Effect of Cow Urine on the Biochemical and Microbial Properties of Cow Dung Derived Biogas Slurry

Biogas slurry (BGS) is an anaerobic digested organic material that can be used as an organic fertiliser. As cow urine (CU) is rich in plant nutrients, it may be used as diluting agent in biogas production to enhance the fertiliser quality of BGS. To explore the potency of CU on the fertiliser quality of BGS, four experimental trials were constructed by mixing cow dung (CD) and CU in varying proportion designated as T0 (50% CD + 50% Water) as control, T1 (50% CD + 50% CU), T2 (40% CD + 60% CU), T3 (30% CD + 70% CU) for biogas production. The quality of BGS was evaluated by studying its biochemical and microbial properties. The enzymatic activities revealed that all the CU amended samples showed better activities than control and were increased with the increase in CU. Compared to the control, the increase in urease, protease and phosphatase activities were 11.6% to 64.6%, 4.6% to 29.6% and 22.1% to 50.0%, respectively while cellulase activities were decreased from 25.9% to 3.1%. Most of the bacterial populations also increased in CU amended samples; total bacteria (TB) 20% to 60%, phosphate solubilizing bacteria (PSB) 33% to 67% and nitrogen fixing bacteria (NFB) 0% to 33%. Phytohormone, indole acetic acid (IAA) content and glycemic index (GI) were also increased with increase in CU (IAA- 23.5% to 59.5% and GI- 6.2% to 100.5%).  With respect to all parameters analysed, CU amended samples can be considered superior to the control one except for their cellulase activities. Thus, utilization of cow urine improves the quality of BGS as organic fertiliser. This finding will help in reducing environmental pollution by utilizing hazardous cow urine as well as improving fertiliser quality of biogas slurry for agronomic use.