Fish pond effluent effects on yield of french beans (phaseolus vulgaris l.) and kale (brasica oleraceae l.) in central Kenya

Abstract

The effects of pond effluent and its interaction with applied mineral fertilisers was assessed in a field experiment with application of mineral fertilisers at recommended rates and irrigation with pond effluent using french beans (Phaseolus vulgaris L.) and kale (Brassica oleraceae) as test crops over two growing seasons. Control treatments included unirrigated and unfertilised plots and irrigation with canal water. The treatments were arran~ed as complete factorial and laid out in randomised complete block design. Plots receiving canal water and fertilisers at recommended rates had the highest yields of 9.1 tonnes of fresh pod ha-1 while those receiving no fertilisers or irrigation had the lowest yield of 1.3 tonnes fresh pod ha-1 • In the second season, significant difference (P~O.05) were observed between treatments in fresh bean pod and fresh kale leaf yield. The fresh pod yield was observed in pond effluent irrigated and fertilised plots, while the lowest was observed in non irrigated not fertilised plots. The highest fresh kale leaf yield of 11.5 tonnes ha-1 was obtained with irrigation with canal water combined with fertiliser application, while the lowest yield of 4.2 tonnes ha-1 was recorded from the non irrigated or fertilised plots. Economic return from kale were significantly higher than from french beans due to a higher economic yield obtained from kale. In the second experiment, the effectiveness of two types of soil occurring at Sagana, a Vertisol (black clay soil) and a Cambisol (red clay soil) in retaining nutrients from pond effluents was investigated. A laboratory experiment was conducted with soil columns containing red or black clay soil and 31, 81 and 161 mm day" effluent xi application intensities were tested on both soils. Both soils retained over 60% of total P from pond effluents, with red clay soil retaining 27% more P than black clay soil. At high effluent loading rate, low % N removal was observed in both soils. Total N removal efficiency declined with time and after 21 days, no N removal was observed where red clay soil was used. A significant difference (P~0.05) was observed in N enrichment between soils. Black clay soil was more enriched by N more than red clay soil, while P enrichment was higher in red clay soil than in black clay soil. This leads to a conclusion that land application process of purifying pond effluents was more effective in P removal but less in N removal.