Screening Of Efficient Herbicides In Oat Field And Its Effects On Oat And Soil Safety

The field experiment was carried out at the semi-arid regions of the Loess Plateau, Gansu Province, from 2011 to 2012, the rules were screened the suitable herbicides in field of husk oat (Avena sativa L.) including Longyan3 and naked oat (Avena nuda L.) as Baiyan2, and combined with the indexes measurement in the laboratory to research the effects of different herbicides with different concentrations on weed control performance and the safety, and yield, quality and physiological characteristics of oats, which aims to make a further study on the regulation effects of micro-ecological processes in different periods after application of herbicides, and thus provide the reference to the internal relation among soil microbes, soil enzymes and soil respiration intensity under herbicides, then set up the comprehensive evaluation model of indexes in three levels on weeds, oats and soil under the impact of herbicides. The main results were as follows:(1) The weed community in oat plots could make a 2 level damage with Lambsquarters, Black bindweed and Ivy glorybind as priority, and it could represent the weed distribution of semi arid zone of northwest China, this condition was necessary to control with chemical herbicides.(2) 13 kinds of herbicides had a significant impact on weed control effects and oats yields. Three treatments which were post-emergence application herbicides as Bromoxynil octanoate plus MCPA-sodium (BOMS) and Flumetsulam plus Florasulam(FLF), and method with manual weeding had higher weed control efficacy which was more than 80%, the hay yield and kernel yield of BOMS and FLF were the highest up to 10739.0kg·hm-2and 3238.3 kg·hm-2, and they were increased with 27.74% and 20.90% in average comparing with the control separately, and higher than the manual weeding. In addition, both pre-sowing application herbicide which was Butralin and pro-emergence herbicides S-metolachlor had better weed control effect. The weed control was less than 50% of Trifluralin and Fluoroglycofen with soil treatments, and the emergence and growth of oats has been suppressed, and two treatments could also cause twisted stalk, leaf spot and other injuries to seedling oats, 2,4-D butylate may increased shelled rates of naked oats.Herbicides affected grain yield mainly through affecting yield components. The indexes such as plant height, ear length and 1000-kernel weight were less effects, but there were significant changes of ear number, kernels number, hay yield and kernel yield. The results of experiment in the second year showed that the effect sequences of weed control and yield increasing for four excellent herbicides were as follow:F3(270 ml·hm-2 FLF)>M3 (2025 ml·hm-2 BOMS)>M2(1350 ml·hm-2 BOMS)>S3(1350 ml·hm-2 S-metolachlor)>F2(180 ml·hm-2 FLF)。Overall, the effects of leaf treatment herbicides were better than soil treatment herbicides.(3) The studies on the quality, physiological and biochemical characteristics of oats by using optimal herbicides such as BOMS and FLF which were screened through two years field experiment showed that:①Herbicides inhibited with chlorophyll content (SPAD), net photosynthetic rate (Pn), transpiration rate (Tr), and stomatal conductance (Gs) of oats. Instead, the intercellular CO2 concentration (Ci) and water use efficiency (WUE) were increased, and antioxidant metabolism enzymes activities in oat leaves were higher than that of the controls under the herbicides stress during the early growth stage. POD and SOD activities had similar trend, which were increased firstly and then decreased during the oat growth periods. CAT activity was relatively stable. MDA content was increased gradually with the time lapse, and reached the maximum at flowering stage. Enzymes activities were subject to different degrees of inhibition with the increase of herbicide concentrations, but MDA content was increased. In addition, there were different photosynthetic responses of herbicides on different oat varieties. The photosynthetic index was sensitive to high concentration of BOMS in different growth period of husk oat, while naked oats’s was sensitive to high concentration of FLF, and FLF had small impact on various antioxidant metabolism enzymes.(2)The content of crude protein, crude ash and mineral elements such as Ca and P in forage and kernel of oats in medium and lower concentrations were promoted, most of treatments were no significant difference in content of neutral detergent fiber and acid detergent fiber, relative feed value compared with the control. While the crude fat content, digestibility dry matter and relative feed value were suppressed by using higher concentration herbicides. Different herbicides in different concentrations had different effects on oat quality, and the content of crude protein and crude ash of oat hay and grain in M2 (1350 ml·hm-2 BOMS) was increased 6.3% and 4.5% in average respectively compared to controls, and this treatment had better quality with higher mineral content and relative forage value.(4) A series of studies based on soil microbial activity and metabolism under applying two kinds of herbicides showed that:①Herbicides on microbial population numbers, enzyme activity and soil respiration intensity varied with the different species of microbe and enzymes and concentrations of herbicides. The ratio of soil bacteria, fungal and actinomycetes population numbers treated with the herbicides were changed, and it showed that bacteria>actinomycetes>fungal. The degree and duration of inhibition of high concentration herbicide treatments exceeded the low concentration treatments. The microbial population numbers treated with herbicide in soil decreased compared with the control, and fungal had the biggest decline, followed by bacteria, the actinomycetes had less sensitivity to herbicide. The soil hydrogen peroxidase activity showed inhibited, but then it increased later by BOMS and FLF under each concentration. The effect of herbicide on the soil invertase activity was inhibited at first, and then it returned to normal with the prolongation of time. Both the effects of herbicide on the alkaline phosphate enzyme activity and urease activities in soil showed the trend of stimulation-inhibition-stimulation, soil respiration intensity had the same regulation, and the trend was increased with the increase of concentration.(2)Through the principal component analysis on soil indexes, we found that there were certain correlations among microbial population numbers, enzyme activity and soil respiration intensity, and the effect of soil microbial population on soil fertility was greatest. The sequence of composite scores of treatments were as follow: M1(BOMS 675 ml-hm-2)>M2(BOMS 1350 ml·hm-2)>F1 (FLF 90 ml·hm-2)>Control>F2 (FLF 180 ml·hm-2)>M3(BOMS 2025 ml·hm-2)>F3 (FLF270 ml·hm-2). While the influence of herbicide to indexes of soil ecosystem recovered after 40 days, and high concentration of herbicide would also lead to the change of soil microbial community, and cause potential harm to the soil fertility and growth of oat.(5) By using principal component analysis to evaluate several aspects such as weed control effect, oat yield, quality, physiological characteristics and soil microorganism quantity, soil enzyme activity and soil respiration metabolism in spraying leaf herbicides as different concentrations of BOMS and FLF comprehensively, and the model was set up as follows:the comprehensive of F= 0.596Z1+0.214Z2+0.113Z3. Cumulative contribution rate of first three principal component factors has been reached 92.277%,the first principal component factor represented for indexes of weed control and oat production, the second principal component represented for micro-ecological processes and activities, the third principal component represents factor as physical and nutritional characteristics of oats. Finally, it was known that BOMS with concentration of 1350 ml·hm-2 applying in oats could have efficient and safe benefits as its highest value of comprehensive evaluation.