| In coastal saline-alkali soil,the change of the groundwater table can affect the contents of soil moisture and salinity and form different double stresses of soil moisture and salinity,thus affecting crop growth and yield.However,the phosphorus(P)deficiency is also a key factor affecting cotton yield in coastal saline-alkali soil.It is a way of alleviate the adverse effects of water-salt stress on cotton yield by the P application.In order to determine the impacts of the P application on cotton yield under groundwater buried depths in coastal saline-alkali soil,the field column experiment of 1 and 2 were conducted in Dafeng,Jiangsu Province(120°34?E,33°24?N).Experiment 1 of groundwater buried depths affecting the contents of soil water and salt,cotton yield with groundwater buried depths(0.6 m,1.0 m,1.4 m,1.8 m,2.2 m,2.6 m in 2013 and 0.4 m,0.8 m,1.2 m,1.6 m,2.0 m,2.4 m in 2014)was conducted in 2013-2014(arid and humid year).The salt-tolerant cultivar of China Cotton Research Institute 79(CCRI 79)was selected as the experimental material.In 2016-2017,the field column experiment 2 of the effects of the P application on soil physical,chemical and biological properties and cotton yield in coastal saline-alkali soil with groundwater buried depths(0.5 m,0.9 m,1.3 m,1.7 m,2.1 m,2.5 m)and phosphorus application rates[0,50,100,150,200 kg·P2O5·ha-1(P0?P50?P100?P150?P200)]was conducted in 2016-2017(normal and arid year),using P-sensitive cultivar of Lu 54 and P-weak-sensitive cultivar of Yuzaomian 9110 as experimental materials.The main results are as follows:1.Effects of the Groundwater Buried Depths on Soil Physical,Chemical and Biological Properties and the Adjusting Effects of the Phosphorus Application in Coastal Saline-Alkali SoilIn coastal saline-alkali land,with the groundwater buried depth increasing,soil relative-water content(SRWC),electrical conductivity of a 1:5 distilled water(EC1:5),soil soluble sodium ion and chloride ion content decreased,while soluble potassium ion content decreased first and then increased,and the content of soil available P,the number of organic P-decomposing bacteria,the number of inorganic P-decomposing bacteria and alkaline phosphatase activity increased first and then decreased.Under different climatic conditions,the groundwater buried depths of 0.4 m,0.5 m,0.6 m,0.9 m and 1.0 m were in the state of waterlogging and high salt;and of 0.8 m,0.9 m were in the state of waterlogging and medium salt;and of 1.4 m was in the state of normal soil-relative water content and high salt;and of 1.8 m,2.1 m,2.2 m and 2.6 m were in the state of mild drought with moderate salt;and of 2.5 m was in the state of mild drought and low salt;and of 1.3 m,1.7 m were in the state of normal soil-relative water content and medium salt;and of 1.2 m,1.6 m,1.7 m,2.0 m,2.1 m,2.4 m were in the state of normal soil-relative water content and low salt.The content of soil soluble sodium and chloride ion were in the medium level,and of soil soluble potassium ion was the lowest,while the content of soil available P,the number of organic P-decomposing bacteria and inorganic P-decomposing bacteria and alkaline phosphatase activity were the highest from the groundwater buried depth of 1.6 m to 1.8 m,where the water-salt stress was the lightest.Meanwhile,the content of soil soluble sodium ion,potassium and chloride ion were the highest,while the content of soil available P,the number of organic P-decomposing bacteria and inorganic P-decomposing bacteria and alkaline phosphatase activity were the lowest from the groundwater buried depth of 0.4 m to 0.6 m,where the water-salt stress was the heaviest.For the same groundwater buried depth,compared with no P application,P application had no effect on SRWC and EC1:5,but could increase the content of soil available P,the number of organic P-decomposing bacteria,the number of inorganic P-decomposing bacteria and alkaline phosphatase activity.In addition,the above indexes increased with the increase of P application rate.When the P application rate increased from P0 to P100,there was a big increase range for the content of soil available P,the number of organic P-decomposing bacteria and inorganic P-decomposing bacteria and the activity of alkaline phosphatase.When the P application rate increased from P100 to P200,the increase range of the above indexes decreased,that is,P100 was the critical point of P application.According to the increase range of the main microbial indexes,the number of soil organic P-decomposing bacteria was more sensitive to P application,compared with other soil indexes.The content of soil available P,the number of organic P-decomposing bacteria and inorganic P-decomposing bacteria,and the activity of alkaline phosphatase for Yuzaomian 9110 were higher than that of Lu 54 under P0 or low P application rate(P50).When the P application rate increased from P0 to P100 and from P100 to P200,the increase range of the above indexes of Yuzaomian 9110 were lower than that of Lu 54.The groundwater buried depth ranges of the lightest and heaviest water-salt stress were 1.6-1.8 m and 0.4-0.6 m,respectively.Soil water-salt stress significantly reduced the content of soil available P,the number of organic P-decomposing bacteria,the number of inorganic P-decomposing bacteria and alkaline phosphatase activity.The function of P application alleviating the double stress was that P application could not only increase the content of soil available P,the number of organic P-decomposing bacteria and inorganic P-decomposing bacteria,and the activity of alkaline phosphatase,but also improve soil quality.In addition,the soil microorganism for Yuzaomian 9110 grew better under low P condition,which could activate more P that is difficult to be absorbed and utilized by plants in the soil.2.Effects of the Phosphorus Application on Cotton Physiological Characteristics under Groundwater Buried Depths in Coastal Saline-Alkali SoilFrom the groundwater buried depth ranges of 1.6 m to 1.8 m,the root vigor,leaf area per plant,the SPAD value,leaf water content,net photosynthetic rate and ratio of K to Na of the completely unfolded main stem top fourth leaves,P uptake of aboveground organs all reached the maximum;In addition,the contents of superoxide dismutase(SOD),peroxidase(POD),catalase(CAT),proline and malondialdehyde(MDA)all reached the minimum;It was indicated that cotton didn't activate excessive antioxidant defense mechanisms and the soil moisture-salinity stress had the least effects on cotton.Meanwhile,from the groundwater buried depth ranges of 0.4 m to 0.6 m,the above indexes of cotton growth all reached the minimum;In addition,the reduction in net photosynthetic rate was mainly due to non-stomatal restriction,and the photo synthetic apparatus of cotton suffered the irreversible damage;Furthermore,the contents of SOD,POD,CAT and proline didn't reach the maximum,but MDA reached the maximum;It was indicated that the antioxidant defense mechanisms in cotton couldn't resist the stress and became invalid;Moreover,the soil moisture-salinity stress had the heaviest effects on cotton.Compared with no P application,P application could enhance the root activity,leaf area per plant,SPAD value,net photosynthetic rate,P uptake of aboveground organs under the heaviest stress.When the P application rate increased from P0 to P100,there was a big increase range for the root activity,leaf area per plant,SPAD value,net photosynthetic rate,P uptake of aboveground organs.When the P application rate increased from P100 to P200,the increase range of the above indexes decreased,that is,P100 was the critical point of P application.According to the increase range of the mian cotton growth indexes,the rates of P uptake of aboveground organs in cotton were more sensitive to P application,which contributed greatly to cotton growth and development.The root activity,leaf area per plant,SPAD value,net photosynthetic rate,P uptake of aboveground organs of Lu 54 were lower than that of Yuzaomian 9110 in the treatment of P0 and P50.In conclusion,the water-salt stress had an adverse effect on cotton growth and development in coastal saline-alkali land.The function of P application alleviating the water-salt stress was that P application could promote the absorption of P for cotton root,thus enhancing the resistance ability of cotton for the water-salt stress,and increasing cotton photosynthesis.The benefit of phosphate fertilizer was the best when the P application rate was 100 kg·P2O5·ha-1 in coastal saline-alkali soil.The root system was more developed and the root vigor was stronger in the stress of low P,thus absorbing and utilizing more P,and having higher photosynthesis for the P-weak-sensitive cotton cultivar of Yuzaomian 9110.3.Effects of the Phosphorus Application on Cotton Biomass and Yield under Groundwater Buried Depths in Coastal Saline-Alkali SoilFrom the groundwater buried depth ranges of 1.6 m to 1.8 m,the total aboveground biomass,boll number,seed cotton weight per boll,seed cotton yield all reached the maximum;It was indicated that the soil moisture-salinity stress was the lightest and had the least effects on cotton.Meanwhile,from the groundwater buried depth ranges of 0.4 m to 0.6 m,the total aboveground biomass,boll number,seed cotton weight per boll,seed cotton yield all reached the minimum;It was indicated that the soil moisture-salinity stress was serious and had the heaviest effects on cotton.Compared with no P application,P application could enhance the total aboveground biomass,boll number,seed cotton weight per boll,seed cotton yield under the heaviest stress.When the P application rate increased from P0 to P100,there was a big increase range for the total aboveground biomass and seed cotton yield.When the P application rate increased from P100 to P200,the increase range of the above indexes decreased,that is,P100 was the critical point of P application.The total aboveground biomass,boll number,seed cotton weight per boll,seed cotton yield for Lu 54 were lower than that of Yuzaomian 9110 in the treatment of P0 and P50.In conclusion,the effects of waterlogging with high salinity stress on cotton growth and yield formation was the heaviest in coastal saline-alkali land.In addition,the suitable groundwater buried depth range for reducing the adverse effects of cotton growth was 1.6-1.8 m.The function of P application alleviating the water-salt stress was that P application could enhance the resistance ability of cotton for the water-salt stress,and increasing cotton biomass and yield.The benefit of phosphate fertilizer was the best when the P application rate was 100 kg·P2O5·ha-1 in coastal saline-alkali soil.The biomass and yield were higher in the stress of low P for the P-weak-sensitive cotton cultivar of Yuzaomian 9110. |
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