Technical Yearbook 2023

TABLE 2. The dry matter production (DMP) of the winter cover crops was determined for the treatments applied in the vineyard irrigated full surface in September for the duration of the study. Treatment no. Catch crop/cover crop combination DMP (t/ha) 2017 2018 2019 2020 1 Pearl millet/Oats 1.56 0.63 0.92 1.84 2 Pearl millet/N-fixing mixture 1.67 4.18 3.71 0.34 3 Dolichos beans/Oats 1.57 0.62 1.05 2.08 4 Dolichos beans/N-fixing mixture 2.78 2.95 3.23 0.77 5 Chicory/Oats 2.20 0.82 1.26 1.85 6 Chicory/N-fixing mixture 1.63 4.74 3.18 0.61 7 None/Oats 2.43 1.14 0.80 1.45 8 None/N-fixing mixture 1.75 4.01 3.01 0.52 LSD (p=0.05) NS 1.63 1.04 1.34

• ARC for infrastructure and resources. • Staff of the Soil and Water Science division at ARC Infruitec-Nietvoorbij for technical support. References https://www.wineland.co.za/winery-wastewater-for irrigation-part-3/

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 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. Acknowledgements • The project was funded by Winetech and the Agricultural Research Council (ARC). vineyard soil. Conclusions

Abstract Wineries produce between 3 to 5 m 3 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. 

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

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TECHNICAL YEARBOOK 2023