Effects Of Irrigation And Cotton Growth On Soil CO₂ Emission Under Drip Irrigation Under Mulch

Object:Crop growth needs good soil moisture environment.Xinjiang is one of the main cotton producing areas in China.In recent years,drip irrigation under film has been proposed for this purpose.The technology saves water and increases production obviously,but it has an impact on the soil moisture environment,especially on the emission of soil gas?CO₂?under the conditions of irrigation and cotton growth.Therefore,studying the effects of irrigation and cotton growth on CO₂ emission in soil under drip irrigation under mulch provides reference for comprehensive control and mitigation of greenhouse gases?CO₂?in agricultural water-saving mode,and has the advantages of achieving water-saving,high-quality and high-yield cotton.Important scientific value and practical significance.Methods:In this paper,drip irrigation cotton was used as the research object.Through barrel planting experiments in 2017 and 2018,the variation characteristics of soil CO₂ concentration and soil moisture at different depths during cotton growth under drip irrigation under different soil textures?sandy soil and loam?and different irrigation frequencies?irrigation time intervals are 3 d,5 d and 7 d?are studied.The photosynthetic physiological indexes?net photosynthetic rate,transpiration rate,stomatal conductance,intercellular CO₂ concentration?and root indicators?root length density,root surface area,root activity?of cotton at different growth stages were monitored.,and the influence of cotton growth on soil CO₂ emission is analyzed.The distribution of soil moisture and soil CO₂ concentration before and after irrigation under different soil texture and non-film drip irrigation conditions were studied by soil column test.The CO₂concentration of different depth soils was analyzed by irrigation amount and irrigation frequency.The impact of the process of moisture infiltration on soil CO₂ emissions.Results:?1?Before irrigation,the soil was in a state of drought,and the CO₂ concentration in each soil layer was at a low level.After irrigation,the soil CO₂ concentration gradually increased.Irrigation frequency,irrigation water volume and soil texture have significant effects on soil CO₂ concentration.With the increase of irrigation frequency and irrigation water volume,the soil CO₂ concentration at different depths shows an increasing trend,and the increase of CO₂ concentration in 20⁴0 cm soil layer is higher than that10 cm and 50 cm.Under the same irrigation frequency and amount,the CO₂ concentration in loam was significantly higher than that in sandy soil.?2?Film mulching increases soil CO₂ concentration.Under high frequency,medium frequency,low frequency irrigation conditions,the CO₂ concentration of the loam mulched treatment was 2.83%,10.17%,0.56%,26.93%and 15.27%higher than that of the non-mulched treatment,respectively.The CO₂concentration of the sand mulched treatment was 20.34%,11.67%,14.61%,18.28%and 14.11%higher than that of the non-mulched treatment.?3?Under the conditions of film mulching and no film mulching,the water content of the two soils was significantly correlated with the CO₂ concentration.Soil temperature of loam had little effect on CO₂concentration and was not sensitive to temperature changes,while the soil temperature of sandy soil has a very significant positively correlated with CO₂ concentration,and the correlation is not obvious.Through fitting,it is found that the interaction of soil temperature and soil water content affects the soil CO₂concentration.The model can explain the variation of soil CO₂ concentration by 52.4%⁷3.5%,which is more explanatory than the single factor model.?4?Under different treatment conditions,the soil CO₂ concentration is upper low and lower high,and increases with the increase of soil depth.The soil CO₂ concentration at 50 cm was about twice as high as that at 10 cm,and the soil CO₂ concentration of cotton planting is about twice as high as that of non-cotton planting.The diurnal variation of soil CO₂ concentration in 10⁵0 cm soil layer under different treatment conditions was the same,all showed a single-peak curve with a peak at 16:30.During the cotton growth period,the CO₂ concentration in the 10⁵0 cm soil layer had obvious season,showing a trend of“rise-down”as a whole,and the highest peak appeared in the flowering and boll period.?5?The CO₂ concentration in the soil during the growth period of cotton has a quadratic relationship with its corresponding soil temperature and moisture content.When the soil temperature is less than 15°C,the soil CO₂ concentration is at a low level;when the soil temperature is 26²8°C,the soil respiration is strongest and the CO₂ concentration reaches a higher level.?6?The interaction between irrigation frequency and soil texture has a extremely significant effects?P<0.01?on cotton net photosynthetic rate?Pn?,transpiration rate?Tr?,stomatal conductance?Gs?,intercellular CO₂ concentration?Ci?,stomatal limit value?Ls?and water use efficiency?WUE?,which mainly affects the size of soil CO₂ concentration through the photosynthetic physiological characteristics of cotton.Pn and Tr have the greatest effect on soil CO₂ concentration,followed by Gs and Ci.Through fitting,it is found that the soil CO₂ concentration is closely related to cotton Pn,Tr,Gs and Ci,showing significant secondary positive correlation,that is,the stronger photosynthesis,the higher the soil CO₂concentration.?7?Under the same soil texture conditions,the root activity decreased with the increase of soil depth,and the root activity of 0²0 cm soil layer was the highest,and it decreased with the increase of irrigation time interval,which was T3>T5>T7.For different soil textures,the root activity of cotton in 0²0 cm and40⁶0 cm sandy soil is higher than that in loam,while the root activity of loam in 20⁴0 cm soil was higher than that in sandy soil.Through correlation analysis and function fitting between soil CO₂concentration and cotton root index,it is shown that soil CO₂ concentration is linearly and positively correlated with cotton root length density,root surface area and root activity,the stronger root activity,the stronger root respiration,and the higher CO₂ concentration in soil.