作为一种有限的自然资源，磷（P）逐渐成为影响全球可持续发展的新挑战。中国农业对全球可持续磷管理意义重大。在中国集约化的农业生产中，通过根际和土壤磷管理来提高磷的利用效率和作物生产力是很有必要的。之前的研究表明，利用LePA模型（legacy phosphorus assessment model）基于土壤磷管理（恒量监控方法）预测中国未来的磷肥需求量会大大降低。本研究利用LePA模型基于根际和土壤磷综合管理预测了在四种减磷情景下我国各县未来的磷肥需求量。四种情景设置分别为：（1）模拟期间磷肥投入量与2012年相同；（2）低磷县先保持2012年的施磷水平，而高磷县先停施磷肥，直至土壤Olsen-P达目标值，然后施磷量均与作物磷带走量相同；（3）低磷县的土壤Olsen-P达目标值后，各县的施磷量每年降低1 – 7 kg ha^-1，然后每年增加0.1 – 9 kg ha^-1至作物磷带走量；（4）低磷县的磷投入量与2012年相同直至土壤Olsen-P含量升高到目标值，而高磷县的磷投入量先每年降低1 – 7 kg ha^-1，再每年增加0.1 – 9 kg ha^-1，然后与作物磷带走量相同。结果表明，情景4分析的我国在2013 – 2080年期间的磷肥需求总量为6.93亿吨，与农民传统施磷量相比降低了57.5%。与基于土壤管理的磷需求量相比，模拟期间我国磷肥总需求量可进一步降低8.0%。我国平均的土壤Olsen-P含量只需维持在17.2 mg kg^-1即可满足作物高产的需求。我们的研究结果为政府出台可持续磷管理的相关政策提供了坚实的基础。

【目的】山羊关节炎-脑炎病毒（Caprine arthritis-encephalitis virus，CAEV）属于反转录病毒科慢病毒属成员，与梅迪-维斯纳病毒（Maedi visna virus）合称为小反刍动物慢病毒（Small ruminant lentiviruses）。该病毒可感染山羊和绵羊，以奶山羊最为易感。在过去四十年间，CAEV在我国传播扩散，并存在不同程度的感染，但有关该病毒基因组特征和可能的来源研究仍然较少，获取在中国流行的CAEV毒株的基因组数据对于开发诊断方法和根除相关疾病具有重要意义。【方法】本研究使用分段扩增和测序的方法获得了1989–1994年间从我国甘肃、贵州、陕西、山东和四川等地感染奶山羊中分离的5株CAEV病毒基因组，通过基因型分析、全基因组比对、遗传进化和种群结构分析来阐释该病毒基因组特征。【结果】我国CAEV与国外毒株基因组相似度为58%–93%，属于B型小反刍动物慢病毒，可进一步归为B1基因型。遗传进化分析结果显示本研究测定的5株病毒与其它两株中国毒株聚集成簇，亲缘关系最近，同源性为98.3%–99.3%；其次是与美国毒株Clements（GenBank登录号NC_001463.1），相似性为91.8%–92.3%；种群结构分析表明我国已测定的7株病毒拥有与其它已知毒株不同的祖先成分。【结论】跨度5年从我国不同省份分离的CAEV毒株具有高度同源性，分离株可能起源于非已知毒株的其它来源。【创新点】本研究完成了我国最早分离的5株CAEV病毒的基因组测序和基因特征分析，确认我国分离毒株高度同源，可能起源于特定的同一祖先，该结果为研制适用于我国CAEV检测的试剂和CAEV流行病学调查与防控奠定了基础。

了解磷组分特征和影响因素对提高土壤磷利用效率具有重要的意义。基于黑土、潮土和塿土的长期定位试验，选择了五种施肥方式并将其分为三组：无磷肥处理（CK/NK）、平衡施用无机肥处理（NPK/NPKS）和有机无机配施处理（NPKM）。对土壤无机磷组分和土壤性质进行了分析，研究了无机磷组分特征及无机磷组分与土壤性质的关系。结果表明，三种土壤中Ca₁₀-P占总无机磷的比例最高，黑土、潮土和塿土分别为33.5%、48.8%、44.8%。长期施肥导致了土壤无机磷累积或耗竭的周期性变化。NPK/NPKS和NPKM处理下，黑土和潮土在施肥后期（10-20年）的磷累积量高于施肥早期（0-10年），而塿土正好相反。黑土中无机磷的累积发生在全部磷组分中，而潮土主要为Ca₈-P、Fe-P和Ca₁₀-P，塿土主要为Ca₂-P、Ca₈-P和O-P。CK/NK处理下，三种土壤的无机磷耗竭主要发生在施肥早期；除活性无机磷（Ca₂-P）和中活性无机磷（Ca₈-P、Fe-P、Al-P）外，黑土和潮土中的Ca₁₀-P，塿土中的O-P也可被作物利用。冗余分析表明，土壤性质解释了每种土壤90%以上无机磷组分的变化，其中，土壤有机质的解释百分比在黑土、潮土和塿土中分别为43.6%、74.6%、38.2%。总之，在非酸性土壤中施用磷肥时，应考虑磷的累积速率和土壤性质驱动的无机磷组分的变化。

本研究选取黄土高原旱地农田系统三个长期定位试验：杨凌（25年）、天水（35年）、平凉（37年），研究长期不同施肥对SOC及其组分，例如：矿质结合态有机碳（MOC）和颗粒有机碳（POC，包含轻组颗粒有机碳和重组颗粒有机碳）的影响。每个试验点包括三个处理：对照（不施任何肥料，CK），施化肥（CF）和化肥与有机肥配施（MCF）。结果表明：施肥显著增加了耕层（0-20 cm）土壤固碳速率，杨凌、天水和平凉三个点化肥处理较CK分别提高134、89和129 kg ha^-1 yr^-1，有机无机配施 分别提高418、153和384 kg ha^-1 yr^-1。杨凌、天水和平凉三个点MOC库分别占总SOC储量的72、67和64%；三个地点CF处理的固碳速率分别为76、57和83 kg ha^-1 yr^-1，MCF分别为238、118和156 kg ha^-1 yr^-1且呈现出MOC饱和的趋势。相应的POC库储量在三个试验点分别占总SOC储量的27、33和36%，其中Light-POC占SOC总量的11、17和22%，Heavy-POC占17、16和15%。三个点CF处理POC库固碳速率分别为58、32和46 kg ha^-1 yr^-1，MCF分别为181、90和228 kg ha^-1 yr^-1。其中，Light-POC在CF处理中的贡献占POC的59、81和72%，在MCF处理中的贡献占POC的60、40和69%，其余则为Heavy-POC的贡献。相比CK处理，单施化肥对MOC和POC占总SOC的比例没有影响，而MCF处理显著降低了MOC占SOC的比例，增加了POC所占比例，主要表现为Light-POC组分的增加。SOC在不同库中的分布与土壤团聚体的分布和稳定性密切相关。本研究表明，施用有机肥不仅能够提高土壤有机碳储量，还可以显著改变土壤有机碳的组成，从而提高土壤有机碳的质量，可能与土壤有机碳的饱和水平有关。

This study investigated the effects of three contrasting soil management regimes and different nutrient treatments on the distribution of water-stable aggregates (>2, 1–2, 0.5–1, 0.25–0.5, and <0.25 mm) and associated soil organic carbon (SOC) and total nitrogen (TN) content in loess soil. A 21-yr long-term experiment was performed, in which soil management regimes include cropland abandonment (Abandonment), bare fallow (Fallow) and wheat-fallow cropping (Cropping). Under Cropping, the following nutrient treatments were employed: control (CK, no nutrient input), nitrogen only (N), nitrogen and potassium (NK), phosphorus and potassium (PK), NP, NPK, and manure (M) plus NPK (MNPK). Results demonstrated that Abandonment significantly increased the content of soil macro-aggregates (>0.25 mm) and mean weight diameter (MWD) at 0–10 and 10–20 cm soil horizons compared with Cropping, whereas Fallow yielded lower values of above two parameters. Abandonment increased SOC and TN contents in all aggregate sizes by 17–62% and 6–60%, respectively, at 0–10 cm soil layer compared with Cropping. Conversely, Fallow decreased SOC and TN contents in all aggregates by 7–27% and 7–25%, respectively. Nevertheless, the three soil management regimes presented similar SOC contents in all aggregates at 10–20 cm soil horizon. Only Cropping showed higher TN content in >0.5 mm aggregates than the two other regimes. Consequently, Abandonment enhanced the partitioning proportions of SOC and TN in >1 mm macro-aggregates, and Fallow promoted these proportions in micro-aggregates compared with Cropping. Under Cropping, long-term fertilization did not affect the distribution of aggregates and MWD values compared with those under CK, except for NPK treatment. Fertilizer treatments enhanced SOC and TN contents in aggregates at all tested soil depths. However, fertilization did not affect the partitioning proportions of SOC and TN contents in all aggregates compared with CK. Comprehensive results showed that different soil management regimes generated varied patterns of SOC and TN sequestration in loess soil. Abandonment enhanced soil aggregation and sequestered high amounts of SOC and TN in macro-aggregates. Long-term amendment of organic manure integrated with NPK maintained soil aggregate stability and improved SOC and TN sequestration in all aggregates in loess soil subjected to dryland farming.

The sustainability of the wheat-maize rotation is important to China’s food security. Intensive cropping without recycling crop residues or other organic inputs results in the loss of soil organic matter (SOM) and nutrients, and is assumed to be non- sustainable. We evaluated the effects of nine different treatments on yields, nitrogen use efficiency, P and K balances, and soil fertility in a wheat-maize rotation system (1991-2010) on silt clay loam in Shaanxi, China. The treatments involved the application of recommended dose of nitrogen (N), nitrogen and phosphorus (NP), nitrogen and potassium (NK), phosphorus and potassium (PK), combined NPK, wheat or maize straw (S) with NPK (SNPK), or dairy manure (M) with NPK (M1NPK and M2NPK), along with an un-treated control treatment (CK). The mean yields of wheat and maize ranged from 992 and 2 235 kg ha-1 under CK to 5 962 and 6 894 kg ha-1 under M2NPK treatment, respectively. Treatments in which either N or P was omitted (N, NK and PK) gave significantly lower crop yields than those in which both were applied. The crop yields obtained under NP, NPK and SNPK treatments were statistically identical, as were those obtained under SNPK and MNPK. However, M2NPK gave a significant higher wheat yield than NP, and MNPK gave significant higher maize yield than both NP and NPK. Wheat yields increased significantly (by 86 to 155 kg ha-1 yr-1) in treatments where NP was applied, but maize yields did not. In general, the nitrogen use efficiency of wheat was the highest under the NP and NPK treatments; for maize, it was the highest under MNPK treatment. The P balance was highly positive under MNPK treatment, increasing by 136 to 213 kg ha-1 annually. While the K balance was negative in most treatments, ranging from 31 to 217 kg ha-1 yr-1, levels of soil available K remained unchanged or increased over the 20 yr. SOM levels increased significantly in all treatments. Overall, the results indicated that combinations of organic manure and inorganic nitrogen, or returning straw with NP is likely to improve soil fertility, increasing the yields achievable with wheat-maize system in a way which is environmentally and agronomically beneficial on the tested soil.

The presence of abundant and diverse communities of macro-arthropods is considered an indicator of sustainability in agroecosystems. This study was designed to investigate the effects of different fertilizer treatments on abundance and diversity of insects of arable loess soil on the Loess Plateau of China. These regimes included a control with no fertilizer addition or manure, treatments with application of mineral fertilizers (N, NK, NP, PK, NPK), treatments with NPK in combination with organic materials such as wheat straw or maize stalk, treatments with two rates of organic manure application; and different crop rotations (Rot.1: winter wheat summer maize; Rot.2: winter wheat summer maize soybean intercropping; and Rot.3: winter wheat or rapeseed summer maize soybean intercropping). Soil macro-arthropods were collected from the plough layer (0-20 cm) and sorted by hand after each harvest in June and October 2001 and 2002. A total of 3 132 individuals were collected, from 7 orders and 55 families, dominated by Formicidae (61.72%) and Staphylinidae (14.24%). The results showed that individuals and groups were significantly influenced by sampling dates, while groups were significantly influenced by the fertilization treatments. Soil insect biodiversity, as determined by the Shannon index, was significantly influenced by fertilization and sampling dates. The abundance of soil insects was positively and significantly correlated with soil moisture content in October 2002. Nitrogen, phosphorus and potassium fertilizers and incorporation of organic materials were favorable factors for abundance and diversity in arable loess soil.