磷（P）是一种不可再生资源，也是植物生长的关键营养元素，对作物产量的提高起着重要作用。磷肥的过量施用在农业生产中很普遍，这不仅浪费了磷肥资源，还造成了磷的积累和地下水污染。为了获得较高的产量和磷素利用效率（PUE），我们假设农业系统的表观磷平衡可以作为确定磷投入阈值的关键指标。因此，我们进行了长达12年的定位田间试验，包括6个施磷处理，施磷量分别为0、45、90、135、180和225 kg P₂O₅ ha^–1，以明确作物产量、PUE和土壤Olsen-P对磷平衡的反应并优化磷投入。结果表明，当磷肥施用量超过某一水平时，周年产量不再增加，当周年磷肥施用量为90–135 kg P₂O₅ ha^–1时可以实现较高的产量和PUE。当磷平衡阈值为2.15–4.45 kg P ha^–1时可以实现最佳产量和最小的环境风险。基于磷平衡阈值估算的磷投入为95.7–101 kg P₂O₅ ha^–1，施磷量在此阈值内时可以协同提高产量与PUE（90.0–94.9%）。此外，本研究发现磷投入-产出平衡框架的建立有助于评估土壤Olsen-P在未来的变化，其中土壤磷平衡每增加100 kg P ha^–1，有效磷含量上升4.07 mg kg^–1。总之，磷平衡可以作为农业生产中磷管理的一个重要指标，为限制磷过剩和制定更高产、高效和环保的磷肥管理策略提供有力参考。

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.

Crop models can be useful tools for optimizing fertilizer management for a targeted crop yield while minimizing nutrient losses. In this paper, the parameters of the decision support system for agrotechnology transfer (DSSAT)-CERES-Maize were optimized using a new method to provide a better simulation of maize (Zea mays L.) growth and N uptake in response to different nitrogen application rates. Field data were collected from a 5 yr field experiment (2006-2010) on a Black soil (Typic hapludoll) in Gongzhuling, Jilin Province, Northeast China. After cultivar calibration, the CERES-Maize model was able to simulate aboveground biomass and crop yield of in the evaluation data set (n-RMSE=5.0-14.6%), but the model still over-estimated aboveground N uptake (i.e., with E values from -4.4 to -21.3 kg N ha-1). By analyzing DSSAT equation, N stress coefficient for changes in concentration with growth stage (CTCNP2) is related to N uptake. Further sensitivity analysis of the CTCNP2 showed that the DSSAT model simulated maize nitrogen uptake more precisely after the CTCNP2 coefficient was adjusted to the field site condition. The results indicated that in addition to calibrating 6 coefficients of maize cultivars, radiation use efficiency (RUE), growing degree days for emergence (GDDE), N stress coefficient, CTCNP2, and soil fertility factor (SLPF) also need to be calibrated in order to simulate aboveground biomass, yield and N uptake correctly. Independent validation was conducted using 2008-2010 experiments and the good agreement between the simulated and the measured results indicates that the DSSAT CERES-Maize model could be a useful tool for predicting maize production in Northeast China.

A novel nodulin gene, GmN479 genomic clone composing of 3 630 nucleotides was isolated from mature soybean nodules using GmN479 cDNA as a probe by subtractive hybridization procedure. GmN479 encodes 170 amino acids with 2.09 kb nucleotides promoter region, and contains two important upstream promoter elements, one is a conserved cis-acting sequence motif 5´-AAAGAT-3´ controlling nodulin gene expression, and the other is typical CAAT boxes. GmN479 gene has a single zinc-finger C2H2 domain YSCAFCQRGFSNAQALLGGHMNIH and a conserved motif, QALGGHMN in the zinc-finger with a short leucine repeat in the LDLELRLGL motif closed to C-terminal. These two conserved motifs share respectively higher identity with those in the floral regulator SUPERMAN gene, indicating that GmN479 may function as a transcriptional regulator, and is a likely candidate for playing a role in nodule-morphogenesis. Blotting data showed that GmN479 is a single copy presenting in the genome of soybean nodule, and its expression profile is similar to that of Lba, but it is different from that of ENOD2. GUS staining showed that GmN479 promoter just functions in the infected cells of nodules, indicating that the GmN479 is one of the truly symbiotically induced host genes, and belongs to a late nodulin gene. The expression pattern of GmN479 gene seems to imply that it may be closely related to the development of the nodule. In a sense, it may be a useful marker for identifying the development of the infected cell system in the nodules of soybean.