Herbicidal Activity Of Pyroligneous Acids And Its Effect On Soil PH And Moisture Content

In order to meet consumers’ demand for organic products,there is an urgent need for effective,natural and environmental friendly herbicides.In this paper,three kinds of biomass dry distillation acid samples: bamboo vinegar(BV),wood vinegar(WV)and Straw Vinegar(SV)were distilled under reduced pressure.The components of their distillates were analyzed by gas chromatography-mass spectrometry(GC-MS),and the field weeding experiment was carried out by diluting several times on the basis of sample stock solution,It lays a scientific foundation for the future application of biomass retort acid in biological herbicides or vinegar herbicides.In order to evaluate whether the long-term use of biomass retort acid will lead to soil acidification,this thesis further conducted a biomass retort acid soil test to test whether the continuous application of high-dose biomass retort acid will have an impact on soil pH and field water holding soil water retention.The three biomass retort acids were compared with acetic acid and sulfuric acid,To evaluate the effect of weeding practices on;The specific experimental process is as follows:1.Three kinds of biomass dry distillation acid samples from different sources were distilled under reduced pressure.The distillates were mainly composed of acetic acid and other organic acids.Then the residual distillates were analyzed by GC-MS.it was found that phenols were the main components of the three samples,most of which were phenol and its derivatives,accounting for 63% of the total amount of bamboo vinegar,69.9% of wood vinegar and 60.1% of Straw Vinegar respectively,These substances may have the effect of increasing the herbicidal activity of biomass retort acid.2.Greenhouse tests were conducted using four indicative plants: wheat(Triticum sativa),radish(Raphanus sativus),cucumber(Cucumus sativus),and Echinochloa crusgalli(L.)Beauv.Greenhouse tests showed that the efficacy of PAs and acetic acid(AA)to control four test plants increased with increasing PAs concentration.The inhibition rates of three tested PAs(BV(0.6～9.2% AA+(0.3～5.0% tar),WV(0.7～5.3% AA+0.5～7.5% tar),and SV(0.5～8.7%AA+0.4～7.0% tar)gave inhibition rates of 55～98%,28～97%,and 44～86%,respectively.3.The results of field herbicidal activity test showed that the three biomass retort acids had good herbicidal effect in 14 days,and the effect was faster than that of the control group by 0.2%glufosinate.Among them,straw vinegar had the best control effect on E.crusgalli,Eleusine indica(L.)Gaertn,Alternanthera philoxeroides(Mart.)Griseb,and Conyza canadensis(L.)Cronq,the control effect of the four tested weeds can reach 93%,which is equivalent to that of 0.2%glufosinate.The field effects of PAs against four weeds were enhanced with increasing concentrations and time after spraying(1 to 14 days).Their control effects against E.crusgalli,E.indica,A.philoxeroides,and C.canadensis were 4～93%,6～91%,18～97%,and 27～97%,respectively.The synergistic effect of the four PAs were ≥0.5 times higher than AA.4.We found that after 1～3 days of spraying with all 5 kinds of acid,the soil pH was not immediately reduced,but from 3 days after application onward it was reduced by a maximum of1.54～1.75,which showed that the soil had some buffering capacity.Over time,the pH began to return to the water control pH value,which showed that the soil also had good restorative capacity.After the second and third times of spraying,the pH change measured showed no cumulative effect,which demonstrated that the soil had adaptive capacity.We accidentally found that bamboo vinegar could improve the soil pH by a maximum of 0.65～1.02,while the other four acids reduced its pH.Bamboo vinegar was found to contain the 6 compounds while wood and straw vinegar contained none of these compounds.These compounds may be a new potential reagent(s)for improving the pH.Three soil sample processing methods tested for determining pH,including the moist soil test,oven-dry soil test and air-dried soil test,all produced extremely and significantly different pH values.Five acids were unable to significantly improve the water holding capacity of the soil.Therefore,based on pH and moisture content,PAS and acetic acid as herbicides have no effects on soil health as herbicides.These results will help to determine the potential of PAs to be developed as non-selective herbicides to control weeds in organic farming.