| Weed invasion in wheat field has become one of the restrictive factors for obtaining high and stable yield of wheat. The loss of wheat yield caused by weed invasion has been up to10%of the total wheat yield in the world. It has become an important issue to our government for agricultural development that how to use herbicides legitimately and to improve the use efficiency of agricultural resources. Herbicides would inevitably affect grain yield and quality of wheat, deposit in wheat grains, plants, and soil, and cause potential or realistic harm to grain hygienic quality and field environment. So it is necessary to investigate the effects of herbicide application on grain yield and quality and physiological mechanism in wheat plants so as to provide a solid base for constructing a safe wheat producing system.The study was conducted on the Experimental Farm of Jiangsu Provincial Key Lab of Crop Genetics and Physiology of Yangzhou University from2008to2010to investigate the effects of tribenuron-methyl, fluroxypyr, isoproturon, puma super and chlorotoluron on weeds, grain yield and quality, leaf photo synthetic parameters of wheat plants, microbial population in soil, and residue in wheat plants and soil. The main results were as follows. 1. Controlling efficacy against wheat weedsThe efficacy of tribenuron-methyl, fluroxypyr, isoproturon, puma super and chlorotoluron against wheat weeds in the field of weak-gluten wheat Yangmai13plants were investigated. Fluroxypyr and tribenuron-methyl produced good weed efficacy on broad-leaf weeds. On the15th day after the spraying of the two herbicides at recommended dosage, the efficacy was higher than90%. However, these two herbicides had ineffective effects against grass family weeds. Puma super had good control effect on grass family weeds and the efficacy at the recommended dosage was about90%, while the efficacy against the broad-leaf weeds was ineffective. Isoproturon and chlorotoluron produced good efficacy against botybroad-leaf and grass family weeds. Compared with the spray in spring, better efficacy was observed in winter.2. Effect of herbicides on wheat grain yieldFive herbicides, including tribenuron-methyl, fluroxypyr, isoproturon, puma super and chlorotoluron, were used at different times at recommended dosage under two treatments of artificial dislodgement and natural conditions. The adverse and positive effects of herbicides on weak-gluten wheat Yangmai13and the relationship between these two effects were analyzed. Under the natural conditions, the spray of herbicides on Yangmai13increased wheat yield by4-20%. A positive correlation was observed between the yield-increasing effect and the efficacy of herbicides. In the treatments of artificial dislodgement, however, the grain yield of Yangmai13was decreased by4-30%. Under the natural conditions, herbicides had positive effects on the component of wheat yield (spike number, grain number, and grain weight). Under the artificial dislodgement conditions, however, negative effects on the component of wheat yield were detected. Of these five herbicides, fluroxypyr had the least negative effect on the yield component of Yangmai13, while isoproturon had the biggest negative effect. The spray of herbicides was not suggested when there was weed occurrence in the wheat field or the occurrence was not serious. However, if the occurrence was serious,20%fluroxypyr was suggested at the recommended dosage in winter and at an increased dosage less than2times of recommended dosage in spring. 3. Effect of herbicides on wheat grain qualityThe adverse and positive effects of herbicides on the grain quality of Yangmai13and the relationship between these two effects were also were analyzed using the same design as grain yield. Under natural conditions, the content of grain protein, wet gluten, and the value of sedimentation were increased when the herbicides was sprayed in either spring or winter, indicating that the grain quality of weak-gluten wheat Yangmai13was adversely affected although there was an increase in grain yield and weed control efficacy. Under the conditions of artificial dislodgement, the content of grain protein, wet gluten, and the value of sedimentation were decreased, indicating that the herbicides probably produced regulating effects on grain quality of weak-gluten wheat Yangmai13. Compared with winter, the spray of herbicides had less significant effects on the grain quality of Yangmai13in spring. Of the five herbicidies, puma super had the smallest negative effect on wheat grain quality, followed by fluroxypyr, tribenuron-methyl, isoproturon, and chlorotoluron.4. Effect of herbicides on physiological and biochemical parameter of wheat plantsEffects of five herbicides (tribenuron-methyl, fluroxypyr, isoproturon, puma super, and chlorotoluron) on physiological and biochemical parameters of weak-gluten wheat Yangmai13plants were studied. On the5th day after treatment (DAT), the SPAD readings and photo synthetic rates of plant leaves were significantly reduced by the application of the five herbicides. The maximum decline in photo synthetic rate (27%) was found on the treatment of isoproturon. Superoxide Dismutase (SOD) activity was significantly affected by the herbicides. It was raised at first, and then returned gradually back to the control level. Similar trend was observed in the activity of peroxidase (POD). On the30th DAT, the activity of POD in most treatments was lower than the control treatment. The activity of Catalase (CAT) was sensitive to the herbicides, which increased significantly on the5th DAT, then gradually decreased and returned to the control level on the30th DAT. There was no observable difference in the content of MDA between the treatments of herbicides and control. The above results indicated that the spray of the five herbicides produced certain inhibitive effects on leaf photosynthetic parameters of wheat plants; the increase in grain yield was mainly due to the removal of weeds and the optimization of growing environment of wheat plants.5. Effects of herbicides on soil microbial population and enzyme activitiesThe effects of two herbicides (isoproturon and tribenuron-methly) on microbial population and soil enzymes activities in wheat field with rice as the prior crop were investigated. Isoproturon had transitory inhibitory effect on soil fungal population in wheat field. The inhibitory effect was activated on the5th after treatment (DAT) and lasted until the60th DAT. The inhibition of isoproturon on bacteria and actinomycetes lasted for a longer time. The activation was initiated on the15th day DAT. The activity of catalase was activated, inhibited, and reactivated when low concentration (1.88g/kg and3.75g/kg) of isoproturon was applied. High concentrations (7.50g/kg and15.00g/kg) of isoproturon inhibited and activated the activity of catalase. Isoproturon at each concentration had inhibition-activation effects on soil urease activity. The activity of invertase was more sensitive to isoproturon, which showed as activation at the beginning, and then experienced a phase of decling. On the60th day of treatment (DAT), isoproturon slightly inhibited the activity of invertase. The differences of activity among enzymes in soil treated with tribenuron-methly were significant. Soil catalase activity was increasingly stimulated by the increased concentration of tribenuron-methly. Urease activity was slightly stimulated by low concentrations of tribenuron-methly (0.13,0.25, and0.50g/kg), but was depressed by high concentration (1.00g/kg).6. Residue characteristics of herbicide in wheat plant and soilThe residue characteristics of five herbicides (tribenuron-methyl, fluroxypyr, isoproturon, puma super, and chlorotoluron) in the plants of weak-gluten wheat Yangmai13and soil investigated using different dosages and different time. Of the tested herbicides, chlorotoluron was hardest degraded. And its half-life period of gradation was up to31-49days in soil and only9-11days in wheat plants. After the degradation during the whole wheat growing season, there was no residue detected in wheat plants. But there was residual in soil, ranging from0.01to0.16mg/kg. The degradation of tribenuron-methyl in wheat plants and soil was faster than chlorotoluron (with a half-life period of gradation of about12d in soil and2-3days in wheat plants). At the harvest stage, residues were not detected both in wheat plants and soil. The half-life period of degradation of fluroxypyr was about10days in soil and3-4days in wheat plants. In the general, basic degradation of fluroxypyr was completed within30days. Similarly, at the harvest stage there was no detected residue both in wheat plants and soil. The degradation rate of isoproturon in wheat plant was faster than chlorotoluron (with a half-life period of2-4days). However, the rate in soil was slower (with a half-life period of about12days). But after about60days of treatment, the degradation was completed and no residue in wheat plants and soil was detected at the harvest stage. Of the five herbicides, the degradation of puma super was the fastest, the half-life period of degradation in the soil or in the plants were both2-3days and no residues were detected both in wheat plants and soil. |
