| The temperature is important factor affecting the formation of wheat growth and yield. Thearea temperature is highly difficult to manual control, but through the different mulching orstraw returning can change the farmland microenvironment on soil temperature, which affectcrop growth. The experiment was conducted to study effects of different plastic film mulchingmodels and straw mulching on soil temperature in0~25cm soil depth, and the effects of soiltemperature on yield of winter and spring wheat, soil respiration and leaf physiological indexwere investigated in a Semi–arid Loess Plateau of Northwestern China from August2011toAugust2012, which could supply enough evidences to further study the effects change of soiltemperature on crop growth and development. The mainly results were as follows:1.Effects of different mulching methods on soil temperatureDifferent mulching methods had dual effects on increasing and decreasing soil temperaturefor winter wheat and spring wheat. For winter wheat, warming effects appeared from sowingstage to turning green stage, and cooling effects did from jointing stage to maturity. Warmingeffects with mulched plastic film was higher than that with mulched straw, but cooling effectswas contrary to warming effects between two mulching methods. In all mulching methods, theplastic film mulching reused again after the first harvest of winter wheat had the highestwarming effects and averagely higher by0.24℃than that un-mulched control in0~25cm soildepth during the whole growth stages, but cooling effect was highest in mulching5cm longwheat straw in summer, and lower by0.68℃than that un-mulched control. However, for springwheat, soil temperature with straw mulching was totally decreased, but soil temperatureincreased in plastic film mulching. There was difference in decreasing soil temperature betweenstraw chopping and whole straw mulching, and the former was larger than that the latter.However, mulching plastic film showed warming effects in soil temperature in the whole growthstage, but decreasing soil temperature appeared at seeding stage and after flowering. Comparedto plastic film mulched methods, the combination of mulching plastic film in summer and wheatstraw returning to the field had highest warming effect, and higher by0.57℃than that inun-mulched control.Different mulching treatments had different diurnal change on soil temperature. Mulchingtreatments in0~25cm soil layers showed that warming effects in the morning, and higher by0.36℃than un-mulched control, but cooling effects did at noon and in the dusk, and was lowerby0.61and0.63℃for winter wheat, respectively. But for spring wheat, mulching treatmentsappeared that warming effects in the morning, but cooling effects did at noon and in the dusk in 0~20cm soil layers.Different mulching treatments had different amplitude changes on soil temperature for thewhole growth period of winter wheat and spring wheat. Mulching treatments can stabilize thechanges of0~25cm soil temperature in the whole growth of winter wheat, and mulching plasticfilm in summer and adding1cm depth soil above plastic film had the best affect with thecoefficient of variation (CV) was lower by6.25%than un-mulched control. however, for springwheat, mulching treatments can intensify the changes of0~20cm soil temperature in the wholegrowth of spring wheat, and s4had the maximum change with its cv higher by4.93percentagepoint than un-mulched control.There were mainly reasons about dual effects on increasing and decreasing soil temperaturefor both plastic film mulching and straw mulching treatments: warming effects appeared that thetemperature drops and the temperature was very low periods by reduced the heat lost to keeptemperature, and in the temperature rising and high temperature periods by preventing heat intothe soil showed the cooling effects.2. Effects of different straw returning methods on soil temperatureDifferent straw returning treatments increased the soil temperature for both winter wheatand spring wheat. Warming effects with wheat straw returning in0~25cm soil layers was higherthan that with corn straw returning for winter wheat, but for spring wheat, the corresponding wascontrary. Mean soil temperature of0~25cm soil depth in straw returning was higher by0.41℃than that in un-returned control. Compared to straw returning treatments, wheat straw returning+plastic film mulching+suppression treatments had the highest warming effect and higher by0.52℃for winter wheat, but warming effect with corn straw returning+plastic film mulching+suppression treatments was maximum and higher by0.75℃than that in un-returned control.Mean soil temperature of0~25cm soil depth in straw returning treatments for winter wheatincreased in a day, and higher by0.76、0.44and0.30℃in the evening, in the morning and atnoon, respectively. For spring wheat, cooling effect appeared slightly in the morning, andwarming effects at noon higher than in the dusk.In all straw returning treatments, straw returning+plastic film mulching+suppressioncould stabilize violent changes of soil temperature for both winter wheat and spring wheat, andother treatments increased the changes. Compared to un-mulched control, corn straw returning+plastic film mulching treatments had the best stabilizing effect, and its CV decreased by4.33%and1.01%for winter wheat and spring wheat, respectively, corn straw returning+un-mulching+un-suppression and corn straw returning+un-mulching+suppression treatments increased thechanges, but its CV increased by0.49%and1.16%for winter wheat and spring wheat, respectively.3.Effects of different mulching methods on soil respirationDifferent mulching treatments could stabilize violent changes of soil CO2flux for winterwheat，but for spring wheat it was contrary, Inhibition effect with straw mulching was higherthan that plastic film mulching. In straw mulching treatments had the best inhibition effect, andlower by5.2%than that in un-mulched control. however, promotion effects with plastic filmmulching was higher than straw mulching, and mulching plastic film in summer and adding1cmdepth soil above plastic film treatments was the highest and higher by8.3%than that inun-mulched control.Different mulching treatments enhanced the soil respiration rate for both winter wheat andspring wheat; both wheat straw returning+mulching plastic film in summer and adding1cmdepth soil above plastic film treatments and mulching plastic film in spring and adding1cmdepth soil above plastic film treatments were obvious improvement, and higher by higher by200.6%and134.4%than that in un-mulched control for winter wheat and spring wheat,respectively.There was not significantly negative correlations (-0.274,-0.223) in mulching treatmentsbetween average soil temperature in0~25cm soil layers and soil CO2flux or soil respiration ratefor winter wheat. Soil temperature and soil respiration rate had significant negative correlations(-0.382*), but there was no significant negative correlation (-0.096) between soil temperatureand soil CO2flux for spring wheat.4.Effects of different straw returning methods on soil respirationDifferent straw returning treatments increased the soil CO2flux and enhanced the soilrespiration rate for both the winter wheat and spring wheat. In different straw returningtreatments,T1and S1was the highest soil CO2flux and the soil respiration rate, soil CO2fluxwas higher by8.4%,9.2%,respectively. The soil respiration rate was higher by222.2%and125.4%than that in un-returned control. The further study showed there was no significantnegative correlation between soil temperature and soil respiration and soil CO2flux.5. Effects of different mulching methods on soil respirationFor most mulching treatments, this decreased the flag leaf temperature for both winterwheat and spring wheat. Compared to un-mulched treatments, plastic film mulching reused againafter the first harvest of winter wheat treatments had the maximum was cooling effect and lowerby1.51℃than that in un-mulched control for winter wheat, but for spring wheat mulching5cmlong wheat straw in summer treatments decreased the minimum and lower by0.75℃than thatin un-mulched control. Plastic film mulching treatments decreased the winter wheat flag leaf stomatal conductance,lowered range of mulching plastic film in summer and adding1cm depth soil above plastic filmtreatments was the highest and lower by73.4%than that in un-mulched control, but for strawmulching treatments increased the flag leaf stomatal conductance, increasing amplitude ofmulching5cm long wheat straw in summer treatments was the maximum and higher by33.7%than that in un-mulched control. Different mulching (except mulching plastic film in spring andadding1cm depth soil above plastic film treatments) methods increased the spring wheat flagleaf stomatal conductance, mulching whole wheat straw in summer treatments increased highlyand higher by46.80mmol·m-2·s-1than that in un-mulched control.Mean soil temperature showed highly significant positive correlation（0.879**，0.769**）with flag leaf temperature in different mulching treatments for both winter wheat and springwheat field6. Effects of different straw returning methods on flag leaf physiological indicatorsDifferent straw returning treatments decreased the flag leaf temperature for winter wheat.Corn straw returning+plastic film mulching+suppression treatments had the maximum loweredrange, and lower by2.02℃than that in un-returned control. Corn straw returning treatmentsincreased the flag leaf temperature and corn straw returning+plastic film mulching+un-suppression treatments increased the maximum and higher by0.61℃than that inun-mulched control, but wheat straw returning treatments decreased the flag leaf temperature forspring wheat，and wheat straw returning+plastic film mulching+suppression treatmentslowered the minimum and lower by0.62℃than that in un-returned control.Different straw returning treatments decreased the flag leaf stomatal conductance for bothwinter wheat and spring wheat, wheat straw returning+plastic film mulching+suppression andcorn straw returning+un-mulching+suppression treatments decreased the maximum, but meanstomatal conductance decreased by56.9%and46.0%for winter wheat and spring wheat,respectively. There were highly significant positive correlation（0.959**，0.918**）between meansoil temperature and flag leaf temperature in different mulching treatments for both winter wheatand spring wheat fieldDifferent mulching and different straw returning could change the microenvironment,especially in the change of ground temperature, which affected soil respiration, soil CO2flux andstomatal conductance of physiological indicators，ultimately influenced the growth developmentand yield; straw mulching could reduce soil temperature, which had a negative effect on springwheat growth and development, but for the other growth period of warming or cooling effect had more positive effect. |
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