Effects Of Different Fertilizer Sources And Tillage Practices On GHG Emissions And Soil Carbon Pool In Paddy Fields

The study aimed to investigate effects of nitrogen fertilizer sources and tillage practices on GHG emissions and soil carbon pool by analyzing their change features under different fertilizer and tillage treatments. Then, we can provide some academic bases and references for decreasing GHG emissions and increasing soil fertility in paddy fields. The treatments were prepared with a split-plot design of a randomized complete block with fertilizer types as the main plots and tillage practices as the sub-plots. The main plots included no nitrogen fertilizer(N0); inorganic fertilizer(IF); organic fertilizer(OF); inorganic fertilizer with organic fertilizer(IF+OF); and slow release fertilizer with inorganic fertilizer(SR), whereas the sub-plots included conventional tillage(CT) and no-tillage(NT). Our main results are as follows:(1) Dual CH4 flux peaks were observed in two rice growing seasons. Two peaks appeared in the tillering and booting stage, respectively, and the highest fluxes were detected in the OF treatments during both two rice growing seasons. Nitrogen fertilizers significantly increased rice field CH4 emissions. OF treatment had the largest seasonal cumulative CH4 emissions of 458 kg ha-1 and 451 kg ha-1 in 2014 and 2015 rice growing seasons, respectively. NT treatment significantly decreased seasonal cumulative CH4 emissions in both 2014 and 2015 rice growing seasons compared to CT treatment.(2) Emissions of N2 O increased following every fertilization. Application of nitrogen fertilizers showed a significant higher increase in the seasonal cumulative N2 O emissions than no nitrogen fertilizer treatment. IF+OF treatment had the largest seasonal cumulative N2 O emissions of 1.21 kg ha-1 and 1.46 kg ha-1 in 2014 and 2015 rice growing seasons, respectively. NT treatment significantly increased seasonal cumulative N2 O emissions in 2015 rice growing season compared to CT treatment.(3) Application of nitrogen fertilizers significantly increased rice gain yield, global warming potential(GWP) and GHG emission intensity(GHGI). SR treatment had higher rice gain yield and lower GWP and GHGI in all fertilizer treatments. NT treatment significantly decreased GWP and GHGI, however it had no significant effects on rice grain yield compared to CT treatment.(4) Net ecosystem economic benefits(NEEB) of paddy field under different fertilizer treatments followed the order of IF+OF>IF>N0>OF>SR; NT treatment significant increased NEEB compared CT treatment. IF+OF+NT treatment had highest NEEB in all experiment treatments.(5) Nitrogen fertilizers application significantly increased 0-5cm soil layer carbon pool management index(CPMI), active carbon fractions and >0.25 mm macroaggregate content after rice harvesting. SR treatment had higher CPMI, microbial biomass carbon(MBC) and easily oxidizable carbon(EOC) content in all fertilization treatments. Application of organic fertilizer significant increased soil dissolved organic carbon(DOC) and 2015 rice growing season 0-5cm soil layer total organic carbon(TOC) content. NT treatment significantly increased MBC, EOC and >0.25 mm macroaggregate content compared to CT treatment.(6) SR+NT treatment had lower GHG emissions, GWP, GHGI and higher grain yields and CPMI in all treatments, so it is a sustainable strategy of increasing production and decreasing greenhouse gases emission. However it is difficult to generalize this strategy to agricultural production at present because of the higher fertilizer price and lower NEEB.