Effect Of Cultural Factors On Morphological Characteristics, Carbon-nitrogen Metabolism And Yield Of Relay-cropping Soybean

The studies consisted of five experiments, they are "effect of different varieties and sowing time on relay-cropping soybean", "effect of sowing time and density of maize on relay-cropping soybean", "effect of different plant-type maize and planting width on relay-cropping soybean", "effect of different nitrogen fertilizer levels on relay-cropping soybean" and "effect of different density on relay-cropping soybean". The effects of cultural factors on morphological characteristics, carbon-nitrogen metabolism and yield of relay-cropping soybean were studied from 2004 to 2006. The results were as follows.1 The changes of relay-cropping soybean morphological characteristicsThe plant height of relay-cropping soybean decreased with the delay of sowing time and widener of planting width, and increased with the increase of dosage of nitrogen fertilizer. Under different planting density, the plant height of late-maturing variety increased with the increase of density, which of early-maturing variety decreased with the increasing of density. The more erect leaf plant type, early sowing time and low density of maize, the lower plant height of relay-cropping soybean were. The speed of plant height increasing from V3 stage to R1 stage was disadvantage to yield formation.The stem diameter of relay-cropping was small before the harvest of maize, but after harvested maize, it increased till R7 stage. The sowing time delayed, density and dosage of nitrogen fertilizer increased, which all led to stem diameter decrease. broader planting width of soybean, relay-cropping with erect leaf plant-type of maize and sown early, which were all advantage to increase of stem diameter of relay-cropping soybean.The dry matter accumulation of relay-cropping soybean stem firstly increased, then decreased, early-maturing variety reached peak value at R5 stage, middle-maturing and late-maturing varieties reached peak value at R6 stage, the fast accumulation period was V3 to R2 stage. With the delay of sowing time, increase of density, excessive usage of nitrogen fertilizer, the dry matter accumulation of stem decreased. Widen planting width of soybean, relay-cropping with erect leaf plant-type maize and sown early, which were all advantage to accumulation of dry matter in stem.LAI of soybean increased after relay-cropping with maize, it firstly increased, then decreased, the fast increasing speed period was V3 to R1 stage. LAI of early-maturing variety reached peak value at R3 stage, that middle-maturing and late-maturing varieties reached peak value at R4 stage, and all decreased with the delay of sowing time, increased with widener of planting width. Under high nitrogen fertilizer level, the appearance time of peak value advanced compared to other treatments, and the speed of decrease accelerated. Relay-cropping with erect leaf plant-type of maize and sown early, that could keep LAI of soybean at a high level and slower decrease speed at latter growth stage.SLW of relay-cropping soybean firstly increased, then decreased, reached peak value at R4 stage, and the fast increasing speed period was V3 to R3 stage. LAW of late-maturing variety was higher than that of early-maturing and middle-maturing varieties, and increased with the delay of sowing time, widener of planting width, increase of density and dosage of nitrogen fertilizer. But relay-cropping with flat leaf plant-type maize and delay of sowing time were all disadvantage to accumulation of dry matter of leaf.2 The rule of carbon-nitrogen metabolism of relay-cropping soybeanThe content of soluble sugar and starch of relay-cropping soybean stem and leaf all increased firstly, then decreased. Soluble sugar content of leaf reached peak value at R4 stage, the high accumulation period of early-maturing and middle-maturing varieties was R2 to R4 stage, that late-maturing variety was V3 to R2 stage. Under high planting density and nitrogen fertilizer levels, soluble sugar content of leaf decreased. Maize was erect leaf plant-type and sown early, widen planting width of soybean, which could prolong accumulation time of soluble sugar and accelerate accumulation speed of soluble sugar. The appearance time of peak value of stem soluble sugar content was difference between different varieties, middle-maturing and late-maturing varieties reached peak mainly at R4 stage, that early-maturing variety reached peak mainly at R6 stage. With the delay of soybean sowing time, increase of planting density, the appearance time of peak value of stem soluble sugar content advanced. Relay-cropping with erect leaf type-plant maize, and sown early, which were advantage to accumulation of soluble sugar of stem at early growth stage of soybean.Starch content of soybean stem and leaf increased firstly, after get to peak value at R4 stage, it decreased, the high accumulation period was V3 to R2 stage. Sown at suitable time, guaranteed appropriate planting density and nitrogen fertilizer, which could promote accumulation and decomposition speed of starch of soybean stem and leaf. Relay-cropping with erect leaf type-plant maize, sown early, and broader planting width of soybean, which were advantage to keep starch content of soybean stem and leaf at a high level.Nitrogen content of relay-cropping soybean stem firstly decreased, then increased, finally decreased. The changes of leaf had difference between different varieties, early-maturing variety decreased all the while, middle-maturing and late-maturing varieties firstly decreased, then increased, finally decreased. The nitrogen content of stem and leaf all increased with the delay of soybean sowing time, decrease of planting density, increase of dosage of nitrogen fertilizer and planting width. Relay-cropping with flat leaf plant-type maize, and delay sowing time, that decreased nitrogen content of stem and leaf of soybean.The activity of SPS, AM and GS of relay-cropping soybean all firstly increased, then decreased, reached peak value at R4 stage, the increasing range from R2 to R4 stage was highest. The changes of NR activity showed difference between different varieties, early-maturing variety firstly increased, then decreased, that middle-maturing and late-maturing varieties firstly decreased, then increased, finally decreased, but the highest increasing range of them were all from R6 to R7 stage. Sown at the first ten days of June, planting density was 0.165 million plants per hm², dosage of nitrogen fertilizer was below 59.8kg.hm^-2, and broader planting width, that were advantage to promote SPS,AM,NR and GS activity. Relay-cropping with flat leaf type-plant maize and delay sowing time, that decreased their activity significantly.3 Relation of morphological characteristics, carbon-nitrogen metabolism and yield of relay-cropping soybeanThe yield of relay-cropping soybean except decide by varieties, also mainly restricted with shading of maize and the length of symbiotic periods with maize. The yield of late-maturing variety was significantly higher than that of early-maturing and middle-maturing varieties, and sown at the first ten-days of June, the yield was highest. Under high planting density and dosage of nitrogen fertilizer, decrease of yield was serious. Relay-cropping with erect leaf plant-type maize and sown early, broader planting width of soybean, which were all advantage to yield formation of relay-cropping soybean.In wheat/maize/soybean system, R2 stage of soybean just was the proceeding or behind harvesting maize, this stage was important of soybean to experience light transfer, so the morphological characteristics and carbon-nitrogen metabolism of relay-cropping soybean in this stage was a key to reflect soybean yield. After harvested maize, soybean appeared compensatory growth until filling stage, so R5 and R6 stage were also important to yield formation of soybean. Path analysis of morphological characteristics,carbon-nitrogen metabolism and soybean yield under different growth stage were did, the results showed that, want to get high yield, should hold relative large LAI, stem diameter and SLW keep at a suitable level, restrict plant height and dry matter accumulation of stem at latter growth stage, hold content of soluble sugar,starch and nitrogen of stem and leaf and activity of NR,AM,SPS,GS at high level at R2 stage. At R6 stage, soluble sugar,starch and nitrogen content of leaf and SPS,NR activity still need retain at high level, but soluble sugar,starch and nitrogen content of stem and AM,GS activity should keep at low level.4 The technique of high yield of relay-cropping soybeanChoose late-maturing variety that whole growth period was about 130d, sown at the first ten days of June, which not only could take great advantage of light and heat resources, but also guarantee wheat sowing on schedule. The best planting density was 0.165 million plants per hm², yield decreased badly at high density. In the condition of soil fertility above organic matter, total nitrogen and available nitrogen content respectively was 53.106g.kg^-1, 2.15g.kg^-1 and 158.542mg.kg^-1, in order to save cost and get high yield in the mean while, could not fertilize or use low dosage nitrogen fertilizer, when the dosage of nitrogen fertilizer reached 78.2kg.hm^-2, the yield decreased badly. The best field combination that could reduce damage of light shortage to soybean in relay-cropping system and ensure high yield and value was relay cropping with erect maize that sown at the last ten-day of March, density was 5.25 thousand plants per hm² and choose planting width 1.17m / 0.83m (soybean/maize).