| dc.description.abstract | The climatic conditions in the Western Cape province in South African (SA) vary considerably and water shortages are inevitable; consequently, sustainable management of soil and water resources should be of increasing concern. Wine production is one of the major production industries in the Lower Orange Northern Cape and Western Cape and produces large volumes of low-quality wastewater. The aim of this study was to investigate the effect of winery wastewater (WW) as an irrigation source on selected soil chemical characteristics and enzyme activities.
Four soils (Stellenbosch clay loam, Stellenbosch sand, Lutzville sand and Robertson clay loam) were collected from the top 0-30 cm layer at different wine producing regions of the Western Cape and placed in plastic bags for transport and storage. After sieving, the soils were placed in 15.2 cm diameter and 20 cm height pots. The pots were irrigated with WW and municipal wastewater (MW) for three simulated irrigated seasons under a controlled environment, where municipal water was used as the control. Each simulated season contained six irrigations and soils were re-irrigated when water content reached 50-60% water deficit, which varied for each soil. Both water sources were analyzed for N, P, K, Ca, Mg, Na, HCO3- and for pH, electrical conductivity (EC), and chemical oxygen demand (COD) at each irrigation event. At the end of each simulated irrigation season, the soils were analyzed for three enzymes (β-glucosidase, phosphatase and urease) and chemical parameters (total N, extractable NO3-, NH4+, P, K, Ca, Mg, and Na, pH, salinity (ECe), organic carbon (OC)).
The WW used in this study had significantly higher amounts of almost all measured soil characteristics when compared to the MW. The WW had higher COD, pH, EC, sodium adsorption ratio (SAR) and potassium adsorption (PAR) and consequently their addition to soils significantly increased these soil chemical characteristics. Analysis of soils after irrigation showed that the initial (baseline) level of β-glucosidase and phosphatase in each of the four studied soils was higher than the levels measured after irrigation with either water source. However, irrigation with MW and WW during the three simulated irrigation seasons for the three study soils resulted in an increase in urease levels, with an exception in the Robertson clay loam.
The content in the WW was one order of magnitude greater for some chemicals (N, P, Ca, Mg, Na, Cl-) and was two orders of magnitude greater for others (K, HCO3.). Most of these elements significantly increased in the soil after irrigation with WW except for N and Ca. The lack of increase in NH4+-N was possibly due to increased ammonia volatilization in soils with higher pH resulting from WW irrigation. The lack of increase in NO3--N may be due to increased denitrification in soils with anaerobic conditions resulting from irrigation with WW with high COD levels. The lack of increase in soil exchangeable Ca may be caused by the formation of calcium carbonates, which is favoured by high pH, high carbonates added, and high Ca.
The increased soil ECe observed was up to four times the initial ECe value. However, the ECe values in the Robertson clay loam soil were similar to the baseline values for all simulated irrigation seasons mainly because the soil ECe values were initially high. The observed salts in the soil exceeded the threshold of 1.5 dS/m that is recommended for vineyards. Also, the in-crease in Na after WW addition resulted in an increased extractable sodium percentage (ExSP). However, this increase did not reach the threshold of 15 to cause soil physical permeability problems.
Winery wastewater contains essential elements and other ions which can have direct effects on soil properties. These effects include the increase in plant-available nutrients when essential elements are added in the irrigation water and the increase in possible enzyme activity if certain essential elements are added. The WW shows potential as irrigation water mainly because it can increase K, P, and urease activity. However, care is needed as the WW may increase salts and Na in the soil to detrimental levels and thus the WW should be monitored constantly. It is worth noting that these detrimental levels may not be reached in the field because this was a closed study and no leaching occurred. Therefore, in an open system, such as field conditions in a vineyard, leaching may remove some salts and Na. | en_US |
