| Maize is the first major grain corn and straw yield is about 300 million tons per year in china. Straw has cellulose, lignin and other material, which are important source of forming organic matter. After straw was returned into the field, it can effectively improve soil physical and chemical properties, increase soil organic matter content. Straw contains a large number of mineral element such as nitrogen, phosphorus and potassium, and iron, copper, zinc, manganese and other trace elements, provides a favorable environment for crop growth, effectively alleviate caused by unbalanced N,P,K in the soil compaction problems, reduce the burning pollution to the environment. With the development of agricultural modernization, straw returned become common farming methods in agricultural production. There were some disputes over the effects of straw returned to the disease. Some people thought that corn straw returned provided a favorable environment for the pathogen, so it make pathogen quantity increased and disease more and more serious. Others thought that corn straw returned might rise the number of bio-control bacteria in soil and enhanced resistance of plants. In this study, according to setting the field experiment of different’amount of straw returned, northern leaf blight of corn was studied in time popular dynamic. The effects of straw returned to soil microorganisms, soil enzymes, corn growth and the defense enzyme were studied. The effect of straw decomposed liquid and phenolic acids to mycelium growth and spore germination of Exserohilum turcicum was tested. The results are as follows:1. The disease index was surveied according to the principles of plant disease epidemic and field trial design. Disease severity of northern leaf blight of corn was that straw returned was serious than not straw returned. At the same time, disease severity of northern leaf blight of corn under different straw returned amount was serious with the increase of straw returned amount. The exponential phase of disease on straw returned was earlier than not straw returned. When the amounts of straw returned were 3750 kg/hm2,7500 kg/hm2and 15000 kg/hm2, the disease index were 15.7,27.5 and 43.5, which were bigger than not straw returned. The temporal dynamic models of northern leaf blight of corn on different straw returned amount were constructed according to the change of northern leaf blight of corn disease index. The dynamic patterns of disease epidemics fitted the model of logistic. Disease epidemic period was deduced according to the temporal dynamic models. The decline phase of disease on straw returned was also earlier than not straw returned. The exponential phases of disease on straw returned amount of 3750 kg/hm2,7500 kg/hm2and 15000 kg/hm2 were shorten 5 d,6 d,7 d than not straw returned. The decline phases of disease on straw returned amount of 3750 kg/hm2,7500 kg/hm2and 15000 kg/hm2 were shorten 2 d,3 d,5 d than not straw returned.2. In this study, corn straw was decomposed and filtered at different time. Effect of corn straw decomposed liquid on mycelium growth and spore germination of Exserohilum turcicum was tested. Corn, straw decomposed liquid inhibited mycelium growth and spore germination of Exserohilum turcicum. When the concentration of straw decomposed liquid was 0.125 g/mL, the inhibition rate of mycelium growth was 38.7%to 58.8%and the inhibition rate of spore germination was 28.8%to 91.9%. The phenolic compounds of corn straw decomposed liquid were identified by HPLC and five phenolic acids compounds including phthalic acid, p-hydroxybenzoic acid, vanillic acid, syringic acid and benzoic acid were observed. Effects of the five phenolic acids on mycelium growth and spore germination of Exserohilum turcicum were tested. The five phenolic acids compounds which inhibited the mycelium growth to some degree produced 14.5% to 100.0% inhibition rate and the process was stronger with the increase of concentration. Benzoic acid and phthalic acid inhibited the spore germination at concentrations of 0.125 to 1.000 mg/mL. P-hydroxybenzoic acid promoted the spore germination at concentrations of 0.063 to 1.000 mg/mL.3. The dynamic changes of soil microorganism and soil enzyme activity were researched through different straw returned in the corn growth period in this study. The study found that the quantities of fungi, bacteria and actinomycetes were improved with the increase of straw returned amount. The numbers of fungi, bacteria and actinomyces had an increasing and downward trend in the corn growth period. At stage of corn tasseling, the numbers of fungi, bacteria and actinomycetes were 9.7×103 cfu·g-1,9.7×105 cfu·g-1 and 6.9×104 cfu·g-1 in 3750kg/hm2,1.3×104 cfu·g-1,1.2×106 cfu·g-1,7.7×104 cfu·g-1 in 7500 kg/hm2,1.8x104 cfu·g-1, 1.2×106 cfu·g-1,8.5×104 cfu·g-1 in 7500 kg/hm2. From the proportion of soil microorganisms, fungi, bacteria and actinomyces were almost not change. The proportion of bacteria in the soil was 92.9%, actinomycetes was 6.7% and fungi had the least proportion. The activity of soil urease, invertase, alkaline phosphatase and catalase were enhanced by straw returned. At stage of com tasseling, the activity of urease in 3750 kg/hm2,7500 kg/hm2 and 15000 kg/hm2 was improved 35.7%,63.4% and 99.8% than not straw returned. At period of bell mouth, the activity of invertase in 3750 kg/hm2,7500 kg/hm2 and 15000 kg/hm2 was improved 22.0%, 33.0% and 34.8% than not straw returned. At stage of com tasseling, the activity of catalase in 3750 kg/hm2,7500 kg/hm2 and 15000 kg/hm2 was improved 4.9%,6.9% and 9.7% than not straw returned. At stage of mature, the activity of alkaline phosphatase in 3750 kg/hm2,7500 kg/hm2 and 15000 kg/hm2 was improved 13.4%,21.6% and 27.1% than not straw returned.4. Corn height, stem diameter, leaf length and leaf width were compared under different amount of straw returned. Com height, stem diameter, leaf length and leaf width were raised with the increase of straw amount. In 3750 kg/hm2,7500 kg/hm2 and 15000 kg/hm2, com height increased 0.5%,4.4%,5.4%, stem diameter increased 1.1%,13.6%,26.9%, leaf length increased 0.7%,3.0%,4.4%, leaf width increased 0.9%,2.7%,5.4%than not straw returned. The activity of root had an increasing and downward trend in the com growth period and the largest value was 12.2 TTFμg·g-1·h-1. The activity of PAL, PPO, POD and CAT were detected on different straw returned in com growth period and found that they also had an increasing and downward trend. At period of bell mouth, In 3750 kg/hm2,7500 kg/hm2 and 15000 kg/hm2, the activity of PAL were 125.5 U·g-1·h-1,123.8 U·g-1·h-1 and 124.6 U·g-1·h-1, the activity of PPO were 3.4 U·g-1·min-1,3.5 U·g-1·min-1 and 3.7 U·g-1·min-1, the activity of POD were 258.0 U·g-1·h-1,316.4 U·g-1·h-1 and 345.4 U·g-1·h-1, the activity of CAT were 37.5 U·g-1·min-1,36.5 U·g-1·min-1 and 38.2 U·g-1·min-1 at period of bell mouth... |
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