Influence of extracellular polymeric substances on the heteroaggregation between CeO2 nanoparticles and soil mineral particles.

Interaction with soil mineral particles (SMPs) and organic matters can significantly determine the fate of nanoparticles (NPs) in the environment such as waters, sediments, and soils. In this study, the heteroaggregation of CeO2 NPs with different soil minerals (kaolinite, montmorillonite, goethite and hematite) and the influence of extracellular polymeric substance (EPS) were studied. The obvious heteroaggregation between CeO2 NPs with different SMPs were demonstrated via co-settling and aggregation kinetics experiments. The variety in the heteroaggregation between CeO2 NPs with different SMPs is mainly induced by the difference in their surface properties, such as surface charge, specific surface areas and surface complexation. The presence of EPS can result in great inhibition on the heteroaggregation between CeO2 NPs with the positive charged goethite by enhancing the electrostatic repulsion between NPs and mineral colloids. However, the influence of EPS on the interaction between CeO2 NPs with negative charged SMPs is more dependent on the steric stabilization. The presence of EPS may promote the migration of CeO2 NPs in environment and then increase their risks to human health and ecosystems. These findings contribute to better understanding interactions between NPs and SMPs and have important implications on predicting the behaviors and risks of NPs in the natural environment.

[Effects of fertilization and planting patterns on soil aggregate and carbon distribution in farmland of the Loess Plateau, Northwest China]. / ç§æ¤æ¨¡å¼å’Œæ–½è‚¥å¯¹é»„åœŸæ—±å¡¬å†œç”°åœŸå£¤å›¢èšä½“åŠå ¶ç¢³åˆ†å¸ƒçš„å½±å“.

Based on a long-term experiment in the Changwu Agro-ecological Experimental Station in Xianyang, Shaanxi, China, we examined the effects of fertilization and planting patterns on soil aggregate quantity, aggregate stability and total carbon and organic carbon distribution in different aggregate fractions through dry and wet sieving methods, as well as the TOC combustion method. There were ten treatments, including uncultivated (R), wheat continuous cropping (CK/W), wheat-corn rotation (L), and nitrogen fertilizer (N), phosphorus fertilizer (P), nitrogen and phosphorus fertilizer (NP), organic fertilizer (M), nitrogen and organic fertilizer (NM), phosphorus and organic fertilizer (PM), nitrogen and phosphorus and organic fertilizer (NPM) for CK/W. The results showed that fertilizer application and planting patterns affected soil aggregate distribution and stability, the contents and contribution rates of total C and organic C. Force-stable aggregate was mainly constituted by >0.25 mm aggregate (>67%), which was reduced by fertilization. Continuous cropping decreased micro-aggregate while rotation facilitated it and the effect was larger than fertilization. Water-stable aggregate was mainly comprised of micro-aggregate (<0.25 mm), the contribution of which was larger than 61%. Both fertilizer application and planting pattern reduced water-stable micro-aggregate. Fertilizer application and planting pattern decreased the percentage of aggregate destruction rate (PAD) and increased macro-aggregate (>0.25 mm, R0.25) content. Organic fertilizer significantly improved total C and organic C concentrations in all the fractions of force-stable aggregates. Continuous cropping and rotation cropping increased total C concentration in all the aggregate fractions while rotation cropping significantly decreased organic C concentration. Single N and P fertilization decreased soil total C concentration, while mixed application of N and P fertilizers, and organic fertilizer significantly increased soil total C concentration. The effect of planting patterns on soil total C was lower than that of fertilization. Both continuous cropping and rotation cropping increased soil total C. Mixed application of N and P fertilizers, and organic fertilizer signifi-cantly increased soil organic C concentration while single N and P fertilization decreased it. The effect of planting patterns on soil organic C was lower than that of fertilization, while rotation cropping did not facilitate soil organic C. Micro-aggregate was the most notable size fraction to total carbon and organic C, with the contribution being 21.2%-33.6%. Fertilization and planting pattern increased the contribution rate of micro-aggregate in soil total C. NP and NPM significantly increased the contribution rate of micro-aggregate in soil total C and soil organic C. The effect of rotation cropping was most obvious in driving the contribution rate of micro-aggregate in soil total C and soil organic C.

[Effects of long-term fertilization on soil organic phosphorus fractions and wheat yield in farmland of Loess Plateau]. / 长期施肥对黄土旱塬农田土壤有机磷组分及小麦产量的影响.

Understanding the effects of long-term fertilization on soil organic phosphorus fractions and wheat yield in the Loess Plateau can provide theoretical support for improving phosphorus conversion, utilization, and rational use of fertilizer. We examined the effects of different fertilizer treatments on soil organic phosphorus fractions, wheat yield and soil properties of a farmland in the long-term (1984-2016) positioning test station of Changwu loess soil. There were eight treatments, including no fertilizer (CK), single application of nitrogen fertilizer (N), single application of phosphorus fertilizer (P), application of nitrogen and phosphorus fertilizer (NP), single application of organic fertilizer (M), nitrogen combined with organic fertilizer (MN), phosphorus combined with organic fertilizer (MP), nitrogen and phosphorus combined with organic fertilizer (MNP). The results showed that the range of soil organic phosphorus content was 244.7-429.1 mg·kg-1 after long-term fertilization. Except for the N treatment, organic phosphorus content was significantly increased by 15.4%-47.9% compared to CK. Long-term application of phosphorus fertilizer changed the content of organic phosphorus fractions in the surface soil (0-20 cm). The treatments of MP and MNP significantly increased the contents of labile organic phosphorus and moderately labile organic phosphorus. The treatments of N, P and NP significantly reduced the content of moderately stable organic phosphorus. The treatments of N, P, NP, MN, MP, MNP all significantly increased the highly stable organic phosphorus. The ratio of soil organic phosphorus fractions to total organic phosphorus content was in order of moderately labile organic phosphorus > highly stable organic phosphorus > labile organic phosphorus > moderately stable organic phosphorus. After long-term fertilizer application, the combination of nitrogen and phosphorus fertilizers, especially with organic fertilizers, significantly increased wheat biomass yield and grain yield. Among all the examined soil properties, organic matter, Olsen-P and total inorganic phosphorus were significantly positively correlated with wheat yield. MP and M could significantly increase the content of Olsen-P, total phosphorus, total inorganic phosphorus, labile organic phosphorus and moderately labile organic phosphorus in the loess soil of Loess Plateau. Our results indicated that the organic and phosphorus fertilizers could improve soil phosphorus components that could be more easily absorbed by crops. In summary, the combination of nitrogen and phosphorus fertilizers, especially with organic fertilizers, could increase soil phosphorus supply in the region and promote the wheat yield, which is important for improving soil quality in the Loess Plateau.

[Distribution characteristics of soil organic carbon under different forest restoration modes on opencast coal mine dump].

The content and storage of soil organic carbon (SOC) were compared in six wood restoration modes and adjacent abandoned land on opencast coal mine dump, and the mechanisms behind the differences and their influencing factors were analyzed. Results showed that the contents of SOC in six wood lands were significantly higher (23.8%-53.2%) than that of abandoned land (1.92 g · kg⁻¹) at 0-10 cm soil depth, the index were significantly higher (5.8%-70.4%) at 10-20 cm soil depth than the abandoned land (1.39 g · kg⁻¹), and then the difference of the contents of SOC in the deep soil (20-100 cm) were not significant. The contents of SOC decreased with increase of soil depth, but the decreasing magnitude of the topsoil (0-20 cm) was higher than that of the deep soil (20-100 cm). Compared with the deep soil, the topsoil significant higer storage of SOC in different woods, the SOC storage decreased with the soil depth. Along the 0-100 cm soil layer, the storage of SOC in six wood lands higher (18.1%-42.4%) than that of the abandoned land (17.52 t · hm⁻²). The SOC storage of Amorpha fruticosa land (24.95 t · hm⁻²) was obviously higher than that in the other wood lands. The SOC storage in the shrub lands was 12.4% higher than that of the arbor woods. There were significantly positive correlations among forest litter, fine root biomass, soil water content and SOC on the dump. Consequently, different plantation restorations significantly improved the SOC level on the dump in 0-100 cm soil, especially the topsoil. But there was still a big gap about SOC level between the wood restoration lands and the original landform. To improve the SOC on opencast coal mine dump, A. fruticosa could be selected as the main wood vegetation.

[Soil organic carbon storage changes with land reclamation under vegetation reconstruction on opencast coal mine dump].

Vegetation reconstruction was an effective solution to reclaim the opencast coal mine dump which was formed in the process of mining. To understand the impact of the vegetation reconstruction patterns' on the mine soil organic carbon (SOC) storage was essential for selecting the methods of vegetation restoration and also important for accurately estimating the potential of the soil carbon sequestration. The study area was on the Heidaigou opencast coal mine, which was 15 years reclaimed coal mine dump in Zhungeer, Inner Mongolia autonomous region, we selected 5 vegetation reconstruction patterns (natural recovery land, grassland, bush land, mixed woodland of arbor and bush, arbor land), and 16 vegetation types, 408 soil samples (0-100 m), to study the effect of the vegetation reconstruction patterns on the SOC storage. The results were showed as follows: (1) on the reclaimed coal mine dump, the vegetation reconstruction patterns significantly affected the SOC content and its distribution in the soil profile (P < 0.05). The surface 0-10 cm SOC content was grassland > shrub land > arbor forest > mixed forest of arbor and shrub > natural recovery land, in which the grassland, shrub land and arbor forest were about 2.2, 1.3, and 1.3 times of natural recovery land (2.14 g · kg(-1)) respectively. The total nitrogen (TN) showed the similar trends. (2) Among the vegetation types, Medicago sativa had the highest surface SOC content (5.71 g · kg(-1)) and TN content (0.49 g · kg(-1)), that were 171.3% and 166.7% higher than the natural recovery land, and two times of Hippophae rhamnoides, Amorpha fruticosa + Pinus tabulaeformis and Robinia pseudoacacia. (3) The effect of vegetation types on SOC mainly concentrated in the 0-20 cm depth, and the effect on TN accounted for 40 cm. (4) For the SOC storage, the order was original landform area > reclaimed dump > new dump and grassland > woodland (including arbor and shrub land). After 15 years revegetation, the soil carbon storage of the grassland, shrub land and arbor land were increased by 15.47 t · hm(-2), 6.93 t · hm(-2) and 6.95 t · hm(-2) respectively in the 100 cm depth, which were equivalent to 2/3, 1/2 and 1/2 of the original landform levels. The results showed a great ability of carbon sequestration.

[Effects of long-term fertilization on wheat yield on Loess Plateau].

The effect of long-term fertilization on the yield of winter wheat was studied on the basis of 18-year located experiment on the Loess Plateau. The results showed that the winter wheat yield increased 418.1 kg.hm-2 under N fertilization, and the average increasing rate was different with precipitation. In average and rain rich year, the average increasing rate were 30.3% and 58.9%, respectively, but in drought year, the yield decreased, and its average decreasing rate was 13.9%. The winter wheat yield under P fertilizer increased in drought year, and decreased in average and rain rich year. The average increasing rate was 6.5% in drought year, and the average decreasing rate was 15.4% and 10.0%, respectively. The average increasing rate in M, NP, PM, NM and NPM was 82.8%, 127.8%, 18.9%, 144.4%, and 169.3%, respectively. In addition, precipitation affected the amount of spike, grains per spike, and weight of thousand-grains.

[Effect of plastic-film mulch on water and nitrogen use by spring maize and on fate of applied nitrogen in the southern Loess Plateau].

The relationships between nitrogen and yield and between water and yield, and the fate of nitrogen under plastic film mulching for spring maize were studied with field plots and microplots in the southern Loess Plateau. The results showed that plastic-film mulching (N120C) could increase maize yield by 46.7%, comparing with no-mulching(N120UC) in same rate of fertilizer. The maize yield potentiality of mulching might be played fully, comparing with CK (no nitrogen), treatments N120 (urea nitrogen 120 kg.hm-2), N180 (urea nitrogen 180 kg.hm-2) and N120 M (urea nitrogen 120 kg.hm-2 + organic manure nitrogen 60 kg.hm-2) could raise grain yield by 41.8%, 43.9% and 34.7%, respectively. Mulching planting raised water use efficiency (WUE) by 57.9%, and raised rainfall use efficiency (RUE) by 54.5%. N120, N180 and N120M improved WUE by 38.4%, 47.4% and 32.4%, respectively, and improved RUE by 42.3%, 43.9% and 34.7%, respectively. Because the organic manure applied was not fully rotted cattle dung, which supplied available nitrogen slowly than urea, it raised yield and WUE to a low extent. Meanwhile, the experiment showed that 73.0%-83.7% of water used by maize from rainfall, which indicated that the key water to determine maize yield was rainfall in spring maize growth period. Mulching planting for maize had little impact on the fate of nitrogen fertilizer. The total recovery of nitrogen had little difference, NUE decreased 7.3%, and residual N in soil raised 6.4%, comparing with N120UC. A great part of the residual N was in 0-20 cm of soil, and no risk occurred for nitrogen leaching and accumulation to deeper soil layers in the first growth season.

[Effect of long-term fertilization on NO3(-)-N accumulation and moisture distribution in soil profiles].

On the basis of long-term fertilization experiments in gully area of Loess Plateau, the relationships among fertilizations, NO3(-)-N accumulation, and moisture distribution in soil profiles were evaluated. The results showed that fertilization and rainfall significantly influenced the yields. NO3(-)-was accumulated in soil profiles under N and P fertilizers and organic manure(NPM) and N and P fertilizer (NP) treatment. The accumulated NO3-N reached 340 kg.hm-2 in 60-120 cm under NPM treatment, and 220 kg.hm-2 in 80-140 cm under NP treatment, respectively. Soil moisture in 100-300 cm was significantly reduced under NPM treatment. Under NP treatment, it was significantly reduced in dry year and normal year, while under organic manure(M) treatment, it was significantly reduced in dry year. Soil moisture under P and CK treatments was relatively stable in different years. N uptake under NPM and NP treatments was significantly decreased in dry year. It reflected the close relationship among soil moisture, crops, and fertilization.

[NO3(-)-N leaching and distribution in soil profile in dry highland of Loess Plateau under long-term fertilization].

The NO3(-)-N accumulation and distribution in soil profile of Loess Plateau dry highland were studied by long-term field trials. The results showed that NO3(-)-N was accumulated in the soil profile under N-fertilization. Application of P-fertilizer or organic manure reduced the NO3(-)-N content and its leaching depth in the soil profile. The deepest depth of NO3(-)-N accumulation was 120-200 cm under N treatment, and the peak of the accumulation was the highest in NPM treatment, with the depth of 60-120 cm. The NO3(-)-N accumulation depth was 80-140 cm for NP. Without nitrogen application, there was no evident accumulation of NO3(-)-N in soil profile. The more nitrogen used, the more NO3(-)-N accumulated in soil profile. Under the same nitrogen application rate, NO3(-)-N accumulation might decrease with increasing P application.