Effects Of Water And Carbon Interaction On Water Productivity Of Winter Wheat In The NCP

The North Plain is an important region of winter wheat production in China,and which is also the region that its ground water was used with overexploitation.There is a conflict between winter wheat irrigation and the reduction of ground water exploitation.To save irrigation water for winter wheat by agronomic measures is of great importance.Our aims of this study are to explore the interactions between water and carbon,to quantitatively analyze the impact of carbon enhancement and irrigation reduction on winter wheat productivity,and to propose water saving measurements for the wheat production and reduction of ground water overexploitation in the North China Plain.The study were carried out in dryland farming experiment station of Dryland Agriculture Institute of HAAFS in 2014²015 and 2015²016 winter wheat growing seasons,with 4 levels of irrigation main treatments:W3（irrigation 80 mm before sowing,turning green to jointing,flowering to grain filling respectively）,W2（irrigation 80 mm before sowing,turning green to jointing respectively）,W1（irrigation 80 mm before sowing）and W0（no irrigation）;4 sub carbon treatments on every water treatments（with the same dosage of NPK）:C3(5200 kg·hm^-2 organic carbon),C2(2600 kg·hm^-2organic carbon),C1(50 kg·hm^-2 organic carbon),C0（no organic carbon as contrast）;2 variety of wheat were planted:V1（Han4589,the water saving type）and V2（Shixin828,the water sensitive type）.Some of the physiological and ecological characteristics and water consumption,grain yield related traits were measured to quantify the effects of water and carbon on grain water productivity of wheat.The result shows that:1.The application of organic carbon in the soil can increase soil water storage capacity but reduce unproductive soil evaporation,and improve water use effectiveness.Under the same amount of water supplement,there was no significant difference in evapotranspiration in the whole growth period of wheat under different organic carbon treatments,but the difference of soil water storage（water supply）and soil evaporation was obvious.C3 and C2 in contrast with C1 treatment,on the average of irrigation treatments,soil water storage in 0¹60cm soil layer of whole growth period were increased by8.3%²3.9%and 1.1%¹2.5%（two years of experiment,the same below）,and soil evaporation were reduced by 2.3%⁴.9%and 0.7%⁸.3%,particularly the soil evaporation was reduced more in the vegetative growth than that in the reproductive period.Under different water treatments,the effect of organic carbon enhancement on increasing soil water storage capacity and reducing soil evaporation was shrinking gradually with the increment of irrigation amount and times.Under W3,W2 and W1treatments,the 2-year mean soil evaporation of whole growth period in C2 treatment were reduced by7.5%,6%and 3.7%in contrast with that in C1 treatment respectively,while soil evaporation in C3treatment were reduced by-0.2%,-3.0%and-2.5%in contrast with that in C2 treatment.From the view of water balance,the application of organic carbon and organic carbon with inorganic fertilizer combination treatments improved the water consumption structure of wheat field,more water was used for wheat transpiration,thus improved the effectiveness of water utility.2.The application of organic carbon in the soil improved leaf transpiration efficiency and leaf Stay Green period,prolonged grain filling duration,so as increased harvest index.Under the same nutrient and water treatments,the leaf chlorophyll content and photosynthetic rate increased with organic carbon enhancement.Compare C3 and C2 with C1 treatments,the leaf chlorophyll increased by 1.4%²8.9%,Pn increased by 4.1%⁹.4%,leaf Stay Green period increased by 2⁴ days,biomass increased by2.0%³6.7%respectively.The root length density of winter wheat increased with organic carbon enhancement in 0¹60cm soil layer.The data showed that the root length density of C3 and C2treatments increased by 3.3%and 7.6%compared with that of C1 treatments,particularly the root length density in 0²0 cm soil layer increased with a much distinguished difference.Meanwhile,the root dry weight density of C3 and C2 decreased by 2.8%³8.4%and-1.6%¹9.5%compared with that of C1 respectively.Under the treatment of high level organic carbon input,the increment of biomass is bigger than that of root weight,and consequently reduced the Root Shoot Ratio by 5.1%²1.4%.Such results indicate that the increasing organic carbon application is more effective to dry matter allocation in shoot canopy,and increase the crop harvest index（HI）by extending the grain filling duration.The HI of C3 and C2 treatment were increased by 4.4%and 1.6%compared with that of C1 treatment.3.The application of organic carbon in the soil increased ear number per unit area,grain yield and water productivity of winter wheat,but the soil water content before sowing has much greater effect on grain yield of winter wheat.The data showed that the organic carbon enhancement in C3 and C2treatments,on the average of irrigation treatments,increased the ear number by 4.8%and 6.6%,as well as grain yield by-1.5%³.6%and 2.2%⁷.1%compared with C1 treatment.The organic carbon enhancement significantly improved Water Use Efficiency（WUE,as Field Water Productivity）by reducing soil evaporation,increasing harvest index and grain yield,and more significant improvement of biomass WUE than that of grain yield.The biomass WUE in C3 and C2 treatments increased by10.8%²0.3%and 0.3%⁷.7%compared with that in C1 respectively,while the grain yield WUE increased by-2.9%⁵.2%and 4.2%⁶.3%with the same comparison.There is a most significant effect of the soil water content before sowing on grain yield and water productivity,and such effect will shrink following the irrigation amount increment and later irrigation timing.On the average of organic carbon treatment,experiment data showed that the grain yield and WUE of W1 treatment were 96.1%¹04.5%and 13.6%²5.4%higher than that of W0,the grain yield and WUE of W2 were 4.7%³2.9%and1.6%⁷.5%higher than that of W1,while the grain yield and WUE of W3 were only 0.2%⁶.0%and-2.7%⁵.3%higher than that of W2.4.The effect of water carbon interaction on water productivity of winter wheat was significant,and there were differences among cultivars.The study showed that water amount,organic carbon dosage and their interaction functioned positively on parameters such as chlorophyll content,net photosynthetic rate,root mass of top soil,grain filling duration,biomass and its WUE,and negatively on root shoot ratio.Particularly,organic carbon application acted negatively on soil evaporation,and positively on grain yield and WUE.In the interaction of water and carbon,water played more important action than organic carbon on grain yield increment,and the effect of organic carbon on improving wheat water productivity reduced gradually as that of water supplement increasing.The result also showed that there existed significant difference in water and carbon interaction between cultivars.The soil evaporation of V1 treatment was measured 3.9%¹1.9%less than that of V2 treatment.Under the same irrigation scheme,all the indices of V1,including grain filling rate and its duration,chlorophyll content,biomass and leaf area index,were observed significantly higher than that of V2.In the condition of water deficit,the 2-year mean grain yield of V1 was recorded 1.6%⁴8.2%higher than that of V2,and the WUE by leaves and WUE by biomass of V1 were calculated 5.0%⁷.3%and 18.0%²1.0%higher than that of V2 respectively,which clearly indicated that Han4589 is a more suitable variety than Shixin828 under the water deficit condition.In su mmary,the organic carbon enhancement improved soil water storage and supply capacity,reduced soil evaporation among plants,regulated crop population structure（root shoot ratio,LAI,etc.）,increased HI and yield,and thereby improved WUE of winter wheat.In this study,the best treatment for improving water productivity of winter wheat is suggested as W2C2V1,i.e.water saving variety,irrigation before sowing and in jointing stage,organic and inorganic combination,are synergic proposed as the effective measures for improving winter wheat productivity while reducing ground water overexploitation in the North China Plain.