Assessing the potential use of struvite and effluent from decentralized wastewater treatment systems (dewats) as plant nutrient sources for early maize ( zea mays) growth.

Abstract

The Decentralised Wastewater Treatment System (DEWATS) effluent has been shown to contain considerable concentrations of mineral elements such as nitrogen (N) and phosphorus (P), which are important for plant growth. The use of effluent for agriculture as a sole nutrient source is limiting in terms of macronutrient and micronutrient content supplied to plants. There is little information about the effects of combining the effluent with struvite and commercial fertilizer for crop production. The study aimed to determine the effect of applying struvite and DEWATS effluent as nutrient sources combined or in combination with urea/single superphosphate (SSP) fertilizers on the growth, nutrient uptake, and biomass production of maize. The specific objectives were: (1) to determine N and P release pattern of struvite when applied solely or combined with urea relative to SSP fertilizers combined with urea in a sandy soil, (2) to determine N and P release pattern of DEWATS effluent applied solely or combined with struvite and or SSP fertilizers in a sandy soil, (3) to investigate the effect of applying struvite and DEWATS effluent as nutrient sources combined together or with urea/SSP fertilizers on the growth, nutrient uptake and biomass production of maize. Two soil incubation experiments were set up under controlled room temperature at 25oC and 80% atmospheric humidity to determine the N and P release pattern of human excreta derived materials (HEDMs) (struvite and DEWATS effluent) with supplementary chemical fertilisers urea and SSP. The first experiment was laid out as a single factor analysis with the following treatments: (i) struvite alone, (ii) urea alone, (iii) SSP alone, (iv) struvite + urea, (v) SSP + urea. Each treatment was replicated 3 times to give 15 experimental units (in 5 litre ventilated containers). The second experiment was also laid out as a single factor comprising the following treatments: (i) effluent alone, (ii) struvite + effluent, (iii) effluent + SSP, and (iv) a control, all replicated 3 times to give 12 experimental units (in 5 litre ventilated containers). The fertiliser materials

were applied to achieve an equivalent of 200 kg N/ha and 60 kg P/ha to meet maize nutrient requirements from the Cartref (sandy soil). The effluent in the study was applied as an irrigation source to achieve a 100% soil water holding capacity while supplying nutrients at the same time. Data was collected on the ammonium N, nitrate N, and extractable P release weekly, for 56 days. A pot trial was set up in 20 litre pots in the tunnel at 26oC air temperature and 65% atmospheric humidity to determine the effect of applying struvite and treated effluent from the anaerobic filters (AF) on growth, nutrient uptake, and biomass production of maize. The pot experiment was set up as a 9 x 2 factorial experiment in a completely randomised design (CRD) with the following treatments: fertilizer combinations (8 levels- (i) struvite + urea (recommended rates); (ii) ) struvite + urea (half recommended), (iii) struvite + effluent (recommended rates); (iv) struvite + effluent (half recommended); (v) SSP + effluent (recommended rates); (vi) SSP + effluent (half recommended); (vii) SSP + urea (recommended rates); (viii) SSP + urea (half recommended) and the control. The second treatment was maize variety with 2 levels –‘Colorado’ and ‘IMAS’. The treatments were replicated three times. Three maize seeds were planted per pot and were thinned 3 weeks after planting to one plant per pot. The amount of water applied as irrigation was based on Cartref soil water requirements. Soil moisture was maintained at 70-100% field capacity. The soil incubation experiment showed that there were significant (P<0.05) differences among treatments- struvite (S), effluent (E), SSP (P), urea (U), struvite + urea (SU), struvite + effluent (SE), effluent + SSP (PE), SSP + urea (PU) and zero fertilizer. The combination of HEDMs and commercial nutrient sources released higher ammonium-N and nitrate-N than sole applications and when commercial SSP + urea was applied together. Ammonium N declined over time and nitrate N increased rapidly over time. The findings suggested that the fertiliser combination of HEDMs and commercial fertiliser increased nutrient N availability to the soil. Phosphorus did not change over time in all treatments. The pot experiment result showed that there were significant (P<0.05)

differences observed in plant height, leaf number, chlorophyll content, dry matter, N and P uptake, and grain + cob yields among the different fertiliser combinations (SE, SU, PE, PU) at both recommended and half recommended application rates. In conclusion, optimising N and P supply through a combination of the effluent and struvite or with inorganic fertilisers could potentially be considered as a better option for providing a balanced supply of nutrients than when applied separately.