In-field fractional use of winery wastewater with raw water (Part 5): Assessment of the below- and above-ground chemical status of grapevines in the lower Olifants River region

Abstract

Wineries produce large volumes of poor-quality wastewater, particularly during harvest. As water resources are limited, wine-grape producers will have to use their natural resources judiciously to produce grapes. Therefore, it is important that the sustainable use of alternative water sources for vineyard irrigation be investigated. In this regard, experimental plots were selected in three selected production areas in the Western Cape Province. Within each region, two plots were selected which differed in soil texture. Grapevines were irrigated with the in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation for four seasons. Results showed that there was a substantial accumulation of salts at the shallow sand experimental plot in the Olifants River region (LOR2) after only two years of the in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation. Furthermore, the accumulation of elements, particularly sodium (Na) and chloride (Cl), in the permanent structure of the grapevines at this particular experimental plot could explain the poor response of the grapevines to the winery wastewater irrigation. Under the prevailing conditions, the wastewater irrigation had to be terminated, and this soil/climate combination should be considered unsuitable for the long-term application of winery wastewater. On a deep sand in the same region, no detrimental effects of the in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation were observed.

Introduction

Wineries produce large volumes of poor-quality wastewater, particularly during harvest. As water resources are limited, wine-grape producers will have to use their natural resources judiciously to produce grapes. Therefore, it is important that the sustainable use of alternative water sources for vineyard irrigation be investigated.^1,2 In this regard, experimental plots were selected in three selected production areas in the Western Cape Province, namely the Coastal, Breede River and Olifants River regions.¹ Within each region, two plots were selected which differed in soil texture. Grapevines were irrigated with the in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation for four seasons.

After only two seasons of using the in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation at the shallow sand experimental plot in the Olifants River region (LOR2), the low yield and poor vegetative growth was a matter of great concern.² Although the fractional ratio was changed from 0.5 to 0.25 in the 2018/19 season, it was evident that large amounts of elements were still being applied via the irrigation. It also did not seem sustainable to apply larger volumes of irrigation to increase the yield. Furthermore, results from the soil analyses after winter 2019 confirmed that in this region of low winter rainfall, that excessive salts applied via the irrigation were not leached sufficiently in winter. Similar results were reported for soils in a pot study.³ Taking above-mentioned into consideration, the in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation at the LOR2 experimental plot had to be terminated at the end of the 2018/19 season to prevent further damage to the grapevines. It is well known that irrigation with saline water can have a detrimental effect on grapevines^4,5 due to accumulation of elements within the grapevine.

Given the substantial amounts of elements applied via the in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation in the Lower Olifants River region, together with the low mean annual rainfall,² the objective of this study was to make an assessment of the below- and above-ground chemical status of the grapevines growing in the Lower Olifants River region. The termination of the fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation at the LOR2 experimental plot and the irrigation thereof for two years with raw water according to the producer’s schedule gave the opportunity to assess the permanent wood structure at the end of the study to give an indication of the recovery, if any, in terms of element accumulation in the permanent wood parts.

Methods

Details of the plot selection, augmentation, climatic conditions, irrigation application, water quality, nutrient load and soil responses were given previously.² Briefly, there was a loamy sand (C1) and sandy clay loam (C2) experimental plot in the Coastal region, a sandy loam (BR1) and sandy clay loam (BR2) experimental plot in the Breede River region, as well as a deep sand (LOR1) and shallow sand (LOR2) experimental plot in the Lower Olifants River. Experimental plots were irrigated using the in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation from the 2017/18 to 2020/21 seasons.

Soil samples were taken from the 0-30 cm, 30-60 cm and 60-90 cm layers in September 2019 at the LOR2 plot. Samples were analysed as discussed previously.² Each of the selected vineyards had an experimental plot that was or had been irrigated with winery wastewater and this was compared to the rest of the surrounding vineyard block which acted as the control.

Soil profile pits were dug at the LOR2 shallow sand experimental plot and control in September 2019. The soil was removed carefully from the profile pit and placed onto a sieve. Roots were separated from the soil and placed into bags. Samples were collected in a similar way at the LOR1 experimental plot and control in May 2021. The excavated roots were washed carefully, dried and analysed by a commercial laboratory as described previously.² Permanent wood was sampled at the LOR2 shallow sand experimental plot and control in September 2019 and July 2021. Permanent wood was sampled at the LOR1 deep sand experimental plot and control in July 2021. Samples were analysed as described previously.

Results

Soil

In September 2019, soil potassium (K) of the LOR2 experimental plot was considerably higher than the control to a depth of 90 cm (Figure 1). In contrast, soil sodium (Na) only tended to be higher to a depth of 60 cm in the root zone. This suggested that the raw water irrigation had leached the Na beyond the root depth. In this case, the Na was probably released over time as the parent material weathered after soil preparation. It should be noted that the soil Na in the 30-60 cm layer of the experimental plot was above the proposed norm of 0.4 cmol/kg, where negative grapevine responses can be expected (Conradie, personal communication).

FIGURE 1. Levels of (A) soil K and (B) Na in the LOR2 shallow sand experimental plot and control, respectively, in September 2019.

Roots

Results indicated that the in-field fractional use (augmentation) of winery wastewater with raw water for irrigation promoted the accumulation of nitrogen (N) and phosphorus (P) in the roots of the LOR2 experimental grapevines (Figure 2).

FIGURE 2. Variation in (A) N, (B) P and (C) K in the grapevine roots sampled from the 0-30 cm and 30-60 cm soil depth layers at LOR2.

Furthermore, the Na and chloride (Cl) in the grapevine roots (Figure 3) sampled from the LOR2 shallow sand experimental plot were substantially higher compared to those of the control, which had been irrigated with raw water only (Figure 3). This indicated that the grapevine stored these elements in its below-ground structure.

FIGURE 3. Variation in (A) Na and (B) Cl in the grapevine roots sampled from the 0-30 cm and 30-60 cm soil depth layers at LOR2.

The in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation promoted the accumulation of P and K in the roots of the experimental grapevines at the LOR1 deep sand plot measured in May 2021 (Figure 4).

FIGURE 4. Variation in (A) N, (B) P and (C) K in the grapevine roots sampled from the 0-30 cm, 30-60 cm and 60-90 cm soil depth layers at LOR1.

In contrast to the LOR2 shallow sand experimental plot, there were no detrimental effects of the in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation on Na and Cl accumulation in the grapevine roots at the LOR1 deep sand experimental plot (Figure 5).

FIGURE 5. Variation in (A) Na and (B) Cl in the grapevine roots sampled from the 0-30 cm, 30-60 cm and 60-90 cm soil depth layers at LOR1.

Permanent wood

At pruning in July 2019, visual observation revealed that salts had precipitated on the grapevine trunks in the LOR2 experimental plot after two seasons of the in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation. The Na, manganese (Mn) and iron (Fe) in permanent wood sampled from grapevines in the LOR2 shallow sand experimental plot in September 2019 was substantially higher compared to the control (Table 1). This indicated that the grapevine stored these elements in the permanent above-ground structure. Although grapevines in the experimental plot were irrigated with raw water from September 2019, the damage to the grapevine trunks was still visible at the end of November 2019. Interestingly, high levels of Na in the 60-90 cm soil layer in the control, i.e. below the root zone, did not seem to have a negative effect on visual grapevine performance. After two years of irrigation with raw water, the levels of Na, Mn and Fe measured in the permanent wood in July 2021 (Table 2) at the LOR2 experimental plot were substantially lower compared to levels in September 2019 (Table 1). There were no general trends in the element contents of the permanent wood of grapevines growing in the experimental plot and control sections at LOR1 (Table 3).

TABLE 1. N, P, K, Ca, Mg, Na, Mn and Fe element contents in the permanent wood of grapevines growing in the experimental plot and control at the LOR2 plot in September 2019.

TABLE 2. N, P, K, Ca, Mg, Na, Mn and Fe element contents in the permanent wood of grapevines growing in the experimental plot and control at the LOR2 plot in July 2021.

TABLE 3. N, P, K, Ca, Mg, Na, Mn and Fe element contents in the permanent wood of grapevines growing in the experimental plot and control at the LOR1 plot in July 2021.

Conclusions

Results showed that there was a substantial accumulation of salts in the soil at the LOR2 experimental plot after only two years of the in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation. Furthermore, the accumulation of elements, particularly Na and Cl, in the permanent structure of the grapevines at the LOR2 shallow sand experimental plot could explain the poor response of the grapevines to the winery wastewater irrigation. Under the prevailing conditions, the wastewater irrigation had to be terminated, and this particular soil/climate combination should be considered unsuitable for the long-term application of winery wastewater. Results showed that the high levels of Na and Cl in the permanent parts could decline if the grapevines were irrigated with raw water. On the deep sand LOR1 experimental plot, no detrimental effects of the in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation were observed.

Acknowledgements

• This report is an output of WRC Project K5/2561, entitled “Use of winery wastewater as a resource for irrigation of vineyards in different environments”. This solicited project was initiated, funded and managed by the WRC. The project was co-funded by Winetech and ARC.
• ARC for infrastructure and resources.
• Staff of the Soil and Water Science division at ARC Infruitec-Nietvoorbij for their assistance, and in particular Mr. F. Baron for his dedicated technical support.
• Backsberg, Madeba, Lutzville Winery and Spruitdrift Winery for permitting the project team to work at their wineries and in their vineyards. Colleagues at the wineries for their assistance and support.
• Mr W. Smit from Netafim for advice and designing the irrigation systems.

References

1. Myburgh, P.A. & Howell, C.L. 2014. Use of winery wastewater as a resource for irrigation of vineyards in different environments. WRC Report No. 1881/1/14. ISBN 978-1-4312-0591-2.
2. Howell, C.L., Myburgh, P.A. & Hoogendijk, K., 2022. Use of winery wastewater as a resource for irrigation of vineyards in different environments. WRC Report No. 2651/1/22. ISBN 978-0-6392-0341-6.
3. Mulidzi, A.R., 2016. The effect of winery wastewater irrigation on the properties of selected soils from the South African wine region.D. dissertation. Stellenbosch University, Private Bag X1, 7602 Matieland (Stellenbosch), South Africa.
4. McCarthy, M.G., 1981. Irrigation of grapevines with sewage effluent. I. Effects on yield and petiole composition. Am. J. Enol. Vitic. 32, 189-196.
5. McCarthy, M.G. & Downton, W.J.S., 1981. Irrigation of grapevines with sewage effluent. II. Effects on wine composition and quality. Am. J. Enol. Vitic. 32, 197-199.

For more information, contact Carolyn Howell at howellc@arc.agric.za.

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