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Advances in Environmental Biology 42 201-215 2010ISSN 1995-0756 2010 American-Eurasian Network for Scientific Information Effects of jugo bean Corresponding AuthorProf Ekpo M Ossom Agronomist Crop Pro

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1 This is a refereed journal and all arti
This is a refereed journal and all articles are professionally screened and reviewed Advances in Environmental Biology, 4(2): 201-215, 2010ISSN 1995-0756© 2010, American-Eurasian Network for Scientific Information Effects of jugo bean [ Corresponding AuthorProf. Ekpo M. Ossom, Agronomist, Crop Production Department, Faculty of Agriculture,University of Swaziland, Private Bag Luyengo, Luyengo M205, SwazilandEmail: emossom@agric.uniswa.sz; ekpossom2@yahoo.com Adv. Environ. Biol., 4(2): 201-215, 2010was positively and significantly (p )with pod fresh mass at harvest (r = 0.831; R0.6906; n = 16), indicating that 69.1% increase inpod mass could be ascribed to CGR. Sole jugo beanhad significantly (p )ative growthrate, RGR (mean, 0.24 g/week) than intercroppedjugo bean (mean, 0.10-0,14 g/week). Correlation datashowed a positive but not significant relationshipbetween RGR and net assimilation rate, NAR (r =0.021; n = 16) at 20 WAP in jugo brean. Thecoefficient of determination (R= 0.0004) impliedthat only 0.04% increase in NAR was associatedwith increased RGR. LA was positively andsignificantly (p )lated with pod freshmass (r = 0.951; R= 0.9044), implying that 90.4%increase in pod fresh mass was associated withincrease in LA. Land equivalent ratio was highest(84.78%) when sweetpotato was intercropped withjugo bean at 66,666 plants/ha, and lowest (74.10%)under intercropping with 133,333 plants/ha of jugobean. It can be concluded that plant growth and yielddepended on plant density; intercropping produced nopod yield in jugo bean but improved totalsweetpotato yield. Farmers should not intercrop jugobean and sweetpotato.Intercropping is the cultivation of two or morecrops at the same time in the same field [1], and isone way to increase the diversity of farming systems.One advantage of intercropping is that the increasedcrop diversity helps to protect crops from insectpests, and if done well, may allow for more efficientuse of limited soil and water resources [2]. Anotheradvantage of intercropping is improved crop yields.When two or more crops with different rootingsystems, a different pattern of water and nutrientdemand, and a different aboveground habit areplanted together, water, nutrients and sunlight areused more efficiently. Therefore, the combined yieldsof two crops grown as intercrops can be higher thanthe yield of the same crops grown as pure stand. crops grown as pure stand.Ipomoea batatas (L.) Lam.] oftenmisunderstood and underrated, is receiving newattention as a life-saving food crop in developingcountries. More than 95% of the global sweetpotatocrop is grown in developing countries, where it is thefifth most important food crop [3]. Sweetpotato is amajor storage root crop commonly grown inSwaziland. It is a short-season crop, which reliablyprovides food on marginal and degraded soils, withlittle labour and few or no inputs from outside thefarm [4]. Though usually planted as a monocrop,sweetpotato can also be intercropped with groundnutL.) or any other crop that a small-scale farmerconsiders important to the family.Jugo bean [(L.) Verdc.], alsoknown as bambara groundnut, and ‘tindlubu’ insiSwati, is indigenous to West Africa, but is nowgrown widely as a crop in the

2 tropical regions ofAfrica [5]. It was r
tropical regions ofAfrica [5]. It was reported [6] that bambara is a popular crop in sub-Saharan Africa.In most rural areas of Swaziland, is plantedon virgin or fallow soils, which have a lower weedpopulation compared to cultivated fields. Itscultivation seems to have preceded the introductionof the common groundnut ( L.). Insome traditional farming systems, isintercropped with cereals. Bambara groundnut issimilar to groundnutin that the flowers curl downinto the ground so that the pods develop and matureunderground. Otherwise, the two plants are quitedifferent in appearance, and belong to differentgenera of the same Fabaceae family. Jugo bean isregarded as being vastly under-estimated andundeveloped as a crop plant; it has the advantage ofbeing reasonably productive even under extremeadverse conditions such as drought and poor soil [5].Sweetpotato has been grown in Swaziland for a longtime, but its significance has not gone beyond itssubsistence use. Although sweetpotato is consumedby almost every Swazi, cultivation has been restrictedto insignificant portions of family land. Mostliterature has always referred to sweetpotato as “awomen’s crop” because it does not require muchenergy input to grow the crop. However, theimportance of sweetpotato as a food security crophas been realized as a result of changes in thephysical and socio-economic environments during theearly 1990s [7].A survey showed that insect pest damage was amajor production constraint in sweetpotato productionin Swaziland [8]. Farmers perceived insect pests asa major production constraint. Farmers in Swazilandobtain their vines from other farmers for planting [8],which might lead to crop disease spreading. Farmersand researchers [9] have intercropped sweetpotatowith maize ( L.). Imports of improvedcultivars of sweetpotato and potato (L.) from international research institutesbroaden the spectrum of planting material forincorporation into evaluation [10].Growth analysis is the procedure of expressingplant growth parameters as the algebraic product ofa series of factors. Among the important growthindices are leaf area ratio (LAR); specific leaf area(SLA); specific leaf mass (SLM); relative growth rate(RGR); crop growth rate (CGR); net assimilation rate(NAR); and absolute growth rate (AGR). Thoughleguminous crops have been associated withsweetpotato in intercropping systems, there are noquantifiable data to show the effects of different jugobean plant population on a fixed population ofsweetpotato when the plants are intercropped. Adv. Environ. Biol., 4(2): 201-215, 2010Therefore, the objective of the experiment was toevaluate the effects of jugo bean plant population ongrowth indices and crop yields in jugo bean-Site and experimental designThe field experiment was conducted in MalkernsResearch Station, Malkerns, which is in theMiddleveld agro-ecological zone of Swaziland, at26.34S, 31.10E; it is 740 m above sea level.Malkerns has a rainfall range of 800-1460 mm anda mean temperature range of 7.3cropping season. The experiment was conductedduring the 2009/2010 cropping season, fromNovember 2009 to April 2010. The experimentaldesign was a randomized complete block design,with 5 treatments, each replicated four times. Thetre

3 atments (T) were: T, sweetpotato only at
atments (T) were: T, sweetpotato only at 33,333plants/ha; T, jugo bean only at 66,666 plants/ha; Tsweetpotato (33,333 plants/ha) intercropped with jugobean (66,666 plants/ha); T, sweetpotato (33,333plants/ha) intercropped with jugo bean (133,333, sweetpotato (33,333 plants/ha)intercropped with jugo bean (33,333 plants/ha).Land preparation, liming, and plantingThe land was prepared using a tractor-mountedmoldboard plow, followed by disc harrowing, afterwhich 1.0-m ridges were constructed using a tractor-mounted disc ridger. Before marking out the plots, acomposite soil sample of the experiment site wastaken (15-cm depth) for soil analysis. Each plotmeasured 5.4 m x 6.0 m, with 7 ridges. Each plotand each replicate were separated from contiguousplots by a 100-cm space. Before planting, and following laboratory testrecommendations of Malkerns Research Station SoilScience Department, dolomitic lime (CaMgCObroadcast and mixed on the ridges, using spades andgarden forks. Thereafter, reconstruction of the ridgeswith spades and hoes was done to maintain therequired ridge size and shape. Vines of sweetpotato(variety, ‘Kenya’) and seeds of jugo bean (‘UNISWARed’) were both obtained from Malkerns ResearchStation, and planted on 7 November 2009, on top ofridges, which were 1.0 m apart. To ensure goodestablishment of the crop, gap-filling of non-sproutedvines and non-emerged seeds was done during thefirst 2 weeks after planting (WAP).Weeding and Fertilizer applicationWeeding was done manually, using a hand hoe,at 4 and 8 weeks after planting (WAP) in all plots.In addition, monocropped jugo bean plots were alsoweeded at 12 WAP. After weeding, ridge re-moldingand earthing-up were done, to ensure that all plantshad sufficient soil around them for tuber and pegformation. At planting, 350 kg/ha of mixed fertilizer,N:P:K, 2-3-2 (38) that also contained 0.5% Zinc, wasapplied to all plots; 50 kg/ha of singlesuperphosphate was also applied to all plots, exceptin monocropped jugo bean. At 6 WAP, side dressingwith 10 parts of urea (45%N) and 50 parts ofmuriate of potash (KCl, 50% K) was applied at arate of 120 kg/ha [11], except where jugo bean onlywas grown. In all cases, the method of fertilizerapplication was the banding and incorporationmethod [4].Data collection, sampling method Data were collected every 4 weeks, starting at 4and ending at 20 WAP. The sample size for growthindices was 5 plants per plot. A destructive samplingmethod was used, whereby measurements were takenafter the plants were removed from the plots [12].Data were collected from Rows 2, 4 and 6 from theright side of the plot; rows 1, 3, 5 and 7 werediscard rows from which no sampling was done. Onerow per plot was reserved for yield determination foreach crop at harvest. Data were taken for the respective growthparameters for each crop species. The LA wasdetermined using the cork-borer method [11]. Usingthis method, 50 leaf discs were punch from leaves ofthe same plot using a cork borer that had a diameterof 1.1 cm. The petioles and all the aboveground partswere removed from the leaves after sampling andbefore taking the leaf mass [12]. The leaf area wascalculated using the following formula [12, 13]: Area of 50 leaf discs (cm Leaf dry

4 mass (g) of plants usedLeaf area =
mass (g) of plants usedLeaf area = Dry mass of 50 leaf discs (g). LAI was computed after calculating LA, by using theLeaf area (cmLeaf area index = Ground area spacing (cm number of plants sampled.Leaf area ratio (LAR) was derived from the leafarea measurements by dividing the leaf area by thetotal dry matter of the aboveground portion [12, 13].Specific leaf mass (SLM) was calculated bydividing the dry mass of leaves (g) by the leaf area), taken from 5 plants/plot on each samplingdate; it is the reciprocal of specific leaf area [12, Adv. Environ. Biol., 4(2): 201-215, 2010 Dry mass, of leaves (g)Specific leaf mass = Leaf area (cmThe following formula [14] was used to determinerelative growth rate (RGR):ln Mwhere M represented the leaf dry mass of theprevious sampling; M represents the current drymass. The corresponding time of sampling was and T, respectively. The ‘ln’ inthe formula stands for natural log, which is usedwhen evaluating the RGR. Crop growth rate (CGR) was determined byusing the total dry mass of plants which weresampled at the respective dates of sampling. Theformula [14] shown below was used to determine 1 x 1 P, and M represent previous mass and latermass obtained, respectively. The corresponding timeof sampling was represented by T and Trespectively. The ‘P’ in the formula representsnumber of plants sampled). Land equivalent ratio (LER) was calculated[Yield of SP in SP-jugo bean mixture] +[Yield of jugo bean in SP-jugo bean mixture]LER = [Yield of pure SP][Yield of pure jugo bean], where SP is the abbreviation for sweetpotato.Yield data were expressed in two forms:marketable sweetpotato tubers per hectare and totalmass of tubers. For jugo bean, yield was expressedas mass of seeds/ha. Marketable tubers [15] werethose tubers that weighed between 100 g and 1.4 kg,and free from harvest wounds and diseases. Theshelling percentage of jugo bean was determined bythe relationship [mass of seed divided by (mass ofpod + seed) before shelling]. Rainfall and airtemperature information were obtained from therecords of Malkerns Research Station [16]Data analysisData were analyzed using MSTAT-C statisticalprogram, version 2.0[17] and mean comparisonswere made using the F-protected least significantdifference for separation [18] at 5% level ofThe distribution of rainfall and air temperature isshown in Table 1. A total of 1,043 mm rainfall wasreceived during the investigation. February 2010recorded the least (89.5 mm) amount of rainfall,whereas January recorded the highest (280.8 mm).The highest (28.2C) and lowest (14.8C) airtemperatures were experienced in February 2010 andin November 2009, respectively.Table 2 shows the results of analysis on whichfertilizer and lime recommendations were based atthe start of the experiment; the data indicate thatsome elements (such as P and K) were available inappreciable quantities in the soil. These results alsoindicated that soil pH (4.9) was acidic.Sweetpotato growth indicesSweetpotato vine length The length of sweetpotato vines (Table 3) showsthat there was a significant (p )vine length among cropping systems only at 12WAP. The sweetpotato intercrop (sweetpotato + jugobean - 66,666 plants/ha) had the longest (148.85 cm)vine

5 s per plant. The correlation coefficien
s per plant. The correlation coefficient of vinelength (Table 4) with tuber yield was positive (r =0.223; n = 16) at 20 WAP. The resultant coefficientof determination (R = 0.0497), implied that 5.0% insweetpotato yield was associated with vine length.Leaf area (LA) There was a steady increase in LA development(Table 5) from 4 to 12 WAP in all cropping systems.The largest mean LA (39390.8 cm) in sweetpotatowas attained when sweetpotato was intercropped withjugo bean at 66,666 plants/ha); the lowest mean LA(25971.0 cm) was recorded in sweetpotatointercropped with jugo bean at 133,333 plants/ha. LAwas positively, but not significantly, correlated toyield of marketable tubers (r = 0.17; n = 16). Thecoefficient of determination (R= 0.0289) indicated Adv. Environ. Biol., 4(2): 201-215, 2010 Temperature and rainfall during the experiment.Month and yearMonthly air temperature (C)Total rainfall (mm)MaximumMinimumMeanNovember 200923.814.819.3269.0December 200927.317.022.2140.3January 201026.416.821.6280.8February 201028.218.623.489.5March 201026.417.722.194.4April 201024.815.220.0169.0Totals156.9100.1128.51043Means26.216.721.4173.8 [16].Soil analysis results and recommendations at the start of the experiment. Parameter ValuepH (HO)4.9Exchangeable acidity (cmolc/kg)0.9P (kg/ha)50.4K (kg/ha)36.4cmolc Mg/kg1.1cmolc Ca/kg0.46Organic matter (%)3.5 Effects of jugo bean plant population on the vine length of sweetpotato vines at 4-20 weeks after planting.Cropping systemWeeks after planting and vine length (cm)Means48121620Sweetpotato at 33,333 plants/ha39.9a64.8a140.1a158.4a161.9a113Sweetpotato + jugo bean at37.1a66.1a148.9b165.2a162.6a116 66,666 plants/haSweetpotato + jugo bean at39.4a63.1a128.5a152.4a154.0a107.5133,333 plants/haSweetpotato + jugo bean40.1a60.9a142.0a154.0a158.5a111.1at 3,333 plants/haMeans39.163.7139.8157.5159.2111.9Numbers followed by the same letters in the same column ar�e not significant at p 0.05.Correlation matrix for growth parameters in sweetpotato at 20 weeks after planting.Growth VineLALAILARSLASLMRGRCGRNARAGRNo. ofMarketaindices lengthplant tubersLA0.137LAI0.1371.000****LAR-0.230.527**0.528**SLA0.473*0.5540.554**0.147SLM0.356-0.404-0.404-0.7-0.1RGR-0.180.367-0.367-0.60.040.236CGR0.06-0.026-0.03-0.620.2130.3360.879***NAR0.339-0.010-0.560.3080.526**0.517**0.663***AGR0.06-0.026-0.03-0.620.2130.3350.879***00.663No. of0.477*0.0440.044-0.190.2320.2890.020.11300.114tubers/plantMarketable0.090.170.171-0.140.080.304-0.338-0.190.2710.190.195Total yield0.2230.3310.3310.09-0.27-0.218-0.342-0.148-0.144-0.15-0.250.254***, Significant at P 01**, Significant at P 05*, Significant at P 10that 2.9% increase in yield of marketable tuberscould be ascribed to an increase in LA.Specific leaf mass (SLM)In general, SLM increased from 4 to 8 WAP,and then declined in all cropping systems (Table 6).At 8 WAP, there was a significant (p )difference in SLM among the cropping systems. Thesole sweetpotato (33,333 plants/ha) had the highestSLM (6.81 mg/cm). SLM was positively but notsignificantly correlated (r = 0.304; R= 0.092; n =16) with marketable tuber yield; the coefficient ofdetermination implied that 9.2% increase inmarketable tuber yield could be ascribed to increasedRelative growth rate (

6 RGR)Table 7 shows sweetpotato RGR at 4-2
RGR)Table 7 shows sweetpotato RGR at 4-20 WAP.Significant (p )observed at 8-12 WAP and 16 WAP. Sole sweetpotato hadsignificantly (p )GR (0.30 g/week) at16-20 WAP. There was a positive but not significantcorrelation (r = 0.02; n = 16) between RGR and thenumber of tubers/plant at 20 WAP. The coefficient Adv. Environ. Biol., 4(2): 201-215, 2010 Sweetpotato leaf area at 4-20 weeks after planting.Cropping systemWeeks after planting and leaf area (cm)Means48121620Sweetpotato at 33,333 plants/ha3697.4a13392.8a44451.0a56422.9a59248.2b35442.5Sweetpotato + jugo bean2647.4a20851.4a54410.4b55470.1a63574.9b39390.8at 66,666 plants/ha Sweetpotato + jugo bean2400.1a10686.1a31945.3a41465.6a43357.7a25971.0at 133,333 plants/ha Sweetpotato + jugo bean2406.4a19864.5a52246.3b56022.8a58914.8b37890.9at 33,333 plants/haMeans2787.816198.745763.252345.356273.934673.8Numbers followed by the same letters in the same column ar�e not significant at p 0.05. Specific leaf mass of sweetpotato from 4 to 20 weeks after planting.Cropping systemWeeks after planting and specific leaf mass (mg/cm)Means 48121620Sweetpotato at 33,333 plants/ha5.34a6.81b5.26a5.32a4.53a5.45Sweetpotato + jugo bean 4.07a5.24a5.25a4.79a4.77a4.82at 66,666 plants/haSweetpotato + jugo bean 5.10a6.54a5.78a5.36a4.55a5.47at 133,333 plants/haSweetpotato + jugo bean 4.512a4.65a4.48a4.65a3.99a4.6at 33,333 plants/haMeans4.765.995.195.034.464.06Numbers followed by the same letters in the same column ar�e not significant at p 0.05.Sweetpotato relative growth rate (g/week) from 4-20 weeks after planting.Cropping systemWeeks after planting and relative growth rate (g/week)Means4-88-1212-1616-20Sweetpotato - 33,333 0.03a0.09a0.41a0.30a0.17 plants/haSweetpotato + jugo bean0.05a0.05a0.37a0.48a0.19- 66,666 plants/haSweetpotato + jugo bean0.07a0.1a0.36a0.40a0.19at 133,333 plants/haSweetpotato + jugo bean0.07a0.04a0.33a0.52a0.19at 33,333 plants/haMeans0.060.070.380.440.18Numbers followed by the same letters in the same column ar�e not significant at p 0.05.of determination (R= 0.0004) indicated that a 0.04%increase in the numbers of tubers/plant could beascribed to RGR.Crop growth rate (CGR)CGR increased between 8 and 12 WAP planting(Table 8), but between 12 and 16 WAP, it declineduntil week 20 WAP. There was a significant (p 0.05) difference in CGR only at 16-20 WAP.Intercropped sweetpotato (sweetpotato + jugo bean at133,333 plants/ha) recorded the highest (15.92/week) CGR at 12-16 WAP. The lowest CGR(5.24 g/cm/week) was attained at 16-20 WAP inmonocropped sweetpotato. CGR was positively, butnot significantly correlated (r = 0.113; Rn = 16) to the number of tubers/plant. Thecoefficient of determination indicated that only 1.3%increase in the increased number of tubers could beassociated with CGR.Number of marketable tubers per plantAs shown in Table 9, there were no marketabletubers at 4 and 8 WAP. Tuber formation started after8 WAP. There was a significant (p )in the number of marketable tubers/plant among thecropping systems from 12 to 20 WAP.Sole sweetpotato had a significantly (p )lower number (2.2 tubers/plant) of marketabletubers/plant at 20 WAP. Correlation data showed thatthe number of tubers/plant was positively but notsignificantly a

7 ssociated with the yield of marketabletu
ssociated with the yield of marketabletubers (r = 0.195; R= 0.038), indicating that 3.8%increase in yield of marketable tubers could beascribed to the number of tubers/plant.Total tuber yields (Table 10) were significantly(p )onocropped sweetpotato (42.89tonnes/ha) and lowest (31.78 t/ha) when sweetpotatowas intercropped with jugo bean at 133,333plants/ha. There were no significant (p )differences among the fresh mass of marketablesweetpotato tubers in the different cropping systems. Adv. Environ. Biol., 4(2): 201-215, 2010Sweetpotato crop growth rate from 8 to 20 weeks after planting.Cropping systemWeeks after planting and crop growth rate (mg/cm/wk)Means 4-88-1212-1616-20Sweetpotato 7.81a37.18a17.68a5.24a13.58 – 33,333 plants/haSweetpotato + jugo bean10.11a34.79a9.77a9.98a12.93- 66,666 plants/haSweetpotato + jugo bean7.49a26.46a15.92a8.69a11.71 at 133,333 plants/haSweetpotato + jugo bean11.80a34.65a8.05a15.88b14.08at 33,333 plants/ha Means9.333.2712.859.9513.08Numbers followed by the same letters in the same column ar�e not significant at p 0.05. Number of marketable tubers/plant from 4 to 20 weeks after planting. Cropping systemWeeks after planting and number of tubers/plantMeans48121620Sole sweetpotato001.95b2.60a2.20a1.35-33,333 plants/haSweetpotato + jugo001.80a3.15b3.35b1.66 bean - 66,666Sweetpotato + jugo001.25a2.55a3.15b1.39 bean at 133,333Sweetpotato + jugo001.30a2.90a2.65a1.37 bean at 33,333Means001.582.82.841.44Numbers followed by the same letters in the same column ar�e not significant at p 0.05.Table 10: Sweetpotato tuber yields (tonnes/ha) at 20 weeks after planting.Cropping systemTuber yields (tonnes/ha)Marketable tubersTotal tubers Sweetpotato – 33,333 plants/ha29.81a42.89bSweetpotato + jugo bean - 66,666 plants/ha 30.74a36.36 aSweetpotato + jugo bean at 133,333 plants/ha30.32a31.78aSweetpotato + jugo bean at 33,333 plants/ha29.34a33.48aMean30.0536.12Numbers followed by the same letters in the same column ar�e not significant at p 0.05.The sweetpotato intercrop with jugo bean at 66,666plants/ha) had the highest (30.74 tonnes/ha) yield ofmarketable tubers, whereas the sweetpotato grownwith jugo bean at 33,333 plants/ha) had the lowestmarketable yield (29.34 tonnes/ha) of sweetpotato,followed by the sole sweetpotato (29.81 tonnes/ha). Jugo bean growth indicesJugo bean plant heightTable 11 and shows a general increase in plantheight from 4 to 12 WAP, but significant differenceswere found only at 16 WAP, when sole jugo bean at66,666 plants/ha was significantly shorter (31.35 cm)than jugo bean intercropped (29.25 cm) at apopulation of 33,333 plants/ha.The correlation matrix (Table 12) shows thatplant height was negatively but not significantlycorrelated (r = - 0.279; R = 0.078) to fresh mass ofpods, implying that 7.8% decrease in fresh mass ofpods could be associated with increase in plantLA and LAITable 13 shows that there were significant (p 0.05) differences in LA among cropping systems at8-20 WAP. Generally, the intercropped jugo beanhad lower LAs at 8-20 WAP. At 20 WAP, the solejugo bean had significantly (p )) than the entire intercropped jugo bean. As shown in Table 12, LA was positively andsignificantly (p )mass (r = 0.951; R= 0.9044)

8 , implying that 90.4%increase in pod fre
, implying that 90.4%increase in pod fresh mass could be ascribed toincreased LA.The intercrop (sweetpotato + jugo bean at133,333 plants/ha) had significantly (p 0.05) lower(2.89) LAI at 20 WAP. Sweetpotato grown inassociation with jugo bean (sweetpotato + jugo beanat 66,666 plants/ha) and the other intercrop(sweetpotato + jugo bean at 33,333 plants/ha) had thesame LAI (4.24) at 20 WAP. The LAI was positivelyand significantly (p )(= 0.528; R2 = 0.2788) and SLA (r = 0.554; R2 = Adv. Environ. Biol., 4(2): 201-215, 2010 Plant height of jugo bean at 4-20 weeks after planting. Cropping systemWeeks after planting and plant height (cm)Means48121620Pure jugo bean16.98a17.86a28.55a31.35b34.22a25.79at 66,666 plants/haSweetpotato + jugo17.05a19.73a27.05a30.15ab33.56a25.31 bean at 66,666 plants/haSweetpotato + jugo17.31a19.50a28.35a29.25a38.41a26.56 bean at 133,333 plants/haSweetpotato + jugo15.96a19.21a25.20a29.25a38.02a25.53 bean at 33,333 plants/haMeans16.8318.8327.293036.0525.8Numbers followed by the same letters in the same column ar�e not significant at p 0.05.Table 12: Relationships among growth indices of jugo bean at 20 weeks after plantingGrowth indicesPlant heightLALAISLMRGRCGRNARLA-0.223LAI-0.2640.937***SLM-0.1330.454*0.510*RGR-0.2220.3280.3310.492*CGR-0.2110.953***0.898***0.482*0.546**NAR-0.09-0.272-0.155-0.2740.021-0.231Fresh pod mass-0.2790.951***0.903***0.446*0.1710.831***-0.218at harvest*, Significant at p 10; **, Significant at p 05; ***, Significant at p 01 Leaf area of jugo bean at 4-20 weeks after planting.Cropping systemWeeks after planting and leaf area (cm)Means48121620Pure jugo bean32.44a1229.51a6813.68b9325.0b15584.58b6597.05 at 66,666 plants/haSweetpotato + jugo37.45a715.83a1251.52a1440.45a1838.66a1056.78bean at 66,666Sweetpotato + jugo36.44a922.68a1445.34a1448.37a1676.95a1105.96 bean at 133,333Sweetpotato + jugo 30.87a648.52a970.46a1366.20a2214.75a1046.16 bean at 33,333Means34.3879.142620.253395.025328.742451.49Numbers followed by the same letters in the same column ar&#x 0.4;e not significant at p 0.05.Specific leaf mass (SLM)As shown in Table 14, jugo bean in all croppingsystems had high SLM values (59.57-140.09 mg/cmat 4 WAP, but all declined in values at 8 WAP,from which time, SLM values never increased toreach the early growth stages. Significant (p )differences in SLM were detected only at 8 and 16WAP. The correlation coefficient of SLM with freshmass of pods was positive and significant (p r = 0.446). The resultant coefficient of determination= 0.1989) indicated that about 20% increase infresh mass of pods could be associated with anincrease in SLM.Relative growth rate (RGR)Table 15 shows that significant (p )differences were observed in RGR at 4-8, 8-12 and16-20 WAP. Except between 12 and 16 WAP, thesole jugo bean generally had a significantly (p 0.05) higher RGR (mean, 0.24 g/week) thanintercropped jugo bean (mean, 0.10-0.14 g/week).Correlation data showed that there was a positive butnot significant relationship between RGR and NAR(r = 0.021; n = 16) at 20 WAP. The coefficient of determination (Rimplied that only 0.04% increase in NAR wasassociated with increased RGR.Crop growth rateThere was a significant (p )CGR among the cropping systems from 4 to 2

9 0WAP (Table 16). Generally, the sole jug
0WAP (Table 16). Generally, the sole jugo bean hadhigher CGR (mean, 2.97 mg/cm/wk) than the jugo Adv. Environ. Biol., 4(2): 201-215, 2010 Specific leaf mass for jugo bean at 4-20 weeks after planting.Cropping systemWeeks after planting and specific leaf mass (mg/cm)Means48121620Pure jugo bean 140.09a7.96a6.32a8.89b7.34a34.12 at 66,666 plants/haSweetpotato + jugo59.57a9.16b11.43a6.50a5.59a18.45bean at 66,666Sweetpotato + jugo78.52a5.45a5.54a7.10a4.50a20.22 bean at 133,333Sweetpotato + jugo92.19 a5.45a7.79 a5.57a6.59a23.52 bean at 33,333Mean92.597.017.777.026.0124.08Numbers followed by the same letters in the same column ar�e not significant at p 0.05.Table 15. Relative growth rate of jugo bean at 4-20 weeks after planting.Cropping systemWeeks after planting and relative growth rate (g/week)Means4-88-1212-1616-20Pure jugo bean0.29b0.42b0.11a0.12b0.24 at 66,666 plants/haSweetpotato + jugo0.24a0.13a0.08a0.11b0.14 bean at 66,666 plants/haSweetpotato + jugo bean0.12a0.14a0.10a0.02a0.1at 133,333 plants/haSweetpotato + jugo0.06a0.19a0.06a0.09a0.1 bean at33,333 plants/haMeans0.180.220.090.090.14Numbers followed by the same letters in the same column ar�e not significant at p 0.05. Crop growth rate of jugo bean at 4-20 WAP.Cropping systemWeeks after planting and crop growth rate (mg/cm/wk)Means4-88-1212-1616-20Sole jugo bean0.72b3.62b2.84b4.71b2.97at 66,666 plants/haSweetpotato + jugo bean0.39a0.47 a0.35a0.64a0.46at 66,666 plants/haSweetpotato + jugo bean 0.22a0.34a0.41a0.04a0.25at 133,333 plants/haSweetpotato + jugo bean 0.10a0.56a0.18a0.62a0.37at 33,333 plants/haMeans0.361.230.951.51.01Numbers followed by the same letters in the same column ar�e not significant at p 0.05.bean intercrops (mean, 0.25-0.46 mg/cmwas positively and significantly (p )d(Table 12) with fresh mass of pods at harvest (r =0.831; R = 0.6906; n = 16). The coefficient ofdetermination, R, showed that 69.1% of pod freshmass could be attributed to CGR.Number of pods/plant at 4-20 WAPTable 17 shows the number of pods per plant at4-20 WAP. There was no pod formation at 4-12WAP in all cropping systems. Only monocroppedjugo bean formed pods (mean, 24.1 pods/plant) at16-20 WAP.Pod yield at harvestTable 18 shows the jugo bean pod yield(tonnes/ha) at harvest. Fig. 1 shows monocroppedjugo bean with pods, whereas jugo bean intercroppedwith sweetpotato developed no pods (Figs. 2-4). Table 19 shows the 100-pod dry mass of jugobean at harvest. There were no pods observed in theintercrops at harvest. Only sole jugo bean had podsby harvest time. The shelling percentage was 62.4%. Land equivalent ratio (LER)The LER (Table 19) was highest (84.78%) in thesweetpotato intercrop (sweetpotato + jugo bean at66,666 plants/ha), followed by the cropping systemin which sweetpotato was intercropped with jugobean at 33,333 plants/ha (LER, 78.06%), and lowest(LER, 74.10%) when sweetpotato was intercroppedwith jugo bean at 133,333 plants/ha. Adv. Environ. Biol., 4(2): 201-215, 2010 Number of pods per plant at 4-20 weeks after planting.Cropping systemWeeks after planting and number of popds/plantMean4812162023Pure jugo bean at 66,666 plants/ha00021.161.761.824.09Sweetpotato + jugo bean at 66,666 plants/ha 0000000Sweetpotato + jugo bea

10 n at 133,333 plants/ha0000000Sweetpotato
n at 133,333 plants/ha0000000Sweetpotato + jugo bean at 33,333 plants/ha0000000Mean0005.2815.415.456.02 Jugo bean pod yield (tonnes/ha) at harvestCropping systemJugo bean pod yield at harvest (tonnes/ha)Pure jugo bean – 66,666 plants/ha2.29Sweetpotato + jugo bean - 66,666 plants/ha0Sweetpotato + jugo bean at 133,333 plants/ha0Sweetpotato + jugo bean at 33,333 plants/ha Mean0.57 Dry mass of 100 pods per cropping system.Cropping system100-pod dry mass (g)Land equivalent ratioPure jugo bean at 66,666 plants/ha47.9bNot applicableSweetpotato + jugo bean at 66,666 plants/ha0a0.85Sweetpotato + jugo bean at 133,333 plants/ha0a0.74Sweetpotato + jugo bean at 33,333 plants/ha0a.78Mean11.980.79Numbers followed by the same letters in the same column ar�e not significant at p 0.05.Fig. 1: Sole jugo bean plant with pods at harvest.Fig. 2: No pod formation in jugo bean planted at 66,666 plants/ha and intercropped with sweetpotato.Meteorological information: Rainfall is the majorlimiting factor in the growth and production of cropsworldwide [19], and more specially in Swaziland,where drought has had devastating effects inagriculture for over 10 years. Adequate moisture iscritical for plants, especially during germination andfruit development. Many countries have constructedirrigation systems to pump water from rivers, lakes, Adv. Environ. Biol., 4(2): 201-215, 2010 Fig. 3:No pod formation development in jugo bean planted at 33,333 plants/ha) and intercropped withFig. 4: No pod development in jugo bean grown at 133,333 plants/ha and intercropped with sweetpotato.and aquifers. Stressing the importance of rain, [20]reported that planting sweetpotato with the onset ofrains in October led to the highest yields in SriSoil acidity is the major problem in mostagricultural soils especially in the Middleved andHighveld of Swaziland (Dr. G.N. Shongwe,University of Swaziland, personal communication,August 2009). The recommended rate of agriculturallime that farmers should use in the Highveld andMiddleved ecological zones of Swaziland is 1-2tonnes/ha of dolomitic lime every 3-4 years (Dr.G.N. Shongwe, University of Swaziland, personalcommunication, August 2009). Lime application isimportant because lime can improve the soil pH,making nutrient elements more available to plantsre available to plantsSweetpotato vine length The lower vine length observed in the intercrop(sweetpotato + jugo bean at 133,333 plants/ha) wasprobably because of high inter-species competitionfor soil nutrients and light that the jugo bean andsweetpotato plants experienced. [22] reported noconsistent trend in sweetpotato vine length.LA and LAIThat intercropped sweetpotato (sweetpotato +jugo bean at 66,666 plants/ha) had significantly (p 0.05) higher LA than the other cropping systemscould be due to the effects of grain legumes whengrown in association with other crops. Variations inthe total LA of a plant depend on changes in thenumber of leaves and leaf size [23]. The higher LAobtained from some intercrop might be due to thefact that the sweetpotato could compete well with thejugo bean and suppress it. Then, the sweetpotatoleaves were better exposed to sunlight, resulting inhigher LA development. In sweet

11 potato, thedevelopment sequence that giv
potato, thedevelopment sequence that gives rise to change inLA with time is much simpler than in cereals [23].The LAI in sweetpotato associated with jugo bean at133,333 plants/ha was lower than in the monocropprobably because of intense inter-species competitionfor soil nutrients and light from the jugo bean. Formost plants, LAI increases with age (up to thebeginning of senescence) and reaches a maximum of Adv. Environ. Biol., 4(2): 201-215, 20102.0 to 5.0 [24]. The optimum LAI of sweetpotato issmall compared with cereals [23]. In aninvestigation involving intercropping of sweetpotatoand groundnut, [25] reported that the lower LAI insweetpotato intercropped with groundnut at 200,000plants/ha could have been due to intense inter-speciescompetition for light and soil nutrients.Specific leaf mass (SLM)Though few studies have been reported on SLMof intercropped sweetpotato [26] reported that SLMincreased with increased carbon dioxideconcentration, and that the number and diameter oftubers increased at high carbon dioxide concentration.[27] reported that the SLM of sweetpotatointercropped with groundnut increased from 4 to 8WAP and then declined in all plant populations,except in pure sweetpotato at 33,333 plants/ha thatkept increasing. Relative growth rate (RGR)RGR is the rate of increase in dry mass per unitof dry mass already assimilated into the plant [23].RGR means the change in relative growth over time[28]. Contrary to the results obtained in thisexperiment, [29] recorded a general decline in RGRof sweetpotato grown in association with groundnut,as the cropping season progressed.Crop growth rate (CGR)CGR measures the efficiency of production of atotal field of plants over a given soil area [28].When the NAR (productivity of each plant) decreases(probably due to increased plant-plant shading), theCGR (productivity of the entire crop over a givenarea of soil) increases [28]. The crop growth rate issimply the rate at which the dry mass of the wholeplant increases [23]. Therefore, the rate at which theplant dry mass was increasing was faster between 8and 12 WAP.Number of marketable tubers per plantOur results agreed with an earlier report ongroundnut intercropping with sweetpotato [30] thatthe number of marketable tubers per plant was notsignificantly reduced. However, in the presentexperiment the number of marketable tubers per plantwas significantly reduced when sweetpotato wasintercropped with jugo bean at 33,333 plants/ha. Nosignificant differences in the number of sweetpotatotubers/plant were observed in an earlier intercroppinglier intercroppingSweetpotato tuber yieldsResearch trials have shown that 20-40 tonnes perhectare of marketable sweetpotato tubers areachievable, depending on variety and management[32]. If left too long in the field, the tubers canbecome oversize, attacked by weevils, and couldbecome unmarketable. Lower marketable tubersobtained in the intercrops in this experiment mighthave been due to inter-species plant competition. Itwas established [15] that in Swaziland, marketabletubers were in the mass range of 100 g to 1.4 kg,but [32] reported marketable grades of roots to bebetween 25 g and 1.0 kg in Australia. In ourexperiment, monocropped sweetpotato had lowernumbe

12 r of marketable tubers because, generall
r of marketable tubers because, generally, eachtuber was large in size, and many were outside themass range desired by customers. An explanation for customers’ preference forsmall-size tubers in Swaziland might suffice. InSwazi cuisine, sweetpotato tubers are thoroughlywashed, and cooked whole and unpeeled. It appearsthat it is to shorten cooking time that smaller-sizetubers are preferred in Swaziland. However, in theWestern Middle Belt ecological zone of Nigeria(around Illorin town) where sweetpotato is a majorcrop, large-size tubers are preferred; this is becauseduring food preparation, tubers are first cut intodesired cooking pieces, after which the pieces arepeeled and cooked. Interestingly, in the Rainforestecological zone of the south-eastern part of Nigeria,where yams ( spp.) and cassava (spp.) are the major tuberous crops grown,sweetpotato is not cultivated, but is a tolerated weedin compound food gardens. During land preparationfor new gardens, sweetpotato tubers seen in the soilare dug up and given to children to roast and eat;adults take no interest in sweetpotato. Jugo bean plant height Plant height of bambara groundnut is usuallyequal to or greater than 35 cm [6]. The taller plantsobtained in the jugo bean intercrops could have beena consequence of inter-species competition betweensweetpotato and jugo bean, especially for water, lightand mineral nutrients. It was noted [33, 34] thatcompetition for light is asymmetric, such that tallerindividuals increase their fitness by intercepting morelight. The main cause for such competition could bethat, the suppressed jugo bean plants were trying togrow higher than, and away from sweetpotato, inorder to be better exposed to solar radiation forenhanced photosynthesis. LA and LAIHigher LA being observed in sole jugo bean Adv. Environ. Biol., 4(2): 201-215, 2010could be because there was no inter-species plantcompetition among monocropped plants. Our resultson the effects of plant competition on plant heightdeviated from an earlier report [35] that increasedLA was observed with increased plant population.Leaf area indexis the ratio of total upper leafsurface of vegetation divided by the surface area ofthe land on which the vegetation grows. Leaf areaindex is a dimensionless value [36]. The trend ofhigher LAI in lower plant populations (sole jugobean) than in higher plant populations as observed inthis experiment could be as a result of higher leafarea obtained in sole jugo bean. The higher leaf areawas achieved as a result of less competition forsunlight, soil nutrients and water within the plants.[12] reported that pure groundnut had significantly (p)tercropped withsweetpotato at 16,667 plants/ha.Relative growth rate (g/week)RGR means the change in relative growth overtime [28]. The trend of higher RGR in lower plantpopulation (sole jugo bean) than in lower plantpopulations as observed in the study could be due tothe exposure of the plants to sunlight and lesscompetition for soil nutrients and water. The RGR ofgroundnut decreased as the cropping seasonprogressed, from 4 to 16 WAP, as observed in thisSpecific leaf mass (SLM)SLM is the reciprocal ofspecific leaf area [12].The trend in SLM in this experiment agreed with thefindings [27] that

13 SLM of groundnut increasedbetween 4 and
SLM of groundnut increasedbetween 4 and 8 WAP and thereafter, declined, asalso observed in this investigation.Number of pods/plantAccording to [6], the expected number ofpods/plant in jugo bean is 100; though this dependson the variety/cultivar grown. The results of thisinvestigation were in agreement with a previousfinding [37] that pod mass/plant, seed mass/plant andnumber of pods/plant, seed yield were closelycorrelated with each other, with the correlationThe pod-yield attained in this experiment wasconsistent with previous findings [29], which showedhigher pod yields in pure crops, on account of nointer-species competition, compared to lower yieldsfrom intercrops that suffered from various degrees ofinter-species competition. The 100-pod dry mass obtained in thisexperiment (47.9 g) was much less than the 85 greported [6]. The shelling percentage of 62.4% wasalso lower than 68% obtained by [6]; [38] reporteda shelling percentage of 75% for monocropped jugoLand equivalent ratio (LER)Land equivalent ratioLER) is a useful conceptfor comparison of the yield of intercropping with thatof a monocrop [39]. The LER data reported in thisjugo bean-sweetpotato investigation did not agreewith previous investigation (on groundnut) in whichintercropping resulted in considerably greater totalEarlier LER [15] for intercropped sweetpotatoand groundnut ranged from a low of 1.19(sweetpotato intercropped with groundnut planted at33,333 plants/ha), to a high of 1.59 (sweetpotatoplanted with groundnut at 66,667 plants/ha). Thelow LER (0.74-0.85) obtained in this experiment wasless than 1.0, indicating that intercropping with jugobean was a disadvantage [39]. The importance oflegume inoculation on nodule formation in legumeswas emphasized [40]. It is our view that the non-formation of pods inintercropped jugo bean in this experiment was not aresult of the absence of the appropriate species of bacteria. If there were no bacteria in the soil, then there would have been nopod formation in sole jugo bean. Jugo beaninoculation is not a recommended agronomic practicein jugo bean production in Swaziland. Pod formationand earthing-up in jugo bean production have beenthe subject of some debate [38]. Results of ridgingtrials show an advantage, but the occurrence ofcan be increased with ridging.Ridging of bambara is, however, practiced by farmersthroughout Africa [38], but in Swaziland, jugo beanis most commonly planted on the flat, and whenpods start to form, earthing-up is done. Some farmersconsider this as reduced expenditure on landIt is concluded that physiological growth indicesas well as crop yields depended on cropping systemand jugo bean density. Since intercropping of jugobean with sweetpotato resulted in zero yields fromjugo bean, farmers are advised to not intercrop jugobean and sweetpotato. Adv. Environ. Biol., 4(2): 201-215, 2010AcknowledgmentThe authors thank Crop Production Department,University of Swaziland, for providing laboratoryfacilities for this investigation. We are also gratefulto Malkerns Research Station, for providing plantingmaterials, field facilities and security for theexperiment.1.van Wolfswinkel, M., 2010. Intercropping ofannual food crops.http:www.agromisa.org/agrobriefs/AB-2.A

14 nonymous, 2009a. Fundamentals of Sustain
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15 hephysiology of tropical field crops. Jo
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