Abstract:
Abstract: Due to the unique geographical environment, North of Xinjiang is exceptionally early mature cotton region with short cotton growing season. Therefore, how to achieve efficient allocation of irrigation water saving and high yield efficiency of cotton production in the short growth period has become a key problem in the production of cotton in northern Xinjiang. This study investigated the effects of irrigation treatments on photosynthetic characteristics and yield of machine-harvested cotton. An experiment was carried out in the year of 2015 in Xinjiang Agricultural University Experimental Base (44°39′N、86°08′E with an altitude of 367 m) of Changji by an single factor randomized block design. Three irrigation times of 10 (D10), 8 (D8) and 6 (D6) were designed following local experience. The total irrigation quota was 4500 m3/hm2. The machine-harvested cotton variety of Xinluzao 57 was for the experiment. During the experiment, soil moisture content, photosynthetic parameters, fluorescence parameters and yield formation characteristics were measured. The results showed that the D6 treatment delayed the time of first water, and its stress degree was higher than those of the other treatments. For the D6, the non-stomatal limitation caused the decrease in the net photosynthetic rate, the max photochemical efficiency, photochemical quenching coefficient and photochemical quantum yield of photosystem II were also significantly lower than those of the other treatments. Meanwhile, the non-photochemical quenching coefficient was increased dramatically, while the recovery capability was poor, which limited the accumulation of above-ground biomass. Due to unreasonable irrigation water allocation at flowering and fruiting stages in the D10 treatment, the net photosynthetic rate decreased as affected by stomatal limitation factors under light water stress, while photochemical quenching coefficient was improved effectively by irrigation in the boll opening stage. At the same time, leaf photosynthetic function duration was extended while the biomass was accumulated more for the vegetative growth and the vegetative organs biomass were higher than the other treatments, which resulted in no significant difference in biomass of the reproductive organs. The D8 treatment could ensure the higher efficient photosynthetic capacity during the whole growth period, and the biomass of reproductive organ was 21.1% and 23.5% than the D10 and D6, respectively. Water use efficiency of leaf in the D8 reached the highest among the treatments, and the yield of D8 was not significantly different from the D10 (P>0.05), but 647.4 kg/hm2 higher than the D6 (P<0.05). Therefore, under the condition of drip irrigation quota for 4 500 m3/hm2, the irrigation allocation method in the D8 treatment was beneficial to improve the photosynthetic capacity of the leaves and promote the distribution of the photosynthetic material to the reproductive organs. Therefore, irrigation before the full budding stage, increasing irrigation quota after the full flowering stage and reducing the water supply in the boll opening stage can effectively improve the photosynthetic capacity of leaves, promote the migration of the photosynthetic substances into the reproductive organs, so as to fulfill the water saving goal and achieve high efficiency of machine-harvested cotton production as well.