Effects of different organic wastes application on net greenhouse gas emission in farmland system

Abstract: The recycling of agricultural organic wastes not only can mitigate its pollution to the environment, provide nutrients for farmland, but also increase soil carbon storage and reduce greenhouse gas (GHG) emissions, which play an important role to climate change. Five kinds of agricultural organic wastes were selected to the wheat-maize rotation system, including crop residue, biogas residue, mushroom residue, wine residue and pig manure, with chemical fertilizer as control. Based on the field trials, the effects of soil carbon storage, soil GHG emissions and net greenhouse gas emissions (NGHGE) were measured. The results from 2013-2015 showed that: 1) Compared with chemical fertilizer control, returning organic materials improved the ability of soil carbon sequestration by 63.52% of 0-20 cm soil during 2013-2015 years of observation, crop residue, biogas residue, mushroom residue, wine residue and pig manure increased by 33.13%、86.34%、75.97%、52.66% and 69.48% in 2013-2015, respectively.Except the treatment of mushroom residue returning, organic material outside the croplands were more conducive to the increasing of soil carbon storage than crop residue. 2) Except crop residues returning, organic materials returning increased soil GHG emissions, soil GWP of crop residues were the lowest one, which was significantly lower than wine residue and pig manure (p<0.05), compared with biogas residue, mushroom residue, wine residue and pig manure, crop residue reduced emissions by 30.23%、27.84%、62.10% and 52.55%, respectively. 3) The values of NGHGE of each treatment were positive, which means all of the treatments were GHG emission sources. Compared with inorganic fertilizer control, except the treatment of mushroom residue returning, other organic amendments reduced GHG emissions and increased soil carbon pool s of the system(p<0.05), crop residues, biogas residues, wine residues and pig manures decreased NGHGE by52.78%、56.30%、54.19% and 90.35%, respectively. Organic materials from outside had a better NGHGE than crop residues. In conclusion, recycling organic wastes is beneficial to the soil carbon storage, although increasing soil GHG emissions, it ultimately presents an enhancement of NGHGE, which reduced total GHG emissions of the whole system. Returning organic amendments such as crop residues, biogas residues, wine residues and pig manures far beyond the croplands had better effects of mitigating GHGs than crop residues.