Effect Of Herbicide On Nitrification In Soil

Nitrogen(N)fertilizers applying is a main way to solve soil nitrogen deficiency,which plays a key role in improving crop yield and crop qual-ity.To meet the needs of population increasing,the amount of N fertilizrs applied in China has been increasing year by year which lead to a harmful effect on soil natural environment.At present,the amount of N fertilizers applied per unit area in China has far exceeded the international upper limit standard(225kg/ha),but the utilization rate of nitrogen fertilizer is relatively low.It was reported that the utilization rate of N fertilizer in China is less than 30%,which is far below that in foreign countries.To reduce N fertilizer loss and increase its use efficiency,the influencing factors of N conversion process have become a research hotspot.Nitrification take an important role in N use efficiency.There are many studies focus on the relationship between soil nitrification and N fertiliz-ers utilization rate at home and abroad.And then,many inhibitors had been used to decrease nitrification rate,such as nitrification inhibitors,urease inhibitors,and so on.Those material inhibitted the activity of mi-croorganisms in the soil,thereby inhibiting the soil nitrification,reducing N loss from soil and improving N fertilizer utilization ratae.The results show that herbicide has a certain inhibitory effect on soil nitrification.However,there is few studies focus on the effects of herbicides on nitri-fication in soil.To understand the relationship between herbicides and ni-trification in soil,eight incubation experiments were conductedin this study.Jiangxi’s vegetable fields,1、To compare the effects of different herbicide types and doses on nitrification in soil and response of different soils to herbicides,we col-lected red soil in dry land of Fujian and Henan fluvo-aquic soil.The re-sults showed that the inhibitory effects of 8 different herbicide types on soil nitrification were quite different under 10 mg/kg soil.In brief,2,4-Dichloroph-enoxyacetic acid butyl ester(2,4-D)has the most inhibi-tory effect among all of them,and followed by fenoxaprop and tribenuron methyl.While,the herbicides of paraquat,acetochlor,isoproturon,para-quat and atrazine were no obvious effect on soil nitrification.Different soils have different responses to herbicides.The results of culturing experiments on Henan fluvo-aquic soil and red soil in dry land of Fujian show that,the nitration rate of Henan fluvo-aquic soil is much faster than that of dryland red soil in Fujian.The inhibitory effects of acetochlor,fenoxaprop and 2,4-D on the nitrification of the two soils were significantly different in the dosage of 10 mg/kg soil.The application of 2,4-D and acetochlor in the Henan fluvo-aquic soil showed a slight inhibi-tory effect on the nitrification activity in soil,and the fenoxaprop effect was not obvious.However,the inhibitory effect of 2,4-D has an obvious inhibitory effects on red soil of Fujian dryland,followed by fenoxa-prop.However,acetochlor has not obvious inhitbition.In a word,2,4-D has an obvious inhibitory effect on nitrification in red soil,but it has poor in-hibition on nitrification in Henan fluvo-aquic soil.The inhibitory effect of herbicides on soil nitrification increases with the amount of usage.2,4-D inhitbited nitrification in fluvo-aquic and red soil under the rates of 5-100 mg/kg soil.There was a positive relationship between the rates of 2,4-D and nitrificationin rates in soil.The inhibition time of nitrification in fluvo-aquic soil was only 3 to 9 days,while,it was longer in red soil,which was more than one month under 50 and 100 mg/kg soil.2、In order to fully investigate the inhibition effect of herbicide on soil nitrification,in this study,the commonly used nitrification inhibitor DCD(dicyandiamide)was used as a control to compare the inhibitory ef-fects of commonly used nitrification inhibitors with 2,4-D.The results showed that the application of 2,4-D and DCD at 10 mg/kg soil and DCD at 6 mg/kg soil all have a certain inhibitory effect on soil nitrification in the same soil(red soil of Fujian dryland).However,the inhibitory effects of 2,4-D and DCD were similar,followed by that of fenoxaprop.The results of culture experiments of 5 soils showed that,the applica-tion of DCD with 10 mg/kg soil in 5 soils could effectively inhibit soil nitrification,and the inhibition time of nitrification process in Henan flu-vo-aquic soil reached 27 days,and 34 days in the red soil in vegetable land of Jiangxi and the calcic cambisols of Shaanxi was 34 days.While slow nitrification rates was observated in red soil in dry land of Fujian and lime concretion black soil in Henan,the suppression time is more than 58 days.To compared with DCD,the inhibitory effect of 2,4-D at 10 mg/kg soil on the nitrification in five soils were quite different.Among them,the inhibitory effects were more obvious in the red soil and lime concretion black soil than in other soil,and they had the same effect as the DCD treatment.The suppression time in red soil and calcic cambisols soil were about 11 days and about one week in Henan fluvo-aquic soil.To further verify the nitrification inhibition effect of 2,4-D five kinds of nitrification inhibitors including DCD,Nitrapyrin,DMPP,2-amino-4-chloro-6-methylpyrimidineand and thiourea were selected as control treatments.The results showed that,2,4-D at 10 mg/kg soil and DCD at 10 mg/kg soil,Nitrapyrin at 2 mg/kg soil,DMPP at 2mg/kg soil,and 2-amino-4-chloro-6-methylpyrimidineand at 2 mg/kg soil and thiou-rea at 4 mg/kg soil had inhibitory effects on soil nitrification,but there were significant differences among them.In brief,2,4-D,DCD,Nitrapyrin and DMPP had obvious effect on soil nitrification,followed by 2-amino-4-chloro-6-methylpyrimidineand and thiourea.From the above,herbicide 2,4-D could effectively inhibit soil nitrifi-cation,in addition to inhibiting the growth of weeds,it also has the effect of reducing soil nitrification rate..However,2,4-D had different inhibition effect on nitrification in different soil types.