Evaluation of selected grass and broadleaf crops suitable for fodder as interception crops where winery wastewater is re-used for irrigation
Fourie, J C
Fourie, J C
Adams, K A
Sassman, L W
Van Huyssteen, I
Objectives and Rationale
Wineries generate approximately 15 330 million litres of wastewater per annum. Irrigation of crops with winery wastewater reduces energy use and treatment cost. Irrigation with winery wastewater needs to be optimised to minimise leaching whilst maximising nutrient removal using a catch crop. In a previous study investigating the use of diluted winery wastewater for vineyard irrigation, Avena strigosa cv Saia (oats) and Pennisetum glaucum cv Babala (pearl millet) removed significant amounts of K from a sandy soil whilst generating additional income. These species, however, consumed significant amounts of N. Additional nitrogen-fixing crops and grain crops adapted to soils with more than 4% clay that reach their peak growing period when wineries produce the highest volumes of wastewater need to be identified. Therefore, the study aimed to identify fodder-producing crops that would intercept sufficient K (and Na) applied via irrigation with diluted winery wastewater on loamy sand to sandy clay loam soils in both open land and a vineyard. The selected fodder-producing crops should minimise/prevent leaching and accumulation of especially K in these soils and should not have a negative impact on grapevine performance and wine quality.
Diluted winery wastewater was applied to an open plot where there were ten different fodder-producing catch crops, plus a control where no catch crop was cultivated in the summer. The vineyard experiment had combinations of three different fodder-producing summer catch crops and two winter cover crop treatments compared to a control. In this instance, catch crops were not cultivated in the control treatment during the summer, but there were still two winter cover crop treatments. Soil chemical status was determined by pretreatment for both the open land and vineyard experiments. After this, soil chemical status was quantified at the end of the irrigation season in April/May and in October after the winter rainfall had ceased. The dry matter production (DMP) and nutrient content of the catch crops cultivated in the open land and vineyard experiments was measured. In the vineyard, the DMP of the winter cover crops and nutrient content were measured. Grapevine and wine responses were quantified in the vineyard.
Vetiver grass, Dolichos beans and Chicory produced the highest DMP on open land. However, the growth of the Fodder beet, Bottlebrush grass and Weeping love grass was poor. Due to the substantially higher DMP of the Vetiver grass on the open land, it extracted more P from the soil than the other catch crops on average over the four years of the study. Dolichos beans extracted the most N and Mg from the soil on average for the trial. Due to the high K, Ca and Na nutrient contents in the foliage of the Chicory, it absorbed the most K, Ca and Na from the soil. In contrast, the Bottle bush grass and Weeping love grass catch crops extracted the least amount of elements from the soil. Except for Chicory, all other catch crops extracted less than 2 kg/ha of the Na applied per year via the winery wastewater. This is substantially lower than the amounts of Na applied via the winery wastewater. In general, there were no differences in soil K, Ca, Mg and Na of the open land experiment that could be related to the different catch crops and bare soil treatments. Under the prevailing conditions, the Vetiver grass also produced enough DMP to produce bales that could be sold. In the vineyard, only Dolichos beans performed consistently in terms of DMP. The Pearl millet and Chicory catch crops produced low DMP. The Dolichos beans accumulated the most N in their foliage. Given that the Dolichos beans produced the highest DMP, it generally extracted the most elements from the soil in the vineyard except Na. The Na extracted from the soil was below 1 kg/ha per year. This is substantially lower than the amounts of Na applied via the wastewater. Under the prevailing conditions, N-fixing cover crops cultivated in winter produced substantially more DMP than oats and extracted substantially more elements from the soil. However, as with the fodder-producing catch crops, the winter cover crops extracted only small amounts of Na from the soil. Irrespective of summer catch crops or winter cover crops in the vineyard, the use of diluted winery wastewater for irrigation increased soil K compared to the raw water treatments. Treatments did not affect vineyard performance negatively regarding yield, berry mass, shoot mass and leaf petiole, blade and juice element composition. In addition, sensory analyses of the wines showed no consistent negative aroma attributes that could be linked to the use of winery wastewater.
Key Conclusion of Discussion
Vetiver grass, Dolichos beans and Chicory showed potential as summer catch crops on open land, taking into consideration either their DMP or the amounts of elements they extracted from the soil. Vetiver grass could have commercial value given that it produced enough DMP to be harvested for alternative uses, but its element uptake for K, Ca and Na was not as good as that of the Chicory. Notably, the catch crops on the open land removed a low percentage of the elements applied via the wastewater. Dolichos beans performed best in the vineyard as a summer catch crop to intercept excessive salts, specifically N, P, K and Ca. However, it should be noted that only low amounts of Na were extracted from the soil. A winter N fixing cover crop should be considered where wastewater is used for irrigation in vineyards. However, it should be chemically controlled, similar to normal cover crop production practices to maintain the benefits of a winter cover crop, and worked into the soil or removed before seed preparation for the summer catch crop. Given the substantially higher DMP of the N fixing cover crops in winter, cultivating such a crop in the open land during the winter should be considered rather than leaving the soil bare. It can be baled after winter to generate further income.
Take Home message for Industry
Vetiver grass, Dolichos beans and Chicory performed best as summer catch crops on the open land. If element uptake from the soil is considered, the Dolichos beans and Chicory performed the best. However, the Vetiver grass produced enough DMP to make bales to sell. However, the summer catch crops still only absorbed a low percentage of elements applied via the diluted winery wastewater irrigation. Fodder beet, Bottlebrush grass and Weeping love grass performed the poorest. Dolichos beans performed best as a summer fodder-producing catch crop in the vineyard. However, the study showed it only absorbed a small percentage of the elements applied via irrigation. It is recommended that the summer catch crop be removed from the vineyard before the seed preparation for the winter cover crop. Although the N-fixing winter cover crop extracted substantial amounts of elements from vineyard soil, it extracted only low amounts of Na from the soil. However, the use thereof in the vineyard is strongly recommended because of all the positive benefits of cover crop cultivation.