Study On The Effect Of Wheat Straw Returning To The Field On The Early Growth Of Rice And Its Mechanism

Wheat straw returning to the field has become the main mode of rice cultivation in rice-wheat double-cropping areas.Because of the limitation of stubble changing time,rice is planted immediately after wheat straw returning to the field.In soil,the transformation of straw and the growth of rice are carried out at the same time,which leads to the contradiction between reactions of straw transformation and rice growth.Especially in the early stage,straw returning to the field often brings obvious influence on rice growth.However,the research on its influence and adjustment measures is seldom carried out.In this study,we take the growth characteristics of rice under the condition of returning wheat straw to the field was taken as breakthrough cut-in point,and use three hybrid rice and three conventional japonica rice as the experimental materials,and set up three straw treatments,which includes returning no straw、half straw and whole straw to the field,combining with the treatment of nitrogen application amount of basal tillers,ultimately,analyze the influence of returning straw to the field to rice early growth on the growth response and physiological performance of rice、the physical and chemical changes in soil,analyze the differences of variety responses and understand the growth characteristics of early-growing and fast-growing varieties under the condition of returning straw to the field.The main results are as follows:1.Under the pot culture condition,straw returning to the field showed obvious growth inhibition on the initial growth of rice,especially on the growth forms in the upper and lower parts of the ground.Under different tillering fertilizer levels,the differences between the treatments of returning straw to field and not returning remained the same.The occurrence of tillers in rice was obviously inhibited by straw returning to the field,and the plant height,SPAD value of leaves and photosynthetic rate in the early growth stage were significantly lower than those in the non-return control.Straw returning to the field also had adverse effects on root traits and root activity in the early growth stage of rice,which also influenced the accumulation of dry matter in heading stage and mature stage.But in the field,a certain degree of growth inhibition at the initial stage can get a fast growth recovery,and it will shows a better growth trend at the seed-setting stage and the positive effect on the field rice yield.2.Under the pot culture condition,straw returning to the field had a certain influence on the yield of rice.The main inhibiting effect on yield is that the final panicle number is significantly lower than that of non-return treatment.After returning the straw to the field,the number of grains per panicle increased,while the seed setting rate and 1000-grain weight of rice were not significantly changed,and the tested varieties showed consistent performance.Compared with field experiment,pot culture conditions enlarged the adverse effects of straw returning to the field,but it still showed that the adverse effects of straw returning to the field were mainly concentrated on the early growth stage,which leads to insufficient tillers of early rice plants,and easily causead verse effects on the yield.3.With the increase of tillering fertilizer amount,the growth and physiological characteristics of rice are obviously improved,and the trend of increasing yield of tested varieties is consistent.The increase of tillering fertilizer amount significantly promoted the occurrence of tillering in early stage of rice and increased the final panicle number.The increase of basal tiller fertilizer level increased SPAD value of leaves,photo synthetic rate and root length,root diameter,root oxidation power of rice plants,and other growth levels and physiological activities of aboveground and underground parts,and promoted the accumulation of assimilation substances.It can be seen that the early growth of rice can be obviously improved by increasing the basal tiller fertilizer,thus improving the yield.On the other hand,under the pot culture condition of this experiment,the increase of basal tillers did not significantly reduce the yield difference between returning straws to the field and not returning them to the field,and the yield of returning straws to the field under different fertilizer levels was still significantly lower than that of returning straws to the field.4.Straw returning to the field also has significant impacts on soil.Under the condition of returning straw to the field,the soil ph and soil redox potential(Eh)decreased significantly.After 15 days of rice harvest,the contents of nitrogen,potassium and phosphorus in the soil were significantly higher than those in the non-returning field.The contents of nitrogen in the semi-returning field and the total returning field respectively increased by 14.2%,27.4%,potassium respectively increased by 27.9%,22.2%and phosphorus respectively increased by 8.1%and 6.0%,respectively.15 days after transplanting,Eh in the soil treated with straw returning to the field was around-200 mv,which was very unfavorable to the growth of rice root.It can be seen that the adverse effects of straw returning to the field at the early stage of rice growth may be mainly concentrated on the decline of eh in the soil and the release of the harmful substances(mainly organic acids which caused the decline of pH).5.The adverse effects of straw returning to the field on the initial growth of rice are different among different rice varieties.Among hybrid rice,yangliangyou No.6 was obviously inhibited by straw returning to the field,while yongyou 2640,an indica-japonica hybrid rice,was relatively insensitive to it,where the reduction of tiller number and final yield in early stage was relatively in a small range.Among conventional japonica rice,huaidao No.5 was less inhibited than Nanjing 5055,where the decrease of tiller number and yield in early stage was smaller.Compared with hybrid rice,conventional japonica rice is relatively more sensitive at early stage,and tiller occurrence is more obviously inhibited.But yongyou 2640 root system growth is less inhibited than huaidao No.5,and its later recovery ability is stronger.Generally speaking,the varieties with good adaptability to straw returning to the field have stronger root growth activity,better root development,less inhibition of overground growth and shorter plant recovery growth process under the condition of straw returning to the field.6.When different concentrations of organic acids were added to the culture medium of hydroponic experiment,the plant height,root length,chlorophyll content and dry matter weight of each variety basically increased slightly at first and then decreased.When the concentration increased to C4(2.5*10-4N),the growth characteristic values of all varieties began to decline significantly,which showed greater influence on seedling root system than that on aboveground.Among the four varieties,the inhibition of high concentration of organic acids on yangliangyou No.6 is strongest.At C4 concentration,the relative growth rate of root length of this variety was the lowest,while that of yongyou 2640 was the highest,which was consistent with the result of pot experiment,in which straw returning to the field had the strongest inhibitory effect on the growth of yangliangyou No.6 at the early stage,and the lowest influence in the root growth of yongyou 2640.It is speculated that rice seedlings can be planted with C4 concentration culture solution in the future,so as to detect whether the variety is suitable for straw returning to the field,and related research needs to be further improved.