Winery wastewater for irrigation (Part 3): Vineyard catch- and cover crop responses

Grapes are an important crop in the Western and Northern Cape. The wine industry makes a significant contribution to the economy in these regions. In 2022, there were 2 487 primary wine grape growers and 524 cellars which crush grapes.¹ The wine industry also provides a large number of employment opportunities, particularly in rural areas. In 2022, the vineyards planted for wine production in South Africa amounted to 89 384 hectares, of which approximately 90% is four years and older.¹ During wine production, wineries produce large volumes of poor-quality wastewater (between 3 to 5 m³ per tonne of grapes crushed).² This wastewater can be used for irrigation, but this delivers substantial amounts of elements to the soil.^3,4

Introduction

In a previous study where diluted winery wastewater was used for irrigation of a Cabernet Sauvignon vineyard, a summer catch crop of Pearl millet and a winter cover crop of oats removed substantial amounts of K from a sandy soil.⁵

There are many benefits to cultivating a winter cover crop in a vineyard.⁶ These include:

• restricting water runoff and erosion;
• maintenance or improvement of the organic matter content of soil;
• reducing water consumption of grapevines;
• weed control efficacy; and
• maximum production of quality grapes.

The aim of this study was:

1. to determine whether irrigation of a vineyard with diluted winery wastewater affected the performance and nutrient content of selected catch crops in a vineyard on loamy sand to sandy clay loam soil,
2. to determine the ability of the selected catch crops to intercept sufficient amounts of Na and K from the soil, and
3. to determine whether a further benefit of winter cover crops could be element interception and to what extent?

Methods

Diluted winery wastewater was 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. Details of the irrigation application and water quality have been given previously.⁷ The dry matter production (DMP) of the catch and cover crops was estimated by sampling the above-ground vegetative growth in a 0.5 m² sub-plot randomly chosen in each plot. Samples were oven-dried for 48 hours at 105°C. A sample was collected from the sub-plot and analysed by a commercial laboratory for macro- and micro-elements. The amounts of the different macro- and micro-elements intercepted by the catch and cover crops were estimated by multiplying the DMP of the species with the concentration of the different elements in the samples harvested for analyses.

Results and discussion

The DMP, which is commonly used as an indication of how well a catch/cover crop grows under prescribed conditions is shown in Table 1. Over the three years of using the catch crops, only the Dolichos beans (T3 & T4) performed consistently with the growth increasing over the duration of the trial. On average, Pearl millet (T1 & T2) produced a DMP of 0.2 t/ha, Chicory (T5 & T6) was 0.04 t/ha and Dolichos beans (T3 & T4) was 1.05 t/ha. The poor performance of the Pearl millet (T1 & T2) catch crop was opposite to the substantial DMP produced by a Pearl millet catch crop in a previous sandy soil trial.⁵ It is possible that this was due to the heavier textured soil in the current study.

The DMP of the winter cover crops is given in Table 2. In particular, in September 2018 and 2019, the growth of the N-fixing winter (T2, T4, T6 & T8) cover crops was substantially more than that of the oats (T1, T3, T5 & T7).

On average over the three seasons, the Chicory (T5 & T6) had the highest P, K, Ca, Mg and Na in its foliage (Figure 1). Dolichos beans (T3 & T4) accumulated the most N in their foliage. Given that Dolichos beans (T3 & T4) produced the highest DMP, it generally extracted the most elements from the soil with the exception of Na (Figure 2).

As expected, the N-fixing winter cover crop (T2, T4, T6 & T8) accumulated higher N in its foliage when compared to the oats, i.e. T1, T3, T5 and T7 (data not shown). The average K contents of the foliage of the oats and N-fixing winter cover crops were 2.25% and 2.94%, respectively. The average Ca contents of the foliage of the oats and N-fixing winter cover crops were 0.28% and 1.07%, respectively. The average Mg contents of the foliage of the oats and N-fixing winter cover crops were 0.11% and 0.29%, respectively. The average Na contents of the foliage of the oats and N-fixing winter cover crops were 1 133 mg/kg and 1 834 mg/kg, respectively.

The N-fixing winter cover crop (T2, T4, T6 & T8) extracted substantially more elements from the soil. In this regard, the oats extracted, on average per year, 18 kg/ha, 3 kg/ha, 29 kg/ha, 4 kg/ha, 1 kg/ha and 1 kg/ha of N, P, K, Ca, Mg and Na from the vineyard soil. The N-fixing winter cover crop extracted, on average per year, 81 kg/ha, 8 kg/ha, 80 kg/ha, 27 kg/ha, 8 kg/ha and 5 kg/ha of N, P, K, Ca, Mg and Na from the vineyard soil.

Conclusions

Dolichos beans performed the best as a summer catch crop in the vineyard to intercept excessive salts, specifically N, P, K and Ca. However, the study showed that it also only absorbed a small percentage of the elements applied via irrigation. Catch crops are probably not the only solution when using winery wastewater for vineyard irrigation. It is recommended that the summer catch crop be removed from the vineyard before the seedbed preparation for the winter cover crop. Although the N-fixing winter cover crop extracted substantial amounts of elements from the vineyard soil, it extracted only low amounts of Na. However, the use thereof in vineyards is strongly recommended, because of all the positive benefits of cover crop cultivation. It should be chemically sprayed similarly to the practices for normal cover crop production to maintain the benefits of a winter cover crop and worked into the soil or removed before seedbed preparation for the summer catch crop. Given the substantially higher DMP of the N-fixing cover crop in winter, cultivating such a crop in the open land during the winter should also be considered rather than leaving the soil bare. It can be baled after winter to generate further income.

Abstract

Wineries produce between 3 to 5 m³ of wastewater per tonne of grapes crushed. Irrigation with winery wastewater adds substantial amounts of elements to the soil, therefore maximising element removal by sowing a catch crop is important. The objective of the study was to identify fodder-producing crops that would intercept sufficient K (and Na) applied via irrigation of a vineyard with diluted winery wastewater. Combinations of three different fodder-producing summer catch crops and two winter cover crop treatments were compared to a control. Dolichos beans performed the best as a summer catch crop in the vineyard to intercept excessive salts, specifically N, P, K and Ca. However, it only absorbed a small percentage of the elements applied via irrigation. Catch crops are probably not the only solution when using winery wastewater for vineyard irrigation. Although the N-fixing winter cover crop extracted substantial amounts of elements from vineyard soil, it also extracted only low amounts of Na from the soil. However, the use of winter cover crops in vineyards is strongly recommended, because of all the positive benefits of cover crop cultivation.

Soil responses will be presented in the next article.

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. SAWIS, 2022. South Africa wine industry statistics, wosa.co.za.
2. Mosse, K.P.M., Patti, A.F., Christen, E.W. & Cavagnaro, T.R., 2011. Review: Winery wastewater quality and treatment options in Australia. Aust. J. Grape Wine Res. 17, 111-122.
3. 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.
4. 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.
5. Fourie, J.C., Theron, H. & Ochse, C.H., 2015. Effect of irrigation with diluted winery wastewater on the performance of two grass cover crops in a vineyard. S. Afr. J. Enol. Vitic. 36, 210-222.
6. Fourie, J. 2021. Cover crops in South African vineyards. ABC Press, Cape Town.
7. Howell, C., Freitag, K. & Sassman, L., 2023. Winery wastewater for irrigation (Part 1): Irrigation application and water quality. WineLand August 2023, 61-63.

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

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