Effects Of Fertilization Measures And Basic Seedlings Under Conservation Tillages On Aroma And Yield Formation In Aromatic Rice

Conservation tillage is an economic and environmental-friendly soil tillage method,and soil tillage is an important agronomic measure that affects rice yield.This research was aimed to find out how different cultivation measures under the conservation tillage condition will affect the yield and quality of aromatic rice and to explore the characteristics and regulatory mechanisms of the formation and accumulation of2-acetyl-1-pyrroline（2-AP）.The field experiments were conducted in the teaching experiment base of South China Agricultural University.In experiment 1,Meixiangzhan 2and Xiangyaxiangzhan as test materials,no-tillage（A1）,less-tillage（A2）,and conventional farming tillage（A3）were each combined with side-by-side fertilization（B1）,conventional fertilization of farmers（B2）,and no fertilizer（B3）separately to explore the effects on flag leaf net photosynthetic rate,accumulation of above-ground dry matter,yield and its constituent factors,rice quality,and 2-AP contents in different parts.In experiment 2 with Meixiangzhan 2 and Xiangyaxiangzhan as test materials,no-tillage（A1）,less-tillage（A2）and conventional plowing（A3）were each combined with low-basic seedlings（C1）,medium-basic seedlings C2),and high-basic seedlings（C3）separately.The combined treatments were conducted to investigate the net photosynthetic rate of flag leaves,accumulation of aboveground dry matter,yield and its constituent factors,rice quality,and2-AP content in each part.In experiment 3 with Meixiangzhan 2 and Xiangyaxiangzhan as test materials,no-till（A1）,less-till（A2）and conventional plowing（A3）were each combined with low-high fertilization（D1）,medium fertilization（D2）,and low fertilization（D3）separately to explore the net photosynthetic rate of flag leaves,accumulation of aboveground dry matter,yield and its constituent factors,rice quality,and 2-AP contents in different parts.In Experiment 4 with Meixiangzhan 2 and Xiangyaxiangzhan as test materials,4 different farming management modes were tested,including no-tillage machine transplanting and simultaneous side-fertilization with reasonable basic seedling and fertilizer amounts（T1）,less-tillage machine transplanting and simultaneous side-fertilization with reasonable basic seedling and fertilizer amounts（T2）,conventional tillage machine transplanting and simultaneous side-fertilization with basic seedling and fertilizing amounts（T3）,and conventional tillage and conventional fertilizing with basic seedling and fertilizing amounts（T4）.Under each mode,the tilling dynamics of fragrant rice,net photosynthetic rate of leaves,accumulation of aboveground dry matter,yield and constituent factors,quality,2-AP contents in different parts,proline contents,pyrroline-5-carboxylic acid contents,1-pyrroline contents,proline dehydrogenase activity,pyrroline-5-carboxylic acid synthetase activity,ornithine transaminase activity,and activity change characteristics were investigated.（1）The machine transplanting with simultaneous fertilization compared with conventional fertilization can significantly increase the yield of aromatic rice and 2-AP contents.Among different treatments,machine transplanting with simultaneous fertilization under no-tillage,less-tillage or conventional tillage all significantly improved rice yields.Specifically,the yields of Meixiangzhan 2 and Xiangyaxiangzhan in the early and late seasons were all large under the simultaneous side deep fertilization,with average increases of 10.12%and 11.25%,respectively.Among different treatments,the machine transplanting with simultaneous deep side-fertilization under no-tillage,less-tillage,and conventional tillage all significantly increased the grain 2-AP contents at the mature stage.Specifically,the 2-AP contents in Meixiangzhan 2 and Xiangyaxiangzhan in the early and late seasons were large under the synchronous deep side-fertilization mode,with average increases of15.36%and 18.18%,respectively.The increase in the yields and mature-stage 2-AP contents may be due to the improvement of nitrogen fertilizer absorption and utilization.The deep side-fertilization compared with conventional fertilization increased nitrogen absorption and utilization efficiency in the early and late seasons by 12.85%and 19.51%respectively.At the same time,the 2-AP contents in the leaves and stem sheaths under simultaneous fertilization were maintained at higher levels compared with conventional fertilization.The 2-AP may be transported by leaves through the stems and sheath to grains,thereby promoting the accumulation of 2-AP in grains.（2）Different basic seedling treatments were significantly different in yields and 2-AP contents during deep-fertilization and simultaneous fertilization of machine-planting in three tillage modes.The average yields increased significantly.The yields of Meixiangzhan2 and Xiangyaxiangzhan in the early and late seasons were large under the treatment of medium and basic seedlings,and the average yields were 5.13 and 4.96 t·hm^-2,respectively.However,among different treatments,the number of low basic seedlings increased significantly in the basic seedling treatment of simultaneous planting and deep fertilization in three tillage modes.As for Meixiangzhan 2 and Xiangyaxiangzhan in early and late seasons,the 2-AP contents of the fragrant rice grains maximized under low basic seedling treatment,and the average yields were 34.71 and 65.24μg·kg^-1,respectively.（3）The yields and 2-AP contents after machine transplanting with simultaneous deep side-fertilization under three tillage modes were significantly different in different fertilizer application rates.The average yields increased significantly,and the yields of Meixiangzhan 2 and Xiangyaxiangzhan in the early and late seasons were high in the treatment of basic seedlings,with average yields of 4.27 and 4.82 t·hm^-2,respectively.Among different treatments,after the basic seedling treatment in the machine transplanting with deep side-fertilization,the number of low basic seedlings increased significantly.The2-AP contents of fragrant rice grains in Meixiangzhan 2 and Xiangyaxiangzhan in early and late seasons all maximized under the treatment of low basic seedlings,and the average yields were 126.40 and 119.89μg·kg^-1,respectively.The leaf and stem sheath 2-AP contents were maintained at high level,and 2-AP may be transported by the leaves through the stalk and sheath to the grain to promote the 2-AP accumulation in the grains.（4）Under continuous no-tillage machine transplanting with simultaneous deep fertilization combined with basic seedlings（4-6 seedlings/hole）and fertilizer application(750 kg·hm^-2)（T4）,the yields of fragrant rice increased,the brown rice rate and the polished rice rate were significantly improved,and the milling quality of the fragrant rice was improved.In the T4 mode,the 2-AP contents of Meixiangzhan 2 and Xiangyaxiangzhan at the mature stage maximized to 42.07 and 56.20μg·kg^-1,respectively.Moreover,the proline dehydrogenase activity,ornithine transaminase activity,pyrroline-5-carboxylic acid synthase activity,proline content,1-pyrroline content,and nitrate reductase activity under T4 were all at high levels.At the same time,this mode was conducive to increasing the2-AP content,ornithine aminotransferase activity,and nitrate reductase activity of leaves of mature-stage fragrant rice.In all,no-tillage machine transplanting with simultaneous deep fertilization combined with reasonable basic seedlings（4-6 seedlings/hole）and fertilization amount(750 kg·hm^-2)is a better cultivation management mode that can simultaneously increase rice yield and 2-AP content.