Effects Of Two Kinds Of Phenoxy Acid Herbicides On Physiological Characteristics And Security Of Millet

Millet was the forage dual-purpose type drought-resistance crops in northern China, which owned the character of strong stress resistance, rich nutrition and so on; Due to weak seedlings and grain, disease weed was the main limited factor influencing the high and stable yield of millet, millet output reduction reached to about 20% in China due to grass harm, and even to die when it was serious. Currently, chemical weeding is the most practical method of weeding in China, while herbicides used widely in the large area grain field are few. Therefore, in order to examine the effects of phenoxy acid herbicides such as 2,4-D butyl and MPCA on physiological characteristics and security of Millet, and screening herbicides and optimum concentration on millet from samples, both safe and efficient. In this experiment, Zhangzagu 10 and Jingu 21 were used as test material to determine the effects on agronomic characteristic, photosynthetic index, chlorophyll fluorescence parameters, protection enzyme activity, MDA content and yield in millet by spraying different dose of 2,4-D butyl and MPCA on the stem and leaf at the 3-5 leaf stage in millet, manual weeding (CKo) and reserving grass (CK1) were set. The main experiments results were as follows:The millet plant height and leaf area were restrained by two kinds of phenoxy acid herbicides:the millet plant height and leaf area were significantly reduced after 5,15 days sprayed 2,4-D butyl, the minimum was reached at T4 dose. After 25 days, the impact of herbicides on millet height and leaf area eased, and the leaf area of T1 treatment is greater than the CK1 treatment, while which is still significant difference between CKo. The impact of MCPA on millet plant height and leaves was slightly less than 2, 4-D butyl, the millet plant height and leaf area were inhibited significantly after 5,15 days, and with the increase of dose the millet plant height and leaf area were gradually decreased, the minimum was reached at T4 dose.25 days after, the height of Millet of T1 dose was greater than CK1, the leaf areas of Zhangza 10 after each dose of herbicides treating were both larger than CK1, while the leaf areas of Jingu 21 after T1 and T2 dose treatments were greater than CK1, the leaf areas of T3 and T4 dose treatments were still less than CK1.The photosynthetic pigment content of two varieties of millet leaves were reduced by two kinds of phenoxy acid herbicides, chlorophyll a and chlorophyll b were reduced mainly, and carotenoids was less affected; The impact of two varieties of millet on photosynthetic pigment content of Zhangza 10 was greatest in the 15 days, however, The impact on Jingu21 was seriously inhibited in the 5 days. What's more, the photosynthetic pigment content of two varieties of millet leaves were recoveried a certain degree with the growth progress of millet.The photosynthetic rate (Pn), stomatal conductance (Gs) and stomatal limitation value (Ls) of millet leaves were showed lower than CKo and CK1, while the internal CO2 concentration (Ci) was higher than CKo and CK1, after two kinds of phenoxy acid herbicides were sprayed about 5 days. The influence of herbicide stress on photosynthetic parameters of millets was eased after 25 days, the Pn, Gs and Ls of millet leaves after treated by T1 and T4 were higher than CKi, while were still below CKo; Ci is less than CKi but still higher than CKo. The non-stomatal factor probably was the main reason of the decline of photosynthetic rate.With the increase of spraying dosage of three kinds of herbicides, the maximal photochemical efficiency of millet leaves (Fv/Fm), the actual photochemical efficiency (PSII) and photochemical quenching (qP) showed depressed significantly, instead, non-photochemical quenching (NPQ) increased and showed a certain dose-effect relationship, so the results indicated that under herbicide stress conditions, PS II complex of millet leaf was subject to the damage, the opening degree of PS II reaction center was reduced, also the activity was weakened, photochemical efficiency was low, the light energy absorbed was released more in the form of heat dissipation, and maybe the increase of NPQ could be seen a kind of self-adjustment mechanism of millet leaves response on herbicide stress.Under different treatments of the herbicide, SOD activity, POD activity and MDA content of the millet leaf were elevated, but membrane lipid peroxidation level was aggravated. Moreover, most POD activeness, SOD activeness and MDA content showed the trend that increased with herbicide spraying dosage increased at first and then decreased in the earlier stage of spraying the herbicide. After spraying 25 days, almost the POD activeness, SOD activeness and MDA content of Zhangza 10 and Jingu21 under the high-dose treatment still maintained higher level and with the significant difference between CKo, which showed that in the drug 25 days or so after that, the effect of high-doses herbicide on the POD activeness, SOD activeness and MDA content of millets has not completely alleviated.The yield of two varieties of millet both showed the trend that increased firstly and then decreased with the increase of the dose, and the minimum was reached at T3 dose, the yield of Zhangza 10 and Jingu21 were reduced 5.94% and 6.72% after sprayed 2,4-D butyl compared with CKo, increased 57.72% and 54.75% after sprayed 2,4-D butyl compared with CK1; The yield of Zhangza 10 and Jingu 21 were increased 62.99% and 61.35% after sprayed MPCA compared with CK1.All the factors indicated that 750 ml/hm2 of 2,4-D butyl and 1800 g/hm2 of MCPA were the most appropriate concentration; The security of MCPA on millet was better, while 2,4-D butyl was poor.