| Livestock Research for Rural Development 28 (5) 2016 | Guide for preparation of papers | LRRD Newsletter | Citation of this paper |
This study evaluated the effect of the application of biosolids from a municipal wastewater treatment plant on the content of humic and fulvic acids in vertic Endoaquept soil cultivated with sugar cane. Eight treatments with a randomized block spatial distribution are evaluated using experimental units of 6 m wide x 20 m long: i) control; ii) mineral fertilizer; iii) dehydrated biosolid 1N and 2N; iv) thermally dried biosolid 1N and 2N; and v) alkalized biosolid 1N and 2N (1N and 2N correspond to doses equivalent to one and two times the nitrogen requirement for sugar cane).
The results show that while values of humic and fulvic acids showed no significant differences between the control, mineral fertilizer and alkalized biosolid treatments, the application of dehydrated and thermally dried biosolid treatments increased humic acid and fulvic acid content in the soil. This finding demonstrates the benefits of applying such biosolids.
Key words: biosolids, fulvic acids, humic acids, vertic Endoaquept
The success of agricultural biosolid application is dependent on the type of treatment applied to the biosolid, soil type, crop type, among other factors. Fruit and vegetable crops are associated with the highest regulatory restrictions due to risks associated with the presence of pathogens, as these crops may come in contact with the soil and may be used directly for consumption without preprocessing (Gattie and Lewis 2004). Figueroa and Cueto (2003), argue that soil with added biosolids should not be used immediately for cultivation and propose a variety of waiting periods and soil treatments.
Agricultural biosolid application affects physical soil properties, improving particle aggregation states and increasing water and air retention capacities; likewise, it improves soil characteristics (e.g., texture), improving root growth conditions and plant water stress tolerance levels (Jacobs and McCreary 2001). Additionally, organic matter degradation in soils with biosolids applications, generates complexing agents that facilitate the solubilization of phosphates combined with iron and aluminum and also it contributes to the gradual release of nutrients from organic compounds that transform slowly (e.g., fulvic and humic compounds), which can improve the state of soil microbial populations (Carvalho and Barral 1981).
An important aspect of biosolid application corresponds with an increase in soil water retention capacities due to decreases in density and increases in porosity (Wong and Ho 1991). As well, as biosolid application improves nutritional features of soils cultivated with sugar cane, greater yields can be achieved (Jamali et al 2008), thus reducing the need for mineral fertilizers (Chiba et al 2008). Studies such as those by Có Júnior et al (2008) and Franco et al (2008) show that biosolid application to sugar cane crops contributes to a higher accumulation of plant nitrogen.
Several phenomena occur when biosolids are added to the ground. One phenomenon commonly observed during the fertilization of soils with biosolids or other materials is a volatilization or loss of nitrogen, which may vary significantly depending on temperature, soil pH, cation exchange capacity, organic matter, surface residue coverage and quality, wind, vapor surface tension and fertilizer dosage features (Sogaard et al 2002; Ferraris et al 2009).
Organic matter applied to soil first transforms into humus (humification) through a rapid process that lasts three to four months and that is performed by various organisms (earthworms, fungi, bacteria, actinomycetes) and under various ecological conditions. During the second stage (mineralization), these compounds are converted into mineral elements (CO2, H2O, NO3-, Ca++, SO4=, etc.). Mineralization occurs more gradually (one year) under optimal ecological conditions (18-20°C, optimal humidity levels, sufficient O2, neutral pH) and is performed by highly specialized organisms (Urbano 1995).
Bertoncini et al (2008) claim that biosolid application, in addition to increasing crop productivity, increases organic matter content and soil capacities to retain water and nutrients (C, N, P and Ca). However, Vieira et al (2005) found that biosolid application based on crop nitrogen requirements may increase risks of nitrogen loss through leaching and may contaminate groundwater. Additionally, while soils with high sand content present lower moisture and nutrient retention capacities, Ebeling et al (2011) found that sandy soil horizons can encourage the formation of humic substances.
This study evaluates the effect of biosolid application from a municipal wastewater treatment plant in the city of Cali, Colombia on the content of humic and fulvic acids of soils cultivated with sugar cane.
A vertic endoaquept soil sample was used and was made suitable for planting via ploughing, ripping and furrowing. After preparing the soil, an isolated soil sample was collected for initial physicochemical analysis to determine appropriate biosolid doses to apply. Soils and biosolids were characterized physicochemically (pH, humidity, organic carbon (Walkley and Black, 1934), Total Nitrogen Kjeldhal - NTK (Kjeldahl 1883), ammoniacal nitrogen, nitrates, nitrites, phosphorus (Bray and Kurtz 1945), potassium calcium and magnesium (USDA and NRCS 2004)).
The agricultural application of biosolid treatments was evaluated differently: i) dehydrated biosolid-BD from anaerobic digestion; ii) thermally dried biosolid (60 °C for 12.58 hours)-BT; and iii) alkalized biosolid (9% quick lime/per 13 days)-BA. An application in doses equivalent to one (1N) and two (2N) times the nitrogen requirement for the crop was carried out using mineralization rates for each biosolid as defined by Silva et al (2013) and nutritional requirements for the crop were defined by Cenicaña (2002), who recommended doses of 100 to 160 Kg/ha of nitrogen, 30 to 50 kg/ha of phosphorus and between 60 and 90 kg/ha of potassium for the variety of sugar cane evaluated (CC8592).
The 2N dose used was determined based on Vieira et al (2005) and Chiba et al (2008), who evaluated doses for up to eight times the nitrogen levels required for sugar cane cultivation in Brazil. Table 1 shows the treatments and the dose applied.
|
Table 1. Treatments and doses used |
|||||
|
Treatment |
Label |
Nitrogen requirement |
Mineralization constant % |
Rate applied t/ha |
|
|
1 |
Control (soil) |
C |
0 |
- |
0 |
|
2 |
Mineral Fertilizer |
F |
0 |
- |
0 |
|
3 |
Dehydrated |
BD1N |
1N |
33 |
11.6 |
4 | Biosolid-BD |
BD2N |
2N |
23.2 |
|
|
5 |
Thermally dried |
BT1N |
1N |
45.7 |
8.5 |
6 | Biosolid-BT |
BT2N |
2N |
16.9 |
|
|
7
|
Alkalized
|
BA1N |
1N |
26 |
21.1 |
Urea (217 kg/ha) and triple superphosphate (97.8 kg/ha) mineral fertilizers were applied one month after the vegetative seeds germinated. An experimental design with experimental units of 6 m wide x 20 m long was used; a random-block experimental design was adopted. Sixty-centimeter-long variety CC 8592 vegetative sugarcane seeds, the most commonly used among mills in the study area (Cenicaña 2002), were planted. Each treatment involved two replications, and the spatial distribution followed a random block distribution.
To evaluate the influence of biosolid application on soil organic matter humification, soil organic matter extraction and fractionation were performed, as soil humic materials consist of a broad set of compounds of various molecular weights (Stevenson 1994): humic acids (HA), fulvic acids (FA) and humins. The analysis was conducted over months zero, four, 10 and 12 based on an adaptation of the methodology reported by authors such as Kononova (1966), Dabin (1971) and Miranda et al (2007) using a solution of Na2P2O7 + NaOH 0.1 M for the extraction of humic and fulvic acids.
Once the FA and HA contents were measured, analysis of variance (ANOVA) was performed with the free statistical software ‘‘R’’ version 2.13.1, for each measurement period to evaluate the effect of biosolid application on organic matter humification. Significant ANOVAs were followed by Tukey´s mean separation test.
The physicochemical results for the soil show that organic carbon content levels are low according to categories defined by Quintero (1993) for soils of the Valley of the Cauca River (Table 2), thus necessitating the use of materials that address such deficiencies to ensure the adequate growth of the sugar cane crops. Other nutrient levels fell within the appropriate range for this type of soil. Additionally, the soil used did not include fecal coliforms, E. coli or helminth eggs, indicating that the soil sample has not been in contact with fecal matter.
|
Table 2. Initial characterizations of the soil and of the dehydrated, thermally dried and alkalinized biosolids |
||||
|
Variable |
Soil |
Dehydrated |
Thermally |
Alkalized |
|
pH |
7.4 |
7.7 |
7.8 |
12.1 |
|
C-Total (g/kg) |
6.8 |
243 |
257 |
218 |
|
N-Total (g/kg) |
- |
25.0 |
25.8 |
18.0 |
|
N-NH4 (mg/kg) |
8.1 |
1824 |
1130 |
113 |
|
N-NO2 (mg/kg) |
1.7 |
0.0 |
0 |
0 |
|
N-NO3(mg/kg) |
4.4 |
33.8 |
17.8 |
34.5 |
|
P-Total (g/kg) |
7.6 |
14.5 |
14.3 |
9.8 |
|
K (g/kg) |
0.2 |
1.0 |
0.94 |
0.72 |
|
Ca (g/kg) |
21.7 |
35.4 |
31.9 |
137.5 |
|
Mg (g/kg) |
9.0 |
5.5 |
5.7 |
5.2 |
|
Total Coliforms CFU/g |
1.0 x 105 |
1,94x107 |
1. x 102 |
0 |
|
Fecal Coliforms CFU/g |
0 |
2,08x106 |
0 |
0 |
|
E. Coli CFU/g |
0 |
1,70x106 |
0 |
0 |
|
Helminth eggs #/g |
0 |
9 |
0 |
0 |
In general, the biosolids evaluated may be used for their higher organic carbon and nutrient contents compare with the soil. While of the content of pathogenic microorganisms and parasites for dehydrated biosolids yielded results similar to those reported by Ramírez et al (2007), there are restrictions on its application for agricultural purposes, as it does not comply with the Colombian law requirements for class A and B biosolids (MVCT 2014). Both thermal drying and alkali treatments guaranteed the generation of a class A biosolid that could be used for agricultural purposes without restrictions according to microbiological perspectives. However, the use of quicklime increases the calcium content of 331% in the alkalinized biosolid compared to the dehydrated biosolid and thermally dried biosolid.
For the control treatment, the results show that over the 12 months, humic acid content (HA) levels ranged from 62 to 191 mg/kg and fulvic acid content (FA) levels ranged from 107 to 190 mg/kg (Table 3). Such values are lower than those found by Fernández et al (2008), who reported 700 mg/kg of HA and 600 mg/kg of FA for soils in Spain, likely because the distribution of humic substances in soils varies with pedogenesis and altitude (Ebeling et al 2011).
|
Table 3. Evolution of Humic Acids (HA) and Fulvic Acids (FA). |
|||
|
Treatment |
Month |
Organic carbon of |
Organic carbon of |
|
Control (soil) |
0 |
105 ±5.5 |
94.5± 12.3 |
|
Control (soil) |
4 |
62.2 ±14.4 |
107 ±2.8 |
|
Mineral Fertilizer |
4 |
78.5 ±39.2 |
286 ±19.7 |
|
Dehydrated Biosolid 1N-BD1N |
4 |
332 ±27.9 |
666±87 |
|
Dehydrated Biosolid 2N-BD2N |
4 |
228 ±172 |
772 ±48 |
|
Thermally dried Biosolid-BT 1N-BST1N |
4 |
309 ±12.8 |
719 ±136 |
|
Thermally dried Biosolid-BT 2N-BST2N |
4 |
395 ±108 |
921 ± 251.7 |
|
Alkalized Biosolid 1N- BA1N |
4 |
256 ±148.3 |
453±52.2 |
|
Alkalized Biosolid 2N- BA2N |
4 |
187 ±115.1 |
372 ±48.2 |
|
Control (soil) |
10 |
176 ±5.7 |
145± 7.1 |
|
Mineral Fertilizer |
10 |
278 ±2.8 |
212 ±16.5 |
|
Dehydrated Biosolid 1N-BD1N |
10 |
488 ±2.4 |
544 ±58.2 |
|
Dehydrated Biosolid 2N-BD2N |
10 |
863 ±137.4 |
268 ± 32 |
|
Thermally dried Biosolid-BT 1N-BST1N |
10 |
588 ± 5.7 |
522 ± 12.9 |
|
Thermally dried Biosolid-BT 2N-BST2N |
10 |
633 ± 80.6 |
623 ± 1.5 |
|
Alkalized Biosolid 1N- BA1N |
10 |
482±139 |
174± 19.3 |
|
Alkalized Biosolid 2N- BA2N |
10 |
228 ±50.9 |
280 ± 28.3 |
|
Control (soil) |
12 |
192± 2.3 |
161± 23.8 |
|
Mineral Fertilizer |
12 |
323 ±38.8 |
242± 19 |
|
Dehydrated Biosolid 1N-BD1N |
12 |
685.± 2.9 |
564± 40.4 |
|
Dehydrated Biosolid 2N-BD2N |
12 |
589 ± 1.1 |
263 ± 1.7 |
|
Thermally dried Biosolid-BT 1N-BST1N |
12 |
684 ± 9.1 |
472 ± 7.8 |
|
Thermally dried Biosolid-BT 2N-BST2N |
12 |
482 ± 2.7 |
338 ± 70.8 |
|
Alkalized Biosolid 1N- BA1N |
12 |
535 ± 71.8 |
180± 22.3 |
|
Alkalized Biosolid 2N- BA2N |
12 |
298 ± 0.9 |
151 ± 24.8 |
Dehydrated, thermally dried and alkalized biosolids increased FA and HA content levels relative to the control treatment at each time-point. While FA content levels were greater than humic content levels during month four, in general, FA content levels decreased while HA levels increased overtime, with HA levels being the highest during month 12. This may be attributable to Ebeling et al.’s (2011) finding that in soils, climate favors the formation of FA to the detriment of HA formation. Stevenson (1994) also found that HA formation can occur via polyphenol routes or through FA molecule polymerization.
Dias et al (2007) reported that most of the carbon associated with soil humic substances that receive contributions from biosolids is associated with humin and HA. Likewise, Lima et al (2010) determined that successive high dosage applications of organic materials to soils increase FA levels rather than HA levels. However, Fernández et al (2008) found that the successive application of composted biosolids and thermally dried biosolids to soils produces the same fraction of HA.
Although the control treatment generated the lowest HA and FA values compared to those of the mineral fertilizer treatment, the ANOVA results for HA showed significant differences, though only for months 10 and 12 (Table 4).
|
Table 4. ANOVA results for HA levels for the treatments evaluated |
|||||
|
ANOVA |
Degrees of Freedom |
Sum of Squares |
Root Mean Square |
f |
p |
|
Humic Acids |
|||||
|
Month 4 |
7 |
195424 |
27918 |
2.82 |
0.10 |
|
Month 10 |
7 |
711540 |
101649 |
5.16 |
0.02 |
|
Month 12 |
7 |
477702 |
68243 |
90.57 |
0.00 |
During month four, no significant soil HA content effects occurred as a result of the treatments. The post-hoc test for months 10 and 12 showed that mineral fertilizer application does not significantly affect HA levels compared to those of the control treatment, confirming that mineral fertilizer application does not influence organic matter humification for HA formation (Table 5).
The application of dehydrated (BD1N and BD2N) and thermally dried (BT1N and BT2N) biosolids only significantly influenced HA levels during month 12 relative to those of the control treatment and fertilizer conditions (Table 5). Likewise, it was found that high doses of these biosolids showed no statistically significant differences between the two doses evaluated, demonstrating that over-applying these biosolids does not improve soil HA content levels. Additionally, it was found that alkalized biosolid application did not influence HA content levels relative to those of the control treatment, limiting their possible application to soils.
|
Table 5. Humic acid post-hoc test results |
|||
|
Treatment |
Compared to |
p Month 10 |
p Month 12 |
|
Control |
Fertilizer |
0.10 |
0.24 |
|
BD1N |
0.43 |
0.00 |
|
|
BD2N |
0.021 |
0.00 |
|
|
BT1N |
0.19 |
0.00 |
|
|
BT2N |
0.93 |
0.00 |
|
|
BA1N |
0.45 |
0.07 |
|
|
BA2N |
0.99 |
0.07 |
|
|
Fertilizer |
BD1N |
0.79 |
0.00 |
|
BD2N |
0.05 |
0.00 |
|
|
BT1N |
0.44 |
0.00 |
|
|
BT2N |
0.99 |
0.01 |
|
|
BA1N |
0.81 |
0.05 |
|
|
BA2N |
0.99 |
0.98 |
|
|
BD1N |
BD2N |
0.27 |
0.10 |
|
BT1N |
0.99 |
1 |
|
|
BT2N |
0.94 |
0.09 |
|
|
BA1N |
1 |
0.01 |
|
|
BA2N |
0.61 |
0.00 |
|
|
BD2N |
BT1N |
0.56 |
0.11 |
|
BT2N |
0.08 |
0.06 |
|
|
BA1N |
0.26 |
0.00 |
|
|
BA2N |
0.03 |
0.00 |
|
|
BT1N |
BT2N |
0.64 |
0.20 |
|
BA1N |
0.99 |
0.11 |
|
|
BA2N |
0.30 |
0.00 |
|
|
BT2N |
BA1N |
0.95 |
0.00 |
|
BA2N |
0.99 |
0.00 |
|
|
BA1N |
BA2N |
0.63 |
0.76 |
The FA content ANOVA results show statistically significant differences for all of the months evaluated (Table 6). However, the post-hoc test results show that the application of mineral fertilizer did not significantly influence FA content levels in the soil for any of the periods evaluated. This result indicates that the use of mineral fertilizers has no effect on soil FA content (Table 7).
The post-hoc test results show that the application of dehydrated biosolids (BD1N and BD2N) and thermally dried biosolids (BT1N and BT2N) influences FA content levels and shows a significant difference, indicating that the application of dehydrated and thermally dried biosolids influences soil FA content (Table 7). Also, the post-hoc test results show that alkalized biosolid application did not significantly influence FA content levels relative to those of the control treatment condition, likely due to alkalization processes.
|
Table 6. Fulvic Acids content ANOVA results for the treatments evaluated |
|||||
|
ANOVA |
Degrees of Freedom |
Sum of Squares |
Root Mean Square |
f |
p |
|
Fulvic Acids |
|||||
|
Month 4 |
7 |
1069502 |
152786 |
19.93 |
0.00 |
|
Month 10 |
7 |
490654 |
70093 |
80.97 |
0.00 |
|
Month 12 |
7 |
322893 |
46128 |
39.01 |
0.00 |
|
Table 7. Post-hoc test results for Fulvic Acids levels of the treatments evaluated |
||||
|
Treatment |
Compared to |
p Month 4 |
p Month 10 |
p Month 12 |
|
Control |
Fertilizer |
0.52 |
0.41 |
0.38 |
|
BD1N |
0.001 |
0.001 |
0.001 |
|
|
BD2N |
0.001 |
0.05 |
0.02 |
|
|
BT1N |
0.001 |
0.001 |
0.001 |
|
|
BT2N |
0.001 |
0.001 |
0.02 |
|
|
BA1N |
0.06 |
0.97 |
0.99 |
|
|
BA2N |
0.18 |
0.29 |
0.99 |
|
|
Fertilizer |
BD1N |
0.04 |
0.001 |
0.00 |
|
BD2N |
0.01 |
0.001 |
0.01 |
|
|
BT1N |
0.02 |
0.001 |
0.0011 |
|
|
BT2N |
0.00 |
0.001 |
0.001 |
|
|
BA1N |
0.58 |
0.87 |
0.65 |
|
|
BA2N |
0.96 |
0.40 |
0.28 |
|
|
BD1N |
BD2N |
0.90 |
0.44 |
0.69 |
|
BT1N |
0.99 |
0.99 |
0.26 |
|
|
BT2N |
0.20 |
0.26 |
0.39 |
|
|
BA1N |
0.35 |
0.001 |
0.001 |
|
|
BA2N |
0.12 |
0.001 |
0.001 |
|
|
BD2N |
BT1N |
0.99 |
0.74 |
0.64 |
|
BT2N |
0.69 |
0.85 |
0.46 |
|
|
BA1N |
0.09 |
0.14 |
0.35 |
|
|
BA2N |
0.06 |
0.99 |
0.13 |
|
|
BT1N |
BT2N |
0.39 |
0.11 |
0.63 |
|
BA1N |
0.02 |
0.001 |
0.001 |
|
|
BA2N |
0.03 |
0.001 |
0.001 |
|
|
BT2N |
BA1N |
0.01 |
0.001 |
0.02 |
|
BA2N |
0.001 |
0.001 |
0.01 |
|
|
BA1N |
BA2N |
0.97 |
0.09 |
0.98 |
Overall, it was found that dehydrated and thermally dried biosolid application significantly influenced soil HA and FA content levels; for the dehydrated biosolid, content levels increased from 123 to 493 mg/kg for FA and from 102 to 558 mg/kg for HA. In the case of the thermally dried biosolid, values increased from 160 to 491 mg/kg for FA and from 187 to 813 mg/kg of HA. This is consistent with what was reported by Dias et al (2007), who found that biosolid application involves a higher accumulation of humic substances in soils.
Treatments involving the application of alkalized biosolids did not significantly influence FA and humic content levels in the soils evaluated (values of 52-342 mg/kg for FA and of 19-346 mg/kg for HA). However, in all cases, FA values were highest during the first few months and decreased during the later months. The opposite trend occurred in terms of HA content levels, which were low during the first months and increased overtime, denoting that HA formation is likely attributable to FA polymerization. This was reported by authors as Aranda and Comino (2012) who found that the low condensation of humic substances can be observed in the prevalence of FA over HA related to the aromaticity and polymerization degree.
This results also shows that the application of these biosolids improves the FA and HA content in soils, potentially benefitting these types of crop, due to that humic subtance may positively influence higher plant metabolism. This function seems to be carried out more readily by low molecular size humic fractions, because they are able to reach the plasma membrane of root cells and then to be translocated (Nardia et al 2012). Also, humic acids could be used to reduce metal accumulation in plants growing in polluted acidic soils and could be used for metal bioremediation in alkaline soils (Zhang et al 2013)
The authors thank to COLCIENCIAS-Colombia for the financial support with the project code 1106-489-25147 and the doctoral scholarship student Jorge Silva and Universidad de Valle-Colombia.
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Received 18 January 2016; Accepted 15 March 2016; Published 1 May 2016