Impacts Of Rice Planting Pattern And Straw Recycling On Crop Yield And Greenhouse Gas Emission Under Rice-barley Cropping System

The average global surface temperature has risen by 0.74??0.56?-0.92??in the past 100 years,which is expected to increase 1.8-4.0?at the end of this century.Rising of atmospheric temperature is due to the dramatic increase in greenhouse gas emissions resulting from human activities.Therefore,greenhouse gas emissions have become a hot topic among the scientific community,politicians and the public.CH₄ and N₂O are considered the most important greenhouse gases exclude CO2.Farmland ecosystem is an important source of greenhouse gas emissions with CH₄ in paddy soil and N₂O in upland.Thus,studies of greenhouse gas emissions under paddy-upland rotation system are particularly essential.Current research on agricultural emissions of greenhouse gas mainly based on the single-season crop under conventional production methods,but rarely study on anniversary scale emissions has been reported.In this study,the experiment was conducted to examine the paddy and upland greenhouse gas emissions and its intensity,and the annual productivity of rice-barley system,the characteristics and intensity of annual greenhouse gas emissions were also discussed.Furthermore,the economic benefit and carbon footprint which were resulted from the annual production of rice-barley system were clarified.We also investigated rice and barley matter accumulation and transportation,N efficiency,rice lodging and grain quality of three mechanical planting methods including dry direct-seeding,wet direct-seeding and transplanting with or without straw recycling in East China.It is important for food security,rural incomes and the reduction of greenhouse gas emissions from farmland under the new situation of our country.Three mechanical planting practices with and without straw recycling were performed for two rice-barley cycles during 2010 to 2012,including dry direct-seeding with?MDSS? and without?MDS?straw recycling,wet direct-seeding with?MWSS?and without?MWS? straw recycling,and transplanting with?MTPS?and without?MTP?straw recycling.For the wet direct-seeding and transplanting methods?i.e.MWSS,MWS,MTPS and MTP?,the irrigation pattern was set as alternate wetting and drying.For the dry direct-seeding methods?i.e.MDS and MDSS?,the fields were maintained for a moist condition during the entire rice growth period.Before planting,each replicate plot was prepared without irrigation and divided into three strips?each at 3 m in width?which were separated by furrows?each at 25 cm in width and 30 cm in depth?.After sowing on the strips,the fields were flooded only for one day and drained out.During the whole growing cycle,the furrows were kept full of water to maintain a moist condition for rice growth,and no obvious water layer was maintained on the seedling strips.Main results are as follows:?1?Rice yield under dry direct-seeding was almost similar with transplanting,but significantly higher than the wet direct-seeding.There were significant differences of rice yields in 2010 between these treatments.The rice yields of MDS and MTP were increased by 8.2%and 12.0%,respectively,compared with MWS.Additionally,rice yields of MDSS and MTPS were enhanced by 8.0%and 10.2%,respectively,though the yield of MWSS was decreased by 6.1%,compared with MWS.Results from the 2-yr field experiment showed that there were no significant differences between the factors of rice production under dry direst-seeding but panicles per area,suggesting that panicles per area might be the key factor to rice production under dry direct-seedling.Therefore,the increase in panicles might compensate the decreases in grain number and grain weight.Furthermore,there were no significant differences of barley yield between rice tillage practices with straw incorporation.?2?The rice lodging index was showed to be transplanting<dry direct-seedling<wet direct-seedling,under different rice tillage practices.Rice quality was decreased with the two direct-seedling methods.The lodging index of MWSS was 37.95%and 52.39%higher than the lodging indexes of MDSS and MTPS,respectively,with straw incorporation.Meanwhile,the lodging index of MWS was 5.93%and 7.43%higher than MDS and MTP,respectively,without straw return.Transplanting and dry direct-seedling decreased the lodging index but wet direct-seedling increased the lodging index,with straw incorporation.Rice cropping practices had significant effects on the lodging index?P<0.01?,as well as interactions of rice cropping practices and straw return on lodging index?P?0.05?.Compared with wet direct-seedling,rice under dry direct-seedling was characterized as increased stem diameter and stems wall thickness,reduced plant height and section modulus,and enhanced banding stress,resulting in a stronger lodging resistance.Straw incorporation had no effect on rice quality?P>0.05?.The responses of rice appearance quality and processing quality to the rice cropping practices were different.There was decreasing trend of amylose contents with both wet direct-seedling and dry direct-seedling.Amylose contents were reduced by 2.7%and 3.2%,respectively.Protein content of rice grain was highest in MTP,and was 1.6%and 0.2%higher than in MDS and MWS,respectively.?3?Nitrogen?N?utilization efficiency of rice under three cropping practices was performed as transplanting>dry direct-seedling>wet direct-seedling.Transplanting showed the highest,and 1.5%and 15.8%higher N utilization efficiency than dry direct-seedling and wet direct-seedling,respectively.Dry matter production efficiency and grain production efficiency of N fertilizer were increased by 5.7%and 16.2%in dry direct-seedling,1.8%and 2.3%in wet direct-seedling,and 1.2%and 2.3%in transplanting,respectively,with straw incorporation.These results suggested that straw incorporation could improve the N efficiency of rice.Barley dry matter production efficiency and grain production efficiency of N were increased by 7.9%and 6.1%in MDSS,17.9%and 20.6%in MTPS,respectively,but were reduced by 8.8%and 10.3%in MWSS,respectively.?4?Dry direct-seedling and transplanting showed significant differences of CH₄ emissions but not N₂O emissions.Dry direct-seedling decreased CH₄ emissions significantly,with an increasing trend in N₂O emissions,under rice paddies.In 2010,cumulative CH₄ emissions were 80.97,28.41,256.03,329.76,321,76 and 488.76 kg ha-1 in MDS,MDSS,MWS,MWSS,MTP and MTPS,respectively.Yield-scaled cumulative CH₄ emission was highest in MTPS,which was 437.7%,146.71%,58.65%,16.45%and 64.9%higher than MDS,MDSS,MWS,MWSS and MTP,respectively.For 100 years' scale,the GWP of CH₄ and N₂O in transplanting and wet direct-seedling were significantly higher than that in dry direct-seedling.There were significant differences of GHGI under different cropping practices.The results above indicated that dry direct-seedling could largely reduce the GHGs emissions in rice paddies while maintaining rice yields.?5?Rice planting pattern and straw recycling affected the CH₄ uptake and N₂O emissions in the following barley growing season.The largest CH₄ absorption was in wet direct-seeding while the smallest was in dry direct-seeding,but the difference was not significant.N₂O emissions were significantly affected by rainfall in all treatments.N₂O emission was MTPS>MDSS>MWSS with straw recycling while MWS>MTP>MDS without straw recycling.The GWP from the following barley growing season in rice transplanting and wet direct-seeding treatments were lower than that in rice dry direct-seeding treatment.Straw recycling significantly reduced N₂O emission in the following barley growing season by 41.35%,50.56%.and 34.41%,in dry direct-seeding,wet direct-seeding and transplanting,respectively.?6?According to the annual effect,annual GWP of dry direct-seeding signifiacnt lower than that of rice transplanting and wet direct-seeding treatments;straw recycling enhanced the annual GWP.Using carbon footprint theory and research methods evaluated carbon footprint under annual production of rice and barley,we found that carbon footprint of annual production in rice dry direct-seeding was 40.90%and 67.99%lower than those in rice transplanting and wet direct-seeding,respectively.Straw recycling did not increase the carbon footprint in rice direct-seeding treatment.The annual carbon footprint in rice transplanting treatment was mainly due to CH₄ emission,fertilizer,irrigation and N₂O emission.CH₄ emission was the dominated which accounted for 67.2%.However,the annual carbon footprint was mainly from nitrogen?more than 30%?,phosphate and N₂O emission.