| Considering the shortage of water resources,serious soil salinization and inefficient use of water and fertilizer in cotton fields in southern Xinjiang.In this study,Xinluzhong 66 was used as a cotton variety,and field capacity(FC)was used as the upper limit of soil water,five soil water lower limit levels were set as 85%FC(T1),75%FC(T2),65%FC(T3),55%FC(T4)and 45%FC(T5),respectively.Field experiments were conducted to study the effects of soil water lower limit control on cotton growth,yield,quality,and cotton nitrogen uptake and utilization under drip irrigation.To explore the changing characteristics of soil water,salt,and nitrogen transport,with a view to exploring water-saving and salt-control irrigation systems and models suitable for the efficient production of cotton in southern Xinjiang.The main conclusions of the study are as follows:(1)The effects of different soil water limits on the water consumption characteristics of cotton fields were explored.As the lower limit of soil water increases,the single irrigation quota gradually decreases,the irrigation frequency gradually increases,and the irrigation quota gradually increases;the average daily water consumption intensity of cotton from seedling stage to the beginning of budding stage is between 0.99 and 2.08 mm/d.At the end of the budding stage to the flowering stage to the boll forming stage,the average daily water consumption intensity is between 2.47 and 5.78 mm/d.At the boll bearing stage,the cotton water consumption intensity is basically between 2.03 and 3.61 mm/d.From the late cotton budding stage to the flowering stage to the bell forming stage is the critical period of cotton water demand,and the water consumption modulus is 56.40?69.66%.Too high and too low lower limit of soil water are not conducive to the reasonable distribution of cotton water consumption modulus coefficient throughout the growth period.When the lower limit of soil water is 75%FC,the water consumption modulus of cotton is the largest in the critical period of cotton water demand.(2)The effect of soil water regulation on cotton growth,dry matter accumulation,yield,quality and water use efficiency was revealed.Logistic model can simulate the change of plant height and dry matter of cotton.With the decrease of the lower limit of soil water,cotton is under drought stress.The plant height,leaf area index and total dry matter on the ground are significantly reduced.The root-shoot ratio is gradually increased,the growth process of cotton is accelerated,the leaf area of cotton is decreased in advance,the boll is early,the yield of cotton is gradually reduced,and the water use efficiency is gradually increased.The distribution of assimilate to seed cotton was not good when the lower limit of soil water was too high or too low.T2 treatment promoted the transport of dry matter to reproductive organs.Soil water regulation significantly affects cotton fiber quality,the lower the soil water limit,the greater the micronaire value,the higher the maturity index,the lower the specific breaking strength and elongation at break.The principal component analysis showed that T2 treatment had the best fiber quality.When the lower limit of soil water is 75%FC,the number of effective bolls,the weight of single boll and the weight of dry matter per plant increase,which significantly promotes the transport of dry matter to reproductive organs.The cotton quality of which is the best,which can obtain at least 98%of the maximum lint yield,and save about 11%of irrigation water,the yield and water use efficiency of seed cotton reach 7146.4 kg/hm~2 and 1.40 kg/hm~2respectively,with high economic benefits.(3)The influence of soil water lower regulation on water and salt transport in cotton fields was analyzed.After irrigation,the soil water content gradually decreased with the increase of the distance from the drip irrigation belt,and characterized by under the belt>narrow row>wide row>bare land,while the soil salt content was in the opposite regular distribution.When the soil water lower limit was set to be high,the more frequent the irrigation,the higher the soil moisture content and the lower salt accumulation,and the more salt can be leached to the outer layer of the film.When the soil water lower limit was set to be low,more salt can be washed out of the crop root zone due to the higher irrigation amount,but the irrigation frequency was low,the irrigation amount was small,salt was accumulated again at the end of the growth period.At the end of the growth period,the salt in the film and outside the film are all accumulated.The salt accumulated in the film was less than the salt accumulated outside the film.The salt content in the main root zone was larger than that in the secondary root zone.The total salt accumulation showed as T3>T5,T1>T2,T4.(4)The effects of soil water lower regulation on soil inorganic nitrogen migration and cotton nitrogen uptake and utilization were discussed.The increase of the lower limit of soil water is beneficial to the absorption of nitrogen and the distribution of nitrogen to the seed cotton,but the higher the lower limit of soil water will promote the absorption of nitrogen in the vegetative organs,and then reduce the proportion of nitrogen distribution in the seed cotton.The absorption and distribution ratio of nitrogen in the T2 treatment of seed cotton is the largest at the bolling stage.The nitrogen absorption efficiency and nitrogen production efficiency of cotton increased with the increase of the lower limit of soil water content,which was conducive to the high yield of cotton,and then improved the nitrogen harvest index.When the irrigation quota is large or the irrigation quota is large,the nitrate nitrogen in cotton root soil will be leached to 60?100 cm soil layer along with the irrigation water,which is not conducive to the nitrogen absorption of cotton.When the lower limit of soil moisture is 75%FC,it is more beneficial for cotton to absorb nutrients and reduce the leaching loss of nitrate nitrogen to the depth of soil layer.(5)A water-saving and salt-control irrigation system and model suitable for the efficient production of cotton in southern Xinjiang are proposed.In order to ensure the yield and quality of cotton,and to save water and salt and reduce nitrogen leaching,the irrigation system of drip irrigation under salt and alkali mulch film in South Xinjiang is preliminarily concluded as follows:FC is the upper limit of soil water,75%FC is the lower limit of soil water,and winter irrigation is carried out during non-growing period with the quota of 300 mm,the irrigation quota for growth period is 334 mm as the water consumption is 509 mm,12 times of irrigation in the whole growth period,8 days of irrigation cycle. |
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