Study On Safety Of Seven Herbicides To Water Direct-seeding Rice

With the increase of rural labor cost and the development of modern agricultural science and technology,the efficient,low-cost rice direct seeding cultivation technique is widely accepted without promotion in Heilongjiang Province,and the scale of rice cultivation has been expanding year by year.However,the weed problem is highlighted in the water direct seeding fields.Whether the weeds can be effectively controlled is directly related to the success of water direct seeding.Most of the existing paddy herbicides are only applicable for the transplanting paddy fields,while the usage of them in the water direct seeding field is not improved yet.The phenomenon of serious reduction or even crop failure is common in the production of direct seeding rice due to the improper selection of herbicides or the inappropriate application time and methods,and it causes heavy economic losses for the growers.Therefore,it is urgent to study the safety of herbicides for the water direct seeding rice to reduce the losses caused by improper use of herbicides.In this paper,the effects of seven herbicides,oxadiazon,oxadiargyl,pyriminobac-methyl,penoxsulam,propyrisulfuron,pyribenzoxim,metamifop,on the direct seeding rice morphology,the physiological and biochemical indexes and the yield was studied by numerous pot experiments.Moreover,the influence factors of herbicide damages were explored in the aspects of rice variety,leaf age,environment(flooding),herbicide application period and dosage.The main results were as follows:1.Effects of pre-sowing soil treatment with oxadiazon and oxadiargyl on the safety of direct seeding rice.The safety of oxadiazon and oxadiargyl for rice was studied in four aspects including herbicide application period,rice variety,flooding environment and dosage.The results show:(1)After the application of oxadiazon and oxadiargyl,the early sowing caused the more serious injury,the lower rice emergence rate,the delayed seedling stage,and the short plants.The application of oxadiazon 225 g a.i./hm~2 4 ~ 6 days before sowing and the application of oxadiargyl 6g a.i./hm~2 6 days before sowing were safe for the emergence and growth of rice.(2)Oxadiazon and oxadiargyl had certain inhibitory effects on the plant height and fresh weight of the 10 tested rice varieties at seedling stage,and the differences of the effects of the same herbicide on different rice varieties were significant.The inhibitory rate of oxadiazon on plant height and fresh weight was relatively high for Songjing 9,Longjing 28 and Longjing 24,but lower for Dongnong 425 and Longdao 6,while that of oxadiargyl on plant height and fresh weight was relatively high for Dongnong 427,Longjing 28 and Longjing 24,but lower for Dongnong 425,Kendao 12 and Kongyu 131.The inhibitory effects of these two herbicides on rice gradually recovered with the growth of rice,which took approximately 18 days.The safety of oxadiazon for 10 rice varieties was higher than that of oxadiargyl.(3)Flooding stress significantly increased the inhibitory effects of oxadiazon and oxadiargyl on plant height and fresh weight of rice,and extended the time required for recovery of rice seedling growth.The herbicide damage increased with the prolongation of flooding time.(4)7 to 14 days after sowing was the sensitive period of plant height growth of rice to oxadiazon and oxadiargyl.The plant height growth with the treatment of 12.5% oxadiazon EC 225,337.5 g a.i./hm~2 and 80% oxadiargyl wp,6g a.i./hm~2 returned to normal after 18 days after sowing,and the growth and yield of rice were not obviously affected.However,the treatment of 12.5% oxadiazon EC,450 g a.i./hm~2 and 80% oxadiargyl wp 9,12 g a.i./hm~2 had significant effects on the physiological and biochemical indexes,such as malondialdehyde content,chlorophyll content,peroxidase activity,catalase activity,of the rice leaves,which causing the severe physiological disorder.Consequently,the rice plant height growth was at a disadvantage,the tiller quality decreased,the effective panicle number,the number of grains per panicle and the seed setting rate were significantly reduced,and finally it resulted the serious reduction.2.Effects of post-sowing soil treatment with pyriminobac-methyl,penoxsulam,propyrisulfuron on the safety of direct seeding rice.For three herbicides,pyriminobac-methyl,penoxsulam and propyrisulfuron,when used for the post-sowing soil treatment,their effects on the seedling growth,tiller and yield of direct seeding rice were studied under the different dosages.The results show: pyriminobac-methyl was safe for the growth and development of rice at the dosage of 90 g a.i./hm~2,but had significant inhibitory effect on the plant height,tiller and root growth of rice at the dosage of 120 g a.i./hm~2 which resulting an obvious reduction.Penoxsulam did not show significant effect on the growth and development of rice at the dosage of 60 g a.i./hm~2,with the inhibition rate of no more than 10% for the rice morphological indexes,such as the emergence rate,plant height,fresh weight of stem and leaf,root length,root fresh weight,tiller number and so on,and there was no noticeable difference of the final yield in comparison.However,a significant inhibitory effect on the rice seedling quality and yield was observed at the dosage of more than 90 g a.i./hm~2,which indicated a poor safety.Likewise,propyrisulfuron had no significant effect on the growth and development of rice at the dosage of 50 g a.i./hm~2,but the poor safety was revealed after the dosage exceeded 100 g a.i./hm~2 when the rice growth was inhibited,the fertility was delayed,and consequently the reduction occurred.These three herbicides had no significant effect on 1000-grain weight of rice.Hence,the main reason for the rice yield reduction was the decrease of the effective panicle number,the number of grains per panicle and the seed setting rate.In a summary,the safety order of the three herbicides for water direct seeding rice was pyriminobac-methyl>penoxsulam>propyrisulfuron.3.Effects of stem and leaf treatment with pyribenzoxim,propyrisulfuron,metamifop on the safety of direct seeding rice.The effects of the application dosages and periods of pyribenzoxim,propyrisulfuron,metamifop on the plant height growth,tiller and yield of rice were explored.The results show: the effect of the treatment with 5% pyribenzoxim EC 60,80 g a.i./hm~2 on plant height,tiller and yield of rice was significantly higher than that of 40 g a.i./hm~2.Similarly,the effect of the treatment with 9.5% propyrisulfuron SC,100 g a.i./hm~2 on plant height,tiller and yield of rice was significantly higher than that of 50,75 g a.i./hm~2.In addition,the effect of the treatment with 10% metamifop EC,240 g a.i./hm~2 on plant height,tiller and yield of rice was significantly higher than that of 120,180 g a.i./hm~2.The three herbicides had higher safety when applied in 2.5-3.0 leaf stage than in 1.5-2.0 leaf stage of rice,and pyribenzoxim was inappropriate to be used in 1.5-2.0 leaf stage.The safety order of the three herbicides was metamifop>propyrisulfuron>pyribenzoxim.