| At present,potassium chloride is the largest commodities in the exploitation of potassium resources in China.Cotton has a large demand for potassium nutrient.The rational application of potassium fertilizer according to the degree of soil salinization can reduce salinity stress of salinized field and improve the nutrient accumulation and cotton yield.Controlled-release potassium chloride could effectively control the release of nutrient,meet the needs of crops growth during the whole growth period through one-off application,thus improve the efficient use of potassium fertilizer.Some difficulties were existed in the preparation of controlled-release potassium chloride fertilizer,such as the preparation of fertilizer core and insufficient research on agronomic benefit evaluation,etc.In this study,two types of potassium chloride(M1 and M2)were granulated by adding diatomite and gypsum,and the third type of round potassium chloride(M3)was obtained from fertilizer company.After coating with resin,three types of controlled-release potassium chloride MOP1,MOP2and MOP3 were obtained.They were compared with applying common potassium fertilizer and no potassium fertilizer.One combined application(common potassium chloride:controlled-release potassium chloride=3:7)and three levels of fertilizer rates(120 kg·hm-2,180 kg·hm-2and 240 kg·hm-2)were set.The effects of three types controlled-release potassium chloride on cotton growth in saline soil,which were studied by field experiment and pot experiment.Combining the static water dissolution rate method and field bag burying method to determine the characteristics of the nutrient release,and to explore the regulatory mechanism of nutrient release of coated controlled-release potassium chloride.The objects of this study were to clarify the effects of controlled-release potassium chloride application on cotton growth,soil and plant nutrient accumulation and fertilizer utilization rate.The main results are as follows:(1)The parameters of powder potassium chloride(M1 and M2)were confirmed by the granulation rate and particle strength in the manufacturing process of potassium chloride particles.The suitable additive amount of urea formaldehyde binder was 2%?4%,and diatomite and gypsum were 8%?10%.The coating thickness of MOP1,MOP2 and MOP3were 4,4.5 and 3.5,respectively.In cotton field soils,the release rate of controlled release potassium was merely 5%in the first 15 d,and showed a trend of MOP1,MOP3 and MOP2from high to low.Generally,the nutrient release rate from higher to lower was MOP2,MOP3and MOP1 after 30 d.(2)The net photosynthetic rate of cotton functional leaves exhibited the maximum value at the flowering and boll stage.At the potassium application rate of 180 kg hm-2,MOP1-2 and MOP2-2 showed the highest values in the net photosynthetic rate(34.10?mol·m-2·s-1and34.05?mol·m-2·s-1,respectively).The values of SPAD exhibited a similar trend as the net photosynthetic rate.The highest values of root surface area and volume were found in MOP2-2 treatment.The shoot dry weight and root dry weight of MOP2-2 were significantly increased by 20.83%and 14.71%compared with MOP3-2 treatment,and were increased by35.94%and 14.71%compared with MOP4-2 treatment.The values of root shoot ratio in different treatments from lower to higher was MOP2-2,MOP3-2 and MOP4-2.(3)The application of controlled-release potassium chloride improved the yield and quality of cotton in saline soil.In 2019,the single boll weight of MOP1-2,MOP1-3,MOP2-2,MOP2-3 and MOP3-3 treatments were significantly higher than other treatments.Compared with MOP4-2 and MOP4-3 treatments,the seed cotton yield of MOP2-2 and MOP2-3treatments were increased by 27.41%and 26.55%,respectively;and the variation of lint yield was nearly consistent with the grain cotton yield.At the potassium application rate of 180kg·hm-2and 240 kg·hm-2,controlled-release potassium fertilizer significantly improved the quality of on cotton fiber.The values of fiber length,fiber uniformity,fiber strength and elongation were increased by 11.05%?12.72%,3.31%?3.79%,7.22%?7.72%and7.08%?8.61%,respectively,compared to control treatment.At the stage of cotton harvest in2020,MOP2-2 treatment significantly increased potassium accumulation in leaves and bolls by 38.72%and 14.35%compared with MOP4-2 treatment,and the nitrogen accumulation in stems was significantly increased by 12.5%.The potassium content of cotton bolls in MOP2-3treatment was significantly increased by 16.74%compared to MOP4-3 treatment.At the stage of cotton bud,the values of plant height and stem diameter in MOP2-3 treatment were significantly increased by 8.10%and 22.58%,respectively,compared with MOP4-3 treatment.Meanwhile,this advantage continued to be maintained at the flowering and boll stage.(4)Various fertilization treatments had no significantly effect on the contents of soil total K and slow-available K in 0?20 cm and 20 cm?40 cm soils.However,the content of soil available K was higher in common potassium fertilizer treatment than others.The accumulation of plant potassium in MOP1-3,MOP2-3 and MOP3-3 treatments were increased by 4.66%,3.00%and 3.49%compared with MOP4-3 treatment.The average biomass of MOP1-2,MOP2-2 and MOP3-2 treatments were increased by 2.72%,8.20%and6.31%,and K use efficiency were increased by 15.59%,15.71%and 13.47%,respectively,compared with MOP4-3 treatment.The K use efficiency from higher to lower was MOP2-2,MOP1-2,MOP3-2 and MOP4-2.In conclusion,the application of controlled-release potassium chloride significantly improved the soil fertility and cotton physiology,promoted the cotton growth,and hence increased the yield and quality of cotton.The optimum rate of potassium fertilizer was reasonable at 180 kg·hm-2,and the controlled-release potassium chloride that fertilizer core prepared with gypsum powder worked best.Therefore,it can be applied in the coastal saline area of the Yellow River Delta,in order to achieve the goal of saving potassium fertilizer resources and achieving the vigorous development of cotton planting in saline soil area. |
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