Effect of Diets with Different Roughage-to-Concentrate Proportions on Manure Methane and Nitrous Oxide Fluxes

Aim: To measure methane and nitrous oxide fluxes from stored manure of buffalo calves fed different roughage to concentrate proportions.

Place and Duration of Study: The study was conducted at Livestock farm of NDRI Karnal Haryana from November 2014 to January 2015.

Methodology: Fifteen Murrah male calves (154.19± 17.77 kg; 6-12 months) were randomly assigned into three groups and were fed maize fodder, wheat straw and concentrate in three different proportions 20:60:20 (T20), 20:40:40 (T40) and 20:20:60 (T60), respectively. The dung samples from each calf were collected during the last week of the feeding trial and stored in heaps (height 61 cm; base radius 26 cm) under a plastic bucket for three months. The stored manure samples were collected every 2 weeks for composition analysis. Gas samples were collected through a sample port on top of each bucket 3 times per day for first 10 days then after every 2 weeks for the rest of storage period and analysed for methane (CH4) and nitrous oxide (N2O) concentrations. The amount of gas emitted was calculated as the product of gas concentration and flow rate of air passing through the exhaust. The emission rate was calculated by adding up gas emitted at each sampling and expressed in different units.

Results: Manure dry matter and organic matter (%) were not affected but nitrogen (%) was higher in T60 as compared to T20 and T40. Average CH4 (mg/kg manure/d; mg/kg volatile solids/d) and N2O (mg/kg manure/d) emission rates were higher in T60 compared to T20. However, CH4 emission expressed as g/animal/d and N2O as mg/animal/d did not (P>0.05) vary between the treatments groups. The fluxes increased up to the mid-storage period and then declined, more during the last week.

Conclusion: Overall, increasing dietary concentrate proportion increased manure CH4 and N2O flux rates but the emissions were very low. Thus, the systems of manure storage in India are not much conducive for greenhouse gas emissions which must be taken into account during the inventory preparation.