| Straw is an important renewable organic resource which can provide necessary nutrient for crop growth.However,straw has not been fully and reasonably utilized due to the difficulties in the collection and the low economic value.It has been reported that short-term straw returning negatively impacts on crop production,which is not conducive to the popularization of straw returning.In order to study the technical measures of cultivating strong wheat seedlings under the condition of rice straw returning,an experiment with three factors,including the duration implemented rice straw returning(1-10 years,expressed by S1-S10 respectively),nitrogen application method and density,was conducted to determine the effects of density and nitrogen application on seedling growth and its related physiological characteristics,population quality,yield and quality of spring wheat cultivar Yangfumai 4 under different conditions of rice straw returning.This study attempted to provide suitable measures for rice straw returning in the middle and lower reaches of the Yangtze River in order to realize vigorous seedlings and high yield of wheat.The main results are as follows:1.The spike number,grain number,1000-grains weight,and grain yield under the S1-S4 treatments were significantly lower than those under treatment without rice straw returning(NS).With the increasing duration of rice straw returning,the spike number,grain number,1000-grains weight,and grain yield under the S5-S10 treatments were higher than those under the NS treatment.Under the condition of the same duration of rice straw returning,spike number,grain number,1000-grains weight,and grain yield of wheat with different nitrogen fertilizer applications showed 5:1:2:2>5:2:2:1>5:3:2:0.The duration of rice straw returning influenced on grain protein content,hardness,bulk density,and flour yield.With the increase of duration of rice straw returning,grain protein content,hardness,bulk density,and flour yield of wheat were also increasing.These parameters under the different nitrogen managements showed 5:1:2:2>5:2:2:1>5:3:2:0.2.The duration of rice straw returning had different effects on the content of nitrate nitrogen,ammonium nitrogen,alkali hydrolyzed nitrogen,available phosphorus,available potassium,and organic matter in different soil layers at maturity.The content of nitrate nitrogen,ammonium nitrogen,alkali hydrolyzed nitrogen,available phosphorus,available potassium,and organic matter in the 0-5 cm soil layer was higher than that in the 5-10 cm soil layer.These parameters in each soil layer with the S1-S10 treatment were higher than those with the NS treatment.With the increase of duration of rice straw returning,the content of nitrate nitrogen,ammonium nitrogen,alkali hydrolyzed nitrogen,available phosphorus,available potassium,and organic matter in the soil at maturity showed an increasing trend.The content of soil organic matter under the S1-S4 treatment increased significantly with the increased duration of rice straw returning,while it under the S5-S10 treatment also increased but with a relatively slight trend.These results indicate that long-term rice straw returning can effectively improve the soil nutrient content.3.Compared with the NS treatment,the straw returning decreased the emergence rate of wheat by 5.4-10.6 percentage points(2017-2018,F=5.964**)and 4.9-8.6 percentage points(2018-2019,F=15.79**),and affected the healthy growth of wheat seedlings at the 3rd-leaf stage.Although these influences were alleviated by increasing the duration of rice straw returning,it could not be eliminated.The duration of rice straw returning and the nitrogen application effect on the quality of wheat seedlings at the 6th-leaf stage.Straw returning decreased the LAI,tiller number,seedling height,and dry matter weight per plant of wheat seedlings at the 6th-leaf stage,and inhibited the normal growth of wheat.However,with the increase of the years of rice straw returning,the adverse effects were gradually slight.The LAI,tiller number per plant,seedling height,and dry matter weight per plant under the most years of rice straw returning were 0.2-0.4,0.2-0.4,1.3-1.9 cm,and 26.3-55.6 mg greater than those under the S1 treatment,respectively.Under the condition of rice straw returning,an increasing application amount of tillering fertilizer increased the root activity,the SPAD value of leaves,the content of soluble sugar in the leaf sheath and blade,but reduced the accumulation of MDA.With the increase of the years of rice straw returning,the effects showed an increasing trend.When the years of rice straw returning reached more than 4 years,the suitable nitrogen fertilizer mode(base fertilizer:tiller fertilizer:jointing fertilizer:booting fertilizer=5:2:2:1)was conducive to cultivate the strong seedlings.4.The SPAD value and net photosynthetic rate of flag leaf under the S1-S10 treatments were higher than those under the NS treatment.The increasing SPAD value and net photosynthetic rate of flag leaf resulted from straw returning increased with the increasing years of rice straw returning.Nitrogen application also regulated the SPAD value and net photo synthetic rate of flag leaf after anthesis.Under the same duration of rice straw returning,the SPAD value of flag leaf after anthesis with different nitrogen application showed 5:1:2:2>5:2:2:1>5:3:2:0.Therefore,long-term rice straw returning and reasonable application of nitrogen fertilizer during the late growth stage can improve the photosynthetic capacity of wheat flag leaves,prolong the functional period of leaves,and further promote the increase of wheat grain yield.5.The accumulation of nitrogen and phosphorus in wheat plants under the S1-S3 treatments was lower than that of the NS treatment.When the years of rice straw returning reached more than 4 years,the accumulation of nitrogen and phosphorus in wheat plants was higher than that of the NS treatment.With the increased years of rice straw returning,the accumulation of nitrogen and phosphorus in wheat plants showed an increasing trend,with the most years of rice straw returning reaching the maximum.Nitrogen fertilizer management also had regulating effects on the accumulation of nitrogen and phosphorus in wheat plants.The total performance of nitrogen and phosphorus accumulation in wheat plants with different nitrogen fertilizer operations from the over-wintering to booting stage under the same duration of rice straw returning showed 5:2:2:1>5:3:2:0>5:1:2:2,and the overall performance at anthesis and maturity stages showed 5:1:2:2>5:2:2:1>5:3:20.Therefore,the combination of rice straw returning and reasonable nitrogen application can improve the absorption and utilization of nitrogen and phosphorus at the late stage of wheat growth.6.Under the same duration of rice straw returning,the spike number,grain number,1000-grains weight,and grain yield with increased tillering fertilizer showed Z3>Z2>Z1(In the Z1 treatment,120 kg · hm-2 basal fertilizer,24 kg·hm-2 tillering fertilizer,48 kg·hm-2 jointing fertilizer and 48 kg · hm-2 booting fertilizer were applied in the Z1 treatment.On the basis that the application rates of basal fertilizer,jointing fertilizer and booting fertilizer were the same as those of Z1 treatment,Z2 and Z3 applied 26.4,28.8 kg-hm-2 of tillering fertilizer,respectively.).The yield increase rate under the Z3 treatment was higher than that under the Z2 treatment.Under the same duration of rice straw returning,the grain protein content,hardness,bulk density,and flour yield of wheat with different nitrogen applications showed Z3>Z2>Zl.The grain protein content,bulk density,and flour yield of Yangfumai 4 were significantly affected by the interaction of the duration of rice straw returning and nitrogen application.7.Under the same duration of rice straw returning,the grain number,spike number,1000-grains weight,and grain yield of wheat under different planting density treatments showed M3>M2>M1(M1,M2 and M3 mean 2.25,2.475 and 2.7 million hm-2 of the seedling number,respectively).The yield under the M3 treatment was higher than the M2 treatment.Under the same duration of rice straw returning,the grain protein content,hardness,bulk density,and flour yield of wheat with different densities showed M3>M2>M1.The interaction of rice straw returning duration and planting density significantly effect on grain protein content,bulk density,and flour yield of Yangfumai 4.8.A short duration of rice straw returning reduced wheat seedling emergence rate,seedling quality,grain yield,and grain quality,but the adverse effects gradually decreased with the increased years of rice straw returning.When rice straw returning was conducted 4 years,the combination treatment of 240 kg · hm-2 nitrogen rate and the ratio of 5:2:2:1 could alleviate the negative effects of rice straw returning on the growth of wheat seedlings,which is conducive to improve the growth of seedlings under the condition of rice straw returning.When rice straw returning was conducted 4 years,however,nitrogen application ratio of 5:1:2:2 improved the soil fertility,enhanced the photo synthetic capacity after anthesis,slowed down the decrease of LAI,increased the post-anthesis dry matter accumulation,adjusted the yield structure,and achieved the purpose of increasing yield and improving quality.In addition,the grain yield and quality of wheat could be improved by properly prolonging the years of rice straw returning along with using Z3 or M39.In conclusion,the yield and quality of Yangfumai 4 were the best under the condition of 2.25 million hm-2 basic seedlings,240 kg·hm-2 nitrogen application,the nitrogen application mode of 5:1:2:2,150 kg·hm-2 phosphorus application,and 90 kg ·hm-2 potassium application amount. |
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