Agric.Re~,25(4):267-278,2004

NUTRIENT MANAGEMENT FOR TUBER CROPS - A REVIEWM.R. Latha, S. Kamaraj and R. Indirani

Department of Soil Science and Agricultural Chemistry,Tamil Nadu Agricultural University, Coimbatore - 641003, India

ABSTRACTTubers are important food crops in tropical world. Tropical tuber crops have hitherto received

inadequate attention. As area increased significantly and new production techniques devised in thelast decade, nutrient management shall remain an essential aspect for improving the quality andquantity of tuocrs. This review gives an account of the nutrient management research carried out ontuber crops.

Tuber crops are the second mostimportant food crop of man next only tocereals. They constitute either staple orimportant subsidiary fooc.: for about a fifth ofthe world's population. Tropical tuber cropshave hitherto received inadequate attention.However the situation is changing and acreagesunder tuber crops have been increasing andnew production techniques were devised in thepast decade.The formation of the InternationalSociety of Tropical Root Crops during the lastdecade is a manifestation of this increasedimportance. Tuber crops are important inseveral aspects. They have a higher biologicalefficiency as food producers and show thehighest rate of dry matter production per dayper unit area among all the crops. Further, theyconstitute important and cheap source of foodand energy. FAO data show that about 400­450 million people in 26 tropical countriesderive 300 Kcal of energy per day fromcassava, a crop that can produce 250 x 103

cal/ha/day as against 176 x 103 for rice and110 x 103 for wheat. Most of the tuber cropsare able to produce economic yields in a varietyof marginal soils and environmental conditions.Their capacity to grow under near droughtconditions is remarkable. Sweet potato can begrown under temperate to tropical conditionsand is also drought tolerant like cassava. Thetubers being rich in starch are beingincreasingly used as raw material for manyindustries such as animal, fish and poultry feed.Obviously, nutrient management shall be an

essential aspect in the management of tubercrops. This paper reviews the research carriedout in this direction.

A. PotatoPotato originated in the Peru-Bolivian

region in the Andes (South America), largelyraised in cool regions where the meantemperature of the growing season does not€xceed 18°C. About 80% of the area underthe crop in the worid is concentrated in thetemperate zone of Europe and western USSR..In India, Potato is grown during the coolseason. About 81% of the potato is grown inplains during winter under short-clay conditions;about 13% in the hills during summer underlong-day conditions and around 6%. in theplateau during the rainy season under almostequinox conditions. In the Nilgiris hills in TamilNadu, it is grown round the year because ofequable climate.

The crop in the hills is grown mainlyon well-drained acidic soils of varying depthsbut that in the plains is grown on alluvial soilswith neutral to alkaline reaction and in theplateau areas on red, black-cotton and mixed­red sandy soils. On drying, the fine-texturedblack soils are prone to develop cracks whichmay expose the tubers to light resulting ingreening and attack by tuber moth.

Nutrient ManagementTuber yield was increased significantly

by application of K alone and in combinationwith P. The response was of linear nature. The

268 AGRICULTURAL RI::.VIEWS

K application at the rate of 80 kg ha-1 hadpronounced residual effect on cheena andsignificant residual effect on maize. Applicationof P alone and in combination with K had littledirect effect on potato and residual effect ofcheena and maize. Farmyard manureapplication at both the levels (15 and 30 tonnesha'l) had significant effect on tuber yield andthe response was linear. Its residual effect" wassignificant on maize. Farmyard manure @ 30tonnes ha'l was able to meet P and K needs ofpotato and other crops in rotation and maintainavailable P status of the soil. Application of40 kg P ha-1from fertilizers could not maintainthe available P and K status of the soil at theinitial level but it was significantly better thanthe control.

Investigations were carried out bySharma et al. (1981) on the acid soil of Shillongand Simla to study the effects of Mg and P onthe yield of potato. In acid soil of Shillong (pH5.2), there was positive response to MgS04upto 20 kg ha-1whereas in Simla soil (pH 6.6),the response to Mg was not significant.However, there were significant responses ofpotato to P on both the soil types. Mg and Phad synergistic effect on the concentration ofeach other whereas the applications of bothMg and P had a depressing effect on theconcentration of Ca in the plant. Mg and Pincreased the dry matter in tubers. .

Application of urea 5 to 10 daysbefore planting in furrows and pre-treatmentof urea with soil for 48 h before applicationincreased its efficiency by 10 and 11% ascompared to its application at the time ofplanting (Singh and Grewal, 1984).Improvement in efficiency of urea wasassociated with greater uptake of Nand' K.Broadcasting of urea before first and secondirrigation after the planting was inferior to itsapplication at the time of planting.

A field study was conducted on slightlyalkaline alluvial soil to ascertain the effect of

PK fertilizers and FYM on potato-wheatrotation during 1979-80 and 1980-81(Upadhyay and Grewal, 1985). Application of20 and 40 kg P ha-1increased the potato yieldand P uptake by tubers but the differences werenonsignificant in both yearsbut were significantin pooled data. Application of 40 and 80 kg Kha'l increased the potato yield and PK uptakeby the tubers significantly. The highest tuberyield and PK uptake by the tubers wereobtained by the interaction of 20 kg P and 80kg K ha·1. The application of 30 tonnes FYMha·1 was at par with 20 kg P plus 80 kg Kha-1, with respect to tuber yield and uptake ofPK by the tubers. The effect of PK fertilizersand FYM was significant on the yield of largesize tubers only. The residual effect of PKfertilizer and FYM was quite pronounced onthe succeeding wheat crop. The economicoptimum doses of P, K fertilizers and FYM forpotato were 15.7 kg P, 112.1 kg K and 26.2tonnes FYM ha-1. Experiments were conductedby Sharma et al. (1988) on soils having varyinglevels of DTPA extractable In to study theresponse of potato to applied In. Significantyield responses to applied In were observedon soils having DTPA extractable In contentup to 0.57 ppm. Applied In did not affect thetuber number1m2• However, it increased theaverage weight of individual tubers, therebyincreasing the tuber number in medium andlarge grades and as such the tuber yield.Application of In increased the concentrationof this element in haulms during both the yearsof study. Uptake of In by potato variedsignificantly at various locations and increasedwith applied In.

Sharma and Grewal (1989) studiedthe effect of methods of zinc application onpotato production. Experiments conducted onzinc deficient alluvial soils revealed that the yieldincreased significantly by zinc application.However, the degree of response varied withthe method of zinc application. Soaking of seed

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tubers in 0.05% ZnS04 solution for 3 h wasfound to be the best, followed by soaking ofseed tubers in 0.025% ZnS04 solution, twofoliar sprays of 0.2% ZnS04 solution at 40and 60 days after planting and soil applicationof 8 kg Zn ha· l at planting. Zinc uptake washighest in soil application of 8 kg. Zn ha· l ,

followed by two foliar sprays of 0.2% Znso4and soaking of seed tubers in 0.05% of ZnS04solution.

Mondal et a/. (1993) conducted a fieldexperiment to evaluate the growth andproductivity of potato unde jifferent fertilizermanagement with particular reference toSulphur, FYM and crop residues. Maximumdry matter production (855 g/m2), tuberbulking rate (16 g/m2/day) and tuber yield (266q/ha) were recorded at 100 kg ha- l each of N,P20 S and K20 in conjunction with 10 tonsha· l FYM. Application of S bearing fertilizer(SSP) improved the growth and tuber yield (9%)as compared to the application of DAP. Themaximum total uptake of nutrients (115.02kg N, 25.31 kg P20 S' 249.11 kg K20 and16.67 kg S ha· l ) were recorded where the cropwas fertilized with 100% of the recommendeddoses of N, P (through SSP) and K. Anyreduction in their doses without application ofFYM/crop residues depleted the soil fertilitystatus. Better net production values (2.16 and2.12) were recorded at 75% of therecommended doses of N, P (through SSP) andK along with FYM and also in the treatmentreceiving 100% of the recommended doses ofN, P (through SSP) and K.

Singh et al. (1994) studied the effectof different levels and methods of nitrogenapplication on storage behaviour of potato cv.Kufri Badshah. They observed that percentageof rotted and sprouted tubers was increasedwith an increased application of N. Method ofN application also showed significant effect onthese parameters. Split application of N, three­fourth as basal dose and one-fourth as top

dressing improved the storage life of potatoas compared to other methods of Napplication.

Minhas et al. (1994) conducted a fieldexperiment to study the effect of P, lime andanimal manUre on crop yields in potato-maize,potato-wheat sequence at Palampur.Phosphorus was applied as SSP @ 26,52 and78 kg P ha·l , lime as CaC03 at 5 tons ha- l

and well decomposed animal manure at lOtha- l besides control. The direct P application,upto 78 kg P ha· l to spring potato and, upto52 kg P ha·l to autumn potato increased theyield significantly. The P applications also hada significant residual effect on yield of thefollowing crop i.e. maize and wheat after springand autumn potato, respectively. The directapplication of animal manure and lime tospring potato and their residual effect on thefollOWing maize crop was not found to beSignificant, however, the direct effect'on thefollOWing wheat crop was significant.

Field experiments conducted bySavitha et al. (2000) at Bangalore during rabi1995 and 1996 revealed that application of180 kg ~O ha· l increased the tuber yield by25.90 per cent over 60 kg K20 ha· l .

Application of K in two splits recorded 5.4and 15.6 per cent higher tuber yield over 100per cent basal and thrice. split application,respectively. Application of 180 kg Kp ha· l

in two splits produced better quality tubers.Application of recommended dose of K (120kg ~O ha· l ) in two splits improved the yieldand. quality of potato tubers due perhaps tohigher uptake of K (73.4 kg ha· l ).

B. CassavaCassava (Manihot esculenta Crantz)

popularly known as tapioca is a native of Brazilin Latin America and was introduced to Indiaby the Portuguese in the 17th Century. As afood crop it was popularized by Shri VisakhamTirunal, the Maharaja of the erstwhileTravancore during AD 1880 to 1885. Its

270 AGRICULTURAL REVIEWS

importance in tropical agriculture is due to itsdrought tolerance (shed/drop the leaves underadverse soil moisture conditions), wide flexibilityto adverse soil, nutrient and managementconditions and time of harvest. Cassava canbe grown in areas of uncertain rains thatprevent the successful cultivation of othercrops.

Cassava with no definite harvest timeand being a photoinsensitive crop can beprofitably cultivated throughout the year. Itsfoliage can produce upto 5t crude proteinhectare'1 year1 (Moore, 1976). Presently, theworld production of cassava is about 165million tonnes (FAO, 1997) of which nearly60% of the production is used as human food.Apart from its role as a staple/subsidiary food,there has been growing recognition of cassavaroots as a low cost energy source for livestockand CUi a raw material for industrial starch andfuel alcohol.

In India, cassava is mainly cultivatedin the Southern States. Though it performswell at lower altitudes, it is being grown up toelevation of 2000 m. It tolerates very hotclimate but critical point seems to exist betweena daily temperature of 18-20°C below whichgrowth is reduced and yield declines rapidly.At reduced temperature, germination isdelayed and leaf formation rate is slow.Ingeneral, crop' growth increases with solarradiation. Shading decreases radiationinterception of cassava which in turn decreasesthe crop growth rate and root yield (Cock,1978). Shading increases stem elongation andinternode length and hence little carbohydrateis available for root growth. A well-drainedloamy soil is the best for the crop. Also, it canbe grown successfully in acid soils of low pH.Optimum soil pH is 5.0 to 6.0.

Nutrient RequirementVinod and Nair (1992) conducted a

field experiment to study the effect of slowrelease N sources on cassava var. Sree

Vishakam at Vellayani. The treatmentsconsisted of urea, neem cake coated urea, ureasuper granule ;; .1d rubber cake coated ureaeach at five levels (50, 75, 100, 125 and 150kg N ha·1). Urea super granule and neem cakecoated urea enhanced the growth charactersof cassava such as plant height, number offunctional leaves, number of nodes and the leafarea index. N@150 kg ha·1 gave better resultsin growth characters. Asokan et al.,(1988) studied the yield and qualitycharacteristics of two varieties, viz.,Noorumuttan (Local type) and H.1687 atgraded levels of N and ~O (60, 120 and 180kg ha·1 each) for three consecutive years. Theresidual soil fertility was analysed after threeyears cropping. The tuber yield for the localtype increased by 35 per cent while that ofH.1687, by 67 per cent due to Nand Kapplication. The yield increase beyond 60 kgha·1 of Nand K was not significant. Tubernumber, tuber length, height of plant, numberof leaves and harvest index were improved byNand K

20 applications. The fertilizer

application reduced the dry matter and starchcontent of tubers. Higher levels of N increasedHCN content of tuber, whereas K had nosignificant influence. There was a general dropin the soil organic carbon after three yearscropping.

Nair et al. (1988) observed theresponse of cassava to graded doses of P inacid laterite soil of high and low-P status forfive years (1980-85) in a high-P soil (av. P =100.8 kg ha·1) and for three years (1983-86)in a low-P soil (av. P = 8.9 kg ha·1) to ascertainthe effect of P - skipping and application ofgraded doses of P respectively in these soils. Itwas observed that in high - P soil, skipping ofP for the first four years had no significantinfluence on the yield of tubers. In low-P soil,even though cassava responded to 100 kg .PPs ha·1 initially, the response graduallydeclined. From the response curves it was

Vol. 25, No.4, 2004 271

observed that the optimum economic dose of experiment to study the effect of applicationP for cassava in laterite soil was 45 kg PPs of Schoenite and 5yngenite, two indigenousha· l . Kabeerathumma and Mohanakumar sources of Kon the yield and quality of cassava,(1990) tested the relative efficiency of and compared with muriate of potash andMussoorie rpck phosphate and single wood ash at different levels of K in acid lateritesuperphosphate with and without FYM on soil. These two sources were at par withcassava in acid laterite soil. The direct effect Muriate of Potash in increasing the tuber yield.of superphosphate was better than that of rock The different sources did not show muchphosphate for tuber production, whereas in influence on starch and HCN contents ofresidual effect rock phosphate was found to tubers, residual available K and K uptake bybe superior. Combined application of FYM and plants, while increasing levels of K applicationboth the P sources was found to be beneficial. resulted in an increase in starch content and aIn case of super phosphate the release of P decrease in HCN content of tubers. Amongwas faster and its fixation was high.It was at a the different levels tried, 100 kg K

20/ha was

slow and steady rate for rock phosphate. Rock found to be the optimum for tuber yield.phosphate along with fYM was a bette;" source Mohankumar and Nair (1983) reported thatof P for cassava in laterite soil. sulphur @ 50 kg ha· l gave significantly more

Field experiments conducted during yield (18%) than the control. Application of 51967 to 1973 in acid laterite soils with varieties resulted in an increase in starch (5.3%) and a5-2380, M-4, H-97 and H-165 and using decrease in HCN content (by 29.2%) of thedifferent rates of Kand N showed that 100 kg tubers. The methionine and total proteinha· l of K20 was optimum and further contents of tubers were also found to increaseapplication resulted in 'luxury consumption'. due to 5 application. The soluble sulphateIt was also observed that the soil available K content of soil and 5 uptake by plants alsolevelcould be maintained at the above rate of increased by 2.30 ppm and 323.5 mg/plantK application. With increasing rates of N and respectively due to its application.K application, increased K uptake was Korah et al. (1988) studied the directobserved. Nand K uptake was significantly and indirect effects of causative factors viz.,correlated with tuber yield of cassava as

available 5, 5 content in plant parts and totalreported by Rajendran et al. (1976). uptake by plants on yield and quality of cassava.

A field experiment was conducted by The treatments consisted of four levels of 5Asokan and 5reedharan (1977) to study the (0, 30, 50 and 75 kg ha· l ) from a combinationeffect of different levels and time of application of 5 containing Nand P fertilizers. N, p,. Kof K in conjunction with FYM in variety H- were given at recommended levels of97. The results indicated that maximum tuber 50:50:50. The maximum positive direct effectyield was obtained at 112.5 kg level of K. was observed for 5 content in leaf (1.6797)Three split application had given a better and maximum negative direct effect forresponse at lower levels of K. FYM gave better available 5 at sixth month. Their correlationresponse at higher levels of K, while utilization with \lield was high and positive (0.9769 andindex showed decrease after 75 kg K. Dry 0.9199). The positive correlation of yield withmatter, starch content and cooking quality were available 5 at sixth month was mainly due toincreased by Kfertilization while, crude protein the positive indirect effect through 5 contentand HCN content showed a decrease. in leaf. The available 5 at third month and at

Nair et aJ. (1980) conducted a field harvest stage was found to have negative effect

272 AGRICULTURAL REVIEWS

on yield in both direct and indirect ways.Response of cassava and sweet potato,intercropped in the coconut garden, toinoculation with Glomus fascicu/atum wasstudied (Sivaprasad et aI., 1989). The differentcultivats .showed varying response toinoculation. Cultivar Ambakadan of cassavaand Kajangadu local of sweet potato recordedan increase in yield of 31.79 and 24 per centdue to VAM inoculation respectively. Glomuscolonisation decreased the yield of H 268 ofsweet potato by 20.4 per cent.

Potty (1990) tested the response ofcassava to VA mycorrhizal inoculation in acidlaterite soil. Root infected cuttings respondedfavourably in both sterile and natural soils anddid not show any disadvantage over the presentday practice of direct planting of cuttings.Significant difference was noticed in dry matterproduction and tuber production in natural soil.Sterilization had very little influence overnatural soil. Rhizosphere microflora favours'theVA mycorrhizal association and vice versa incassava root region. Total microbial activity waselevated due to mycorrhizal association.Mycorrhizal cassava plants showed higherphosphorus uptake at low phosphorus levels.Micronutrients like copper and zincaccumulated in leaf tops of VA mycorrhizalcassava plants.

The inter-relationship of N, P, K, Caand Mg in cassava was studied by Pushpadaset al. (1976). The major treatments werefactorial combinations of three levels each ofNand P in one and K and Ca in the otherexperiment with two varieties M4 and 11-105as the minor treatments. Samples of petiolesfrom the middle one-third of the total leaveswere collected at 62 days, 136 days and 203days after planting and analysed for N, P, K,Ca and Mg. N, P and K content of the tissueincreased with the application of N, P and Krespectively but N, P and Mg decreased withthe application of K. Lime application

increased Ca content only during the first stageof sampling whereas N, P and K had noinfluence on the Ca content. It was also foundthat H-I05 was superior to M4 in K contenton all the three sampling dates.

C. Sweet PotatoSweet potato (Ipomoea batatas L.

Lam.), believed to have originated in or aroundnorthern South America (Huaman, 1992) canbe grown on a wide range of soils, but sandyloams reasonably high in organic matter witha permeable subsoil are ideal. It requires aminimum of 500 mm rainfall.The tuber is animportant source of carbohydrate. Certainvarieties having yellow flesh are rich incarotene, a precursor of vitamin A. The ediblesweet potato is variously referred to as a root,a root-tuber or a tuber. Sweet potato is a shortmaturity crop, tolerant to a wide range ofgrowing conditions. In India, sweet -potato isconsidered as a famine relief crop as it hadplayed a pivotal role in alleviating the Bengalfamine of 1942. Asia accounts for 78.7 percent of the area under cultivation and the majorshare (67.7 per cent) goes to China (FAO,1997). As regards production, 93.1 per centis accounted by Asia where the contributionof China alone is 87.7 per cent with aproductivity of 19.9 t ha·1.In India, sweet potatois grown to an extent of 0.14 m ha with anannual production of 1.17 mt and productivityof 8.3 t ha·1. The major sweet potato growingstates in India are Orissa, Uttar Pradesh andBihar. The crdp is usually raised as a rainfedcrop, utilizing the south-west monsoon (June­August) as kharif crop and with supplementalirrigation during the north-east monsoon(October-December) as rabi season crop.

Sweet potato can be grown on a widevariety of soils, but sandy loams, reasonablyhigh in organic matter with permeable subsoilare ideal. On heavy clays, shoots and leavesgrow well, but the yield is poor with tubers ofirregular shape. Dry and compact soil favours

Vol. 25, No.4, 2004 273

lignification leading to the formation of pencillike roots and more vine growth. Sajjanpongseand Roan (1982) found that too high or toolow compaction did not favour tuber formationand according to them, the optimum bulkdensity for higher yield was between 1.3 and1.5 g cc· l . The optimum pH of the soil forsweet potato cultivation is 5.6 to 6.6. Sweetpotato is listed among the acid resistant cropsand it cannot withstand salinity and alkalinity.Salinity significantly reduces growth of stemsand roots and results in lateral rolling of leaflobules, reduction in leaf size and necrosis ofolder leaves (Villafane, 1997). Foliar analysisof salt-stressed plants revealed theaccumulation of Na+ and Cl' ions to > 400 percent in leaves as compared to plants irrigatedwith tap water, suggesting the lack of extrusionmechanism.

Nutrient RequirementMuraleedharan Nair et aJ. (1976)

studied the effect of levels and time ofapplication of N on its uptake by three sweetpotato varieties. The variety J.14 recordedhigher total N uptake followed by J .13 andthe local one. Among the individualcomponents, N uptake by tuber was mainlyresponsible for varietal differences in total Nuptake. There was increase in total N· uptakeupto 100 kg N ha't, the differences in uptakeby tubers contributing to the. differencesbetween levels of application while, time ofapplication was found to have no conspicuouseffect. Between the stages, there was anincrease in total Nuptake by tubers till harvest,whereas a decline in N uptake by vines wasobserved from 60th day till harvest. Such apattern of N uptake by plant parts indicatesthat there was translocation of a considerableportion of N stored in the vegetative tissues tothe developing tubers.

Alexander et al. (1975) studied thecomparative performance of three sweetpotato varieties under different methods of

application of N. The results showed significantvarietal difference in tuber yield. The varietyH-42 recorded the highest tuber yield followedby H-41 and the local variety. Regarding

Jmethods of N application, the treatmentdifferences were not significant. However,there was a trend towards the superiority of Napplication half basally and the other halfthrough foliage 35 days after planting. Thetreatment with a reduced dose of 37.50 kgbasal N ha- l with 18.75 kg N ha· l throughfoliage was statistically at par with the othertreatments receiving the total dose of 75 kg Nha- l .

Desmond et al. (1991) conducted fieldexperiments in Typic Paleudalt with low tomoderate N levels to compare storage root andfoliage yield and N concentration in six sweetpotato cultivars developed under N fertilizerindependent (NA) and N fertilizer dependentconditions (NFD). Nitrogen rates 0,60 and 120kg ha- l were used. The NA cultivars as a grouptended to outyield the NFD cultivars at no N inboth years, whereas differences were notevident at 60 or 120 kg ha· l N rates. PetioleN concentration was increased generally withincreases in N rates from 0 to 120 kg ha- l in1984 and 1985. In 1985, petiole N increaseswere more progressive and more definite forthe NFD cultivars, whereas there was a dropin petiole N among NA cultivars when N wasincreased from 60 to 120 kg ha- l .

The Nand K requirement of sweetpotato var chindamoni in rainfed uplands ofKerala was studied by Asokan et al. (i984).They observed that linear tuber yield increaseupto 17.4 t ha- l (maximum) was recorded at90 kg level of N. A quadratic response modelwas fitted to the data on yield response topotash. The most economic dose of ~O wasfound to be 60.4 kg ha- l . With increasing levelsof Nand K20, the sugar content of the tubersdecreased, whereas the starch contentincreased. The root to shoot ratio was

274 AGRICULTURAL REVIEWS

decreased at higher levels of nitrogen.

Padmaja and Sreenivasa Raju (1999)studied the response of sweet potato to twosources Le., K

ZS0

4and KCI and four levels of

K viz., 0, 10, 20 and 40 kg Kp ha-1. Theresults showed that the effect of sources wasnon-significant while significantly r.ighest tuberyield of 28.2 t ha-1 was recorded at 40 kg KzOha·1. The dry matter production (42.89 q ha­l), K-content (2.66%) and K-uptake (114.1 kgha-1) at tuber initiation stage recorded at 40 kgKzO ha-1 level were significantly higher thanother levels of K. There was increase in drymatter production (75%), tuber yield (26.2%)and K-uptake (215.5%) over control atharvesting stage of the crop. Contents of forms.of K in soil viz., water soluble, exchangeableand IN HN03 extractable Kshowed a decreasefrom tuber initiation to maturity stage.

Nair and Mohankumar (1984)conducted the field experiments to study theinfluence of different levels of NPK and limeon the yield and quality of sweet potato in anacid laterite soil. NPK at 75:50:75 and limeat 2t ha-1 were found to be optimum. Lime atthe above rate not only increased the yield butalso improved the quality by increasing starchand sugar contents in the tuber. Limeapplication was beneficial in increasing the pHand available P in the soil. The uptake of NPKand Ca by the plant also increased due toliming. Experiment conducted by Kandasamyet al. (1988) under pot culture conditions tofind out the effect of inoculation of VAMendophytes (Glomus fasciculatum and G.mosseae) and (Azospirillum brasilense) eitheralone or in combination on sweet potatorevealed that joint inoculation of VAM andAzospirilJum significantly enhanced the shootlength and its dry weight. Combination of thesetwo organisms increased the tuber weight andits starch content besides enhancing the NandP content of plants.

Studies on the effect of planting

patterns, fertility levels and growth regulatorson sweet potato revealed that mixeq cultureof two sweet potato varieties Cross-4 and PS­5 in alternate rows with 30 x 15 cm spacingrecorded maximum tuber yield. Increasinglevels of N-K regimes gaJe significantly higherweight of tubers per plant, increased tuber drymatter content and ultimately higher tuberyield. Regulating plant growth through theapplication of CCC @ 200 ppm at 30, 50and 70 days of planting recorded the highesttuber yield. Two-tier cropping in sweet potatowith closer spacing, optimum nutrition andregulated crop growth was found desirable foryield maximisation (Mishra et aJ., 1992).

D. YamYams are monocotyledonous plants of

genus Dioscorea and comprising about sixhundred species (Coursey, 1967) of which thepopular edible species are D. rotundata Poir(African yam/white yam), D. aJata (Water yam),D. esculenta (Chinese yam), D. cavenensisLam. (yellow yam), D. bulbifera (ariel yart:!) andD. trifida L. (cush-cush yam). About two-thirdof the world production comes from.WestAfrica. The phenology of yam species showsan annually repeated cycle of growth for six toten months and dormancy for two to fourmonths, and these two phases approximatelycorrespond to wet and dry seasons respectively.Economically important part of the plant. is itsunderground stem tuber, which is used for itspropagation. Yams are grown in India sinceancient times and D. alata is said to be of Indianorigin. It is a rich source of carbohydrates,certain vitamins and has high calorific value.Starch constitutes the predominantcarbohydrate component in most of the speciesof yams, the range being 11 - 39 per cent indifferent species. Protein content ranges fram6 - 13 per cent on dry weight basis (Martll:land Thompson,1973). Africa is the largestproducer of yams in the world where it is astaple food. Major share in yam production in

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Africa comes from Nigeria. Total worldproduction of yam is 299.4 mt from an areaof 32.82 million ha, of which Nigeria aloneproduces 195.7 mt from an area of 21.70million ha (FAO, 1997). The world averageproduction is 9.12 t ha-1 while that of Nigeriais 9.02 t ha-1• In Asia yams are grown in anarea of 17,000 ha producing 242,000 tonswith an average yield of 14.49 t ha·1.

Yams are tropical crops and thrive wellunder warm sunny weather with plenty ofrains. The crop requires a temperature of 25to 30°C.Evenly distributed rainfallof 100-150cm spread over six to seven mqnths period isideal. However, most rotunda cultivars can begrown with far less rainfall (IITA manual, 1982).The most critical period of rainfall/moisture isthe first five months after planting (Waitt,1963). Yam production is also significantlyinfluenced by day length (Onwueme, 1978). It·hasbeenfou~dthatshorterdaysfavourtuber

formation and development while longer days(> 12 hours) apparently influences vine growth.

Deep and loose friable soil of any kindwith adequate nutrient and moisture status iswell suited for the growth and development of~ams. The crop can, however, withstand dryconditions to a good extent. Coursey (1967)reported that maintaining optimum moistureregime from fourteenth to the twentieth weekof growth was ideal for better developmentand yield of tubers.

Nutrient RequirementKabeerathumma et al. (1991) studied

the uptake pattern of N. P and K by threeDioscorea species. From the analysis ofperiodically harvested plants, it was found thatthe maximum utilization of Nand K byDioscorea esculenta and D. rotundata occurredwithin 5-7 months a~r planting, whereas thedemand of P for these species was found tocontinue with maturity of the crop. InDioscorea aJata the maximum utilization of allthe three nutrients was found to be within 5

months after planting. However, theconcentration of these nutrients in plant partswas maximum in the early stages of growth(3-5 months after planting). The tuber of D.aJata was observed to be richer in N, P and Kas compared to the other two species. Theratio of Nand K utilization and the extent ofsoil depletion were also discussed.

An experiment was undertaken to findout the optimum dose of fertilizers for yamsand aroids and the economics of cultivation ofthose crops when grown under partial shadesituations in coconut garden. The resultsindicated that greater yam recorded maximumyield with full dose of fertilizer, lesser yam with75 per cent of recommendation and elephantfoot - yam with 50 per cent of therecommendation of fertilizer for open situation.The maximum benefit cost ratio was obtainedwith elephant food yam followed by greaterand lesser yam (Pushpakumari and Sasidhar1992).

Experiments were carried out todetermine the effect of NPK fertilizers on theyield and storage quality of yellow yam. Therewere three rates each of N, P and K.The mosteconomic fertilizer combination for total freshtuber yield was N67.20 K67.20 kg/ha. Resultsobtained further show that fertilizers appliedto yams in the field had no significant effecton the storage quality of the tubers in the barn(Azih, 1976).

E. TaroTaro (CoJocasia escuJenta) is believed

to have originated in South-Central Asia,perhaps India or Malaysia. Cultivation of tarois widespread in India, Burma, China, Japan,Hawaii, Egypt, Africa and the Caribbean. Totalarea under taro in the world is 10.78 mha ofwhich Asia's share is 1.44 mha (FAO, 1997).World average for cormel yield is 6.1 kg ha·1

yield, while the figure for Asia is 12.39 kgha-1. Cormel production in the world is657.3 mt.

276 AGRICULTURAL REVIEWS

Taro requires warm climate withplenty of moisture, available in the tropical andsub-tropical countries of the world. It can aswell as grown even in the warmer temperateregions. An important character of the crop isits ability to withstand waterlogged and reducedconditions, since it can transport O~ from theleaves to the roots under reduced condition(UTA, 1982). Taro grows well on all types ofsoils, the ideal type being deep well drained,friable loams, particularly alluvial.

Nutrient RequirementField experiments were conducted for

two seasons by Ashokan and Vikraman Nair(1984) to study the response of taro to appliedNand K. Application of Nand K increasedthe tuber yield. Among the higher levels, effectof nitrogen alone was significant. The cormelto corm ratio was improved by N ana Kapplications. The data were found to be in goodfit to a quadratic response surface model andthe economic optimum doses of Nand Kworked out from this model were 89 and 79kg ha·1 respectively. The number and size oftubers increased upon Nand K applications.The dry matter percentage of corms was notsignificantly influenced, while the starchcontent increased significantly with higherlevels of Nand K.

Field experiments were conducted tostudy the nutrient uptake pattern of CoJocasia.From periodical plant analysis, it was foundthat the nutrient removal by the crop wasmaximum at harvest stage. For an averageproduction of 17 tonnes of tubers with abiomass production of 6.2 tonnes 124.6 kgN, 19.2 kg P and 134.97 kg K per ha wereremoved by the crop. Except for P, there wasa peak demand for N at third month and K atone to two months of growth (Kabeerathummaet aJ., 1984).The authors also conducted a fieldexperiment to study the uptake pattern ofsecondary and micronutrient~. From analysisof periodically harvested plants, it was found

that the peak periods of removal of thenutrients was between 3rd - 5 th month .However, peak demand for all the secondarynutrients as well as Fe and Mn was in the early2nd or3rd months of growth, while the demandfor Zn and Cu was observed to be aroundmaturity stage. In general, all themicronutrients showed a tendency toaccumulate in the root with an advancementin the growth stage of the crop. An averageproduction of 17 tonnes of edible tubers witha totaklry biomass of 6.2 t ha·1 removes 30.42kg Ca, 15.87 kg Mg, 11.80 kg S, 10.25 kgFe, 1.69 kg Mn, 647 g of Zn and 93 g of Cufrom the soil.

In another experiment, total uptakeof N increased significantly up to 80 kg Nha·1• but increasing levels of P and Kapplicationhad significant effect on the uptake of thesenutrients at all levels tried. Thr·ee splitapplication of Nand K was superior to twosplits for the uptake of Nand·K by taro(Mohankumar and Sadanandan, 1990).

Mohankumar and Sadanandan (1989)observed that application of varying levels ofNand K had significant effect on increasingthe plant height and LAI, but graded doses ofP did not show any significant effect on thesetraits. Tuber and total dry matter productionincreased significantly upto 80 kg Nand 100kg Kz0 ha·1• Levels of P20 S had no significanteffect on these characters.

F. ArrowrootArrowroot (Maranta arundinaceae)

commonly known as 'West Indian Arrowroot'is a herbaceous plant primarily grown for itsquality starch which is valued as food stuff,particularly for infants and infirms. It is alsoused in making various bakery products, specialglue and paste as a base for face powder, asice cream stabilizer and in carbonless paperused or computer printouts.Arrowroot starchpossesses demclcent properties and is used inthe treatment of intestinal disorders. It is also

Vol. 25, No.4, 2004 277

employed in the preparation of barium mealsand in manufacture of tablets. The fibrousmaterial which remains after the extraction ofstarch is used as a cattle feed or manure.

The crop is a native of tropicalAmerica and has long been cultivated in theWest Indies particularly St. Vincent which isthe main producer of Arrowroot starch. InIndia, it is grown in North Eastern States, WestBengal, Assam and in Southern India mostlyin Kerala as a rainfed crop in limited areas 10

homesteads.

The crop grows best at temperaturesof 20-30°C. A minimum annual rainfall of 95­150 cm is required but sufficient soil moisturethroughout the growing period is of primeimportance. The crop thrives best irt deep, welldrained, slightly acid loam soils with partialshade.

Nutrient RequirementField experiments were conducted by

Maheswarappa et al. during 1995-96 and1996-97 at CPCRI, Kasaragod to find out theeffect of agronomic practices on growth ofarrowroot grown as intercrop in coconutgarden. Sett sizes (15-20 g and 25-30 g) didnot show significant difference with respect to.different growth characters, whereas, lowerplant population (111 thousand ha·1) showedsuperiority in plant height, number of leaves,leaf area, LAI and LAD over higher densitytreatment (166 thousand ha·1). Among organicmanures, FYM, Vermicompost applied aloneand FYM + NPK treatments showedsignificantly superior growth attributescompared to Composted Coir Pith appliedalone and NPK alone. Control had significantlylower growth characters.

G. Yam beanYam bean {Pachyrrhizus erosus (L)

Urban} also called Potato-bean belongs to thefamily Leguminaceae. Yam bean is a starchyroot crop with comparatively high sugar

content and a moderately good source ofascorbic acid.

In India, tender tubers are consumedas a fruit and the taste resembles that ofChinese water chestnut. Because of high watercontent, low calories and bulky nature, it isgood for salad preparation for those who wan~

to adopt dieting. The mature seeds have highcontent of alkaloids and insecticidal properties.In many developed countries, the tubers areprocessed, canned and many sweetpreparations are made.

The crop has originated from hotmoist region of the river Amazon, is nowcultivated in Philippines, China, Indonesia,Nepal, Bhutan, Burma and India. In India, it isgrown in parts of West Bengal, Bihar, Orissaand Assam. Yam bean requires a hot humidclimate and adapts well in sub tropical and hottemperate zones.Fertile, well drained, sandyloam soil is best suited for cultivation of yambean. This crop adapts well to loamy and clayloam soil. Optimum soil pH requirement is 6.0-7.0.

Nutrient RequirementExperiment involving three levels of

Nand K (40, 80 and 120 kg ha·1) along withan absolute control (NoRa) was conducted tostudy the influence of Nand K on theperformance of two yam bean entries (RM -1and L-109) during two successive years.Uniform basal dose of 60 kg PPs ha·1 wasapplied except control plots. There was nosignificant yield variation between the twoentries; however, RM-1 produced significantlyhigher tuber yield in the second year. The tuberyield was found maximum under N120 K60which was on par with N120 K40 and N120 K120•

But N120~ produced longer tubers. Highestnet income (Rs.14,188.10) per ha wasobtained by the application of 120 kg Nand 80kg KzO over no application of fertilizer. TSScontent was found maximum in the tubers ofcontrol plots (Sen and Mukhopadhyay, 1989).

278 AGRICULTURAL REVIEWS

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Series 9: 139-192.Kabeerathamma, S. and Mohankumar, B. (1990). J. Root Crops, 16: 65-70.Kabeerathumma, S: et a/. (1985). J. Root Crops, 11: 51-56.Kabeerathumma, S. etal. (1991). J. Root Crops, 17: 26-30.Kabeerathumma, S. et a/. (1984). J. Root Crops, 10: 29-32.Kandasamy, D. et a/. (1988). J. Root Crops, 14: 37·42.Korah, PA et a/. (1988). J. Root Crops, 14: 51-54.Maheswarappa, H.P. et al. (1998). Mysore J. Agric. Sci., 32: 257-263.Martin, FW. and Thomson, AE. (1973). J. Agric. Univ. of Puerto Rico., 57: 78-83.Minhas, R.S.et ai.(1994). J. Indian Potato Assoc. 21: 142-146.Mishra, S. et al. (1992). J. Root Crops, 18: 6-9.Mohan Kumar, B. and Nair, P.G. (1933). J. Root Crops, 9: 15-20.Moh'l'1kumar, C.R. and Sadanandan, N. (1989). J. Root Crops, 15: 103-108.Moha'1kumar, C.R. and Sadanandan, N. (1990). J. Root Crops, 16: 92-97.Mondal, S.S. et a/. (1993). J. Indian Potato Assoc., 20: 139-143.Moore, C.P. (1976). In: Memoria der Seminario Interacional de Ganaderia Tropical, Acapullo, Gurreso MEXICO 8-

12, March 1978, pp.47-63.Muraleedharan Nair, G. et a/. (1976). J. Root Crops, 2: 19-24.Nair, P.G. and Mohankumar, B. (1984). J. Root Crops, 10: 17-21.Nair. P.G. et al. (1980). J. Root Crops, 6: 21-24.Nair, P.G. et al. (1988). J. Root Crops, 4: 1-9.Onwueme. I.C. (1978). The Tropical Tuber Crops. John Wiley and Sons. New York.Padmaja, G. and Sreenivasa Raju, A (1999). ANGRAU J. Res., 27: 24-29.Potty, VA (1990). J. Root Crops, 16: 132-139.Pushpadas, MV. et al. (1976). J. Root Crops, 2: 23-33.Pusphakumari, R. and Sasidhar, v.K. (1992). J. Root Crops, 18: 99-102.Rajendran, N. et al. (1976). J. Root Crops, 2: 35-37.Sahota, T.S. and Singh, Mukhtar (1985). J.lndian Potato Assoc., 12: 1-12.Sajjaponsge, A and Roan, Y.C.(1982). First Integ. Nat. Symp. on Sweet Potato, Taiwan.Savitha, B. et al. (2000). Mysore J. Agric. Sci., 34: 193-198.Sen, H. and Mukhopadhyay, SK (1989). J. Root Crops, 15: 33-37.Sharma, R.C. et al. (1981). J. Indian Potato Assoc., 8: 183-189.Sharma, U.C. and J.S.Grewal. (1989). J. Indian Potato Assoc. 16: 38-41.Sharma, U.C. et aI. (1988). J. Indian Potato Assoc. 15: 21-26.Singh, J.P. and Grewal, J.S. (1983). J. Indian Potato Assoc., 10: 16-23.Singh, J.P. and Grewal, J.S. (1984). J. Indian Potato Assoc., 11: 61-66.Singh, T.P. etal. (1994). J.lndian Potato Assoc., 21: 125-128.Siva Prasad, P. et al. (1989). J. Root Crops, 15: 49-53.Upadhyay, N.G. and Grewal, J.S. (1985). J. Indian Potato Assoc., 12: 63-69.Villafane, R. (1997). Agronomia TropicaJe(Maracayi, 47: 131-139.Vinod, G.S. and Nair, V.M. (1992). J. Root Crops, 18: 124-125.Waitt, AW. (1963). Field Crops Abstract, 16: 145-157.