Variation in kikuyu grass yield in response to irrigation with secondary and advanced treated wastewaters

Treated wastewater, also called as recycled water, is a reliable source of water for various non-potable purposes. One of the most common uses of recycled water has been for irrigation. A soil column study was carried out for a period of one year. The objective of this study was to determine the effect of irrigation using two different types of treated wastewaters on kikuyu grass (Pennisetum clandestinum) production in the absence of any kind of chemical fertilisers. Soil irrigated with secondary treated wastewater, MBR (Membrane Bioreactor), resulted in highest annual grass production (16,241 kg of dry-matter per hectare (kg DM/ha)) compared to advanced treated wastewater, IDAL (Intermittently Decanted Aerated Lagoon), and tap water (TW) with annual yields of 7028 and 14,216 kg DM/ha, respectively. Irrigation waters, soil extracted waters and soil samples from different depths of the columns were analysed. Sodium adsorption ratio (SAR), exchangeable cations, electrical conductivity (EC) and pH changed in each experimental column due to different characteristics of applied irrigation waters. The results indicate that high contents of nitrogen and phosphorous in MBR water compensated for the presence of moderate salinity level that contributed to the higher production of grass compared to other two types of irrigation waters. The increase in pH from initial amount of 5.9 to 7.3 in top part of IDAL-irrigated soil may have resulted in low grass yield. This pH increase can be attributed to the high concentrations of cations in the irrigation water in the lack of sufficient amount of nitrogen. Overall, the study demonstrated that a relatively higher grass yield in the absence of any types of fertilisers is possible with recycled water irrigation using secondary treated wastewater. Further, the recycled water irrigation with advanced treatment of wastewater, while costs more, does not result in increased yield benefits.