Abstract:Effective weed control is an important measure to reduce the risk of stable yields in direct seeded rice, and pre-sowing soil flame treatment is an effective means of suppressing weed seed germination prior to sowing by non-chemical methods. In order to clarify the law of the influence of the temperature field on the germination rate of weed seeds in soil flame treatment, the structural parameters of the header pipe in the fuel diversion component were investigated by using numerical simulation. The results of the numerical simulation and validation test showed that when the inner diameter of the header pipe d was 20mm and the gas input flow rates were 1.0~3.5m3/h, the maximum flow deviation rates Δη were within 3.0%, more uniform gas flow distribution between outlet branches. Based on the numerical simulation results, a flame combustion device was designed to study the effects of six types of LPG fuels with input flow rates (1.0~3.5m3/h) on the flame height and the flame temperature distribution, and a full-factorial test was carried out by using the tractor traveling speed, fuel input flow rate, and soil depth as test factors, and the effect of temperature field on the germination pattern of weed seeds was studied using common weed seeds among rice fields. The test results showed that the flame height and the maximum value of flame temperature were both increased with the increase of fuel input flow rates under normal temperature and pressure operating environment; when the tractor traveled at a speed of 2.36km/h and the fuel input flow rates were 2.5m3/h, 3.0m3/h and 3.5m3/h, the soil temperature could reach 92.83℃, 116.58℃ and 156.83℃, respectively; compared with the unflamed treatment control group, when the soil temperature reached 92.83℃, the germination rate of seeds of Leptochloa chinensis (L) Nees and Cyperus difformis were significantly reduced at the significance level of α=0.05, but the germination rate of seeds of Digitaria sanguinalis and Eclipta prostrata were not significantly affected, and the germination rate of seeds of the four weeds were significantly reduced when the soil temperature reached 116.58℃ and 156.83℃. When the soil temperature reached 156.83℃, the germination of seeds of four weed species Digitaria sanguinalis, Eclipta prostrata, Leptochloa chinensis (L.) Nees and Cyperus difformis-were decreased by 94.82%, 87.81%, 86.54% and 84.05%, respectively. The results of the field test showed that the soil flame treatments had significant germination inhibiting effects on Echinochloa crusgalli, Digitaria sanguinalis, Eclipta prostrata, and Cyperus difformis, and their relative weed control rates Y was greater than or equal to 80.00%.
