Acidification of a Forest Tree Nursery Soil1

R. E. MULLIN2

ABSTRACT

Artificial acidification of nursery soils for coniferousseedling production is being studied on soils which havebecome alkaline through continuous use. Three methodsof acidification are being examined, acidification of theirrigation water, incorporation of acid peat, and incorpora-tion of powdered S. The experimental work is being doneon red pine (Pinus resinosa, Ait.) seedbeds used for pro-duction of 3-0 shipping stock. The experiment is inthree sections, starting in consecutive years, each runningfor three years in the nursery, and providing trees forobservations in the laboratory and after outplanting.Acidification of the irrigation water, to pH 6.0 by auto-matic injection of H2SO4 has shown no measurable effecton soil pH or seedlings. Addition of acid peat, 60 cubicyards per acre, at about pH 5.0, showed some reductionin soil pH but not to the level desired, and no effect wasdetermined on the seedlings. Addition of powdered S at750, 1,500 and 2,250 pounds per acre has been mosteffective. The soil pH has been reduced proportionately,with that of the heaviest treatment to about pH 5.0, withsome fluctuation, and the effect has not diminished aftermore than three years. The S treatment of 2,250 poundscaused mortality in the seedbeds, whereas the lessertreatments caused an increase in survival. Sulphur addi-tion also resulted in taller, thicker, heavier seedlings withthe first level causing a large increase, the second a minor(plateau effect), and the high level a large increase again.Information on the planting success of the seedlings is notyet available.

T HE ONTARIO DEPARTMENT of Lands and Forests oper-ates several large-scale permanent nurseries, devoted

chiefly to the production of coniferous planting stock. Inrecent years the pH in many areas in the nurseries hasrisen above that recommended for coniferous production-pH 5.0 by Wilde (20), and pH 5.2 to 5.8 by Stoeckelerand Jones (18)—and is now in the alkaline range. Thecauses are not known but may include continuous cultiva-tion, elevation of alkaline subsoil, irrigation with alkalinewater, and residue from fertilizers.

A research program was started in 1959 to study theeffects of several techniques for increasing acidity on soilpH, seedling survival and growth, and the planting suc-cess of the trees. The work was done at Orono Nursery,about 50 miles east of Toronto, with red pine (Pinusresinosa, Ait.) as the test species. Included were anexperiment on fallow ground, Experiment A, conductedfor one growing season and an experiment on seedbedsconstructed and sown in the fall of 1959, Experiment B.

'Contribution No. 63-6, Ontario Dept, of Lands and Forests,Research Branch, Maple, Ontario, Canada. Presented beforeDiv. S-7, Soil Science Society of America, Nov. 18, 1963,Denver, Colo. Received August 26, 1963. Approved January9, 1964.

2Research Forester. The author gratefully acknowledgesthe help of Prof. K. A. Armson of the Faculty of Forestry,Univ. of Toronto, in planning the work and preparing thereport.

LITERATURE REVIEWHolmes and Faulkner (9) reported use of a H2SO4 drench

(4% H2SO4, 1.1 gallons per square yard) and applicationof S at approximately 665, 1,330, and 1,995 pounds peracre in a nursery a year before sowing. There were no apparenteffects on growth although nearly all treatments increasedseedling survival in the nursery. Neither soil pH changes inthe nursery nor differences among seedlings in or after leavingthe nursery were recorded.

Hiltbold and Adams (8) studied the effects of H2SO4,(NH4)2SO4, NHiNOs, and other chemicals in reducing pH,using a 7-week incubation period in the soil. All treatmentsreduced soil pH but no plants were involved. When S islimiting, its addition to alfalfa will affect the proportions ofamide and sugar more than actual S content of the plant (14).

Stoeckeler and Arnemann (17) have presented a table sug-gesting the S to be added to reduce a silt loam from onespecified pH to another. Pratt and Bair (13) developed abuffer method for estimating the S required to bring analkaline soil to a greater acidity, although there was no directcorrelation in certain types of soils.

Aldrich and Gauch (1) in discussing the actions of fertilizersdescribed (NH4)2SO4 as acid forming, and NH4NO3 as slightlyacid forming. Repeated dressings of (NH4)2SO4 have been sug-gested as a safe method of supplying N and acidifying thesoil (3). However, the rapid loss of N by leaching and byvolatilization has been observed (5). Janssen (10) also foundthat inorganic N fertilizers (including (NH4)2SO4) had noresidual effects of practical importance.

Spurway (16) published a list of pH preferences whichgave an optimum range of pH 5.0 to 6.0 for red pine, thetest species. Leyton (11) working with Sitka spruce (Piceasitchensis Bong. Carr) found that pH had a marked effect ongrowth in the nursery which he considered ". . . as due to thedifferences in pH per se. . . ." But, Wilde (19) has questionedthe use of the term pH, its meaning, and importance. He sug-gested that the pH may be of minor importance to the growthof plants when there is a sufficient supply of available nutrients.

METHODS AND PROCEDURESExperiment A.

This was conducted during the 1959 growing season onfallow ground in a seedbed compartment. It was a split-plotdesign of 3 replications, each containing the following treat-ments :

Main plots— U Control: Irrigated with untreated water.6.5 Irrigation water adjusted to pH 6.5 by

addition of H2SO4.6.0 Irrigation water adjusted to pH 6.0.5.5 Irrigation water adjusted to pH 5.5

Sub-plots— N Control: No addition of peat.P Addition of acid peat at 60 cubic yards

per acre.Sub-sub-plots— 1. Control: No addition of S.

2. Addition of S at 500 pounds per acre.3. Addition of S at 1,000 pounds per acre.4. Addition of S at 1,500 pounds per acre,

(sub-sub-plot was 10.0 feet by 8.7 feet)Before the plots were laid out a grid of 200 pH measure-

ments were taken on May 5, using a Vz inch by 6 inch samplingtube, distilled water added to soil in 1-ounce sampling cups,and a battery operated pH meter. Readings were taken totenths of a pH unit. Peat was applied to the plots on May 14and the entire area rototilled. The S was added on May 25,using the same procedure.

An oscillating lawn sprinkler, adjusted to a rectangular area,was used for irrigation. Untreated water was obtained directlyfrom the small creek used for regular nursery irrigation. Theexperiment was irrigated at the same time as the adjacentseedbed areas, adding about 1 inch of water on June 3, 10, 17,and 24; July 7, 15, and 28; and August 6 and 17.

441

442 SOIL SCIENCE SOCIETY PROCEEDINGS 1964

Without PeatUN = Untreated I r r i g a t i o n W a t e rUP= Untreated Irr igat ion Water plus Peat (60 cu.yds/acre!

6,5 6.0pH OF I R R I G A T I O N WATER

With Peat

LEGEND

A—————— No S j i phu rO - - - - - Su lphur ot 500 ios/oc-e

X — — - — — Sulphur at 1000 lbs ac re

O - . . . . . . . S u l p h u r a t 5 0 0 lbs/acre

SULPHUR TREATMENT

6,5 6.0pH OF I R R I G A T I O N W A T E R

Fig. 1—Effects of acidification of irrigation water, at pH's5.5, 6.0, and 6.5; addition of peat, at 60 cubic yards peracre; and addition of S at 100, 1,000 and 1,500 poundsper acre. Measurements at end of one season on fallowsoil. Each point is average of 12 measurements.

Experiment B.This was started in late summer of 1959, on a seedbed area

near Experiment A. Again a split-plot design was used, butwith five replications.

Main plots— U6.0

Sub-plots—

Control: Irrigated with untreated water.Irrigation water adjusted to pH 6.0 byaddition of H2SOj. This value was select-ed for the automatic acid-injection sys-tem installed at the pumphouse (2 ) .Control: No addition of peat.Addition of acid peat at 60 cubic yardsper acre.Control: No addition of S.Addition of S at 750 pounds per acre.Addition of S at 1,500 pounds per acre.Addition of S at 2,250 pounds per acre,(sub-sub-plot was 11.0 feet by 7.5 feet)

The changes in S levels were made as a result of observa-tions from Experiment A. Pratt (12) has reported the use ofS, up to 4,000 pounds per acre.

The plots were laid out in late August and the pH sampledbefore treatment by the same procedure but with 6 samplesfor each sub-sub-plot. In early September the peat and Swere applied as in Experiment A.

Sub-sub-plots— 1.2.3.4.

Fig. 2—Effects of acidification of irrigation water, at pH6.0; addition of acid peat, at 60 cubic yards per acre;and addition of S at 750, 1,500 and 2,250 pounds peracre. Measurement at end of third season in red pineseedbed. Each point is average of 30 measurements.

In November, 8 standard seedbeds, 3.5 feet by 30.0 feetwere constructed in each replication. Red pine seed of On-tario Zone 5E (7), pelleted with methocel and captan 50, wassown by hand at a rate of 4.5 ounces per bed (untreatedweight).

During 1960, 1961, and 1962 the beds were maintained inthe same way as regular seedbeds. They were shaded duringthe first year only. All weeding was done by hand, at 2-weekintervals in spring and decreasing in frequency during theyear. Irrigation was also done in accordance with routinepractice. About one inch of water was added 5 times in 1960,4 times in 1961, and 9 times in 1962.The beds were fertilized as follows:

1960 July 11, 18. (NHi^SCX in water, to total about 520pounds per acre.

1961 May 16, June 28. NH4NO3 pellets, to total about 260pounds per acre.

1962 June 5, 18, July 10. NHUNO, pellets, to total about 500pounds per acre.

Two other cultural treatments were applied to all beds. Inthe spring of 1961 (at 1-0) the beds were thinned to approxi-mately 30 to 40 per square foot by cutting seedlings at groundlevel with scissors. In late June 1962, all beds were rootpruned with a horizontal blade at approximately 5-inch depth.

The soil in this part of the nursery has been classified in theOntario Soil Survey as Brighton Gravelly Sand (21). It is aglacial fluvial deposit, consisting of coarse sands and gravels,mainly of limestone origin. The drainage is rapid and excessive.Analysis shows 83.5% sand, 12.1% silt and 4.4% clay in thesurface soil. Samples taken in 1958 showed a base exchangecapacity of approximately 5.0 me. per 100 g. (range 3.9 to7.8), an organic matter content of about 1.7% (range 1.0 to3.5), and a pH of about 7.7 (range 6.8 to 8.2).

RESULTS AND DISCUSSIONEffects on Soil pH

Because pH values are in a geometic progression ratherthan arithmetic there has been some doubt that theyshould be averaged. Shiue and Chin (15), however, con-sidered that over short ranges averaging is permissible.The same authors noted that " . . . pH values should bedirectly used in statistical analysis without transformation.. . . " Groenewoud (6) warned that frequency distribu-tions of pH are not always normal or near normal.

MULLIN: ACIDIFICATION OF A FOREST TREE NURSERY SOIL 443

Histograms of data in these experiments do not showskewness or kurtosis so analysis of variance has been usedto make comparisons. Results of the final pH measurementin Experiment A, the 1-year test on fallow soil, are givenin Fig. 1. The most important factor in reduction of thesoil p H is obviously the S (significant at the 0.1% level).Addition of peat also reduced the pH generally (signifi-cant at the 5.0% level). However, effects of irrigation withwater at three levels of acidity were not significant. Therewere no qualifying interactions.

The pH data from Experiment B, for the end of thethird growing season were also examined by analysis ofvariance. Effects of the acidified water and the additionof peat were not significant. However, the effect of Slevel was highly significant (at the 0.1% level). Theseresults have been summarized in Fig. 2. The data suggeststhat the application of acidified water has resulted inlower pH even though not significant. There is also asuggestion of the buffering action of peat at the higherlevels of acidity.

The influence of the S at the end of the third year canbe summarized as follows: no S (control), pH 6.5; 750pounds, pH 6.0; 1,500 pounds, pH 5.3; and 2,250 pounds,pH 5.0.

It should be noted that the average pH of the untreatedplots at the end of the third growing season, pH 6.5 was

considerably lower than that at the beginning, pH 7.4,even though the pH of the untreated irrigation waterwhich these beds received rises considerably during thegrowing season. In 1960 the pH of the irrigation waterrose from about 7.7 on June 1 to 8.3 on September 10.The increase in soil acidity may be caused in part by thelack of cultivation in three years and the presence ofseedlings.

On this sandy soil the 1,500 pounds per acre of S hasreduced the pH from approximately 7.5 to < 5.5. Thisis in comparison with 2,200 pounds per acre recommendedfor a silt loam (17).

Because the addition of S was primarily responsible forthe change in pH, it is interesting to note the timing,fluctuations in, and duration of its influence. Figure 3shows the pH changes of each level of S from the pre-treatment sampling of August 1959, pre-sowing samplingof November 1959, and sampling just before lifting inSeptember 1962.

The lowering of pH was apparent in the fall a fewmonths after application. By the following spring each Slevel had caused a decrease approximating that at the endof the study. The pH remained low for at least threeseasons. In contrast to these results, Edwards and Holmes(4) suggested that effects of S would not be fully realizedin one season.

F e r t i l i z e r Added

6.0-

5.5-

,

,\

\

NO SULPHUR ————SULPHUR 750 lbs/cere - - - -SULPHUR 1500 lbs/acre _--SULPHUR 2250 lbs/acre • • • • • •

— A- -o-- X

• • D

DATES OF pH MEASUREMENT

Fig. 3—Course of pH for 3 years in response to addition and incorporation of S at 750, 1,500 and 2,250 pounds per acre.Measurements taken in red pine seedbeds during pre-treatment (Aug. 29, 1959), post-treatment and pre-sowing (Nov. 7,1959), and pre-lifting (Sept. 7, 1962) on 3-0 shipping stock. Each point is average of 120 measurements.

444 SOIL SCIENCE SOCIETY PROCEEDINGS 1964

Table 1—Influence of S application on seedlings. Averagesfrom 2,000, 3-0 seedlings.

Rate of Sulfurapplication

None750 Ib. /acre

1,500 Ib. /acre2,250 Ib. /acreSignificance

Top length,collar -bud tip

24.424.624.625.1NS

Root length,collar -

longest root

34.535.034.538.10.1%

Stemdiameter,

2 inchabove collar

0.440.470.480.510.1%

Oven-dryweight,

24 hoursat 105' C.

grams6.567.637.878.980.1%

Top-rootratio ,

oven-dryweights

6.236.196. 165.92

NS

The normal seasonal fluctuation of pH is probablypartly obscured by the fertilizer applications. No generalconclusions may be drawn because the fertilizers variedfrom year to year, and because pH measurements werenot taken at prescribed intervals after fertilizing. The(NH4)2SO4 in 1960 appears to have had only minorinfluence in comparison with the NH4NO3 in 1961 andin 1962 (1960, (NH4)2SO4 at 520 pounds per acre; 1961,NH4NO3 at 260 pounds per acre; 1962 NH4HO3 at 500pounds per acre). This would appear to be contrary to theusual concept that (NH4)2SO4 would create greater acidity(1). It can also be observed that the effects of the fertilizerson pH were minor in comparison with S and were largelynoneffective after two months.

Effects on Seedling Mortality in the NurseryIn September 1960, at the end of the first growing

season, the living trees were counted in six randomlyplaced plots (3.6-inch by 3.5-foot frame placed across thebed) in each sub-sub-plot. Analysis of the data showedthat neither acidification of the water nor addition of peathad materially affected survival. However differences insurvival due to addition of S were significant at the 0.1%level, with no significant interactions.

Survival per square foot averaged: no S (control), 122.6;750 pounds, 133.2; 1,500 pounds, 133.5; and 2,250pounds, 98.6.

Apparently the two lower levels of S were beneficial atthis stage, possibly by reduced damping-off. On the otherhand, the highest level of S resulted in mortality.

Effects on Size and Balance of SeedlingsAt the 3-0 stage, on September 26, 1962, randomly

selected samples of 25 trees were taken from each sub-sub-plot for laboratory measurement. The trees wereloosened by machine and pulled by hand.

Results of data analysis are summarized in Table 1.Only the effects of the levels of S were found to be sta-tistically significant in any of the several analyses. Theaddition of S has resulted in a taller, thicker, heavier treewith a lower top-root ratio. Edwards and Holmes (4) alsofound beneficial results of adding S when measured interms of mean height. The improvement in growth wasobviously not a linear relationship. The first level of Scaused a large increase, the second a minor increase orplateau effect, and the third a relatively large increaseagain.

The growth response is probably caused in part bychanges in levels of growth factors related to the pHreduction, and partly to the direct addition of S. It isimpossible from the data to speculate to what degree thesetwo effects are individually responsible.

in irpv T