Study On The Optimal Nitrogen Management Strategies For Winter Wheat In The North China Plain

It is an important strategy to improve N fertilizer use efficiency by optimizing topdress N based on plant nutrition diagnosis. However, due to the genotype differences, the criteria of plant nutrition diagnosis are always not the same with different crop varieties. In order to provide parameters for N recommendation index of wniter wheat (zhongmai-175), an experiment with8treatments was carried out in Langfang, Heibei province, the amount of N supply (0-90cm soil Nmin at regreen+N topdressing at regreen+N topdressing at flowering) for each treatment were67,120,180,240,300,360and420kg N/ha, respectively. During winter wheat growth stages, soil and plant were sampled at key stages; plant N%, basal stem nitrate, leaf SPAD value and soil nitrate nitrogen were measured and analyzed too. The main results are showed as follows.Nitrogen application can improve or significant improve nitrogen content of grain and straw. And N supply has significant correlation with N content of grain and straw, respectively. When the amount of N supply after regreen (0-90cm soil Nmin at regreen+topdressing N at regreen and flowering) were90,180,300,420kg N/ha, the content of grain N were2.46%,2.81%,2.89%and2.93, respectively, which were10%,25%,29%and31%higher than those of no N application treatment (soil Nmin at regreen=67kg N/ha); the content of straw N were0.38%,0.52%,0.62%and0.64%, respectively, which were13%,55%,84%and88%higher than those of no N application treatment.Nitrogen application can also improve or significant improve plant N%, basal stem nitrate and leaf SPAD vaules. At early inflorescence emergence stage (GS52), leaf SPAD value and plant N%were increased with the increasing amount of N supply. After the critical highest value, which were respectively59.5and2.9%, leaf SPAD value and plant N%began to decrease slowly. However, with the increasing of N supply, the concentration of basal stem nitrate was almost increased at a range from0to2100kg NO3/L. At first awns visible stage (GS49), the amount of soil Nmin at0-90cm has significant correlations with dignosis criteria of plant nitrition such as plant N%, leaf SPAD value and basal stem nitrate, respectively. Further more, there were also significant correlations between N supply at GS49(0-90cm soil Nmin+topdress N at GS49) and N content of grain and straw at harvest, respectively. Therefore, plant nutrition dignosis can be used for topdress N recommendation instead of soil Nmin at this growth stage.During winter wheat growth stages, there were significant correlations between plant N%and basal stem nitrate, between plant N%and leaf SPAD value, and between basal stem nitrate and leaf SPAD value, respectively at end of tillering (GS29), mid boot stage (GS43),80%of inflorescence emerged stage (GS58) and medium milk stage (GS75). And these diagnosis criteria can be used for topdress N recommendation and grain protein forecast. To obtain a higher quality of wheat grain (protein, nitrogen content), SPAD was the best alternative for topdress N recommendation instead of soil Nmin. And more plant samples should be collected for topdress N recommendation based on basal stem nitrate, for the variance of basal stem nitrate concentration is large. Besides, SPAD at early flowering stage (GS63), plant N%and basal stem nitrate at GS75are the best indicators to predict grain protein content at harvest.