Slow release characteristics of mepiquat chloride from starch matrices coated cotton seed

Chinese. 【目的】用改性交联淀粉囊化的缩节安（SRD）对棉花种子进行包衣，研究其在水中和土壤中的释放特性。【方法】用水中溶出法、土壤恒温培养法、. 4C-DPC同位素标记法和生物试法测试。【结果】SRD在水中的释放动态为S形曲线，完全溶出的时间约为15 min，较对照（CK，缩节安直接拌种）延长10 min左右，在1.5、5和10 min的累积释放率分别相当于CK的40.3%、24.8%和64.0%。SRD在土壤中的释放动态为抛物线，这是释放和降解互相抵消后的结果，SRD累积释放率达到的最高值（此时释放与降解的速度相等）仅为CK的1/3左右，达到最高值的时间较CK推迟约10 d，在土壤中的存留时间为50 d以上，较CK延长2倍多；. 4C-DPC同位素标记试验表明，种子表面的SRD在土壤中呈非匀速减少，且在70 d内的减少速度一直慢于CK，这使其棉花幼苗体内的14C放射性活度低于CK；SRD包衣种子在出苗后30 d内的株高一直高于CK，0～10 d的株高日增量大于CK，10～20 d与CK相当，20～30 d又大于CK。【结论】SRD具有缓释性能，且呈非匀速释放，这有利于延长缩节安的有效作用期、减少棉田用工、并提高棉花化控技术的标准化水平。

English. [ Objective ] This research was conducted to examine the release characteristics of slow-release mepiquat chloride （SRD）, which is encapsulated by crosslink modified starch, from surface of cotton seeds in water and soil. [Method] Water dissolution, soil leaching, isotope-labeled （. 4C-mepiquat chloride） and biological assay were used in this research. [Result] The dynamics of mepiquat chloride release of SRD in water was a S-type curve. The period for complete dissolution of mepiquat chloride of SRD was about 15 nin, which is 10 min longer than that of control （substituting crosslink modified starch with water）. The cumulative mepiquat chloride release rate of SRD in water in 1.5, 5 and 10 min was equal to 40.3%, 24.8% and 64.0% of control, respectively. The dynamics of mepiquat chloride release of SRD in soil was a parabola, which resulted from the joint action of release and degradation. The highest value of cumulative mepiquat chloride release rate of SRD （appearing in the time when release rate is equal to degradation rate） was less than 1/3 of that of control and appears 10 d later than the latter. The period for SRD existing in soil could reach up to more than 50 d and increased more than two-fold when compared with control. The . 4C-labeled SRD coated aroundcotton seeds decreased in non-constant speed in soil, and the decreasing speed of SRD was always slower than that of control, which resulted in fewer . C radioactivity in SRD-treated seedlings relative to control. The plant height of SRD-treated seedlings was higher than that of control all along during 30 d period after emergence, and its plant height increment per day was higher than control from 0 to 10 d after emergence, but equal to control from 10 to 20 d, from 20 to 30 d, higher than control again. [Conclusion] The evidence in present study demonstrated the slow release behaviour of mepiquat chloride within starch matrices, and indicated that this type of SRD release mepiquat chloride in a non-constant speed mode. SRD application is beneficial to prolonging the duration of effective action of mepiquat chloride, reducing the labour time for spraying mepiquat chloride in cotton field and enhancing the standardization level of mepiquat chloride chemical manipulation in cotton production.