Study On The Low Dosage Technology Of Herbicide In Summer Cornfield In Tai’an

In this study, the economic threshold of weed control and the critical period of weed competition on corn were established based on weeds species, community composition and dynamics of growth in cornfield. High efficiency, low toxicity, low residue, and safe herbicides were screened from biological activity and safety on corn. Additives and the application technology were also selected and optimized. Furthermore, Minimum Lethal Herbicide Dosage(MLHD) techniques abroad were introduced and studied. Finally the precise dosage, which was reduced more than 30% of herbicides, was proposed and a system for low dosage using methods was established in summer cornfield. This research makes up the defects of traditional chemical control system, which is monotonous in techniques and long-term application of high residual herbicides.The main research contents and results are as follows:1. Weed species, dominant species, community composition, and weed occurrence principles were comprehensively surveyed in summer cornfield of Tai’an. The weeds in this area belongs to 51 species of 18 families, among them Poaceae, Asteraceae, Amaranthaceae,Chenopodiaceae, Portulacaceae were the dominant families. The dominant species were crabgrass, goosegrass, dry millet, redroot amaranth, purslane, lambsquarters, etc.; there are also three combination of dominant species:(1) the crabgrass-dominant community:crabgrass-redroot amaranth-purslane, crabgrass-redroot amaranth-dry millet,crabgrass-redroot amaranth-false daisy;(2) the eleusine-dominant communities:eleusine-redroot amaranth-purslane, eleusine- purple nutsedge- false daisy, etc.,(3) the dry millet-dominant communities: dry millet-redroot amaranth-field bindweed, dry millet-purslane-redroot amaranth and so on.2. The economic thresholds and critical period of competition of weeds in summer cornfield was found. The relationship between corn yield loss and different weed densities was measured. The results showed a significant positive correlation, which is Y = 0.6803+0.0728 x(r = 0.9951 **). Based on the formula, when weed density in cornfield is more than30-34 plants /m2, the medication must be rid of them in order to control harmful weeds. Theeffects of weeds on corn yield loss at different times was investigated and the result showed that the relationship is Y = 0.2495 +0.1884 x(r = 0.9890 **), which indicated that 13-15 days after sowing corn were the critical period of competition. Therefore, the weed control should be performed before critical period in order to make the dangers of loss below the allowed level.3. A series of high-efficient, broad-spectrum, and low residual herbicides including acetochlor ? atrazine were screened out for Tai’an through field trials. The optimal dose of these herbicides for cornfield was also determined. Together with rational usage of additives,the amount of more than one-third usage of herbicides could be reduced compared with conventional methods to get the same effect.4. The MLHD from Netherlands was introduced. Plant photosynthesis meter(PPM) was used to study the inhibition of photosynthesis by herbicides. The systematic study showed that MLHD technology significantly reduced the amount of herbicides and saved the cost of medication. It could also effectively control weeds, reduced environmental pollution and environmental risks, and increased corn production.5. A low dosage technology system of herbicides was built in summer corn filed. The system, which was set up in economic, ecological, and environmental protection point of view,the spirit of "optimization, simplification, and quantification" principle, can make up for the defects of traditional chemical control system of weeds.