Plastic-film Mulching And Fertilizers Affect Growth And Soil CO₂ Emissions Of Spring Maize In Dryland On The Loess Plateau,China

Food security problems,due to the fast-growing human population and loss of farmland,and climate change,caused primarily by increased concentrations of CO₂ in the atmosphere,have become global issues that seriously threaten developing countries.The rain-fed farmland area is accounting for 50% of the total farmland area in China,approximately.It is essential for ensuring national food security.Maize?Zea mays L.?is one of the most popular grain crops in dryland areas.However,the maize grain yield in the area is always maintained at a low level due to the limited water resources.The grain yield production potential is not fully excavated.Therefore,there is still a long way to go to enhance the yield further,and shorten the yield gap in the future.In addition,the overuse of chemical fertilizers is a common problem during the maize production,resulting in decreased nitrogen?N?use efficiency,increased N losses and the risk of environmental pollution.Therefore,optimizing grain production system in dryland,improving grain yield and water/fertilizer use efficiency of maize,have a great important practical significance for protecting food security of the country in the future,and achieving the sustainable development of regional agriculture and environment.Accordingly,a 2-year field experiment was conducted in 2013-2014 years to investigate the effects of field management practices?six treatments: no mulching with urea,NU;no mulching with controlled release fertilizers,CRFs,NC;transparent plastic-film mulching with urea,WU;transparent plastic-film mulching with CRFs,WC;black plastic-film mulching with urea,BU;black plastic-film mulching with CRFs,BC?on growth and soil CO₂ emissions of spring maize in rain-fed farmland on the Loess Plateau,China.The main results of this study were concluded as follows:?1?Plastic-film mulching can increase topsoil temperatures and soil water contents.Early in the growing season,the soil temperatures was in the following order of,transparent plastic-film mulching?PMw?> black plastic-film mulching?PMb?> no mulching.Soil temperature was higher by 0.2–2.2? in the transparent mulching treatments than in the black mulching treatments.Late in the growing season,soil temperature was often higher in the no mulching treatments than in the mulching treatments.The soil water storage?SWS?was in the following order of,PMb>PMw>no mulching.In the upper 40 cm soil layers,about 6–20 mm soil water in all treatments was replenished at harvest time compared with that at sowing time in 2013.However,the soil water content in 2014 was decreased at the 120 cm soil layer compared with that at sowing time.?2?Mulching practices and urea types significantly affected the height,LAI and biomass grain yield of maize?P<0.05?.A significant “mulching×urea”?P<0.05?interaction effect was also observed in these in two years.During the experimental years,the maize height was in the following order of,PMw>PMb>no mulching.LAI increased throughout the growing seasons,and peaked in mid-July in both years.Subsequently,LAI decreased because of leaf losses.In general,LAI under mulching treatments were higher than that under no mulching treatments.Early in the growing season,LAI under transparent plastic-film mulching treatments were higher than that under black;Late in the growing season,LAI under black plastic-film mulching treatments were higher than that under transparent.Early in the growing season,the biomass grain yield of maize was in the following order of,PMw>PMb>no mulching;However,late in the growing season,biomass grain yield of maize under black plastic-film mulching treatments were significantly higher than under other treatments?P<0.05?.Biomass grain yield of maize under no mulching treatments were lowest during the whole growing stage of maize in both experimental years.Early in the growing season,there was no significant differences in the growth traits of maize under the two fertilization treatments;However,late in the growing season,LAI and biomass grain yield of maize under CRFs treatments were higher than under urea treatments.?3?The mulching practices and urea types significantly affected the grain yield and water use efficiency?WUE?of maize in the two experimental years?P<0.05?.Except NC plot in 2013,grain yield under CRFs treatments were significantly higher than under urea treatments?P<0.05?.In general,the grain yield in 2014 were higher than in 2013.Compared with NU?9.18 t ha-1?,yields in the WC,BC,BU,and WU plots in 2013 increased by 34.5%,32.4%,28.5%,and 13.4%,respectively,but yields in the NC plot decreased by 1.5%.In 2014,the highest yield was recorded in the BC plot?16.64 t ha-1?,whereas the lowest was recorded in the control?13.18 t ha-1?.WUE under PMb were significantly higher than that under PMw?P<0.05?.ET was similar for all treatments in the two years?P>0.05?.?4?The trends for soil CO₂ emissions were similar throughout the study period,with gradually increasing levels in August and sharply decreasing levels in September in the both experimental years.In the two early growth stages of maize,the soil CO₂ emissions were in the following order?highest to lowest?: PMw>PMb>no mulching,that was soil CO₂ emissions under mulching treatments were higher than under no mulching.In contrast,the order of soil CO₂ emissions was reversed: no mulching>PMw>PMb in the late growing stage of maize.In general,diurnal variation of soil CO₂ emissions under treatments at each growth stage was in the the order of,silking stage>jointing stage>maturing stage>seeding stage,which all showed as single curves.Compared with other treatments,diurnal variation of soil CO₂ emissions under BC treatments were the largest in seeding stage,jointing stage and maturing stage,but were the lowest in the silking stage both in two years.Fertilization only significantly affected the soil respiration rate during the flare opening stage of maize in 2013?P?0.01?,the seedling stage and the blooming stage of maize in 2014?P?0.01?.“Mulching×urea” significantly affected the soil respiration rate during the flare opening stage and milking stage of maize in 2013?P?0.05?,the seedling stage,the flare opening stage and the blooming stage of maize in 2014?P?0.05?.?5?The results showed that there was no correlation between soil CO₂ emissions and soil temperatures and soil water contents at 5 cm depth or at other soil depths?P>0.05?.However,the result showed that there was significantly correlation between soil CO₂ emissions and daily mean air temperature?P < 0.05?.The correlation relation can be well fitted by exponential equation and the correlation coefficient R2 was between 0.249⁰.407.The results also showed that there was no correlation between soil CO₂ emissions and daily average relative humidity and photosynthetically active radiation?P>0.05?.?6?Mulching and urea types significantly affected the cumulative soil CO₂ emissions and the cumulative soil CO₂ emissions per unit grain yield in both years?P<0.01?,and significant “mulching×urea”?P<0.05?interaction effects were also observed.In both experimental years,cumulative soil CO₂ emissions were 3.2% and 11.2% lower in the BC?18.63 t ha-1 in 2013;26.38 t ha-1 in 2014?treatment than in the NU treatment,respectively.The highest soil CO₂ emissions per unit grain yield were noted for the WU treatment?2.27 in 2013 and 2.33 in 2014?,while the lowest were noted for the BC treatment?1.54 in 2013 and 1.59 in 2014?.The cumulative soil CO₂ emissions per unit grain yield were significantly lower?27.1% in 2013 and 29.3% in 2014?in the BC treatment than in the NU treatment?P<0.05?.Therefore,the study found that the BC plot was the treatment with the highest grain yield and the lowest soil CO₂ emission of maize in the two experimental years.