Research Note
Cover Crop Water Use in Relation to Vineyard Floor Management Practices Michela Centinari,1,2 Ilaria Filippetti,1 Taryn Bauerle,2 Gianluca Allegro,1 Gabriele Valentini,1 and Stefano Poni3* Abstract: The aim of our study was to compare soil evaporation (Es) versus cover crop (Festuca arundinacea var. barfelix) evapotranspiration (ETcc) within a vineyard ecosystem and to investigate the effect of mowing in reducing cover crop evapotranspiration, and, hence, its below-ground competitiveness. The study was carried out in a 2-year-old Sangiovese (Vitis vinifera L.) vineyard, grafted to SO4, in Bologna, Italy. Mini-lysimeters and a portable gas-exchange chamber system were used to investigate cover crop evapotranspiration in relation to mowing and bare soil management practices. Our results show that, immediately after mowing, ETcc markedly decreased, with the percentage of reduction ranging from 35 to 49%, depending on the amount of clipped biomass. The extent of the ETcc reduction decreased over time as the cover crop regrew. Over the 28-day period following the mowing, soil evaporation was 35 and 48% lower than mowed and unmowed cover crop evapotranspiration, respectively. This study shows that mowing could be used as a water management strategy to decrease vine cover crop competition over a short time period. Key words: chamber system, cover crop, water use, mowing, mini-lysimeter, Vitis vinifera L.
In the last decade, cover crops, either resident or sown species, have largely been used as a vineyard floor management practice in cool climates due to their advantages over other more traditional weed control techniques, such as soil tillage and herbicide sprays (Battany and Grismer 2000, Baumgartner et al. 2008, Morlat and Jacquet 2003). In Mediterranean climates characterized by summer drought and variable yearly precipitation, apprehension over excessive vine water stress has limited the introduction of cover crops as a viable floor management strategy. In a Mediterranean vineyard no significant difference in vine water use, calculated for the entire growing season, was found between cover crops and bare soil interrow management treatments (Monteiro and Lopes 2007). However, the cover crop species stopped growing or even dried out dur-
ing the summer period. Moreover, data from this study were based only on soil moisture measurements taken underneath the vines and no information was given on vineyard evapotranspiration (ET) as well as on the contribution of the single components (vine, cover crop, soil) to total ET. While is it is known from other agricultural and natural systems that soil evaporation (Es) is less than vegetated systems (Stannard and Weltz 2006), we are not aware of any study comparing soil evaporation versus the water used by cover crops within a vineyard ecosystem. Management of cover crops for facilitated vineyard access (Olmstead 2006) and enhanced soil coverage has largely been achieved through mowing (Guerra and Steenwerth 2012). After two mowing events in the vineyard interrow in the middle of May and June, a cover crop of Festuca arundinacea L. cv. Centurion yellowed and declined in growth rate (Celette et al. 2005). The authors concluded that consecutive mowing along with decreased soil water availability may lead to a considerable reduction in cover crop water use, and, hence, its below-ground competitiveness. However, to our knowledge, no data are available on the reduction in cover crop evapotranspiration (ETcc) obtained through mowing or on ETcc rates during cover crop regrowth. Therefore, the objectives of the present study were to evaluate the effect of mowing on ETcc and to compare water loss (Es, ETcc) related to different soil management techniques (bare soil, unmowed and mowed cover crop).
Dipartimento di Colture Arboree, Sezione Viticola del Centro Interdipartimentale di Ricerche Viticole ed Enologiche, Università di Bologna, Viale G. Fanin 46, 40127 Bologna, Italy; 2Department of Horticulture, Cornell University, 134A Plant Sciences Building, Ithaca, NY 14853; and 3Istituto di FruttiViticoltura, Università Cattolica del Sacro Cuore, Via Emilia Parmense 84, 29100 Piacenza, Italy. *Corresponding author (email:
[email protected]; tel: +390523599271; fax: +390523599268) Acknowledgments: This research was supported by the University of Bologna for M. Centinari. The authors are grateful to Barbara Bucchetti and Emilia Colucci for their technical support and help in field determinations. The critical reading of the manuscript by J.E. Vanden Heuvel (Cornell University) is gratefully acknowledged. Manuscript submitted Mar 2013, revised May 2013, accepted May 2013 Copyright © 2013 by the American Society for Enology and Viticulture. All rights reserved. doi: 10.5344/ajev.2013.13025 1
Materials and Methods Experimental site. The experiment was conducted in 2007 at the University of Bologna, Italy (44°30’N; 11°24’E) in a 2-year-old Sangiovese (Vitis vinifera L.) vineyard grafted 522
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to SO4 rootstock and spaced 1 m and 2.8 m along and between the rows. Vineyard soil was loam (39% sand, 39% silt, and 22% clay) with an organic matter content of 1.8% and a pH of 7.8. Field capacity and wilting point were calculated after Saxton and Willey (2005) and set at 0.29 cm 3/cm3 and 0.14 cm 3/ cm3, respectively. A chemical weed control strip was applied under the vines (0.6 m wide) and a perennial cover crop (Festuca arundinacea var. barfelix) was sown in the interrow area in fall 2006. Cover crop vegetation was planted on two-thirds of the length of each interrow, with the other one-third cultivated. Throughout the course of the study the cover crop had 100% soil coverage and weed species growth was minimal. The experimental design was a randomized complete block with three treatments and two replicates per treatment. The three treatments were (1) interrow soil tillage (ST); (2) interrow cover crop mowed (MG); and (3) interrow cover crop unmowed (UMG). Vineyard soil management consisted of two vegetation mowing events (22 May and 12 July) and two soil tillage events (22 May and 10 July) (Table 1). Mini-lysimeter measurements. Interrow cover crop evapotranspiration (ETcc) and soil evaporation (Es) were determined gravimetrically using a mini-lysimetric approach (Boast and Robertson 1982) (Figure 1A). Thirty-six 0.25 m deep plastic pots with an internal diameter of 0.25 m were used as mini-lysimeters (MLs). In March (day of year [DOY] 60 and 61) a cover crop soil core was transplanted into 24 mini-lysimeters, while the other 12 were filled with a bare soil core; the pots were then watered and positioned in previously dug holes. Mini-lysimeters were installed within a single interrow of the vineyard according to a randomized complete block design with three treatments (ST, MG, UMG) and two replicates per treatment. Twelve mini-lysimeters were assigned to each treatment. Each experimental unit (plot) covered an interrow area of 22.4 m 2 and consisted of six mini-lysimeters arranged in two transects, each one comprised of three pots. For each transect one pot was positioned midway between the rows and the other two at a distance of 0.8 m from the east and west vine row. On 22 May (DOY 142) the cover crop in the 12 minilysimeters assigned to the MG treatment was hand trimmed to 4 cm, while the surrounding area was mechanically mowed.
On the same day, soil tillage was implemented in the ST treatment. During this operation, ST mini-lysimeters were removed from the field, soil inside the pots was lightly cultivated using a hammer and a chisel, and then positioned back into their location. Mini-lysimeter measurements started the day before mowing and were continued through 19 June (DOY 141 to 170). Over the study period the mini-lysimeter cover crop was well established and actively growing. Daily ETcc and Es (mm/day) were gravimetrically determined by weighing all mini-lysimeters on 24-hr intervals starting at 0900 hr, except during days when precipitation occurred or drainage was observed from the bottom of the pots. Daily evaporation (mm/day) was calculated as the change in pot weight per day (kg/day) per m 2 of mini-lysimeter surface area and converted to mm/day. To estimate vineyard ETcc and Es, mini-lysimeter data were weighed by the fraction of soil surface covered by the cover crop or soil tilled, equal to 0.79 (Centinari et al. 2012). Chamber system measurements. A portable chamber (Centinari et al. 2009) operating as an open system (Figure 1B) was used to assess the reduction in ETcc obtained through
Table 1 Timetable of vineyard floor management events, sampling dates (2007), and measurements (mini-lysimeter and portable gas-exchange chamber). Date 21 May 22 May 23 May 10 June 19 June 10 July 11 July 12 July a
DOY 141 142 143 161 170 191 192 193
Eventa MG; ST
Measurementa Mini-lysimeter (DOY 141–170) Chamber (before, after MG) Chamber (UMG vs MG) Chamber (UMG vs MG) Chamber (MG vs ST)
ST MG
Chamber (MG vs ST) Chamber (before, after MG)
MG: interrow cover crop mowed; ST: interrow soil tillage; 0and UMG: interrow cover crop unmowed.
Figure 1 View of one mini-lysimeter (A) and the portable gas-exchange system used in the study (B).
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mowing in relation to cover crop height and clipped biomass and to monitor diurnal ETcc and Es trends in the UMG, MG, and ST treatments over the course of the experimental period. Readings were taken in correspondence with the two mowing events carried out in the vineyard (DOY 142 and 193), specifically before and after cutting. First the chamber was lowered onto an unmowed cover crop plot located in the middle of the interrow and data were collected for 15 min. After removing the chamber, the cover crop was cut to 5 cm, the chamber was replaced over the same plot, and data were collected for an additional 15 min. Measurements were repeated on two plots on DOY 142 and on three plots on DOY 193 between 1200 and 1500 hr at saturating light conditions (PAR ≥ 1200 µmol/m 2s). Chamber measurements were also taken four times throughout the month following the first mowing. On DOY 143 and 161, 1 and 19 days after mowing, respectively, readings were conducted in the UMG and MG interrow, on three cover crop plots per treatment. On DOY 170 and 192, readings were taken on three plots located in the MG and on three plots in the ST interrow. On all four of those dates (DOY 143, 161, 170, 192), readings were collected approximately every two hours throughout the day. To estimate vineyard ETcc and Es, chamber data were weighed by the fraction of soil surface covered by the cover crop or soil tilled, equal to 0.79. Environmental data. Hourly solar radiation, precipitation, air temperature, air humidity, and wind speed were recorded by an automatic weather station located in the vineyard 2 m above the vine canopy. Volumetric soil water content was measured by time domain reflectrometry (TDR) (Trase system 1, Soil Moisture Equipment, Santa Barbara, CA). For each treatment, 15 cm long TDR probes were installed in six mini-lysimeters (one transect for each experimental unit) and an additional six probes were positioned outside the pots, at the same distance from the rows as the mini-lysimeters. Soil moisture readings were periodically taken over the study period shortly after all the mini-lysimeters were weighed (~1000 hr). Additionally, for each treatment, three couples of 30 cm long TDR probes were installed in correspondence with plots where chamber measurements were taken. Cover crop biomass and leaf area determination. Before and after mowing, cover crop height was measured on 30 leaves in each mini-lysimeter and on 100 leaves in each chamber plot. For MG, mini-lysimeters, and chamber plots, aboveground biomass was clipped, collected, and fresh and dry matter data were recorded. Mini-lysimeter cover crop height was subsequently measured on a sample of 30 leaves per pot on DOY 161 and 170. For chamber plots, leaf area was estimated and leaf area index (LAI) calculated as m 2 of green leaf area per m 2 of ground area. Cover crop LAI was estimated using the linear relationship between cover crop height and LAI (R 2 = 0.92). The relationship was obtained by periodically collecting cover crop samples on undisturbed plots. A 10 x 10 cm square grid was positioned on a grassed area, and the height of 100 leaves was measured. Leaves were then scanned using Photoshop Elements (Adobe, San Jose, CA) and green leaf area was
estimated using image-analysis Image J software (National Institutes of Health, Bethesda, MD). Statistical analysis. Soil volumetric moisture and minilysimeter ETcc (MG, UMG) and Es (ST) over time were analyzed using proc MIXED repeated measures (SAS Institute Inc., Cary, NC). Tukey pairwise comparison test was used to compare means among treatments (UMG, MG, ST) ( p < 0.05). For pair comparisons, t test was used.
Results Mini-lysimeter data. Aboveground dry clipped biomass at mowing date (DOY 142) was 1.86 t/ha. At the end of the experiment, 28 days after mowing, MG cover crop height and LAI averaged 10 cm and 4.5 m 2/m 2 , while UMG cover crop was 20 cm and 9 m 2/m 2 , respectively. Over the study period, cumulated water used by mini-lysimeters assigned to UMG, MG, and ST treatments was 56.7, 45.3, and 29.4 mm, respectively. Average daily water use differed among the three treatments (p < 0.001) (UMG = 4.34 mm/day; MG = 3.38 mm/day; ST = 1.97 mm/day). Over the first four days after mowing, MG used an average of 30% less water than UMG. However, from day eight to the end of the study period differences between the two cover crop treatments decreased, ranging from 13 to 20%. Throughout the experimental period ST Es was 48% and 37% lower than UMG and MG ETcc, except for days following a rain event (such as day 19; 23) when ST E s was similar to MG ETcc (Figure 2). After mowing, recorded rainfall over the 28-day period was 70 mm. Hence, soil water content inside mini-lysimeters was always above the wilting point (14.4% v/v), resulting in plant available water for evaporation (data not shown). For each treatment, soil water content did not differ between the mini-lysimeters and the surrounding area (0 to 15 cm) ( p < 0.05) nor did it differ in mini-lysimeters among treatments, although average soil moisture was slightly higher in the ST than in the MG and UMG treatments (ST = 26.8% v/v; MG = 26.3% v/v; UMG = 25.8% v/v). It must be noted that soil
Figure 2 Vertical bars represent the daily water use (ETcc, Es, mm/day) for the unmowed cover crop (UMG), mowed cover crop (MG), and bare soil tillage (ST) measured using mini-lysimeters. Measurements were taken the day before mowing (-1) and during the 28-day period following the mowing (1–28). Points indicate the daily average solar radiation (W/ m2). Data are mean values ± SE (n = 12). Arrows indicate rain events.
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moisture readings were taken to monitor if plant available water remained above the permanent wilting point and not as a means to estimate ETcc or Es. Chamber system data. After mowing (DOY 142 and 193), ETcc markedly decreased with the percentage of reduction, between 35 and 49%, dependent on the amount of clipped biomass and initial cover crop height (16 to 30 cm). An exponential relationship between percentage of ETcc reduction and dry clipped biomass was observed (r 2 = 0.97; Figure 3). The day after mowing (DOY 143), ETcc hourly rate in the MG plots was consistently lower (p < 0.01) than UMG plots, with MG using an average of 26% less water than UMG (Figure 4A). Cover crop height and LAI averaged 5 cm and 2 m 2/ m2, respectively, for MG and 18 cm and 8 m 2/m2, respectively, for UMG. Nineteen days after mowing (DOY 161) similar ETcc hourly rates were observed in the UMG and MG plots (Figure 4B). MG ETcc was significantly lower than UMG ETcc only during the first measurement of the day ( p = 0.01). On DOY 161, MG cover crop height and LAI were 10 cm and 4.5 m 2/m 2, respectively, whereas corresponding UMG values were 21 cm and 9.4 m 2 /m 2 . On DOY 170 and 192, hourly ETcc rate in MG plots was higher ( p < 0.001) than that in ST plots (Figure 5). On either day, average ETcc was ~76% higher than Es.
Discussion Regardless of sample methodology, mini-lysimeter or portable gas-exchange chamber, results showed that mowing was effective at reducing ETcc. Not surprisingly, in the period following mowing, the extent of the ETcc reduction decreased as the cover crop regrew. Chamber data taken 19 days after mowing showed that hourly ETcc rates in the MG and UMG plots were very similar (Figure 4B). Although cover crop leaf area, expressed as LAI, was higher in the UMG (9.4 m 2/m 2) than in the MG (5 m 2/m 2) plots, several layers of leaves may have been in the shade. The amount of green leaf area exposed to the sun in the MG and UMG plots could have been
Figure 3 Relationship between the percentage of cover crop evapotranspiration (ETcc) reduction and dry biomass (g/m2) clipped at the time of mowing (DOY 142, 193).
nearly identical at that point, resulting in similar ETcc rates in the two treatments. Moreover, the MG cover crop may have transpired more actively than the UMG cover crop due to the younger leaf tissue age during regrowth (Asseng and
Figure 4 Hourly trend of cover crop evapotranspiration (ETcc, mm/hr) in the unmowed (UMG) and mowed (MG) interrow one day (A) and 19 days (B) after mowing. ETcc rates were determined using a gas-exchange chamber system. Points indicate hourly solar radiation values (W/m2). Within a single measurement session, significant differences between UMG and MG treatments are denoted by asterisks (p < 0.01). ETcc values are mean ± SE (n = 3).
Figure 5 Hourly trend of cover crop evapotranspiration and soil evaporation (ETcc, Es, mm/hr) in the mowed (MG) and bare soil tillage (ST) within the interrow. E rates were determined using a gas-exchange chamber system. Points indicate hourly solar radiation values (W/m2). Data were collected one day (A) and one month (B) after ST was implemented. Within a single measurement session, significant differences between treatments are denoted by asterisks (p < 0.001). Values are mean ± SE (n = 3).
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Hsiao 2000). Similar to our results, Asseng and Hsiao (2000) reported a reduction in evapotranspiration of alfalfa, equal to ~70%, in correspondence to a mowing event. However, 21 days later, the extent of this reduction was reduced to 12%. Mini-lysimeter measurements taken on the same day as chamber readings (19 days after mowing) showed a difference in ETcc between UMG and MG treatments of ~20% (Figure 2). Lower cover crop height in MG mini-lysimeters (6.5 cm) than in the surrounding MG area (10 cm) perhaps restricted cover crop rooting depth and volume, explaining the higher differences in ETcc between the MG and UMG treatments observed when using mini-lysimeters as compared to the chamber. However, mini-lysimeter data confirmed that the mowing has a reducing effect on ETcc, which decreases over time. In other studies, mowing the vineyard interrow at the beginning of the dry summer season (end of May, beginning of June) resulted in a strong vegetation reduction due to low soil water availability, which was not able to recover until the fall (Celette et al. 2005, Monteiro and Lopes 2007). Under their experimental conditions, ETcc reduction obtained with mowing may have not decreased over time as in our study. However, low soil water content observed in those studies likely had a stronger effect in reducing ETcc than mowing. Mini-lysimeter data shows that ST Es and MG ETcc were similar after a rainfall event, when the soil surface was wet (Figure 2). After the shallow soil layers dried, E s dropped quickly. Similarly, Yunusa et al. (2004) found that vineyard Es peaked to 4.7 mm/day following a rainfall and dropped to ~1 mm/day a few days later. Moreover, Es contribution to total vineyard evapotranspiration rapidly decreased from 65% during a wet period to 27% one week later in the absence of precipitation. Our chamber data confirmed the large differences in water fluxes from bare soil and cover crops when used as an interrow floor management system (Figure 5).
Literature Cited Asseng, S., and T.C. Hsiao. 2000. Canopy CO2 assimilation, energy balance, and water use efficiency of an alfalfa crop before and after cutting. Field Crops Res. 67:191-206. Battany, M.C., and M.E. Grismer. 2000. Rainfall runoff and erosion in Napa Valley vineyards: Effects of slope cover and surface roughness. Hydrol. Process. 14:1289-1304. Baumgartner, K., K.L. Steenwerth, and L. Veilleux. 2008. Cover-crop systems affect weed communities in a California vineyard. Weed Sci. 56:596-605. Boast, C.W., and T.M. Robertson. 1982. A “micro-lysimeter” method for determining evaporation from bare soil: Description and laboratory evaluation. Soil Sci. Soc. Am. J. 46:689-696. Celette, F., J. Wery, E. Chantelot, J. Celette, and C. Gary. 2005. Belowground interactions in a vine (Vitis vinifera L.)-tall fescue (Festuca arundinacea Schreb.) intercropping system: Water relations and growth. Plant Soil 276:205-217. Centinari, M., S. Poni, I. Filippetti, E. Magnanini, and C. Intrieri. 2009. Evaluation of an open portable chamber system for measuring cover crop water use in a vineyard and comparison with a mini-lysimeter approach. Agr. Forest. Meteorol. 149:1975-1982. Centinari, M., S. Poni, D.S. Intrigliolo, D. Dragoni, and A.N. Lakso. 2012. Cover crop evapotranspiration in a northeastern US Concord (Vitis labruscana) vineyard. Aust. J. Grape Wine Res. 18:73-79. Guerra, B., and K. Steenwerth. 2012. Inf luence of f loor management technique on grapevine growth, disease pressure, and juice and wine composition: A review. Am. J. Enol. Vitic. 62:149-164. Morlat, R., and A. Jacquet. 2003. Grapevine root system and soil characteristics in a vineyard maintained long-term with or without interrow sward. Am. J. Enol. Vitic. 54:1-7. Monteiro, A., and C.M. Lopes. 2007. Influence of cover crop on water use and performance of vineyard in Mediterranean Portugal. Agric. Ecosyst. Environ. 121:336-342. Olmstead, M.A. 2006. Cover Crops as a Floor Management Strategy for Pacific Northwest Vineyards. College of Agriculture, Human, and Natural Resource Sciences, Washington State University, Prosser.
Conclusions
Saxton, K.E., and P.H. Willey. 2005. The SPAW model for agricultural field and pond hydrologic simulation. In Watershed Models. D.K. Frevert and V.P. Singh (eds.), pp. 400-435. Taylor & Francis, Boca Raton, FL.
Our results show that, immediately after mowing, ETcc markedly decreased, with the percentage of reduction ranging from 35 to 49%, depending on the amount of clipped biomass. ETcc recovered over time as the cover crop regrew. Mowing could be effectively used as a short-term water management strategy to reduce cover crop competition on the vine.
Yunusa, I.A.M., R.R.Walker, and P. Lu. 2004. Evapotranspiration components from energy balance, sapf low and microlysimetry techniques for an irrigated vineyard in inland Australia. Agr. Forest. Meteorol. 127:93-107.
Stannard, D.I., and M.A. Weltz. 2006. Partitioning ET in sparsely vegetated rangeland using a portable chamber. Water Resour. Res. 42:W02413.
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