Housing system in dairy cow farms affects green house gas emissions from manure

This study is part of the evaluation process of the Rural Development Policy adopted by the Italian Region of Emilia Romagna during the period 2007-2013. The study was aimed at assessing the emissions of methane (CH4) and direct nitrous oxide (N2O) from manure handling in relation to the housing system in dairy cow farms. A total of 1,403 dairy farm records were considered. The following eight housing systems were evaluated: tie stall with straw (#847), tie stall without straw (#7), straw yard (#125), straw loose yard (#21), free stall cubicle with mattress (#96), free stall cubicle with straw (#61), free stall cubicle tail-tail with straw (#109), free stall cubicle head-head with straw (#137). Single farm demographic structure (cows, heifers and calves consistencies) was obtained from the National Bovine Registry and was referred to the years 2009-2011. Total live weight yr-1 (LW) for each livestock category was calculated considering 600 kg LW, 300 kg LW and 100 kg LW for cows, heifers and calves, respectively. Liquid and solid manure yield yr-1 and nitrogen excreted yield yr-1 were calculated according to the housing system, livestock categories and total LW as indicated by the regional nitrogen balance database. Volatile solid (VS) yield yr-1 were calculate as 73% and 82% of liquid and solid manure dry matter, respectively. Greenhouse gases emitted were estimated by using a Tier 2 approach as suggested in the guidelines provided by the International Panel on Climate Change (IPCC). Specific conversion factors calculated at regional basis and used in the Italian National Inventory Report (NIR) were applied to calculate CH4 manure emissions from total VS. The specific conversion factors were 15.32 g CH4/kg VS and 4.8 g CH4/kg VS for liquid and solid manure, respectively. Direct N2O emission were calculated using the emission factors adopted in the NIR and correspondent to 0.001 kg N2O-N/kg N excreted and 0.02 kg N2O-N/kg N excreted for liquid and solid manure, respectively. The CH4 and N2O emissions were calculated for each farm and expressed as kg CO2 equivalent (CH4, kg x 25; N2O, kg x 310) to account for the Global Warming Potential (GWP). Livestock Units (LSU) were calculated for each farm as 1 LSU equivalent to 600 kg live mass, 0.6 LSU equivalent to 300 kg live mass and 0.1 LSU equivalent to 100 kg. The CH4, N2O and total GWP (mean ± SD) were referred to LSU yr-1. The variation of emissions were evaluate by GLM (general linear model) where housing system was set as categorical variable and kg CH4, N2O and CO2 eq. emitted for LSU yr-1 as independent variables. The differences were analyzed by Tukey test and the significances were set for value of p<0.01. The emissions of CH4 were greater for straw yard housing system with value of 19.35±0.65 kg CH4/LSU year-1 (p<0.01). The CH4 emissions were related both to the great amount of solid and liquid manure produced in this housing system. The tie and free cubicle stall systems without the use of straw produce only liquid manure and were associated to high CH4 emissions with values of 18.0 ± 0.17 and 17.8 ± 0.53 CH4/LSU year-1, respectively. The other systems that produced more solid manure emitted less CH4 with the lower value of 13.6±0.54 kg CH4 LSU year-1 (p<0.01) for free stall cubicle with straw. The N2O emissions were related to the amount of N excreted in the liquid or solid manure produced. When housing system produced only liquid manure, the emissions of N2O were low due to the low emission factor adopted (0.001). The free cubicle and tie stall systems without the use of straw showed the lower N2O emissions (p<0.01) with values of 0.30 ± 0.16 kg N2O/LSU yr-1 and 0.31± 0.09 kg N2O/LSU yr-1, respectively. On the other hand, when housing system was straw based, high yield of solid manure were produced and greater N2O emissions were achieved due to high emission factor adopted (0.02). The housing systems tie and free cubicle stall with the use of straw and straw yard loose pointed out the grater N2O emissions (p<0.01) with values of 1.86±0.07, 1.84±0.09 and 1.86±0.12 kg N2O/LSU yr-1, respectively. When the greenhouse gasses were considered together to account at GWP, the housing systems without use of straw showed lower values (p<0.01) of GWP corresponding to 540±42 and 547±30 kg CO2 eq./LSU yr-1 for free cubicle and tie stall systems without straw, respectively. The lower GWP in these housing systems were related to the lower N2O emissions. In the systems with higher use of straw the GWP resulted greater (p<0.01) with values of 948±35, 945±40, 937±22, and 916±38 kg CO2 eq./LSU yr-1 for straw yard, straw loose yard, tie and free cubicle stall with straw, respectively. Interestingly, changing the disposition of animal in free cubicle stall with straw impacted on final GWP. The tail to tail disposition emitted 757±31 kg CO2 eq./LSU yr-1 compared with head to head system that accounted for 869± 22 kg CO2 eq./LSU yr-1 (p<0.01). This result is likely to be related to a lower intake of straw and consequently lower emission of N2O in tail to tail free stall. In synthesis, the housing systems which produced mostly solid manure emitted more nitrous oxide; conversely, the housing systems which produced mainly liquid manure emitted more methane. The greater conversion factor of nitrous oxide to carbon dioxide equivalent affected negatively the final GWP of housing systems based on the use of straw. Housing systems that use no organic litter such as mattress or sand are oriented to produce more liquid manure and may result more sustainable in terms of GWP. However, it has to be noticed that, compared to liquid manure, the solid manure increases the carbon sink potential when applied to arable soil as fertilizer. These trade-offs associated with utilization of inorganic versus organic bedding materials surely need further investigations. Their results will help in orienting future agro-environmental policies toward mitigation options which may reduce GWP of dairy production.