Response Mechanism Of The Growth And Soil Micro-environment In Root Zone Of Greenhouse Tomato To Oxygation

Although subsurface drip irrigation?SDI?has higher irrigation efficiency compared with other irrigation methods,root zone often undergoes oxygen deficit due to the continuous saturated wetting front near emitters.Oxygen deficit affected root growth,the absorption of nutrients and water of root and transportation of nutrients and water from root to aboveground part,and then affected crop metalism and thus affected crop yield and quality.Oxygation is developed from SDI,which uses venturi air injector to suck air into irrigation water to form aerated water.This study evaluated the impact of oxygation under different irrigation amounts and trickle-buried depths conditions on soil micro-environment,crop growth,fruit yield,water use efficiency?WUE?and fruit quality,and then the comprehensive evaluation of various treatments was conducted through principal component analysis based on the impacts of different treatments on fruit yield,WUE and fruit quality.Four experiments,which included two spring-summer experiments and two autumn-winter experiments,were conducted in a greenhouse.Twelve treatments combining oxygation?O?and no-aerated SDI?S,the control?and three irrigation levels?W1,W2 and W3,with crop-pan coefficients of 0.6,0.8 and 1.0,respectively?and two trickle-buried depths?D1 and D2,corresponding to 15 cm and 25 cm?were conducted.The main conclusions were as follows:?1?Compared with SDI,which only supplies irrigation water,oxygation supplies a mixture which included irrigation water,micro-bubbles,and air dissolved in irrigation water.Thus,oxygation effectively improved soil aeration conditions.Compared with the control,soil oxygen concentration in the spring-summer experiment and the autumn-winter experiment with oxygation treatment significantly increased by 6.86 and 8.01%?P<0.05?,respectively.Meanwhile,soil air-filled porosity with oxygation has the trend of increasing,with air-filled porosity in the spring-summer experiment and the autumn-winter experiment increasing by 4.29%and 3.09%,respectively,compared with the control.Oxygation can not only effectively slow down the trend of rapidly decreasing of soil oxygen concentration during irrigation,but also ensure the minmum value of soil oxygen concentration not too low.?2?Oxygation effectively improved soil aeration condition,which ensured the smooth flow of gas exchange of air-soil-crop root zone.In other words,oxygation ensured the O₂demand of crop root and soil microorganisms and the smooth discharge of soil CO₂ to air,compared with SDI.Thus,soil respiration?including soil microbial respiration and plant root respiration?and the abundance of soil major microorganisms significantly increased with oxygation.Compared with the control,soil respiration with oxygation significantly increased by 23.2%and 28.3%?P<0.05?,respectively,in the experiments of spring-summer and autumn-winter.The abundance of soil bacterial,fungi and actinomycetes with treatment W3D1O significantly increased by 39.2%,37.1%and 39.3%?P<0.05?,respectively,in the experiment of spring-summer,and significantly increased by 31.6%,47.9%and 35.8%?P<0.05?,respectively,in the experiment of autumn-winter,compared with treatment W3D1S.In the experiments of spring-summer and autumn-winter,soil microbial respiration with treatment W3D1O significantly increased by 15.3%and 10.9%?P<0.05?,respectively,and plant root respiration with treatment W3D1O significantly increased by 28.7%and 76.7%?P<0.05?,respectively,compared with treatment W3D1S.?3?Oxygation effectively improved soil micro-environment,and then improved root and aboveground growth.In this experiment,root morphology index at harvest with oxygation,including root diameter,length density,surface area and volume density,significantly increased by 26.04%,30.65%,29.58%and 31.76%?P<0.05?,respectively,compared with the control.Stem diameter and leaf area at harvest with oxygation significantly increased by 6.47%and 20.11%?P<0.05?,respectively,compared with the control.Aboveground dry weight and harvest index with oxygation also significantly?P<0.05?increased,compared with the control.And compared with the control,the flowering duration of the first and third ear with oxygation significantly prolonged by 0.89 d and 1 d?P<0.05?,respectively.These results all showed that oxygation effectively improved crop growth performance.?4?On the basis of improving soil micro-environment and plant growth and development,oxygation ultimately affects crop yield and quality.In this experiment,oxygation had significant?P<0.05?or extremely significant?P<0.01?positive effects on the yield per plant,fruit weight,WUE,the content of lycopene,VC,soluble sugar and sugar-acid ratio.Compared with the control,these index with oxygation in the spring-summer experiment significantly increased by 22.6%,20.0%,23.16%,39.0%,36.4%,26.8%and 31.7%?P<0.05?,respectively;and in the autumn-winter experiment significantly increased by 20.3%,20.2%,19.91%,28.1%,35.7%,22.7%and 28.4%?P<0.05?,respectively.?5?Although the increase of irrigation level had significant?P<0.05?or extremely significant?P<0.01?positive effects on the yield per plant,fruit number and weight;significant?P<0.05?or extremely significant?P<0.01?negative effects were obtained for IWUE,the content of soluble sugar,and the content of lycopene and organic acid in the spring-summer experiment.The change of trickle-buried depths had no significant effects on IWUE,fruit yield and quality factors?P>0.05?;except in the spring-summer experiment,the sugar-acid ratio in D2 treatment significant?P<0.05?higher than in D1 treatment.?6?The comprehensive scores of twelve treatments were obtained from principal component analysis based on the differences in the effects of twelve treatments on yield indexes?yield per plant,fruit number per plant and fruit weight?,WUE and fruit quality indexes?lycopene,VC,soluble sugar,organic acid and sugar-acid ratio?.It can be seen that in both the spring-summer experiment and the autumn-winter experiment,the comprehensive scores of the six control treatments ranked in the bottom six,and the six oxygation treatments ranked in the top six.In the spring-summer experiment,the optimal treatment was W1D2O,and in the autumn-winter experiment,the optimal treatment was W2D1O.Thus,treatment W1D2O(oxygation treatment with k_cp being 0.6 and drip depths being 25 cm)in the spring-summer experiment and treatment W2D1O(oxygation treatment with k_cp being 0.8 and drip depths being 15 cm)in the autumn-winter experiment could best meet the requirements of reducing irrigation water application and improving fruit yield and quality of greenhouse tomato,respectively.In a word,the exploration of optimal treatment provided a theoretical basis for the practical application of oxygation.