Journal of Soils and Sediments

, Volume 18, Issue 4, pp 1400–1408 | Cite as

Slow nitrogen release from humic substances modified with aminoorganosilanes

  • Natalia A. Kulikova
  • Olga I. Filippova
  • Alexander B. Volikov
  • Irina V. Perminova
Natural Organic Matter: Chemistry, Function and Fate in the Environment

Abstract

Purpose

The purpose of the present study is to evaluate slow-release nitrogen capabilities of soil amendments obtained by modification of humic materials from peat and lignite with alkoxyorganosilanes carrying different amine substituents.

Materials and methods

The humates from lignite and peat were modified using (3-aminopropyltriethoxy)-silane (APTES) and (1-aminohexamethylenene, 6-aminomethylene)-triethoxysilane (AHATES). The obtained derivatives were characterized using elemental analysis and Fourier transform infrared spectroscopy. Nitrogen release in the form of ammonia or nitrate was evaluated using dissolution tests under sterile aqueous conditions as well as long-term soil experiments. Ammonium and nitrate were determined using ion-selective electrodes. Activity index (AI) was calculated from the dissolution tests. For soil trials, arable Retisol was sampled from 0- to 5-cm layer in Yaroslavl region (Russia). The soil experiments were conducted over 78 days using (NH4)2SO4 as an activator of nitrification and 3-amino-1,2,4-triazole as an inhibitor of autotrophic nitrifying bacteria.

Results and discussion

Modification of lignite and peat humates leads to an increase in nitrogen content up to 2 and 4.3 %, respectively, in case of APTES, and up to 3 and 6 %, respectively, in case of AHATES. All humic derivatives gradually released N upon dissolution in water over 6 days up to 51 % of the total N. The AI values ranged from 4 to 13 %. Amendment of soil with the modified humic materials induced an increase in nitrate content resulting from nitrification of released ammonia by soil microflora. This was confirmed by aminotriasole experiments. The nitrogen release occurred slowly: over the first week of incubation, it did not exceed 36–69 % of the total N content. The higher release rate of ammonium nitrogen was observed for CHS-AHATES versus CHS-APTES derivative, whereas no difference was seen between the two peat derivatives, which showed release rate on the level of CHS-AHATES derivative. Positive effect of all modified humic materials lasted over 78 days.

Conclusions

Modification of lignite and peat humates with two aminoorganosilanes carrying one and two nitrogen atoms in the amine substituent brought about twofold to threefold enrichment of the parent humic materials with nitrogen, which was capable of slow release upon incubation in soils. It was released in the form of ammonia and transformed to nitrates by autotrophic nitrifying soil microflora. There was no clear relationship established between structure of amine substituent of organosilane and slow-release properties of the corresponding humic derivatives. The conclusion was met that principal application of aminoorganosilane derivatives of humic substances (HS) is soil structuring, whereas nitrogen-fertilizing capabilities might be considered as beneficial added-value feature of these humic products.

Keywords

Aminoorganosilanes Humic substances Modification Slow nitrogen release fertilizers Soil amendments 

1 Introduction

Humic substances (HS) comprise from 50 to 90 % of natural organic matter (NOM) in soil and water ecosystems as well as in peat, lignites, and sapropels (Thurman 1985; Orlov 1990; Clapp et al. 1993). The beneficial effects of HS on crops have been numerously reported: they enhance efficiency of nutrient use, replace synthetic plant growth regulators, improve fruit quality, increase water stress tolerance, decrease disease incidence, induce early growth and flowering, and others (Chen and Aviad 1990; Canellas et al. 2010, 2015; Trevisan et al. 2010). In addition, HS improve soil fertility by increasing bioavailability of nutrients, sustaining salt balance, and improving physical soil properties. This provides for better aeration, drainage, water retaining capacity, and others (Stevenson 1994). Despite these multiple benevolent functions, agricultural applications of humic materials remain rather limited. HS are mostly used as biostimulants for foliar applications, whereas their application as soil conditioners is complicated by poor retention onto soil matrix of highly soluble sodium and potassium humates (Clapp et al. 2007). To overcome this problem, modification of humic materials is needed aimed at increasing its retention within the upper soil profile.

Recently, we have demonstrated a good promise for a use of 3-aminopropyltriethoxy-silane (APTES) as a humate modifier, which enabled production of ecologically safe, nature-inspired soil conditioners: they efficiently sorbed onto clay minerals, improved re-assembly of soil aggregates, and restored their water stability (Volikov et al. 2016a). The presence of amine functionality in this modifier allowed us to hypothesize that the aminoorganosilane derivatives of HS might also serve as a source of slow-release nitrogen. This is because new materials developed for more efficient use of nitrogen in fertilizers involve coating with different polymers (Pereira et al. 2015) such as starch-urea-borate adhesives (for coating slow-release urea) (Naz and Sulaiman 2014), starch matrix modified by vinyl acetate (Niu and Li 2012), and other hydrophylic polymers (Mikkelsen 1994). Given that aminoalkoxysilanes are capable of producing polymer-like networks of silsesquioxanes during their interaction with HS, which we have demonstrated in our recent work using in situ small-angle scattering (SAXS) technique (Volikov et al. 2016b), this might retard nitrogen release from the humic derivatives modified with aminoorganosilanes.

The objectives of this research were twofold: firstly, we have evaluated nitrogen release in the form of ammonia or nitrate species from aminoorganosilane derivatives of HS under sterile conditions in aqueous solutions, and secondly, we monitored ammonia and nitrate release in soils amended with the modified HS using long-term soil experiments. To reach these objectives, we used two different aminoorganosilanes for HS modification, which contained one nitrogen atom in the form of primary amine group (APTES) and two nitrogen atoms in the form of primary and secondary amine groups: (1-aminohexamethylenene, 6-aminomethylene)-triethoxysilane (AHATES). The corresponding structural formulas of the both aminoorganosilanes are shown below.

A use of the above alkoxysilane modifiers carrying different amine substituents was to explore benefits of the corresponding humic derivatives in the context of their nitrogen slow-release capabilities.

2 Materials and methods

2.1 Humic materials

Two types of humic materials were used in this study isolated from lignite and peat. Commercially available potassium humate (Sakhalin Humate) from leonardite was used as a source of lignite humic material and designated as CHS. Peat sodium humate (PHS) was obtained from fen peat sampled in Tver Region (Russia) using single extraction with 1 M NaOH. All reagents used for HS isolation were of analytical grade.

2.2 Functionalization of the humic materials using aminoorganosilanes

Technical grade (3-aminopropyl)triethoxysilane (APTES) and (1-aminohexamethylenene, 6-aminomethylene)-triethoxysilane (AHATES) were purchased from Penta Ltd. (Moscow). The silanes were used as purchased without further purification. The reaction stoichiometries were calculated on the basis of carboxyl group content in CHS and PHS as described in our previous publications (Perminova et al. 2012; Karpiouk et al. 2012). The carboxyl group content was determined using Ca-acetate method (Swift 1996) and accounted for 2.7 and 2.9 mmol g−1 for CHS and PHS, respectively. Given that 1 g APTES contains 4.5 mmol of amine groups, a 2:1-M ratio of COOH to NH2 groups was reached by treating 1.2 g of CHS or 1.3 g or PHS with 1 g of APTES. For 1 g of AHATES containing 3.9 mmol of amine groups, weights of CHS and PHS were 1.4 and 1.45 g, respectively. Prior to synthesis, a weight of CHS or PHS was dissolved in distilled water in a beaker while stirring with a magnetic stirrer. A required aliquot of APTES or AHATES was added dropwise to the obtained humate solution under continued stirring, and pH of the reaction mixture was adjusted to 4 with 5 M HCl. Then, the solution was transferred into a round bottom flask and rotor-evaporated to dryness. The reaction product was further cured in a vacuum oven at 120 °C for 6 h. The resulting derivatives were stored in sealed vials. They looked like darkly brown amorphous powders. The samples were designated as CHS-APTES, CHS-AHATES, PHS-APTES, or PHS-AHATES. The reaction scheme is shown in Fig. 1.
Fig. 1

Modification scheme of HS with aminoorganosilanes in aqueous medium: a APTES and b AHATES

2.3 Characterization of the parent and functionalized humic materials

Elemental analyses (C, H, N) were performed on a Varo EL analyzer. The Si content was determined using a conventional spectrophotometric method described elsewhere (e.g., Carlson and Banks 1952). Ash content was determined as a weight residue after combustion of the humic sample placed in a quartz tube at 750 °С during 40 min.

Fourier transform infrared spectroscopy (FTIR) spectra of HS and their derivatives were acquired using spectrometer IR-200 (Thermo Nicolet, USA) in the range of 4000–400 cm−1. The standard methods using KBr pellets were applied.

2.4 Determination of activity index of the parent and functionalized humic materials

Assessment of nitrogen release from the parent and functionalized HS was performed according to Kaempffe and Lunt (1967). A weight of 125 mg of the parent or functionalized HS was placed in the sterile plastic tubes, added with 25 mL of sterile distilled water, capped, shaken, and left for 21 days in the dark. After that, the concentration of NH4 + и NO3 was determined using ion-selective electrodes EKOM-NH4 or EKOM-NO3 (Econiks, Russia). Then, the solutions were boiled for 1 h and again analyzed for NH4 + and NO3 content as described above. The amount of N in the solution released after boiling refers to the maximum amount of N that can be dissolved in water. Based on these data, we calculated the activity index (AI) of the studied humic materials according to Trenkel (1997):
$$ \mathrm{AI}=\frac{\mathrm{CWIN}\hbox{-} \mathrm{HWIN}}{\mathrm{CWIN}}\times 100\% $$
where CWIN is the cold water-insoluble nitrogen (a sum of NH4 + и NO3 ) and HWIN is the hot water-insoluble nitrogen (a sum of NH4 + и NO3 ). The parameter AI relates to the part of nitrogen in the fertilizer that can be slowly released in the environment due to dissolution. All experiments were performed in triplicates.

2.5 Soil experiments on nitrogen release

The topsoil samples of arable Retisol (WRB 2014) were collected from 0- to 5-cm layer in Yaroslavl region (Russia) (56.856927, 38.295715) and air-dried. The soil samples had texture of silty loam and pH value of 6.9. The content of organic C (C org) was 29.9 g kg−1, K2O 110 mg kg−1, and P2O5 490 mg kg−1. The contents of labile NH4 + and NO3 were determined according to Mineev (2001) and accounted for 0.2 and 71 mg kg−1, respectively.

For nitrogen release experiments, a 100-g weight of soil was placed into a 100-mL sterile plastic cup and saturated with the solutions of humic materials (5 g L−1) up to 100 % of field water capacity, which corresponded to the dosage of 2.25 mg of the humic material per 1 g of soil. Distilled water saturated soil was used for blank experiments. Then, the saturated soil samples were air-dried and analyzed for nitrifying capacity (Mineev 2001). For this purpose, they were re-wetted with distilled water up to 60 % of field water capacity and incubated for 8 days at 28 °C. Ammonia sulfate (NH4)2SO4 (0.2 g kg−1 of soil) was used as an activator and 3-amino-1,2,4-triazole (aminotriazole, 0.2 g kg−1 of soil) as an inhibitor of nitrifying bacteria. The contents of labile NH4 + and NO3 were determined after 8 days of incubation using ion-selective electrodes (Mineev 2001). Soil nitrifying capacity (rate of nitrate formation) was calculated as a difference between the N-NO3 contents in milligram per kilogram of soil after and before incubation normalized to the experiment duration (8 days). Then, the soil was incubated for 70 more days and analyzed for the contents of labile NH4 + and NO3 . The moisture content was kept constant throughout the experiments by adding distilled water when needed. The experiments were performed in triplicate.

2.6 Statistical data analysis

The data presented are the average results of three replicates. Differences between average values were tested with a two-way analysis of variance (ANOVA) with silane modifier and HS presence as two fixed factors. A least significant difference (LSD) test was used for comparisons between paired means at P < 0.05.

3 Results and discussion

3.1 Characteristics of the humic materials treated with aminoorganosilanes

The data on elemental compositions of the parent humic materials from lignite and peat and of their APTES and AHATES derivatives are presented in Table 1. As it was expected, the functionalized humic materials had significantly higher N content as compared to the parent HS, and the highest N contribution was seen with the both AHATES derivatives. In addition, H/C atomic ratios for the silanized derivatives were higher as compared to the parent HS due to the presence of propyl and hexamethylene chains in APTES and AHATES, respectively.
Table 1

Elemental compositions of the parent HS and their aminoorganosilane derivatives

Humic material

Content (% mass)

Atomic ratio

C

H

N

C/N

H/C

CHS

31.7

2.9

1.2

29.93

1.07

CHS-APTES

31.6

3.5

2.5

14.62

1.32

CHS-AHATES

33.5

3.9

3.6

10.93

1.38

PHS

40.9

4.1

3.1

15.23

1.19

PHS-APTES

38.8

4.3

4.3

10.49

1.32

PHS-AHATES

38.2

5.5

5.1

8.72

1.71

FTIR spectra of the APTES humic derivatives (Fig. 2a) were characterized by appearance of two strong absorption bands of Si–O–C bonding at 1100 and 1050 cm−1, which are present in the spectrum of APTES. The carboxylate band positioned at 1560 cm−1 in the parent humic materials (CHS and PHS) shifted to 1640 cm−1 in the silanized HS, which might be indicative of substantial contribution of amide >C=O (amide I) bonds usually located at 1630–1695 cm−1. This is consistent with our findings on amide formation in humic materials treated with APTES and cured at 120 °C (Volikov et al. 2016c). The presence of amide bond was also confirmed by high peak intensity at 1560 cm−1 (amide II and carboxylate) and a weak band at 1265 cm−1 (amide III). In case of AHATES derivatives (Fig. 2b), broadening of the carboxylate peak (1560 cm−1) as well as of >C=O of amide I and amide III peaks (1690 and 1268 cm−1, respectively) was detected. This might indicate strong interactions between HS and both aminoorganosilanes via electrostatic binding of protonated aminoorganosilanes to negatively charged humic molecules preceding with formation of covalent amide bonding.
Fig. 2

FTIR spectra of the parent HS from lignite (CHS) and peat (PHS) and of their different aminoorganosilane derivatives: a APTES derivatives and b AHATES derivatives

3.2 Nitrogen release from the aminoorganosilane humic derivatives in aqueous solutions: sterile conditions

The kinetic curves of nitrogen release from the aminoorganosilane humic derivatives under study are shown in Fig. 3. The kinetic experiments were conducted in aqueous solutions under sterile conditions to exclude impact of microbial transformations. The results demonstrate a gradual release of nitrogen over the first 6 days upon dissolution of all humic materials under study. Exceptionally high nitrogen release was observed for the parent CHS material—up to 51 % of the total N, which was not the case both for the parent peat HS and for the aminoorganosilane derivatives of CHS and PHS. Nitrogen release from the APTES and AHATES derivatives of CHS accounted for 23 and 26 % of the total nitrogen content, respectively, whereas for peat derivatives, it did not exceed 9 %. AHATES derivatives of the both humic materials released more of water-soluble nitrogen (related to its total content in the sample) as compared to the APTES ones (Table 2). At the same time, the AI values for AHATES derivatives were lower as compared to APTES derivatives, despite the higher total nitrogen content in the both AHATES derivatives (Table 1). This might be connected to the presence of secondary amino group in the structure of AHATES, which is less susceptible to hydrolysis and biodegradation.
Fig. 3

Nitrogen release from the parent humic materials (CHS and PHS) and their aminoorganosilane derivatives in water under sterile conditions

Table 2

Nitrogen release from the parent HS and their aminoorganosilane derivatives on the twenty-first day of dissolution in water

Humic material

N released (% of the total content in the humic material)

AI (%)

N-NO3

N-NH4 +

Sum of N-NO3 and N-NH4 +

CHS

4.9 ± 0.1

46.0 ± 0.2

51 ± 0.3

40 ± 7

CHS-APTES

1.1 ± 0.1

21.8 ± 0.1

23 ± 0.2

13 ± 2

CHS-AHATES

0.2 ± 0.1

26.5 ± 0.1

26 ± 0.2

6 ± 2

PHS

0.6 ± 0.2

3.4 ± 0.1

4 ± 0.3

6 ± 3

PHS-APTES

0.2 ± 0.1

3.2 ± 0.1

3 ± 0.2

5 ± 1

PHS-AHATES

0.2 ± 0.1

8.7 ± 0.2

9 ± 0.3

4 ± 1

LSD

0.3

0.4

0.5

4

±Standard deviation

Comparison of the derivatives by the source of the parent humic material shows that the AI values for the peat humic derivatives were much lower than those for the corresponding CHS derivatives (Table 2). This might indicate poorer suitability of peat humic materials with respect to preparation of slow-nitrogen-release fertilizers. However, caution should be exercised with this conclusion, while we have no plausible explanation with respect to exceptionally high release of water-soluble N from the CHS sample registered in our study. We cannot refer such a substantial difference in N release behavior to specific structural features of lignite HS (there are no substantial differences seen in FTIR spectra of those humic materials in Fig. 2). Given that water-soluble nitrogen was released from CHS in the form of ammonium ions, we might rather suggest that this commercial humate was partially contaminated with ammonium ions: CHS was used in our studies as it is, whereas its aminoorganosilane derivatives were cured for few hours in a vacuum oven at 120 °C. This curing procedure had to eliminate ammonium contamination from the corresponding derivatives.

Comparison of the AI values obtained for all aminoorganosilane derivatives (4–13 %) with those reported in the literature shows that they are much lower as compared to, for example, formaldehyde urea-based fertilizers, whose AI succeeds 40 % (Trenkel 1997). It should be noted, however, that in case of urea, the nitrogen release results rather from microbiological transformation than from dissolution, and the AI value cannot serve as a relevant measure of the potentially available nitrogen. To estimate this value, we studied nitrogen release from the parent and modified humic materials as a result of microbial transformation under soil conditions.

3.3 Nitrogen release from the aminoorganosilane derivatives of HS upon their incubation in soil

As it can be deduced from Table 2, the nitrogen released from the humic derivatives in the course of dissolution mostly in the form of ammonia (Table 2). This allowed us to suggest that nitrification might be the prevailing process of the released nitrogen transformation in soil, which implies conversion of ammonium to nitrate. We measured nitrification rate in the blank soil (without humic amendments) in the absence and presence of nitrification initiator (NH4)2SO4. The results are shown in Table 3 and Fig. 4. The obtained rates in blank experiments accounted for 4.96 and 5.1 mg kg−1 day−1, respectively (Table 3). A lack of substantial increase in the nitrification rate in the presence of initiator demonstrates favorable conditions for the growth of nitrifying microorganisms in the soil (arable Retisol) used in this study.
Table 3

The rate of nitrate and ammonia formation in the soil samples amended with the modified humic materials in the absence and presence of nitrification initiator—ammonium sulfate

Humic material

Nitrogen release (mg kg−1 day−1)

Nitrogen release (mg kg−1 day−1

N-NH4 +

N-NO3

N-NH4 +

N-NO3 )

No additive

(NH4)2SO4

Blank

0.03 ± 0.01

4.96 ± 0.02

0.09 ± 0.03

5.10 ± 0.01

CHS

0.04 ± 0.01

9.09 ± 0.01

0.03 ± 0.01

6.58 ± 0.02

CHS-APTES

0.06 ± 0.01

6.24 ± 0.05

0.13 ± 0.01

9.90 ± 0.02

CHS-AHATES

0.06 ± 0.01

6.53 ± 0.09

0.07 ± 0.01

7.59 ± 0.02

PHS

0.09 ± 0.01

6.37 ± 0.03

0.09 ± 0.01

7.06 ± 0.08

PHS-APTES

0.04 ± 0.01

4.22 ± 0.05

0.09 ± 0.01

9.07 ± 0.05

PHS-AHATES

0.04 ± 0.01

5.69 ± 0.07

0.06 ± 0.02

10.62 ± 0.01

±Standard deviation. LSD = 0.5

Fig. 4

Nitrate content in soils amended with the aminoorganosilane humic derivatives in the absence (left panel) and presence (right panel) of nitrification initiator—(NH4)2SO4

Table 3 shows that incubation of the aminoorganosilane humic derivative-amended soils was accompanied by a very low ammonia release (similar to that observed in the non-amended soil). The highest rate of nitrogen release was observed in soil amended with the CHS sample (Table 3), which was characterized with the largest AI value (40 %) as a result of its presumable characterization with ammonium ions.

Figure 4 shows a substantial increase in the nitrate formation rate in the humic derivative-amended soils as compared to the control experiments: 115–180 % increase was observed if compared to the “no additive” trials, and even higher increase—up to 130–208 %—was observed in the presence of (NH4)2SO4. This might mean that all ammonia released during incubation of the humic derivative-amended soils was completely transformed into nitrates. This is in agreement with a lacking increase in the ammonia content in the presence of (NH4)2SO4 added as an initiator and might be indicative of fast ammonium oxidation in the selected soil. In addition, complete nitrification of the humic-released ammonium in the amended soils conforms to the direct relationship observed between the released amount of water-soluble N (Table 2) and nitrification rate in soil without additives (Table 3). The corresponding correlation coefficient accounted for 0.89, which is statistically significant at P < 0.05.

To obtain a direct evidence of soil microbial nitrification, we conducted incubation of soils amended with the humic derivatives over 8 days in the presence of aminotriazole—inhibitor of autotrophic activity of nitrifying microorganisms. The corresponding results are shown in Table 4 and Fig. 5. Introduction of aminotriazole into amended soils brought about an increase in the content of ammonia and a substantial decrease in the content of nitrates: the latter dropped to 5–34 % of the values in the untreated soil. This reveals preferential transformation of ammonium released from the aminoorganosilane derivatives of HS by soil autotrophic microflora. At the same time, the highest nitrification rate in the presence of aminotriazole was observed for CHS-AHATES, which might be indicative of its nitrification by heterotrophic microflora.
Table 4

The rate of nitrate and ammonia formation in the soil samples amended with the modified humic materials in the presence of (NH4)2SO4 and nitrification inhibitor—aminotriazole

Humic material

Nitrogen release (mg kg−1 day−1)

N-NH4 +

N-NO3

Blank (no humic material)

0.61 ± 0.12

0.44 ± 0.03

CHS

0.64 ± 0.01

0.40 ± 0.09

CHS-APTES

0.57 ± 0.06

0.37 ± 0.05

CHS-AHATES

0.87 ± 0.08

0.55 ± 0.03

PHS

0.54 ± 0.07

0.36 ± 0.01

PHS-APTES

0.87 ± 0.09

0.47 ± 0.01

PHS-AHATES

0.78 ± 0.09

0.56 ± 0.02

±Standard deviation. LSD = 0.5

Fig. 5

Nitrate content in soil trials amended with the aminoorganosilane humic derivatives incubated over 8 days (left panel) and 78 days (right panel) in the presence of nitrification inhibitor—aminotriazole

Incubation of soils amended with the aminoorganosilane humic derivatives over the next 70 days demonstrated that ammonia content in all trials dropped to negligibly small values, which were excluded from further consideration. In the absence of additive (ammonium sulfate), the nitrate content was the same as in the blank soil ranging from 91 to 110 % of control (Fig. 5). The only exception was the soil sample amended with the CHS-AHATES derivative, which was characterized with much higher nitrate content reaching 35 and 70 % of the values seen in the non-inhibited soils on the 8th and 78th days of incubation, respectively. It should be noted that this very derivative induced the highest nitrification rate in the presence of aminotriazole (Table 4). The latter might be connected to considerable contribution of heterotrophic nitrification in oxidation of ammonia released from CHS-AHATES, which is also in agreement with the observed low efficiency of (NH4)2SO4 in case of CHS-AHATES. However, the similar trends were not observed for PHS-AHATES derivative, which does not allow us to assign the observed effect solely to the peculiar feature of chemical structure of AHATES—the presence of secondary amine in its aliphatic chain. We believe that the observed effects might rather result from interplay of both chemical and microbial processes specific to this soil.

The above soil experiments demonstrated long-term positive effect of the aminoorganosilane derivatives of HS on nitrate content in the amended soils. They clearly showed nitrifying capabilities of soil microflora with respect to both types of amine nitrogen present in the aminoorganosilane modifiers used in this study. Nitrification kinetics allow us to conclude on slow-release properties of this nitrogen: only 36 to 69 % of its total content in the derivatives was released over the first week of incubation. The higher release rate of ammonium nitrogen was observed for CHS-AHATES versus CHS-APTES derivative, whereas no difference was seen between the two peat derivatives, which showed release rate on the level of CHS-AHATES derivative.

4 Conclusions

Modification of lignite and peat humates with two aminoorganosilanes carrying one and two nitrogen atoms in the amine substituent brought about twofold to threefold enrichment of the parent humic materials with nitrogen, which was capable of slow release upon incubation in soils. It was released in the form of ammonia and transformed to nitrates by autotrophic nitrifying soil microflora. The soil experiments demonstrated long-term positive effect of the aminoorganosilane derivatives of HS on nitrate content in the amended soils. At the same time, there was no clear relationship established between structure of amine substituent of organosilane and slow-release properties of the corresponding humic derivatives: soil microflora was capable to utilize both types of amine nitrogen present in the aminoorganosilane modifiers used in this study. The conducted research allows us a conclusion that the aminoorganosilane derivatives of HS do contain nitrogen, which can be slowly released during their incubation in soil. However, nitrogen-fertilizing capabilities of these derivatives are much less pronounced as compared to soil structuring effects shown in our previous publications (Volikov et al. 2016a) and can be considered as an added-value property upon their principal application as soil amendments aimed at restoration of soil structure.

Notes

Acknowledgments

This work was supported by the Russian Science Foundation (grant no. 16-14-00167).

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.

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Copyright information

© Springer-Verlag Berlin Heidelberg 2016

Authors and Affiliations

  • Natalia A. Kulikova
    • 1
    • 2
  • Olga I. Filippova
    • 1
  • Alexander B. Volikov
    • 3
  • Irina V. Perminova
    • 3
  1. 1.Department of Soil ScienceLomonosov Moscow State UniversityMoscowRussia
  2. 2.Bach Institute of Biochemistry, Research Center of Biotechnology of the Russian Academy of SciencesMoscowRussia
  3. 3.Department of ChemistryLomonosov Moscow State UniversityMoscowRussia

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