Winery wastewater for irrigation (Part 4): Soil responses

Wineries use potassium (K) and sodium (Na) based cleaning agents which results in high levels of these elements in its wastewater.¹ Therefore, using winery wastewater for irrigation adds substantial amounts of these salts to the soil.

Introduction

In a previous study where diluted winery wastewater was used for irrigation of a Cabernet Sauvignon vineyard growing on sandy soil, soil K and Na increased with a decrease in the dilution of the winery wastewater.² The use of the in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation in different environments also increased soil K and extractable potassium percentage (ExPP).³

Wastewater containing high levels of K could be beneficial to overall soil fertility, except where accumulation of K in soils causes excessive uptake by grapevines. This could have negative effects on wine pH which is important for red wine colour stability. However, excessive Na application and accumulation thereof with no concomitant increase in Ca and/or Mg could have negative effects on soil chemical and physical properties. This could reduce grapevine growth, yield and quality, particularly if the elements accumulate to toxic levels. Furthermore, if deep leaching of accumulated K and Na occur during winter, it could pollute natural water resources in the long run.

The objective of this study was therefore to determine the effect of irrigation of open land and a vineyard with diluted winery wastewater on the soil chemical status in loamy sand to sandy clay loam soil.

Methods

Diluted winery wastewater was applied to open land on the Nietvoorbij research farm where 10 different fodder producing catch crops (Table 1) were compared to a control treatment where no catch crop was cultivated in summer. Diluted winery wastewater was also applied to a Shiraz vineyard on the Nietvoorbij research farm where combinations of three different fodder producing summer catch crops and two winter cover crop treatments were compared to a control. Catch crops were not cultivated in the control treatment during the summer, but there were still two winter cover crop treatments. The region has a Mediterranean climate. Details of the irrigation application, water quality, catch and cover crop responses have been given previously.^4,5,6 The soil chemical status was determined pre-treatment for both the open land and vineyard experiments. Soil chemical status was quantified every year at the end of the irrigation season in April/May and in October after the winter rainfall had ceased.

Results and discussion

In general, there were no significant differences in the K, Ca, Mg and Na of the open land experiment that could be related to the different summer catch crop and bare soil treatments (Table 1). Trends over time for four years for the open land are given in Figure 1. The use of diluted winery wastewater for irrigation of the open land increased soil pH_(KCl), K and Na regardless of the catch crops cultivated when compared to the pre-treatment values (Figure 1). This was expected given the large amounts of salts added via the irrigation⁴ and the inability of the catch crops to take up these salts.⁵

Irrespective of catch crops, the application of diluted winery wastewater (T1 – T6) rather than raw water (T7 & T8) in the vineyard tended to increase soil K, particularly in the 0 – 150 cm soil layer (Table 2). This was to be expected given that winery wastewater contains high levels of K and substantial amounts of K were applied via irrigation.⁴ Furthermore, the catch crops absorbed only a small amount of the elements applied via the irrigation.⁶ Similar findings with respect to soil K have been reported previously where diluted winery wastewater was used for vineyard irrigation² or where the in-field fractional use (augmentation) of winery wastewater with raw water for vineyard irrigation was used.³ The ExPP increased for treatments in the current study where diluted winery wastewater was used for irrigation rather than where raw water was used for irrigation (data not shown). Similar responses have been reported previously.^2,3,7,8

Trends after three years for the Shiraz vineyard are given in Figure 2. Irrespective of catch crops, the use of diluted winery wastewater for irrigation of the vineyard increased soil K compared to the raw water treatments compared to the pre-treatment values (Figure 2). Consequently, ExPP increased (data not shown).

Conclusions

There were no significant differences in soil K, Ca, Mg and Na that could be related to the different summer catch crop and bare soil treatments of the open land where diluted winery wastewater was used for irrigation. Using diluted winery wastewater for irrigation of the open land increased soil pH_(KCl), K and Na over time regardless of the catch crops cultivated. The application of diluted winery wastewater rather than raw water in the vineyard, regardless of the catch crop cultivated, tended to increase soil K, particularly in the top-soil. This was expected given that winery wastewater contains high levels of K. Although irrigation with diluted winery wastewater had almost no other effects, element accumulation particularly with respect to K and Na, might be more prominent in regions with lower winter rainfall. It should be noted that in lighter textured soils, more effective leaching is likely to result in less salt accumulation.

Abstract

Wineries use potassium (K) and sodium (Na) based cleaning agents which results in high levels of these elements in its wastewater. Using winery wastewater for irrigation therefore adds substantial amounts of these salts to the soil. The objective of this study was to determine the effect of irrigation of open land and a vineyard with diluted winery wastewater on the soil chemical status. Diluted winery wastewater was applied to open land where the soil of 10 different fodder producing catch crops were compared to the soil of a control where no summer catch crop was cultivated. Diluted winery wastewater was also applied to a Shiraz vineyard where combinations of three different fodder producing summer catch crops and two winter cover crop treatments were compared to a control. Catch crops were not cultivated in the control treatment during the summer, but there were still two winter cover crop treatments. The region where the field trials took place has a Mediterranean climate. There were no significant differences in soil K, Ca, Mg and Na of the open land experiment that could be related to the different summer catch crop and bare soil treatments. Trends after four years showed that using diluted winery wastewater for irrigation of the open land increased soil pH_(KCl), K and Na regardless of the catch crops cultivated when compared to pre-treatment values. The application of diluted winery wastewater rather than raw water in the vineyard, regardless of the catch crop cultivated, tended to increase soil K, particularly in the top-soil. It should be noted that in lighter textured soils, more effective leaching is likely to result in less salt accumulation in the top-soil. Irrigation using diluted winery wastewater might also cause more prominent K and Na accumulation in regions with low winter rainfall.

Acknowledgements

• The project was funded by Winetech and the Agricultural Research Council (ARC).
• ARC for infrastructure and resources.
• Staff of the Soil and Water Science division at ARC Infruitec-Nietvoorbij for technical support.

References

1. Howell, C.L. & Myburgh, P.A., 2018. Management of winery wastewater by re-using it for crop irrigation – A review. S. Afr. J. Enol. Vitic. 39, 116-121.
2. Myburgh, P.A. & Howell, C.L. 2014. The impact of wastewater irrigation by wineries on soil, crop growth and product quality. WRC Report No. 1881/1/14. ISBN 978-1-4312-0591-2.
3. 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.
4. Howell, C., Freitag, K. & Sassman, L., 2023. Winery wastewater for irrigation (Part 1): Irrigation application and water quality. Winelands August 2023, 61-63.
5. Howell, C., Freitag, K. & Sassman, L., 2023. Winery wastewater for irrigation (Part 2): Evaluation of catch crops on open land. Winelands September 2023, a-b.
6. Howell, C., Mulidzi, R., Sassman, L. & Freitag, K., 2023. Winery wastewater for irrigation (Part 3): Vineyard catch- and cover crop responses. Winelands October 2023, x-y.
7. Mulidzi, A.R., Clarke, C.E. & Myburgh, P.A., 2015. Effect of irrigation with diluted winery wastewater on cations and pH in four differently textured soils. S. Afr. J. Enol. Vitic. 36, 402-412.
8. Mulidzi, A.R., Clarke, C.E. & Myburgh, P.A., 2018. Annual dynamics of winery wastewater volumes and quality and the impact of disposal on poorly drained duplex soils. S. Afr. J. Enol. Vitic. 39, 305-314.

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

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