Abbreviations used (in alphabetical order)

%Al/CECe: aluminum saturation of the effective cation exchange capacity

A: absorbance

AAS: atomic absorption spectroscopy

AF: alcoholic fermentation

ANOVA: analysis of variance

C: control

C1: contrast 1

C2: contrast 2

Cab: calcium concentration in blades

Caff: caffeic acid

Cag: calcium concentration in grape seeds

Cap: calcium concentration in petioles

Cat: (+)-catechin

CCE: calcium carbonate equivalent

CEC: cation exchange capacity

CECe: effective cation exchange capacity

CI: confidence interval

C.I.: color index

Cou: p-coumaric acid

Epi: (-)-epicatechin

Fer: trans-ferulic acid

Gall: gallic acid

GY: grape yield

ICP-AES: inductively coupled plasma atomic emission spectroscopy

Kb: potassium concentration in blades

Kg: potassium concentration in grape skins

Kp: potassium concentration in petioles

Malv: malvidin-3-O-glucoside

Mgb: magnesium concentration in blades

Mgg: magnesium concentration in grape seeds

Mgp: magnesium concentration in petioles

pH: real acidity

pH_KCl: pH in KCl 1N

pH_W: pH in water

Resv: trans-resveratrol

S: percentage of base saturation

SF: sugar foam

SOM: soil organic matter

SPE: solid phase extraction

ta: tartaric acid

TA: total acidity

TAnth: total anthocyanin content

Tc: tannin concentration

TPI: total polyphenol index

TSS: total soluble solids

W100: weight of 100 berries

Introduction

With an approximate land area affected by soil acidity of 4 billion ha, representing about 30% of the total ice-free land area of the world (Sumner and Noble, 2003), this edaphic characteristic is one of the most yield-limiting factors for crop production as a result of high Al³⁺ levels and low availability of basic ions in both surface and subsurface soil.

Liming is one of the main methods used by farmers to enhance the fertility of acid soils because it decreases the contents of exchangeable Al³⁺ through replacement with Ca²⁺ and Mg²⁺, and also the contents of soluble Al³⁺ by precipitation with the hydroxyl anions generated by carbonate hydrolysis in the soil solution. Additionally, liming has beneficial effects on soil structure since it improves soil structural stability (Lanyon, 2001; Hansen and Cass, 2002), and it plays a significant role in the control of certain plant pathogens (Havlin et al., 2014). The effectiveness of liming materials depends on (i) their neutralizing power, which is accounted for by their calcium carbonate equivalent (CCE), and (ii) their fineness (Edmeades and Ridley, 2003; Álvarez et al., 2009). However, soil has a huge buffering capacity that is able to diminish the effects of all kinds of amendments, and the soil acidification process is accelerated by factors such as acid rain and excess application of ammonium-based inorganic nitrogen fertilizers (Zheng, 2010).

Liming is usually performed before vineyard implantation, increasing the soil pH and cation exchange capacity (CEC) values (Joris et al., 2012). Appropriate soil liming after vineyard planting is a high-potential strategy to minimize the toxic effects of Al in established vineyards. However, some common liming materials, such as limestone (CaCO₃), used in agriculture to increase yield potential lose their effectiveness in vineyards established on acid soils due to the low solubility and mobility of carbonate in the soil profile, the liming effects being usually limited to the lime application/incorporation sites (Soratto and Crusciol, 2008). Among certain strategies used to ameliorate subsurface soil acidity, it can be cited the replacement of lime by the surface application of more soluble materials (Castro and Crusciol, 2013).

Dolomitic limestone and sugar foams are two materials often used for liming. Dolomitic limestone comprises mainly the mineral dolomite, which is made of a calcium and magnesium double carbonate (CaMg(CO₃)₂). Two important characteristics of this liming material are (i) its high neutralizing capacity, which is higher than that of limestone because of the lower atomic weight of magnesium compared to calcium, and (ii) its low dissolution rate, which is approximately 100-fold lower than that of calcite (Loeppert and Suarez, 1996). Sugar foams are sugar beet-manufacturing residues, which arise from the purification-flocculation of colloid matter in the beet extract by treatment with lime and carbon dioxide (Vidal et al., 2006). This industrial by-product can be used to correct soil acidity and Al phytotoxicity in acid soils because of its high content in active lime. In addition, this liming material contains abundant organic matter and several essential micronutrients (Vidal et al., 1997).

Although the application of sugar foams to the soil is a common practice used worldwide, especially in the last 20 or 30 years due to the improvements observed in some soil properties (Sikora and Azad, 1993), little is known about its effects on the quantity and quality of grapes cultivated on acid soils. Sugar foams may effectively counteract the symptoms of aluminum toxicity in plants, which brings about poor growth and low yields. Specifically, in old vineyards on acid soils, the root system ends abruptly at the depth where the pH value drops and the Al³⁺ concentration becomes relatively important (Meyer et al., 1984). In the same way, Cançado et al. (2009) reported that, as in many other plant species, the primary site and target of Al stress in grapevine rootstocks is confined to the actively growing root tip, revealed by a severe inhibition of root growth. Moreover, Kirchhof et al. (1991), in their research on Vitis vinifera cv. Chardonnay, showed how acidic soil conditions, mainly in the subsoil, depressed growth of vine root system. Finally, Wooldridge et al. (2010), on a mixture of cv. Pinot noir and Chardonnay with several rootstock vines cultivated on acid soils, found a more reduced root stress when compared to those cultivated on unlimed soils.

Although extensive research has been carried out on the effects of liming on the properties of acid soils, its effects on nutrient distribution in vine vegetative parts (leaf blades and petioles) and grape berries as well as on crop yield and must and wine quality are still not fully understood. So far the influence of soil liming on Ca, Mg and K contents in grape berries has not been investigated. This is an important knowledge gap because these elements remarkably affect grape juice quality and therefore the vinification process. In the present work, we analyzed the effects of adding two different lime amendments, i.e. dolomitic limestone and sugar foam, on (i) soil acidity, (ii) concentration ranges of Ca, Mg and K in leaf tissues, i.e. blades and petioles, and grape berries, (iii) grape yield and, finally, (iv) must and wine quality characteristics.

Materials and methods

1. Study site

A commercial vineyard located 556 meters above sea level in the municipality of Cacabelos (León; Spain; 42°36'N lat and 6°45'W long) was selected as the study site (Figure 1). From a climatic point of view, the grape growing region would be classified as Region I (≤ 1,390 Celsius degree-days) based on the classification system of Amerine and Winkler (Jackson, 2014). The mean reference evapotranspiration (FAO Penman-Monteith) and mean rainfall were, respectively, 922 and 616 mm yr^-1 for 2000-2011 (SIAR, 2012). From a bioclimatic point of view, the site would be classified as upper meso-Mediterranean based on the "thermotypes" classification and subhumid based on the "ombrotypes" classification (IGME, 1995). The soil under study corresponded to an Inceptisol, suborder Xerept, group Haploxerept according to Soil Survey Staff (2010). The parent material of the soils in the study area is made of Tertiary sediments (IGME, 1995). Accordingly, Fe oxyhydroxides are the most common clay minerals in the vineyard soils developed on these Tertiary sediments (Fernández-Calviño et al., 2009), from which calcium minerals are almost completely absent.

Figure 1. Map of the location of the research area (latitude and longitude are showed in Universal Transverse Mercator coordinates).

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2. Experimental treatmentsThe research was conducted on a 60-year-old Vitis vinifera L. cv. Mencía vineyard over three consecutive seasons (2009, 2010 and 2011), and the planting density was 4,166 (1.5 m × 1.6 m) plants per hectare. The plants had been grafted on Rupestris du Lot rootstock, which is considered as highly sensitive to soil acidity (Fráguas, 1999). Planting lines displayed a north-south orientation. The trellising system involved head training, with 4-5 arms per plant. Winter pruning left thumb-sized arms with two buds. The vineyard had no irrigation system. No fertilizers or extra amendments other than those used in this research were applied during the study period. The liming factor was applied at three levels (control (C), dolomitic limestone (DL) and sugar foam (SF)), with three replications per level. The study plot was split into nine 450-m² subplots. The treatment replications were distributed among the nine subplots in a completely random design.

Results

2. Soil properties

The time evolution of pH_W, Ca, Mg, K, Al and S levels for the treatment and control subplots throughout the three years of monitoring is shown in Figures 2 and 3. Apparently, there are some differences in performance efficiency between both liming materials. More specifically, sugar foam seemed to decrease Al levels more than dolomitic limestone.

Figure 2. Temporal evolution of pHW, Ca, Mg, K, Al and S over three years (2009-2011) after liming at 0-30 cm soil depth. Standard errors are shown as bars (± 1 SE mean). C: control; DL: dolomitic limestone; S: sugar foam.

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An ANOVA was used to investigate if the differences between liming treatments were statistically significant, and furthermore, if they depended on the soil depth, the year of sampling, and the interactions between both. According to the ANOVA, there was a significant effect (P<0.05) of liming in all soil properties (Table 3). By contrast, the effect of soil depth was not significant (P>0.05) in any of the soil properties. Additionally, the effect of liming did not significantly change with the soil depth, which was revealed by the non-significant interaction (P>0.05) between liming and soil depth factors (L x D). There was a significant effect (P<0.05) of year of sampling on exchangeable Ca and K levels. Even though the interactions between liming and year of sampling (L x Y), depth and year of sampling (D x Y), and all three factors (L x D x Y) were non-significant in all soil properties, Ca and K were studied as a function of year and liming, whereas pH_W, Mg, Al and S levels were studied as a function of just liming. To know if there were significant differences between liming materials, the “between groups” variance was split into two summands through two contrasts (Table 4).

Table 3. Factorial analysis of variance performed on soil properties at veraison stage.

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Factor	dfM	dfR	pHW		Ca		Mg		K		Al		S
			F	P-value	F	P-value	F	P-value	F	P-value	F	P-value	F	P-value
Liming (L)	2	36	13.9	***	12.3	***	6.25	**	3.77	*	14.9	***	12.4	***
Year (Y)	2		1.09	0.35	4.23	*	0.30	0.75	11.8	***	0.72	0.49	1.06	0.36
Depth (D)	1		0.09	0.76	0.11	0.74	0.06	0.82	1.27	0.27	0.28	0.60	0.03	0.87
L × Y	4		0.86	0.5	1.60	0.2	0.82	0.52	0.52	0.72	0.21	0.93	0.67	0.62
L × D	2		0.39	0.68	0.33	0.72	0.32	0.73	0.03	0.97	0.39	0.68	0.22	0.80
Y× D	2		0.3	0.74	0.23	0.8	0.16	0.85	0.39	0.68	0.11	0.9	0.13	0.88
L × D × Y	4		0.13	0.97	0.23	0.92	0.04	0.99	0.86	0.50	0.17	0.96	0.06	0.99

*significant at the P<0.05 level; **significant at the P<0.01 level; ***significant at the P<0.001 level; df_M, degrees of freedom of the model; df_R, degrees of freedom of the residuals of the model. pH_W, pH in water; S, percentage of bas saturation; Ca, Mg, K and Al (exchangeable Ca, Mg, K and Al, respectively).

Table 4. Effects and effect sizes of liming against control (C1), and liming with sugar foam against liming with dolomitic limestone (C2), on soil properties at veraison stage.

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Soil parameter	Factor	Contrast	Meand	dfR	t-ratio	P-value	r
pHW	L	C1	0.39	51	4.31	***	0.52
		C2	0.39	51	3.75	***	0.47
Ca (cmol(+) kg-1)	L in 2009	C1	0.26	15	1.29	0.22	#
		C2	0.64	15	2.71	*	0.35
	L in2010	C1	0.60	15	2.05	0.06	#
		C2	0.71	15	2.10	0.05	#
	L in 2011	C1	1.44	15	3.52	**	0.44
		C2	0.74	15	1.57	0.14	#
Mg (cmol(+) kg -1)	L	C1	0.30	51	3.46	**	0.44
		C2	0.19	51	1.89	0.07	#
K (cmol(+) kg-1)	L in 2009	C1	0.02	15	0.74	0.47	#
		C2	0.04	15	1.29	0.22	#
	L in 2010	C1	0.01	15	0.06	0.95	#
		C2	0.03	15	0.85	0.41	#
	L in 2011	C1	0.01	15	0.3	0.77	#
		C2	0.09	15	2.58	*	0.34
Al (cmol(+) kg-1)	L	C1	-0.60	51	-5.03	***	0.58
		C2	-0.49	51	-3.54	***	0.44
S (%)	L	C1	21.9	51	4.31	***	0.52
		C2	20.1	51	3.41	**	0.43

*significant at the P<0.05 level; **significant at the P<0.01 level; ***significant at the P<0.001 level. pH_W, pH in water; S, percentage of base saturation; Ca, Mg, K and Al (exchangeable Ca, Mg, K and Al, respectively); Mean_d (mean differences between control and amendments for contrast 1, and between sugar foam and dolomite for contrast 2); df_R (degrees of freedom for the residuals of the model); r (effect size).

The first contrast (C1) revealed that just liming significantly increased pH_W, S, Ca (in the year 2011) and Mg, and significantly decreased Al levels. The second contrast (C2) revealed that sugar foam significantly increased pH_W, S, Ca, and Mg, and decreased Al levels significantly more than dolomitic limestone. Specifically, at the end of the investigation, liming (C1) made the average Al levels decreased by 0.71 ± 0.26 cmol(+) kg^-1 (95% CI), whereas it made the average Ca and Mg levels increased by 1.44 ± 0.43 cmol(+) kg^-1 (95% CI) and 0.47 ± 0.16 cmol(+) kg^-1 (95% CI), respectively. These increments in both exchangeable cations (Ca and Mg), as well as the decrease in Al saturation caused by liming, were summed up by the increase in S. Specifically, at the end of the investigation, the average S level increase in limed subplots was 33.2 ± 11.9% (95% CI) compared to control subplots. Similarly, the different effect of the liming material sugar foam in comparison to dolomitic limestone (C2) was observed in pH_W and S, which increased by 0.52 ± 0.51 (95% CI) and 17.0 ± 16.4 (95% CI), respectively, and Al, which decreased by 0.57 ± 0.81 (95% CI). The inverse relationship between levels of Ca, Mg and S on the one hand and Al on the other can be observed in Figure 4.

Figure 4. Relationship between Ca, Mg, Al and S levels in soil as a function of just liming. Al in cmol(+) kg-1; S (percentage of base saturation) in %.

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3. Leaf nutrient contents

Means and standard errors of blade and petiole nutrient contents, arranged by liming material, are shown in Figure 5. ANOVA was used to determine if the slight differences between liming treatments were statistically significant, and furthermore, if they depended on the year of sampling and the interactions between these two factors. According to the ANOVA, there were no significant effects of the liming factor on any of the nutrient contents in both blades and petioles (Table 5). Interestingly, there was a significant effect (P<0.05) of year of sampling on Ca and Mg content in blades and petioles, as well as on K content in blades. Additionally, the interaction between liming and sampling year (L x Y) was non-significant (P>0.05) in all the nutrients evaluated.

Figure 5. Bar graphs of blade (Cab, Mgb and Kb) and petiole (Cap, Mgp and Kp) element composition at veraison (2009-2011). Average values are displayed within bar graphs. Standard errors are shown as bars (± 1 SE mean). The shaded areas in the graphs illustrate the concentration ranges that are optimal for adequate vine growth at veraison according to Fregoni (2005). C: control; DL: dolomitic limestone; SF: sugar foam.

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Table 5. Factorial analysis of variance performed on calcium, magnesium and potassium content in blades and petioles at veraison stage.

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Factor	dfM	dfR	Cab (%)		Mgb (%)		Kb (%)		Cap (%)		Mgp (%)		Kp (%)
			F	P-value	F	P-value	F	P-value	F	P-value	F	P-value	F	P-value
Liming (L)	2	18	1,31	0,29	0,20	0,82	1,86	0,18	0,49	0,62	0,79	0,47	0,02	0,98
Year (Y)	2		18,8	***	4,45	*	15,2	***	51,8	***	4,43	*	3,14	0,07
L × Y	4		0,18	0,95	0,14	0,97	0,55	0,7	0,31	0,87	0,13	0,97	0,66	0,63

*significant at the P<0.05 level; ***significant at the P<0.001 level; df_M, degrees of freedom of the model; df_R, degrees of freedom for the residuals of the model; Cab, Mgb and Kb (calcium, magnesium and potassium contents in blades respectively); Cap, Mgp, and Kp (calcium, magnesium and potassium contents in petioles, respectively).

4. Yield, must quality and grape nutrient contents

Means and standard errors of grape nutrient contents (Cag, Mgg and Kg), yield parameters (GY and W100) and must quality properties (pH, TA and TSS) in the treatment and control subplots are shown in Table 6.

Table 6. Means and stardand errors (SE) of yield parameters, must quality properties and grape nutrient contents at harvest time.

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Year	Amendment	GY (kg ha-1)		W100 (g)		pH		TA (g ta l-1)		TSS (ºBaumé)		Cag (%)		Mgg (%)		Kg (%)
		Mean	SE	Mean	SE	Mean	SE	Mean	SE	Mean	SE	Mean	SE	Mean	SE	Mean	SE
2009	C	6156	1211	226	14,8	3,45	0,08	5,50	0,19	12,9	0,07	0,22	0,02	0,14	0,00	2,40	0,44
	DL	6912	1560	214	13,0	3,47	0,05	5,35	0,48	12,9	0,33	0,24	0,03	0,15	0,01	1,77	0,15
	SF	7041	1863	229	6,66	3,45	0,02	5,73	0,15	13,0	0,00	0,28	0,01	0,15	0,01	1,81	0,20
2010	C	6409	1384	175	11,6	3,30	0,04	5,28	0,15	12,3	0,07	0,33	0,02	0,15	0,01	1,03	0,10
	DL	6985	1095	178	12,6	3,31	0,04	5,33	0,08	12,6	0,35	0,37	0,05	0,16	0,01	1,22	0,20
	SF	8234	1840	189	3,65	3,36	0,02	5,53	0,09	12,9	0,18	0,27	0,02	0,15	0,00	1,39	0,24
2011	C	4050	700	194	10,2	3,42	0,05	3,40	0,21	13,0	0,20	0,30	0,05	0,14	0,01	1,18	0,07
	DL	5155	753	203	7,47	3,41	0,00	3,90	0,13	13,0	0,12	0,31	0,03	0,16	0,01	0,98	0,15
	SF	5157	1555	202	10,5	3,38	0,01	5,04	0,42	12,7	0,18	0,25	0,01	0,15	0,01	1,18	0,06

GY (grape yield); W100 (weight of 100 berries); TA (total acidity expressed as the equivalent content of tartaric acid (ta) in g l^-1); TSS (total soluble solids); Cag, Mgg and Kg (calcium, magnesium and potassium contents in grapes, respectively).

According to the ANOVA, liming had no significant effects on any of the nutrient contents. Interestingly, there was a significant effect of year of sampling on Mgg (P<0.05) and Kg (P<0.001). The non-significant interaction between liming and sampling year (L x Y) (P<0.05) revealed that the effect of sampling year on grape nutrient contents did not change with liming. Additionally, there were no significant effects of the liming factor on any of the yield parameters and must quality properties except for TA (P<0.01). In the year 2011, both C1 and C2 were significant (P<0.05) in the above parameter. Interestingly, there was a significant effect of year of sampling on pH (P<0.01) as well as on W100 and TA (P<0.001). It is also interesting to note the absence of significant interactions (P>0.05) between liming and sampling year (L x Y). Although there are no significant differences with the control subplots in terms of productivity, an increasing trend in grape yields could be observed in limed subplots. Specifically, just liming with either sugar foam or dolomite limestone increased grape yields by nearly 30% at the end of the experiment (2011). These results might be important to farmers in economic terms.

Discussion

In the Haploxerept acid soil studied in this work, liming was effective in decreasing soil acidity, and specifically, sugar foam was more effective than dolomitic limestone. These results agree with those of García Navarro et al. (2009) who, in their assays on Anthrosols and Luvisols (FAO, 2006), reported that the application of sugar foam on dryland crops produced a positive impact on soil fertility through an increase in soil pH_W and exchangeable Ca contents. Additionally, although liming materials were incorporated with one-pass tillage at a soil depth of 20-30 cm, no significant differences in soil properties were found between the arable and the underlying soil layer (0-30 and 30-60 cm).

In spite of the higher CCE of dolomitic limestone compared to sugar foam, the latter was more efficient as liming material than the former. This remarkable higher efficiency of sugar foam over dolomitic limestone could be explained by the higher solubility of Ca(OH)₂ over CaMg(CO₃)₂, which is roughly three orders of magnitude higher. Similarly, the higher exchangeable Mg in soils limed with sugar foam compared to dolomitic limestone subplots could be explained by the higher solubility of Mg(OH)₂ compared to CaMg(CO₃)₂. These results agree with those of Augustin et al. (1997), who investigated the chemical reactions of magnesium fertilizers when they are applied to the soil, and suggested that magnesium fertilizers can be grouped into four classes according to their dissolution rates: MgSO₄ > MgO ≈ Mg(OH)₂ > slag lime ≈ dolomitic limestone ≈ magnesite > basalt. These results differ from the previous findings of Vidal et al. (2006) in their comparative study of several liming materials (sugar foam, dolomitic lime, calcium carbonate and gypsum) developed from acid soils under laboratory conditions. The latter authors, based on the results for the leachate properties, reported that limed soils with dolomitic limestone showed significantly more exchangeable Mg than those treated with sugar foam. This indicates the need for caution when comparing data derived from laboratory and field studies.

Although chemical soil analysis indicates the potential availability of some nutrients that vine roots may take up, leaf analysis is often the most reliable method of assessing vine nutritional status. Moreover, because the vine integrates the variability in the soil explored by its roots, leaf analysis is often the basis of the fertilizer recommendation programs for vines. However, in the present study, data from soil testing and leaf analysis have indicated that there is no clear relationship between them. Although blades have higher sensitivity to detect individual macronutrient deficiencies or excesses (Romero et al., 2014), results in blade nutritional diagnosis also have not provided any further evidence supporting any significant effect of liming on tissue cation composition at veraison.

Assuming that liming did not significantly increase yield grape, an increasing trend has been found in limed subplots. The increase sequence in yield data (C˂DL˂SF) is consistent with those obtained for Ca and Mg data (C˂DL˂SF), as well as for Al data (C˃DL˃SF). In view of the foregoing considerations, soil liming may be advisable close to the vine root system. However, in many established vineyards the use of lime could be difficult as a result of the existence of trellis systems.

Although soils that are rich in Ca promote the accumulation of sugar (Jiang and Zhang, 2012), the findings of the current study did not show any significant increase in this parameter. Despite the fact that liming did not cause significant differences in yield quality properties, it is interesting to note that TA decreased more in control than in limed subplots (particularly during the last two years) (Figure 7), and more when sugar foam was used. A possible explanation for these results may be related to the grape K content, which, when excessive, may decrease must TA resulting in an increase in must pH (Conde et al., 2007). The higher K content in leaf tissues showed by limed subplots (although not significant) does not seem to be in agreement with a reduction in K uptake in limed soils. However, this issue could originate from the combined effect of rainfall during the annual vegetative cycle and liming. Thus, Chatonnet (2005) reported that late rainfall close to harvest leads to fast K uptake by vine roots, which drops must TA without necessarily affecting must pH. In 2011, an abnormal rainy August (34.6 mm) and rainfall (8.2 mm) ten days before harvest occurred. Although these conditions are similar to those reported by Chatonnet, no significant differences in Kg were found in this research and several questions remain unanswered.

Figure 7. Monthly rainfall (top) and differences in total acidity (TA) between control and limed subplots (bottom), during the period of investigation. Dashed lines correspond to months of harvest (Sp: September).

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As reported by Yokotsuka et al. (1999), the addition of limestone to the native soil significantly influenced both tannin concentration and color parameters in Mencía wines in every vintage of the experiment; however, there was a weak consistency in the trends observed. This, together with the results obtained in blades and petioles as well as in grapes and yield, suggests that the specific physiological characteristics of the combination of rootstock and scion, along with marked nutrient storage in the woody parts of the vine, make assessing grapevine responses to amendment application particularly challenging (Jackson, 2014; Olego and Garzón, 2014). However, since soil chemistry is an important factor in terroir, vine nutrition can be instrumental to the specific growth pattern of the vine and thus cause a specific canopy architecture and therefore a ripening pattern (Goode, 2013).

Wine quality is the result of a complex set of interactions (terroir effect), which include soil variables. With respect to the vine’s productive system, soil and climate represent the two physical elements fundamental to understand the concept of terroir (van Leeuwen and Seguin, 2006); compared to climate, soil is an even more complex system. Thus, the impact of the pedologic environment on wine quality is difficult to analyze singularly and separately from the rest of the productive system (Seguin, 1986). Accordingly, it is difficult to study the effects of soils that have been artificially modified to improve yield on grape and wine composition, because the soil influences hydro and mineral nutrition and the functioning of the root system. Although phenolic compounds are heavily influenced by the vintage, soil type, mesoclimate and cultural practices (Nadal, 2010), as for the measurements of tannin concentration and color parameters, no definite trends (with consistency before and after wine ageing) in phenolic compounds have been found in the present study as a consequence of liming. Caution must be taken in interpreting the influence of soil amendments on phenolic compounds, as climatic differences between vintages added uncertainty to their interpretation. Additionally, phenolic compounds in wines varied between seasons, regardless of variations in winemaking practices (i.e. different age in the French oak barrels used per vintage) which also could affect wine composition (Cohen and Kennedy, 2010). However, although the composition of wine is heavily dependent on the winemaking technique (Cortell et al., 2008), understanding the impacts of soil types on the phenolic compounds in grapes and wines is necessary for developing an effective viticulture management program (Li et al., 2011).

Conclusion

As expected, liming with either sugar foam or dolomitic limestone decreased soil exchangeable aluminum, improved supply of calcium and magnesium, and increased soil pH and base saturation in acid Haploxerept cultivated with Vitis vinifera L. cv. Mencía. However, sugar foam behaved as a more efficient liming material than dolomitic limestone. This fact may be explained by the higher solubility of sugar foam calcium and magnesium components in the soil. The reduced efficiency of dolomitic limestone might be partly offset by a greater durability.

Although the increasing trend in grape yield with liming, more pronounced with sugar foam than with dolomitic limestone, was not significant, this might have an important economic impact. Finally, no significant trends in properties related to must and wine quality were found. Maybe more evident trends in these must and wine properties would have appeared using higher liming doses or extending the monitoring span to more years. Further research needs to examine more closely the impact of the changes in soil composition on wine quality.

Acknowledgements : This work was funded by the “Excelentísima Diputación Provincial de León”. We are specially grateful to “Losada Vinos de Finca, S.A.” for assistance in the research project.

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