不同氮（N）水平下玉米的生理和代谢差异是田间合理氮素营养管理的基础，对提高氮肥利用率和减少环境污染具有重要作用。本文在明确长期不同氮肥处理下玉米氮效率和产量响应的前提下，利用非靶代谢组学方法分析了相应的差异代谢物及其代谢途径的差异。结果表明，氮胁迫（包括缺乏和过量），通过调节碳代谢产物（包括糖醇和TCA循环中间体）和氮代谢产物（包含各种氨基酸及其衍生物）影响碳氮代谢的平衡。缺氮胁迫时，L-丙氨酸、L-苯丙氨酸、L-组氨酸和L-谷氨酰胺显著下调，而过量氮时，L-缬氨酸、脯氨酸和L-组氨酸显著上调。除了上述碳氮代谢中的糖醇和氨基酸外，在该实验条件下，一些次生代谢物如黄酮类化合物（包括山奈酚、木犀草素、芸香素和香叶木素）和激素类（包括吲哚乙酸、反式玉米素和茉莉酸）可以初步被筛选作为氮胁迫诊断的指标。本研究还表明，N2处理（120 kg·ha^-1 N）和N3处理（180 kg·ha^-1 N）的叶片代谢水平相似，这与12年试验中两处理之间生理指标和产量的变化趋势一致。本研究在代谢水平上验证了氮肥减施即施用量从180 kg·ha^-1（当地推荐）减少到120 kg·ha^-1的可行性，为不降低产量条件下减少氮肥施用，进而提高氮肥利用率和保护生态环境提供了理论基础。

The physical and chemical heterogeneities of soils make the soil spectral different and complicated, and it is valuable to increase the accuracy of prediction models for soil organic matter (SOM) based on pre-classification. This experiment was conducted under a controllable environment, and different soil samples from northeast of China were measured using ASD2500 hyperspectral instrument. The results showed that there are different reflectances in different soil types. There are statistically significant correlation between SOM and reflectence at 0.05 and 0.01 levels in 550–850 nm, and all soil types get significant at 0.01 level in 650–750 nm. The results indicated that soil types of the northeast can be divided into three categories: The first category shows relatively flat and low reflectance in the entire band; the second shows that the spectral reflectance curve raises fastest in 460–610 nm band, the sharp increase in the slope, but uneven slope changes; the third category slowly uplifts in the visible band, and its slope in the visible band is obviously higher than the first category. Except for the classification by curve shapes of reflectance, principal component analysis is one more effective method to classify soil types. The first principal component includes 62.13–97.19% of spectral information and it mainly relates to the information in 560–600, 630–690 and 690–760 nm. The second mainly represents spectral information in 1 640–1 740, 2 050–2 120 and 2 200–2 300 nm. The samples with high OM are often in the left, and the others with low OM are in the right of the scatter plot (the first principal component is the horizontal axis and the second is the longitudinal axis). Soil types in northeast of China can be classified effectively by those two principles; it is also a valuable reference to other soil in other areas.

The effect of long-term straw return on crop yield, soil potassium (K) content, soil organic matter, and crop response to K from both straw and chemical K fertilizer (K2SO4) were investigated in a fixed site field experiment for winter wheat-summer maize rotation in 6 years for 12 seasons. The field experiment was located in northern part of North China Plain with a sandy soil in relatively low yield potential. Two factors, straw return and chemical K fertilizer, were studied with two levels in each factor. Field split design was employed, with two straw treatments, full straw return of previous crop (St) and no straw return, in main plots, and two chemical K fertilizer treatments, 0 and 60 kg K2O ha–1, as sub-plots. The results showed that straw return significantly increased yields of winter wheat and summer maize by 16.5 and 13.2% in average, respectively, and the positive effect of straw return to crop yield showed more effective in lower yield season. Straw return significantly increased K absorption by the crops, with significant increase in straw part. In treatment with straw return, the K content in crop straw increased by 15.9 and 21.8% in wheat and maize, respectively, compared with no straw return treatment. But, straw return had little effect on K content in grain of the crops. Straw return had significant influences on total K uptake by wheat and maize plants, with an increase of 32.7 and 30.9%, respectively. There was a significant correlation between crop yield and K uptake by the plant. To produce 100 kg grain, the wheat and maize plants absorbed 3.26 and 2.24 kg K2O, respectively. The contents of soil available K and soil organic matter were significantly affected by the straw return with an increase of 6.07 and 23.0%, respectively, compared to no straw return treatment. K2SO4 application in rate of 60 kg K2O ha–1 showed no significant effect on wheat and maize yield, K content in crop straw, total K uptake by the crops, soil available K content, and soil organic matter. The apparent K utilization rate (percentage of applied K absorbed by the crop in the season) showed difference for wheat and maize with different K sources. In wheat season, the K utilization rate from K2SO4 was higher than that from straw, while in maize season, the K utilization rate from straw was higher than that from chemical fertilizer. In the whole wheat-maize rotation system, the K absorption efficiency by the two crops from straw was higher than that from K2SO4.