Investigating the effects of irrigation water management techniques using anaerobic baffled reactor (ABR) effluents for crop production.
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Date
2018
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Abstract
The discharge of treated effluents from anaerobic baffled reactor (ABR) into surface and ground water bodies poses a challenge to the environment and can cause pollution. The need for the optimal use of land without a yield penalty in urban and peri-urban (UP) settlements such as Newlands KwaMashu Experimental site, Durban, South Africa is vital. The volume of ABR effluent generated by a decentralized wastewater treatment systems (DEWATS) in UP settings increased with population, urbanization and improved living conditions. Hence, the need to cultivate effluent irrigated crops is paramount and synonymous to treated wastewater reuse and management. Therefore, the study evaluated the effects of irrigation management techniques and intercropping on the growth and yield of flood irrigated Cocoyam (colocasia esculenta) and rice (oryza sativa l.) using ABR effluents. It was hypothesised that irrigation management techniques and intercropping do have a significant effect on the growth and yield of Cocoyam and rice irrigated with treated domestic wastewater
An open field trial using basin (flood) irrigation with ABR effluent and a pot experiment inside a tunnel house, for zero effective rainfall, were conducted concurrently with the same treatments in 2017 and 2018 planting seasons at the Newlands KwaMashu Experimental site, Durban, South Africa. The irrigation water management treatments consisted of alternate wetting and drying (AWD), conventional flood irrigation (CFI) and continuous wetting without flooding (WWF) and the cropping systems were sole Cocoyam, sole rice and intercropped Cocoyam and rice. The treatments with WWF was the control for Cocoyam and CFI was control for rice. Each of the treatments was replicated three times in a randomized complete block design (RCBD) layout.
Cocoyam from the open field and pot trials showed that the effects of the treatments were significant (P < 0.05) on the number of irrigation events, amount of irrigated water and daily water balance. The treatments had no effect on the growth parameters (plant height, leaf number and leave area index (LAI) (P > 0.05)). The treatments effects were, however, highly significant (P < 0.001) with respect to yield components (biomass, corm mass, corm number, corm size, harvest index), corm yield and water productivity (WP). The control (WWF) produced the highest yields of 7.52 and 9.84 t/ha for 2017 and 2018 seasons, respectively for field trials. The control (WWF) produced the highest yields of 4.97 and 6.40 t/ha for 2017 and 2018 seasons, respectively for pot trials.
The result for field and pot trials for rice revealed that the effects of irrigation management techniques were highly significant (P < 0.001) on number of irrigation events, amount of irrigation and daily water balance. However, there were no significant differences (P > 0.05) between irrigation management techniques with respect to the number of tillers per plant but significant (P < 0.05) on the number of panicles per plant. Similarly, irrigation management treatments did not differ significantly (P > 0.05) with respect to plant height and leaf area index (LAI). Significant differences (P < 0.05) were observed with respect to rice yield, though the treatment was not significant (P>0.05) with respect to rice yield in 2018 season. The effect was also significant (P < 0.05) on water productivity. The treatments AWD produced the highest grain yields of 5.68 in 2017 and 6.38 t/ha in 2018 season for field trials. The AWD treatments had the highest yields of 2.32 and 3.21 t/ha for 2017 and 2018 seasons, respectively for pot trials. The effect of intercropping was significant (P<0.05) with respect to the total number of irrigation and total water use. There was a significant reduction (P<0.05) on the plant heights of both Cocoyam and rice under intercropping. A significant (P<0.05) reduction also occurred on the number of Cocoyam leaves per plant, number of panicles per plant and number of tillers per plant for rice. Intercropping significantly reduced (P<0.05) the Cocoyam corm and rice grain yield over the two seasons as compared to sole cropping. The land equivalent ratio (LER) showed that intercropping Cocoyam with rice was not productive (LER < 1) than sole cropping of Cocoyam. It was established that there was no significant (P>0.05) effects of the treatments with respect to the growth parameters but was significant on the yield of sole Cocoyam and sole rice. The yields of Cocoyam under intercropping were 4.96 and 6.96 t/ha for 2017 and 2018 seasons while grain yields under intercropping were 0.84 and 1.0 t/ha for 2017 and 2018 seasons.
This study concluded that both AWD and CFI resulted in yield reduction and WP as compared to WWF, and as such, not recommended for Cocoyam production in order to improve the productivity. AWD irrigation with ABR effluent should be encouraged among rice farmers and therefore, recommended among the rice farmers closer to ABR effluents. It was also concluded that over the two season period, intercropping Cocoyam and rice was not productive under any of the three irrigation management techniques applied. The hypothesis is thus accepted for yield and rejected for the growth parameters.
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Doctoral Degree. University of KwaZulu-Natal, Pietermaritzburg.