Effects Of Supplemental Irrigation Stage And Depth Of Soil Layers Expected For Water Infiltrating On Grain Yield And Water Use Efficency In Wheat

The experiment was carried out from 2012 to 2014 under field conditions in the Yanzhou city(35°40′ N, 116°41′E, 55 m above sea level), Shandong Province, northern China. In 2012~2013, eight treatments were designed as irrigating at jointing, sowing + jointing, winter + jointing, jointing + anthesis and sowing + jointing + anthesis stages to increase soil water content in the 0~140 cm(D140) soil layers, sowing, jointing and anthesis with 60 mm respectively and the rainfed condition.Meanwhile, in 2012~2013, different methods of testing water content were applied such as FDR, TDR,SWR and dry-owing at winter, jointing and anthesis in 0~20 cm(D20), 0~40 cm(D40) and 0~60 cm(D60) soil layers. The target relative soil water content at winter, jointing and anthesis was 80%, 70% and 70%, respectively.The effects of different irrigation stages and depth of soil layers expected for water infiltrating on water consumption characteristics, carbon and nitrogen metabolism and grain yield of winter wheat, the main results as follow:1 Effect of irrigation stages and depth of soil layers expected for water infiltrating on grain yield and water use efficiency of winter wheat1.1 The distribution of root and water use characteristic of wheatIrrigation at sowing refrained the growth of wheat root in the 0~20 cm soil layer, but the root length density, root surface area density and root dry weight density increased. Irrigation at winter improved the growth of root after turn-green. The root length density, root surface area density and root dry weight density decreased with increasing the depth of soil layers. No irrigation at anthesis or irrigation one time promoted the growing down of root and increased the root length density, root surface area density and root dry weight density in the 60~100 cm soil layers. Irrigation at sowing and jointing or irrigation at winter and jointing improved the growth of root in the 20~40 and 40~60 cm soil layers.Under the same irrigation amount and irrigation stage, comparing to D140, D20 decreasedby 12.2~43.1mm of total irrigation amounts and 1.9~35.1mm of water use amounts. Irrigation at sowing, jointing and anthesis, D20 decreased by 42.5mm of total irrigation amounts and 19 mm of water use amounts, compared with D140. The highest water use was observed in the 80~200 cm soil layers. Irrigation at anthesis decreased the water use of the 80~200 cm soil layers. Under the same irrigation stage and irrigation times, comparing to D140 with 70% of target relative water content and 60 mm, D20 with 100% of target relative water content decreased the total irrigation amount and water use, but soil water use increased.1.2 The temperature of soilUnder D20, the soil temperature in the 0~30 cm soil layers in irrigation at sowing was lower by 0.4~16.8℃ than that in no irrigation at sowing. Meanwhile, the accumulated temperature difference between two treatments increased as the depth of soil layers decreased. Irrigation at winter increased the temperature from pre-winter and ture-green. Comparing to irrigation at sowing + jointing and winter + jointing, the soil temperature increased after jointing. The accumulated temperature increased 60.3~136.7℃ during the growing season, compared with irrigation jointing + anthesis and winter + jointing + anthesis.Wheat temperature each soil in each period daily changed in periodic, with "S" curve of decreasing or increasing gradually by the surface to the deep. The biggest daily maximum and minimum temperature in 5 cm soil layer; in the 5 ~ 30 cm soil layers soil temperature variation amplitude gradually slow down. Different irrigation treatment has a significant influence on soil temperature, seeding time fill irrigation decreased soil temperature variation amplitude; Irrigation at winter within 2 days after irrigation, the soil temperature was significantly higher than that of the irrigation at sowing stage.1.3 The endogenous hormoneABA content at jointing and anthesis decreased with increasing irrigation times, GA content shows the trend of increasing with the increase of irrigation frequency. The ABA content of flag leaf under irrigation at sowing + jointing + anthesis was lower than of other treatments, however, the GA content was higher than that of other treatments. The Lowest ABA and highest GA content from jointing to anthesis were obtained under irrigation at sowing + jointing + anthesis stages.1.4 The senescence of flag leafAfter anthesis, the catalase(CAT) activity of the flag leaf reduced with increasing irrigation frequency, soluble protein content showed a trend of increase with increasing irrigation frequency. The MDA content under irrigation 3 times was lower than that of other treatment from 0 days to 28 days after anthesis. However the soluble protein content was higher. It indicated that irrigation at winter + jointing + anthesis was beneficial to reduce the damage of wheat flag leaf cell membrane structure, flag leaf senescence, to maintain a higher level of cell metabolism.1.5 The carbon metabolism of wheatThe wheat flag leaf photochemical efficiency(Fv/Fm), the largest flag leaf actual photochemical efficiency of the flag leaf(Φ PSII) and electron transfer efficiency(ETR) and photosynthetic rate(Pn) was improved under irrigation at sowing, winter, jointing and anthesis. The Fv/Fm, Φ PSII, ETR, Pn and water use efficiency of flag leaves under irrigation at sowing + jointing + anthesis or winter + jointing + anthesis were higher than those of other treatments.In this study in the irrigation 0~3 times condition, the soluble sugar accumulation increased with decreasing the irrigation times. The soluble sugar accumulation of flag l eaves decreased with increasing the irrigation times after anthesis, which promoted soluble sugar to grain starch. Increasing irrigation times enhanced the ability of supply from the leaves. Under the same irrigation stage and times, no significant difference on the soluble sugar accumulation between D20 with 100% of target relative water content and D140 with 70% of target relative water content.The 13 C isotope distribution ratio in the grain yield at 14 and 28 days after anthesis was higher than that at 0 day after anthesis, which indicated that the contribution of the flag leaf photosynthetic carbon assimilation substance to grain yield increased. The 13 C assimilation accumulation under irrigation at winter + jointing + anthesis was higher than that of other treatments, which indicated that irrigation at winter + jointing + anthesis improved the ability of assimilation.Irrigation at sowing, winter, jointing and anthesis increased the dry matter accumulation(DMA). The DMA under irrigation 3 times was higher those under irrigation 2 times, 1 time and 0 time. Irrigation at anthesis increased the contribution ratio of dry matter accumulation to grain yield. Under the irrigation at jointing and anthesis, increasing irrigation at sowing or winterenhanced the dry matter from vegetative organs to grain yield and DMA after anthesis. Under the same irrigation stages and times, there was no significant difference on DMA between D20 with 100% of target relative water content and D140 with 70% of target relative water content and 60 mm of irrigation.1.6 The nitrogen metabolismComparing to irrigation 2 times, irrigation 3 times increased the amounts of accumulated nitrogen nutrition organs and transport amounts, increased the grain nitrogen accumulation, but no significant effect on the nitrogen utilization efficiency was observed. Under irrigation at jointing and anthesis, there was no significant difference on nitrogen accumulation and transportation and nitrogen use efficiency between increasing irrigation at sowi ng and irrigation at winter.Under the same irrigation stages and times, D20 with 100% of target relative water content and D140 with 70% of target relative water content and irrigation 60 mm had the same effect on nitrogen accumulation, transportation and nitrogen use.1.7 The grain yield and water use efficiencyIn the both two growing seasons, grain yield showed the tendency of increase with the increase of irrigation frequency, but no significant difference was observed between irrigation at sowing + jointing + anthesis and irrigation at winter + jointing + anthesis.Under the same irrigation stages and times, in 2012~2013, the grain yield between D140 and irrigation 60 mm did not differ, but irrigation amounts reduced 25.4~57.2 mm and water use efficiency increased. In 2013~2014, D20, D140 and irrigation 60 mm had no difference on grain yield, the irrigation amount of D20 reduced 9.8mm~42.5mm, moreover, water use efficiency of D20 increased 0.3kg·hm-2·mm-1~1.3kg·hm-2·mm-1. It indicated that under the same irrigation stages and times, D20 with 100% of target relative water content or D140 with 70% of target relative water content can be excavated under the high yield level greater potential of water saving.2 The accuracy and stability of different instrument methodsThe results showed that the relative error between the FCv-m and FCm is 0.4%~2.6%. The FCm is the soil field capacity measured by the traditional method, the FCv-m is other kind of soil field capacity that was calculated from FCv measured by FDR and SWR method and expressed by the mass percentage of water to soil. The goodness of fit of the model describing the relationship between the WCv measured by FDR method and the WCm measured by drying method was highest, the goodness of fit of the model describing the relationship between the WCv-m calculated from WCv measured by FDR method and the WCm was also the highest. There was no significant difference among RWCv, RWCv-m measured by FDR method and RWCm measured by drying method. The RWCv is equals to WCv divided by FCv and multiplied by 100, the RWCv-m is equals to WCv-m divided by FCm and multiplied by 100, the WCv-m is equals to WCv divided by soil bulk density. The RWCm is equals to WCm divided by FCm and multiplied by 100. There was a significant positive correlation between the soil temperature and the relative error between WCv-m measured by TDR method and WCm measured by drying method. The WCv-m measured by TDR method was higher at sowing, anthesis and maturity stage, but was lower at Pre-winter and jointing stage. There was a significant negative correlation between the soil moisture content and the relative error between WCv-m measured by SWR method and WCm measured by drying method. The measurement accuracy of SWR method was higher under the condition of higher soil moisture content. The measurement accuracy and stability of FDR method were higher, which have hardly affected by soil temperature and moisture in the growing season of winter wheat. The same effect of supplemental irrigation based on testing soil moisture with traditional drying method on the yield and water use efficiency of winter wheat was obtained as the required amount of supplemental irrigation was directly calculated by the WCv and FCv measured by FDR instrument method.