Abstract: By the methods of ¹⁵N-foliar feeding and ¹⁵N dilution, a pot experiment of double-cropping wheat and cotton was conducted to study the nitrogen absorption and allocation in cotton plant under effects of wheat and cotton root mass. Three treatments were installed, i.e., no separation of wheat and cotton roots (treatment I), separation with nylon net (treatment II), and separation with plastic film (treatment III). The results showed that both the competition of ¹⁵N absorption between wheat and cotton root, and the translocation of absorbed ¹⁵N from wheat root to cotton were existed in the wheat-cotton double-cropping system. The absorbed ¹⁵N by cotton root was mostly allocated in aboveground part, and less in root. The aboveground part of cotton had the highest N utilization rate (NUR) in treatment I and the lowest one in treatment III, but the Ndff was lower in treatment I than in treatments II and III. At the early flowering stage of cotton when wheat was harvested and its straw was amended in situ, the absorbed nitrogen by cotton was mainly from the applied ¹⁵N, but not from the amended wheat straw. The allocation of absorbed ¹⁵N in different organs of cotton was quite different, being much higher in reproductive organs than in other organs. The biomass of cotton plant was also higher in treatment I than in treatments II and III.

Key words: Stellera chamaejasme, Seed germination, Population regeneration, Poisonous plant