EFFECT OF SIMULATED ACID RAIN ON THE YIELD OF SOYBEAN

Y O S H I H I S A K O H N O

Biology Department, Abiko Research Laboratory, Central Research Institute of Electric Power Industry, 1646 Abiko, Abiko City, Chiba 270-11, Japan

and

T A K U Y A K O B A Y A S H I

College of Horticulture, Chiba University, 648 Matsudo, Matsudo City, Chiba 271, Japan

(Received February 23, 1989; revised April 20, 1989)

Abstract. Soybean seedlings (Glycine max) were exposed to simulated acid rain containing sulfate ion only or a mixture of sulfate, nitrate and chloride anions, using a cont inuous rain generating system in a side opened glasshouse. Plants were subjected to acid rain t reatment twice a week, for a 1 or 3 hr period at a rate of 2.2 or 5.0 mm hr 1, respectively. Dry seed yield in plants treated with simulated acid rain at pH 2.0, in the three of 4 experiments conducted over a 3 yr period, was significantly less than that at pH 3.0 or higher. Simulated acid rain t reatment at pH 3.0 or higher did not significantly affect yield compared to pH 5.6; however, plants exposed to simulated acid rain at pH 4.0 tended to yield more than those treated with pH 5.6 rain. Based on the current 3 years of research in which results from 4 experiments were combined, rain acidity at current levels in Japan would not directly affect seed production of selected cultivars of soybean.

1. Introduction

The previous report by Kohno and Kobayashi (1989) showed that simulated acid rain treatments at pH 3.0 or higher did not induce significant adverse effects on the growth of soybean seedlings, but acidic rain treatment at pH 2.0 significantly reduced leaf area, dry matter accumulation and root nodule production. Plants subjected to simulated acid rain at pH 4.0, showed a slight growth stimulation compared with those exposed to rain at pH 5.6. The stimulation of growth might be associated with an increased number of root nodules at pH 4.0. Those findings suggested that the current level of ambient rain acidity in Japan, would not have an adverse effect on the growth of soybean (Kohno and Kobayashi, 1989).

Evans and Lewin (1981) reported that an increase in seed yield occurred when plants were exposed to simulated acid rain at pH 3.1; their later reports (Evans et al., 1981, 1983, 1985) indicated that simulated acid rain treatments reduced soybean seed yield. However, Irving (1983) and Irving and Miller (1981) concluded that the acid precipitation simulant produced no statistically significant effect on seed yield. Recent reports of field exposure experiments, conducted in the United States, concluded that there is no adverse or detectable effect on soybean seed yield by current levels of rain acidity (EPRI, 1987; NAPAR 1988).

Monitoring network data for precipitation revealed that mean rain pH observed currently in Japan was 4.5 or 4.7; pH values of bulk rain samples lower than 4.0 were rare (CRIEPI, 1985; Tamaki and Hiraki, 1986). In contrast to precipitation chemistry studies, yield responses of Japansese agricultural crops have not been

Water, Air, and Soil Pollution 45:173-181, 1989. © 1989 Kluwer Academic Publishers. Printed in the Netherlands.

174 YOSHIHISA KOHNO AND TAKUYA KOBAYASHI

investigated to any extent. This report describes results of 4 experiments conducted over a 3 yr period to

determine the effects of acid rain on the yield of two soybean cultivars.

2. Materials and Methods

2.1. EXPERIMENT I

Conditions of individual experiments are summarized in Table I. The first experiment was conducted during the growing season of 1985. Soybean seeds (Glycine max

(L.) Merr. cv. Sapporomidori ; f rom Snow Brand Seeds Co., Hokkadido, Japan)

were sown in plastic pots (5 seeds to a pot, pot size: 11.3 cm diameter × 18 cm

depth) filled with 1.5 L of volcanic ash soil. Seedlings were thinned to one plant per pot 7 days after seeding. Fertilizer containing N, P, and K, was applied to the soil at a rate of 160:160:160 kg ha -1 as N:PzOs:K20 prior to seeding.

In this experiment, stock solution for simulated acid rain was prepared with

only H2SO 4. Deionized water was used as a diluent and the control (pH 5.6). Stock

solution was further diluted with deionized water to provide designated acidity

levels for p H 4.0, 3.0, and 2.0. Simulated acid rain exposure treatments, using a continuous rain generating

system, previously described (Kohno and Kobayashi, 1989), were initiated 9 days after seeding. Exposures were conducted in the early morning or evening to avoid

treatments under high temperatures and high irradiances during the day. Plants were treated with diluted HzSO 4 solution as a simulated acid rain, twice

a week for a 1 hr period at a rate of 2.2 mm hr -I. Because the total precipitation

applied for 5 weeks in this experiment was only about 20 ram, deionized water

was supplementally irrigated to avoid water deficit. Each treatment had 24 pots which were rerandomized prior to every exposure,

to avoid shading effects. The experiment was conducted in a glasshouse, with sides and roof tops open, but seedlings did not receive any ambient rain.

2.2. EXPERIMENT II

Soybean seeds (cv. Early Hakucho; from Takii Seed Co., Kyoto, Japan) were sown as described in Experiment I. Young seedlings were thinned to one plant per pot 10 days after seeding. Solutions of mono-potass ium phosphate and ammonium nitrate were applied to the volcanic ash soil prior to seeding to provide N, P, and K at a rate of 200:200:200 kg ha -1.

Plants were treated with deionized water as the control or simulated acid rain containing sulfate, nitrate and chloride anions in a concentration ratio of 2:1:1, which was a mean equivalent to those found in ambient rain of Japan (CRIEPI, 1985; Kohno and Kobayashi, 1989). Because plants were subjected to acid rain treatment twice a week during the growing season, for a 1 hr period at a rate of 5 mm hr -1, the total precipitation was 90 mm for 9 weeks. Since this was only

E F F E C T OF S I M U L A T E D ACID RAIN ON T H E YIELD OF SOYBEAN 175

about one fifth of the nationwide weekly average during the growing season in Japan, deionized water was supplementally irrigated to avoid water deficit.

Each treatment was composed of 30 pots, rerandomized to avoid shading effects as in Experiment I. Mean temperature inside the opened glasshouse in July was

23.4 °C with a range 15.9 to 37.4 °C.

2.3. EXPERIMENT III

After harvesting the second experiment, the 3rd experiment was conducted similarly to Experiment II. As the early vegetative growth development was relatively faster than in the preceding experiment, plants were subjected to acid rain treatments for 7 weeks prior to harvest. As described in the previous experiments, deionized water was supplementally irrigated.

Each treatment was composed of 30 pots, rerandomized to avoid shading effects as in Experiment II. Mean temperature inside the opened glasshouse in August

was 26.9 °C with a range 19.1 to 36.4 °C.

2.4. EXPERIMENT IV

In the previous three experiments, plants were cultivated in small plastic pots. Hence, frequent supplemental irrigation with deionized water was required to avoid water deficit, due to greater evapotranspiration from the large biomass, small volume for root growth and less precipitation applied. To avoid difficulty, a large box cultivation system was applied to simulate field conditions in the opened glasshouse for Experiment IV. The boxes (80 cm wide, 80 cm long and 33 cm deep) were insulated with 5 cm thick polystylene boards. The bot tom of the box had drainage holes, and the bot tom 3 cm was filled with coarse river sand to drain excess water. The upper 30 cm was filled with volcanic ash soil which was fertilized with N, P, and K at a rate of 80:160:160 kg ha -1 and well mixed prior to seeding.

Forty-nine uniform 11-day-old soybean seedlings (cv. Early Hakucho) grown in seed beds, were selected and transplanted in the array of 7 × 7 rows into each box. Twenty-four young seedlings were removed to adjust the plant density and to avoid shading effects in the early vegetative stage. Five additional seedlings were removed on July 2 when plants were at the end of the flowering stage and some had started to set tiny pods. Thus, the final plant density was 20 plants per box; the innermost 8 plants in each box were harvested for statistical analysis. Each treatment had 2 boxes which were randomized in the open glasshouse.

Plants were subjected to acid rain treatments twice a week during the growing season, for a 3 hr period at a rate of 5 mm hr -1. The amount of weekly precipitation was 30 mm in this experiment and was still less than the 50 mm ambient mean weekly average for the regular growing season. To prevent water deficit, supplemental irrigation with deionized water was provided through drip irrigation tubes uniformly arrayed on the surface of the soil; thus, irigation water was prevented from contacting soybean leaves.

Mean temperature inside the opened glasshouse in July was 27.6 °C with the

176 YOSHIHISA KOHNO AND TAKUYA KOBAYASHI

TABLE I

Experimental conditions of simulated acid rain treatment in soybean

Experiment

Condition I II III IV

Year 1985 1986 1986 1987 Cultivar a SM EH EH EH Pot size b 1 1 1 2 Fertilizer c 1 2 2 3

Seeded 7/02 5/07 8/10 5/19 First exposure 7/11 5/22 8/20 6/08 Final exposure 8/10 7/20 10/01 8/04 Harvested 9/02 8/07 10/23 8/11 Total cultivated days 93 92 74 84

Plants per treatment 24 30 30 16

pH level d 1 1 1 1 Concn of H ÷ (mN) e 1 1 1 1 Anion component f 1 2 2 2

Rain intensity (mm hr -1) 2.2 5.0 5.0 5.0 Rain event (number week 1) 2 2 2 2 Exposure time (hr event 1) 1 1 1 3 Duration of exposure (week) 5 9 7 9 Total events (number) 9 18 13 18 Total precipitation (mm) 19.8 90.0 65.0 270.0

a SM: Sapporomidori, EH: Early Hakucho. b 1: Plastic pot; top: 11.3 cm diameter; bottom: 9.7 cm diameter; hight: 18 cm; surface area: 0.01 m 2.

2: Box: 80 cm wide × 80 cm long ×30 cm hight; surface area: 0.64 m 2. c 1: 160-160-160 kg ha < as N-P2Os-K20.

2: 200-200-200 kg ha < as N-P-K. 3: 80-160-160 kg ha 1 as N-P-K.

d 1: 5.6 (Control), 4.0, 3.0, and 2.0 c 1: 0 (Deionized water for control), 0.1 mN, 1 mN, and 10 mN for pH 5.6, 4.0, 3.0 and 2.0, respectively. f 1: Single solution of 8042- from H2SO 4.

2: Mixture solution of SO42 from H2804, NO 3- from HNO3, and C1 from HC1.

r a n g e f r o m 18.0 to 38.6 °C. T h a t in A u g u s t was 27.0 °C w i t h t h e r a n g e f r o m

19.2 to 38.0 °C.

3. Results

3.1. EXPERIMENT I

E v e n w h e n s o y b e a n p l a n t s we re s u b j e c t e d to o n l y 20 m m o f s i m u l a t e d a c i d r a i n

c o n t a i n i n g o n l y su l f a t e a n i o n , t h e d r y s eed w e i g h t o f p l a n t s t r e a t e d a t p H 2.0 was

s i g n i f i c a n t l y less t h a n t h a t o f p l a n t s t r e a t e d a t p H 3.0 o r h i g h e r ( T a b l e II) . A t

p H 2.0 t h e r e l a t i v e y ie ld was 6 2 . 5 % o f t he c o n t r o l a t p H 5.6. S e e d y ie ld a t p H

4.0 was a b o u t 13% h i g h e r t h a n t h a t o f t h e c o n t r o l , a n d t h a t a t p H 3.0 w as a b o u t

EFFECT OF SIMULATED ACID RAIN ON THE YIELD OF SOYBEAN

TABLE II

Yield of soybean plants exposed to simulated acid rain in Experiment I

177

pH

Yield component 5.6 4.0 3.0 2.0

Dry seed weight per plant (g) 3.2 bc a 3.6 c 2.7 b 2.0 a Relative yield (% of pH 5.6) 100.0 112.5 84.4 62.5

Seed number per plant 25.0 c 26.2 c 20.7 b 15.0 a Seed number per fruited pod 1.6 a 1.5 a 1.5 a t.5 a Dry weight per seed (g) 0.13 a 0.14 a 0.13 a 0.13 a

Total pod number per plant 22.3 bc 22.8 c 18.6 b 13.4 a Fruited pod number per plant 16.0 c 17.4 c 13.5 b 9.8 a

3-seed pod number per plant 1.8 a 1.2 a 1.1 a 1.0 a 2-seed pod number per plant 5.5 b 6.3 b 4.9 ab 3.3 a 1-seed pod number per plant 8.8 b 9.9 b 7.5 ab 5.6 a 0-seed pod number per plant 6.3 a 5.3 a 5.1 a 3.5 a

a Within a row, any two means having a letter in common are not significantly different at the 5% level by Tukey's HSD multiple range test. (N=24).

16% less than that of the control .

Dry weight per seed and n u m b e r of seeds per frui ted pod were not affected

by acid rain t reatment . However, numbers of total and fruited pods per p lant

significantly decreased at pH 2.0. Thus, reduct ion in dry seed p roduc t ion per p lant

at the low p H t rea tment was associated with a decrease in n u m b e r of fruited pods

per plant .

3.2. EXPERIMENT II

In the second experiment , s imula ted acid ra in con ta ined sulfate, ni trate, and chloride

an ions with mean concen t ra t ion ratios equivalent to those in ambien t rain. Total

precipi ta t ion applied dur ing the cul t ivat ion was 4.5 times that in Exper iment I.

Yield of dry seed per p lant was no t significantly affected by acid rain t rea tments

at pH 3.0 or higher; however, that at pH 2.0 was significantly less than that of

the control at p H 5.6 (Table III). Relative yield was 83.7% of that for the control

at pH 5.6. Total pods per p lan t and dry weight per seed in this exper iment were

not affected by acid rain t reatments . Seed yield reduct ion at p H 2.0 was a t t r ibuted to a significant decrease in number s of seeds per pod.

3.3. EXPERIMENT III

This exper iment was conducted f rom Augus t th rough October, 1986. Plants grew

faster in the early vegetative stage than did those of the preceding experiment.

Soybean seed yield per p lan t was not affected by acid ra in t rea tments at any pH

level, even at p H 2.0 (Table IV).

Yield c o m p o n e n t analysis indicated that total n u m b e r of pods per p lant at pH

178 YOSHIHISA KOHNO AND TAKUYA KOBAYASHI

TABLE III

Yield of soybean plants exposed to simulated acid rain in Experiment II

pH

Yield component 5.6 4.0 3.0 2.0

Dry seed weight per plant (g) 4.9 b a 5.2 b 4.9 b 4.1 a Relative yield (% of pH 5.6) 100.0 106.1 100.0 83.7

Seed number per plant 19.1 b 20.6 c 19.5 bc 16.5 a Seed number per fruited pod 1.7 b 1.7 b 1.7 b 1.4 a Dry weight per seed (g) 0.26 a 0.25 a 0.25 a 0.25 a

Total pod number per plant 11.4 a 12.4 a 11.4 a 12.0 a Fruited pod number per plant 11.0 a 12.1 b 11.2 ab 10.7 a

3-seed pod number per plant 1.0 ab 1.1 ab 1.3 b 0.6 a 2-seed pod number per plant 6.1 b 6.3 b 5.7 b 4.5 a 1-seed pod number per plant 3.9 a 4.6 ab 4.1 a 5.6 b 0-seed pod number per plant 0.4 a 0.3 a 0.2 a 1.3 b

a Within a row, any two means having a letter in common are not significantly different at the 5% level by Tukey's HSD multiple range test. (N-30).

TABLE IV

Yield of soybean plants exposed to simulated acid rain in Experiment III

pH

Yield component 5.6 4.0 3.0 2.0

Dry seed weight per plant (g) 4.0 a a 4.4 a 4.4 a 4.1 a Relative yield (% of pH 5.6) 100.0 110.0 110.0 102.5

Seed number per plant 20.8 ab 21.6 ab 22.7 b 20.3 a Seed number per fruited pod 1.9 b 1.9 b 1.9 b 1.8 a Dry weight per seed (g) 0.19 a 0.20 ab 0.19 a 0.21 b

Total pod number per plant 10.9 a 11.8 ab 12.2 b 11.5 ab

a Within a row, any two means having a letter in common are not significantly different at the 5% level by Tukey's HSD multiple range test. (N=30).

5.6 w e r e s i gn i f i c an t l y l o w e r t h a n t h o s e a t p H 3.0. N u m b e r o f seeds p e r f r u i t e d

p o d were l o w e r a t p H 2.0 t h a n at p H 5.6, 4.0 or 3.0; h o w e v e r , d r y w e i g h t p e r

s eed at p H 2.0 was s i gn i f i c an t l y g r e a t e r t h a n t h a t at p H 5.6. N o s ign i f i can t y ie ld

r e d u c t i o n was r e c o r e d d u e to c o m p e n s a t i o n a m o n g the y ie ld c o m p o n e n t p a r a m e t e r s .

3.4. EXPERIMENT IV

T h e b o x c u l t i v a t i o n s y s t e m in the c u r r e n t e x p e r i m e n t p r o v i d e d c o n d i t i o n s s imi l a r

to t h o s e in t he f ield, ie, a l a rge r r o o t i n g zone . T h u s , s t r e s ses c a u s e d by h i g h

t e m p e r a t u r e a n d low w a t e r m o i s t u r e c o n t e n t in t h e r o o t z o n e were l o w e r t h a n

in t he p r e v i o u s sma l l size p o t e x p e r i m e n t s .

EFFECT OF SIMULATED ACID RAIN ON T H E YIELD OF SOYBEAN

TABLE V

Yield of soybean plants exposed to simulated acid rain in Experiment IV

179

pH

Yield component 5.6 4.0 3.0 2.0

Dry seed weight per plant (g) 7.3 b a 7.7 b 6.7 b 4.9 a Relative yield (% of pH 5.6) 100.0 105.5 91.8 67.1

Seed number per plant 26.6 b 27.5 b 24.9 ab 20.9 a Seed number per fruited pod 1.6 b 1.7 b 1.6 b 1.1 a Dry weight per seed (g) 0.28 b 0.28 b 0.27 b 0.24 a

Total pod number per plant 16.3 ab 16.7 ab 15.2 a 18.5 b Fruited pod number per plant 15.3 b 15.0 ab 13.6 ab 12.3 a

3-seed pod number per plant 1.1 ab 1.7 b 0.8 ab 0.4 a 2-seed pod number per plant 9.0 b 8.6 b 9.3 b 6.1 a 1-seed pod number per plant 5.4 ab 5.2 ab 3.9 a 7.3 b 0-seed pod number per plant 1.1 a 1.7 a 1.6 a 6.2 b

a Within a row, any two means having a letter in common are not significantly different at the 5% level by Tukey's HSD multiple range test. (N-16).

This system produced higher yields than the small pot approach. Dry seed weight from plants treated with simulated acid rain at pH 3.0 and higher was not affected, even when the simulated acid rain treatment was 270 mm which was 3 times that in Experiment II. However, as in Experiments I and II, seed yield at pH 2.0 was significantly lower than that at pH 3.0 or greater (Table V). Relative seed yield at pH 2.0 was 67% of that for the control at pH 5.6.

Total number of pods per plant treated with acid rain at pH 2.0 was significantly greater than that at pH 3.0; conversely, number of empty pods increased at pH 2.0. Dry weight per seed and number of seeds per pod decreased significantly at pH 2.0. Yield component analysis indicated that reduction of dry seed weight per plant at pH 2.0 was due to a combination of decreases in number of fruited pods per plant, number of seeds per fruited pod and dry weight per seed.

4. Discussion

Evans and Lewin (1981) reported that simulated acid rain at pH 3.1 decreased the dry mass of both stems and leaves of soybean plants grown in a greenhouse, but increased seed yield due to a larger dry mass per seed. In contrast, soybean plants grown under standard agronomic practices and exposed to simulated acid rain showed decreased yield (Evans et al., 1981, 1983, 1985). Irving (1983) and Irving and Miller (1981) suggested that the possibility for harmful effects of acidic precipitation on soybean yield are minimal. Recent reports by EPRI (1987) and NAPAP (1988) concluded that current ambient rain acidity may have little or no

180 YOSHIHISA KOHNO AND TAKUYA KOBAYASHI

significant direct effects on agricultural crop growth and yield under typical field conditions.

Our experimental results indicated that seed yield of soybean grown in the opened glasshouse was not affected by simulated acid rain treatment at pH 3.0 or higher. Hence, we conclude that current ambient rain with a mean pH of 4.5 or 4.7 (CRIEPI, 1985; Tamaki and Hiraki, 1986), found in Japan, does not affect yield of soybean grown in the field. This finding coincides with that of previous reports (Irving, 1983; EPRI, 1987; NAPAP, 1988).

In general, the current experimental results, consisting of 4 experiments conducted during a period of 3 yr, indicated that yield reduction in soybean by the simulated acid rain treatment at pH 2.0 was due to a decrease in number of fruited pods or seed number per pod. Evans et al. (1985) indicated two soybean cultivars differed in response to simulated acid rain; 'Amsoy' showed a seed yield reduction due to a decrease in pod number per plant, but 'Williams' did not show a yield reduction. Because our experiments were conducted with different cultivars under different experimental conditions, the conclusions drawn can not be applied to other soybean cultivars without additional research.

Current experimental results suggested that the total amount of acidic precipitation may not be important in reducing yields. Relative yield reduction was similar for 20 mm of precipitation in Experiment I and 270 mm in Experiment IV. Thus, the amount of simulated acid rain added may not be critical, but that with high acidity may affect reproductive processes, rather than vegetative (Kohno and Kobayashi, 1989). Therefore, the effects of strongly acidic rain on flowering, fruiting and/or pod filling processes should be investigated.

As described in the previous report (Kohno and Kobaysahi, 1989), the simulated acid rain treatment at pH 4.0 tended to produce higher seed yields than did deionized water at pH 5.6. This tendency was probably correlated with stimulation of vegetative growth and increased root nodules of plants treated with simulated acid rain at pH 4.0 (Kohno and Kobayashi, 1989). These stimulatory effects might be associated with plant uptake of sulfate and nitrate as nutrients from simulated rain components, even though Evans et al. (1986) concluded that ambient N deposition rates do not significantly affect yields of agricultural crops, and concentrations of 11 elements, including S and N, in the soybean leaves exposed to simulated acid rain were not significantly affected (EPRI, 1987).

The pH of bulk samples of cultivated soils were slightly but significantly affected by the simulated acid rain treatments (Kohno and Kobayashi, 1989). This suggests that surface soil chemistry may change significantly, but the effects of such changes on plant growth and yield are not known. Moskowitz et al. (1985) estimated that if acid deposition in the United States were reduced by 10% in 1982, the yields of field grown soybean cultivars would be greatly increased. However, they suggested that effects of acid precipitation might be less important than those of dry deposition such as 03, and other environmental stresses such as water stress. Thus, further research is needed to assess long term interactive effects of acidic precipitation

E F F E C T OF S I M U L A T E D ACID RAIN ON T H E YIELD OF SOYBEAN

and other environmental factors on soybean and other agricultural crops.

181

Acknowledgment

The authors extend their thanks to Dr. Charles D. Foy, Climate Stress Laboratory, Natural Resources Institute, ARS, USDA, Beltsville, MD 20705, U.S.A., for his critical reading of this manuscript and editorial suggestions.

References

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EPRI: 1987, Acid Deposition: Effects on Agricultural Crops. EPRI EA-5149, Final Report, April, Electric Power Research Institute, 3412 Hillview Ave., Palo Alto, CA 94304, U.S.A.

Evans, L. S., Canada, D. C., and Santucci, K. A.: 1986, Environ. Exp. Bot. 26, 143. Evens, L. S. and Lewin, K. F.: 1981, Environ. Exp. Bot. 21, 103. Evans, L. S., Lewin, K. F., Conway, C. A., and Patti, M. J.: 1981, New Phytol. 89, 459. Evans, L. S., Lewin, K. F., Patti, M. J., and Cunningham, E. A.: 1983, New Phytol. 93, 377. Evans, L. S., Lewin, K. F., Santucci, K. A., and Patti, M. J.: 1985, New Phytol. 100, 199. Irving, E M.: 1983, J. Environ. Qual. 12, 442. Irving, E M. and Miller, J. E.: 1981, J. Environ. Qual. 10, 473. Kohno, Y. and Kobayashi, T.: 1989, Watel, Air, and Soil Pollut. 43, 11. Moskowitz, E D., Medeiros, W. H., Oden, N. L., Thode, H. C., Jr., Coveney, E. A., Jacobson, J.

A., Rosenthal, R. E., Evans, L. S., and Allen, F. L.: 1985, Effects of Acid Deposition on Agricultural Production. BNL 51889, September, Brookhaven National Laboratory, Upton, NY, U.S.A.

NAPAP: 1988, Annual Report 1987 to the President and Congress, National Acid Precipitation Assessment Program, Office of the Director, 722 Jackson Place, NW, Washington, D. C. 20503, U.S.A.

Tamaki, M. and T. Hiraki: 1986, Kankyo Gijutu 15, 1.