Influence of Soil Amendments on Potato Growth, Mineral Nutrition,and Tuber Yield and Quality on Very Strongly Acid Soils1

C. R. LEE AND M. L. MAcDoNALD2

ABSTRACT

Potatoes (Solatium tuberosum L.) were grown in greenhouse soil potcultures to evaluate soil amendments that might modify the fertility ofvery strongly acid Ultisols and improve potato production. Raising soilpH from 4.6 to either 4.9 or 5.2 with dolomitic limestone increasedtuber yield and improved tuber quality. Superphosphate applied aloneor in combination with dolomitic limestone also increased tuber yield.Tuber specific gravities were not improved with superphosphatealone, but only with combinations of superphosphate and dolomiticlimestone. Cow manure applications increased tuber yield, but did notimprove tuber specific gravity or quality. Manganese toxicity symp-toms and potato leaf Mn content increased with cow manure applica-tions. Magnesium sulfate alone or in combination with superphos-phate was beneficial to potato tuber yield. Tuber quality was alsoimproved with the combination of magnesium sulfate and superphos-phate. The application of either potassium bicarbonate or Fe chelatedid not improve potato growth, tuber yield, or quality. It was con-cluded that potato production on very strongly acid Ultisols can beimproved either by raising soil pH to 4.9 with dolomitic limestone orby the application of Ca phosphate and Mg fertilizers without raisingsoil pH. Cow manure also improved potato tuber yield but did notimprove tuber quality.

Additional Index Words: potatoes, soil acidity, aluminum toxicity,manganese toxicity, soil amendments.

KTATOES, Solanum tuberosum L., have been reported to_ e sensitive to the concentrations of Al and Mn when

grown in hydroponic nutrient solution and sand cultures(14,15,16). From these experiments the influence of Al andMn on the growth, mineral nutrition, and tuber yield andquality of the potato plant has been described. The practicalimplications of this knowledge were evaluated in green-house soil cultures to which various soil amendments wereapplied. Soil amendments, based on the information ob-tained in hydroponic experiments and from available litera-ture, were designed to modify the fertility of very stronglyacid Ultisols and evaluate soil management practices thatwill improve potato production on acid Ultisols. This paperpresents the results of these experiments.

EXPERIMENTAL PROCEDUREBulk quantities of two Caribou loam soils were obtained from

two widely separated locations in a major potato producing area ofNew Brunswick, Canada, in the fall of the year. Each soil wassieved through a 2-mm screen, mixed thoroughly, and 5.22 kg ofsoil (oven-dry basis) was placed in a clay pot (25 cm) lined with apolyethylene plastic bag with a hole cut in the bottom for drainage.Soil treatments were applied to the potted soil on a soil weightbasis and each pot was labeled accordingly. Each pot of soil plustreatment was mixed thoroughly, repotted, watered with distilled

'Contribution from Agriculture Canada, Research Station Fredericton,New Brunswick, Canada. Received. Approved 3 Feb. 1977.2Research Soil Scientist and Technical Research Assistant, respectively.Senior author is presently located at Environmental Effects Laboratory,U. S. Army Engineer Waterways Experiment Station, Vicksburg, MS39180.

water, and covered to incubate for 1 month in the greenhousebefore cropping. Soil samples were obtained before planting.

Uniform potato plants approximately 7 cm in height were ob-tained in May as reported in an earlier paper (15). Each plant wastransplanted with a seed piece removed into a pot of treated soil inthe following manner. Two liters of soil were removed from eachpot of soil. A basal fertilizer was banded on the surface of the soilremaining in the pot. One-half liter of soil was poured over the fer-tilizer band. A potato plant was then placed with its roots spreadover the surface of this layer of soil. The remaining 1.5- liters soilwere then poured in around the plant to cover the roots. Soils weremaintained in a moist condition with the daily addition of distilledwater until a small amount of water drained from each pot. Potatotops and tubers were harvested in September at maturity (120days). Plant tops were oven dried at 70°C and weighed. Potatotubers were graded according to size, weighed, and the averagespecific gravity of the tubers from each plant was determined.

Soil pH was determined on each sample using a 1:1 soil/watersolution ratio. Soil extractable Al and Mn were determined usingIN KC1 for a 1-min shake at a 1:10 soil/solution ratio. Aluminumand manganese concentrations in soil extractions were analyzedby a modified 8-hydroxyquinoline method (27) and atomic absorp-tion spectrophotometry, respectively.

Experiment 1.A four-by-three complete factorial experiment with four potato

varieties (Netted Gem, Sebago, Katahdin, and Green Mountain)and three pH levels (4.6, 5.3, and 5.7) were arranged in a ran-domized complete block design with eight blocks. Sufficient quan-tities of dolomitic limestone were added to each pot of soil to ob-tain the two higher pH levels. Reagent grade CaCO3 and MgCO3were used to simulate dolomitic limestone (dolomite) containing70% CaCO3 and 30% MgCO3. The basal fertilizer was appliedpartly in liquid and partly in powder form. A solution containingthe equivalent of 80 ppm of N as NH4NO3, 66 ppm of K as KC1,and 6.0 ppm of Mg as MgSO4-7H20 was applied in a band. Theequivalent of 70 ppm of P as Ca(H2PO4)2 • H20 was spread inpowder form over the band of liquid fertilizer. Mean maximumand minimum air temperatures during the experiment were 30 and16°C, respectively. Light intensity was in excess of 21,528 lu-mens/m2 throughout the experiment.

Experiment 2.Fourteen soil treatments (Table 1) were arranged in a ran-

domized complete block design with six blocks. 'Sebago' potatoplants were grown to maturity (120 days). The basal liquid fertil-

Table 1—Soil amendments applied to a very strongly acid Caribousoil, experiment 2.t

LabelCLIL2PLjPL2P0I^OL2OMgMgPKKPFe

Soil treatmentCheckDolomiteDolomite2,240 kg/ha superphosphate (86 ppm P)2,240 kg/ha superphosphate (86 ppm P)2,240 kg/ha superphosphate (86 ppm P)56 metric tons/ha cow manure56 metric tons/ha cow manure56 metric tons/ha cow manure242 kg/ha Mg (108 ppm Mg) as MgSO4Combination of Mg + PKHC03 as K source in basal fertilizerCombination of K + P56 kg/ha (25 ppm) FeEDDHA

pH4.6pH4.9pH5.2pH4.6pH4.9pH5.2pH4.6pH4.9pH5.2pH4.6pH4.6pH4.6pH4.6pH4.6

573

574 SOIL SCI. SOC. AM. J., VOL. 41, 1977

Table 2—Influence of soil amendments on the growth and tuber yield and quality of potato plants

Tubers per plant

Soiltreatment

CheckLIL2

SoilpH

4.65.35.7

Potatotop yield

g

10.5 aj12.6 b13.3 c

Tuber size (cm)Number Knobby 0-2.5 2.5-3.7 3.7-5.1

f t

5.1+ TotalSpecificgravity

—————————————————————————————————— B ———————————————————————————————Experiment If

8a7a7a

O a6a

11 a

14 a11 a10 a

49 a44 a41 a

68 a59 a64 a

37 a71 a62 b

168 a191 b190 b

1.072 a1.086 b1.085 b

Experiment 2CheckL>L2PL,PL2POL,0L20MgMgPKKPFe

4.64.95.24.64.95.24.64.95.24.64.64.64.64.6

10.2 b9.3 bcde9.8 bed9.4 bcde9.9 be

10.0 b14.2 a13.3 a14.0 a9.4 bcde8.5 e8.8 cde8.7 de9.7 bcde

7a7a5a6a6a7a8a7a6a7a6a7a5a8a

..-..

_--

--„

--

12 a5a5a6a7a

12 a10 a3a6a9a6a5 a5a9a

73 ab35 be51abc23 c38abc,43abc74 ab67 ab54abc53abc39abc78 a18 c57abc

30 de109 ab76 abcde

110 ab132 a98abc24 e

119 a86 abed59 bcde

117 ab41 cde57 bcde26 de

Oa16 a38 a16 a15 a32 a39 a

O a56 a17 a

O aO a

50 aO a

115 h165 cd170 be155 cde192 a185 ab147 def189 a202 a138 efg162 cd124 gh130 fgh

92 i

1.062 ef1.070 ab1.072 a1.065 cde1.072 a1.072 a1.064 def1.066 bcde1.068 abed1.063 ef1.070 abc1.059 fg1.056 g1.064 def

t Experiment 1: Main effect of soil pH over four potato varieties.I Values under each heading within each experiment followed by different letters are significantly different at P = 0.05 according to Duncan's New Multiple Range Test.

izer used in all pots consisted of 80 ppm of N and 70 ppm of P asNH4NO3 and (NH4)2HPO4 and 66 ppm of K as KC1 except forthose treatments where KHCO3 was substituted as the source of K.

Dolomitic limestone as simulated in Experiment 1 was usedto raise soil pH. Superphosphate was simulated usingCa(H2PO4)2- H20 plus CaSO4 according to the general compositionof superphosphate consisting of 8.6% P as Ca(H2PO4)2• H20 and12% S as CaSO4. Cow manure was homogenized in a blender toform a slurry and applied at a rate equivalent to 56 metric tons/ha(50% moisture basis). Iron was applied to the soil at a rate of 56kg/ha (25 ppm) in liquid form as FeEDDHA, Sequestrene 138 Fechelate (Giegy Chemical Corp.).

When approximately 10% of the plants started to bloom, thethird mature leaf from the apex of each plant was removed forchemical analysis. The sampled leaf was rinsed in distilled waterand oven dried at 70°C. Plant material was digested and analyzedas reported in an earlier paper (14). Mean maximum and minimumair temperatures during the experiment were 28 and 15°C, respec-tively. Light intensity was in excess of 21,528 lumens/m2

throughout the experiment.

RESULTS AND DISCUSSIONPlant and tuber yields are discussed on a per plant basis,

that is, the weight of plant top or tubers from each pot. Sta-tistical comparisons of treatment means were made accord-ing to Duncan's New Multiple Range test. All differencesdiscussed are significant at the 5% level of significance.

LIMELiming acid soils is the most common method in North

America and abroad for correcting reduced crop productionon acid soils (5,11,18,23,29,30). Considerable research hasbeen conducted on the effects of liming acid soils,.theresults of which have been compiled by Pearson and Adams(22). However, the application of lime has also been shownto enhance the outbreak and occurrence of common scab ofpotatoes [Streptomyces scabies (Thaxt), Waksman andHenrici] (2,10,21,26). Consequently, the application oflime in areas of potential scab infection has been curtailedand many potato-producing soils in eastern North Americahave soil pH values of 5.0 and below.

The lime treatments evaluated in this study were designedto determine the minimum amount of dolomite required toalleviate the reduced plant growth occurring on acid Ul-tisols. Hutchinson and Hunter (13) have reported thatexchangeable soil Al can be reduced and the production ofalfalfa (Medicago saliva L.) and barley (Hordeum vulgar eL.) enhanced by liming Caribou and Thorndike soils inMaine, to pH 5.5 or above, but not above 6.0. Odland andAllbritten (21) reported that soil reaction of 5.5 or highertended to induce scab. Based on these reports, lime addi-tions in the present experiments were limited to pH 5.7 andbelow.

Raising soil pH from 4.6 to 5.3 or 5.7 in experiment 1increased the size of potato tops and increased both the totaltuber yield and specific gravity of the tubers for all potatovarieties (Table 2). While the weight of potato tops in-creased with increasing soil pH, the healthiest tops were ob-served at pH 5.3. Potato tops at pH 4.6 exhibited typical Mntoxicity symptoms of black specks on lower stems and pet-ioles and dropped their leaves prematurely, similar to thatdescribed by Berger and Gerloff (5). Potato tops at pH 5.7were not as green and as healthy in appearance as those atpH5.3.

While there were no differences in the yield of smalltubers at each pH level, the yield of large tubers (>5.1 cm)increased whenever the pH was raised (Table 2). Similartotal tuber yields and tuber specific gravities were obtainedat the higher pH levels. These data indicate that raising thepH of this Caribou soil to 5.3 was as good as pH 5.7. Theonly interaction observed among potato varieties and pHlevels was related to specific gravity of the tubers produced(Fig. 1). Sebago potato tubers increased in specific gravityas the soil pH increased (Fig. 1). 'Green Mountain' potatotubers increased in specific gravity at pH 5.3 with littlechange in specific gravity at pH 5.7. However, both 'NettedGem' and 'Katahdin' potato tubers showed the highest spe-cific gravities at pH 5.3.

Since experiment 1 results indicated that raising the pH ofan acid Caribou soil to pH 5.3 was as good as pH 5.7, a sec-

LEE & MAC DONALD: INFLUENCE OF SOIL AMENDMENTS ON POTATOES ON ACID SOIL 575

GREEN MOUNTAIN

2.000 r

1.095 -

1.090 -

1.085 -

1.080 '

1.075 -

1.070

1.065

Fig. 1—Influence of soil pH on specific gravity of four potato varieties

ond acid Caribou soil was limed from pH 4.6 up to 4.9 and5.2 (experiment 2). On this soil, total tuber yield increasedby 45% and tuber specific gravity was increased at thehigher pH values (Table 2). There were more larger tubers(3.75-5.1 cm size) at soil pH 4.9 and 5.2 than at pH 4.6.There was no difference in the size of potato tops at each pHlevel.

The addition of dolomite decreased the amounts of soilextractable Al and Mn and decreased the contents of Al,Mn, and Mn/Fe ratios in potato tops (Table 3). The additionof dolomite tended to increase Ca and Mg contents of potatoleaves although statistical significance was obtained onlyfor Mg contents at the higher pH values. While dolomite did

not affect P contents of potato leaves, tissue K contentswere suppressed by dolomite applications.

These experiments indicate that maintaining acid Caribousoils at a pH of 4.6 results in reduced tuber yields and lowerspecific gravities. Liming to pH 4.9 or 5.2 should be ade-quate to obtain increased tuber yield and higher tuber spe-cific gravities. Reduced tuber yield and percentage dry mat-ter have been reported at soil pH ranges of pH 4.68 to 4.90(24) and pH 5.2-5.6 (28) in New York. However, raisingsoil pH up to 5.2 in New Brunswick appears to be sufficientfor increased tuber yield and quality.

SuperphosphatePhosphorus has been shown to counteract the toxic ef-

fects of soil acidity and Al toxicity for some crops (1,19).Calcium phosphate has been reported to be a better sourceof P than other P carriers when the Mn toxicity susceptible'Keswick' potato variety is grown on St. Andre' soil in theProvidence of Quebec (8). Accordingly, the application of2,240 kg/ha of superphosphate (86 ppm of P) was evaluatedat each soil pH level.

The addition of superphosphate alone or in combinationwith dolomitic limestone increased tuber yield over that ofthe check (Table 2, Experiment 2). There were more largetubers (3.7-5.1 cm) resulting from superphosphate applica-tions. Tuber specific gravity increased only with superphos-phate in combination with dolomite (Table 2). Plant topyield was not influenced with superphosphate treatments.Soil-extractable Al and tissue Al decreased with superphos-phate alone or in combination with dolomite. High rates ofapplied phosphorus will precipitate and reduce the solubilityof Al and will reduce plant uptake of Al. While soil extract-able Mn and tissue Mn decreased with superphosphatealone or in combination with dolomite, tissue Mn/Fe weredecreased only when dolomite was applied in combinationwith superphosphate. There were no differences observed intissue P, K, Ca, or Mg contents with superphosphate alone.Tissue K, Ca, and Mg contents for superphosphate in com-bination with dolomite were similar to those of dolomite ad-ditions alone. Some of the best tuber yields and quality wereobtained with the application of 2,240 kg/ha of superphos-phate at a pH of 4.9.

Table 3—Influence of soil amendments on soil pH, soil extractable Al and Mn, and potato leaf contents of Al, Mn, Mn/Fe, P, K, Ca, and Mg(experiment 2).

Soiltreatment

CheckL,L2PL,PL2P0L,0L20MgMgPKKPFe

SoilpH

4.64.95.24.64.95.24.64.95.24.64.64.64.64.6

1JVKC1Soil extractableAl

84 a50 f26 h77 cd45 g22 i77 cd45 g23 hi83 ab72 e80 be75 de84 a

Mn

3.2 be1.4 ef0.6 f3.5 b1.1 ef0.6 f4.4 a1.9 de0.7 f3.2 be2.5 cd2.4 cd2.0 de3.4 b

Al— ppm ——————

157 b99 d

100 d123 cd116 cd112 cd135 be116 cd100 d206 a130 bed154 b120 cd156 b

Mn

1,764 be482 i320 i

1,147 def414 i2781

2,879 a1,312 cde

624 ghi1,570 bed1,085 efg1,082 efgh

715 ghi1,984 b

Mn/Fe

10.1 be3.0 fgh2.2 gh7.3 cd2.3 gh1.6 h

19.2 a6.7 de3.6 efgh4.7 defgh4.8 defgh6.2 def5.1 defg

12.2 b

Leaf contentP

0.241 a0.245 a0.264 a0.269 a0.265 a0.269 a0.256 a0.244 a0.252 a0.259 a0.261 a0.268 a0.262 a0.274 a

K_______ 9

4.5 abc3.8 def3.8 def4.3 bcde3.7 ef3.5 f4.4 abed3.9 cdef3.7 ef4.1 cdef3.7 ef5.0 a4.3 bcde4.8 ab

Ca& ————————

1.01 be1.24 ab1.35 ab1.19 ab1.20 ab1.17 abc1.11 abc1.31 ab1.44 a1.03 be1.17 abc0.83 c0.82 c1.00 be

Mg

0.20 e0.42 cd0.51 be0.19 e0.37 d0.46 bed0.40 d0.47 bed0.56 b0.71 a0.51 be0.17 e0.22 e0.20 e

t Values under each heading followed by different letters are significantly different at P - 0.05 according to Duncan's New Multiple Range test.

576 SOIL SCI. SOC. AM. J . , VOL. 41, 1977

Organic MatterChelation has been shown to be an effective method of

correcting Al toxicity (3). The presence of complexed Al aseither citrate, EDTA, or in soil organic matter extract didnot exert a toxic effect on the growth of maize (Zea maysL.) seedlings. The application of organic material in theform of cow manure was made to evaluate its complexingeffect on the soluble Al in acid Ultisols in order to counter-act the toxic effects of Al on the potato plant.

The addition of 56 metric tons/ha of cow manure in-creased the size and yield of potato tops (Table 2). Whilepotato plants grew larger, plant stems, petioles, and leavesexhibited typical Mn toxicity symptoms. These observa-tions are supported by the chemical analysis of soil andplant tissue samples (Table 3). The addition of cow manureincreased the soil extractable Mn resulting in an increase inplant tissue Mn and higher Mn/Fe concentration ratio (Table3). A similar effect of enhanced Mn toxicity in potatoes byapplying compost has been reported by Cheng and Ouellette(7). Despite Mn toxicity symptoms, total-tuber yield wasincreased over the check whenever cow manure was appliedwith or without dolomite (Table 2). Higher total tuber yieldswere obtained when dolomite was added in combinationwith cow manure (Table 2). This increase in tuber yield cor-responded to a decrease in both soil extractable and planttissue Al and Mn contents when dolomite was added incombination with cow manure (Table 3). The specific grav-ity of the tubers was not different from that of the checktubers.

Terman et al. (26) indicated that the addition of manuredoubled the K concentration in the soil solution whichresulted in increased scab on potato tubers. There were noindications of increased scab incidence on tubers grown insoil amended with cow manure in experiment 2.

The application of cow manure can improve the generaltilth of a Caribou loam and may result in higher tuberproduction but the tubers may be of low 'specific gravity.These data also point out that observance of Mn toxicitysymptoms on potato stems, petioles, and leaves does notalways mean reduced tuber production.

Magnesium SulfateThe addition of MgSO4 to nutrient solutions containing

toxic concentrations of Al has been reported to alleviate Altoxicity in corn plants (9). Magnesium sulfate at a rate of170 kg/ha has been reported to almost completely remedyMn toxicity in potatoes (17). These reports, plus the factthat supplemental Mg is usually a common ingredient of po-tato fertilizer in eastern Canada, led to an evaluation of aMgSO4 soil amendment in this research.

The addition of 242 kg/ha of Mg (108 ppm Mg) asMgSO4 increased the total yield of tubers per plant (Table2). The specific gravity of these tubers was not differentfrom the check tubers. Plant tissue Al was increased overthe check plants, while Mn/Fe concentration ratios werereduced (Table 3). These data agree well with previousresults in hydroponic cultures (16) where increasing Al con-centrations counteracted high Mn concentrations in potatoplants by increasing the Fe content in plant tissues andreducing the Mn/Fe concentration ratio in plant tissues.

Magnesium concentrations in potato leaves were highestwhen magnesium sulfate was applied (Table 3).

Magnesium Sulfate Plus SuperphosphateThe combination of Mg and superphosphate amend-

ments, when applied to the soil, increased the yield and spe-cific gravity of potato tubers over that of the check and simi-lar to that of liming the soil to pH 5.2 (Table 2). Plant topswere reduced as was the Mn concentration in plant leaves(Table 3).

These data suggest that the addition of Mg and Ca phos-phate to an acid Caribou soil (pH 4.6) may result in potatoproduction similar to that obtained when the soil is limed topH 5.2. This soil amendment would be beneficial to thosepotato growers who experience that liming their acid soilsresults in scab incidences. Increased tuber production canbe obtained with a combination of Mg and Ca phosphatewithout raising the pH of the soil. Recently considerable in-terest has developed over the beneficial effects of applyingrock phosphate to acid mining spoils on the establishmentand growth of various plants (4). These amended spoilshave final pH values approximately 4.0 to 4.5. The use ofground rock phosphate may also be beneficial to potatoproduction on very strongly acid Ultisols of eastern NorthAmerica.

Potassium BicarbonateThe use of potassium bicarbonate as the source of K in

commercial fertilizers has been suggested to help alleviatepoor potato production resulting from Mn toxicity (6).

The application of K as KHCO3 reduced the growth ofplant tops and did not affect tuber yield (Table 2). The spe-cific gravity of tubers tended to be reduced with KHCO3 ad-ditions. The use of KHCO3 did reduce both the Mn concen-tration and the Mn/Fe concentration ratios in plant leaves.However, this soil amendment did not alleviate the pooryield or quality of potato tubers produced in this verystrongly acid Ultisol.

The combination of KHCO3 and superphosphate resultedin essentially the same results as above for KHCO3 alone.

These results suggest that the use of KHCO3 as the sourceof K in commercial fertilizers may not be of any practicalbenefit on very strongly acid Caribou soils of eastern NorthAmerica.

Iron ChelateHigh levels of Fe in the growth medium have been

reported to suppress the toxic effect of Al to rice plants (25).Manganese toxicity in plants has been related to a Mn-in-duced Fe deficiency (20). Increasing the Fe concentrationavailable for plants suffering from Mn toxicity has beenshown to reduce the effects of Mn toxicity (12). If this is thecase with the potato plant, then increasing the Fe availableto the plant might alleviate the effects of Mn toxicity.

The application of 56 kg/ha (25 ppm) of iron chelate asFeEDDHA did not have any beneficial effects on potato topgrowth and reduced tuber yield (Table 2). The Mn/Fe con-centration ratio was not affected by the addition of Fe to thesoil.

The results suggest soil-applied Fe chelate will not allevi-

ate the poor potato growth in acid Caribou soils. Foliarsprays of Fe chelate may have some beneficial effects onMn toxicity in potatoes; however, economics may renderthis amendment impractical.

CONCLUSIONSManagement practices that seem promising for potato

production on very strongly acid Ultisols in eastern Canadaappear to exist along two avenues:

1. For potato growers who want to lime their soil, limingto pH 4.9 with dolomitic limestone (dolomite) willincrease both tuber yield and quality. Additional soilapplication of either 2,240 kg/ha of superphosphate(86 ppm P) or 56 metric tons/ha of cow manure willfurther increase tuber yield. However, a lower tuberquality may result with cow manure.

2. For potato growers who do not wish to lime their soilsfor fear of scab, increasing soil levels of Mg, Ca, andP by one application of 2,240 kg/ha of MgSO4 (108ppm Mg) plus 2,240 kg/ha of superphosphate (86 ppmP) will increase both the tuber yield and tuber quality.While 56 metric tons/ha of cow manure will produce asimilar yield of tubers as above, the quality of thetubers may be lower.

While these conclusions are based on the results of green-house experiments, further research is necessary to evaluatethese management practices under field conditions onvarious soil types with different potato varieties. Lowerrates, frequency of application, and cheaper sources of Caphosphate and Mg should be evaluated. The influence ofthese management practices on the long-term developmentof potato scab should also be studied.