Analysis Of Nitrogen Uptake And Utilization And The Interspecific Relationship In Oil Flax/Soybean Intercropping System

Intercropping is a widely adopted practice in many labor-intensive cultivation, with the aim of harvesting at least two crops in one field during a certain period. The practice is an alternative agronornical stratagy to check the problem posed by the ever increasing population pressure and the shortage of food resources. Nitrogen is the highest input nutritient in agriculture and it affects the yield advantage of many intercropping systems. However, it is unclear the effect of nitrogen application rate on the system of oil flax and soybean, which is a new intercropping system in northern dry farming land in china. There is some problems associated with over fertilization and inhibited symbiotic N2 fixation of soybean in the systems. Thus, field trials were conducted in Yu Zhong City of Gansu Province in 2014 and 2015 with three nitrogen levels: N₀（0 kg/hm2）、N₁（75 kg/hm2）and N2（150 kg/hm2） and three planting patterns: sole cropping oil flax、sole cropping soybean and intercropping oil flax and soybean, to study the interspecific competition, nitrogen source uptake and utilization mechanics, and rhizosphere micro ecology effect in the oil flax/soybean system.The results were as follows:1.Oil flax/soybean intercropping system exhibitied interspecific advantages.The land equivalent ratio（LER） based on biomass and yield were greater than 1.With increased nitrogen application, the LER initially increased before peaking at N₁ treatment, and subsequently declined. LER of oil flax was greater than LER of soybean, so oil flax as the main crop increased the yield of the system. The interspecific competition ability of oil flax was better than soybean under N₀ and N₁, but weaker under N2.2. The aboveground dry matter accumulation, yield, harvest index of oil flax and yield and harvest index of soybean increased under intercropping. With increased nitrogen application, the indices of above also increased under sole cropping. The aboveground dry matter accumulation and yield of oil flax and the harvest index of oil flax and soybean initially increased before peaking with N₁ treatment, and subsequently declined under intercropping. Compared with sole cropping, the aboveground dry matter accumulation of soybean decreased under intercropping. Nitrogen application also increased the aboveground dry matter accumulation of soybean. With increased nitrogen application, the aboveground dry matter accumulation of soybean also increased both under the sole cropping and the intercropping systems.3. The distribution proportion of grain in dry matter at the mature stage of oil flax under intercropping system increased by 8.36% than it was under sole cropping. Compared to sole cropping, the translocation of dry matter before anthesis, the accumulation of dry matter after anthesis and the contribution rate of dry matter assimilation to grains increased by 28.59%, 47.48% and 4.16% respectively under intercropping. Under sole cropping, the distribution proportion of grain in dry matter at the mature stage of oil flax, the translocation of dry matter before anthesis, the accumulation of dry matter after anthesis increased with nitrogen application. Under intercropping, they initially increased before peaking at N₁ treatment, and subsequently decreased. The distribution proportion of stem and Spike axis and Kernel husk in dry matter declined with N₁ treatment under the intercropping, and, therefore, the distribution and the distribution proportion of grain in dry matter increased.4. The soybean nodules number and the dry weight of soybean nodules increased initially before peaking at flowering stage, and subsequently declined under sole cropping. The soybean nodules number and the dry weight of soybean nodules increased with the growth stage all the time and peaked at the seed-filling period under intercropping. At the same nitrogen level, the soybean nodules number and the dry weight of soybean nodules were higher under sole cropping than that under intercropping at the stage of flower budding and flowering, and they were lower than intercropping at the stage of seed filling. The soybean nodules number and the dry weight of soybean nodules were increased initially before peaking at N₁ treatment and subsequently declined.5. The nitrogen accumulation and nitrogen uptake intensity of oil flax during all the growth stages in the intercropping system was higher than that in the sole cropping. In the sole cropping, the nitrogen accumulation in the aboveground and seeds of oil flax and soybean under N2 treatment were the greatest in the three nitrogen levels at the maturity stage. In the intercropping system, the two indices increased initially before peaking at N₁ treatment and subsequently decreased. The nitrogen uptake intensity of oil flax was at peak during the nutrition stage.6. The distribution of nitrogen accumulation in different organs: grain>stem>non grain. In the sole cropping, the rate of distribution of nitrogen accumulation in grain increased with nitrogen application. In the intercropping, it increased initially before peaking at N₁ treatment and subsequently declined. Moderate amount of nitrogen promoted the nitrogen accumulation in grains. In intercropping, the translocation of nitrogen and the translocation rate from vegetative organs to grain after anthesis and the contribution of nitrogen accumulation to gain were higher than that in sole cropping. Under the sole cropping, the translocation rate from vegetative organs to grain after anthesis and the contribution of nitrogen accumulation to gain were highest in the N2 treatment. Under the intercropping, the translocation of nitrogen and the translocation rate from vegetative organs to grain after anthesis and the contribution of nitrogen accumulation to grain in the N₁ treatment were higher by 38.98% and 8.16%、4.46% and 10.12%、2.44% and 1.33% than that in N₀ and N2 respectively.7. The nitrogen harvest index of oil flax and soybean in oil flax/soybean intercropping system was higher than that in the sole cropping by 1.39% and 2.86%, respectively. The nitrogen harvest index was lower after the first increase trend accompanied the increase of the nitrogen application rate in oil flax/soybean intercropping system. The N₁ treatment in the intercropping system had the greater N harvest index. The findings indicated that applied N reduced the N harvest index in the sole cropping, but increased N harvest index in intercropping system.The agronomic utilization rate of nitrogen fertilizer, utilization rate of nitrogen absorption and nitrogen partial productivity of oil flax in the intercropping system was, respectively, greater than that in the sole cropping. The agronomic utilization rate of nitrogen fertilizer and nitrogen partial productivity of soybean in intercropping system was greater than that in the sole cropping by 26.22% and 16.33%, respectively. The agronomic utilization rate of nitrogen fertilizer of oil flax in intercropping system under N₁ treatment was greater than that in the sole cropping under N2 treatment by 8.28%. The utilization rate of nitrogen absorption and nitrogen partial productivity of oil flax in the intercropping system under N₁ treatment was higher than that in the sole cropping under N2 treatment by 61.31% and 48.22%, respectively. The agronomic utilization rate of nitrogen fertilizer, utilization rate of nitrogen absorption and nitrogen partial productivity of soybean in the intercropping system was, respectively, greater than that by 19.85%, 52.06% and 48.22% in the sole cropping, respectively, and the utilization rate of absorption of nitrogen in season was the greatest under N₁ treatment.8. The average soil NO₃-N content in the 0-100 cm soil layer during all the growth stages of oil flax was 8.69 mg/kg. The soil NO3-N content under N₁ and N2 treatments increased by 9.53% and 53.35% respectively compared with that under N₀ treatment. The findings indicated that application of N fertilizer significantly increased soil NO3-N content. After harvesting soybean, the soil NO3-N content of oil flax and soybean in the intercropping decreased by 20.32% and 11.62% respectively compared with that in the sole cropping. The soil NO3-N content in 0-100 cm soil layer during the full-flowering stage of oil flax was the highest. The soil NO3-N content in 0-20 cm soil layer was greatest during all the growth stage in the intercropping system. The soil NO3-N content in 0-20 cm soil layer under N₁ and N2 treatments increased by 34.25% and 41.38% respectively compared with that under N₀ treatment.9. After harvesting oil flax, the absorption of N nutrient of oil flax in 0-60 cm soil layer reduced by 7.70% in the intercropping system than that in the sole cropping. In the intercropping system, the absorption of N nutrient of oil flax under N2 treatment was greater by 51.42% and 21.58% respectively than that under N₀ and N₁. In the sole cropping, it was greater by 56.19% and 21.96% respectively. The absorption of N nutrient of oil flax in 60-100 cm soil layer in the sole cropping declined by 9.36% compared with that in the intercropping system. In the sole cropping, the absorption of N nutrient of oil flax under N2 was greater by 45.88% and 21.82% respectively than that under N₀ and N₁ treatments, while it was greater by 55.73% and 20.4% respectively in the intercropping system. After harvesting soybean, the absorption of N nutrient of soybean in 0-60 cm soil layer in the intercropping system reduced by 16.11% compared with that in the sole cropping. The absorption of N nutrient of soybean in the sole cropping under N2 treatment was greater by 50.87% and 1.53% respectively than that under N₀ and N₁ treatments, and it was higher by 50.06% and 1.69% respectively than that in the intercropping system. The absorption of N nutrient of soybean in 60-100 cm soil layer in the sole cropping was higher by 21.26% than that in the intercropping system. In the sole cropping, the absorption of N nutrient of soybean in 60-100 cm soil layer under N2 treatment was higher by 54.53% and 14.68% respectively than that under N₀ and N₁ treatments, and in the intercropping system, it was higher by 53.19% and 10.94% respectively.