Effect Of Water And Nitrogen Application Control On Root Growth And Yield Of Cotton(Gossypium Spp.)

Root-soil interface is the main channels for soil water and nutrients into plants. Root isthe core content of the root-soil interface and the material basis, whose distribution andfunction directly or indirectly influence the growth of the aboveground and the survival anddevelopment of the whole plant. Cotton is the most important economic crop in oasisagriculture in arid areas in China. In the research, through improving irrigation andfertilization ways, changing root soil water status and its distribution in the section tooptimize the cotton root morphology, structure, and physiological characteristics. In turn, toenhance cotton plants water and fertilizer absorption and utilization efficiency, furthermore, torealize the high-efficient and high-yield and water-saving cultivation of cotton in arid areas isvery important. This research was conducted in pipe cultivation condtion and focused on twoaspects of the root domain volume and the irrigation depth, different water and nitrogenamount were set and the model of drip irrigation under membrane with fertilization wasadopted to study the relationship of morphological and physiological adaptations and yieldformation on cotton under the condition that root growth space is confined. At the same timethe field test experiment was carried out and the change trend of root morphological andphysiological and leaf physiological characteristics under different yield levels were observed.On the basis of comprehensive study, the influence of changing root growth environment onroot morphological and physiological traits and its relationship with the aboveground growth.The main research contents and results were as follows:1. Influence of water and nitrogen supply amount on root morphological characteristicsof cotton in root restriction was studied. Root surface area index （RAI）, the root lengthdensity （RLD） and root volume density （RVD） and root mass density （RMD）, root systembiomass and root shoot ratio were lower than controls in the root restriction. The aboveparameters among different water and nitrogen treatments were rank in the orde of W₀N₀（water and nitrogen deficit）>W₁N₀（nitrogen deficit）>W₀N₁（water deficit）>W₁N₁（water andnitrogen in moderation）. The root restriction and water and nitrogen supply all reduce the rootquality.2. Influence of water and nitrogen supply amount on root physiological activity of cottonin root restriction was studied. Root antioxidant protective enzymes （SOD, POD, CAT）activity were significantly lower than control. Water and nitrogen supply effectively adjustedthe root growth. The activity of root protective enzyme system among different water andnitrogen treatments were rank in the orde of W₁N₁>W₀N₁>W₁N₀>W₀N₀. Under the conditionof root restriction, optimization of water and nitrogen supply during growth stages, enhancethe activity of root antioxidant protective enzyme system, postpone root senescence.3. Influence of water and nitrogen supply amount on leaf physiological characteristics and yield of cotton in root restriction was studied. Compared to the control, at the same waterand nitrogen supply, from flowering to full boll openning stage, leaf antioxidant protectiveenzymes （SOD, POD, CAT） activity, leaf net photosynthetic rate （Pn）, stomatal conductance（Gs） and light chemical quenching coefficient （qP） were significantly lower, but the potentialmaximal photochemical efficiency （Fv/Fm）, actual photochemical efficiency （ΦPSII） werenot affected. At both full flowering stage and full boll openning stage, root biomass weresignificantly lower, but the aboveground biomass, bud and boll biomass and seed yield wereall significantly higher than the control. At the treatment of root restriction cooperatingmoderate water and nitrogen supply, the aboveground biomass, bud and boll biomass weresignificantly increased. Consequently, the boll number per plant, single boll weight and seedyield were all significantly higher than other treatments. Under the condition of root domainvolume limited, optimizing the water and nitrogen supply at growth stages, can improve leafphotosynthetic performance, increase dry matter accumulation aboveground and allocationproportion to the reproductive organs.4. Influence of different water and nitrogen supply on root morphological characteristicsof cotton under different irrigating depth was studied. In the0-40cm soil layer, RVD, RMD,RAI and RLD were in the order of CK（drip irrigation on the soil surface）> H₀（irrigationdepth was20cm underground）> H₁（irrigation depth was40cm underground）. While in the40-80cm and80-120cm soil layers, the above parameters were shown as CK <H₀<H₁. Waterand nitrogen supply significantly （P <0.05） decreased root quality. Among different waterand nitrogen treatments, all the root morphological parameters, root biomass and Root-shootratio all performed W₀N₀> W₁N₀> W₀N₁> W₁N₁. In upper soil layer （0-40cm soil layer）,root quality was reduced with the increase of the irrigation depth and the supply of water andnitrogen, and the depth of the irrigation was the main effect factor. In the soil layers underirrigation depth, the water and nitrogen supply became the main factor to reduce root amount.5. Influence of different water and nitrogen supply on root physiological characteristicsof cotton under different irrigating depth was studied. At different irrigating depths, rootantioxidant protective enzymes （SOD, POD and CAT） activity in each soil layer were shownas H₀> CK> H₁. At the different supply of water and nitrogen, root protective enzymesactivity performed W₁N₁> W₀N₁> W₁N₀> W₀N₀. This showed that shallow undergrounddrip irrigation and the supply of water and nitrogen were beneficial to improve the rootantioxidant activity of protective enzyme system, postpone root senescence on the whole.Water and nitrogen supply was the main effect factor to determine the root protective enzymesactivity. At the treatment of moderate water and nitrogen supply （W₁N₁） cooperating withirrigation depth20cm underground （H₀）, root protective enzymes activity was the highest.6. Influence of different water and nitrogen supply on leaf physiological characteristics and yield of cotton under different irrigating depth was studied. The response of leafantioxidant protective enzymes （SOD, POD and CAT） activity, leaf gas exchangeparameters（Pn, Gs）, and chlorophyll fluorescence parameters （Fv/Fm, Φ PS Ⅱ, qP） toirrigation depth, interaction among irrigation depth and water and nitrogen supply were allconsistent with root protective enzymes activity. Among all treatments, aboveground biomassof plant and yield were consistent with Pn, but the performance of root biomass androot-shoot ratio is on the contrary. This showed that shallow irrigation undergroun withappropriate water and nitrogen management is advantageous to the coordination of the growthaboveground and underground of cotton plant, alleviate the contradiction between vegetativegrowth and reproductive growth, to achieve optimization in resource.7. Using the cotton under-mulch-drip irrigation in the field in large scale as experimentalmaterial, the change of root system growth and development in the fields with different yieldlevels was studied. With the increase of yield levels, the total soil RLD, RAI, RVD and RMDdecreased; root and leaf antioxidant protective enzymes （SOD, POD and CAT） and nitratereductase （NR） activity increased. While the root-shoot ratio and root biomass reduced,aboveground biomass, yield and its components increased with the increase of yield levels. Incotton production with higher levels of yield, both the decrease of root-shoot ratio and theincrease of root physiological activity promoted the growth aboveground, optimized the yieldstructure and components, increased production eventually.Through the comprehensive analysis of the root morphological and physiologicalcharacteristics and the relationship with aboveground biomass and yield of cotton, theconclusion was drawn that in the condition of under-mulch-drip irrigation in arid areas, highaboveground biomass was necessary to improve the cotton yield level, but great root growthwas not necessary, root moderately shrinking reduced root redundancy. According to theresults from this paper, the root-shoot ratio of0.21-0.32of cotton in the field is optimum.Through the regulation of water and fertilizer under-mulch-drip irrigation to control the sizeof root system, increase root physiological activity （SOD, POD, CAT and NR） can be used asthe main direction of high yield cultivation and the selection indicators of root morphologyand physiology in genetic improvement of cotton varieties.