| Xinjiang has the largest cotton plantation area of China due to its favourable natural and climatic conditions. However, the lack of water resources, particultural for agriculture production, is very serious, the contradiction between supply and demand of water resources has become more and more apparent. Thus, how to effectively utilize the limited water resources and improve water use efficiency is the main concern for cotton production in this area. In2009-2010, an experiment was conducted in Xinjiang with cotton as research crop under drip irrigation (e.g. drip irrigation under mulch and subsurface drip irrigation). The characteristics of soil moisture dynamic variation, plant growth, seed cotton yield, fibre quality as well as water use efficiency were investigated. The main results are as following.(1) Calculation method of average soil water content in soil profile under mulched drip irrigation conditions was put forward.3sampling points were taken at the wide row under film, the narrow row under film and the bare ground out of film, respectively, the estimated average soil moisture (in the horizontal direction, using the area weighted method to calculate average soil moisture of each soil layer, and calculating average soil moisture in vertical direction with integral weighted method) was very close to the true values estimated by layered integration method at the vertical profile based the high-density sampling. The result based on observations of12probes showed that the suitable location of burying soil moisture sensors was0～10,20～30,40～50and60～80cm below soil surface, and selecting the data of3sampling points to calculate average soil moisture could truly reflect the soil moisture of the profile.(2) The influence of water stress at the squaring stage and at the flowering-boll stage on the plant height, stem diameter and leaf area of cotton were analyzed. Moderate water deficit occurring at squaring stage (with the lower limit of soil moisture for irrigation as60%of field capacity) could inhibit the above-ground vegetative growth plant excessive growth of cotton, promote root growth and development, and has an advantage of transporting the photosynthate to fruits which providing a good base for high-yield formation. Heavy water stress (with the lower limit of soil moisture as50%of field capacity) at the squaring stage could inhibit the normal growth and development of cotton, excessive water (with the lower limit of soil moisture as75%of field capacity) result in vigorous growth of cotton plant and were not conducive to cotton yield. Water stress at the flowering-boll stage not only inhibited the growth and development of cotton, but also increased the shedding rate of buds and bolls, and the negative effect increased with degree of water deficit imposed. Compared with the treatment of surface drip irrigation under mulch, subsurface drip irrigation could help the cotton root to penetrate into deep soil layers, and was favorable to the root system to absorb soil moisture within the deeper layer (the average density of root weight at the depth of43～70cm increased37.64%).(3)The effect of water control at different growth stages on cotton quality was expounded. Moderate water deficit at the squaring stage could increase the lint percentage of blossom before frost, fibre length and breaking tenacity of cotton fibre, but excessive water stress lower the fibre length and breaking tenacity of cotton fibre. Heavy water stress at flowering-boll stage could decrease the fibre length of cotton, and the response of the fibre length to water stress increased with the degree of water stress, however, moderate water stress could increase the breaking tenacity of cotton fibre, and heavy water stress dramatically reduce the breaking tenacity of cotton. The fibre uniformity index, elongation and micronaire of cotton were little sensitive to water stress in this study. Compared with the treatment of drip irrigation under mulch, the subsurface drip irrigation was more beneficial to the improvement of the fibre quality of cotton, the fibre length, breaking tenacity, elongation and the uniformity index under subsurface drip irrigation improved by0.18%-0.97%,0.84%～1.88%,0.99%～2.53%and0.96%～1.61%, separately.(4) The influence of different irrigation methods on water consumption and water use efficiency of cotton was analyzed. The water consumption of cotton in the whole growth stage was453～540mm, of which during the seedling stage, squaring stage, flowering-boll stage and boll opening stage accounted for17%～22%,14%～19%,49%～58%and6%～15%, respectively, and it decreased with the degree of water stress imposed. Compared with surface drip irrigation under same water treatment conditions, the water consumption of subsurface drip irrigation increased by4.42%-8.98%, the seed cotton yield of which in other treatments also increased in various degrees besides the treatment of heavy water stress at the squaring stage, and water use efficiency between two irrigation ways had a little difference.(5) The estimation models of water requirement for cotton under drip irrigation in Xinjiang province were established based on pan evaporation, effective accumulated temperature and leaf area index of cotton, respectively. The models were verified by using the measured values in2008, and the result showed that average relative error of simulated values was2.37%～13.53%(based on leaf area index model),0.68%-21.72%(based on the effective accumulated temperature model) and1.77%-14.35%(based on pan evaporation model), separately. The average relative error of cumulative water consumption for simulated values during the squaring stage and flowering-boll stage was1.52%～5.53%and0.29%～8.88%, respectively. Therefore, the established models could satisfy the precision needs of calculating crop water requirement for real time irrigation.(6) The irrigation index and irrigation pattern were determined to achieve high yield, high quality and efficiency for cotton production under drip irrigation in Xinjiang province. As for one tube controlling four rows of cotton,45mm of irrigation water was applied to ensure emergence after sowing, no water applied at both the seedling stage and boll opening stage, and irrigation water quota was22.5mm and37.5mm with7d of irrigation frequency at the squaring stage and flowering-boll stage, respectively. Under the irrigation way of two tube controlling four rows of cotton and subsurface drip irrigation, irrigation water quota was30mm and22.5mm at the squaring stage and flowering-boll stage, respectively, when the lower limit of soil moisture at the squaring stage and flowering-boll stage was60%and75%of field capacity respectively, and the irrigation water quota was30mm and35mm at the squaring stage and flowering-boll stage, respectively, in the case of the accumulated pan evaporation reached75mm an50mm at the squaring stage and flowering-boll stage, separately.Main highlights of this paper:①The suitable method to calculate average soil water content in soil profile and the layout scheme of the soil moisture monitoring probes in drip irrigation under mulch were put forward.②The estimation model of water consumption for cotton under drip irrigation in Xinjiang province was established based on the pan evaporation and it can satisfy the precision needs of calculating crop water requirement for real time irrigation.③The irrigation index and irrigation pattern were determined in order to achieve high yield, high quality and efficiency for cotton production under drip irrigation in Xinjiang province, particularly, the irrigation pattern based on accumulated pan evaporation due to the advantages of simple equipment and easy operation could be popularized and applied. |
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