The main goal of this research study was to establish the physicochemical characteristics of sewage sludge, and the nutrients needed to enhance the properties of soil with a view to exploiting were potential for agriculture. The example used was the cultivation of radish ( Raphanus sativus). The findings are intended as a contribution towards making agriculture sustainable. This study was carried out to assess the response of radish ( Raphanus sativus L.) to doses of sewage sludge applied in medium texture soils, and the socioeconomic contributions that such cultivation of radish would make. Levels of 0.25 and 75 ton/ha of sewage sludge plus the equivalent dose of 25 ton/ha of sewage sludge vermin compost by California Red were used after making a randomized experimental design with three replicates. 30 days after sowing radish seeds, the following data were collected: the number of leaves per plant (NLP); plant height (PH in cm); root diameter (RD) and tubercle production (TP ton/ha). In addition, the pH, EC-electric conductivity (EC), and soil organic matter (SOM) were determined. Statistical analysis showed that 25 and 50 tons/ha gave the best results for the parameters assessed. The estimated increase in family mean income from selling radish crops fertilized with sewage sludge is around 17%.
Problems arise when the wastes and pollutants generated by human activity are disposed of into the environment. Examples include those arising from domestic waste, sewage treatment, the production of crude matter, general services and from many other human activities. Therefore, research has taken an increasing interest in this problem since many of the chemical and biological properties of these kinds of waste can result in seriously jeopardy to public health and the environment [
One of the alternative ways of disposing of Sewage sludge (SS), suggested in the literature, is to apply it in agriculture as soil fertilizer [
According to Ramamurth et al. [
The quality of radish is assessed mostly by its external aspect, flavor and nutritional values. Hence, in order to increase the size and productivity of the radish crop and to improve the appearance of radish, farmers need to use heavy fertilization with mineral fertilizers so as to achieve a good market quotation for their crop. It is mineral fertilization which, in many cases, has the predominant impact on production in both technological and socioeconomic matters [
The production of high quality seedlings is one of the most important steps in the cultivation of root plants [
This study set out to establish the physicochemical characteristics of sewage sludge, and to investigate its nutrients with a view to using it to improve the soil and improve its potential for agricultural use so as to grow radish (Raphanus sativus) and increase the yield. This research also evaluates the effects on fertility of applying sewage sludge and assessing what socioeconomic contribution so doing may make to sustainable agriculture.
The field study in support of this research project was conducted in an experimental area, sited in the United Families Community, in the neighborhood of Santa Mônica, in the town of Camaragibe, Pernambuco, Brazil, between September 2007 and March 2008. The 4500 m² site is located in an irregularly occupied area, where local people engage on a multitude of socioeconomic activities (which includes cultivating root plants, fruits and vegetables, raising livestock, producing handicrafts and offering diverse services). The community which consists of four families who reside in four houses built in the territory is classified as a low-income community. The soil is classified as a latosolic, dystrophic Yellow Argisol (Brazilian Company of Agriculture and Livestock Research, EMBRAPA [
In accordance with Köppen’s classification which is used by the American Society of Meteorology (AMS), the dominant climate is rainy monsoon tropical with dry summers. The mean annual temperature is 24.8˚C with a mean maximum temperature of 30.2˚C and a mean minimum of 19.3˚C. The lowest temperatures are registered from June to September. The annual rainfall is 1,715.7 mm, and the driest period occurs between October and December. The winds are light, with a mean speed of 159 km per day predominately in the South-Sout- heastern direction. The relative humidity is high, an average of 83%, and evaporation is 2122 m a year as measured by a class evaporation pan [
Before radish is sown, a physicochemical characterization of the soil layer was made at depths from 0 to 20 cm, in accordance with EMBRAPA [
The sewage sludge used in the experiment was collected from the drying bed of the Sewage Treatment Station of the Integrated (Transport) Terminal of Pernambuco―ETE/TIP, in the city of Recife, state of Pernambuco, Brazil. This station treats domestic sewage. After the material was collected, it was prepared in order to assess its chemical composition according to APHA [
The experimental design used was randomized blocks with five different treatments (zero, 25, 50 and 75 ton/ha of sewage sludge collected from ETE/TIP over 25 ton/ha of sewage sludge vermin compost by California Red) and three repetitions. The brickwork vegetable plots were one meter long by six meters wide and had a depth of 0.20 m. They were divided into 21 rows with a space of 0.35 m between the rows and 0.15 m between the plants. The plants used in the assessments were the ones in the central area, the size of the useful area being two square meters.
The (apagar: sowing of) radish (Raphanus sativus L.) was sown directly at a depth of 1.5 cm, using 10 grams of seeds of the Crimson Giant cultivar per vegetable plot. After germination (from three to five days), the plants were thinned, thus leaving only those that presented well-developed foliage, as recommended by Ramamurthy et al. [
pH (H2O) | P mg kg−1 | Cu mg kg−1 | Fe mg kg−1 | Zn mg kg−1 | Mn mg kg−1 | Cd mg kg−1 | Pb mg kg−1 | Na cmolcdm−3 | K cmolcdm−3 | Ca cmolcdm−3 | Mg cmolcdm−3 | N g kg−1 | C g kg−1 | OM g kg−1 | C/N |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
5.1 | 45 | 155 | 169 | 548 | 207 | 010 | 120 | 0.3 | 2.1 | 9.4 | 1.2 | 22.5 | 28.5 | 49.3 | 12.7 |
(Values based on dry matter).
daily, with a view to providing enough water for the good development of radish in the periods when precipitation was absent. Shading with banana leaves or palm-tree leaves was also used in order to avoid high levels of evapotranspiration in the warmest periods and the plot was manually weeded or with the aid of a hoe to keep the cultivation free from weeds. The radish was harvested 30 days after sowing, with sampling from the useful area previously assigned to each vegetable plot in 10 equidistant spots. An immediate count was made of the number of leaves per plant. The height of the plants was measured (in centimeters, from the base to the apex of the largest dimension of the leaf) as was the diameter of the roots (with a caliper rule and the data were collected in centimeters). The aerial part was promptly discarded after they were measured and the roots were washed and weighed. The average weight of each treated radish was calculated and the corresponding values converted to ton/ha in accordance with Yagioka et al. [
The results showed the number of leaves per plant (NLP), plant height (PH in cm), root diameter (RD in cm), and tubercle production (TP ton/ha) all increased as described in
Treatments1 (ton/ha) | NLP | PH (cm) | RD (cm) | TP (ton/ha) | INCOME PER PLOT3 (US$) |
---|---|---|---|---|---|
0 SS | 5.0b2 | 10.4b | 3.56b | 12.56c | 4.32 |
25 SSV | 7.7a | 17.2a | 4.12a | 17.45b | 6.01 |
25 SS | 7.6a | 17.8a | 3.95a | 18.02a | 6.20 |
50 SS | 7.5a | 17.5a | 3.87a | 17.66b | 6.08 |
75 SS | 4.2b | 12.7b | 3.42b | 12.06c | 4.14 |
Total | - | - | - | - | 26.79 |
1SS = sewage sludge; VSS = vermin compost sewage sludge by California red. 2Average values followed by the same letter had no difference between them by the Tukey test at 5% probability. 3sold as radish sauce = 129 grams.
In order to compare the effects of the corresponding treatment levels of 25 ton/ha of sewage sludge?SS and sewage sludge vermin compost―SSV on the radish, the Student “t” test was performed in order to examine the hypothesis H0 and H1 (
The results of pH, EC, P and OM of the soil treated with equivalent levels of 0, 25, 50 and 75 ton/ha of sewage sludge?SS are presented using box plot graphics. These graphics are used so as to be able to visualize values from the perspective of both the possibility of the equality of the mean values as well as of the dispersion values of each set of samples (using the same treatment). In these graphics, the tendencies of dependent variables can be observed when the factor or independent variable varies.
In
The electric conductivity (EC) of the soil (
Depent variable * | SSV | SS | T | g l | P |
---|---|---|---|---|---|
NLP | 7.40000 | 7.80000 | −2.82843 | 2 | 0.105573 |
PH | 17.80000 | 18.00000 | ---- | 2 | --- |
RD | 4.28500 | 3.97500 | 1.11391 | 2 | 0.381236 |
TP | 17.80500 | 17.78000 | 0.06043 | 2 | 0.957305 |
*NLP = number of leaves per plant; PH = plant height?cm; RD = root diameter―cm; TP = tubercle production―ton/ha.
as the levels increase, there is a trend for the values of EC to decrease. This decrease in the saline concentration of the surface of the soil is probably due to soluble or in suspension ions being washed out, caused by the run-off flow of water due to rainfall and/or irrigation. Similar patterns were obtained by Epstein et al. [
The EC of the soil at all levels of SS and during the entire experiment remained below 2000 µS/cm, the threshold above which soils are considered saline [
Dependent variables* | LEV | LE | T | g l | P |
---|---|---|---|---|---|
P | 39.52000 | 36.38000 | 11.9711 | 8 | 0.000002 |
pH | 6.30000a | 6.20000a | --- | 8 | --- |
CE | 2.08200 | 1.98600 | 2.5936 | 8 | 0.031932 |
MO | 26.0800b | 26.78000b | -1.7734 | 8 | 0.114088 |
P = interchangeable phosphorus; pH (H2O) = hydrogen ionic potential. Ratio 1:2.5 (soil: water); CE = electric conductivity-µS/cm; MO = organic matter.
does not provide a solid indication as to the degree of salinization of the soil of the experiment, bearing in mind that this criterion was developed based on the conductivity of saturation extracts. In addition, there is the possibility of depending on the kind of soil and the local rainfall pattern for the levels of the residues used in this experiment as having occasioned, even transiently, salinity problems and their adverse effects on the development of the plant.
The available P values in the plots fertilized with sewage sludge increased to a level of 50 ton/ha in comparison with the non-fertilized fields (
The organic matter content (
In order to compare the effects in the soil of the treatment with the corresponding level of 25 ton/ha of sewage sludge―SS and of sewage sludge vermin compost―SSV, the Student “t” test was applied so as to verify the hypothesis H0 and H1 (
The characterization of sewage sludge is an important parameter for applying sewage sludge, as nutrient supplementation, in the soil for agricultural purposes. In addition, the cultivation of radish showed a positive response to the levels of 25 to 50 ton/ha of sewage sludge used. The use of corresponding levels of 25 ton/ha of sewage sludge was statistically similar to the same levels of sewage sludge vermin compost by California Red, with the exception of organic matter. The production of the “Crimson Giant” radish cultivar remained at the accepted interval for this vegetable. The use of sewage sludge levels of 25 to 50 ton/ha positively increases the pH to 6.5, decreases the electric conductivity (EC), and OM of the soil with a linear effect of the levels used. The nutrient contents (nitrogen and phosphorous) were high in all levels of the sludge samples taken from the anaerobically digested sewage sludge containing the highest concentrations. Generally higher C/N ratios were recorded in the sludge samples which are an indication that there is limited mobilization of nitrogen by incorporation into cell mass which makes the nitrogen contents available at a later period when plants most need them during their growth period. The results point to families increasing their consumption of radish as well as the perspective of trading conditions for the surplus products being improved. The results provided a better understanding of the use of sewage sludge as a promising fertilizer of the soil. They also show there can be an approximately 17% increase in mean family income from the sale of radish fertilized with sewage sludge; TP (ton/ha) values can increase by up to 43.47% using 25 SS, and the highest income per plot corresponded to US$6.20 when the controlled treatments were compared.
The research was supported by the International Federation of Catholic Universities (FIUC), the National Council for Scientific and Technological Development (CNPq), and the Science and Technology Foundation of the State of Pernambuco (FACEPE). The authors are also grateful to the Catholic University of Pernambuco for the use of laboratories.
Vanessa N.Lima,Ricardo V. Trótski O.Silva,PatríciaNunes,Paulo H.da Silva,KyrialeMorant,Rosileide F. S.Andrade,Aline E.Nascimento,Galba M.Campos-Takaki,Arminda SaconiMessias, (2016) The Cumulative Effects of Sewage Sludge Compost on Raphanus sativus L: Growth and Soil Properties. Green and Sustainable Chemistry,06,1-10. doi: 10.4236/gsc.2016.61001