Assessing the potential use of struvite and effluent from decentralized wastewater treatment systems (dewats) as plant nutrient sources for early maize ( zea mays) growth.
Loading...
Date
2021
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
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.
Description
Masters Degree. University of KwaZulu-Natal, Pietermaritzburg.