Effects Of Nitrogen Application On Growth And Development Characteristics Of Relay Cropping Soybean

Relay-planting soybean pattern is dominant in southern China. However, studies on relay-plantingsoybean are so defective that it may influence the development of soybean. Soybean accumulates vastprotein by itself; and grows well with adequate nitrogen fertilizer. This experiment was carded out tostudy the effects of different nitrogen managements on relay-cropping soybean's root morphological andphysiological characteristics, the accumulation and distribution of photosynthetic yield, nitrogenmetabolism, the yield and seed quality used limited-pod type soybeans (Gongxuan1# & Zhongdou32#) inwheat/raise/soybean cropping system. The main results showed as follows:1. Most of studies have been concentrated on the effects of nitrogen on the aerial parts, but less on theroots. The optimal treatments on the dry root weight, root nodule number, length of first lateral root andbleeding sap were the low nitrogen levels (45 and 90 N kg·ha^-1) at the growth stages of V3-R5. Length offirst lateral root, dry root weight and bleeding sap all were positive correlated with the application amountof nitrogen at the growth stage of R7. The relation between the root-top ratio and nitrogen levels was aquadratic curve at growth stages of V3-R5, but root-top ratio had a linear relationship with the nitrogenlevels at the very late growth stage. The relation between bleeding sap-top ratio (y=Bleeding sap/drymatters) and days (x) after V3 (11th, Aug, 2005) was a negative exponential correlation(Y=1.0357e^-0.03823X). The content of NO₃^--N in bleeding sap was more than that of NH₄⁺-N; it was alsoraised with the increasing of nitrogen amount. Root activity had a peak during the whole growth stage ofrelay-planting soybean. The activity of soybean roots was enhanced by low nitrogen levels (45 and 90 Nkg·ha^-1). High nitrogen levels(180 and 225 N kg·ha^-1) postponed the appearance of the peak value of rootactivity at the growth stage R3 and maintained a high level(＞116.00μg·g^-1 FW·h^-1) at the very late growthstage(R7).2. The feasible nitrogen management delayed leaf senescence. The leaf dry matter yield, SPAD values, andsoluble protein content was increased, but decreased the MDA content by using nitrogen. Under the samenitrogen application rate, higher topdressing ratio improved soluble protein and soluble sugar content. Theappropriate ratio of basic to dressing (4:6,2:8) was beneficial to decrease MDA content in leaf, to increasechlorophyll content and dry matter yield. In a certain range of nitrogen application rate, nitrogen applyingratios of topdressing nitrogen at blooming stages are propitious to increasing photosynthetic yield, whichare mainly resulted from nitrogen adjusting to biological activity component in leaves. The effect ofinteraction between nitrogen application levels and application ratios was obvious. The optimal treatmentson delaying the leaf senescence were the B2 treatment (80 N kg·ha^-1) and nitrogen application ratios of4:6-2:8.3. The feasible nitrogen management adjusted the acumination and transfer of dry matter. The dry matteryield was still consonant with the logistic growth cure under the different nitrogen management. However, the maximum increasing rate and the day of maximum increasing rate was different by the differentnitrogen management. The high nitrogen levels and overall using nitrogen (B1, B4) affected the balanceof physiological metabolism, and disadvantaging for dry matter accumulation. As the apparent outputratio is concerned in the different nutrient organs, which of leaf is the highest, petiole takes second place,stem is lower. The feasible nitrogen applied levels and topdressing nitrogen at blooming stages (4:6, 2:8)could adjust the ratio of dry matter, increasing the ratio of contributions to seed.4. The feasible nitrogen management may accelerate the nitrogen accumulations and distribution ofnutrient organs. The accumulations of nitrogen were similar with that of dry matter. Both of them emergedto tendency of irreversible exponential growth. The nitrogen fertilizer observably increased nitrogencontent in relay-cropping soybean. The relationship beteewn the nitrogen content and nitrogen appliedlevels was parabola, and the optical applied levels was 40-80 Nkg·ha^-1. The ratio of basic to dressing wasexcellent at 4:6. Among the three nutrient organs, the nitrogen content ratio showed that nitrogen in leafwas more than stem and petiole. Nitrogen in pod was more than that in leaf. The max nitrogenaccumulation in leaf was appeared at the growth of R4, which in stem was appeared at the growth of R5,but which in petiole was not clear changes in the whole growth stages.5. The nitrogen utilization efficiency was improved by feasible nitrogen management, but high nitrogenlevels restrained the absorption and utilization ratio of nitrogen. Under the same nitrogen applied levels,top-dressing at the bloom stage could improve absorption and recovery ratio of nitrogen. At the sametimes, nitrogen agronomy efficiency was increased observably. The best nitrogen applied level was 80Nkg·ha^-1, and the ratio of basic to dressing in range of 4:6-2:8, accelerating nitrogen metabolism,improving nitrogen fertilizer utilization ratio.6. The effects of nitrogen adjustment were dissimilar at the different growth stages. Nitrate reductaseactivity (NRA) was raised with the increasing of nitrogen amount at the growth stages of V4-R1 and R7,but when increased to the N2 treatment (80 Nkg·ha^-1), the trend was opposite at the growth stages ofR4-R5. The glutamine synthetase activity (GSA) of N2 treatment was higher than other treatments afterthe pod formation stage. Nitrogen application was beneficial to increase soluble protein accumulation.The optimal treatment is B4 treatment (using all nitrogen fertilizer at blooming stage) among the fourtreatments of assigned proportion of nitrogen, and the interaction between nitrogen levels and applicationratios were observably diversity at the whole growth stages.7. The appropriate nitrogen management remarkably improved soybean yield. The relationship betweenthe nitrogen applied levels and yield was a parabola. Under the 72.41 Nkg·ha^-1, the yield improved withthe increasing of the nitrogen applied levels, but the other way round as the upper the 72.41 Nkg·ha^-1. Thevalid ramification, seed filling and100-seed weight were improved by the ratio of basic to dressing inrange of 4:6-2:8, but changing the ratio of basic to dressing could not alter the soybean yield. There wascorrelation between yield and seed filling, ratio of seed to tem, number of full pod; the yield components refer had a significant positive correlation with yield.8. The protein and crud fat content was the highest under the nitrogen applied level of 80 Nkg·ha^-1. Thenitrogen as basic using was advantage to improve crud fat content. However, the protein content wasincreased when the increasing amount of nitrogen as dressing at bloom stage. Both the protein content andthe crud fat content had a significant positive correlation with yield, but the relationship between theprotein and the crud fat content was not clearly.