitrogen application. Bangladesh Journal of Agricultural Research 34[1]: Njoka, E. M., Muraya, M. M. and Okumu, M. [25]. The influence of plant density on yield and yield components of common beans Phaseolus vulgaris [L]. Agricultura Tropica et Subtropica. 38[1]: Pawar, S. U., Kharwade, M. L. and Wawari, H. W. [27]. Effect of plant density on vegetative growth and yield performance of different varieties of French bean under irrigated condition. Karnataka Journal of Agricultural Sciences 2[3]: Shirtliffe, S. J. and Johnston, A. M. [22]. Yield-density relationships and optimum plant populations in two cultvars of dry beans [Phaseolus vulgaris L.] grown in Saskatchewan. Canadian Journal of Plant Science 82: