Effect of cow-urine based bio-stimulant on microbial activity in soybean (Glycine max) under vertisols of Chhattisgarh

Introduction

Cow urine is recognized as a valuable organic nutrient source rich in nitrogen, potassium, micronutrients, enzymes, hormones, and several bioactive compounds that promote plant growth and soil health. Unlike solid cow dung, which requires microbial decomposition before nutrient release, cow urine contains readily available nutrients such as urea, uric acid, soluble phosphates, and potassium salts that can be directly utilized by plants through foliar spray or soil application (Pradhan et al., 2017) [11] . Being inexpensive, eco-friendly, and easily available to farmers through livestock systems, cow urine has gained importance in sustainable and organic agriculture. Soybean (Glycine max L.) is one of the most important leguminous crops cultivated worldwide due to its high protein and oil content. Soybean seeds are rich in proteins, essential amino acids, minerals, vitamins, and unsaturated fatty acids, making them highly nutritious for human consumption (Pringgohandoko and Padmini, 1999) [12] . In Chhattisgarh, soybean is predominantly cultivated under rainfed conditions by small and marginal farmers. However, low productivity is often associated with imbalanced fertilizer use, declining soil fertility, poor microbial activity, and increasing input costs. Cow urine-based bio-stimulants have shown considerable potential in improving nutrient availability, nutrient uptake, soil biological activity, and crop productivity. The organic compounds present in cow urine serve as substrates for soil microorganisms, thereby stimulating microbial multiplication, enzymatic activities, and nutrient mineralization. Enhanced microbial activity improves rhizosphere processes, nutrient cycling, and biological nitrogen fixation in legumes such as soybean (Hungria et al., 2006) [8] . Studies have also reported that cow urine increases beneficial microbial populations and soil enzyme activities such as dehydrogenase, phosphatase, and urease, which are important indicators of soil biological health (Dinesh et al., 2010) [5] . Therefore, cow urine-based bio-stimulants may provide a sustainable alternative for improving soybean productivity and maintaining soil fertility under Vertisol conditions.

Materials and Methods

A field experiment entitled "Effect of Cow Urine-Based Bio-stimulant on Microbial Activity of Soybean in Vertisol of Chhattisgarh" was conducted during the kharif season of 2023 at the Research cum Instructional Farm of Indira Gandhi Krishi Vishwavidyalaya, Raipur, Chhattisgarh. The experimental soil was Vertisol in nature. Soybean variety CG Soya 11-15 was used as the test crop. The experiment was laid out in a Randomized Block Design (RBD) with ten treatments and three replications. The treatments consisted of different levels of recommended dose of fertilizers (RDF) combined with cow urine-based bio-stimulant applied through seed soaking, foliar spray, and soil application. Recommended agronomic practices were followed throughout the crop period. Observations on plant growth, nodulation, yield attributes, nutrient uptake, soil nutrient status, and microbial activity were recorded at different crop growth stages. Plant samples were analyzed for nitrogen, phosphorus, and potassium uptake using standard analytical procedures. Soil samples collected after harvest were analyzed for available nitrogen, phosphorus, potassium, microbial population, phosphatase activity, dehydrogenase activity, and microbial biomass carbon. The experimental data were statistically analyzed using analysis of variance (ANOVA) appropriate for RBD. The dry weight of nodule per plant was presented in Table 4.2 and Figure 4.3, the dry weight of nodules were ranged between 0.16 to 0.36 g/plant. The highest dry weight of nodule of soybean was associated with treatment T 8 (75% RDF + Seed soaking through 20% bio-stimulant + Foliar spray of 20% bio-stimulant at 30 and 45 DAS) 0.36g/plant as compared with T 1 (Control) 0.16/plant. However, the values were at par of treatment T 2 (100% RDF (NPK @ 20:60:30 kg/plant)) 0.35g/plant, T 10 (75% RDF + Soil application of 20% bio-stimulant at 10 DAS) 0.35 g/plant and T 6 (75% RDF + Foliar spray of 20% bio-stimulant at 30 and 45 DAS) 0.34 g/plant. The highest seed yield was recorded with 100% RDF (19.21 q ha⁻¹), followed by T 8 (75% RDF + seed soaking and foliar spray of 20% bio-stimulant) with 18.35 q ha⁻¹, which was statistically at par with 100% RDF. Treatments involving 75% RDF combined with bio-stimulant applications also produced yields comparable to full RDF, indicating a potential saving of 25-50% chemical fertilizer without significant yield reduction. The lowest yield was recorded in the control (14.43 q ha⁻¹). The enhanced yield under integrated nutrient management may be attributed to improved soil biological activity, nutrient mobilization, uptake, and translocation promoted by the cow urine-based bio-stimulant. Similar findings were reported by Deotale et al. and Gupta and Yadav. Application of cow urine-based bio-stimulants showed no significant effect on soybean stover yield. The highest stover yield was recorded with 100% RDF (T 2 ) at 21.97 q ha⁻¹, while the lowest was observed in the control (T 1 ) at 17.21 q ha⁻¹. Although stover yield increased with increasing fertilizer levels from 50% to 100% RDF, the differences were statistically non-significant. Similar biological yield across treatments may be attributed to the medium to high availability of soil nutrients (N, P, and K) in the experimental field, along with comparable plant population and growth parameters among treatments.

Uptake of Nitrogen

Nitrogen uptake in soybean seed, stover, and total biomass was significantly influenced by the application of cow urinebased bio-stimulants and fertilizer levels. The highest seed, stover, and total nitrogen uptake were recorded with 100% RDF (T 2 ), registering 112.03, 60.07, and 172.10 kg ha⁻¹, respectively. Among the bio-stimulant treatments, T 8 (75% RDF + seed soaking + foliar spray of 20% bio-stimulant at 30 and 45 DAS) showed the highest nitrogen uptake and remained statistically at par with 100% RDF. All treatments significantly outperformed the control, indicating that integrated use of RDF and bio-stimulants enhanced nutrient uptake through improved plant growth and yield. Similar results were reported by Ghoya et al. and Shaziya et al.

Uptake of Phosphorus

Phosphorus uptake in soybean seed, stover, and total biomass was significantly influenced by the application of cow urine-based bio-stimulants and fertilizer levels. The highest total phosphorus uptake was recorded with 100% RDF (T 2 ) at 10.50 kg ha⁻¹, followed closely by T 8 (75% RDF + seed soaking + foliar spray of 20% bio-stimulant at 30 and 45 DAS) with 10.46 kg ha⁻¹, which remained statistically at par with 100% RDF. All treatments significantly increased phosphorus uptake over the control (7.99 kg ha⁻¹). Among bio-stimulant treatments, T 8 showed the highest seed and total phosphorus uptake, indicating improved nutrient absorption and utilization through integrated nutrient management. Similar findings were reported by Ghoya et al. and Shaziya et al..

Uptake of Potassium

Potassium uptake in soybean seed, stover, and total biomass was significantly influenced by the application of cow urinebased bio-stimulants and fertilizer levels. The highest total potassium uptake was recorded with 100% RDF (T 2 ) at 82.69 kg ha⁻¹, followed closely by T 10 (75% RDF + soil application of 20% bio-stimulant at 10 DAS) with 81.51 kg ha⁻¹ and T 8 (75% RDF + seed soaking + foliar spray of 20% bio-stimulant at 30 and 45 DAS) with 79.89 kg ha⁻¹. In seed uptake, T 8 recorded the maximum potassium uptake (30.14 kg ha⁻¹), while all treatments significantly outperformed the control (52.35 kg ha⁻¹ total uptake). The enhanced potassium uptake under integrated nutrient management may be attributed to improved nutrient availability, uptake, and translocation promoted by the cow urine-based biostimulant. Similar findings were reported by Ghoya et al. and Shaziya et al..

Available Nitrogen, Phosphorus, Potassium

The application of cow urine-based bio-stimulants showed a non-significant effect on available soil nitrogen after soybean harvest. Soil available nitrogen increased from the initial value of 213.25 kg ha⁻¹ before sowing to a range of 246 kg ha⁻¹ in the control (T 1 ) to 263.4 kg ha⁻¹ in T 8 (75% RDF + seed soaking + foliar spray of 20% bio-stimulant at 30 and 45 DAS). Although differences among treatments were statistically non-significant, the overall increase in soil nitrogen after harvest may be attributed to biological nitrogen fixation by soybean. Similar findings were reported by Ghoya et al.. The applied treatments significantly influenced the available phosphorus status of the soil after soybean harvest. The highest available soil phosphorus was recorded in T 2 (100% RDF) with 21.81 kg ha⁻¹, while the lowest was observed in the control (16.73 kg ha⁻¹). Among the bio-stimulant treatments with 75% RDF, T 10 recorded comparatively higher available phosphorus (19.89 kg ha⁻¹). Application of 50%, 75%, and 100% RDF increased soil phosphorus status, with the greatest improvement observed under 100% RDF, likely due to higher phosphorus application and partial fixation in soil. Reductions in available phosphorus in some treatments may be attributed to greater crop uptake. Similar findings were reported by Ghoya et al.. The application of cow urine-based bio-stimulants had a non-significant effect on available soil potassium after soybean harvest. Available soil potassium increased from the initial value of 345.4 kg ha⁻¹ before sowing to a range of 373 kg ha⁻¹ in the control to 401.8 kg ha⁻¹ under 100% RDF treatment. Differences among treatments were statistically non-significant, possibly due to the release of potassium from exchangeable to available forms in the soil, which maintained a balanced potassium status across treatments. Similar findings were reported by Ghoya et al..

Soil Rhizobial Population

Soil rhizobial population density increased with crop growth and was influenced by the application of cow urine-based bio-stimulants. At 30 DAS, rhizobial population ranged from 6.176 to 6.308 log₁₀/g of rhizosphere soil, with the highest population recorded in T 10 , followed by T 8 and T 2 , while the control showed the lowest population. A similar trend was observed at 45 DAS, where rhizobial population ranged from 6.594 to 6.768 log₁₀/g of soil, with T 10 again recording the maximum population and the control the minimum. The increase in microbial population may be attributed to enhanced organic activity due to cow urinebased bio-stimulant application. Similar findings were reported by Boraiah et al..

Phosphatase Activity:

Acid phosphatase activity in soybean rhizosphere soil was significantly influenced by different bio-stimulant treatments. At 60 DAS, the highest activity was recorded in T 8 (75% RDF + seed soaking + foliar spray of 20% biostimulant) with 15.20 µg PNP g⁻¹ soil hr⁻¹, followed by T 10 (14.86) and T 2 (11.98), while the lowest activity was observed in T 1 (control) with 8.28 µg PNP g⁻¹ soil hr⁻¹.

After harvest, maximum phosphatase activity was recorded in T 6 (12.36), closely followed by T 10 (12.20), T 8 (12.18), and T 2 (12.05), whereas the minimum was again found in T 1 (8.08 µg PNP g⁻¹ soil hr⁻¹). The increased phosphatase activity was attributed to enhanced microbial activity due to the application of cow urine-based bio-stimulant.

Conclusion

The experiment concluded that application of cow urinebased bio-stimulant significantly improved soybean yield, soil microbial population, rhizobial population, dehydrogenase activity, phosphatase activity, and microbial biomass carbon. Among all treatments, 75% RDF + seed soaking with 20% bio-stimulant + foliar spray of 20% biostimulant at 30 and 45 DAS proved most effective. This treatment recorded the highest seed yield (18.35 q ha⁻¹), which was statistically comparable to 100% RDF (19.01 q ha⁻¹), indicating a saving of 25% RDF. Nutrient uptake (N, P, and K) under 50-75% RDF with bio-stimulant was also comparable to 100% RDF. Soil available phosphorus after harvest was highest under 100% RDF application. Overall, bio-stimulant application enhanced crop productivity and soil biological health while reducing fertilizer requirement.

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