Allelopathic Effects Of Wheat Straw On Rice Seedling And Its Manipulation Technique

It has raised public concern that open burning of crop straw contributes to environmental pollution, significantly, while returning straw to field is an important practice to reduce burning and utilize the resource. A large collection of papers stated that returning straw to field can improve physicochemical properties of soil, add soil nutrients and increase crop output, while some reports argue that after being returned to field, straws in their decomposition process may produce toxic substances to crop of next year, leading to low crop output. Therefore, this paper aims to provide theoretical basis for expliciting the allelopathic effect of wheat straw on rice and preventing rice seedlings from the effect of the toxic and harmful substances from wheat straw decomposition.The experiments were carried out to investigate the allelopathic effects of wheat straw on rice seedling and its manipulation technique.The experiments were carried out through plate culture method, sand culture method and soil culture method. The first experiment was carried out to investigate the effects of wheat straw extract and decomposing liquids on rice seed germination and seedling growth, to explicit the allelopathic effect of wheat straw on rice. To explicit the allelopathic effect of phenolic acids on rice, the second experiment was carried out to investigate the effect of exogenous phenolic acids(p-hydroxybenzoic acid, vanillic acid, ferulic acid, syringic acid, protocatechuic acid, gallic acid, p-coumaric acid, sinapic acid, caffeic acid and salicylic acid) at different concentration on seed germination and seedling growth of rice. The last experiments were carried out to control the decompose rate of wheat straw and the skill of rice seedling, to avoid the effect of the toxic and harmful substances to rice seedling from wheat straw decomposition. Main results of the study were as follows:1. Compared with the control, wheat straw extract and decomposed liquids decreased the rice seed germination index and the rice plant biomass, chlorophyll content and root activity, significantly (P<0.05), while increased the rice plant malondialdehyde content, significantly (P<0.05). The wheat straw decomposing fluid demonstrated stronger allelopathic effect than rice straw extraction, and wheat leaf extracts demonstrated stronger allelopathic effect than stem extract, and the15days decomposing liquid demonstrated stronger allelopathic effect than7days decomposing liquid. Four kinds of extraction solution or decomposing liquid diluted five times decreased the inhibition effect on rice germination and plant growth. The total phenolic content of wheat straw extract and decomposed liquids were high, the content ranged from90.80～222μg ml-1. The total phenolic acid content and rice plant fresh weight, root activity, chlorophyll and rice germination index was significantly negative correlated, while a significant positive correlation with the rice plants malondialdehyde content was also observed. Wheat straw extract and decomposed liquids both expressed allelopathic effect on rice, its intensity was related with straw decomposing method, different parts of straw and decomposition time, and the allelopathic potential of wheat straw was related with the total phenolic acid content in the extract or liquids.2. The seed germination index in all of the phenolic acids treatments were promoted at the lower acid concentrations but inhibited at higher concentrations as compared with the control treatment. The plant biomass, chlorophyll content and root activity of rice were also enhanced at its lower concentrations but inhibited at its higher concentrations for most kinds of phenolic acids, while the malondialdehyde content of rice indicated the opposite trend. The allelopathic effect of the phenolic acid solution on rice was related to the phenolic acid varieties and their concentrations. The threshold of the allelopathic effect on rice for different kinds of phenolic acids was different.3. The rice stem length, aboveground biomass, chlorophyll content and carotenoid content were inhibited by all the wheat straw decomposing treatments, while the rice plant malondialdehyde content was promoted by them. Mix applying straw treatments and nitrogen applying treatments were able to release the inhibition to rice more than surface applying straw treatments and no nitrogen applying treatments from wheat straw decomposition. The more the moisture content, the less the toxic effect from wheat straw returning. Surface applying straw treatments and nitrogen applying treatments were able to increase the total phenolic content of soil more than mix applying straw treatments and no nitrogen applying treatments. Almost all the treatments increased the pH value of soil, significantly (P<0.05). The rice seedling treatments of drought stress and low nutrition stress both decreased the rice stem length, biomass, chlorophyll content and carotenoid content, inhibiting the rice growth. Adding straw treatment, adding straw decomposing production treatment and adding phenolic acid mixture treatment increased the rice stem length, aboveground biomass and chlorophyll content, reinforcing the antireversion force of rice seedling to toxicant by wheat straw decomposed.To sum up, wheat straw extract and decomposed liquids decreased the rice seed germination index and the rice plant biomass, chlorophyll content and root activity, significantly (P<0.05), while increased the rice plant malondialdehyde content, significantly (P<0.05). The wheat straw decomposing fluid demonstrated stronger allelopathic effect than rice straw extraction. The allelopathic effect of the phenolic acid at different varieties and concentrations on rice seed germination and seedling growth was different. Optimizing the way of wheat straw returning and controlling the rice seedling technique could reduce the allelopathic effect of wheat straw on rice seedling growth.