土壤微生物生物量氮（MBN）在土壤中包含了最大比例的生物活性氮（N），是土壤氮循环的重要参与者。农业活动（例如作物轮作和单作）极大地影响了农业生态系统中的MBN。但是，目前农业生态系统中作物轮作和单作对MBN影响的研究极其缺乏。因此，本文基于203个已发表的文献进行整合分析（Meta 分析），以量化在合成氮肥施用下轮作和单作系统对MBN的影响。本研究发现，作物轮作显著提高了MBN的响应比（RR），并在旱地轮作条件下达到最高水平。然而，旱地作物单作并没有改变MBN的响应比，但是，水稻单作中MBN的响应比有所增加。作物轮作和单作系统之间的差异可能是由于不同的种植管理方式、氮素添加的方式、添加量和施肥年限所致。与作物单作系统相比，作物轮作对土壤总氮（TN）的增加幅度更大，对土壤pH的降低幅度较小。MBN的RR与矿质N的RR仅在作物轮作系统中正相关，MBN的RR与土壤pH的RR仅在单作系统中正相关。随机森林和结构方程模型的结果表明，MBN变化的主要驱动因素在作物轮作系统中是土壤矿质N和TN，在单作系统中是土壤pH。总之，本研究表明，轮作由于改善了土壤氮源，可以作为提高MBN的有效途径，从而提高MBN对由于大量施用化学氮肥导致的低pH的抵抗力。

目前人们对原生动物转移磷酸盐和改善玉米生长的能力还知之甚少。本文旨在探讨Colpoda cucullus能否通过转移磷来提高玉米的磷素水平。在根箱的外室土壤中接种纤毛虫C.cucullus，并添加KH232PO4、磷矿粉（RP）、普钙（SP）或磷酸铵（AP），然后在内室种植玉米。结果表明，接种C.cucullus的玉米植株³²P放射性显著高于对照。此外，接种C.cucullus后玉米干物质显著增加了25.07%，氮磷钾含量增加了1～36% (P<0.05)。接种纤毛虫后，根箱内室土壤速效磷也提高了30%以上（P<0.05）。由此推测，磷素可能由接种的C.cucullus从外室运输到内室，然后被玉米植株吸收。

 

Biochar has been widely applied as a soil amendment in many parts of the world, which can enhance soil organic carbon (SOC) sequestration and nutrient availability beyond the fertilizer effect.  Enriched in poly-condensed aromatic C forms, biochar-C is difficult to be degraded and can hold carbon in soils for hundreds to thousands of years.  Biochar production and incorporation in soil would play critical roles in climate change mitigation.  Over the last decades, numerous researches have highlighted the beneficial roles of biochar in soil amendments.  The specific ecological functions of biochar have not been clearly described because of its diversities and complexities.  For example, biochar helps to ameliorate soil acidity and increase soil aggregated carbon, but the role of microbial interactions between biochar and soil has not been well understood.  In this special issue, we selected four papers contributed by Yuan et?al. (2019), Chen et?al. (2019), Guan et?al. (2019) and Shi et?al. (2019), as a window to reflect the latest research progress of this field in China.  Yuan et?al. (2019) investigated the diversity of microbial carbon use patterns in paddy soils amended with straw or straw-derived biochar in a 3-year field experiment; Chen et?al. (2019) reported that steam explosion of crop straws could improve the characteristics of biochar; Guan et?al. (2019) evaluated the effects of uncharred maize straw and charred maize straw amendments on organic carbon contents in bulk soil and in various soil aggregate-size and density fractions; Shi et?al. (2019) summarized the positive effects and mechanisms involved in the correction of soil acidity, the alleviation of aluminum toxicity and the increase of soil pH buffering capacity by applying crop residue biochar.  Through this special issue, we hope to further boost the basic and applied researches with related to the ecological functions of biochar from different aspects in soil in China and abroad. 

Seven inorganic amendment materials were added into arsenic (As) contaminated soil at a rate of 0.5% (w/w); the materials used were sepiolite, red mud, iron grit, phosphogypsum, ferrihydrite, iron phosphate, and layered double oxides (LDO). Plant growth trials using rape (edible rape, Brassia campestris L.) as a bio-indicator are commonly used to assess As bioavailability in soils. In this study, B. campestris was grown in a contaminated soil for 50 days. All of the inorganic amendments significantly inhibited the uptake of As by B. campestris. Following soil treatment with the seven aforementioned inorganic ammendments, the As concentrations in the edible parts of B. campestris were reduced by 28.6, 10.5, 8.7, 31.0, 47.4, 25.3, and 28.8%, respectively, as compared with the plants grown in control soil. The most effective amendment was ferrihydrite, which reduced As concentration in B. campestris from 1.84 to 0.97 mg kg–1, compared to control. Furthermore, ferrihydrite-treated soils had a remarkable decrease in both non-specifically sorbed As and available-As by 67 and 20%, respectively, comparing to control. Phosphogypsum was the most cost-effective amendment and it showed excellent performance in reducing the water soluble As in soils by 31% and inhibiting As uptake in B. campestris by 21% comparing to control. Additionally, obvious differences in As transfer rates were observed in the various amendments. The seven amendment materials used in this study all showed potential reduction of As bioavailability and influence on plant growth and other biological processes still need to be further explored in the long term.

It remains unclear whether biochar applications to calcareous soils can improve soil fertility and crop yield. A long-term field experiment was established in 2009 so as to determine the effect of biochar on crop yield and soil properties in a calcareous soil. Five treatments were: 1) straw incorporation; 2) straw incorporation with inorganic fertilizer; 3), 4) and 5) straw incorporation with inorganic fertilizer, and biochar at 30, 60, and 90 t ha-1, respectively. The annual yield of either winter wheat or summer maize was not increased significantly following biochar application, whereas the cumulative yield over the first 4 growing seasons was significantly increased. Soil pH, measured in situ, was increased by a maximum of 0.35 units after 2 yr following biochar application. After 3 yr, soil bulk density significantly decreased while soil water holding capacity increased with adding biochar of 90 t ha-1. Alkaline hydrolysable N decreased but exchangeable K increased due to biochar addition. Olsen-P did not change compared to the treatment without biochar. The results suggested that biochar could be used in calcareous soils without yield loss or significant impacts on nutrient availability.

Innovative measure is a urgent requirement for managing the huge volume of municipal sewage sludge. The hydrothermal carbonation (HTC) shows some potential advantages for using hydrochar as a soil conditioner. The aim of this work was to investigate the properties of hydrochars, by means of the HTC of municipal sewage sludge under different temperatures (190 and 260°C) and reaction hours (1, 6, 12, 18 and 24 h). The HTC led to the decreases of N, O and H contents by more than 54.6, 37.9 and 10.0%, respectively, and slight changes of C content. The Py-GC-MS analysis showed that a large proportion of fatty acids, in particular hexadecanoic acid, transferred into alkenes, olefins and aromatic compounds. The 13C-NMR and fourier transform infrared spectra (FTIR) confirmed the transformation and changes in chemical structure in which hydrochar contained lower oxygen-containing organic C of O-alkyl, carboxylic and carbonyl C and aliphaticity, but higher aromatic C and aromaticity. The rich hydrophobic functions induced in high positive charges in the charred sludge. The HTC facilitated the pore structure development, proved by higher specific surface area and specific pore volume, with a maximum of 17.30 and 0.83 cm3 g-1, respectively. The availabilities of N, P and K markedly reduced during HTC treatment. The activities of most heavy metals were depressed though they accumulated in the hydrochar. Further work is required to investigate the values and risk of the charred sludge amended to soil.