Influence Of Three Long Residue Herbicides On Soybean Rhizosphere Environment And Studies On In-Situ Bioremediation

Soybean is not only an important food crop in china, but also a characteristic oil crop inHeilongjiang province. Soybean yield plays an important role in Chinese national economydevelopment and people's daily life. Crop yield and quality had been increased as using chemicalweed control technology, at the same time it also led to a series of environmental problems.Development and application of some kinds of super-high efficient herbicides such as sulfonylurea,imidazolinones occupied the herbicide market after the 80's in 20 centuries. Imazethapyr,chlorimuron-ethyl and clomazone were the representative sorts and were widely applied in springsoybean produce areas in China. Such kinds of long residue herbicides applied in soybean field didnot only injure the succeeding susceptible crops, but also destroyed the environment of soybeanrhizosphere deeply. Studies on the influence of Imazethapyr, chlorimuron-ethyl and clomazone onsoybean rhizosphere will nail down effect of long residue herbicides on soybean rhizosphereenvironment, and make theory foundation regulating the environment of soybean rhizosphere toaccelerate nutritive material translation and its absorption through measure, so as to realize highyield and quality of soybean. This paper studied the influence of three long residue herbicidesImazethapyr, chlorimuron-ethyl and clomazone on soybean rhizosphere environmnent and its in-situbioremediation for the destroyed environment of soybean rhizesphere by the long residueherbicides. The results of the experiment were as follows:1. After applying imazethapyr, the bacteria population increased significantly, the fungi'sincreased in short time, and then inhibited, and the actinomycetes' also increased in short time, andgradually recovered to the normal level.After applying chlorimuron-ethyl, The bacteria population decreased significantly, and thefungi's increased significantly, the actinomycetes' increased in a short time, but subsequentlydecreased in soybean rhizesphere soil.The herbicide clomazone stimulated bacteria of soybean rhizesphere for a long time, and themore of application dose, the greater of the stimulative effects. If clomazone content in soil washigher, the fungi number increased in short period and subsequently decreased. Under the normalapplication dose 2250g/hm~2, the fungi decreased, but the actinomycetes increased under higher application dose.2. After applying imazethapyr, chlorimuron-ethyl, the amount, fresh and dry weight ofsoybean nodule distinctly decreased. The more the application dose was, the bigger the decreasedproportion was. There was not influence on soybean nodule when clomazone application dose was2250g/hm~2, but the amount, fresh and dry weight of soybean nodule distinctly decreased atclomazone 2500g/hm~2 and 2750g/hm~2.3. The influence of imazethapyr on three soil enzymes showed that soil urease activity wasseriously inhibited and this inhibition increased as application dose added, but the activityrecovered to normal level after 35 days of application. Soil cellulase activity was distinctlyadvanced, subsequently recovered to normal level. Soil phosphatase activity showed higher activityin a short time, but subsequently was inhibited in a long time.The influence of chlorimuron-ethyl on three soil enzymes are as follows: Soil urease activitywas seriously inhibited, cellulase activity was distinctly advanced; phosphatase activity wasdistinctly advanced also in a short time, but rapidly declined significantly.The influence of clomazone on three soil enzymes are as follows: Soil urease activity wasinhibited at first and then advanced. Cellulase activity was advanced significantly in 28 days, andthen gradually recovered. Phosphatase activity was advanced significantly in 21 days, butsubsequently recovered to the normal.4. Initially, There was no degradation effect, the lag phase was 12 hours, henceforthdegradation microorganism IZP-1 began to rapidly degrade imazethapyr, and the degradation ratewas over 90% up to 72 hours. The lag phase was postponed 24 hours, when adding carbonresources such as glucose, lactose, cane sugar, mult sugar and sodium citrate to the culture medium,but the final degradation effect was not influenced. The optimal temperature was 25℃and pHacidity was 5-7 in degradation.There was not obvious lag phrase during the course of degradation microorganism YW-1degrading the herbicide chlorimuron-ethyl, and the degradation speed was stable. To 36 hours, thedegradation ratio was 40%, and the residual ratio was zero to 96 hours. The extra carbon sourcesdidn't influence on degradation effect. 30℃and pHS-7 is the optical growth condition of YW-1.The compound degradation microorganism CZ-1+CZ-2 could completely degrade clomazone,and there was not obvious lag phrase. In 36 hours, the degradation ratio was 90%, and clomazonewas completely degraded in 48 hours. Adding carbon sources, the lag phrase of degradation was 36hours, and subsequently clomazone was rapidly degraded. The optical degradation condition was25℃-30℃and pH8-9.5. Degradation microorganism IZP-1 could partly bio-remedy the influence of imazethapyr onthe amount, fresh and dry weight of soybean nodule. The lower application dose of imazethapyrwas, the better the in-situ bioremediation effect was received.Degradation microorganism YW-1 could partly bio-remedy the influence of chlorimuron-ethylon the amount, fresh and dry weight of soybean nodule. The compound degradation microorganism CZ-1+CZ-2 could completely bio-remedy theinfluence ofclomazone on the amount, fresh and dry weight of soybean nodule.6. Degradation microorganism IZP-1 could weaken the simulative effect of imazethapyr onfungi, the fungi population obviously decreased initially, and began to increase up to mid-July. Theactinomycetes population increased continually and was higher than the control. IZP-1 could partlybio-remedy the influence of imazethapyr on fungi and actinomycetes population.After applying degradation microorganism YW-1, the fungi population decreased, and higherthan the control. The actinomycetes population increased and accelerated their growth andpropagation. YW-1 could partly bio-remedy the population of fungi and actinomycetes.The compound degradation microorganism CZ-1+CZ-2 could decreased the fungi populationthat increased after applying clomazone, and was higher than the control, namely the in-situbioremediation was not complete. The compound degradation microorganism CZ-1+CZ-2 madeactinomycetes population change more stably and could bio-remedy actinomycetes populationpartly.7. Degradation microorganism IZP-1 could completely bio-remedy the influence ofimazethapyr on soil urease, cellulase and phosphatase activity, and there was no side effect whenimazethapyr didn't influence on the three enzymes.Degradation microorganism YW-1 could partly bioremedy the effect of chlorimuron-ethyl onsoil urease, cellulase and phosphatase activity, and there was no side effect.The compound degradation microorganism CZ-1+CZ-2 could only partly but not completelybio-remedy the influence of clomazone on soil urease, cellulase and phosphatase activity also.The influence of imazethapyr, chlorimuron-ethyl and clomazone on soil urease, cellulase andphosphatase activity could recover naturally before Mid-July, namely the in-situ bioremediation ofthree long residue herbicides degradation microorganism could react effectively before this time.