Pertanika J. Trap. Agric. Sci. 19(1): 61-67 (1996)ISSN: 0126-6128

© Penerbit Universiti Pertanian Malaysia

Response of French Bean (Phaseolus vulgaris L.) to Rate and Ratio ofPotassiulIl Fertilizer Application

U.R. SANGAKKARAFaculty of Agriculture

University of PeradeniyaSri Lanka

Keywords: French bean, potassiwn, growth, yields

ABSTRAK

Kajian lapangan telah dijalankan untuk menilai kesan baja potasium, apabila digunakan pada nisbahyang berbezasebagai baja pangkal atau permukaan terhadap pertumbuhan vegetatif, lenggai tak matang dan hasil biji benihkacang peranchis. Begitu juga kualiti biji benih untuk tujuan penanamanyang ditentukan oleh percambahan sebelumatau selepas kekurangan nilai dikawal. Kadar penggunaan baja pada kadar (100:0,50: atau 0: 100 telah ditambahsemasa penanaman (pangkal) atau pada pembungaan (peringkat R 1-pembajaan permukaan). Pertumbuhankacang perancis tidak dipengaruhi oleh potasium. Perbezaannya, pertumbuhan vegetatif dan komponen palingberhasil jelas meningkat sehingga 100 kg K20 per hektar. Penggunaan kadar yang diberikan hanya padapenanaman (100:0) meningkatkan pertumbuhan vegetatif dibandingkan dengan bila kadar itu diasingkan.Penggunaan pada pembungaan semata-semata (0:100) mengurangkan semua parameter terukur, menentukankeperluan potasium sewaktu penanaman. Hasillenggai tak matangyang dituai untuk tujuan penanaman sayur nyatatidak bertambah oleh dua penggunaan dalam nisbah 50:50 (pangkal: pembajaan permukaan). Kualiti biji benihditentukan oleh percambahan sebelum dan selepas kekurangan nilai dikawal juga terlibat dan penggunaanberasingan 100 kg K20 dalam nisbah 50:50 meningkatkan percambahan.

ABSTRACT

A field study was undertaken to evaluate the iffect of potassium fertilizer, when applied in different ratios, as abasal or top dressing on vegetative growth, immature pod and seedyield of French bean as well as seed quality forplanting purpose determined by germination before and after controlled deterioration. The ratios of fertilizerapplication at a given rate of 100:0,50: or 0:100, were added at planting (basal) or atflowering (R1 stage - topdressing). Establishment of French bean was not affected by potassium. In contrast, vegetative growth and mostyield components increased significantly with up to 100 kg K20 per ha. Application ofa given rate only at planting(100:0) enhanced vegetative growth compared with a split rate. Application at flowering alone (0: 100) reduced allmeasured parameters, confirming the requirement ofpotassium at planting. Yields of immature pods harvested forvegetable purposes were not significantly increased by the two applications in the ratio of 50:50 (basal: topdressing). Seed quality determined by germination before and after controlled deterioration was also affected andsplit applications of 100 kg K20 in the ratio of 50:50 increased germinability.

INTRODUCTION

Piggot (1986) illustrated a greater require­ment of potassium at flowering in Frenchbean to facilitate the heavy sink effect bydeveloping pods and seeds, and the role ofthis nutrient in the translocation of photo­synthates. Thus general application atplanting alone can lead to deficiencies,

especially when the crop is grown for seedover a long period of time (Tindall 1983;Adams et al. 1985). Thung (1991) suggestedthat potassium would become a limitingfactor for successful production of Frenchbean, due to high rates of utilization anddepletion of this element. Thus a study wasconducted to identify the impact of differ-

U.R. SANGAKKARA

ent rates of potassium application on yieldsof immature pods and mature seed ofFrench bean and to determine the effectsof applying selected rates either at planting(basal), at planting and flower initiation(basal and top dressing) or at floweringalone (top dressing) on growth and yields ofimmature pods and mature seeds. Theimpact of these treatments on the qualityof seeds for planting material was alsodetermined by controlled deterioration, asfarmers generally cultivate this crop fromseeds of previous seasons.

MATERIALS AND METHODS

The experiment was carried out at theexperimental unit of the Faculty of Agri­culture, University of Peradeniya, SriLanka (7°N, 81 oE, 470 m above sea­level), which has a tropical south Asianmonsoonal climate (Domros 1974), with amean annual rainfall of 1700 mm spreadover two seasons (the rainfall over theexperimental period beginning ovember,1989 was 548 mm) with a mean monthlytemperature of 27.4 ± 1.24oC, and humid­ity of75.2 ± 2.320/0. The daylength was 11­12 hours. The soil at the site is classified asan Alfisol, with a sandy clay loam texture.The important characteristics of the top 30cm were as follows:- pH(1.25 H 20) 6.54 ±0.31, organic C (Walkley and Black) 0.66%(w/w), Total N (kjeldahl) 0.42%, ex­changeable K 121 ppm and a CEC of42.2 m eq per 100 g of soil.

Uniform seeds (germination 95.20/0) ofthe bushy type of French bean (varietyWade) were planted in well-prepared 2 x 3m seed beds, at a spacing of 20 x 10 cm.The crop was managed as per recommen­dations of the Department of Agriculture(1988) and was manually weeded on twooccasions. No supplementary irrigation wasrequired.

The fertilizer treatments adopted wereequivalent to 0,50, 100 or 150 kg K 20 per

ha, supplied In the form of KCl (60%K 20). Uniform rates of 50 kg P205 and 30kg were applied at planting. The selectedpotassium levels were applied in thefollowing ratios at planting (basal) or atflower initiation (Rl) (Fageira et al. 1991):(A) 100:0 (B) 50:50 and (C) 0: 100. At thetime of the top dressing of potassium,nitrogen equivalent to 15 kg per ha wasapplied, irrespective of application ofpotassium, to maintain uniformity. Theexperiment was laid out as a randomizedblock design with four replicates, withfertilizer treatments randomized withinthe block.

Crop establishment (percentage ofplanted seed) was determined at 8 daysafter planting. Thereafter, four plants wereremoved from each plot at 6-day intervalsup to flower initiation (Rl) and dry weightsdetermined by desiccation at 80°C for 48hours. These data were used to calculaterelative growth rates (g/g/wk). The ratio ofRGR of fertilized plants to that of thecontrol (OK20) was computed to determinethe treatment effect on vegetative growth.

At 500/0 flowering (growth stage R3),30 plants within each plot were tagged todetermine flower and pod numbers andseeds per pod. At the time of immature podharvest (R7), 15 of the tagged plants wereused to determine yields per plant andweight of immature pods. The other 15plants were harvested at full maturity (R8)when most mature pods had begun to split,and seed yield per plant and 100-seedweight were obtained.

The controlled deterioration testsadopted were similar to those described byMatthews and Powell (1987) and Hamptonet al. (1992). Thus, four replicates, eachcontaining 40 g of seeds obtained from thedifferent potassium treatments were soakedin deionized water to obtain a 24% seedmoisture content. The quantity of wateradded was determined by the equation

62 PERTANIKA J. TRap. AGRIC. SCI. VOL. 19 NO.1, 1996

POTASSIUM FERTILIZER FOR FRENCH BEAN

described by Hampton et at. (1992). There­after, the seed samples were sealed inaluminium foil and incubated for 72 hoursat 4SoC. Germination of seeds before andafter controlled deterioration was evaluatedby counting the number of normal seedlingsat 14 days after planting to a depth of 2.Scm in sand. Statistical analysis was carriedout by ANOVA and comparisons by LSD,as described by Gomez and Gomez (1981).

RESULTS AND DISCUSSION

TTegetative (;roovth

Rates and ratios of potassium fertilizerapplication had no impact on the establish­ment of French bean (Table 1). In contrast,the ratios of relative growth rates (RGR)illustrate the benefits of applying potassiumin enhancing the development of theemerged seedling. The RGR of plants inthe control (0 K 20) plots was 0.043(± 0.002) g/g/wk, which was considered

the baseline. The RGR ratio increasedsignificantly with increasing rates of K 20,although the increment with ISO kg K 20was marginal over that of 100 kg K 20.Thus 100 kg K 20 could be consideredoptimal for good vegetative growth ofFrench bean under the conditions of thistrial.

Application of potassium levels atplanting (100:0) developed the highestRGR, while the supply of So% of a givenrate at planting depressed growth. Theabsence of K 20 at planting showed growthrates similar to those of the control. Thisclearly illustrates the requirement of potas­sium in the basal fertilizer, as the elementinfluences the vegetative growth phase ofthe plant (Wolley et at. 1991). However, athigher rates of K 20 (i.e. ISO kg), applica­tion of So% of potassium at planting doesnot increase the RGR ratio significantlyover that of the 100:0 (basal: top dressing)

TABLE 1Effect of rate and ratios of potassium fertilizer application on vegetative growth of French bean

Rate (kg K 2O) Ratio* Establishment (%) RGR Ratio** Days to Flowerper ha Initiation

0 76 1.0 3950 A 87 a+ 1.23 a 34 a

B 93 a 1.08 b 37 bcC 95 a 1.02 c 39 c

100 A 89 a 1.42 a 31 aB 94 a 1.25 b 35 bC 96 a 0.95 c 40 c

150 A 95 a 1.46 a 30 aB 91 a 1.34 b 33 bC 95 a 1.06 c 39 c

LSD P = 0.05 (Means) 5.02 0.024 2.11Interaction NS * *

* Ratio of application - A = lOO:O, B = 50:50, C = 0: lOO(Basal: top dressing) at planting and flowering

** RGR ratio = RGR of treatment (units of RGR g/g/wk)RGR of control (0 K 20)

+ In a coloumn, means within a given role of fertilizer followed by a common letter are not significantlydifferent (p = 0.05)

PERTANIKA J. TROP. AGRIC. SCI. VOL. 19 NO.1, 1996 63

U.R. SANGAKKARA

ratio of the same quantity. This is due toadequate supply of the element for earlygrowth by this ratio at this rate.

FloweringApplication of potassium at ratios of 100:0or 50:50 (basal: top dressing) reduces thetime to flower initiation in French bean(Table 1), and lack of K 20 at plantingdelays this process, which could be attri­buted to the weaker growth of the plantsshown by RGR ratios. Number of flowerson a plant is significantly increased byapplication of 50 or 100 kg K 20 atplanting, due to better vegetative growthat these rates and ratios. This may beattributed to reduced photosynthetic pro­cesses and carbohydrate metabolism (Ting1982; Fageira et al. 1991), which influencethe initiation of the reproductive phase inplants.

Pod and Seed Numbers

A similar phenomenon is observed on podnumber (Table 2), although potassiumfertilizer probably does not have an impacton the process of pollination. However,

flower abortion could be enhanced inconditions of potassium deficiency inlegumes (Hanway and Johnson 1985),which could influence the number of podsper plant. At the lower rates of K 20, splitapplication (50:50 basal : top dressing)reduced number of flowers and pods perplant. This was not seen at the highest rate,due to the application of sufficient quan­tities at planting. At all rates, application ofall potassium at flowering (0: 100) reducedflower and pod number, due to poor earlygrowth of the plant. The importance ofpotassium in enhancing reproductivegrowth in French bean (Fageira et al.1991) could also have affected pod growth.

Seed number per pod (Table 2) was notinfluenced by the rates and ratios ofpotassium application, except in the con­trol treatment where the reduction wasmarginal. However, pod and seed develop­ment were influenced by the rates andratios of potassium. The absence of potas­sium in the basal fertilizer reduces both podand seed weights significantly. This con­firmed the importance of potassiumthroughout the growth of the crop.

TABLE 2Effect of rate and ratio of potassium application on yield components of French bean

Rate Ratio* Flowers/ Pods/Plant Seeds/Pod Wt of Pod 100-seed Wt(kg K 2O/ha) Plant (g) (g)

0 6.2 4.0 4.5 4.9 17.4250 A 16.2 a + 12.5 a 5.2 a 7.1 a 23.46 a

B 10.3 b 8.8 b 5.4 a 7.3 a 24.15 bC 6.5 c 4.5 c 5.0 a 5.2 b 19.15 c

100 A 24.6 a 20.6 a 5.2 a 8.6 a 25.44 aB 20.2 b 17.5 a 5.6 a 8.9 a 28.40 bC 6.9 c 4.8 b 5.1 a 6.1 b 22.16 c

150 A 26.5 a 20.5 a 5.2 a 8.7 a 26.24 aB 25.4 a 20.1 a 5.3 a 9.2 a 30.65 bC 8.5 c 5.9 b 4.9 a 6.2 b 22.68 c

LSD P = 0.05 (Means) 3.9 4.81 1.96 0.76 4.09Interaction * * NS * *

* Ratio of applications - A = 100:0, B = 50:50, C = 0: I 00 (Basal: top dressing) at planting and flowering+ In a column, means within a given rate of fertilizer followed by a common letter are not significantly different

(p = 0.05)

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Pod and Seed Yields

Application of potassium only on plantingalso reduced pod weight marginally, andseed weight significantly as both these areimportant sinks and the supply of carbohy­drates is influenced by potassium (Mengeland Kirby 1987). Thus, application ofpotassium at planting and flowering en­sures an adequate supply for plant growth,thereby increasing seed weight signifi­cantly. The greater impact of spilt applica­tion on seed weight could also be attributedto the longer period taken for seedmaturity, as compared with that of im­mature pods harvested as a vegetable.Application of low rates of potassium atplanting alone may not meet the demand ofthe crop during seed development due tothe high solubility of this element, whichleads to leaching losses, especially under therainfed conditions which prevailed duringthis study.

Application of potassium increasedboth pod and seed yield of French bean(Table 3), due to better vegetative growthand enhanced values of yield components.Although yields are further increased with

150 kg K 20 the increment between 100and 150 kg is marginal. Thus, in this study,application of 100 kg K 20 per ha isconsidered the optimal rate, which corre­sponds to most potassium fertilizer recom­mendations for French bean in the humidtropics (Tindall 1983; Thung 1991).

Withholding potassium in the vegeta­tive phase reduces both pod and seed yieldssignificantly. This confirms the importanceof potassium in basal fertilizers for Frenchbean, as for other legumes (Hanway andJohnson 1985). However, immature podyields are not significantly increased byapplying potassium at planting and flower­ing, especially at 100 or 150 kg K 20 per ha.At 50 kg K 20 per ha, there is a significantincrement in pod yield when all of thepotassium is applied as a basal dressing.This could be attributed to the influence ofpotassium on the vegetative growth, as asplit application of 50 kg K 20 may notprovide adequate quantities for optimalgrowth rates (Table 1). Thus farmersgrowing this crop for vegetative purposescan obtain high yields with one applicationof potassium at planting.

TABLE 3Effect of rate and ratio of potassium fertilizer application on fresh pod and seed yield of french beans

Rate (kg K 20jha) Ratio* Pod Yield + (gjp1ant) Seed Yield** (gjp1ant)

a50 A

BC

100 ABC

150 ABC

LSD (P = 0.05) within a rate of K 20Means of ratesInteraction

20.469.666.528.6138.1146.638.4153.7159.968.3

9.451.96

*

4.8214.4615.844.96

23.5727.94

6.9525.8231.959.962.610.96

*

* Ratio of applications - A = 100:0, B = 50:50, C = 0:100 (Basal: top dressing) at planting and flowering+ Pod yield determined by the harvest of fresh immature pods for vegetable purposes** Seed yield corrected to 20% moisture at harvest

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U.R. SANGAKKARA

Application of potassium only at plant­ing reduced seed yield significantly. Thussplit applications are required, except at thelowest rate (50 kg K 20 per ha). In contrastto pod production, optimal seed yields areobtained by split applications, althoughmost farmers cultivating this crop applyfertilizers once at planting (Thung 1991).The longer period of growth required forseed production needs a split applications ofthis soluble nutrient. The study alsoillustrates that applications of 100 kg K 20as a split application provides similar yieldsto those of applying 150 kg K 20 atplanting. Thus, judicious applications ofpotassium also reduces the quantity re­quired.

Seed Q,uality

Potassium fertilizer influences seed qualityof French bean due to its role in plantmetabolism (Fageira et al. 1991). Thus seedgermination is increased significantly by theaddition of 100 kg K 20, irrespective of the

ratio of the application (Table 4), as arepod and seed yields, for which this is theoptimal rate (Table 3). As for seed yields,a pplication of potassium at floweringreduces germination, both before and aftercontrolled deterioration. Thus, for optimalseed quality, potassium is required fromplanting. A comparison of germinationvalues again indicates the importance ofsplit applications of potassium in increasingseed quality for planting purposes, asmeasured by germination before and aftercontrolled deterioration. The patterns ofgermination due to potassium are notaltered by controlled deterioration. This isclearly evident at 100 and 150 kg K 20,while the effect at 50 kg K 20 is marginal.This illustrates that potassium is required atboth the vegetative and reproductivephases for high yields of good quali tyseed, which can be used for immediateconsumption or planting at a later season,the latter being more important in thedeveloping world of Asia.

TABLE 4Effect of rate and ratio of application of potassium fertilizer on germination pattern of French bean after

controlled deterioration

Rate of K 20 (kgjha) Ratio* Germination (%)

before cd after 72 hrs cd

0 42 1850 A 57 31

B 59 39C 47 24

100 A 74 52B 91 72C 51 31

150 A 81 54B 94 67C 53 36

LSD (P = 0.05) Within a rate of K 20 6.01 .4.90Means of rates 3.84 2.37Interaction * *

* Ratio of applications - A = 100:0, B = 50:50, C = 0: 100 (Basal: top dressing) at planting and flowering+ Germination determined by number of emerged normal seedlongs in 7 days

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CONCLUSIONS

Potassium is a prerequisite for optimalyields of legumes, including French beanas this field study clearly illustrates. Bothrates and ratios of potassium applicationinfluence vegetative growth, pod and seedyields and the quality of seeds, measured interms of germinability. Farmers producingimmature pods for vegetable purposesshould apply potassium at planting toobtain high yields. In contrast, for theproduction of high seed yields (for bothconsumption and planting) applications atplanting and at flowering are required.This will ensure good seed quality deter­mined by controlled deterioration, forplanting purposes. Split applications canreduce the requirement of fertilizer potas­SIum.

ACKNOWLEDGMENTS

Gratitude is expressed to Messres N.Gamage and E.R. Piyadasa for researchand technical assistance. The funds pro­vided by the Canadian InternationalDevelopment Agency through ARESA,Sri Langka under a research grant (CIDA/86/21) are gratefully acknowledged.

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(Received 25 February 1994)( Accepted 20 January 1996)

PERTANIKA J. TROP. AGRIC. SCI. VOL. 19 NO.1, 1996 67