Effects Of Different Water Management On Growth And Physiological Characteristics And Greenhouse Gas Emissions Of Dry Direct Seeding Rice

Rice is one of the twelve main crops in the modern world,and also one of the main food crops in China.China’s rice planting area is about 30.7 million hectares,and its planting area accounting for 26%of the country’s total area of grain crops.Black soil is not only a valuable natural resource in the world,but also a high fertility soil resource supporting the developm ent of human society.The black soil in Northeast China is one of the three black soil belts in the world.Heilongjiang Province in Northeast China is the largest commercial rice production base in China,and also the most important japonica rice production base.At present,the rice planting in the northeast black soil area has been mainly based on seedling transplanting and flooding irrigation,which has the problems of large water consumption and low utilization efficiency of irrigation water.At the sam e time,with the rapid development of China’s economy,the number of rural migrant workers is increasing,and the rural labor force is decreasing,which leads to the rising cost of rice planting.Therefore,it is of great significance to carry out the research on high-yield,efficient and water-saving rice planting model in northeast black soil region for the efficient use of agricultural water resources,the protection of national food security and the sustainable development of agriculture.In this study,the dry direct seeding rice in the black soil region was taken as the research object.According to different water management schemes,four treatments were implemented:flooded irrigation dry direct seeding rice（YH）,wet irrigation dry direct seeding r ice（SH）,dry irrigation dry direct seeding rice（HH）,and transplanting flooded rice（CK）.Among them,transplanting flooded rice was the control.The pit test was carried out from 2018 to 2019 to study the growth and development,photosynthetic physiologica l characteristics,water use,greenhouse gas emissions,soil inorganic nitrogen content,yield and its components of dry direct seeding rice under different water management conditions.The entropy weighted TOPSIS model was used to comprehensively evaluate the advantages and disadvantages of different rice planting models,and the optimal planting model of dry direct seeding rice suitable for northeast black soil region was proposed.The main results are as follows:（1）The rice height of different treatments increased gradually from the early tillering stage to the heading and flowering stage,reached the maximum in the milk stage,and remained unchanged in the yellow ripening stage.Compared with the control treatment,the rice height of dry direct seeding treatments were reduced by 8.69%～22.58%.The change trend of dry matter weight of root,stem,sheath and leaf of rice in different treatments was first increased and then decreased,while the change trend of dry matter weight of panicle was gradually incre ased.Compared with the control treatment,the dry matter weight of rice organs of dry direct seeding treatments decreased in varying degrees.Dry direct seeding rice can improve root activity at later growth stage,but not promote dry matter transfer to p anicles.The higher the soil moisture content in dry direct seeding rice field,the higher the rice harvest index and the total dry matter weight of aboveground at mature harvest.（2）The photosynthetic rate,stomatal conductivity and transpiration rate of the conventional transplanting flooded rice and dry direct seeding rice were all showed inverted V shape,and reached the maximum in the heading and flowering stage.Compared with CK,the photosynthetic rate of YH,SH and HH were reduced by-13.09%～18.54%,-11.80%～22.83%and 13.58%～44.17%,respectively.The transpiration rate of YH,SH and HH were reduced by-9.98%～42.68%,-9.55%～44.26%and 23.87%～55.38%,respectively,compared with CK.The stomatal conductivity of YH,SH and HH were reduced by-30.46%～20.93%,-26.11%～22.04%and14.63%～46.98%,respectively,compared with CK.From the early tilllering stage to the milk stage,the variation of intercellular CO₂concentration of the control treatment was 164.40～290.38μmol·mol^-1,and the variation of intercellular CO₂concentration of dry direct seeding treatments was 199.70～285.92μmol·mol^-1.（3）The law of water consumption of conventional transplanting flooded rice was not changed by dry direct seeding rice.The water consumption amount and water consumption intensity of different treatments were basically showed M shape,and the maximum water consumption amount and water consumption intensity were all appeared in the jointing and booting stage.Compared with CK,the total water consumption amount of YH,SH and HH were significantly reduced by 23.60%～26.70%,13.80%～38.50%and 39.90%～50.80%（P<0.05）,respectively.The water consumption intensity of YH,SH and HH were significantly reduced by1.0～1.5 mm/d,1.6～2.0 mm/d and 2.3～2.7 mm/d（P<0.05）,respectively,compared with CK.Dry direct seeding cultivation could improve the water use efficiency of rice leaves from the early tillering stage to the heading and flowering stage,among them,the water use efficiency of HH reached the highest.Compared with CK,the yield water use efficiency of YH,SH and HH were significantly increased by 29.37%～33.74%,50.55～52.97%and 56.73%～59.02%（P<0.05）,respectively.（4）Compared with traditional transplanting cultivation,dry direct seeding cultivation reduced the yield of rice,but the difference was not significant（P>0.05）.Compared with conventional transplanting flooded rice,the grain number per spike,setting percentage and thousand kernel weight of dry direct seeding rice decreased in varying degrees,but the effective panicle number increased.Under different water management conditions,the yi eld of dry direct seeding rice increased first and then decreased with the total water consumption amount.According to the experiments in 2018 and 2019,when the total water consumption amount was0.39 m³/m²,the rice yield reached the maximum correspondingly.The effect of water consumption amount in the jointing and booting stage on effective panicle number and setting percentage of dry direct seeding rice was greater than that in other growth stages.（5）Under different water management conditions,the emissions of methane and nitrous oxide in dry direct seeding rice fields increased first and then decreased during the whole growth period.The maximum emissions of methane appeared in the jointing and booting stage,while the maximum emissions of nitrous oxide appeared in the heading and flowering stage.Dry direct seeding rice can significantly reduce greenhouse effect of paddy field.Compared with CK,the methane emission of YH,SH and HH were decreased by 1.05～29.53 mg/（m²·h）,11.73～40.76mg/（m²·h）and 17.38～50.60 mg/（m²·h）,respectively.The GWP of YH,SH and HH were decreased by 6715.58 kg/hm²,15166.85 kg/hm² and 22146.43 kg/hm²,respectively,compared with CK.The GWP_y of YH,SH and HH were decreased by 18.73%,47.14%and 61.87%,respectively,compared with CK.The nitrous oxide emission of YH,SH and HH were increased by 14.73～51.03μg/（m²·h）,20.69～57.99μg/（m²·h）and 21.57～71.35μg/（m²·h）,respectively,compared with CK.（6）The change law of NH₄⁺-N and NO₃^--N contents in 0～20 cm,20～40 cm and 40～60cm soil layers of different treatments were consistent.Compared with CK,the average content of NH₄⁺-N of YH,SH and HH were decreased by-11.72%～19.12%,-18.84%～16.82%and-10.01%～10.83%,respectively.The average content of NO₃^--N of YH,SH and HH were increased by 2.65～31.78 mg/kg,3.41～26.87 mg/kg and 4.43～19.32 mg/kg,respectively,compared with CK.The flooding irrigation was beneficial to the absorption of NH₄⁺-N by dry direct seeding rice,and wet irrigation and dry irrigation dry direct seeding cultivation were beneficial to the absorption of NO₃^--N by rice.In 0～20 cm dry direct seeding rice field,with the increase of soil depth,soil temperature had a greater impact on NH₄⁺-N content and methane emission.There was a positive correlation between methane emission and nitrous oxide emission in dry direct seeding rice field,while NH₄⁺-N content and NO₃^--N content were negatively correlated.（7）In this study,entropy weight method and TOPSIS model were organically combined.Twenty-one indexes were selected from the aspects of growth and development,photosynthetic physiology,water use,yield and its components,greenhouse gas emissions and soil inorganic nitrogen content of rice to construct the evaluation system of different rice planting models.The weight of each index was determined by the entropy weight method,and the TOPSIS model was used to calculate the four different rice planting models.The order of advantages and disadvantages was SH>HH>YH>CK.The evaluation results showed that the wet irrigation dry direct seeding planting model was the ideal rice planting model.