Evaluation of soil health and microbial diversity in organic cotton cultivation farming

Introduction

Modern agriculture has largely depended on the intensive use of chemical fertilizers and pesticides to maximize crop productivity. Although this approach has contributed to increased yields, continuous application of inorganic inputs and the practice of monocropping have accelerated the depletion of soil nutrients, reduced soil fertility, and adversely affected long-term agricultural sustainability. The indiscriminate use of synthetic fertilizers has also raised concerns regarding soil degradation, environmental pollution, and the decline of beneficial soil microorganisms. These issues have highlighted the need for sustainable nutrient management practices that can maintain crop productivity while preserving soil health. Organic farming has emerged as a promising production system that emphasizes the use of natural and renewable nutrient sources instead of synthetic chemicals. Nutrient management in organic agriculture primarily depends on green manures, farmyard manure, compost, vermicompost, biofertilizers, and various fermented organic formulations such as Panchagavya, Jeevamrutha, cow urine, vermiwash, and biodigester liquid. These organic inputs improve soil physical, chemical, and biological properties by enhancing nutrient cycling, increasing microbial activity, and maintaining soil organic carbon, thereby supporting sustainable crop production. Cotton is one of the most important commercial crops in India and plays a vital role in the country's agricultural economy. It is cultivated over approximately 11.25 million hectares with an annual production of about 34.23 million bales (Anonymous, 2020) [1] . Although India is one of the world's leading cotton-growing countries in terms of cultivated area, its average lint productivity of 510 kg ha⁻¹ remains below the global average of 621 kg ha⁻¹. Improving productivity without compromising soil quality is therefore essential for the long-term sustainability of cotton cultivation. The demand for organically produced cotton has increased steadily in recent years due to growing consumer awareness of environmental conservation and sustainable textile production. Worldwide, organic cotton occupies nearly 0.46 million hectares, with an estimated production of 241,276 metric tonnes (1.1 million bales). India continues to be the largest producer of organic cotton, contributing nearly 80 percent of global organic cotton output among the twenty-three organic cotton-producing countries. Within India, organic cotton is cultivated on about 57,705 hectares, producing approximately 258,823 bales, accounting for nearly one-fourth of global organic cotton production. The global market for organic cotton has also expanded rapidly, increasing from US$583 million to US$4.3 billion, reflecting the rising preference for environmentally sustainable textile products (Anonymous, 2014) [1] . Despite the increasing importance of organic cotton cultivation, research on efficient nutrient management using organic inputs is still inadequate. Information regarding the combined use of different organic nutrient sources for enhancing crop productivity, improving soil fertility, and promoting beneficial soil microbial populations remains limited. Therefore, developing an integrated organic nutrient management strategy is essential for achieving sustainable cotton production while conserving soil resources and maintaining long-term soil productivity. The present study has been undertaken to evaluate suitable combinations of organic nutrient sources for improving cotton yield, soil fertility, and soil biological health under organic production systems.

Materials and Methods

A field experiment was carried out at MARS, Dharwad during the cropping seasons of 2020-21 and 2021-22 to evaluate the influence of organic manures, green leaf manure, liquid organic formulations, and micronutrients on cotton yield and economics. The experimental soil was medium-deep black with medium organic carbon content (0.48%) and available nutrients of 264.70 kg N ha⁻¹, 21.80 kg P₂O₅ ha⁻¹, and 285.30 kg K₂O ha⁻¹. The study was conducted in a split-plot design with three replications. The main-plot treatments included three nutrient management options: M₁ consisted of the recommended dose of fertilizers (80:40:40 kg N:P₂O₅:K₂O ha⁻¹) combined with farmyard manure (FYM) at 5 t ha⁻¹. M₂ involved the application of enriched compost, vermicompost, and green leaf manure, each contributing one-third of the recommended nitrogen dose. M₃: included enriched compost, vermicompost, and green leaf manure, each supplying one-third of the recommended dose of fertilizers. The sub-plot treatments comprised five liquid organic and micronutrient sprays: L₁ was foliar application of panchagavya at 5% during sympodial branching, square initiation, flowering, and boll development stages. L₂ included bio-digester solution at 20%. L₃ consisted of cow urine at 10% concentration. L₄ was application of vermiwash. L₅ comprised borax at 0.2% combined with magnesium sulphate. In addition, a control treatment (T₁) was maintained with the recommended dose of fertilizers (80:40:40 kg N:P₂O₅:K₂O ha⁻¹) along with FYM at 5 t ha⁻¹. Organic inputs such as farmyard manure, enriched compost, and green leaf manure were incorporated into the soil 15 days before sowing based on treatment requirements. Vermicompost was applied in two splits: 50% as basal application before sowing and the remaining 50% as top dressing at 60 days after sowing (DAS). In the control plots, chemical fertilizers along with FYM were applied as per standard agronomic recommendations. Prior to sowing, cotton seeds were treated with cow urine, Azospirillum, phosphatesolubilizing bacteria (PSB), Pseudomonas striata, Trichoderma spp., and cow dung slurry. The hybrid cotton variety DHH-11, obtained from the Agricultural Research Station (ARS), Hebballi, Dharwad, was used. Sowing was performed manually by dibbling two seeds per hill on 12 July 2020 in the first year and 8 June 2021 in the second year. The nitrogen concentration in plant samples was determined using the Kjeldahl digestion method, phosphorus was estimated by the vanadomolybdate yellow colour method, and potassium content was measured using a flame photometer. Rhizosphere soil adhering to the roots was collected carefully for microbial analysis. The population of actinomycetes was estimated on Kuster's agar medium, and the results were expressed as colony-forming units (CFU) per gram of oven-dry soil.

Results and Discussion

Significant variation was observed in the uptake of nitrogen, phosphorus, and potassium due to different organic nutrient sources. Among the organic treatments, the application of enriched compost, vermicompost, and gliricidia leaf manure in equal proportions (1/3 each) along with RDF recorded higher uptake of N, P₂O₅, and K₂O (72.53, 14.26, and 77.3 kg ha⁻¹, respectively) compared to the same organic combination supplied with RDN. In the integrated nutrient management treatments, FYM @ 5 t ha⁻¹ combined with RDF resulted in the greatest uptake of N, P, and K (79.0, 17.1, and 80.9 kg ha⁻¹), showing noticeable improvements over EC + VC + GLM with RDN. Enhanced nutrient absorption was associated with increased dry matter accumulation and higher seed cotton yield. Foliar feeding with panchagavya @ 5% improved nutrient uptake (74.33 N, 15.23 P₂O₅, 79.36 K₂O kg ha⁻¹) compared to biodigester spray, and it remained statistically similar to borax + MgSO₄ and vermiwash treatments. When combined treatments were considered, EC + VC + GLM with RDF plus panchagavya recorded the highest nutrient uptake (73.80 N, 15.16 P₂O₅, 78.4 K₂O kg ha⁻¹), although it was at par with RDF + FYM integrated with borax + MgSO₄ or vermiwash sprays. Similar findings have been reported in earlier studies, where integrated nutrient management improved plant efficiency and biomass production through better source-sink balance. The maximum nutrient uptake (80.20 N, 17.39 P₂O₅, 81.82 K₂O kg ha⁻¹) was observed under FYM + RDF + panchagavya, and it was comparable with treatments involving borax + MgSO₄ and vermiwash. This response may be linked to improved plant growth and dry matter production. Boron application likely enhanced nitrogen metabolism, protein formation, and translocation of assimilates, thereby supporting yield formation. Soil organic carbon content differed significantly among treatments. Higher values were recorded under EC + VC + GLM combinations (5.5-5.6 g kg⁻¹) compared to FYM + RDF (5.2 g kg⁻¹), while RDF + FYM showed relatively lower values than fully organic or integrated systems. Panchagavya spray also improved organic carbon (5.5 g kg⁻¹), comparable to borax + MgSO₄ treatment. Sravani et al. (2024) [8] observed that organic sources play a key role in enhancing efficient utilization of the native as well as applied nutrients through matching nutrient availability.The highest soil organic carbon (5.7 g kg⁻¹) was observed with EC + VC + GLM plus RDF and panchagavya, exceeding RDF + FYM and showing similarity with borax + MgSO₄ and vermiwash treatments. Available soil N, P₂O₅, and K₂O were also significantly influenced by treatments. EC + VC + GLM with RDF showed higher values (282.5, 28.8, 328.3 kg ha⁻¹) than FYM + RDF. Addition of foliar sprays, especially panchagavya, further enhanced nutrient availability and performed better than biodigester spray, while remaining comparable to borax + MgSO₄, vermiwash, and cow urine applications. The highest available N, P₂O₅, and K₂O (284.4, 29.7, 330.0 kg ha⁻¹) were recorded under EC + VC + GLM with RDF and panchagavya, representing increases of 5.66%, 23.51%, and 13.40% over FYM + RDF. This improvement is likely due to intensified microbial activity and nutrient cycling in the soil. Combined application of EC (1/3) + VC (1/3) + gliricidia GLM (1/3) equivalent to RDF recorded significantly higher actinomycetes, phosphorus solubilising bacteria, N 2 -fixers, enzymes mainly phosphatase and dehydrogenase activity and soil respiration rate (73.19 cfu X10 6 / g of soil, 26.84 cfu X10 3 / g of soil, 39.65 cfu X10 2 / g of soil (Table 3-5), 26.15 cfu X10 3 / g of soil, 29.52 cfu X10 3 / g of soil, 25.01µ pnp/g of soil/hr, 11.99 µ TPF/g of soil/day, and 9.51 mg of C or CO 2/ hr/100 g of soil respectively) at 60 DAS as compared to application of FYM @ 5 t ha -1 + RDF. The foliar spray of panchagavya @ 5% in combination with organic manures recorded significantly higher population of actinomycetes, N 2 -fixers and PSM, phosphatase and dehydrogenase enzyme activity and soil respiration rate over foliar spray of bio-digester @ 20% with organic manures and was on par with borax @ 0.2% + MgSO 4 @ 1% and vermiwash @ 20%. Among the different treatment combinations, application of EC (1/3) + VC (1/3) + gliricidia GLM (1/3) equivalent to RDF with foliar spray of panchagavya @ 5% recorded significantly higher actinomycetes, N 2 -fixers and Psolubilizer, phosphatase and dehydrogenase enzyme activity and soil respiration rate over RDF + FYM and was on par with EC (1/3) + VC (1/3) + gliricidia GLM (1/3) equivalent to RDF with borax @ 0.2% + MgSO 4 @ 1%, EC (1/3) + VC (1/3) + gliricidia GLM (1/3) equivalent to RDF with vermiwash @ 20% and EC (1/3) + VC (1/3) + gliricidia GLM (1/3) equivalent to RDF with cow urine @ 10%. These results are in line with the findings of Solaiappan (2004) [9] . Fatma Kaplan (2025) [6] observed that application of organic and bio-organic fertilizer applications significantly increased soil organic matter and macronutrient levels (N, P, K), while promoting microbial activity and nutrient cycling. It can be concluded that integrating EC, VC, and Gliricidia GLM in equal proportions to meet the recommended dose of nitrogen (RDN), together with foliar application of panchagavya at 5%, is an effective strategy for improving soil biological health and sustaining cotton production.

References

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