Abstract
The increasing cost of synthetic fertilizers, combined with their associated environmental impacts and yield instability, has promoted the use of local waste products and cover crops in vineyards. We assessed the effects of cover crop mixtures combined with organic and industrial wastes on grape yield and quality over two full growing seasons in a vineyard (Vitis vinifera) in Eastern Canada. The experimental treatments were arranged in a nested design with three replicates. Four cover crop mixtures: (i) oats + pea + hairy vetch (OPV), (ii) oats mixed with red clover (ORCl), (iii) timothy + alsike + red clover (TM), and (iv) control with no cover crop (CONT) were applied to main plots and five fertility treatments (fertilizer without N [NDEF], full synthetic fertilizer [FERT], wood ash [WA], municipal solid food waste [MSFW], and mussel sediment [MS]) were applied to subplots. During the second growing season, only half of the subplots received fertility treatments. Grape yield for the most productive cover crop and amendment combinations were ORCl × MS (9.52 mg/ha) > OPV × MSFW (9.49 mg/ha) > TM × WA (8.81 mg/ha) > ORCl × MSFW (8.28 mg/ha). The lowest grape yields were obtained with combinations of CONT with either NDEF (3.86 mg/ha) or WA (3.61 mg/ha). The highest berry sugar concentrations among the cover crops were obtained under TM floor management combined with NDEF (16.43 Brix), MS (16.03 Brix), and MSFW (15.98 Brix). Grape yield was affected by cover crop only during the second growing season, but berry sugar was not. Cover crop floor management strategies and organic or industrial wastes can be used as sources of nutrients or soil conditioners for vineyards in the cool humid climate of Eastern Canada.
- cover crops
- grape yield and quality
- inorganic fertilizer
- municipal solid food waste
- mussel sediments
- wood ash
Management practices that include cover crops and local waste products have been promoted in vineyards in recent years. The benefits of these practices include a variety of solutions to agronomic and environmental problems. Cover crops can directly impact vine growth and grape production and quality (Monteiro and Lopes 2007, Volaire and Lelièvre 2010, Giese et al. 2014), while local waste products show potential as nutrient sources and soil conditioners (Nendel et al. 2007, Sharifi et al. 2013). However, little is known about the effects of combining cover crops and local waste products on vine growth and grape yield and quality. This understanding is particularly critical for developing alternatives to synthetic fertilizers, desirable due to the increasing cost of synthetic fertilizers and their associated yield instability and environmental impacts.
Nova Scotia, Canada, is a fast-growing wine production area located in the mid-temperate zone with humid continental climate. Vineyards are mainly established in areas with steep slopes characterized by light textured soils, low soil organic matter (SOM) content, low soil fertility, low water holding capacity, and often, due to high gravel content and shallow depth, a high risk of nutrient leaching. Combining cover crops and local waste products could improve soil physical properties and provide an alternative to synthetic fertilizers (Sharifi et al. 2014).
Cover crops are typically planted after minor soil preparation in the alleys between grapevines. Cool- or warm-season grasses, alone or in combination with legumes, may perform well in Nova Scotia, but selection of the most appropriate species depends on specific needs. Cool-season grasses exhibit a growth pattern that parallels the vigorous growth of grapevines in spring. This growth pattern could impose competition for water when soil moisture reserves, supplemented by seasonal rains, contribute to excessive growth of grapevines (Giese et al. 2014). Cover crop management can also reduce nitrogen (N) availability and modify vine vigor and N status. The reduction in vegetative growth can increase cluster exposure and therefore be beneficial for berry composition and wine quality (Monteiro and Lopes 2007). A four-year study in Oregon showed that berry N concentration was reduced by competition with a grass cover crop (Gouthu et al. 2012). Wine from cover-cropped vineyards in China had higher concentrations of aroma compounds than those from vineyards with bare soil (Xi et al. 2011). Cover crops also affected the spatial and temporal distribution of water in the soil profile, and thus water and nutrient uptake by vines (Celette et al. 2008). In sloping vineyards, cover crops can mitigate runoff, soil erosion, and the risk of nutrient leaching. Leguminous cover crops contribute to N and maintain soil quality and fertility (Sharifi et al. 2014).
Biowastes and nutrient-rich industrial by-products are valuable nutrient sources and soil conditioners in agricultural systems (Sharifi et al. 2013, Weber et al. 2014). They are used in vineyard production systems with success (Nendel et al. 2007), but rarely in Nova Scotia (Sharifi et al. 2013). The easy access and possibilities for incorporation into soils could create an environmentally benign, safe, and economically viable alternative method of disposal for these by-products (Cabral et al. 2008). Adding biowaste composts to a silty loam soil improved the aggregate stability and thus enhanced the resistance of soil to water erosion (Annabi et al. 2011). Biowaste composts increased total porosity, improved water penetration and air circulation, and increased water retention in soil (Weber et al. 2007). Combining the benefits of biowastes and nutrient-rich industrial by-products and the characteristics of vineyard soils in Nova Scotia has great potential for practical impact and adoption.
Few studies have explored the interaction between cover crop floor management (Monteiro and Lopes 2007) and biowastes and nutrient-rich industrial by-products (Weber et al. 2014) on grape yield and quality. We hypothesized that balancing vine nutrient requirements using soil amendments combined with cover crops can produce comparable grape yield and quality to that of synthetic fertilizers. The objective of this study was to assess the effects of cover crop floor management and amendments applied to the vineyard on grape yield and quality.
Materials and Methods
Experimental site
The study was initiated in 2011 in a vineyard established in 1999 on a Bridgewater loam-drumlin phase cryorthods (Soil Survey Staff 2010) located at St. Mary’s in the LaHave River Valley area of Lunenburg County (lat. 44°22′N; long. 64°31′W). The soil is gravelly, sandy clay loam developed on slate-derived till overlying a granite batholith. It is moderately well-drained, shallow, and stony. Lunenburg County is characterized by an undulating to rolling drumlinized till plain that slopes in a southeasterly direction toward the Atlantic Ocean. During the three years preceding the study, no fertilizer or amendments were applied to the vineyard. Resident vegetation was mowed and mulched with a lawn tractor. Elevations range from a high of about 270 m inland. The 30-year average daily temperature varies between 9.3°C in October and 19.5°C in July during the growing season (May to October). The local climate is humid continental with 1323 mm annual rainfall, of which 641 mm falls during the growing season.
Leon Millot was the grape variety used in this study. It is a vigorous, productive, and hardy red French hybrid grape used for winemaking. It ripens midseason with good sugar and moderate acid. It is a sister to the Marechal Foch variety, but Leon Millot ripens a week earlier on average and has greater vigor and smaller bunch size. Leon Millot was bred in 1911 by crossing the hybrid variety 101-14 O.P. (Millardet et de Grasset) (Vitis riparia × Vitis rupestris) with Goldriesling (Vitis vinifera). Leon Millot is grown on its own roots, like most hybrid vines. Dormant pruning was in March of each year and prunings were left on the ground in the vine rows. In late April, vine rows without a permanent cover crop were tilled to prepare the seedbed. A unique local low-wire trellis system called the LaHave River Valley trellis was used to train the vines to resist high wind and early autumn frosts. Shoots were tucked into trellis catch wires after flowering in early July. The first shoot thinning also occurred at this time. Vines were hedged in August to limit the effects of excessive vine vigor on the low trellising. Leon Millot grapes reach veraison in late August to early September. A heavy summer pruning allowed the grape bunches to have direct sunlight, build sugar, and develop red color. Harvest was in mid-October. Pest and disease management was consistent with local recommendations (Craig 2013). Ignite (glufosinate ammonium) herbicide was applied three times during the growing season to all treatments to keep a 0.50 m weed-free zone under the vines that minimized competition for nutrients and water.
The experimental treatments consisted of three cover crop mixtures and a control applied to main plots and five fertility treatments assigned to subplots in a nested design with three replicates. The cover crop treatments were (i) a mixture of oats (Avena sativa L.) + pea (Pisum sativum L.) + hairy vetch (OPV), (ii) a mixture of oats and red clover (ORCl), (iii) a mixture of 70% timothy (Phleum pratense) + 15% alsike (Trifolium hybridum) + 15% red clover (commercially called triple mix; TM), and (iv) a control with no cover crop (CONT). The CONT treatment alleyway was tilled and sprayed with herbicide (Ignite) as needed during the growing season. The five fertility treatments were (1) synthetic fertilizer minus N (NDEF), (2) synthetic fertilizer with N (FERT), (3) wood ash (WA), (4) municipal solid food waste (MSFW), and (5) mussel sediments (MS). In 2012, individual subplots were divided into two parts and fertility treatments were applied to one part only. The result was a cross-nested experimental design. The FERT application rate was based on soil tests and provincial recommendations. NDEF consisted of 83 kg K/ha as potassium chloride (KCl) + 40 kg S/ha as MgSO4 (7 H2O) and elemental S (90%) + 24 kg Mg/ha as MgSO4 (7 H2O) + 2.4 kg B/ha as elemental B (15%). The FERT treatment was the same composition as NDEF + 40 kg N/ha as NH4NO3. The WA originated from Brooklyn Power Ash (Brooklyn, Nova Scotia, Canada) and was applied at 6.3 mg/ha on a dry weight (DW) basis. Using this application rate, the estimated total supply of K was 83 kg/ha, with the assumption that 80% of the total WA potassium was available in the first year (Sharifi et al. 2013). Nitrogen as NH4NO3 (34% N) and sulfur as MgSO4 (7 H2O) (90% S) were applied at 40 kg/ha in the WA treatment. The MSFW was applied at 13.4 mg/ha on a DW basis based on the assumption that 15% of the total N is available in the application year (Sharifi et al. 2014). Nitrogen was applied at 30 kg N/ha and K was applied as KCl (62% K) at 83 kg K/ha to balance the nutrients in the MSFW. MS was applied at 42,000 L/ha to supply 99 kg/ha N based on the assumption that 40% of total N in the MS is available in the application year. Potassium was applied at 83 kg K/ha due to the low concentration of K in this amendment. The individual subplots were 5 m × 2 m and consisted of three measurable vines and two guard vines. The space between the vine rows was 1.8 m, and interrow space was 1.0 m.
The soil was tilled down to 10 cm with a rototiller. Amendments were manually applied in a 1.3 m wide band between vine rows. In 2011, the amendments were lightly incorporated into the soil during seedbed preparation. In 2012, the amendments were top-dressed on the soil with permanent cover crops (ORC and TM) and incorporated for treatments with annual cover crops (OPV). The seeding rates for the cover crops were 80 kg/ha for oats, 30 kg/ha for hairy vetch, 100 kg/ha for pea, 6 kg/ha for RCl, and 15 kg/ha for TM. Oats and hairy vetch were broadcast and then incorporated into the soil. The other cover crop seeds were broadcast on the top of the soil. After all cover crops were seeded, the alleyways were packed with a roller. The cover crops were mowed once in mid-June, twice in early and late July, and once in mid-August.
Grape yield, cluster weight, and number
Grape bunches were harvested in mid-October in 2011 and 2012. Grape yield was determined by harvesting clusters on the three innermost vines of each subplot with a set of harvesting pruners. Harvested clusters were counted, weighted, and placed in a 20-L bucket. The average weight was calculated by dividing the total weight of clusters per vine by the number of clusters. Approximately 100 berries were taken from each subplot, dried and ground, and freeze-dried at −80°C for quality indicators analysis.
Grape quality indicators analysis
The soluble solids or sugar content (Brix) was measured on a representative sample of 100 freshly harvested berries using a hand-held refractometer. Total phenolic compounds and antioxidant capacity were measured for all fertility treatments × TM cover crop mixture. Total phenolic compounds were extracted and analyzed as described (Singleton and Rossi 1965, Folin and Ciocalteau 1927) with modifications. Briefly, 0.125 g powdered freeze-dried sample was mixed with 10 mL extracting solution (40% acetone, 40% methanol, 20% Milli-Q water, and 0.1% formic acid) in a 50-mL centrifuge tube. The suspension was vortexed and sonicated at #15 for 30 sec and left under dim light for 30 min. The sample was centrifuged at 10,000 × g for 15 min and the supernatant was transferred to a clean 50-mL centrifuge tube and refrigerated. The concentration of phenolic compounds was determined on a multiscan Spectrum microplate reader (Thermo-Fischer Scientific, Verta, Finland).
The antioxidant capacity was determined under dim light using the oxygen radical absorbance capacity assay as described (Prior et al. 2003). Approximately 0.050 g finely-ground lyophilized grape tissue was mixed in 50-mL centrifuge tubes on ice with 10 mL extracting solution (70% acetone, 29.5% Milli-Q water, and 0.5% acetic acid) and sonicated at #15 for 1 min. The suspension was centrifuged at 5000 rpm for 15 min, the supernatant was transferred to a 25-mL volumetric flask, and it was kept in the dark until analysis on a fluoroscan ascent FL 96-well microplate reader (Thermo-Fischer Scientific). During analysis, the AAPH 2,2′-azobis (2-amidinopropane) dihydrochloride was used as a peroxyl generator and 6-hydroxy-2-5-7-8 tetramethylchroman-2-carboxylic acid (Trolox) as a standard.
Leaf petiole N concentration
Leaf petioles (20 to 25) opposite the first, newest flower cluster on the terminal end of the shoot were sampled at flowering in the first week of July in 2011 and 2012. The leaf petioles were oven-dried at 60°C for 48 hr, ground in a Thomas-Wiley mill (Thomas Scientific, Swedesboro, NJ) to pass through a 2-mm sieve, and analyzed using an Elementar VarioMAX CNS analyzer (Skjemstad and Baldock 2007).
Cover crop biomass and N concentration
Cover crop samples were taken in the field using a 0.50 m2 quadrant per plot in 2012. Cover crops were mowed in mid-June, in early and late July, and in mid-August. The aboveground biomass inside the quadrant was cut at 6 cm above the soil surface, stored on ice in coolers, and weighed. The samples were then oven-dried at 60°C for at least 48 hr. Oven-dried samples were ground in a Thomas-Wiley mill (Thomas Scientific) to pass through a 2-mm sieve. C and N were measured in cover crop ground tissues using an Elementar VarioMAX CNS analyzer.
Statistical analysis
All data were tested for normality using the SAS univariate procedure. Analysis of variance (ANOVA) was performed separately for each year using Proc Mixed of SAS, version 9.3 (SAS Institute, Inc., Cary, NC, 2010). For parameters measured in 2011 (grape yield, average cluster weight and number, leaf petiole N, and soluble solids), replications were considered as random effects and cover crop, amendment, and their two-way interaction as fixed effects. For parameters measured in 2012, replicates were considered as random effects and cover crop, amendment, application frequency, and their two- and three-way interactions as fixed effects. Adding application frequency as a third factor allowed determination of the residual effect of fertility treatments on studied parameters. Differences among least square means (LSMEANS) for all treatment pairs were tested at a significance level of p = 0.05. Where appropriate, means were compared with a combination of orthogonal and polynomial contrasts: CONT versus OPV, ORCl, and TM; OPV versus ORCl; OPV and ORCl versus TM; NDEF versus other; FERT versus MS, WA, and MSFW; WA versus MSFW; and MS versus MSFW.
Results
Weather
Growing season rainfall was 871.3 mm in 2011 but only 597.4 mm in 2012 (Table 1). The average rainfall recorded during the past 30 years was lower than in 2011 but greater than in 2012. The highest monthly rainfall was 329.8 mm and 159.0 mm in Oct 2011 and 2012, respectively, while the lowest monthly rainfall was 43.1 mm in Sept 2011 and 54.1 mm in Aug 2012. The distribution of rainfall shows higher monthly values in 2011 than in 2012 except in September. The average growing season temperature was greater in 2012 (16.3°C) than in 2011 (14.6°C). The mean monthly temperatures were always higher in 2012 than in 2011. The average temperature during the past 30 years was higher than in 2011 but lower than in 2012.
Grape yield and quality
In 2011, grape yield was significantly affected by cover crop, but the extent differed with amendments (Table 2). Grape yield was increased by MSFW under OPV (53%) and ORCl (46%), by WA under TM (50%) and ORCl (40%), and by MS under ORCl (53%) and OPV (41%), compared with NDEF combined with the same cover crops. In addition, grape yield was increased by MSFW under OPV (41%) and ORCl (32%), by WA under TM (37%) and ORCl (24%), and by MS under ORCl (41%) and OPV (26%) over that of the CONT × FERT treatment. Grape yield also increased by 42% under OPV × FERT but only by 20% under CONT × FERT over NDEF combined with cover crops (Figure 1). Some combinations of cover crops × amendments also resulted in lower grape yield, including OPV × NDEF (0.70 kg/vine), TM × MSFW (0.79 kg/vine), and OPV × WA (0.68 kg/vine). In contrast, grape yield was significantly affected only by cover crops in 2012 (Table 3). On average, grape yield increased 25% with floor cover crops (1.27 kg/vine) over CONT (0.95 kg/vine). Some annual variability was observed: a trend toward lower grape yield in 2011 than in 2012. Cover crops significantly affected cluster weight and number in 2011 but only the cluster number in 2012 (Table 2 and 3). The greatest cluster weight and number were always obtained with floor cover crops. The three amendments had equal performance on grape yield, cluster weight, and cluster number compared to the recommended synthetic fertilizer. In 2012, the plots were divided into two subplots and amendments were applied to one. There were no differences between the two subplots in grape yield, cluster weight, or cluster number.
Soluble solids, phenolics, and antioxidants
The sugar concentration was affected by cover crops and the extent was influenced by amendments in 2011 (Table 2). The sugar varied between 12.80 Brix for CONT × MSFW and 16.43 Brix for NDEF × TM combinations (Figure 2). TM mixture resulted in more sugar than the other cover crops across the amendment treatments. There was a trend of low sugar under CONT across amendment treatments, and the lowest values were obtained in combination with NDEF (13.10 Brix) and MSFW (12.80 Brix). In contrast, the sugar did not significantly vary across cover crops under FERT treatment and averaged 14.55 Brix. In 2012, sugar was significantly affected only by frequency of amendment applications and averaged 12.90 Brix from two-year amended plots and 13.73 Brix from one-year amended plots.
Phenolic and antioxidant concentrations were only determined in berry samples harvested in 2011 under TM and the five amendment treatments. There were significant differences among amendments for these two berry quality indicators. Phenolics averaged 10.0 mg/g DW across NDEF and MSFW but 11.5 mg/g DW across FERT, WA, and MS (Figure 3). Antioxidants increased 9% under MSFW relative to synthetic fertilizers and other amendments (Figure 4).
Leaf petiole N content
Leaf petiole N concentration was not affected by cover crop or amendment and averaged 3.93% in 2011 (Table 2). In contrast, leaf petiole N was significantly affected by cover crops in 2012 (Table 3). The highest leaf petiole N concentration was 4.09% under CONT, and the lowest averaged 2.76% across OPV, ORCl, and TM.
Cover crop biomass
Cover crop biomass was determined in 2012 only and was significantly affected by cover crop, amendment, and frequency of amendment application (Table 3). Total cover crop biomass was 956 kg/ha under ORCl, 727 kg/ha under TM, and 607 kg/ha under OPV. The cover crop biomass followed the order WA (630 kg/ha) > FERT (622 kg/ha) > MS (560 kg/ha) > MSFW (556 kg/ha) > NDEF (494 kg/ha), and was greater in plots with one-year amendment applications (595 kg/ha) than with two-year amendment application (550 kg/ha).
Discussion
The cover crops used in this study have been tested in Nova Scotia under other cropping systems (Lynch et al. 2012, Sharifi et al. 2014). Grape yields obtained here are consistent with values obtained in a Mediterranean vineyard in Spain (Romero et al. 2015) but were lower than those measured in a Mediterranean vineyard in Portugal (Lopes et al. 2011). Leon Millot is an interspecific hybrid characterized by small, winged, cylindrical, and loose clusters. Its average cluster weight was 0.068 kg/vine at four Iowa State University research sites (Domoto et al. 2008). Increased grape yield with cover crop floor management is consistent with other vineyard studies and can be attributed to soil quality improvement and regulation of vine vegetative growth and vigor (Tesic et al. 2007, Hatch et al. 2011). However, conflicting results have also been observed. In Mediterranean Portugal, there were no significant effects of floor management strategies on grapevine yield during three growing seasons, mainly due to high soil water-holding capacity and low water consumption by the cover-cropping systems (Monteiro and Lopes 2007). Other studies also report no significant effects of cover crop floor management on grape yield (Baumgartner et al. 2008, Mercenaro et al. 2014). Finally, our results differ from those reported from a dry climate, low-vigor vineyard in Mediterranean Portugal, where significant reductions in berry size, cluster weight, and grape yield were observed under resident vegetation-based floor management strategies compared with bare-tilled soils (Lopes et al. 2011).
The annual variability in grape yield could be due to differences in fruitfulness and/or number of nodes retained on the vines during winter pruning. Grape yields in 2011 were on average half those of 2012. This is consistent with differences in cluster number during the two growing seasons. Unfortunately, we cannot provide the number of nodes retained during winter pruning. It is, however, interesting to observe that in 2011, some combinations of cover crop and amendments resulted in grape yields similar to those of 2012. These combinations include OPV × FERT, × MSFW, and × MS; ORCl × MSFW, × WA, and × MS; and TM × WA. The reasons for improved grape yield with these combinations are not clear, but may be associated with better nutrient availability and use of excess water from rainfall. The differences in yield among treatments in each growing season were not due to numbers of nodes retained in the previous year, as all the vineyard management practices, including pruning, were consistent across treatments. Thus, the differences in yield are attributed to treatment effects in each year.
Values of petiole N concentration measured in this study were higher than the reported 0.8 to 1.3% reported for complete vineyard floor cover crops in North Carolina (Giese et al. 2014). A mature Merlot vineyard in California also had low petiole N concentrations of between 0.41 and 1.17% (Steenwerth et al. 2013). High petiole N concentrations in our study, particularly in N-fertilized or amended soils, could be explained by adequate soil mineral N. A study at the same experimental site showed that soil mineral N increased in cover-cropped plots over the growing season (Messiga et al. 2015). Greater petiole N concentration in CONT plots than in cover-cropped plots indicates some competition for N between vines and cover crops. Petiole N concentration was measured at flowering, before cover crops were mowed. This suggests cover crops could scavenge soil mineral N resulting from early season N mineralization and limit the risk of N leaching. The N accumulated in cover crops could then be returned to the soil through mowing and incorporation.
Cover crop biomass measured in our study was in the range of other values reported: 201 to 4017 kg/ha (Mercenaro et al. 2014) and 205 to 3400 mg/ha (Giese et al. 2014). In 2012, cover crop biomass was greater in plots with one year of amendment application than with two years of application. This result could be explained by reduced growth of permanent cover crops following top-dressed application of amendments. The cover crop mixtures ORC and TM had lower biomass in plots with two years of amendment application (data not shown) than with one year of application, indicating reduced growth and biomass production. The overall low cover crops biomass measured in this study is attributed to low fertility and short growing seasons at the study location.
Trends of low grape yield, petiole N concentration, and cover crop biomass obtained under NDEF across the cover crop mixtures (Figure 1, Tables 2 and 3) indicate inadequate N supply to both cover crops and vines. These results suggest that low nutrient availability, particularly N, when combined with competition between vine and cover crops, can potentially contribute to reduced grape yield. Chemical weeding was compared with natural grass and sown grass at three sites; reduced vine vigor, grape yield, and must N concentration was found in cover-cropped vineyards (Gontier et al. 2011). As cover crop floor management is implemented in vineyards, fertilization management must meet the needs of both crops (Colugnati et al. 2004). In 2012, cover crop floor management decreased petiole N concentration below that of CONT plots but not soluble solids. We did not measure berry antioxidants and phenolic compounds in any cover crop but TM. It is therefore difficult to determine from this study whether cover crops affect grape and wine quality. However, cover crop floor management did not affect grape yeast assimilable N in California (Lee and Steenwerth 2011). Sugar concentrations were within the range of those obtained in one Mediterranean vineyard in Spain (Serrano et al. 2012) but were lower than those obtained in a five-year study of another Mediterranean vineyard in Spain (Gouthu et al. 2012, Lopes et al. 2011, Mercenaro et al. 2014). Cover crop effect on berry sugar concentration was not consistent over time. In 2012, a year with below-normal rainfall and high grape yield, cover crop did not affect sugar concentration. In 2011, with above-normal rainfall and low grape yield, TM mixture maintained higher berry sugar concentration across amendment treatments, probably due to higher water use than the other cover crop mixtures that decreased the surplus water available for vines (Efetha et al. 2009). This assumption is supported by lower sugar concentrations in berries from treatment combinations involving CONT and amendments, which lacked cover crop or natural vegetation that could compete with vines for water and nutrients (Figure 2). It is also possible that the degree of cover crop summer dormancy differed among the cover crop species evaluated in this study that go dormant in summer. Summer dormancy is defined by four criteria: (1) reduction or cessation of leaf production and expansion, (2) senescence of mature foliage, (3) dehydration of surviving organs, and (4) formation of resting organs (Volaire and Norton 2006). Broad cover crop varietal differences exist in dormancy responses to water and nutrient availability during the growing season (Volaire and Lelièvre 2010). Timothy is considered a summer-active plant (Stanisavljevic et al. 2011) and would likely use more water than other species/cultivars during midsummer. Red clover is a legume with a taproot and prefers high summer rainfalls (Brown et al. 2005). Timing, amount of biomass produced, and cover crop regrowth following mowing could also impact water use among cover crop treatments under excess water availability and therefore, the sugar concentration of berries. In a study conducted in New York on N efficiency of orchardgrass and tall fescue, the amount of biomass harvested in spring was greater for orchardgrass, but tall fescue had greater total biomass from subsequent harvests of the grasses’ regrowth during the growing season (Cherney et al. 2002). An unrestricted water supply is required before flowering to optimize light interception and the production of assimilates during reproductive development. However, moderate water deficits during veraison are beneficial for grape quality. Our results showed that timothy could compete with vines during phases of rapid shoot growth and veraison, and thus reduced plant vigor and increased berry sugar concentration. The contrasting results obtained in this study for grape yield and sugar concentration make it difficult to rank the cover crop mixtures. For grape yield, OPV and ORCl provided good sugar concentration but TM showed the best performance.
The organic and industrial wastes tested in this experiment have confirmed their potential as nutrient sources and soil conditioners that could complement or substitute for synthetic fertilizers in other cropping systems in Nova Scotia and elsewhere. The WA was used in this study due to its high K concentration (1.64%) with an assumed 80% availability during the first year. N concentration was the main criterion for choosing MSFW (2.51%) and MS (0.94%), which have an assumed availability in the first year of 15 and 40%, respectively. Grape yields in 2012, which had below-normal rainfall, show that the three amendments were similar to FERT (Table 3). Notably, amendment applications had significant interaction effects with cover crop mixtures for grape yield and quality in 2011, which had above-normal rainfall. The best combinations of organic and industrial wastes and cover crops always provided better grape yields than the best combinations of FERT and cover crops (Figure 1). Results over two years show that the three amendments could be combined with selected cover crop mixtures in Nova Scotia vineyards to reduce use of synthetic fertilizers while maintaining adequate grape yield.
An eight-month incubation experiment demonstrated that WA from three Nova Scotia sources was an effective liming agent and potassium source for agricultural production systems (Sharifi et al. 2013). In an organic potato system in Nova Scotia, soil organic biomass, particulate organic matter biomass, and microbial biomass C were greater under papermill biosolid and MSFW composts than under synthetic fertilizer (Sharifi et al. 2014). This study is one of the few instances in which MS has been tested as a nutrient source or soil conditioner in Nova Scotia. The effects of MS application on grape berry yield, sugar, phenolics, and antioxidants show that this industrial waste could be a good source of nutrients for grape production. Similar conclusions could be drawn for WA and MSFW. The beneficial effects of amendments over inorganic fertilizer have been observed in other vineyards and are associated with improved soil properties. Long-term organic management of a vineyard soil induced stable modifications of soil physical and chemical properties at both the macro-and micro-aggregate scales (Navel and Martins 2014). Due to increasing production pressures imposed on agricultural soils and their subsequent decrease in fertility, integrating organic and industrial wastes into agricultural soils has become a common practice and a priority to improve the productivity and quality of soils. Soils under vineyards are particularly prone to fertility decline due to their sensitivity to surface runoff, especially in situations with sloping landscape (Navel and Martins 2014). Our results demonstrate that these organic and industrial wastes support grape productivity, allowing the opportunity to improve the quality of these soils.
Conclusion
The combination of cover cropping with biowastes and nutrient-rich industrial by-products resulted in similar grape yield and quality to synthetic fertilizer. Some promising cover crop and amendment combinations were found in 2011, when grape yields were low due to differences in fruitfulness and/or nodes retained during winter pruning. The combinations included OPV or ORCl × MSFW, TM or ORCl × WA, and ORCl or OPV × MS and resulted in increased grape yield over CONT × FERT and NDEF combined with cover crops. These cover crop mixtures and amendment combinations could balance the vine nutrient requirements, including for N, and produce comparable grape yield to synthetic fertilizers. TM mixture resulted in higher berry sugar concentrations than the other cover crops across biowastes and nutrient-rich industrial by-products, but no significant variation was observed under FERT. Repeated additions of biowastes and nutrient-rich industrial by-products over two growing seasons decreased the berry sugar concentration below that of a one-year application. Thus, the combination of cover crops and amendments balances the vine’s nutritional requirements better than conventional vineyard management practices involving synthetic fertilizers on bare soil.
Acknowledgments
Funding for this research is provided by Nova Scotia Department of Agriculture and Fishery, Technology Development 2000 program. Support by our industry partner, Petite Riviere Vineyards, is greatly appreciated. Amendments were supplied by LP Consulting (wood ash), Northridge Farms, Ltd. (municipal solid food waste compost), and Prince Edward Aqua Farms Ltd. (MS). Special thanks to the Nova Scotia Department of Agriculture and Fishery and Dalhousie University, Faculty of Agriculture (former name: Nova Scotia Agricultural College) for supporting the Nutrient Management Research Chair position previously held by Dr. Mehdi Sharifi at the Environmental Sciences Department.
- Received February 2015.
- Revision received June 2015.
- Revision received August 2015.
- Accepted August 2015.
- Published online December 1969
- ©2016 by the American Society for Enology and Viticulture