Soil water content and nitrogen are the main factors that affect crop yield formation, moreover, water and fertilizer are obviously relevant to each other during the production of wheat. Only more reasonable use of nitrogen and water could enhance the yield of wheat effectively. In this experiment, wheat cultivar ChangWu 134 and ChangHan 58 were selected, and four nitrogen levels were set for pot experiment: (1) No nitrogen (N0); (2) nitrogen application amount 0.12gN/kg (N1); (3) nitrogen application amount 0.24gN/kg(N2);(4)nitrogen application amount0.36gN/kg (N3). Water contents of pots were weighing during post-anthesis and three water levels were set: (1) Normal water supply during the whole growth period (W1), the soil water contents maintained 75 %-85 % of field capacity; (2) moderate water stress (W2), soil water contents kept the same level to W1 before anthesis, and then maintained 55 %-65 % of field capacity from anthesis to filling stage; (3) serious water stress (W3), soil water contents kept the same level to W1 before anthesis, and then maintained 35 %-45 % of field capacity from anthesis to filling stage; In the filling stage, two wheat cultivars were exposed to different water stresses, and we assayed and analyzed the effects of the interaction of nitrogen and water on the grain filling characteristics of superior and inferior grain, the metabolism of dry matter and nitrogen in post-anthesis. Basing on these investigations, we could systematically study and discuss the transport of dry matter and nitrogen of wheat under the interaction of water and nitrogen in post-anthesis.
The main conclusion:
1. The nitrogen treatments and post-anthesis water stressessignificantly affected the final yield formation of wheat, the moderate stress on the one hand enhanced the yield formation of ChangWu 134, but on the other hand reduced that of ChangHan 58. The wheat yield formation could be enhanced by the increased application of nitrogen, but it also declined under serious water stress in ChangHan 58. The kernels per spike and biomass all rose with the increased nitrogen application and declined with the increased water stresses. The thousand seed weight was significantly lower under the treatment of N0 than the other treatments including N1, N2 and N3, and under these treatments it showed no difference. The harvest indexes of both ChangWu 134 and ChangHan 58 all firstly declined and then rose with the increased application of nitrogen, and another tendency showed that the harvest indexes finally dropped after a temporary increase with the increase of water stress. The results indicated that appropriate nitrogen application and moderate water stress could enhance the wheat harvest index.
2. The nitrogen treatments and post-anthesis water stresses significantly affected the filling characteristics of inferior and superior grain of both two cultivars. The application of nitrogen increased the maximum theoretic grain weight and the maximum theoretic dry weight (W0) of both inferior and superior grains of the two cultivars, while water stress played an opposite role. Under the same treatment, the maximum theoretic dry weight showed significantly higher in superior grain than in inferior grain, and significantly higher in ChangWu 134 than in ChangHan 58. During the whole growth stage, the filling rate was significantly higher in superior grain than in inferior grain. The correlation analysis indicated that, the thousand seed weight of superior grain was positively related to the average rate and the total time of filling stage, while the thousand seed weight of inferior grain was related to the date that the maximum filling showed up.
3. Under the both nitrogen treatments and water treatments, there was a similar dynamic change in post-anthesis plant dry matter in both ChangWu 134 and ChangHan 58, they all firstly rose and then dropped during filling. The accumulation of dry matter was enhanced by the application of nitrogen while reduced by water stresses. The dry matter accumulation in leaf, stem and sheath of ChangWu 134 all showed higher than ChangHan 58 in both pre-anthesis and post-anthesis stages. The contribution made by the post-anthesis dry matter to grain was significantly higher than that of pre-anthesis dry matter.
4. Under the both nitrogen treatments and water treatments, the N concentration of inferior and superior grain were significantly differed from each other, although at the fifth day the N concentration of inferior grain was higher than superior grain, the N concentration of superior was ultimately dominated. The dynamic change of the N concentration in both inferior and superior grain all increased after the first decreases. The development of plant organ, the accumulation of N in the total grain and the transport amount of N in the post-anthesis nutritive organ of both ChangWu 134 and ChangHan58 were significantly affected by the interaction of nitrogen and water during anthesis and mature stages, they all rose with the increase of the amount of supplied N and dropped with the decrease of soil water content. The accumulated N contents in the nutritive organ and mature seeds of ChangHan58 took an advantage of ChangWu134, but the transport amount of N in nutritive organ of ChangHan58 was lower tha ChangWu134. 5. The effects of nitrogen and water stress that impacted on the amount of accumulated nitrogen(TNA), nitrogen production efficiency(NPE), nitrogen agronomic efficiency(NAE), nitrogen use efficiency(NUE), Nitrogen production efficiency（PFPN） and nitrogen harvest index (NHI) of ChangWu 134 and ChangHan 58 all reached a highly significant level. Under the same N level, TNA, NAE, NUE and PFPN of ChangWu 134 all showed a tendency of W1>W2>W3. While under different N treatments of N0, N1 and N2, NPE showed a trend of W3>W1>W2, and on the contrary increased in the N3 treatment. NHI dropped gradually under the nitrogen treatment of N0, while declined after an increase under N1, N2 and N3. In terms of TNA and NPE, ChangHan 58 has the similar trend with ChangWu 134, however, NAE, NUE and PFPN of it showed a fall after a temporary rise and NHI was overall increased. Under different water treatments, in both two cultivars of CahngWu 134 and CahngHan 58, TNA, NPE, NAE, NUE and PFPN all dropped with the increase of the amount of the supplied nitrogen. The NHI of ChangWu 134 firstly rose and then declined with the increase of the amount of the supplied nitrogen, the maximum showed under N2 treatment.
KEY WORDS: Winter wheat (Triticum aestivum L.), Nitrogen and water intercation, Grain-filling characteristics ,Dry matter mobilization, Nitrogen mobilization, Grain yield.