Impacts of Urban waste use on Soil Microbial activities in Urban Agriculture
Rayim Wendé Alice Naré1*, Stephania Boua2, Rockia Marie Nadege Zerbo1, Richard Madege3
1Département Substances Naturelles, Institut de Recherche en Sciences Appliquées et Technologies (IRSAT)
2Université Joseph Ki-Zerbo
3Department of Crop Science and Horticulture, Sokoine University of Agriculture, Morogoro, Tanzania
*Corresponding Author E-mail: alice.nare@gmail.com
Abstract:
Urban waste use in agriculture is a common practice in West Africa, especially in Burkina Faso. The contribution of urban waste to improve soil fertility in well know. However few studies have been done on the impact of urban waste use on soil microorganism. The objective of this work was to assess the potential impact of urban waste application on soil microbial activities. The Soil Induced Respiration (SIR) of soil amended with urban wastes was 0.049 mg C g−1 soil h−1 and significantly higher (p = 0.00586) than the values in soils amended by manure and control soil that was respectively 0.0212 (0.0087) mg C g−1 soil h−1 and 0.0114 (0.0050) mg C g−1 soil h−1. The urban waste amendment used has significant effects on lag time (Tlat) (p = 0.0203) and maximal response (Tmax) (p = 0.00787). Anabolic variables (lag time and Tmax) have been perturbed also by urban waste. In the soil amended by urban waste, the lag time has been decreased by 50%. Soil amended with urban waste has the lowest lag time (25.7778 (2.75) h) compare to soil amended with manure (47.9444 (4.61) h) and uncultivated soils (53.50 (10.50) h). The same trend was observed with time for maximal response (Tmax) with value of 56.3333 (12.4929) h in soil amended with urban waste, 95.8888 (3.4247) h in soil amended with organic manure and 93.1111 (11.3442) h in control soils. The Tmax has been reduced by 53% in soil amended by urban waste. The urban waste use lead to microbial biomass increase and rapid grow of soil microorganism. The results suggest that adding urban waste to soils is likely to result in carbon sequestration in the soil.
KEY WORDS: Soil, Urban Waste, Microbial Activities.
INTRODUCTION:
The application of organic resources plays a key role in West African agricultural systems due to very low level of organic matter content and very little or no mineral fertilizer input.
In this region, continuous and intensive cropping without restitution lead to negative nutrient balances 1. It is well known that an improved management of organic resources could be a key element in the maintenance of soil fertility (Ouédraogo, Mando, & Zombré, 2001). In urban agriculture, the use of wastes, such as sewage sludge and compost from local municipal green waste collections has been shown to increase organic matter, organic carbon, major nutrients, water holding capacity, soil porosity, treble C storage 3,4 and increase the concentrations of dissolved organic carbon (DOC) in soil 4. However, the undesirable effects of municipal organic waste addition has been known to be the increase of heavy metals concentration in soils.
In 2010, in Ouagadougou (Burkina Faso), more than 300 000 tons of Urban Solid Waste (USW) is produced per annum and is forecasted that it will increase with the population growth. The report indicated that of the total USW produced per year, only 6% was recycled in compost or pellets 5. In urban farming, the farmers use municipal organic waste for soil amendment. Farmers add urban waste in the field during the dry season in pile. The USW is spread at the beginning of the rainy season. The urban wastes are then put at aerobic decomposition before they can be used as source of nutrients. Along with urban wastes other amendment which farmers use include cattle, pig and chicken manure. In recent years, microbiological indicators and biochemical properties have been widely used to evaluate and predict long-term trends of soil quality6,7. Among the indicators of microbiological activity are the microbiological catabolic and anabolic processes. During anabolism the microbes utilize substrates, generate cells, die, and directly contribute to the stable soil organic carbon (SOC) pool 8. Impacts of soil management on anabolism and catabolism have been reported by many authors. 6 have showed that SIR (microbial anabolism parameter) increased with the dose of organic amendment. However, SIR decreased when moderate doses of pig slurry or high doses of digested + dried sludge were tested. The authors have concluded that catabolic and anabolic processes differ in their responses with differences in soil management.
In Burkina Faso the studies on urban waste have been done on the quality of urban waste compost and their impacts on soil physical and chemical properties9 and sorghum yields10.
Compared to other organic matter, the studies on the catabolic and anabolic response of the soil microorganisms due to application of urban waste in Burkina Faso are lacking in the previous reports. This study therefore, is for the first time reporting the impact of urban waste on soil microbial activities in soils of Burkina Faso
MATERIALS AND METHODS:
Soil sampling and preparation:
Soil samples were collected at the peri-urban fields in Ouagadougou (12.3714° N, 1.5197° W). The site receives 600 to 900 mm of annual precipitation and has a mean annual temperature of 28.2 °C and the climate is classified as South-Sudanian11.
Before taking soil samples, litter materials on the soil surface were removed. The, the samples were collected at 0-10 cm depth using a soil auger (6 cm diameter).
Soil samples were collected from farms which were previously under the following three treatments; urban waste (A1), manure (A2) and the uncultivated (A3). A total of eight soil samples were collected in July 2017. For each treatment (manure and urban waste), three farms were selected. Two controls soils in uncultivated plots which had never received input was selected as uncultivated soils. From each plot, soil samples were collected from five sampling points to one composite sample of 1.5 kg. Soils samples have been kept at room temperature before preparation and analysis.
Visible roots and plant debris were removed before drying and sieving through 2 mm mesh. The prepared soil were later subjected to determination of respiratory parameters as well as the physical and chemical characteristics.
Soil physical and chemical characteristics:
The physical and chemical characteristics like granulometric composition, pH value, total carbon, total nitrogen (N), total phosphorus (P), total potassium (K) and Cation exchange Capacity (CEC) were determined.
Soil pH was determined using an electronic pH-meter in 1 g of soil to 2.5 ml of water. Total carbon content was determined using Walkley and Black method 12. Determination of N, P and K involved digesting the samples in a mixture of H2SO4– Se–H2O2 at 450°C for 4 h according to 13. An automatic colorimeter (Skalar SANplus Segmented flow analyzer, Model 4000-02, Breda, the Netherlands) was used to determine the N and P contents in the digested solution. K was determined using a flame photometer (Jencons PFP 7, Jenway LTD, Felsted, England).
Soil incubation:
Field capacity was determined by first oven drying three sub-samples (50 g each) of the starting soil. The oven dry samples were then saturated with water followed by draining them for 4 hours before determining water retention gravimetrically. In the laboratory, the air-dried soil was re-wetted to 60% of field capacity and pre-incubated them at 30°C for five days to stabilize the respiration rate.
Soil respiration:
Models described in previous works 14–16 were used in this study (Figure 1).
Figure 1: A model of soil microbial respiration kinetics after substrates addition.
Ten (10) grams of soil was incubated for 7 days to stabilize respiration rate. The Substrate Induced Respiration (SIR) was initiated by adding 0.3 g, 49.0 mg, and 7.5 mg of glucose, (NH4)2SO4 and KH2PO4 respectively. The SIR reflects microbial biomass and was calculated according to the method described by 17. The lag time, the maximum respiration (Rmax), the maximum time (Tmax) and the exponential growth phase (µ) were calculated according to the method described by 18 and 14.
Respiration was measured hourly using a computerized respirometer (Respicond III, Nordgren Innovations, Umea˚, Sweden). The evolved CO2 was captured in a potassium hydroxide (KOH) solution and the conductivity of this solution was measured by platinum electrodes. The decrease in conductivity of the KOH solution during the accumulation of CO2 was used to calculate the amount of CO2 respired 15,19, and it was renewed when it was saturated.
STATISTICAL ANALYSIS:
Statistical analyses were conducted using R V 5.3.3 software. Data distributions were checked for normality using the Shapiro–Wilk W test before using analysis of variance (ANOVA). Mean separations were carried out with the Student's T-test. Differences were significant when p<0.05.
A multivariate statistical method using a Principal Component Analysis (PCA) was carried out to study the structure of the dependence and correlation between the physicochemical and microbiological soil properties in different soils.
RESULTS AND DISCUSSION:
There was no differences in granulometric composition of soils amended with urban waste, manure and uncultivated soils (Figure 2). Sand was the dominant fraction of all soils with an average content over 75%. The highest content of sand parts was found in soil amended with urban waste samples (77%) and the lowest in uncultivated soil samples (73%). Soils amended by urban waste were characterized by the highest content of silt fraction (17.66%) compare to the other type of land use that are lower respectively 14 % and 15% for soils amended by manure and uncultivated soils. The average content of clay fraction in all samples was low and did not exceeded 12% in all cases of amendment use. The increase of sand proportion in soil amended by urban waste compare to soil amendment by manure and uncultivated soil can be explain by the sand contained in urban waste during the collect. According to 20, the use of municipal waste increase the proportion of particles and make the soil more stable.
Figure 2. Granulometric composition of soil samples from different treatments
A1 = soils amended with Urban Waste; A2 = soils amended with Manure; A0 = Uncultivated soils
Table 1: Chemical characteristics of soils samples from different treatments.
|
Traitment |
pH (H2O) |
C |
N |
CN |
P |
K |
CEC (mmol c dm3) |
|
|
|
mg g-1 |
|
|
mg kg-1 |
|
|
|
A1 |
6.27 |
6.41 |
0.5 |
12.82 |
558.66 |
692 |
1.57 |
|
A1 |
6.98 |
6.17 |
0.6 |
10.28 |
503 |
610 |
3.13 |
|
A1 |
7.05 |
5.55 |
0.46 |
12.06 |
670.33 |
1196 |
3.47 |
|
Mean |
6.76 (0.35) |
6.04 (0.36) |
0.52 (0.06) |
11.74 (1.02) |
577.33 (69.57) |
832.67 (259.08) |
2.73 (0.83) |
|
A2 |
5.66 |
4.16 |
0.42 |
9.90 |
391 |
677.67 |
2.05 |
|
A2 |
5 |
3.67 |
0.37 |
9.91 |
335 |
610 |
1.51 |
|
A2 |
5.84 |
4.94 |
0.44 |
11.23 |
307.33 |
474.67 |
2.48 |
|
Mean |
5.5 (0.36) |
4.2 (0.52) |
0.41 (0.02) |
10.30 (0.65) |
344.44 (34.80) |
587.44 (84.39) |
2.014 (0.39) |
|
A0 |
6.04 |
4.41 |
0.31 |
14.22 |
754 |
610 |
2.1 |
|
A0 |
6.64 |
6.59 |
0.53 |
12.43 |
503 |
1322 |
2.06 |
|
Mean |
6.34 (0.3)* |
5.5 (1.09) NS |
0.42 (0.11) NS |
13.325 (0.895) NS |
628.5 (125.5)* |
966 (356) NS |
2.08 (0.02) NS |
A1 = Soil treated with waste, A2= Soil treated with manure, A3 = Uncultivated soils
The use urban waste in peri urban agriculture in Ouagadougou (Burkina Faso) has significantly affected soil Substrate Induced Respiration (SIR). The SIR of soil amended with urban wastes was 0.049 mg C g−1 soil h−1 and significantly higher (p = 0.00586) than the values in soils amended by manure and control soil that was respectively 0.0212 (0.0087) mg C g−1 soil h−1and 0.0114 (0.0050) mg C g−1 soil h−1 (Figure.3). SIR is an estimate of the microbial biomass in the soil17 showing that soil amended with urban waste contain more microorganisms compare to soils amended with organic manure and uncultivated soils. In peri urban agriculture in Ouagadougou, farmers add urban waste in the field during the dry season in pile and spread it at the beginning of the rainy season. The urban waste is then put at aerobic degradation before using. Our results are similar to those of6 that found that soils amended with aerobically digested sludge have higher SIR compare to those amended with anaerobically digested sludge. The SIR is a catabolism variable of microorganisms in soils and is positively correlated with soil organic carbon21. This confirm our results because the organic carbon are higher in the soils amended with urban waste (6.04 mg C g-1 soil) compared to the control soil (5.55 mg C g-1 soil) and soil amended with manure (4.2 mg C g-1 soil) (Table 1). This supports the high rate of nutrients in urban waste and its importance for urban agriculture. Previous studies have found that microbial biomass was increased for manure and sludge in a field experiment22,23 but not increased for compost compared to an untreated control 24. However, it is reported that in arable lands there is a decrease in the size of the microbial biomass and in the efficiency with which it uses C substrates21. The intensive use of urban waste (annually) can explain the high proportion of microbial biomass and carbon.
Figure 3. Impact of urban waste and manure on soil Substrate Induced Respiration (SIR).
A1 = Soil treated with waste, A2= Soil treated with manure, A3 = Uncultivated soils
Impact of urban waste on soil catabolism variables:
The response variables representing the anabolic processes were the slope during the exponential growth phase (μ. h-1)25, the time after substrate addition during which the respiration rate remained constant (lag time, h) and the maximum respiration rate (Rmax, mg CO2 h-1 g-1soil) (Figure. 1).
Anabolic variables (lag time and Tmax) have been perturbed also by urban waste. This study has demonstrated that soils amendment with urban waste had significant effects on lag time (Tlat) (p = 0.0203) and maximal response (Tmax) (p = 0.00787). Urban waste decreased the lag time by 50%. Soils amended with urban waste had the lowest lag time (25.7778 (2.75) h) compared to soil amended with manure (47.9444 (4.61) h)and uncultivated soils (53.50 (10.50) h). The same trend was observed with time for maximal response (Tmax) with value of 56.3333 (12.4929) h in soil amended with urban waste, 95.8888 (3.4247) h in soil amended with organic manure and 93.1111 (11.3442) h in uncultivated soils (Table 2). The Tmax has been reduced by 53% in soil amended with urban waste compared to soils amended with manure and uncultivated soils. The reduction of lag time and Tmax revealed a fast growth of microorganisms in these soils (Figure 5). Microbial anabolism is an important pathway of SOC stabilization. It is the in vivo turnover pathway in which microbes utilize substrates generate cells, die and directly contribute to the stable SOC pool 8. In this study, urban waste influenced microbial anabolism compared to soil that was amended with manure and the uncultivated soils.26 found a microbial growth roughly doubled in amended soils compared to the unfertilized control. The increase of microbial growth due to urban waste treatment in soils has been confirmed by the result of the exponential growth phase (μ), the maximum respiration rate and cumulative CO2. The exponential growth phase (μ) and the maximum respiration rate have been insignificantly affected by the type of amendment used in soil (p = 0.266 and p=0.374 respectively). The influence of urban wastes on growth phase (μ), maximum respiration (Rmax) and cumulative CO2 of soils was not significantly (Table 2). The exponential growth phase (μ) was 5 times more in soils amended with urban waste (0.61 (0.49) h) than in soils amended with manure (0.12 (0.07) h) and the uncultivated soils (0.0225 (0.0074) h). The maximum respiration rate increased slowly (0.2984 (0.04056) mg C g−1 soil h−1) in soils amended with urban waste compared to the soils that were amended with manure (0.2400 (0.0377) mg C g−1 soil h−1) and uncultivated soils (0.264 (0.0273) mg C g−1 soil h−1). The cumulative CO2 was higher in soil amended with urban waste (15.8216 (0.3036) mg C g−1 soil h−1) compare to soils amended by manure 13.6000 (1.2920) mg C g−1 soil h−1and uncultivated soils (13.061 (0.3382) mg C g−1 soil h−1) (Figure 4). This finding is in agreement with 27 who found that the cumulative CO2 is more in arable land compare to soils from forest, grassland and urban areas.
a) urban waste
b) manure
c) uncultivated
Figure 4. Cumulative CO2 of soil samples amended with:
a) urban waste
b) manure
c) uncultivated
Figure 5. Microbial respiration kinetics of soils amended with
Table 2: Impacts of the use of urban waste, manure and uncultivated soils on microbial respiration variables
|
Traitments |
Lat time |
Rmax |
Tmax |
µ |
Cumulated CO2 |
|
A1 |
23.6666 |
0.3541 |
42.3333 |
1.31 |
15.3933 |
|
A1 |
29.6666 |
0.2586 |
72.6666 |
0.25 |
16.0626 |
|
A1 |
24 |
0.2825 |
54 |
0.26 |
16.0089 |
|
Mean |
25.7778 (2.7532) a |
0.2984 (0.04056) a |
56.3333 (12.4929) |
0.61 (0.49) a |
15.8216 (0.3036) a |
|
A 2 |
41.5000 |
0.2124 |
92.0000 |
0.16 |
15.2737 |
|
A 2 |
50.3333 |
0.2144 |
100.3333 |
0.18 |
13.3979 |
|
A 2 |
52.0000 |
0.2934 |
95.3333 |
0.03 |
12.1285 |
|
Mean |
47.9444 (4.6074) b |
0.2400 (0.0377) a |
95.8888 (3.4247) b |
0.12 (0.07) a |
13.6000 (1.2920) a |
|
A 0 |
64.0 |
0.2367 |
105.3333 |
0.0300 |
12.7225 |
|
A 0 |
43.0 |
0.2913 |
96.0000 |
0.0150 |
13.3989 |
|
Mean |
53.5 (10.5) b |
0.264 (0.0273) a |
100.6666 (4.66665) b |
0.0225 (0.0074) a |
13.061 (0.3382) a |
|
P value |
0.0203 |
0.374 |
0.00787 |
0.266 |
0.0599 |
Principal component analysis (PCA) of the chemical and microbial data, revealed that Dim1 accounted for 51.26% the total variation, and Dim2 for 19.63% of the total variation. Therefore, 70.89% of total variance was explained by these two components (Figure. 6).
The most pronounced result of the PCA analysis was the separation of all variables (chemical variables, SIR, μ and Rmax) and anabolic response variable lat time and Maximun time (lat time and Tmax) by PC1.
The chemical variables (having positive values along Dim1) were associated to Rmax, SIR, and μ but having negative correlation with Tlat and Tmax (with negative values in Dim1).
The PC2 tended to separate all the variables from catabolic variable (SIR) and anabolic variables (μ).
SIR and μ were negatively correlated with chemical variables and Rmax described by Dim2 (Figure 6). SIR and μ were positively correlated each other and described by Dim2 and Dim1.
The PCA analysis revealed that the anabolism (Tlat and Tmax) variables were influenced by soil treatment. 18, showed that the fundamental difference between catabolic and anabolic processes was reflected in the differences in their responses to variations in soil conditions.
Figure 6. Soil chemicals variables affecting microbial catabolic and anabolic responses
CONCLUSION:
The current study showed that soil microorganisms responded to urban waste addition through enhanced microbial biomass measured throughout SIR. The urban waste increased the microbial growth in the soil compared to soil amended with organic manure and uncultivated soil. Microbial anabolism is an important pathway of SOC stabilization. This would suggest that adding urban waste to soils is likely to result in carbon sequestration in the soil.
In further attempts to explain biogeochemical processes combining analyses of microbial respiration kinetics with molecular level processes will be of great significance.
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Received on 11.06.2019 Modified on 21.06.2019 Accepted on 13.07.2019 ©A&V Publications All right reserved Research J. Science and Tech. 2019; 11(3):208-216. DOI: 10.5958/2349-2988.2019.00031.7 |
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