| The shortage of water is a worldwide problem, especially in the arid area in northwest of China. The contradiction between supply and demand of water resources becomes one of the key problems to confine the agricultural and economic development for arid area. According to water shortage problem, the brakish water distributed widely in northwest arid area of China is increasingly applied for irrigation cotton and other crops. Salinity (include trace elements) in the brackish water as nutrients can promote cotton growth and its yield. But, using brackish water without appropriate method would result in salinization of the soil. It is important for theoretical and partical significance to prove up soil water, salt and heat distribution and transfer rules on the condition of drip irrigation under membrane with brackish water, and to make proper irrigation regime and fertilization for cotton in northwest China.Three years field experiments and one year pot experiments were conducted to research the relationship of cotton, water, salts and nutrient elements for establishing the optimal system of cotton-water-solute under the mulched drip irrigation with brackish water.The experiments were carried out in cotton fields in Water Conservancy Administration Irrigation Experimental Station of Ministry of Water Resources located in Bayingolin Mongol Autonomous Prefecture of Xinjiang between2008and2010. Two irrigation lines were installed for each four rows of cotton. The experiments include2control irrigation treatments,4alternative irrigation treatments and4deficit irrigation treatments in three replicates randomly. Undisturbed soil samples were sampled to measure the soil dry density and lithology. Then, the soil moisture characteristic curves at various depth were obtained. The field soil moisture capacity was measured after the basin irrigation treatments. The soil matric potential were monitored in-situ using Depressimeter; the soil water content were monitored using; and The soil water content, EC and temperature were monitored in-situ using Soil Moisture Neutron Instrument, Stevens Hydra Probe soil sensors and Geothermometer. Soil were sampled at different time to measure soil electric conductivity EC1:5. Cotton growth were monitored timely and the yield were measured after harvest. Pot experiments were conducted in a greenhouse at Wuhan Botanical Garden. Chinese Academy of Sciences from March to October2012. The pot experiments used soilless culture and included30orthogonal tests with6NaCl levels and5Mn levels in three replicates randomly. The cotton growth were monitored timely and harvested130days after germination. Cotton dry weight were weighed. And14elements contents in cotton were measured after acid digestion, such as B, Ca, Cu, Fe, K, Mg, Mn, Na, Zn and so on.Many mthematical methods were used to analyze experimental data. Mathematical tools, such as SPSS, Matlab and Surfer were used to process experimental data. And numerical simulation was used to assist the field experiments. The specific obejectives were to prove up soil water, salt and heat distribution and transfer rules under mulched drip irrigation with brackish water in cotton field; to analyze the effects of irrigation water-salt and soil water-salt on cotton; to build cotton-water-salt production function considering growth season; to make proper mulched drip irrigation regime with brackish water and evaluation the long time effect of this regime; to research on the combined effect of salinity and Mn on cotton; to research the optimal system of cotton-water-solute in field under mulched drip irrigation with brackish water. Then, the resuts may be concluded as fllows.(1) Under mulched drip irrigation with brackish water, more irrigation quantity, wetting front expanded farther; more irrigation quantity, soil water content variation became periodic change faster; soil water content eventually varied cyclically with the increasing of irrigation times at the same irrigation ration. Soil water content variation was influenced by initial water content; smaller initial water content, the soil water content increased more slowly; for different initial water content, the soil water content approached to similar at the same depth with the time; the effect of initial water content on the soil water content variation reduced with the increasing of irrigation ration; the effect of initial water content on the soil water content variation increased with the depth. Soil water content at0-60cm depth was influenced significantly by evapotranspiration; soil water content fluctuated with irrigation. The soil water content between control and alternative irrigation treatments were close; the soil water content of deficit irrigation treatments were influenced by irrigation quantity significantly and were different for different treatments in root zone. The soil moisture in root zone of all the treatments could meet the cotton root water uptake.(2) Under mulched drip irrigation, saline irrigation would take salt into soil and make the soil electric conductivity EC15increase; the drip irrigation wetting font and naked soil surface were easy to be accumulated salt. Irrigation quantity increased in cotton flowering-belling stage, so the leaching fraction increased. And soil salt in root zone decreased, then, soil EC15decreased. Initial salinity significantly influenced soil salt migration; when the initial salinity was higher than irrigation salinity, saline irrigation was leaching irrigation; the soil salt veried differently for different treatments. The soil salt transport was influenced significantly by initial salinity, irrigation quantity, irrigation water quality and so on. Therefore, taking initial condition into account, irrigation water quantity and quality’needed to be adjusted to meet the cotton salt tolerance. (3) Under mulched drip irrigation with brackish water, soil temperature at0-40cm depth fluctuated periodically with ari temperature; soil temperature under40cm veried little and were influenced unobviously by air temperature. During one variation period, namely one day, membrane mulched soil temperature was the same with naked soil temperature at0:00to12:00; mulched soil temperature at0-15cm depth were higher than that of naked soil at12:00to24:00. On the condition of mulching membrane, cotton mulching soil temperature at0-15cm depth were lower than that of no cotton mulching at12:00to24:00during a variation period but they were close at0:00to12:00. The soil temperature under15cm was influenced little by mulching membrane or cotton. Soil temperature affected soil water transport and root water uptake; and it was influenced by air temperature, coverings and so on; mulching membrane to increase soil temperature was beneficial for cotton germination.(4) Under mulched drip irrigation with brackish water, when irrigation water electric conductivity ranged from3.35to4.86dS/m, the salt in water as nutrient promoted cotton yield. Cotton yield of treatment irrigated fresh water in cotton early stages that was poor salt resistance but brackish water in late stages was the highest; the least yield fluctuation were observed in the treatment irrigated fresh water in cotton flowering-belling stage but brackish water in other stages at2008to2010. Crop sensitivities to water stress during the different growth stages ranged from early flowering-belling (most sensitive)> seedling> budding>late flowering-belling (least sensitive), while sensitivities to salt stress ranged from late flowering-belling> budding> seedling> early flowering-belling. When the irrigation water NaCl concentration was greater than35mmol/L, conductivity EC was greater than6.11dS/m, irrigation water salinity inhibited the cotton vegetative growth (height, root and stem dry weight) and promoted the cotton reproductive growth. Under mulched drip irrigation with brackish water, the sensitive coefficient (ki) of cotton budding stage to soil water-salinity was-0.249and that (k2) of flowering-belling was0.887.(5) Fresh water was used to leach salinity before sowing and mulched drip irrigation with brackish water was used during growth season. Based on calculation, for a cotton growth season, irrigation water quantity was283m3/Mu befroe sowing,39m3/Mu during budding stage, and424mJ/Mu during flowering-belling stage. Irrigation water quantity calculated on the basis of ideal conditions was not benefit for water conservation. Adjusted amount was:102m3/Mu (15cm) before sowning, no irrigation during seedling stage,27m3/Mu during budding stage (dripper discharge was2.2L/h, and rrigation duration was4hours) with15d irrigation frequency,297m3/Mu during flowering-belling stage with29.7m3/Mu for ecach irrigation (discharge rate was2.2L/h, and rrigation duration was4.6hours). Soil water-salt-heat model was verified using experimental data; the model results indicated that under the same planting structure and irrigation regime, the irrigation regime could meet the water demand of cotton growth and the soil salinity is lower than cotton salt tolerance during the growth season; salinity would not accumulate in the root zone during the next10years. The final adjusted irrigation regime was proper which cound meet water demand and salt tolerance of cotton.(6) When the NaCl concentration in the irrigation water was15-25mmol/L, cotton vegetative growth was the best. Interactive effect on cotton growth and yield between NaCl and Mn in the irrigation water was not observed but antagonistic effect was observed. Contents of nutrient elements, Ca、Mg、Na、B、Mn and Zn, in cotton leaves were higher than other organizations; contents of nutrient element K in cotton bolls were higher than other organizations; and nutrient elements, Cu and Fe were not so movable that they were easy to accumulate in roots. Under mulched drip irrigation with brackish water, NaCl concentration levels in the irrigation water affected uptakes and distributions of nutrient elements in cotton.(7) The irrigation regime and fertilization recommended was:102m3/Mu (15cm) before sowning (urea:30kg/Mu, diammonium phosphate:10kg/Mu, compound fertilizer with45%potassium sulfate:50kg/Mu, farm manure:1m3/Mu, trace element fertilizer:0.5kg/Mu), no irrigation during seedling stage,27m3/Mu during budding stage (dripper discharge was2.2L/h, and rrigation duration was4hours) with15d irrigation frequency and additional fertiliazation (urea:10kg/Mu, diammonium phosphate:2kg/Mu, compound fertilizer with45%potassium sulfate:15kg/Mu, trace element fertilizer:0.1kg/Mu),297m3/Mu during flowering-belling stage with29.7m3/Mu for ecach irrigation (discharge rate was2.2L/h, and rrigation duration was4.6hours) and additional fertilization on the third, sixth and ninth irrigation (each fertilization was as following:urea:12kg/Mu, diammonium phosphate:2kg/Mu, compound fertilizer with45%potassium sulfate:15kg/Mu, trace element fertilizer:0.1kg/Mu). |
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