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Agriculture Ecosystems an d Enviro nme nt 47 ( t 993 ) 117-134 117Elsevier Science Publishers B.V., Ams terdam

o i l s o l u t i o n r e s p o n s e t o a c i d i c d e p o s i t i o n i n an o r t h e rn h a r d w o o d f o re s t

L . E . R u s t a d * ,a , I .J . F e r n a n d e z a , R . D . F u l l e rb , M . B . D a v i d c , S .C . N o d v i n d,W . A . alteman eaDepartment of Plant Soil and Environme ntal Science University of Maine Orono M E 04469 USAbCenter or Earth and Environmental Science SUN Y-Plattsburgh Plattsburgh N Y 12901 USACDepartment of Forestry University of Illinois Urbana IL 61801 USAaNational Park Service-Cooperative Park Studies Unit Forestry Wildlife and FisheriesUniversity of Tennessee Knoxville TN 37901 USAeDepartment of Mathematics Universi ty of Maine Orono M E 04469 USA

b s t r a c t

An intensive plot-scale acidification experiment evaluated the effects of H2SO4, HNO3, and com-bined H2SO4 and HNO3 treatments on the chemistry of soils and soil solutions in a northern hard-wood forest. Treatments were delivered to 18 plots (each of 15 m 15 m, three plots per treatment)during 20-week field seasons by a hill-slope irrigation system and consisted of two levels of H2SO4( ~ 2000 and 4000 eq ha - 1year- 1 , two levels of HNO3 ( ~ 2000 and 4000 eq ha - ~year- ~ , one levelof combined H2SO4/HNO3 ( ~ 2000 eq ha-t year-~ each of SO2- and NO3- ), and a control (wateronly).Soil solutions responded rapidly to all treatments with increased leaching of SO2- and/or NO~-(depending on treatment) accompanied by increased leaching of Ca 2+ and Mg2+ from the upper Bhorizon. As solutions passed through the upper 25 cm of soil, mean SO~- concentrat ions decreasedby 50--86% of ini tial values in all S treatments and mean NO~- concentrations decreased by 71-93%of ini tial values in the low nitrogen treatments. This reflected the importance of anion adsorption forSO2- and biological immobil ization for NO~- in these forested Spodosols. Mean NO~- concentra-tions, however, remained constant with depth in the high ni trogen treatment, suggesting that this highrate of NO~- input exceeded the p lant /soi l capacity to immobilize N. During the autumn and winterfollowing the treatment period, soil solution SO~- and NO~- concentrations were greater for treatedsoils than for those o f the control for 2-7 months. This suggests that anion desorption from soil ex-change sites occurred in response to lowered soil solution concentrat ions of these strong acid anions.

I n t r o d u c t i o nO v e r t h e l a s t t w o d e c a d e s t h e r e h a s b e e n c o n s i d e r a b l e c o n c e r n t h a t a c i d i cd e p o s i t i o n m a y d e c r e a s e t h e p r o d u c t i v i t y o f f o re s t so i l s. S t u d i e s h a v e s h o w n

t h a t a t m o s p h e r i c d e p o s i t i o n o f s tr o n g a c i d s c a n in c r e a s e b a s e c a t i o n l e a c h i n ga n d t h e m o b i l i z a t i o n o f to x i c m e t a l s e .g . A P ) , d e c r e a s e s o il p H a n d b a s es a t u r a ti o n , c h a n g e m i n e r a l w e a t h e r i n g ra t es , a n d a l t er so i l b i o l o g y N a t i o n a l*Corresponding author.

1993 Elsevier Science Publisher s B.V. All fights reserved 0167 -880 9/93 / 06.00

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1 18 L.E. Rustad et al./Agriculture, Ecosystems and Environment 47 1993) 117-134

Acid Precipitation Assessment Program, 1987; Fernandez, 1989). In addi-tion, changes in the chemistry of soil solutions, such as elevated levels of strongacid anions, H + and A1n+, may have adverse impacts on the chemistry andbiology of associated surface waters (Goldstein et al., 1984).Investigations into the complex interactions between atmospheric deposi-tion, forest soils, and surface waters have been limited because of the long-term nature of forest ecosystem development, the hypothesized subtle butchronic effects o f acidic deposition, and the high heterogeneity of forest soils.Ideally, long-term, highly replicated studies of the response of whole ecosys-tems to ambient levels of acidic deposition should be used to evaluate theeffects of elevated strong acid additions to forested ecosystems. An alterna-tive is to experimentally manipulate whole ecosystems or ecosystem compo-nents with acid additions to simulate altered deposition scenarios.The External Plot Experiment (EPE) of the Watershed Manipulation Proj-ect (WMP) is a multiple-year study designed to evaluate dose-response re-

lationships for HzSO4 and HNO additions to soils at the Bear Brook Wa-tershed in Maine (BBWM), and to assess the biogeochemical mechanismscontrolling these responses. The objective of this paper is to report on theresponse of soil solutions to the first year and a half of chemical manipulation.e thods

Site descriptionThe EPE study site is located in eastern Maine (4451 '55 N, 686'25W) approximately 50 km from the Atlantic Ocean. It is on the southeast-facing slope of Lead Mountain, approximately 100 m due east of the BBWMcatchments. The vegetation is dominated by America beech Fagus grandi-folia Ehrb. ) (approximately 40 years old ) with a small component of yellowbirch Betu la alleghaniensis Britt.), sugar maple Acer saccharum Marsh. ),red maple Acer rubrum L. ), and red spruce Picea rubens Sarg. ). Spodosolsoils are coarse-loamy, mixed, frigid Typic Haplorthods formed from com-pact basal till (David et al., 1990), and the bedrock is primarily metamor-phosed quartzites and calc-silicates with granitic intrusions.

Experimen tal designIn the spring of 1987, six 15 mX 15 m plots were established within theexperimental area on each of three elevational contours (245, 260 and 275m) , making a total of 18 plots of 225 m 2 each. Each plot was surrounded by a1 m treated buffer strip to avoid edge effects. The plots on the same contourwere situated 15 m apart with approximately 30 m between contours (Fig.1 ). Six treatments were randomly assigned to one plot on each of the three

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L.E. Rustad et aL /Agriculture, Ecosystems and Environment 47 1993) 117-134 1 19

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L . E . R u s t a d e t al . /A g r i c u l tu r e , E c o s y s t e m s a n d E n v i r o n m e n t 4 7 1 9 93 .) 1 1 7 - 1 3 4 2

rrigation systemT h e i r r i g a t io n s y s t e m t h a t d e l i v e r e d tr e a t m e n t s o l u t i o n s t o t h e p l o t s c o n -s i s t ed of :( 1 ) a w a t e r s u pp l y s ys t em ;( 2 ) a w a t e r s t o ra g e s y s t e m n e a r t h e w a t e r s u p p ly ;( 3 ) a p u m p t o t r a n s f e r w a t e r fr o m l o w e r s t o ra g e t a n k s t o u p p e r d o s i n g a n df l u s h i ng t anks ;( 4 ) u p p e r d o s i n g a n d f l u s h i n g t a n k s ;( 5 ) p r e s s u r e r e g u la t o r s a n d p a r t i a l c i rc l e s p r ay n o z z l e s a t t h e f o u r c o m e r so f each p l o t ;( 6 ) c a l c i u m c a r b o n a t e n e u t r a l i z a t io n b e d s ( F ig . 1 ) .T h e w a t e r s u p p l y s y s te m i s b a s e d o n a s u b s u rf a c e w a t e r i n t e r c e p t i o n s y s t e ma d j a c e n t t o B e a r B r o o k . W a t e r d r a i n s b y g r a v i t y f r o m t h i s s y s t e m i n t o f o u r

8 0 0 0 1 s to r a g e t a n k s a n d i s p u m p e d u p s l o p e ( a b o u t 6 0 v e r t ic a l m ) t h r o u g hP V C p i p e s ( 7 .5 m i n d i a m e t e r ) t o s i x 4 0 0 0 1 d o s i n g t a n k s a n d s i x 1 5 0 0 1f l u s h in g t a n k s . T h e t r e a t m e n t a c i d s ar e a d d e d t o t h e d o s i n g t a n k s w h e n t h e ya r e a b o u t 2 0 f u ll , a n d m i x i n g is a c h i e v e d b y t h e a g i ta t i o n o f f il li n g t h e t a n k s.T r e a t m e n t s o l u t io n s a r e d e l i v e r e d t o t h e p l o t s b y g r a v it y t h r o u g h a s y s t e m o fs ix p o l y e t h y l e n e p i p e s ( 5 c m i n d i a m e t e r ) , e a c h l e a d i n g to o n e p l o t o n e a c ho f t h r e e r o w s o n t h e b a s i s o f t r e a t m e n t t y p e . T h e e n d s o f t h e s e p i p e s h a v ec h e c k v a l v e s b e l o w t h e p l o t n e t w o r k to a l l o w t h e l i n e s t o b e d r a i n e d t h r o u g hc a l c i u m c a r b o n a t e n e u t r a l i z a t i o n b e d s . S o l u t i o n s a r e a p p l i e d t o e a c h p l o tt h r o u g h f o u r 9 0 a r c s p r a y n o d e s l o c a t e d a t t h e f o u r c o m e r s o f e a c h p l o t.P r e s s u r e r e g u l a to r s , i n l i n e w i t h e a c h o f th e n o z z l e s, e n s u r e t h a t e a c h n o z z l ede l i ve r s s o l u t i ons a t t he s am e r a t e .S p r i n k l e r a p p l i c a t i o n u n i f o r m i t y w a s t e s t e d e x t e n s i v e l y b e f o r e a c i d t r e a t -m e n t s b e g a n a n d e v a l u a t e d u s i n g a c o e f f i c ie n t o f u n i f o r m i t y ( C h r i s t i a n s e n ,1 9 4 2 ) . T h e m e a n ( + S D ) c o e f f i c ie n t o f u n i f o r m i t y f o r t h e p l o t s w a s 6 7 _+ 6 ,w i t h a ra n g e f r o m 5 7 to 7 4 . T h i s c o m p a r e s w i t h t h e m e a n c o e f f i c i e n t o fu n i f o r m i t y f o r a m b i e n t t h r o u g h f al l ( t e s te d o n t h r e e o f t h e p l o t s ) , w h i c h w a s75 ___ 10. 7 , wi t h a r ange o f 63 . 1 - 83 . 9 . T hes e eva l u a t i ons i nd i c a t ed t ha t t heu n i f o r m i t y o f a p p l i c a t i o n f o r t h e s p r i n k le r s w a s r o u g h l y s i m i l a r t o t h a t o f a m -b i en t t h r oughf a l l .Trea tme nt appl ications

P r i o r t o a c i d a d d i t io n s , 1 .6 m m d e p t h o f u n t r e a t e d w a t e r w a s a p p li e d to t h ep l o t s t o w e t t h e v e g e t a t i o n a n d s o i l su r fa c e s. T h e p l o t s w e r e t h e n i r r i g a t e dw i t h 4 . 3 m m o f t re a t m e n t s o l u ti o n . I n th e i n i t ia l t r e a t m e n t s e a so n ( 1 9 8 8 ) ,w e e k l y t r e a t m e n t a p p l i c a t i o n s b e g a n o n 2 5 J u l y a n d c o n t i n u e d u n t i l 1 0 O c -t o b e r; i n t h e s e c o n d t r e a t m e n t s e as o n ( 1 9 8 9 ) , t r e a t m e n t s b e g a n o n 2 4 M a y

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122 L.E. Rusta d e t al . /Agriculture , Ecosystems an d Environment 47 1993) 117-134and continued until 2 October Table 1 ). Target loads and concentrationswere decreased in 1989 to make the experiment more comparable with theadjacent whole watershed manipulation Erickson et al., 1990). Treatmentresults from an additional two years of treatment 1990 and 1991 ) and asubsequent recovery period 1993) will be discussed in a later paper. Thecumulative increase in hydrologic flux to the plots was 4.7 cm in 1988 and9 6 cm in 1989 against a background throughfall hydrologic flux of about 90cm year- 1.So il solution collections an d an alyses

This paper reports on soil solutions collected from the autumn of 1987 toMay 1990. Soil solutions were collected on a 2-4 week schedule. Volumeswere measured in the field, and samples were bulked by lysimeter type, plot,and depth for chemical analyses.Within 7 days of collection, pH and acid neutralization capacity ANC)were measured and subsamples were filtered through a 0.4/~m filter for anal-ysis of cations, anions, Si, and NHg, and through a 0.7 gm glass-fiber filterfor dissolved organic carbon DOC) . Aliquots for cations, Si, and DOC wereacidified prior to analysis, and anion aliquots were stored at 4 C. Table 2 liststhe procedures for sample analysis. Standard quality assurance procedureswere followed for all analyses as detailed in the citations in the Methods sec-tion Table 2).Statistical analyses

All data were tested for normality using a Kolomogorov test Conover,1980). Data that did not fit a normal distribution were transformed loga-T a b l e 2Soi l so lu t ion ana ly t ica l me th odsP a r a m e t e r D e s c r i p t i o n R e f e re n c epH Poten t iom et r ic H i l lm an e t a l ., 1985A N C A u t o m a t e d t i t r a t io n H i U m a n e t a l ., 1 9 85w i t h G r a n P l o tBase ca t ions H a me a tom ic absor p t ion H i l lm an e t a l ., 1985( Ca , Mg, K , N a ) spec t r oscopyA l u m i n u m F u r n a c e a t o m i c H i l l m a n e t a l ., 1 9 85a b s o r p t i o n s p e c t ro s c o p yA n i o n s( SO4, N O 3, C ) I on chr om atogr aphyA m m o n i u m A u t o m a t e d c o l o ri m e t ryS i A u t o m a t e d c o l o r i m e t r yD O C L i b e r a t i o n o f C O e a n d I Rd e t e r m i n a t i o n

HiUm an et a l ., 1985A nonymous , 1986aA nonymous , 1986bA m er ican Publ ic H ea l th A ssoc ia t ion , 1981

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L . E . R u s t ad e t a l. / A gr i c u l t ure , E c osy s t e m s and E n v i ronm e n t 47 I 993) I 17 - 134 2 3

r i thm ical ly an d re tes ted for norm al i ty . In a l l cases , the log ar i thm ic t ransfor -m a t i o n w a s f o u n d t o b e a d e q u a t e t o a p p r o x i m a t e a n o r m a l d i s t ri b u t i o n , a n da l l subsequen t s t a t i s ti ca l ana lyses were pe r formed on the t r ans formed da ta .T rea tme nt e f fec ts were eva lua ted us ing ana lys i s o f va riance . The R yan -E i -no t -Gabr ie l -Welsch mul t ip le F t e s t was used to pe r form mean sepa ra t ionsbecause i t appea r s to be the mo s t pow er fu l s t ep-down m ul t ip le - stage te s t inthe l it e r a tu r e Ram sey , 1978) , and i t i s a l so compa t ib le wi th the ove ra l lAN OVA F te st , in tha t i t r e jec t s the nu l l hypothes i s when the F t e s t does soSta t is t ica l An alys is Sys tems Ins t i tute SAS ) , 1985 ) . Dif ferences between thetwo f i e ld seasons by lys ime te r type , dep th , an d t r ea tm ent were inves t iga tedby m eans o f a s t andard t -t e st , and co r r e la tion ana lyses were used to eva lua tere la t ionships among soi l solut ion parameters . Al l s ta t is t ica l analyses wereper form ed us ing procedu res of SAS 1985 ) .esults and discussion

r e t r e a tme n t s o i l s o lu tio n c h e m is t r yIn the upper so i l so lu t ions i .e . t ens ion Bhs hor izon, zero- tens ion O hor i -zon ) , C a 2+ was the do min ant ca t ion in so lu t ion and SO4 - was the dom inan tan io n on a cha rge equ iva len t bas i s Tab le 3 ) . A pproxim at ions o f o rgan ic an-ions , based on D OC concen t r a t ions and e lec t roneu t r a l ity de fic it s , sugges tedtha t DO C was a l so imp or tan t in sur f ace hor izons . I n the low er so i l so lu t ionsi .e. Bh hor izo n) , the dom inan t ca t ion in so lu t ion was N a + , and SO4 - andC1- were the dom inan t an ions .Al though so lu t ions co l lec ted f rom both lys ime te r types showed s imi la rchem ica l tr ends , c lea r d if f e rences ex i s ted be tween the t ens ion and ze ro- ten-s ion lys imeters . Zero- tens ion ly s imeter solut ions were cons is tent ly more ac idicand mo re h igh ly co lored , had h ighe r SO 2- and low er S i concen t r a t ions , andwere genera l ly mo re var iable tha n tens ion lys imeter solut ions Table 3) . Th esedif ferences can be a t t r ib uted to the fac t tha t soi l solut ions col lec ted by zero-tens ion lys ime te r s cons i s ted p r imar i ly o f macropore f low which , a f t e r pas s ingthrough organ ic hor izons , had r e la t ive ly b r ie f con tac t wi th the mine ra l so i lma t r ix . So i l so lu t ions co l lec ted by t ens ion lys ime te r s may co ns i s t o f a g r ea te rpropo r t ion of mic ropore f low, which shou ld have a longer t ime to equ i l ib r a te

with the minera l soi l Sw is tock e t a l. , 1990) . Because the overa l l chem icalt r ends obse rved in the ze ro- tens ion lys ime te r so lu t ions were s imi la r to thosein the t ens ion ly s ime te r so lu tions , the r em ain ing d i scuss ion i s r e s tr i c ted totens ion lys ime te r so lu t ion r e su l ts .I n the p r e t r ea tme nt da ta , the wi th in- t r ea tm ent va r iab i l i ty a s soc ia ted wi thdif ferences amon g plots was ge nera l ly as large , or larger , tha n th e am ong-t r ea tme nt va r iab i l i ty , which r e su l ted in f ew s ign i f i can t p r e t r ea tme nt d i ff e r-

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124 L.E. Rus tad et al. /Agriculture, Ecosystems an d Environment 47 1993) 117-134Table 3Pretreatment soil solution chemistry for tension and zero-tension lysimeters. Coefficients of variationgiven in parentheses. Sample numbers range from 40 to 107

Tension lysimeter solutions Zero-tension ysimeter solutionsU p p e r d e p t hH 13 (392) 40 (102)Ca 79 (37) 200 (63)Mg 32 (35) 99 (69)K 18 (70) 53 (87)Na 70 (33) 57 (53)NH4 3 (190) 5 (222)AI 17 (68) 25 (49)Si 132 (28) 94 (64)SO4 74 (31) 272 (73)NO3 7 (180) 9 (188)CI 61 (74) 58 (71)ANC 17 (113) -22 (388)DOC 802 (66) 2272 (78)L o w e r d e p t hH 1 (99) 17 (104)Ca 77 (27) 74 (36)Mg 30 (20 40 (31)K 10 (40) 10 (92)Na 91 (22) 94 (25)NH, 2 (116) 3 (351)AI 5 (102) 16 (69)Si 112 (32) 62 (31)SO4 101 (22) 150 (32)NO3 8 (133) 7 (235)CI 62 (43) 79 (36)ANC 24 (68) -1 1 (234)DOC 249 (104) 304 (205)Units are tool 1-1 for AI and Si, gmol C 1-1 for DOC, and geq 1-1 for all other parameters.

e n c e s a m o n g t h e t r e a t m e n t s . D i f f e r e n c e s o b s e r v e d a m o n g t r e a t m e n t s a f t e ri n i t i a t i o n o f a c i d a d d i t i o n s w e r e t h e r e f o r e a t t r ib u t e d t o t r e a t m e n t e ff e c ts .

Soi l solut ion response to acid manipu lat ions

verview o f responseS o il s o l u t io n c h e m i c a l p ro p e r t i es s h o w e d c l e a r a n d r a p i d r e s p o n se s t o t r e a tm e n t s . I n th e u p p e r l y si m e t e r s o l u t io n s c o n c e n t r a t io n s o f b o t h S O 2 - a n dN O ~ - i n c r e a s e d r e l a t i v e t o t h o s e i n t h e c o n t r o l f o r a l l S a n d N t r e a t m e n t s

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L.E. Rusta d e t al . / Agriculture , Ecosys tems and Env ironment 47 1993) 117-134 25

respectively (Table 4). As solutions passed through the upper 25 cm of thepedons, mean SO 2- concentrations decreased significantly by 50-86 of ini-tial values. Mean NO~- concentrations decreased significantly with depth inthe LN and NS treatments (by 71-93 of initial values) but remained vir-tually constant with depth in the HN treatments. The decreasing concentra-tions of SO2- with depth may be attributed to the adsorption of SO2- by thesoil exchange complex. This trend is consistent with the increase in soil-ad-sorbed SO 2- observed in the upper solum using buried soil bags (David etal., 1990). The decreasing concentrations of NO~- with depth as observed inthe LN and NS treatments reflect the importance of biological immobiliza-tion for NO~-. The constant NO~- with depth observed in the HN treatment,however, indicates that this high rate of NO~- input exceeds the capability ofthe so il/plant system to assimilate the added N.In 1988, SO42- concentrations were depressed in the HN treatment at bothdepths; in 1989, SO 2- concentrations were depressed in the HN treatmentonly at the lower depth (Table 4; Figs. 2 (a) and 2 (b )) . This trend is consis-tent with the hypothesis that high HNO3 loadings decrease soil solution pHand increase positive charge on oxide surfaces, thereby increasing soil anionexchange capacity and SO2- retention. The increase in positive surface chargemay have been greater during the 1988 field season when treatment solutionconcentrations were 1.7 times greater than those applied in the 1989 fieldseason (Table 1 ). A similar loss of soil solution SO 2- and stream SO2-(Nodvin et al., 1986, 1988; Fuller et al., 1987) in response to nitrification-induced acidification was observed following wo clearcutting experiments atthe Hubbard Brook Experimental Forest, NH.Increased concentrations of strong acid anions in solution due to treat-ments were generally accompanied by elevated concentrations of H +, A1n 4,and base cations (Table 4). Of these cations, Ca 2 and Mg2 showed themost consistent response to the treatments (Table 4; Fig. 2). They were alsothe cations most strongly correlated to the strong acid anions (Table 5). Theseresults suggest that the mineral acidity in soil solutions associated with thetreatments was neutralized primarily by cation exchange processes which weredominated by the exchange of H + for Ca 2 and Mg2.These results are consistent with those reported by David et al. ( 1991 ) andFernandez and Rustad (1990) who showed that Ca 2 and Mg2 were thedominant counter-ions for experimental additions of SO 2- and NO~-. Theyare also consistent with those of David et al. (1990), who showed significantincreases in exchangeable Ca 2 and Mg2 in soil bags bur ied below the forestfloor in the HS plots of the experiment reported here. They attributed thisincrease in exchangeable Ca 2+ and Mg2 to a release of these cations fromthe forest floor to soil solution during the initial stages of acidification withsubsequent adsorption in the mineral soil below.Perhaps a more integrated approach to examining the ionic composition of

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F i g . 2 . T e m p o r a l tr e n d s i n m e a n c o n c e n t r a t i o n s o f: a ) S O ~ - i n u p p er t e n s i o n l y s i m e t e r s o l u-t i o n s; b ) S O 2 - i n l o w e r t e n s i o n l y s im e t e r s o i l s o l u t io n s ; c ) N O ~ - i n u p p e r t e n s i o n ly s i m e t e rs o l u ti o n s ; d ) N O i n l o w e r t e n s i o n l y s im e t e r s o il s o l u ti o n s ; e ) C a 2 + i n u p p e r te n s i o n ly s i-m e t e r s o l u ti o n s ; f ) C a 2 + i n l o w e r t e n s io n l y s i m e t e r s o i l so l u ti o n s ; g ) M g 2 + i n u p p e r t e n s i o nl y s i m e t e r s o l u t i o n s ; h ) M g 2 + i n l o w e r t e n s i o n l y s i m e t e r s o i l s o l u t i o n s ; i ) K + in u p p e r t e n s i o n

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l y s i m e t e r s o l u ti o n s ; ( j ) K + i n l o w e r t e n s i o n l y s i m e t e r s o i l s o l u ti o n s ; ( k ) N a + i n u p p e r t e n s i o nl y s i m e t e r s o l u ti o n s ; ( 1 ) N a + i n l o w e r t e n s i o n l y s i m e t e r s o i l s o l u t io n s ; ( m ) H + i n u p p e r t e n s io nl y s i m e t e r so l u t io n s ; ( n ) H + in l o w e r t e n s i o n l y s i m e t e r s o il s o l u t io n s ; ( o ) A I + i n u p p e r t e n s i o nl y s i m e t e r s o lu t i o n s ; ( p ) A I + i n l o w e r t e n s i o n l y s i m e t e r s o i l s o l u t io n s . T r e a t m e n t p e r i o d s a r ei n d i c a t e d b y a r r o w s . T h e l e g e n d i s a s f o l l o w s : . , c o n t r o l ; I , H N ; * , H s ; [ ~ , L N ; , L S ; ~ , N S .

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130 L . E . R us t ad e t a l. / A gr ic u lt ure , E c osy s t e m s and E nv i ronm e n t 47 1993) 117- 134Table 5Pearson s correlation coefficients for SO4 and NO3 by tr eatment type

Control Sulfur treatment s Nitrogen treatments504 NO3 504 NO3 504 NO3

H - 0.41 - 0.46 0.69 - 0.07 - 0.24 0.50Ca 0.21 0.60 0.93 0.31 - 0.32 0.69Mg - 0.08 0.34 0.94 0.18 - 0.35 0.71K 0.20 -0.0 1 0.28 -0. 01 -0. 11 0.38Na 0.54 0.28 0.31 0.05 0.27 -0 .1 0NH4 0.03 0.15 0.19 0.11 -0 .2 3 0.27AI - 0.38 - 0.40 0.79 - 0.06 - 0.14 0.50Si - 0.16 - 0.06 0.56 0.27 0.03 0.15SO4 - - 0.06 - 0.17 - - 0.60N O 3 0.06 - 0.16 - -0 .6 0 -CI 0.06 0.11 0.02 0.20 0.35 0.27AN C 0.27 0.20 - 0.70 0.03 0.18 - 0.49DOC -0 .4 4 -0 .1 8 0.57 0.10 0.16 0.05Vol ume 0.21 0.49 - 0.36 - 0.11 - 0.06 - 0.11Correl ation coefficients indica ted in bold are significant at the 0.0001 level.

so lu t ions is th rough the r e la tive mag ni tude of minera l bases CB; Na + , K ,M g 2+, Ca 2+ ) vs . m inera l ac ids CA ; SO42- , NO ~- , C 1-) . I f CB CA is posi-t ive , then ne t minera l base ex i s t s in so lu t ion , and /or an a l t e rna te an ion i ssuppor t ing hydrogen ion concen t r a t ions e .g . o rgan ic ligands , HCO~- ) . I fC B - CA i s nega t ive , then m inera l ac ids a r e suppor t ing hydrogen ion Bakere t al ., 1990) . I n con t ro l p lo t s , CB -CA was pos i t ive bo th yea r s , in upper an dlower lys ime te r so lu t ions Table 4 ) , ind ica t ing the p r esence of ne t minera lbase . I n the HS and HN p lo t s , CB-CA was dr iven nega t ive a t bo th dep ths ,ind ica t ing the p r esence of ne t m inera l ac id due to the s t rong ac id add i t ion .

Temporal trendsAnalys i s o f t emp ora l t r ends in so i l so lu t ion chemica l r e sponse F ig . 2 )s h o w e d t h a t b o t h S O 2 - a n d N O ~ - c o n c e n t r a ti o n s r e s p o n d e d i m m e d i a t e ly tot r ea tmen ts and con t inu ed to inc r ease th rough out the t r ea tme nt pe r iod F igs .2 a ) -2 d ) ) . Fo l lowing the t e rmina t ion o f t r ea tments , excess SO~- r e ta inedby so i ls dur ing t r ea tm ent was r e leased back to so i l so lu tions . For the LS t rea t -ments , equ i l ib r ium w i th am bien t SO 2- depos i t ion was apparen t ly ach ievedwi th in a few months . F or the HS t r ea tments , i t appear s tha t SO 2- desorp t ionwas ex tens ive enough to p r even t a r e tu rn to s teady s ta te condi t ions be fore ther enewed in i t i a t io n of t r ea tments . I n con t r as t , NO~- concen t r a t ions qu ick lyre turn ed to contro l levels because these soi ls hav e l i t t le to n o cap aci ty to ad-sorb th i s an ion , an d the l im i ted r e ten t ion in cap i l l a ry so il so lu tions i s qu ick ly

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L.E. Rusta d et al. /Agriculture, Ecosystems and Environment 47 1993) 117-134 3

f lushed f rom the p edon . Com par i sons o f the r e sponse o f upper so i l so lu t ionswi th lower so i l so lu t ions fo r SO 2- showed a sma l le r , more g r adua l inc r easein SO 2- concen t r a t ions a t the lower dep th , w hich i s ind ica t ive o f su l f a te r e-t en t ion occur r ing in the so lum above . So i l so lu t ion ca t ion concen t r a t ions ,pa r t i cu la r ly Ca 2+ an d Mg 2+ , c lose ly pa r a l l e led an ion concen t r a t ions in o rde rto m a in ta in e lec tr i cal neu t r a l i ty (F igs . 2 ( e ) -2 (p ) ) .1988 v s 19 89Although so i l so lu t ion chemica l t rends were s imi la r in bo th the 1988 and1989 f i e ld seasons, m ean concen t r a t ions o f mos t m a jor so i l so lu t ion cons t it -uen t s were lower in 1989 tha n in 1988 (Tab le 4 ; F ig . 2 ) . T h is may be a t t r ib -u ted to the fo l lowing: ( a ) t r ea tment concen t r a t ions were dec reased by 14-49 in 1989 (Table 1 ) ; ( b ) p ro ton a t ion of ox ide sur faces ma y have occurr eddur ing the 1988 f i e ld season , r e su l t ing in a g r ea te r r e ten t ion of SO 2- andNO~- a nd a r educed leach ing of ca t ions in the 1989 f i e ld season ; and /o r ( c )

the inc r eased ava i lab i l i ty o f NO~- , and to a l e sse r ex ten t SO 2 - , in the l a t t e rha l f o f the 1988 growing season may h ave s t imula ted b io log ica l ac t iv i ty andthe re fore inc r eased ne t up tak e of nu t r i en t s in the 1989 growing season . Thefac t tha t l i tt e r fa l l , a ind ica tor o f p roduc t iv i ty , was g r ea te r in 1989 than in1988 (K. Nade lhof f e r , pe rsona l comm unica t ion , 1990) , suppor t s th i s l a t t e rhypothes i s .Variabi l i ty in responseIn te rpre t ing the r e sponse o f so il so lu t ions to exper ime nta l manip u la t ionscan be d i f f icu l t g iven the inhe ren t va r iab i l i ty in fo r est so i l s and so i l so lu t ions(D av id an d Ger tn er , 1987; D av id e t a l ., 1990; Swis tock e t a l ., 1990 ) , and the

a r t i f i c ia l va r iab i l i ty induced by sampl ing t echn iques (Barbee and Brown,1986; Li taor , 1988) . In th is s tudy, soi l solut ion v ar iabi l i ty was genera l ly greaterin the ze ro- tens ion lys ime te r s than in the t ens ion lys ime te r s and in the u pperlys ime te r s than in the lower lys ime te r s (Tab le 3 ) . O f the ind iv idu a l so il so-lu t ion co ns t i tuen t s measured , va r iab i l i ty was cons i s ten t ly h ighes t f o r AN C,N O , a n d N H + a n d l o w e s t f o r N a + , C l - , a n d S i ( T a b l e s 3 a n d 4 ) .Desp i te the h igh degree o f va r iab i l i ty a s soc ia ted w i th lys ime te r so lu tions ,t r ea tm ent e f fec ts cou ld be de tec ted , and were genera l ly cons i s ten t ac ross thethr ee p lo t s pe r t r ea tmen t a s i l lus t r a ted in F ig . 3 ( a ) . An excep t ion was N O ~concen t r a t ions in the H N t r ea tment , in which two of the p lo ts (A2 an d C 1 )showed a c lea r r e sponse to the t r ea tmen ts in bo th 1988 and 1989 , whereas theth i rd p lo t (B1) r e sponded to the t r ea tments in 1988 bu t show ed li t t le re -sponse in 1989 (F ig . 3 ( b) ) . Di f f e rences in r esponse ma y be a t t r ibu ted to :n o n - u n i f o r m i t y o f t r e a t m e n t s o l u ti o n a p p l i c at i o n , m a c r o p o re c h a n n e l i n g o ft r ea tm ent so lu t ions away f rom in d iv idu a l lysime te r s, and d i f fe r ences in thephys ica l , chemica l , and b io log ical p roper t i e s o f the so i l su r rounding the ind i -v idua l lys ime te rs .

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L.E . Ru sted et el . /Agr icu l tur e Ecosystems and En v i ronm ent 47 1993) 117- 134

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R e s u l t s f r o m a p e r i o d o f 1 .5 y e a rs o f s t ro n g a c i d a d d i t i o n s u n d e r f i e ld c o n -d i t i o n s i n d i c a t e t h a t e x p e r im e n t a l m a n i p u l a t i o n w i t h d i f f er e n t le v e ls o f H 2 S O 4a n d H N O 3 r e su l te d in in c r e a se d le a c h i n g o f S O ~ - a n d N O 3 - a c c o m p a n i e d b ya i n c r e a s e d l o s s o f b a s e c a t i o n s a n d A I 3 + f r o m t h e u p p e r s o l u m . S o i l s o l u t i o nc h e m i c a l c o m p o s i t i o n r e s p o n d e d r a p i d ly t o t r e a tm e n t s , a n d s o l u t i o n c o n c e n -t r a t io n s r e m a i n e d e l e v a t e d a b o v e c o n t r o l c o n c e n t r a t i o n s f o l l o w i n g t h e te r-m i n a t i o n o f t r ea t m e n t s f o r 2 - 7 m o n t h s , i n d i c a ti n g th a t a n i o n s s o rb e d o n t o

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L.E. Ru stad e t al . /Agriculture , Ecosys tems a nd Env ironm ent 4 7 199 3) 117-134 133exchange s it e s dur ing the t r ea tm ent pe r iod w ere desorbed back in to so lu t iondur ing r ecovery . The mu l t ip le -yea r na tur e o f th i s s tudy i s in ten ded to fu r the reva lua te the im por tance of so i l p rocesses wi th s lower k ine t i c s, inc lud ing Ncyc l ing and the incorpo ra t ion of S in to o rgan ic so i l poo ls. L ikewise , the p oor lyunder s tood long- te rm dyna mics o f r ecovery wi l l be ex amined .cknowledgmentsThe au thor s would l ike to acknowledge the cons ide rab le con t r ibu t ion ofW a r r e n H e d s t r o m i n t h e d e s i g n a n d i m p l e m e n t a t i o n o f th e i r r ig a t i o n s ys te m ,the e f fort s o f Be t ty Lee in p r epa ra t ion of the m anusc r ip t , an d the sup por t o fthe f i e ld and lab ora tory c r ews who he lped mak e th i s r e sea r ch poss ib le . Th isr esea rch was conduc ted th roug h the suppo r t o f the US E nvi ron me nta l P ro tec -t ion Agency . Al though the r e sea r ch desc r ibed in th i s a r t i c le has been fundedby the US Envi ronmenta l P ro tec t ion Agency , i t has no t been sub jec t to the

EPA s po l icy rev iew a nd the r e fore does no t neces sa r ily r e flec t the v iews of theAgency.

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