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Influence of cover crop on water use and performance of vineyard in Mediterranean Portugal
Agriculture, Ecosystems and Environment 121 (2007) 336–342 www.elsevier.com/locate/agee
Influence of cover crop on water use and performance of vineyard in Mediterranean Portugal Ana Monteiro *, Carlos M. Lopes Instituto Superior de Agronomia, Universidade Tecnica de Lisboa, Tapada da Ajuda, 1349-017 Lisboa, Portugal Received 8 May 2006; received in revised form 14 November 2006; accepted 16 November 2006 Available online 28 December 2006
Abstract Grapevine yield, vigour, fruit quality and vineyard dynamics were studied in the Estremadura Region of Portugal with a Mediterranean oceanic bioclimate. A 3-year study was carried out in a 15-year-old ‘Cabernet Sauvignon’ non-irrigated vineyard. Three treatments were compared: soil tillage (control), permanent resident vegetation, and permanent sown cover crop. The sward treatments induced changes in the weed dynamics by increasing annual and perennial grasses and perennial broad-leaved species, while annual broad-leaved species spread and persisted under a tillage system. Compared to soil tillage, the two sward treatments showed a higher water use, primarily during the spring. In the third season of the experiment, compared to cultivation treatment the two sward treatments showed a significant, favourable reduction in vine vegetative growth. The sward treatments did not affect grapevine yield or berry sugar accumulation compared to the control, but reduced must acidity and increased berry skin total phenols and anthocyanins. # 2006 Elsevier B.V. All rights reserved. Keywords: Grapevine; Soil tillage; Cover crops; Flora; Growth; Yield; Berry composition
1. Introduction Vineyard cover cropping is widely used in the world’s winegrowing regions, mainly in areas with summer rainfall or with irrigation. Cover crop information abounds and many functions are well known—e.g. prevention of erosion, easier mechanisation, ground cover, diminution of ground pressure and improvement of soil structure (Folorunso et al., 1992; Geoffrion, 1999, 2000). Nutrient competition, mainly from grass cover crops (e.g. a reduction in the nitrate in the soil), can induce a low level of must nitrogen content (Le Golf-Guillou et al., 2000; Maigre and Aerny, 2001). Furthermore, especially in the case of permanent covers, plant species diversity has been found to be higher (Gut et al., 1997). In deep soils and high vigour situations living green ground covers can be an advantage, because the increase in water consumption can induce a reduction in grapevine * Corresponding author. Tel.: +351 213 653 162; fax: +351 213 635 031. E-mail address: [email protected] (A. Monteiro). 0167-8809/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.agee.2006.11.016
vegetative growth and consequently an improvement in both the fruit zone microclimate and grape and wine quality (Pacheco et al., 1991; Agulhon, 1996; Geoffrion, 1999). In areas of low summer rainfall and high evaporative demand, as is the case with some non-irrigated vineyards in Portugal, cover cropping can be disadvantageous if the competition for water leads to severe vine water stress and consequently to negative effects on growth, yield and berry quality (Williams and Matthews, 1990). The objectives of the present study were to determine the influence of permanent green cover on flora dynamics, water use, grapevine vigour, yield and berry composition in a nonirrigated vineyard growing in a Mediterranean climate.
2. Materials and methods The experiment was set up in 2002 at Quinta de Pancas, Alenquer (Estremadura Winegrowing Region), Central Portugal (lat. 398010 N; long. 98060 E), in a sloping vineyard (7%) that had been under cultivation since establishment.
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The soil was a sandy clay loam with the following average characteristics: clay 24.3%; silt 20.2%; sand 55.5%; organic matter 0.7%; pH 8.4. The total soil available water, up to 1.0 m depth, was 182 mm, calculated as the difference between field capacity and the lower limit of water uptake, reached on the permanent sown cover crop at the end of the season of the driest year (2003), before the first rainfall. The weather data was recorded by an automatic weather station (Pulsiane, Pulsonic1, Orsay, France) located within the experimental vineyard. Data were collected in a commercial 15-year-old ‘Cabernet Sauvignon’ (Vitis vinifera L.) vineyard, grafted on 110 R rootstock. The vineyard had a planting density of 4000 vines per hectare, spaced 1.0 m within and 2.5 m between east-west oriented rows. Vines were trained on a vertical shoot positioning with a pair of movable wires, and spur-pruned on a bilateral Royat Cordon system. Shoots were trimmed twice, between bloom and veraison, at a height of about 1.0 m. The experimental design was a randomized complete block with three treatments and four replications per treatment. Each replicate (plot) had four rows with 100 vines each, and all the grapevine measurements were made in the two central ones. The three treatments were: (1) soil tillage between rows (ST); (2) permanent resident vegetation cover between row (RV); (3) permanent sown cover crop between row (SCC); 50 kg ha1, with a mixture of 60% grasses (Lolium perenne L. ‘Nui’, L. multiflorum Lam. ‘Bartı´ssimo’, Festuca ovina L. ‘Ridu’, F. rubra ssp. rubra ‘Echo’) and 40% legumes (Trifolium incarnatum L. ‘Red’, T. repens L. ‘Huie’ and T. subterraneum L. ‘Claire’), sown in March 2002. In all the treatments a 0.8 m-wide herbicide strip was achieved beneath the vines allowing a width of the planter of about 1.7 m. A single application, just before budbreak, of the foliage herbicide 1800 g a.i. ha1 glyphosate (ROUNDUP 3601, Monsanto) was done. The herbicide was sprayed using a motorized knapsack, with one APG 110 V Albuz1 flat-fan nozzle delivering 500 l ha1 at 200 kPa. With the exception of soil management, fertilization, vine pest and disease control and other cultivation practices, including grapevine canopy management were similar in all treatments. For fertilization 39 kg ha1 of N and P and 63 kg ha1 of K were supplied evenly over the surface of the soil every 2 years, at the beginning of March. Conventional soil tillage treatment included vegetation mowing in the first week of February – a common operation that aims to shred vine prunings – and a soil cultivation with a spading machine in spring (budbreak) and a rotary tiller in summer (end June) to incorporate the vegetation into the soil. In the two cover cropping treatments the vegetation was mowed by a flail mower twice a year, namely before vine budbreak (first week of February) and at vine flowering (end of May or first week of June), to a height of 10–15 cm.
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2.1. Assessments and data analysis Vegetation above-ground biomass was periodically assessed from March until September. Shoots from each species were harvested by cutting plants at soil surface level inside four randomized 0.5 m2 areas per plot (16 samples per treatment). Dry matter per species was recorded. Plant species from the survey carried out at the end of April were grouped according to annual grass species, annual broad-leaved species, perennial grass species and perennial broad-leaved species. Species biomass values were complemented by a relative biomass value for each species, using the method described by Derksen et al. (1993) and Streit et al. (2003), but applied to species biomass instead of species density. Soil water content was monitored using a capacitance probe (Diviner 20001; Sentek Environmental Technologies, King Town, Australia). Three access tubes per plot (12 per treatment) were placed along the row between two contiguous vines. Readings were taken periodically between budbreak and harvest, at increments of 0.1 m from soil surface to a depth of 1.0 m. At harvest a sample of 200 berries per plot was collected and weighed and the juice was analyzed for pH, soluble solids (8Brix), determined by refractometry, and titratable acidity by titration with NaOH (OIV, 1990). Total phenols were determined by spectrophotometry, measuring ultraviolet absorption at 280 nm (IFT), and berry skin anthocyanins were measured using the sodium bisulphite discoloration method (Ribe´reau-Gayon et al., 1972). The harvest from 40 previously selected vines per treatment (10 per plot) was monitored by recording the number of clusters and their total weight per vine. At winter shoot number and fresh pruning weight per vine were also recorded. ANOVA were carried out in accordance with GLM procedures, from the SAS1 program package (SAS Institute, Cary, NC, USA).
3. Results During the experimental period (2002–2004) the mean air temperature ranged between 10 8C (the mean minimum monthly temperature in January 2003) and 23.6 8C (the mean maximum monthly temperature in August 2003), and the mean total annual rainfall was 885.3, 941.8 and 564.4 mm, in 2002, 2003 and 2004, respectively. At the end of April 2002–2004 the vegetation biomass in the soil tillage treatment (ST) was 137, 538 and 92 g m2, respectively. This was similar to the other two treatments. During the 3-year study, in ST the annual broad-leaved species comprised the majority of the plant species surveyed, but some perennial broad-leaved species were also present. The grasses, annuals and perennials scarcely grew in ST (Table 1). In April 2002 a total of 29 species were surveyed in ST, where three families were dominant:
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Table 1 Effect of soil management strategies on spring (April 2004) plant relative biomass (%) 3 years after experiment set-up Plant groups
Relative biomass (0–100) ST
Annual grass species Annual broad-leaved species Perennial grass species Perennial broad-leaved species Other monocotyledons
2.2 87.5 0.0 10.2 0.1
RV b a c b a
15.2 49.1 10.2 25.4 0.1
SCC a b b a a
16.1 36.3 40.8 6.8 0.0
a b a b a
ST: soil tillage; RV: resident vegetation; SCC: sown cover crop. In each row different letter suffixes show statistically significant differences at P < 0.05 by LSD test.
Oxalidaceae (52% of the total biomass), with a single species Oxalis pes-caprae L.; Geraniaceae and Asteraceae. In April 2003 and 2004, in the ST treatment the number of species did not change, but Medicago polymorpha L. showed the highest biomass, followed by the Geraniaceae species. When it came to the permanent resident vegetation (RV) the number of species surveyed was similar to ST, but the proportion of each plant group changed annually, with the grasses being favoured by the mowing. Total biomass was also dominated by the Fabaceae M. polymorpha. In the permanent sown cover (SCC) sown Poaceae and Fabaceae dominated, with six species from each family. The shoot biomass of the perennial grasses increased from 5% in 2002 to 45% in 2004 of the total above-ground biomass. Significant changes in the relative biomass of the plant groups between treatments were registered in 2004 (Table 1). The annual grass species increased their presence in the sward treatments, with values that were statistically similar for the two of them, but higher than for the ST. The increase in this plant group in RV was due to the presence of Avena sterilis L. (from the vineyard seed bank), and in SCC
to the sown species L. multiflorum. In the ST treatment plant community composition was dominated by annual broadleaved species, with a significantly higher relative biomass than RV and SCC. In the permanent sown cover crop the perennial grass species, which were dominated by L. perenne, showed a significantly higher relative biomass than ST and RV. The sown species of Fabaceae and Festuca spp. presented a poor germination rate and a weak growth, which seems to indicate that they were not well adapted to the vineyard environment and conditions. The perennial broadleaved species increased their presence and dominance in RV, with a significantly higher relative biomass than the other two treatments, which returned similar values. Veronica anagallis-arvensis L., Rumex cripus L., Lavatera spp., Picris echioides L. and Arisarum vulgare O. Targ. Tozz were the dominant species. The total vegetation biomass evolution pattern was similar for the three seasons. In the sward treatments the amount of above-ground biomass increased in the spring and the mowing at the end of May induced a strong and similar reduction in vegetation, which was unable to recover until harvest. The sown and resident species stopped growing or even dried out during the summer, thus creating dead mulch. In ST, after the first cultivation (ca. 1 month after budbreak) the soil was kept almost bare until harvest. Any plant that was able to germinate or re-grow was destroyed by the second cultivation in the middle of June. 3.1. Water use The seasonal pattern of volumetric soil moisture in the 0–1.0 m profile for the second and third season of the experiment showed a decreasing trend throughout the growing season in all the three treatments (Fig. 1). At the first measurement at the beginning of the season all the treatments presented similar soil moisture values. As the season progressed, while the two sward treatments
Fig. 1. Effect of soil management strategies on volumetric soil moisture (0–1.0 m) measured in situ during 2003 (A) and 2004 (B) growing seasons. Each point represents the mean and standard error of the measurements made on 12 access tubes. Vegetation mowing: first week of February and at the end of May; soil cultivation: budbreak and at the end of June.
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showed similar values of volumetric soil water content, ST presented higher values. These differences increased from late spring to mid summer and then stabilised until the end of the season. This pattern was similar to that observed in 2002 (data not shown), except for the end of the season when extraordinarily high amounts of rainfall in September (175 mm) induced a rapid recovery of the soil moisture to the spring values right across the profile. In order to estimate the daily average water used, the amount of rainfall and the water depletion in the first 1.0 m of soil were calculated for the three main vine growth periods of the 2003 and 2004 seasons (Table 2). Between budbreak and bloom in both seasons ST presented a significantly lower daily water use than the two sward treatments, which returned similar values. Between bloom and veraison (June to the beginning of August) the three treatments presented statistically similar values for water use. During the ripening period (August to the end of September) in 2004 the two sward treatments presented similar daily water use values, but both were significantly lower than that of the ST treatment. A similar trend was observed in 2003, but it was not statistically significant. The total water use during the entire growing season was higher in 2003 than in 2004, but no significant differences were observed among treatments (Table 2). The water used was not uniformly extracted from all the soil layers, as can be seen from the example of the 2004 soil water depletion curves (Fig. 2). During the spring, while the two sward treatments show an extraction of water which, albeit more intense in the upper layers, spans the entire profile, ST presents a significant lower extraction from both upper (0–0.50 m deep) and deep layers (0.50–1.0 m deep), where almost no water was extracted (between 0.80 and 1.0 m deep). Between bloom and veraison the three treatments extracted water uniformly from all the soil layers. During the berry ripening period, while the ST depletion curves show an almost uniform water extraction from all soil layers, the two sward treatment depletion curves show a significant increase in volumetric soil moisture in the upper layers (0–0.50 m).
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3.2. Vegetative growth and yield The effect of soil management strategies on vine vegetative growth was evaluated using the winter pruning weight, which increased from 2002 to 2004 in all treatments, but with a lower rate for the two sward treatments when compared to ST. No significant differences were observed in the shoot number per vine. In the first year of the experiment all the treatments presented similar values for pruning and shoot weight, but in the last year a significant vegetative growth reduction was observed in the RV (0.78 kg vine1) and SCC (0.75 kg vine1) treatments, compared to the ST (0.95 kg vine1). The same trend was observed in the 2003 season, although the values were not statistically significant at the 0.05 level. In this experiment no significant differences were observed in either grapevine yield (average of 2.9 kg vine1) or juice soluble solids (average of 22.08 Brix) and pH (average of 3.35) in any of the three seasons. However, in 2003 and 2004 the ST treatment presented significantly higher must titratable acidity and lower berry skin total phenols and anthocyanin content than the two sward treatments, each of which returned statistically similar values. For example in 2004 the titratable acidity was 8.05, 6.69 and 7.20 g tartaric acid l1 and skin anthocyanin content was 1027.0, 1269.0 and 1182.3 mg l1, respectively, for ST, RV and SCC.
4. Discussion Results of this 3-year study of soil management systems indicate that annual broad-leaved species spread and persist under tillage systems. These results match those of other studies (Derksen et al., 1993; Ba`rberi and Lo Cascio, 2001; Felix and Owen, 2004). Most of the annual and perennial broad-leaved species surveyed in the ST treatment did not appear in the SCC treatment, which suggests that the sown species – mainly the dominant L. perenne – were capable of competing with any potential weed and were quite adaptable to the local environmental conditions. The programmed number and time of the mowing seemed to improve and enhance cover crop establishment and performance.
Table 2 Effect of soil management strategies on estimated average water usea over the three main grapevine growth periods during 2003 and 2004 seasons Daily water use (mm day1) Budbreak–bloom
Total water use (mm) Bloom–veraison
Veraison–harvest
2003
2004
2003
2004
2003
ST RV SCC
2.85 b 3.25 a 3.17 a
1.58 b 2.05 a 2.15 a
1.30 a 1.12 a 1.33 a
0.95 a 0.85 a 0.96 a
0.74 a 0.58 a 0.67 a
Rainfall
187.8
33.2
13.4
0.8
11.6
Budbreak–harvest 2004 1.18 a 0.83 b 0.87 b 45.6
2003
2004
357.1 a 371.7 a 382.6 a
221.8 a 226.0 a 240.9 a
212.8
79.6
ST: soil tillage; RV: resident vegetation; SCC: sown cover crop. In each column different letter suffixes show statistically significant differences at P < 0.05 by LSD test. a Data obtained from the sum of the rainfall with soil water depletion from 0 to 1.0 m soil depth, assuming the absence of runoff, deep percolation and capillary rise of groundwater.
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Fig. 2. Soil water depletion curves measured in situ on four grapevine phenological phases of the 2004 growing season in the three treatments. Each point represents the mean of the measurements made on 12 access tubes. ST: soil tillage; RV: resident vegetation; SCC: sown cover crop.
Permanent resident vegetation induced the spread of some perennial broad-leaved species because they could regrow after mowing—a trait that can be considered negative, as some of these weeds are very competitive with vines for nutrients and water (Gulick et al., 1994; Lopes et al., 2004). Nevertheless, the RV treatment had a positive effect on flora diversity in that it induced the presence of some Fabaceae (M. polymorpha) and Poaceae annual species (A. sterilis)
and decreased most of the annual broad-leaved species, such as some Geraniaceae and Asteraceae. When compared to soil tillage, the sward treatments were effective in reducing soil water content during the spring. The almost complete water depletion in the upper layers that was observed in the sward treatments at bloom time may have induced both the death of the vine roots in the upper layers and the development of a deeper root system in order to explore moist layers, as reported by Morlat and Jacquet (2003). This hypothesis is sustained by the shape of the ST depletion curves during the berry ripening period, which shows an almost uniform water extraction from all the soil layers, unlike the sward treatments, in which no water was extracted from the upper layers (0–30 cm). The higher water use during berry ripening in the ST treatment can be attributed to the greater evapotranspiration caused by both the greater availability of soil water and the probably higher soil evaporation that is to be expected from bare soil. In the sward treatments the significant increase in the volumetric soil moisture in the upper layers from veraison to harvest shows that water use was lower than the contribution made by rainfall. This indicates either a reduced root system in those layers, and/or lower soil evaporation caused by the mulch effect of cover cropping residues. The additional water consumption during spring (ca. 0.5 mm d1) presented by the sward treatments compared to the ST is within the range of those reported by Bo¨ll (1967) and Griebel (1996). The total water use for the entire season showed no significant differences between treatments. Nevertheless, the percentage of the total water use of the swards to soil tillage in 2003 and 2004 was 4 and 7% and 2 and 9% higher in RV and SCC, respectively. However, these differences should be looked at with care, because the extrapolation of water depletion from the 1.0 m soil depth assumes that no water was lost by runoff and/or deep percolation, and that no water was extracted from deeper soil layers other than the 1.0 m depth. Prichard et al. (1989) found that when ‘Blando’ brome was grown in a Central Californian orchard and used as mulch throughout the summer, seasonal water use equalled that of bare soil. By contrast, in Germany Griebel (1996) estimated a 35% increase in the vineyard evapotranspiration rate due to a mixed stand, compared to clean cultivation between budbreak and bloom. These differences in vine water use can primarily affect vine growth if the water stress occurs earlier on (Williams and Matthews, 1990), as was the case in 2004. Indeed, only in the last year of the experiment were we able to detect a significant reduction in pruning weight in the sward treatments, compared to ST. Several authors (Morlat et al., 1993; Caspari et al., 1997; Geoffrion, 2000; Maigre and Aerny, 2001; Afonso et al., 2003) have already reported this effect of sward treatments on grapevine growth as a consequence of cover crop competition for water. This growth reduction can be
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beneficial to grape health and berry composition, especially in high vigour situations, as it induces a more favourable balance between vegetative and reproductive growth, and allows a more open canopy and consequently a better microclimate in the cluster zone (Dokoozlian and Kliewer, 1996). The individual shoot weight – one of the best indicators of vine vigour (Champagnol, 1984) – obtained in the sward treatments at the end of the third season of the experiment, is still within the optimal vigour and vine balance range (20–40 g fresh weight per shoot; Smart et al., 1990). The absence of significant effects of the soil management strategies on grapevine yield components during all three seasons can mainly be attributed to the higher soil waterholding capacity of this terroir and the low additional water consumption by the cover cropping systems. The effects of the cover crops on berry composition, which were detected in the titratable acidity and skin total phenols and anthocyanin content, can be explained by the indirect effects of the mild water stress on vegetative growth reduction. The consequent reduction in the competition between vegetative and reproductive growth and lower canopy density can increase cluster exposure, which in turn reduces titratable acidity and improves fruit colour and anthocyanin concentrations in red grape varieties (Dokoozlian and Kliewer, 1996; Keller and Hrazdina, 1998; Spayd et al., 2002). The two sward treatments presented a similar behaviour, thereby enabling us to conclude that the resident vegetation is the best choice for a cover crop, as it does not need to be sown. Acknowledgements This study was supported by the Portuguese Ministry of Agriculture and Rural and Fisheries Development, AGRO Program, Action 8 (2002), Project no. 104—Viticultural technology for optimising grape quality: soil and canopy management. We thank Nuno Fernandes, Joa˜o Pedro Machado and Ama´lia Arau´jo for their excellent technical assistance.
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Influence of cover crop on water use and performance of vineyard in Mediterranean Portugal Ana Monteiro *, Carlos M. Lopes Instituto Superior de Agronomia, Universidade Tecnica de Lisboa, Tapada da Ajuda, 1349-017 Lisboa, Portugal Received 8 May 2006; received in revised form 14 November 2006; accepted 16 November 2006 Available online 28 December 2006
Abstract Grapevine yield, vigour, fruit quality and vineyard dynamics were studied in the Estremadura Region of Portugal with a Mediterranean oceanic bioclimate. A 3-year study was carried out in a 15-year-old ‘Cabernet Sauvignon’ non-irrigated vineyard. Three treatments were compared: soil tillage (control), permanent resident vegetation, and permanent sown cover crop. The sward treatments induced changes in the weed dynamics by increasing annual and perennial grasses and perennial broad-leaved species, while annual broad-leaved species spread and persisted under a tillage system. Compared to soil tillage, the two sward treatments showed a higher water use, primarily during the spring. In the third season of the experiment, compared to cultivation treatment the two sward treatments showed a significant, favourable reduction in vine vegetative growth. The sward treatments did not affect grapevine yield or berry sugar accumulation compared to the control, but reduced must acidity and increased berry skin total phenols and anthocyanins. # 2006 Elsevier B.V. All rights reserved. Keywords: Grapevine; Soil tillage; Cover crops; Flora; Growth; Yield; Berry composition
1. Introduction Vineyard cover cropping is widely used in the world’s winegrowing regions, mainly in areas with summer rainfall or with irrigation. Cover crop information abounds and many functions are well known—e.g. prevention of erosion, easier mechanisation, ground cover, diminution of ground pressure and improvement of soil structure (Folorunso et al., 1992; Geoffrion, 1999, 2000). Nutrient competition, mainly from grass cover crops (e.g. a reduction in the nitrate in the soil), can induce a low level of must nitrogen content (Le Golf-Guillou et al., 2000; Maigre and Aerny, 2001). Furthermore, especially in the case of permanent covers, plant species diversity has been found to be higher (Gut et al., 1997). In deep soils and high vigour situations living green ground covers can be an advantage, because the increase in water consumption can induce a reduction in grapevine * Corresponding author. Tel.: +351 213 653 162; fax: +351 213 635 031. E-mail address: [email protected] (A. Monteiro). 0167-8809/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.agee.2006.11.016
vegetative growth and consequently an improvement in both the fruit zone microclimate and grape and wine quality (Pacheco et al., 1991; Agulhon, 1996; Geoffrion, 1999). In areas of low summer rainfall and high evaporative demand, as is the case with some non-irrigated vineyards in Portugal, cover cropping can be disadvantageous if the competition for water leads to severe vine water stress and consequently to negative effects on growth, yield and berry quality (Williams and Matthews, 1990). The objectives of the present study were to determine the influence of permanent green cover on flora dynamics, water use, grapevine vigour, yield and berry composition in a nonirrigated vineyard growing in a Mediterranean climate.
2. Materials and methods The experiment was set up in 2002 at Quinta de Pancas, Alenquer (Estremadura Winegrowing Region), Central Portugal (lat. 398010 N; long. 98060 E), in a sloping vineyard (7%) that had been under cultivation since establishment.
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The soil was a sandy clay loam with the following average characteristics: clay 24.3%; silt 20.2%; sand 55.5%; organic matter 0.7%; pH 8.4. The total soil available water, up to 1.0 m depth, was 182 mm, calculated as the difference between field capacity and the lower limit of water uptake, reached on the permanent sown cover crop at the end of the season of the driest year (2003), before the first rainfall. The weather data was recorded by an automatic weather station (Pulsiane, Pulsonic1, Orsay, France) located within the experimental vineyard. Data were collected in a commercial 15-year-old ‘Cabernet Sauvignon’ (Vitis vinifera L.) vineyard, grafted on 110 R rootstock. The vineyard had a planting density of 4000 vines per hectare, spaced 1.0 m within and 2.5 m between east-west oriented rows. Vines were trained on a vertical shoot positioning with a pair of movable wires, and spur-pruned on a bilateral Royat Cordon system. Shoots were trimmed twice, between bloom and veraison, at a height of about 1.0 m. The experimental design was a randomized complete block with three treatments and four replications per treatment. Each replicate (plot) had four rows with 100 vines each, and all the grapevine measurements were made in the two central ones. The three treatments were: (1) soil tillage between rows (ST); (2) permanent resident vegetation cover between row (RV); (3) permanent sown cover crop between row (SCC); 50 kg ha1, with a mixture of 60% grasses (Lolium perenne L. ‘Nui’, L. multiflorum Lam. ‘Bartı´ssimo’, Festuca ovina L. ‘Ridu’, F. rubra ssp. rubra ‘Echo’) and 40% legumes (Trifolium incarnatum L. ‘Red’, T. repens L. ‘Huie’ and T. subterraneum L. ‘Claire’), sown in March 2002. In all the treatments a 0.8 m-wide herbicide strip was achieved beneath the vines allowing a width of the planter of about 1.7 m. A single application, just before budbreak, of the foliage herbicide 1800 g a.i. ha1 glyphosate (ROUNDUP 3601, Monsanto) was done. The herbicide was sprayed using a motorized knapsack, with one APG 110 V Albuz1 flat-fan nozzle delivering 500 l ha1 at 200 kPa. With the exception of soil management, fertilization, vine pest and disease control and other cultivation practices, including grapevine canopy management were similar in all treatments. For fertilization 39 kg ha1 of N and P and 63 kg ha1 of K were supplied evenly over the surface of the soil every 2 years, at the beginning of March. Conventional soil tillage treatment included vegetation mowing in the first week of February – a common operation that aims to shred vine prunings – and a soil cultivation with a spading machine in spring (budbreak) and a rotary tiller in summer (end June) to incorporate the vegetation into the soil. In the two cover cropping treatments the vegetation was mowed by a flail mower twice a year, namely before vine budbreak (first week of February) and at vine flowering (end of May or first week of June), to a height of 10–15 cm.
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2.1. Assessments and data analysis Vegetation above-ground biomass was periodically assessed from March until September. Shoots from each species were harvested by cutting plants at soil surface level inside four randomized 0.5 m2 areas per plot (16 samples per treatment). Dry matter per species was recorded. Plant species from the survey carried out at the end of April were grouped according to annual grass species, annual broad-leaved species, perennial grass species and perennial broad-leaved species. Species biomass values were complemented by a relative biomass value for each species, using the method described by Derksen et al. (1993) and Streit et al. (2003), but applied to species biomass instead of species density. Soil water content was monitored using a capacitance probe (Diviner 20001; Sentek Environmental Technologies, King Town, Australia). Three access tubes per plot (12 per treatment) were placed along the row between two contiguous vines. Readings were taken periodically between budbreak and harvest, at increments of 0.1 m from soil surface to a depth of 1.0 m. At harvest a sample of 200 berries per plot was collected and weighed and the juice was analyzed for pH, soluble solids (8Brix), determined by refractometry, and titratable acidity by titration with NaOH (OIV, 1990). Total phenols were determined by spectrophotometry, measuring ultraviolet absorption at 280 nm (IFT), and berry skin anthocyanins were measured using the sodium bisulphite discoloration method (Ribe´reau-Gayon et al., 1972). The harvest from 40 previously selected vines per treatment (10 per plot) was monitored by recording the number of clusters and their total weight per vine. At winter shoot number and fresh pruning weight per vine were also recorded. ANOVA were carried out in accordance with GLM procedures, from the SAS1 program package (SAS Institute, Cary, NC, USA).
3. Results During the experimental period (2002–2004) the mean air temperature ranged between 10 8C (the mean minimum monthly temperature in January 2003) and 23.6 8C (the mean maximum monthly temperature in August 2003), and the mean total annual rainfall was 885.3, 941.8 and 564.4 mm, in 2002, 2003 and 2004, respectively. At the end of April 2002–2004 the vegetation biomass in the soil tillage treatment (ST) was 137, 538 and 92 g m2, respectively. This was similar to the other two treatments. During the 3-year study, in ST the annual broad-leaved species comprised the majority of the plant species surveyed, but some perennial broad-leaved species were also present. The grasses, annuals and perennials scarcely grew in ST (Table 1). In April 2002 a total of 29 species were surveyed in ST, where three families were dominant:
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Table 1 Effect of soil management strategies on spring (April 2004) plant relative biomass (%) 3 years after experiment set-up Plant groups
Relative biomass (0–100) ST
Annual grass species Annual broad-leaved species Perennial grass species Perennial broad-leaved species Other monocotyledons
2.2 87.5 0.0 10.2 0.1
RV b a c b a
15.2 49.1 10.2 25.4 0.1
SCC a b b a a
16.1 36.3 40.8 6.8 0.0
a b a b a
ST: soil tillage; RV: resident vegetation; SCC: sown cover crop. In each row different letter suffixes show statistically significant differences at P < 0.05 by LSD test.
Oxalidaceae (52% of the total biomass), with a single species Oxalis pes-caprae L.; Geraniaceae and Asteraceae. In April 2003 and 2004, in the ST treatment the number of species did not change, but Medicago polymorpha L. showed the highest biomass, followed by the Geraniaceae species. When it came to the permanent resident vegetation (RV) the number of species surveyed was similar to ST, but the proportion of each plant group changed annually, with the grasses being favoured by the mowing. Total biomass was also dominated by the Fabaceae M. polymorpha. In the permanent sown cover (SCC) sown Poaceae and Fabaceae dominated, with six species from each family. The shoot biomass of the perennial grasses increased from 5% in 2002 to 45% in 2004 of the total above-ground biomass. Significant changes in the relative biomass of the plant groups between treatments were registered in 2004 (Table 1). The annual grass species increased their presence in the sward treatments, with values that were statistically similar for the two of them, but higher than for the ST. The increase in this plant group in RV was due to the presence of Avena sterilis L. (from the vineyard seed bank), and in SCC
to the sown species L. multiflorum. In the ST treatment plant community composition was dominated by annual broadleaved species, with a significantly higher relative biomass than RV and SCC. In the permanent sown cover crop the perennial grass species, which were dominated by L. perenne, showed a significantly higher relative biomass than ST and RV. The sown species of Fabaceae and Festuca spp. presented a poor germination rate and a weak growth, which seems to indicate that they were not well adapted to the vineyard environment and conditions. The perennial broadleaved species increased their presence and dominance in RV, with a significantly higher relative biomass than the other two treatments, which returned similar values. Veronica anagallis-arvensis L., Rumex cripus L., Lavatera spp., Picris echioides L. and Arisarum vulgare O. Targ. Tozz were the dominant species. The total vegetation biomass evolution pattern was similar for the three seasons. In the sward treatments the amount of above-ground biomass increased in the spring and the mowing at the end of May induced a strong and similar reduction in vegetation, which was unable to recover until harvest. The sown and resident species stopped growing or even dried out during the summer, thus creating dead mulch. In ST, after the first cultivation (ca. 1 month after budbreak) the soil was kept almost bare until harvest. Any plant that was able to germinate or re-grow was destroyed by the second cultivation in the middle of June. 3.1. Water use The seasonal pattern of volumetric soil moisture in the 0–1.0 m profile for the second and third season of the experiment showed a decreasing trend throughout the growing season in all the three treatments (Fig. 1). At the first measurement at the beginning of the season all the treatments presented similar soil moisture values. As the season progressed, while the two sward treatments
Fig. 1. Effect of soil management strategies on volumetric soil moisture (0–1.0 m) measured in situ during 2003 (A) and 2004 (B) growing seasons. Each point represents the mean and standard error of the measurements made on 12 access tubes. Vegetation mowing: first week of February and at the end of May; soil cultivation: budbreak and at the end of June.
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showed similar values of volumetric soil water content, ST presented higher values. These differences increased from late spring to mid summer and then stabilised until the end of the season. This pattern was similar to that observed in 2002 (data not shown), except for the end of the season when extraordinarily high amounts of rainfall in September (175 mm) induced a rapid recovery of the soil moisture to the spring values right across the profile. In order to estimate the daily average water used, the amount of rainfall and the water depletion in the first 1.0 m of soil were calculated for the three main vine growth periods of the 2003 and 2004 seasons (Table 2). Between budbreak and bloom in both seasons ST presented a significantly lower daily water use than the two sward treatments, which returned similar values. Between bloom and veraison (June to the beginning of August) the three treatments presented statistically similar values for water use. During the ripening period (August to the end of September) in 2004 the two sward treatments presented similar daily water use values, but both were significantly lower than that of the ST treatment. A similar trend was observed in 2003, but it was not statistically significant. The total water use during the entire growing season was higher in 2003 than in 2004, but no significant differences were observed among treatments (Table 2). The water used was not uniformly extracted from all the soil layers, as can be seen from the example of the 2004 soil water depletion curves (Fig. 2). During the spring, while the two sward treatments show an extraction of water which, albeit more intense in the upper layers, spans the entire profile, ST presents a significant lower extraction from both upper (0–0.50 m deep) and deep layers (0.50–1.0 m deep), where almost no water was extracted (between 0.80 and 1.0 m deep). Between bloom and veraison the three treatments extracted water uniformly from all the soil layers. During the berry ripening period, while the ST depletion curves show an almost uniform water extraction from all soil layers, the two sward treatment depletion curves show a significant increase in volumetric soil moisture in the upper layers (0–0.50 m).
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3.2. Vegetative growth and yield The effect of soil management strategies on vine vegetative growth was evaluated using the winter pruning weight, which increased from 2002 to 2004 in all treatments, but with a lower rate for the two sward treatments when compared to ST. No significant differences were observed in the shoot number per vine. In the first year of the experiment all the treatments presented similar values for pruning and shoot weight, but in the last year a significant vegetative growth reduction was observed in the RV (0.78 kg vine1) and SCC (0.75 kg vine1) treatments, compared to the ST (0.95 kg vine1). The same trend was observed in the 2003 season, although the values were not statistically significant at the 0.05 level. In this experiment no significant differences were observed in either grapevine yield (average of 2.9 kg vine1) or juice soluble solids (average of 22.08 Brix) and pH (average of 3.35) in any of the three seasons. However, in 2003 and 2004 the ST treatment presented significantly higher must titratable acidity and lower berry skin total phenols and anthocyanin content than the two sward treatments, each of which returned statistically similar values. For example in 2004 the titratable acidity was 8.05, 6.69 and 7.20 g tartaric acid l1 and skin anthocyanin content was 1027.0, 1269.0 and 1182.3 mg l1, respectively, for ST, RV and SCC.
4. Discussion Results of this 3-year study of soil management systems indicate that annual broad-leaved species spread and persist under tillage systems. These results match those of other studies (Derksen et al., 1993; Ba`rberi and Lo Cascio, 2001; Felix and Owen, 2004). Most of the annual and perennial broad-leaved species surveyed in the ST treatment did not appear in the SCC treatment, which suggests that the sown species – mainly the dominant L. perenne – were capable of competing with any potential weed and were quite adaptable to the local environmental conditions. The programmed number and time of the mowing seemed to improve and enhance cover crop establishment and performance.
Table 2 Effect of soil management strategies on estimated average water usea over the three main grapevine growth periods during 2003 and 2004 seasons Daily water use (mm day1) Budbreak–bloom
Total water use (mm) Bloom–veraison
Veraison–harvest
2003
2004
2003
2004
2003
ST RV SCC
2.85 b 3.25 a 3.17 a
1.58 b 2.05 a 2.15 a
1.30 a 1.12 a 1.33 a
0.95 a 0.85 a 0.96 a
0.74 a 0.58 a 0.67 a
Rainfall
187.8
33.2
13.4
0.8
11.6
Budbreak–harvest 2004 1.18 a 0.83 b 0.87 b 45.6
2003
2004
357.1 a 371.7 a 382.6 a
221.8 a 226.0 a 240.9 a
212.8
79.6
ST: soil tillage; RV: resident vegetation; SCC: sown cover crop. In each column different letter suffixes show statistically significant differences at P < 0.05 by LSD test. a Data obtained from the sum of the rainfall with soil water depletion from 0 to 1.0 m soil depth, assuming the absence of runoff, deep percolation and capillary rise of groundwater.
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Fig. 2. Soil water depletion curves measured in situ on four grapevine phenological phases of the 2004 growing season in the three treatments. Each point represents the mean of the measurements made on 12 access tubes. ST: soil tillage; RV: resident vegetation; SCC: sown cover crop.
Permanent resident vegetation induced the spread of some perennial broad-leaved species because they could regrow after mowing—a trait that can be considered negative, as some of these weeds are very competitive with vines for nutrients and water (Gulick et al., 1994; Lopes et al., 2004). Nevertheless, the RV treatment had a positive effect on flora diversity in that it induced the presence of some Fabaceae (M. polymorpha) and Poaceae annual species (A. sterilis)
and decreased most of the annual broad-leaved species, such as some Geraniaceae and Asteraceae. When compared to soil tillage, the sward treatments were effective in reducing soil water content during the spring. The almost complete water depletion in the upper layers that was observed in the sward treatments at bloom time may have induced both the death of the vine roots in the upper layers and the development of a deeper root system in order to explore moist layers, as reported by Morlat and Jacquet (2003). This hypothesis is sustained by the shape of the ST depletion curves during the berry ripening period, which shows an almost uniform water extraction from all the soil layers, unlike the sward treatments, in which no water was extracted from the upper layers (0–30 cm). The higher water use during berry ripening in the ST treatment can be attributed to the greater evapotranspiration caused by both the greater availability of soil water and the probably higher soil evaporation that is to be expected from bare soil. In the sward treatments the significant increase in the volumetric soil moisture in the upper layers from veraison to harvest shows that water use was lower than the contribution made by rainfall. This indicates either a reduced root system in those layers, and/or lower soil evaporation caused by the mulch effect of cover cropping residues. The additional water consumption during spring (ca. 0.5 mm d1) presented by the sward treatments compared to the ST is within the range of those reported by Bo¨ll (1967) and Griebel (1996). The total water use for the entire season showed no significant differences between treatments. Nevertheless, the percentage of the total water use of the swards to soil tillage in 2003 and 2004 was 4 and 7% and 2 and 9% higher in RV and SCC, respectively. However, these differences should be looked at with care, because the extrapolation of water depletion from the 1.0 m soil depth assumes that no water was lost by runoff and/or deep percolation, and that no water was extracted from deeper soil layers other than the 1.0 m depth. Prichard et al. (1989) found that when ‘Blando’ brome was grown in a Central Californian orchard and used as mulch throughout the summer, seasonal water use equalled that of bare soil. By contrast, in Germany Griebel (1996) estimated a 35% increase in the vineyard evapotranspiration rate due to a mixed stand, compared to clean cultivation between budbreak and bloom. These differences in vine water use can primarily affect vine growth if the water stress occurs earlier on (Williams and Matthews, 1990), as was the case in 2004. Indeed, only in the last year of the experiment were we able to detect a significant reduction in pruning weight in the sward treatments, compared to ST. Several authors (Morlat et al., 1993; Caspari et al., 1997; Geoffrion, 2000; Maigre and Aerny, 2001; Afonso et al., 2003) have already reported this effect of sward treatments on grapevine growth as a consequence of cover crop competition for water. This growth reduction can be
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beneficial to grape health and berry composition, especially in high vigour situations, as it induces a more favourable balance between vegetative and reproductive growth, and allows a more open canopy and consequently a better microclimate in the cluster zone (Dokoozlian and Kliewer, 1996). The individual shoot weight – one of the best indicators of vine vigour (Champagnol, 1984) – obtained in the sward treatments at the end of the third season of the experiment, is still within the optimal vigour and vine balance range (20–40 g fresh weight per shoot; Smart et al., 1990). The absence of significant effects of the soil management strategies on grapevine yield components during all three seasons can mainly be attributed to the higher soil waterholding capacity of this terroir and the low additional water consumption by the cover cropping systems. The effects of the cover crops on berry composition, which were detected in the titratable acidity and skin total phenols and anthocyanin content, can be explained by the indirect effects of the mild water stress on vegetative growth reduction. The consequent reduction in the competition between vegetative and reproductive growth and lower canopy density can increase cluster exposure, which in turn reduces titratable acidity and improves fruit colour and anthocyanin concentrations in red grape varieties (Dokoozlian and Kliewer, 1996; Keller and Hrazdina, 1998; Spayd et al., 2002). The two sward treatments presented a similar behaviour, thereby enabling us to conclude that the resident vegetation is the best choice for a cover crop, as it does not need to be sown. Acknowledgements This study was supported by the Portuguese Ministry of Agriculture and Rural and Fisheries Development, AGRO Program, Action 8 (2002), Project no. 104—Viticultural technology for optimising grape quality: soil and canopy management. We thank Nuno Fernandes, Joa˜o Pedro Machado and Ama´lia Arau´jo for their excellent technical assistance.
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