Effects Of Rainwater-Harvesting Planting With Supplemental Irrigation And Planting Densities On The Growth And Photosynthetic Physiology Of Maize In The Semi-Arid Regions

In the semi-arid regions of northwest China,the rainwater-harvesting planting system is being gradually implemented in order to improve soil moisture status and water use efficiency.This study aimed to improve the efficiency of the rainwater-harvesting planting system by investigating the effects of three planting densities(L:52,500 plants ha^-1;M:75,000 plants ha^-1;H:97,500 plants ha^-1)and four kinds of supplemental irrigation modes?NI:no irrigation;IV:irrigation at the 11-leaf stage;IS:irrigation at the silking stage;and IVS:irrigation at the11-leaf and silking stages?in a semi-arid area?Pengyang County,Ningxia?.Through field experiments in two consecutive years?2015-2016?,the effects of different supplementary irrigation methods and planting density on farmland soil moisture,water consumption characteristics,maize growth,photosynthetic physiology characteristics,grain yield,and water use efficiency were analysed.The main results are described here in.1.Effects of rainwater-harvesting planting with supplemental irrigation and planting densities on farmland soil moisture and water consumption characteristics?1?The rainwater-harvesting planting with supplemental irrigation led to increased soil water content in the 0-200 cm soil layer after maize silking,especially at the filling stage.At the filling stage,the two-year average soil water content of IV,IS,and IVS treatments increased 7.2%,9.4%,and 13.6%respectively,compared with NI.The effect of planting density on soil water content was small before the 11-leaf stage of maize,while at the silking,filling and maturity stages,soil water content decreased significantly with increasing planting density.The rainwater-harvesting planting with irrigation and planting density mainly affected soil water storage in 0-60 and 60-120 cm soil layers but had little effect in the120-200 cm soil layers.?2?At growth stages before the 11-leaf stage of maize,evapotranspiration and water consumption rate increased with increasing density,and the planting density had less effect with more precipitation.After maize silking,the evapotranspiration and water consumption rate decreased with increasing planting density,especially at the silking to filling stage.At silking to filling stage,average evapotranspiration in both years under medium and high densities was reduced by 9.8%and 20.3%respectively,compared with low density.Supplemental irrigation at the 11-leaf stage mainly increased evapotranspiration and water consumption rate during the 11-leaf to silking stage,whereas irrigation at the silking stage significantly increased evapotranspiration and water consumption rate during the silking to filling stage.From the 11-leaf to silking stage of maize,the two-year average evapotranspiration of IV and IVS treatments increased by 12.3%and 13.5%,compared with NI.From the silking to filling stage,average evapotranspiration increased by 37.6%and54.3%in IS and IVS,respectively,compared to NI.2.Effects of rainwater-harvesting planting with supplemental irrigation and planting densities on maize growth and lodging resistance?1?In 2015 and 2016,supplemental irrigation at the 11-leaf stage increased the root length density and root surface area density in the 0-20 cm soil layer at the silking stage,which was conducive to root growth in the surface soil.However,no irrigation at the 11-leaf stage promoted the extension of the root system to the deep soil.The rainwater-harvesting planting with irrigation can delay the root decay of maize at later growth stages.At the dough stage,compared with NI,the two-year average root length density of 0-100 cm soil layers increased by 28.7%,48.8%,and 55.2%,respectively,and the root surface area density increased by 40.4%,64.9%,and 80.5%,respectively.Compared with no irrigation,supplemental irrigation also significantly increased the leaf area per plant,aboveground dry matter,root weight per plant,and root/shoot ratio at the dough stage,and the increase was higher in IS than in IV.Although the irrigation volume of IVS was twice that of IS,it did not significantly increase the leaf area per plant and aboveground dry matter,but reduced the root/shoot ratio,and increased the plant height and centre of gravity.IVS increased the risk of maize lodging.?2?At the silking and dough stages,the average root length density and root surface area density of the 0-100 cm soil layer under medium and high densities significantly increased compared with low density.However,the root weight per plant and stem diameter under high density was significantly reduced compared with low density,the ear height and ear height coefficient significantly increased,and the root/shoot ratio was significantly reduced relative to the medium density,which increased the maize lodging rate under high density.Under the medium and high densities,the two-year average root lodging rates were4.1 and 10.1 times higher than that under the low density,respectively,and the stem lodging rates were 6.8 and 36.3 times higher,respectively.3.Effect of rainwater-harvesting planting with supplemental irrigation and planting densities on maize leaf and photosynthetic physiology characteristics?1?For both years at the 11-leaf,silking,and filling stages,there were no significant differences in relative chlorophyll content of leaves among different irrigation methods under low density,but under medium and high densities the leaves relative chlorophyll content of IS and IVS were higher than NI at filling stages.Under the same irrigation modes at the dough stage,the leaves relative chlorophyll content decreased significantly with increasing density.After irrigation at the 11-leaf or silking stages in both years,supplemental irrigation treatments significantly increased the relative water content of leaves compared with NI,and the increase in the drought year?2016?was higher than in the normal flow year?2015?.Compared with NI,IV increased relative water content before silking,while IS significantly increased it at filling stage.At the silking and filling stages,high density planting significantly reduced relative water content compared to the low or medium density.?2?After irrigation at the 11-leaf stage in the two years,compared with NI,IV and IVS significantly increased leaf stomatal conductance?Gs?,intercellular CO₂ concentration?Ci?,net photosynthesis rate?Pn?and transpiration rate?Tr?,but reduced the leaf water use efficiency?WUE_L?.In the drought year before irrigation at the silking stage,IV and IVS increased Gs,Ci,Pn,and Tr significantly compared with NI,but there was no significant difference in the normal flow year.In the two years after irrigation at the silking and filling stages,IS and IVS increased Gs,Tr,and Pn compared with NI,and increased WUE_L significantly at the filling stage.At the filling stage,the average Pn for both years increased by 17.0%,27.2%,and 30.3%in IV,IS,and IVS,respectively,compared with NI.At the filling stage in the same irrigation modes,Ci increased with increasing density,while Gs,Tr,Pn,and WUE_L decreased.Compared with low density,the two-year average Pn of medium and high density decreased by 8.1%and 27.6%,respectively,and high-density planting significantly reduced the photosynthetic capacity of leaves.?3?After irrigation at the 11-leaf stage and before irrigation at the silking stage,compared with NI,IV and IVS reduced the initial fluorescence?Fo?of the leaves,and increased the maximum fluorescence?Fm?and variable fluorescence?Fv?of the dark reaction,and thereby significantly increased the photosystem II potential activity?Fv/Fo?and photosystem II maximum photochemical efficiency?Fv/Fm?;there was a large difference under high density in drought years.In both years,after irrigation at the silking and filling stages,under the same density,IS and IVS significantly reduced Fo and increased Fm,Fv,Fv/Fo,and Fv/Fm,compared with NI.At the filling stage,compared with NI,the two-year average Fv/Fo of IV,IS,and IVS increased by 17.8%,27.6%,and 35.1%,respectively,and average Fv/Fm increased by 8.4%,11.4%,and 12.6%,respectively,which indicated that irrigation at the silking stage significantly increased photosynthetic performance of maize leaves.At the filling stage,under the same irrigation method,Fo increased with the increase of density,but Fm,Fv,Fv/Fo,and Fv/Fm decreased,and there was a significant difference between high and low density in the drought year.During the filling stage,the leaves were seriously damaged under high planting density.Compared with low density,the two-year average Fv/Fo and Fv/Fm were reduced by 19.3%and 5.9%,respectively.4.Effect of rainwater-harvesting planting with supplemental irrigation and planting densities on maize dry matter accumulation and light energy utilization?1?In 2015 and 2016,maize was severely affected by drought stress after silking,resulting in significant reduction in the leaf area index.Compared with NI,IS and IVS treatments provided moisture for the reproductive growth of maize,which significantly increased the leaf area index and biomass at the dough stage.In the normal flow year,irrigation method had no significant effect on the total dry matter accumulation before maize silking,but in the drought year,the total dry matter accumulation before maize silking in IV,IS,and IVS significantly increased compared to NI.In both normal and drought years,the total dry matter accumulation of IS and IVS significantly increased after maize silking compared with NI,and there was no significant difference between IS and IVS.In both years,at the 11-leaf,silking,filling,and dough stages,medium and high-density planting significantly increased leaf area index compared with low density,which was beneficial to the accumulation of dry matter.?2?Two-year experiments showed that,compared with low density,medium and high-density planting significantly increased the photosynthetically active radiation interception rate at the 11-leaf,silking,and filling stages,thus significantly increasing the photosynthetically active radiation accumulation during the whole growth period.Compared with low density,although high density planting significantly improved the radiation use efficiency before maize silking,the radiation use efficiency decreased significantly aftermaize silking,resulting in no significant difference in radiation use efficiency during the whole growth period.In the drought year,the radiation use efficiency before maize silking and during the whole growth period of IV,IS,and IVS significantly increased compared with NI,but the difference was not significant in the normal flow year.Regardless of normal or drought year,the radiation use efficiency after silking of IV,IS,and IVS significantly increase compared with NI,and IS was significantly higher than IV.However,IV and IS did not significantly increase the photosynthetically active radiation accumulation after maize silking over the whole growth period compared to NI,suggesting that rainwater-harvesting planting with supplemental irrigation mainly increased the dry matter accumulation to increase the radiation use efficiency,but has little effect onphotosynthetically active radiation accumulation.The average of both years showed that M-IS obtained the highest radiation use efficiency(1.56 g MJ^-1).5.Effect of rainwater-harvesting planting with supplemental irrigation and planting densities on grain yield and water utilization of maize?1?In both years,the bare tip length increased significantly,and the 100-grain weight decreased significantly with increasing planting density.The grain number per row and grain number per ear under medium density were significantly higher than under high density,but there was no significant difference in number of rows per ear.This result indicated that planting density mainly affected grain number per ear by changing grain number per row,and the number of rows was less affected by density.In two years,the grain yield under medium and high density was significantly higher than that under low density,and the two-year average grain yield increased by 8.8%and 9.7%,respectively,compared with low density.Compared with low density,medium and high-density planting also significantly improved the water use efficiency of grain yield?WUE_G?,water use efficiency of biomass yield?WUE_B?,irrigation water use efficiency of grain yield?IWUE_G?,irrigation water use efficiency of biomass yield?IWUE_B?,and irrigation production efficiency of grain yield?IWP_G?,and the increase in the drought year was higher than in the normal year.However,compared to medium density,high density planting did not significantly increase grain yield,WUE_G,IWUE_G,or IWP_G,and significantly reduced the harvest index.?2?Compared with no irrigation,supplemental irrigation significantly reduced the bare tip length,and increased the ear length,ear diameter,grain number per ear,and 100-grain weight,thereby significantly increasing grain yield.Compared with NI,the two-year average grain yields for IV,IS,and IVS treatments increased by 13.2%,21.3%,and 22.6%,respectively.Although the irrigation volume of IVS was 2 times that of IS,at the same density,IVS did not significantly increase grain yield,PUE,WUE_G,or WUE_B compared to IS,and significantly reduced IWUE_G,IWUE_B,and IWP_G.We also found that in the drought year,under medium and high densities,WUE_G,IWUE_G,and IWP_G under IS treatment were significantly higher than IV.The average of data from both years shows that,although the highest grain yield(13.3 t ha^-1)was obtained in the treatment with two applications of irrigation under medium density?M-IVS?,there was no significant difference with M-IS treatment(13.2 t ha^-1).The highest WUE_G(30.8 kg ha^-1 mm^-1),IWUE_G(35.3 kg ha^-1 m^-3),and IWP_G(6.9 kg ha^-1 m^-3)were obtained under M-IS treatment,increasing by 5.7%,98.5%,and92.6%,respectively,compared with M-IVS.In summary,under the rainwater-harvesting planting,medium density planting(75,000plants ha^-1)combined with supplemental irrigation(375 m³ ha^-1)at the silking stage can promote the growth of maize,increase the photosynthetic performance of leaves,and finally increase the grain yield and utilization efficiency of water and radiation.The two-year average net income also showed that M-IS treatment received the highest net income(15,400yuan ha^-1).Therefore,in the semi-arid regions of northwest China,medium density planting combined with supplemental irrigation at the silking stage is a suitable planting model that can effectively increase maize production,water and light energy utilization efficiency.