65 Figure 5.1 Effect of the amount of water lentil use on dry matter and nitrogen uptake (mgpot-1) of chard. 78 Figure 5.2 Effect of soil and amount of water lentil and urea application on K and Fe absorption in Swiss chard.
GENERAL INTRODUCTION
- Background
- Problem Statement
- General Objective
- Specific Objectives
- Hypotheses
There is a lack of information worldwide about the use of duckweed as a source of plant nutrients, but there is potential. There is limited information on the use of duckweed as a source of crop nutrients and its impact on crop and residual soils.
LITERATURE REVIEW
Nutrients from Agricultural wastes
Management of agricultural wastes and impact of excess nutrients on environment
10 agricultural fields have been non-point sources of sediments and nutrients, such as N and P (Mateo-Sagasta et al., 2017). Recent evidence of environmental pollution includes acidification and eutrophication of surrounding aquatic ecosystems (Isikhungusethu Environmental Services, 2012; Shabalala et al., 2013), in addition to ammonia volatilization and greenhouse gas emissions.
Aquatic macrophyte boom and potential of nutrient recovery
Duckweed characteristics and impact on aquatic ecosystems
- Biophysical factors affecting occurrence and growth of duckweed
- Impact of duckweed on aquatic ecosystems
Duckweed can prevent growth of other plants by shading them with its dense mats that create anaerobic environments for rooted aquatic macrophytes, as well as reduce the abundance of phytoplankton (Landesman et al., 2011). The tremendous capacity of duckweed to accumulate nutrients, heavy metals, phenols, pesticides, dioxins and pathogens from water in a short period of time (Zayed et al., 1998; Gao et al., 2000; Cheng and Stomp, 2009; Fujisawa et al. , 2010; Xu et al., 2012) offer several opportunities for exploitation of the aquatic plants, selected ones of which will be reviewed.
Exploitation of duckweed
- Duckweed for wastewater phytoremediation
- Duckweed as feed supplement
- Duckweed for green energy and bioplastics
- Duckweed for crop nutrient supply
Duckweed proteins have a similar amino acid composition to that of most leaf proteins (Leng et al., 1995). Duckweed has been reported to have very low lignin content because the plants do not require mechanical support (Tao et al., 2017).
Features of agricultural production systems in South Africa
The potential value of duckweed as a nutrient source could be particularly important in the Midlands region of KwaZulu-Natal, where macrophytes occur on large commercial farms that produce large amounts of organic waste from their intensive production systems. Therefore, differences in soil texture and other physico-chemical characteristics in smallholder farming systems can affect the breakdown of water lentil and, consequently, its effectiveness as an organic fertilizer.
Purposeful culturing of duckweed
Soil texture did not affect soybean mineralization until after 6 weeks of incubation, with clay and loam soils having similar but higher net mineralization than sandy soils. 27 quality and quantity of duck biomass for plant nutrient supply in group systems do not exist.
Conclusion
Abstract
Introduction
Do sources of nutrients influence the occurrence of genera and species, and tissue elemental composition of duckweed. Determine the elemental composition of water whether the duckweed occurs together or not.
Method and materials
- Study Area
- Sampling and analysis
- Data analysis
Water samples were randomly collected as grab samples (Environmental Protection Agency, 2013), in 250 ml plastic bottles from the upper 20 cm water column. After filtration through 2.5 μm pores, water samples were analyzed for pH using the PHM 210 meter radiometer.
Results
- Occurrence of duckweed species
- Elemental composition of duckweed species and composition of water pooled across
- Tissue elemental composition of sole Wolffia and sole Lemna species across sites38
- Elemental composition of tissue and water where Wolffia and Lemna species co-
There were significant differences in the Zn content of Lemna spp., with ducks from the goat farm (Lydgate) having the highest levels and those from the crocodile farm (Wartburg) the lowest. Water from poultry (Ichanga) and sugar cane and horticulture (Camperdown) enterprises had the lowest pH while that of pigs was among the highest (Table 3.7).
Discussion
This finding suggested that Wolffia spp. may be more efficient in the uptake of K as supported by Garbey et al. 2004) who postulated that the phenomenon may be due to physiological characteristics related to nutrient storage in the tissue of the species. Similarity in tissue N, Zn and Al for all habitat types grouped by duckweed occurrence generally implied similar levels of the elements in water in different habitats. It suggested that enterprises releasing high concentrations of N and P into water reduce the uptake of these elements by Wolffia and Lemna spp. encouraged, when it occurred separately.
Therefore, based on observations of the above authors, the distribution of the genera may not be limited to the availability of micronutrients in water.
Conclusion
DECOMPOSITION OF WOLFFIA ARRHIZA RESIDUES RAPIDLY
- Abstract
- Introduction
- Materials and methods
- Duckweed and soil sampling
- Duckweed and soil characterisation
- Nitrogen and phosphorus mineralisation in soil
- Soil P fractionation
- Statistical analysis
- Results
- Ammonium-N
- Nitrate-N
- Mineral-N
- Fractionation of inorganic-P
- Discussion
- Conclusion
The Baynesfield B and Ukulinga soils had similar ammonium N concentrations, which were lower than the Baynesfield A soil. 64 At the 2% rate, the Baynesfield soils had a similar extractable P concentration that was lower than that of the Ukulinga soil. At the 3% rate, Ukulinga soil had the highest extractable P concentration and the Baynesfield B soil had the lowest.
The concentration of extractable sodium hydroxide-P increased significantly with the application rate of duckweed for all soil types (Figure 4. 5).
PRE-INCUBATION OF DUCKWEED BIOMASS IMPROVES NITROGEN
Abstract
Introduction
The use of duckweed as fertilizer can be an environmentally friendly option although the suitability of duckweed species to provide nutrients to various crops on different soil types has not been assessed. The differences in elemental composition of duckweed can affect its efficiency as sources of plant nutrients. 73 responses, such as “Can the use of duckweed reduce the impact of non-point pollution from anthropogenic sources to adjacent water bodies and benefit agricultural ecosystems through plant nutrient supply.
Does a period of pre-incubation of biomass of different duckweed species in soil improve its efficiency as a plant nutrient source given their low C:N ratio?" The aim of this study was to determine the effects of (i) duckweed (W. arrhiza) biomass as nitrogen source, (ii) pre-incubation period for W .
Methods and Materials
- Soil and duckweed
- Pot experiment 1
- Pot experiment 2
- Duckweed, Plant and Soil Analyses
- Data analysis
The Soil and Analytical Services Laboratory of the KwaZulu-Natal Department of Agriculture provided the N recommendation (100 kg N ha-1) for Swiss chard. P and K for Swiss chard were supplemented as the difference between the recommended rates based on soil test values from. Duck food, soil and Swiss chard samples were analyzed for C and N using the LECO Trumac CNS Auto-analyser Version 1.1x (LECO Corporation, 2012).
The results of chard uptake were obtained from the product of tissue nutrient content and dry matter (g pot-1).
Results
- Shoot dry matter and elemental uptake of Swiss chard
- Residual soil chemical properties after growth of Swiss chard
- Shoot dry matter and nutrient uptake of Swiss chard after pre-incubation of
- Residual soil chemical properties after pre-incubation of duckweed and growth of
Rates of 100 and 200 kg N ha-1 had similar N uptake by Swiss chard that was lower than the positive control. For regosol, the uptake of K by Swiss chard from the rate of 200 kg N ha-1 and the positive control was higher than that of the control and 50 kg N ha-. For ferralsol, the highest Swiss chard absorption of K was from the positive control while the lowest was from the negative control.
Pre-incubation of both species of duckweed for 28 days resulted in higher Zn uptake from Swiss chard than all treatments except the positive control.
Discussion
87 Table 5.8 Effect of the period of incorporation of duckweed on the residual chemical properties of the soil after chard grown in the ferral sol. This view was supported by the findings of the experiment in which duckweed was pre-incubated before chard was planted. Pre-incubation of duckweed for 28 days could have been essential to obtain sufficient N uptake and all other nutrients, resulting in a comparable Swiss chard dry matter to the positive control.
This observation was confirmed by the lower dry matter of Swiss chard in the negative control and both types of water lentil included at transplanting (without pre-incubation) than in the same type pre-incubated for 28 days.
Conclusion
NUTRIENT CONCENTRATION AND REPLENISHMENT OF SLURRY
Abstract
Introduction
Growing conditions, such as nutrient strength and harvest frequencies, are critical to nutrient uptake and subsequent growth of duckweed. Adopting a cropping regime that favors duckweed development at an appropriate density in varied concentration of medium is essential for efficient operation of the duckweed culture system. However, not all duckweed genera and species are effective in recovering nutrients, as their growth rate and quality are both strain- and climate-specific (Zhao et al., 2015).
For Lemna, Spirodela and Landoltia species, water lentil production systems with variable media concentration, stocking densities and harvesting frequency for nutrient recovery, biomass and starch accumulation are frequently reported in the literature (Sultan et al., 2000; Cheng et al., 2002; Xu and Shen 2011a; Xiao et al., 2013; Zhang et al., 2014; Zhao et al., 2014a, b).
Materials and methods
- Swine lagoon water sampling and duckweed conditioning
- Effects of replenishment of SLW and harvesting frequency on duckweed biomass
- Effects of concentration of SLW and its replenishment on duckweed biomass and
- Effects of concentration of SLW and harvesting frequency on duckweed biomass
- Harvesting and analyses of duckweed biomass and swine lagoon water
- Data analysis
The treatments were three levels of SLW supplementation (twice a week, once a week and no supplementation) and three levels of harvest frequency (twice a week, once a week and once every two weeks). A 3 x 3 factorial experiment arranged in a randomized complete block, with three replications, was set up in the growth room to determine the effects of SLW concentration and time. The treatments were two levels of SLW concentration (5 and 10% dilution with distilled water) and three levels of harvesting frequency as described in Section 6.3.2.
Plastic containers (surface area 545 cm2) as in Section 6.3.2, are filled to a depth of 5 cm with diluted solution of SLW.
Results
- Effects of replenishment of SLW and harvesting frequency on duckweed biomass
- Effects of concentration and replenishment of SLW on duckweed biomass and N
- Effects of concentration of SLW and harvesting frequency on duckweed biomass
Replenishment frequency of 10% SLW concentration had no effect on fresh biomass. The fresh biomass collected from the 5% concentration of SLW replenished once and twice a week was similar and significantly higher than when the solution was not replenished. Reducing the SLW concentration from 15 to 5% increased the fresh biomass yield when the solution was supplemented once or twice a week.
The C content of ducks from 5% SLW was higher than that from 15% SLW concentration.
Discussion
The ranges of growth rates in this study were lower than those obtained by Muradov et al. This scenario confirms the findings that efficient use of duck food for nutrient uptake and biomass depends on species and concentration of nutrient solution (Zhao et al., 2014b). The C and C/N ratio of duck food generally decreased as either the concentration of SLW or the frequency of solution replenishment increased, confirming the observation of Wang et al. 2014) of reduced C and C/N ratio as NH4+ concentration increased.
A decrease in C content in duckweed at a higher SLW concentration, with a correspondingly higher NH4+-N concentration, could increase the risk of NH4+-N stress, which could disrupt the C/N balance and plant growth could be negatively affected and biomass accumulation could be inhibited (Zhang et al., 2011).
Conclusion
GENERAL DISCUSSION, CONCLUSION AND RECOMMENDATIONS
General discussion
The success of duckweed in wastewater in the natural environment indicated the dilution of the growth medium, which also affected the distribution by genera. The dry matter response of chard to the addition of water lentil (W. arrhiza and L. minor) can be explained by rapid biomass decomposition and N mineralization. This was supported by the lack of response of chard phosphorus uptake in Chapter 5, Section 5.4.1, which showed limited the plant's ability to utilize the nutrient as water lentil decomposition continued.
The soil used in the experiments had lower nutrient levels than the duck biomass, implying that the soils could benefit from the change in duck biomass.
Conclusion
Manual methods include the use of nets and boats which can be used by small-scale farmers although time consuming. Drying duck biomass can be a challenge that can negatively affect its use, since it is more than 90% water. Pre-incubation of duckweed biomass for at least 28 days improved nutrient availability and uptake, resulting in greater Swiss chard dry mass that was comparable to urea application.
Duckweed dry matter increased while tissue N decreased with decreasing SLW concentration from 15 to 5% as NH4+-N in the water was depleted.
Recommendation
Effect of duckweed (Lemna minor) as a supplement to fertilizer nitrogen on the growth and yield of rice. 2016. The abundance and diversity of heterotrophic bacteria as a function of harvest frequency of duckweed (Lemna minor L.) in recirculating aquaculture systems. A review of the role of duckweed in nutrient recycling and as a source of animal feed.
Potential of duckweed in converting wastewater nutrients into valuable biomass: A pilot-scale comparison with water hyacinth.
