Influence of liquified humic acid application on chemical and biological characteristics of Vertisol of Chhattisgarh

Introduction

Maintaining and enhancing soil fertility is increasingly important due to the growing complexity of nutrient-related constraints. Organic matter plays a critical role in improving soil physical, chemical, and biological properties (Stevenson, F. J. 1994) [1] . Reduced soil organic matter also limits the availability of secondary and micronutrients. Humic and nonhumic substances reflect the quality of soil organic matter, with humic substances formed through microbial, enzymatic, and chemical decomposition of plant and animal residues (Flaig, 1975) [2] . Their chemically reactive functional groups directly and indirectly influence plant growth. Humic substances, comprising humins, humic acids, and fulvic acids, represent the largest fraction of soil organic matter and play a dominant role in soil conditioning and plant development. Physically, they improve soil structure and water-holding capacity; chemically, they function as nutrient adsorption and retention complexes, keeping essential elements available to plant roots (Randhawa and Broadbent, 1965) [3] and biologically, they stimulate microbial activity by serving as a source of nutrients and energy. Humic acid is recognized as one of the most significant natural organic compounds in agriculture (Ampong et al., 2022) [4] . Derived from the decomposition of plant and animal materials, it improves soil structure, texture, microbial activity, and water-retention capacity (Nardi et al., 2021; Shah et al., 2018) [5,6] enhances micronutrient availability through chelation, and facilitates nutrient uptake (Yang et al., 2021) [7] , while reducing the absorption of toxic heavy metals (Wu et al., 2017) [8] . Furthermore, humic acid stimulates growthregulating hormones such as auxins and cytokinin's, improves photosynthesis, nutrient metabolism, and stress tolerance (Canellas et al., 2020; Jindo et al., 2020) [9,10] .

It also enhances membrane permeability, mineral transport, protein synthesis, enzymatic activity, and beneficial microbial populations (Khaled et al., 2011) [11] . Given these multifaceted benefits, humic acid represents a promising tool for improving soil fertility, nutrient-use efficiency, and crop productivity. Thus, evaluating the influence of liquified humic acid on rice performance under Vertisol conditions of Chhattisgarh is essential for developing sustainable nutrient management strategies.

Materials and Methods

The experimental site was located at at the Research cum Instructional Farm, Indira Gandhi Krishi Vishwavidyalaya, Raipur (C.G.), situated in the central agro-climatic zone of Chhattisgarh. The field experiment was carried out during the Kharif seasons of 2023 and 2024 on rice crop to study the effect of foliar application of liquified humic acid on the chemical and biological properties of Vertisol under rice cultivation (cv. Rajeshwari). The field experiment was laid out in a Randomized Block Design (RBD) with ten treatments replicated three times: T 1 -Control (N 0 :P 0: K 0 ), T 2 -RDF (120:60:40), T 3 -RDF + Root dipping with liquified Humic Acid (1ml L⁻¹), T 4 -RDF + liquified Humic Acid FS @ 2.5 ml L⁻¹, T 5 -RDF + liquified Humic Acid FS @ 5 ml L⁻¹, T 6 -RDF + liquified Humic Acid FS @ 10 ml L⁻¹, T 7 -80% RDF + Root dipping with liquified Humic Acid (1ml L⁻¹) , T 8 -80% RDF + liquified Humic Acid FS @ 2.5 ml L⁻¹, T 9 -80% RDF + liquified Humic Acid FS @ 5 ml L⁻¹, T 10 -80% RDF + liquified Humic Acid FS @ 10 ml L⁻¹. The experimental soil was a Vertisol (locally known as Kanhar), classified as fine montmorillonitic, hyperthermic Ustic Chromustert, deep and clayey in texture, and neutral to alkaline in reaction. Rice variety Rajeshwari was used as the test crop. The Soil pH was determined in 2.5:1 water-soil suspension (Piper, 1966) [12] soil suspension after pH determination was stored overnight and EC of the supernatant liquid was determined by Solu-bridge as described by Black [13] . The organic carbon was determined by Walkley and Black's rapid titration method. Available nitrogen was estimated by alkaline potassium permanganate method, available phosphorus by Olsen's method (1954) [14] method, and available potassium was determined by neutral normal ammonium acetate extractant and detected by Flame photometer as described by Hanway and Heidal [15] . Available micronutrients (Fe, Zn, Mn, Cu) were extracted using DTPA (Lindsay and Norvell, 1978) [16] . Soil microbial biomass carbon (SMBC) and nitrogen (SMBN) were determined by the chloroform fumigation-extraction method (Vance et al., 1987; Brookes et al., 1985) [17,18] . The calculation for microbial biomass of soil: [19] . Slightly higher EC values were observed under 100% RDF (120:60:40 NPK) treatments compared to the control, the differences were nonsignificant and may be due dissolution of fertilizers in the soil solution, releasing higher concentrations of soluble salts such as nitrates, phosphates, potassium, and sulfates. The results were in close conformity to those obtained by Sathiya Bama et al. (2003) [20] , while higher OC was recorded under @ RDF + liquified humic acid FS @ 10 ml L -1 (T 6) and the lowest in the control. Pooled data across both years confirmed the non-significant influence of liquified humic acid and inorganic fertilizer combinations on soil available nitrogen, phosphorus and potassium. This may be attributed due to short-term experimentation, adequate initial soil fertility, rapid plant uptake, and the indirect role of humic acid in improving nutrient use efficiency rather than directly contributing nutrients. No variation in the Soil N was also reported by Layek et al.

(2018) [21] and Banjare et al. (2022) [22] . Application of inorganic fertilizer either alone or in combination with liquified humic acid were not significantly influenced available Fe, Zn, Cu, and Mn may be due to the foliar application of humic acid, which has minimal interaction with soil, and the strong buffering and fixation of micronutrients in soil, limiting changes in their availability. These findings are supported by earlier studies conducted by Clapp et al. (1999) [23] , (Stumm and Morgan, 1970) [24] and Sharif et al. (2002) [25] .

Soil biological properties 3.2.1 Soil microbial biomass carbon

The combined application of inorganic fertilizer and foliarapplied liquified humic acid had a non-significant effect on soil microbial biomass carbon (SMBC) and nitrogen (SMBN) during both of the years as presented in Table -4.

The pooled value of SMBC ranged from 180.68 to 213.09 μg C g -1 soil, with the highest recorded under @ RDF + liquified Humic Acid FS @ 10 ml L -1 (T 6 ), followed by @ RDF + liquified Humic Acid FS @ 5 ml L -1 (T 5 ), and these both treatments were statistically at par with the remaining treatments. The increase in SMBC may be attributed to the positive effect of foliar-applied humic acid on root growth and root exudation, which provide readily available carbon substrates for soil microorganisms, thereby enhancing microbial growth and activity. The lowest (180.68 μg C g -1 soil) soil microbial biomass carbon (SMBC) was noticed under unfertilized plot (T 1 ). Similar findings have been documented by Sellamuthu and Govindaswamy (2003) [26] , Li et al. (2019) [27] , and Sarangthem et al. (2023) [28] .

Soil microbial biomass nitrogen (SMBN)

The pooled SMBN values ranged from 35.62 to 52.58 μg N g -1 soil, with the maximum under @ RDF + liquified Humic Acid FS @ 10 ml L -1 (T 6 ), followed by @ RDF + liquified Humic Acid FS @ 5 ml L -1 (T 5 ) and found at par with rest of the treatments. The foliar application of humic acid along with RDF enhanced SMBN by improving root growth, nutrient uptake, and root exudation, which enriched the rhizosphere environment and supported microbial proliferation. The lowest SMBN (35.62 μg N g⁻¹ soil) was observed under the unfertilized plot (T 1 ). Similar findings have been documented by Sellamuthu and Govindaswamy (2003) [26] , Li et al. (2019) [27] , and Sarangthem et al. (2023) [28] and El-Ghamry et al. (2009) [31] . The lowest (35.62 μg N g -1 soil) soil microbial biomass nitrogen (SMBN) was noticed under unfertilized plot (T 1 ). These results indicate that while humic acid application slightly enhanced microbial biomass, the effects were not statistically significant.

Conclusion

The study concluded that the application of inorganic fertilizers either alone or in combination with foliar-applied liquified humic acid did not significantly influence soil chemical and biological properties during Kharif 2023 and 2024. Soil pH, EC, organic carbon, available nutrients, micronutrients, soil microbial biomass carbon (SMBC), and soil microbial biomass nitrogen (SMBN) remained statistically non-significant across treatments. However, comparatively higher values of SMBC and SMBN were observed under @ RDF + liquified Humic Acid FS @ 10 ml L⁻¹ (T 6 ). The non-significant response may be attributed to the short-term nature of the experiment, adequate initial soil fertility, and the indirect role of humic acid in improving nutrient use efficiency.

References

1. Stevenson FJ. Humus chemistry: genesis, composition, reaction. 2nd ed. New York: John Wiley & Sons Inc.; 1994. p. 36.
2. Flaig W. An introductory review on humic substances: aspects of research on their genesis, their physical and chemical properties, and their effect on organisms. In: Povoledo D, Golterman HL, editors. Humic substances: their structure and function in the biosphere. Proceedings of the International Meeting; 1972 May 29-31; Nieuwersluis, The Netherlands. Washington (Netherlands): Centre for Agricultural Publishing and Documentation; 1975. p. 366-371.
3. Randhawa NS, Broadbent FE. Soil organic mattermetal complexes: 5. Reactions of zinc with model compounds and humic acids. Soil Sci. 1965;99:295300.
4. Ampong K, Thilakaranthna MS, Gorim LY. Understanding the role of humic acids on crop performance and soil health. Front Agron. 2022;4:848621.
5. Nardi S, Schiavon M, Francioso O. Chemical structure and biological activity of humic substances define their role as plant growth promoters. Molecules. 2021;26(8):2256.
6. Shah ZH, Rehman HM, Akhtar T, Alsamadany H, Hamooh BT, Mujtaba T, et al. Humic substances: determining potential molecular regulatory processes in plants. Front Plant Sci. 2018;9:263.
7. Yang F, Tang C, Antonietti M. Natural and artificial humic substances to manage minerals, ions, water, and soil microorganisms. Chem Soc Rev. 2021;50(10):6221-6239.
8. Wu S, Li R, Peng S, Liu Q, Zhu X. Effect of humic acid on transformation of soil heavy metals. IOP Conf Ser Mater Sci Eng. 2017;207(1):012089.
9. Canellas LP, Canellas NOS, Irineu LE, Olivares FL, Piccolo A. Plant chemical priming by humic acids. Chem Biol Technol Agric. 2020;7:1-7.
10. Jindo K, Canellas LP, Albacete A, Figueiredo dos Santos L, Frinhani Rocha RL, Carvalho Baia D, et al. Interaction between humic substances and plant hormones for phosphorous acquisition. Agronomy. 2020;10(5):640.
11. Khaled H, Fawy HA. Effect of different levels of humic acids on the nutrient content, plant growth and soil properties under conditions of salinity. Soil Water Res. 2011;6(1):21-29.
12. Piper CS. Soil and plant analysis. Asian ed. Bombay: Hans Publishers; 1966. p. 368-374.
13. Black CA. Methods of soil analysis: Part I and II. Madison (WI): American Society of Agronomy; 1965.
14. Olsen SR, Cole CV, Watanabe FS, Dean LA. Estimation of available phosphorus in soils by extraction with sodium bicarbonate. Circ US Dept Agric. 1954;939:1-19.
15. Hanway JJ, Heidel H. Soil analysis methods as used in Iowa State College Testing Laboratory. Bull. 1952;57:1-131.
16. Lindsay WL, Norvell WA. Development of a DTPA soil test for zinc, iron, manganese, and copper. Proc Soil Sci Soc Am. 1978;42:421-428.
17. Vance ED, Brookes PD, Jenkinson DS. Microbial biomass measurements in forest soils: the use of the chloroform fumigation incubation method in strongly acidic soils. Soil Biol Biochem. 1987;19:697-702.
18. Brookes PC, Landman A, Pruden G, Jenkinson DS. Chloroform fumigation and release of soil N: a rapid direct extraction method to measure microbial biomass N in soil. Soil Biol Biochem. 1985;17:837-842.
19. Tahir MM, Khurshid M, Khan MZ, Abbasi MK, Kazmi MH. Lignite-derived humic acid effect on growth of wheat plants in different soils. Pedosphere. 2011;21(1):124-131.
20. Sathiya Bama K, Selvakumari G, Shanthi R, Singaram P. Effect of humic acid on nutrient release pattern. Madras Agric J. 2003;90:10-12.
21. Layek J, Das A, Idapuganti RG, Sarkar D, Ghosh A, Zodape ST, et al. Seaweed extract as organic bioInternational Journal of Advanced Biochemistry Research https://www.biochemjournal.com stimulant improves productivity and quality of rice in eastern Himalayas. J Appl Phycol. 2018;30(1):547-558.
22. Banjare L, Banwasi R, Jataw GK, Shrivastav LK. Effect of seaweed extract on yield and nutrient uptake of rice in a Vertisol. Pharma Innov J. 2022;11(3):21932198.
23. Clapp CE, Chen Y, Magen H, Cline VW. Stimulation of plant growth by humic substances. Cambridge: Royal Society of Chemistry; 1999. p. 255-263.
24. Stumm W, Morgan JJ. Aquatic chemistry: an introduction emphasising chemical equilibrium in natural waters. London: Wiley Interscience; 1970.
25. Sharif M, Khattak RA, Sarir MS. Effect of different levels of lignitic coal derived humic acid on growth of maize plants. Commun Soil Sci Plant Anal. 2002;33:3567-3580.
26. Sellamuthu KM, Govindaswamy M. Effect of fertilizer and humic acid on rhizosphere microorganisms and soil enzymes at an early stage of sugarcane growth. Sugar Tech. 2003;5(4):273-277.
27. Li Y, Fang F, Wei J, Wu X, Cui R, Li G, et al. Humic acid fertilizer improved soil properties and soil microbial diversity of continuous cropping peanut: a three-year experiment. Sci Rep. 2019;9(1):1-9.
28. Saranthem I, Mishra LK, Haldhar SM. Nature-based solutions for climate resilient agriculture: embracing the 5A approach. In: XVI Agricultural Science Congress 2023; 2023 Oct 10-13;
29. Kochi, India. Kochi: ICARCMFRI; 2023. p. 52.
30. El-Ghamry AM, Abd El-Hai KM, Ghoneem KM. Amino and humic acids promote growth, yield and disease resistance of faba bean cultivated in clayey soil. Aust J Basic Appl Sci. 2009;3(2):731-739.