Distribution of carbon and nitrogen in water-stable aggregates and soil stability under long-term manure application in solonetzic soils of the Songnen plain,northeast China

Purpose

Excessive exchangeable sodium and high pH significantly decrease soil structural stability and permeability. Long-term application of cattle manure is an important management practice that can affect water-stable aggregates (WSAs), as well as aggregate stability and distribution of soil organic carbon (SOC) and total nitrogen (TN) in solonetzic soils.

Material and methods

Experiments were carried out in a randomized complete block design comprising five treatments according to the cattle manure application history: corn (Zea mays) with manure applied for 1, 5, 12, and 17 years were used as the experimental treatments and corn without manure application was used as a control. Soil properties, including WSAs, mean weight diameter (MWD), and SOC and TN concentrations in bulk soils and WSAs, were measured across all treatments. The relationships among the measured soil attributes were determined using stepwise regression analysis.

Results and discussion

Results indicated that micro-aggregates mainly accumulated in soils without manure application, while manure application significantly increased macro-aggregates formation. MWD was highest when manure was applied to the soil for 1 year, decreased after 5 years, and increased again after 12 years. SOC and TN concentrations in bulk soils and WSAs increased with the number of years of manure application, with the highest concentrations observed for 17 years in bulk soils. Stepwise regression analysis showed that WSAs 2–5 mm, SOC in WSAs 0.25–0.5 mm, and TN in WSAs 0.1–0.25 mm were dominant independent variables affecting aggregate stability, and that SOC in WSAs 0.25–0.5 mm and TN in WSAs <0.1 mm were dominant independent variables affecting SOC and TN concentrations in bulk soils, respectively.

Conclusions

Long-term application of manure to a solonetz significantly increased macro-aggregates and aggregate stability as well as SOC and TN in bulk soils and all aggregate sizes. These results are likely related to binding agent production as well as C and N accumulation from manure application.     

Mycorrhizal function on soil aggregate stability in root zone and root-free hyphae zone of trifoliate orange

Arbuscular mycorrhizal fungi (AMF) influence soil aggregate stability through their hyphae, roots, and glomalin-related soil protein (GRSP); however, the individual effect of these factors is difficult to distinguish. Pots separated by a 37-μm mesh bag buried in the middle of each pot was used to establish root zone (root + hyphae) and hyphae zone (roots free), where the Poncirus trifoliata seedlings were colonized by Funneliformis mosseae or Paraglomus occultum in root zone. AMF inoculation significantly increased shoot, root, and plant’s total biomass, soil organic carbon, GRSP fractions, 2–4 and 1–2 mm size water-stable aggregates, and mean weight diameter (MWD) in root or hyphae zone. Within root zone, root colonization and biomass presented stronger relationship with MWD than GRSP fractions. While, within hyphae zone, total of GRSP fraction was significantly correlated with MWD. The study, suggested further that root biomass and colonization were the main mechanisms in root zone for improving aggregate stability, whereas total of GRSP fractions was of paramount importance in hyphae zone. Mycorrhizal effect on aggregate stability was observed to be contrastingly different between root zone and hyphae zone.     

Soil aggregate stability and organic matter as affected by land-use change in central Iran

This study aimed to evaluate the soil aggregate stability and selected soil quality indicators in various land uses in a semiarid region in central Iran. Random soil sampling was used to collect soil samples from surface (0–5 cm) and subsurface (5–25 cm) soil layers in rangelands of different condition classes, dry farmland and abandoned land. The aggregate size distribution indices including mean weight diameter (MWD), geometric mean diameter (GMD) and median diameter (D₅₀) of water-stable aggregates in the collected soil samples were measured. Our findings showed that percent of macroaggregates (>0.25 mm) of the surface and subsurface layers in rangelands of different condition classes were significantly higher than dry farmlands and abandoned lands (P < 0.05). Results showed that the trend of changes in soil organic matter was similar to soil aggregate stability in different land uses in both soil layers as follows: rangeland with good condition > rangeland with poor condition > abandoned land > dry farmlands. The structural stability indices (i.e. MWD, GMD and D₅₀) of rangelands with good condition were significantly greater than other land uses (P < 0.05). This highlights the importance of maintaining native rangeland to prevent organic matter loss, structure deterioration and soil erosion.     

Soil structure changes due to different land-use practices in the central Zagruos region,Iran

In this study, the effect of land-use treatments and the feasibility of fractal dimension to quantify soil aggregate stability were investigated in the central Zagrous, Iran. For this purpose, the non-linear fractal dimension (D_nl), linear fractal dimension (D_l) and the mean weight diameter (MWD) of aggregates were compared. Soil samples from three sites with four adjacent land-use types, namely: forest area (F), cultivated lands adjacent to forest (CAF), pasture (P) and cultivated lands adjacent to pasture (CAP) were collected. Results showed that soils under cultivated lands had higher bulk density (BD) (1.30–1.38 Mg m^?3) compared to the adjacent soils under forest (1.19 Mg m^?3) and pasture (1.21 Mg m^?3). In the 0–15 cm layer, soil organic matter (SOM) content in the cultivated plots were respectively 30% and 31% lower compared to the forest and pasture soils. The lowest CVs belonged to D_nl (5–8%) demonstrating that D_nl was more accurate than D_l (8–14%) and MWD (30–53%) methods. CAP had the largest value of D_nl, while P had the smallest value of D_nl. Difference of D_nl between forest and pasture was not significant, whereas both of them significantly differed from CAF and CAP. D_l did not differ significantly between forest and CAF. There were significant differences between forest and pasture for the measured MWD. Both fractal dimensions had negative correlation with MWD, SOM, hydraulic conductivity (HC) and macroaggregates (>0.25 mm) and positive correlation with BD and total porosity (TP).     

利用地统计学技术预测流域尺度土壤团聚体稳定性及团聚体结合有机碳含量空间分布

The association of organic carbon with secondary particles (aggregates) results in its storage and retention in soil. A study was carried out at a catchment covering about 92 km2 to predict spatial variability of soil water-stable aggregates (WSA), mean weight diameter (MWD) of aggregates and organic carbon (OC) content in macro- (> 2 mm), meso- (1-2 mm), and micro-aggregate (< 1 mm) fractions, using geostatistical methods. One hundred and eleven soil samples were collected at the 0-10 cm depth and fractionated into macro-, meso-, and micro-aggregates by wet sieving. The OC content was determined for each fraction. A greater percentage of water-stable aggregates was found for micro-aggregates, followed by meso-aggregates. Aggregate OC content was greatest in meso-aggregates (9 g kg?1), followed by micro-aggregates (7 g kg?1), while the least OC content was found in macro-aggregates (3 g kg?1). Although a significant e?ect (P = 0.000) of aggregate size on aggregate OC content was found, however, our findings did not support the model of aggregate hierarchy. Land use had a significant e?ect (P = 0.073) on aggregate OC content. The coe?cients of variation (CVs) for OC contents associated with each aggregate fraction indicated macro-aggregates as the most variable (CV = 71%). Among the aggregate fractions, the micro-aggregate fraction had a lower CV value of 27%. The mean content of WSA ranged from 15% for macro-aggregates to 84% for micro-aggregates. Geostatistical analysis showed that the measured soil variables exhibited di?erences in their spatial patterns in both magnitude and space at each aggregate size fraction. The relative nugget variance for most aggregate-associated properties was lower than 45%. The range value for the variogram of water-stable aggregates was almost similar (about 3 km) for the three studied aggregate size classes. The range value for the variogram of aggregate-associated OC contents ranged from about 3 km for macro-aggregates to about 6.5 km for meso-aggregates. Kriged maps of predicted WSA, OC and MWD for the three studied aggregate size fractions showed clear spatial patterns. However, a close spatial similarity (co-regionalization) was observed between WSA and MWD.     

种植苹果树对渭北果园土壤胶结物质分布的影响

本研究通过系统研究种植果树对土壤胶结性物质的演化规律及其与土壤团聚体稳定性之间关系的影响,探索影响果园土壤团聚体状态的因素,以期为果园科学管理提供理论依据。在渭北旱塬苹果主产区分别选取10 a、20 a的苹果园和农田(冬小麦-夏玉米轮作,对照)各4个,在果树冠层投影范围内距树干2/3处逐层采集0~100 cm土层土壤样品和0~50 cm土层原状土壤样品,研究不同植果年限果园及农田土壤剖面黏粒、有机质、CaCO_3等团聚体胶结物质的分布及其与团聚体稳定性之间的关系。结果发现:在0~100 cm土层范围内,各果园土壤黏粒含量基本随土层深度的增加而递增,且在0~40 cm土层表现为农田10 a果园20 a果园,40 cm以下土层则呈现相反的态势;种植果树相比农田可显著增加0~100 cm土层土壤有机质总储量,但随着种植果树年限的增加,土壤有机质总储量呈递减趋势;在0~100 cm土层土壤CaCO_3总储量表现为10 a果园农田20a果园,但在0~40 cm土层CaCO_3含量及储量表现为10 a果园农田20 a果园,而40~100 cm土层则为20 a果园10 a农田。皮尔森相关分析发现(29)0.25 mm土壤团聚体的数量和平均重量直径(MWD)与土壤黏粒、有机质和CaCO_3含量密切相关,其中机械稳定性团聚体的数量和稳定性主要受土壤中CaCO_3、有机质含量的影响,水稳性团聚体的数量和稳定性主要受土壤中黏粒和CaCO_3的影响。总之,植果显著改变了土壤中黏粒、有机质、CaCO_3的演化过程和趋势,随植果年限增加,果园土壤黏粒和CaCO_3在土壤较深土层淋溶淀积明显;各果园土壤有机质总储量虽然高于农田,但随植果年限增加,有逐渐减少的趋势。可见植果明显加速了渭北黄土塬地土壤的残积黏化和钙化过程,影响着表层土壤团聚作用和底层土壤的紧实化和坚硬化程度。     

Changes in microbial biomass C, soil carbohydrate composition and aggregate stability induced by growth of selected crop and forage species under field conditions

The effects of growth of various crop and forage species on microbial biomass C, soil carbohydrate content and monosaccharide composition, and mean weight diameter (MWD) were investigated in two field experiments. One experiment was conducted over one growing season (4 months) whereas the other had been conducted for three consecutive growing seasons (32 months). In the four-month experiment, aggregate stability (estimated as MWD) of soil from experimental plots followed the order Italian ryegrass > prairie grass > phacelia = pea = maize. At the 32-month site the order was perennial ryegrass > annual ryegrass > perennial white clover = barley. At both sites crops with the greatest root mass and root length density had the greatest effect on increasing MWD. In all cases, rhizosphere soil had a significantly higher microbial biomass and MWD than non-rhizosphere soil. However, organic C, total content of acid-hydrolysable carbohydrate and content of individual monosaccharides in acid hydrolysates were similar in rhizosphere and non-rhizosphere soil. The fraction of soil carbohydrate extractable with hot water (representing about 6-8% of the total carbohydrate content) was significantly higher in the rhizosphere soil. This fraction has a galactose plus mannose over arabinose plus xylose ratio of 2.1–2.3 indicating that it was predominantly of microbial origin. It is suggested that the carbohydrate fraction extractable with hot water is made up of exocellular microbial polysaccharides that are involved in stabilizing soil aggregates in the rhizosphere. By comparison with arable crop species, grass species have a larger root mass and root length density, and therefore a higher microbial biomass and larger production of carbohydrate extractable with hot water. As a result they have a more marked effect on improving soil aggregate stability.     

Long-term effects of biochar amount on the content and composition of organic matter in soil aggregates under field conditions

Purpose

Soil aggregates play an important role in promoting soil fertility, as well as increasing the sink capacity and stability of soil carbon. In this study, we consider the following research questions:1. Under field conditions, do different dosages of biochar increase the soil aggregation after 3 years of application?2. How does the application of biochar affect the concentration and distribution of soil total organic carbon (TOC) and total nitrogen (TN) in different sizes of aggregates?3. Can the application of biochar alter the composition of organic carbon in soil aggregates?

Materials and methods

Different amounts of biochar (up to 90 t ha^?1) were applied to a calcareous soil in a field experiment in 2009 along with the application of chemical fertilizer annually and the returning of winter wheat and summer maize straws. After 3 years, 0–20-cm soil samples were taken to measure the size distribution of soil water-stable aggregates by wet sieving, the concentrations of TOC and TN in whole aggregates and light or heavy fractions by elemental analysis equipment, and composition of TOC by Fourier transform infrared (FTIR) and pyrolysis-gas chromatography/mass spectrometer (Py–GC/MS).

Results and discussion

(1) The 3 years of biochar application had no significant effects on degree of soil aggregation but reduced the breakage of large soil aggregates (>1000 μm); (2) biochar significantly increased the contents of TOC and TN in soil macro-aggregates (>250 μm), as well as their ratios to total soil amount. Biochar also significantly increased the contents of TOC and TN in light fractions as well as the C/N ratio, which made the soil organic matter more active. The biochar dosage showed a significant positive correlation with organic carbon, total nitrogen, and C/N ratio in light fraction components of aggregates (>250 μm). Biochar mainly affected the organic matter in the heavy fraction components of macro-aggregates; (3) from the Py–GC/MS results, biochar increased the CO₂ content originated from active organic carbon.

Conclusions

Long-term application of biochar improved the stability of soil aggregates, increased the contents of TOC and TN as well as organic carbon and total nitrogen in macro-aggregates, and usually increased the contents of CO₂ originated from active organic carbon in light fractions. The findings were helpful in evaluating the effects of biochar on soil aggregation and organic matter stability.

     

Structural stability and carbohydrate contents of an ultisol under different management systems

An understanding of the dynamics of soil carbohydrate pools is necessary for assessing the impact of organic residue management in organic matter build up and structural stability in tropical ecosystems. The objectives of this study were to evaluate temporal changes in aggregate stability and cold water-soluble, hot water-soluble and acid-soluble carbohydrate fractions of a sandy soil under different organic residue management practices. The soil is an Nkpologu sandy clay loam (fine-loamy, kaolinitic, isohyperthermic, typic kandiustult) at Nsukka in southeastern Nigeria. In July 1995, it was incorporated with complete fertiliser (N:P:K = 12:12:17 at 480 kg/ha) (F); rice mill wastes (RW, 10 t/ha); RW+F; poultry manure (PM, 10 t/ha) and RW (5 t/ha)+PM (5 t/ha) up to the 0–20 cm depth. A control, tilled up to the 0–20 cm depth, was also included. Surface soil samples (0–20 cm), collected at 3, 6 and 12 months after residue applications were used to measure changes in aggregate stability by mean weight diameter (MWD), total OC and carbohydrate pools.

In all treatments MWD increased whereas the concentrations of acid-soluble, hot water-soluble and cold water-soluble carbohydrates decreased with sampling time. Also irrespective of the type of amendment, the carbohydrate concentrations at each sampling period varied in the order, acid-soluble>hotwater-soluble>coldwater-soluble. Aggregate stability correlated very poorly with all the carbohydrate fractions and OC. The correlation coefficient values were rather low and did not mean much in the physical interpretation of these results. This shows that these carbohydrate pools were not very effective in stabilizing the soil aggregates.     

稻壳及稻壳生物炭对土壤团聚体稳定性及有机碳分布的影响

【目的】长期种植雷竹(Phyllostachys praecox)会导致土壤酸化加剧,土壤结构破坏。我们比较了施用不同量稻壳和稻壳生物炭对土壤理化性状和团聚体组成的影响,以寻求实现雷竹的可持续生产的有效措施。【方法】采用盆栽方法进行雷竹幼苗试验,供试土壤长期种植雷竹,pH为5.3。设置分别施用稻壳、稻壳生物炭10 t/hm² (10H、10B)和30 t/hm² (30H、30B)处理,以不施稻壳和稻壳生物炭的处理为对照(CK)。雷竹幼苗生长262天后,采集土样测定土壤基本理化性质,采用湿筛法筛分不同粒级土壤团聚体,测定各粒级团聚体中有机碳和全氮含量。【结果】30H和30B处理均显著降低了<0.053 mm粒级团聚体含量,显著提高了水稳性团聚体的平均重量直径(MWD)、几何平均直径(GMD)以及>0.25 mm粒级团聚体(R0.25)含量;10H和10B处理对水稳性团聚体的MWD、GMD以及R0.25含量均无显著影响。30B处理显著增加了>2 mm、0.25～2 mm、0.053～0.25 mm粒级团聚体中有机碳含量,其中增...     

The effect of tea plantation age on soil water-stable aggregates and aggregate-associated carbohydrate in southwestern China

Soil carbohydrates constitute an important component of soil organic matter (SOM), and substantially contribute to the stabilization of soil aggregates. Here, we aimed to investigate the distribution of water-stable aggregates and carbohydrates within water-stable aggregates of soil in tea plantations located in Zhongfeng Township of Mingshan County, Sichuan, which is in southwest China. Samples were collected from tea plantations of different ages (18, 25, 33, and 55 years old) and an area of abandoned land was used as a control(CK). We also examined correlations between soil carbohydrates fractions and aggregate stability. The results showed that the mean weight diameter (MWD) of soil aggregates in the tea plantations was significantly higher than that the control. Furthermore, the soil aggregate stability was significantly enhanced in tea plantations, with the 25-year-old plantation showing the most pronounced effect. Soils in the plantations were also characterized by higher concentrated acid-extracted carbohydrate content, and carbohydrate content in both surface and sub-surface layers were higher in the 25-year-old plantation. We also detected a significant positive correlation between the carbohydrate content of soil and MWD after tea plantation (P < 0.01). Notably, the association between dilute-acid extracted carbohydrate and the aggregate stability showed the highest correlation, indicating this carbohydrate fraction could be used as an index to reflect changes in soil quality during tea plantation development. We should develop a potential fertilisation programme to maintain SOM- Carbohydrates within aggregates and the appropriate pH for preventing soil structure degradation after 25 years of tea planting.     

Distribution of charred plant fragments in particle size fractions of Japanese volcanic ash soils

Abstract

To gain a better understanding of the distribution of charred plant fragment C (CPFC) and its contribution to organic C (OC) in the particle size fractions of Japanese volcanic ash soils, each of four soil samples was divided into six particle size fractions, namely three sand-sized aggregate (20–53, 53–212 and 212–2,000 µm) fractions, one silt-sized aggregate (2–20 µm) fraction, and two clay-sized aggregate (< 0.2 and 0.2–2 µm) fractions. Furthermore, after HCl–HF treatment of these aggregate fractions, sub-fractions of less than specific gravity (s.g.) 1.6 g cm^?3 (< 1.6 fraction) were isolated using s.g. 1.6 g cm^?3 sodium polytungstate solution. Microscopic observation indicated that the charred plant fragments, which are black or blackish brown, were the main components in the < 1.6 fractions. Therefore, the OC in this fraction was designated as CPFC. In all the soils studied, the quantitative distribution of the CPFC of the silt-sized aggregate fractions to total CPFC of whole soils, ranging from 59 to 84%, was greatest among the aggregate fractions. The sum of the distribution (%) values of the CPFC in the three sand-sized aggregate fractions varied from 6.9 to 33%, while that in the two clay-sized aggregate fractions ranged from 1.1 to 9.4%. Similar to the CPFC, in all soils, the quantitative distribution of the OC in the aggregate fractions was greater in the silt-sized aggregate fractions (52–76%) than in the other aggregate fractions (0.1–20%). In all soils, the quantitative contribution of total CPFC to total OC of whole soils ranged from 10 to 28%. The CPFC/OC values in the aggregate fractions were 21% or more in 10 samples from a total of 24 fractions, with a maximum value of 34%. On the basis of the findings obtained in the present study, it is assumed that in Japanese volcanic ash soils the silt-sized fraction is an important reservoir of CPFC and OC, and CPFC merits attention as one of the constituents of OC in particle size fractions.     

广东省赤红壤区土壤团聚体有机碳和铁氧化物特征及稳定性

通过野外采样和室内分析相结合,以广东省赤红壤区花岗岩(G)、第四纪红土(Q)和砂页岩(S)母质发育的林地(FL)、水田(PF)和旱地(UL)土壤为研究对象,分析了土壤团聚体有机碳及其组分和不同形态铁氧化物含量,探究了其对土壤团聚体稳定性的影响及贡献。结果显示:(1)3种母质发育的3种利用方式土壤团聚体均以>0.25 mm为主,2~5 mm团聚体以花岗岩母质发育林地土壤最高(58.51%),0.25~2 mm团聚体以花岗岩(62.93%)和第四纪红土(59.21%)母质发育水田和旱地土壤最高;土壤团聚体平均重量直径(MWD)和几何平均直径(GMD)以砂页岩母质发育林地土壤最高;(2)3种母质发育林地土壤团聚体有机碳及其组分主要分布在2~5 mm粒径中,水田和旱地土壤团聚体有机碳及其组分主要分布在<0.053 mm粒径中;3种母质发育林地土壤团聚体铁氧化物含量主要分布在<0.053,0.25~2 mm粒径中,水田和旱地土壤团聚体铁氧化物含量主要分布在<0.053 mm粒径中。(3)相关分析和主成分分析表明,MWD、GMD与团聚体HAC、HAC/FAC、Fe fr和Fe co呈显著相关(P<0.05);不同母质和利用方式以砂页岩母质发育的林地土壤团聚体胶结能力最好。研究表明,不同母质和利用方式土壤团聚体HAC、HAC/FAC、Fe fr和Fe co含量分布差异显著,进而影响了土壤团聚体分布和稳定性,同时砂页岩母质发育的林地土壤团聚体结构较稳定。     

不同施肥措施及施肥年限下土壤团聚体的大小分布及其稳定性

土壤团聚体的数量和质量直接影响着土壤性质和有机碳固存。研究不同施肥措施及施肥年限对采煤塌陷区复垦土壤团聚体的重量分布比例及其稳定性的影响,可为该区农业生产和土壤质量提升提供科学依据。采集复垦6,11年定位试验不同施肥处理耕层(0—20 cm)土样,选取不施肥(CK)、平衡施氮磷钾化肥(NPK)、单施有机肥(M)、有机无机肥配施(MNPK)4个处理,利用干筛法和湿筛法获得4种粒径的团聚体/粉黏粒组分(>2,0.25~2,0.053~0.25,<0.053 mm),用>0.25 mm团聚体的含量(R0.25)、平均重量直径(MWD)、团聚体破坏率(PAD)和土壤不稳定团粒指数(ELT)表示团聚体的稳定性,同时测定土壤有机碳含量。结果表明:施肥年限较施肥措施对土壤团聚体的含量及稳定性产生了更显著的影响。干筛条件下,施肥6,11年均显著降低了各处理0.053~0.25 mm团聚体和<0.053 mm组分的含量,降幅分别为68.39%~87.37%,69.63%~78.32%(6年)和90.01%~93.68%,78.29%~83.93%(11年);湿筛条件下,施肥11年显著提高了各处理>2 mm团聚体的含量,增幅达473.35%~645.16%,但是显著降低了0.053~0.25 mm团聚体的含量,降幅为43.67%~57.54%。土壤团聚体的稳定性也随着施肥年限的增加而逐渐增强,表现为DR0.25、WR0.25和MWD值呈增加趋势,而PAD和ELT值呈降低趋势。土壤有机碳含量与DR0.25、WR0.25、MWD水稳性呈极显著正相关关系,而与PAD和ELT呈极显著负相关关系。本研究表明,该区域连续培肥11年提高了土壤大团聚体的含量而伴随着微团聚体含量的显著减少,导致土壤结构越来越稳定。这对于提高采煤塌陷区复垦土壤肥力、改善土壤结构产生了良好的效果。     

RELATIONSHIP OF SOIL EXTRACTABLE AND FERTILIZER BORON TO SOME SOIL PROPERTIES,CROP YIELDS,AND TOTAL BORON IN COTTON AND WHEAT PLANTS ON SELECTED SOILS OF PUNJAB,PAKISTAN

Boron (B) is an essential microelement, which is necessary for reproductive organs including pollen tube formation in wheat (Triticum aestivum L.), and flowering and boll formation in cotton (Gossypium hirsutum L.) The study was associated with wheat-cotton rotation in 80 farm fields, belonging to different soil series, in four districts of cotton belt of Punjab, Pakistan to assess concentrations of extractable B in soils [0.05 M hydrochloric acid (HCl) extractable B], and added fertilizer B and their relationship to some soil physico-chemical properties [pH, organic matter (OM), calcium carbonate (CaCO₃) and clay content], yields and total B concentrations in wheat and cotton plants. All soils had alkaline pH (7.45 to 8.55), high CaCO₃ content (2.14 to 8.65%), less than 1.0% OM (0.33 to 0.99%), low plant available-P (Olsen P less than 8 mg kg^?1 soil) and medium ammonium acetate extractable potassium (K) (< 200 mg K kg^?1 soil). Of the 80 soil samples, 65 samples (81%) were low in available B (<0.45 mg B kg^?1, ranging from 0.11 to 0.43 mg B kg^?1) Of the corresponding 80 plant samples, leaves B concentrations were below critical levels (<10 mg B kg^?1 for wheat; <30 mg B kg^?1 for cotton) for all the tested samples for wheat and cotton. The regression analysis between plant total B concentrations and soil extractable B concentrations showed strong linear positive relationships for both wheat (R² = 0.509***, significant at P <0.001) and cotton (R² = 0.525***, significant at P <0.001). Further regression analysis between extractable soil B and wheat grain yield as well as between wheat leaves total B and wheat grain yield also depicted strong linear relationships (R² = 0.76 and 0.42, respectively). Boron fertilizer demonstration plots laid out at farmers’ fields low in extractable B, in each district not only enhanced grain yields of wheat crop but also contributed a significant increase towards seed cotton yield of succeeding cotton crop through residual B effect. In conclusion, the findings suggest that many soils in the cotton belt of Punjab may be low in extractable B for wheat and cotton, especially when these crops are grown on low OM soils with high CaCO₃ content.     

Biochar addition drives soil aggregation and carbon sequestration in aggregate fractions from an intensive agricultural system

Purpose

Biochar application is deemed to modify soil properties, but current research has been mostly conducted on the degraded land in tropical regions. Using six consecutive years of biochar field trial, we investigated effects of biochar on soil aggregates, structural stability, and soil organic carbon (SOC) and black C (BC) concentrations in aggregate fractions. The findings have important implications in managing soil structure and SOC sequestration in high fertility soils of the temperate areas.

Materials and methods

The study had four treatments: control; biochar rate at 4.5 (B4.5) and biochar rate at 9.0 t ha^?1 year^?1 (B9.0); and straw return (SR). Soil samples were collected from 0–10-cm layer, and aggregate size distribution was determined with the wet-sieving method. Then, the mean weight diameter (MWD) of aggregates and the aggregate ratio (AR), i.e., the ratio of the >250 μm to the 53–250 μm size were calculated to assess the structural stability. Total SOC and BC concentrations in bulk soil (<2 mm) and separated fractions (i.e., >2000, 250–2000, 53–250, and <53 μm) were measured.

Results and discussion

The B4.5 and B9.0 significantly increased macroaggregate (250–2000 μm) and MWD and AR indices relative to the control. Comparing to the SR, the improvements in soil aggregation under biochar treatments were limited. Additionally, more SOC in larger fractions (>2000, 250–2000, and 53–250 μm) and BC in extracted fractions under biochar soils were observed. These results implied that biochar addition enhanced both native SOC and BC physical protection by aggregation.

Conclusions

Biochar application is effective in mediating soil aggregation, and thus improves both native SOC and BC stabilization in an intensive cropping system of North China.

     

生物有机肥配施化肥对设施土壤养分含量及团聚体分布的影响

本研究以番茄–黄瓜轮作下的设施土壤为研究对象，共设4个处理（1/2化肥氮+1/2生物有机肥氮，COF；全部施用生物有机肥氮，OF；全部施用化肥氮，CF；不施肥处理，CK），探讨生物有机肥配施化肥对设施土壤养分含量及团聚体分布和稳定性的影响。研究结果表明，相较于单施化肥处理，施用生物有机肥均提高了土壤有机碳、全氮、全磷、全钾、有效磷、速效钾养分含量和土壤pH，分别提高了9.61%~54.28%、7.38%~35.45%、31.86%~98.53%、40.88%~96.40%、3.02%~15.99%、0.96%~18.23%和0.73%~7.03%；单施生物有机肥或与化肥配施均可使土壤大团聚体（>0.25 mm）比例上升，微团聚体（<0.25 mm）比例下降，显著提高了土壤团聚体平均重量直径（MWD）、几何平均直径（GMD）和>0.25 mm团聚体含量（R_0.25）（P<0.05），且土壤团聚体稳定性随着施入生物有机肥年限的增加而增加；相关分析表明，MWD、GMD和R_0.25均与>2 mm和0.25~2 mm团聚体质量分数呈显著正相关（P<0.05），与<0.053 mm团聚体组成呈极显著负相关（P<0.01），与0.053~0.25 mm团聚体组成呈显著负相关（P<0.05）。生物有机肥替代化肥更有利于提高土壤养分含量、大团聚体的数量及团聚体的稳定性。     

Nutrient Element Contents and Cation Exchange Capacity in Fine Fractions of Southeastern Nigerian Soils in Relation to Their Stability

Abstract

Soils collected from 15 locations from SE Nigeria at the 0‐ to 20‐cm depth were studied for the nutrient elements of fine fractions and their role in the stability of the soils. The objective was to understand the role of these elements in the stability of the aggregates. The fine fractions were clay and silt, and elements measured in the fine fractions were exchangeable sodium (Na⁺), potassium (K⁺), calcium (Ca²⁺), magnesium (Mg²⁺), exchangeable acidity (EA), cation exchange capacity (CEC), and available phosphorus (P). The aggregate stability was measured at the microlevel with clay dispersible indices and water‐stable aggregate (WSA) <0.25 mm, and at macrolevel with other WSA indices and mean‐weight diameter (MWD). Soils varied from loamy sand to sandy clay. There were more exchangeable cations, CEC, EA, and available P in clay than in the silt fraction. Whereas EA values ranged from 2.8 to 10.4 cmol kg^?1, they were between 1.6 and 9.2 cmol kg^?1 in silt. The CEC in the clay fraction was from 7.4 to 70 cmol kg^?1 and between 4.0 and 32.8 cmol kg^?1 in the silt fraction. The WDC were from 50 to 310 g kg^?1 while the average dispersion ratio (DR) was generally higher than the corresponding clay‐dispersion ratio (CDR), and the MWD ranged from 0.45 to 2.68 mm. Soils with WSA skewed mostly to higher WSA (>2–1.00 mm) had a higher MWD. Exchangeable Ca²⁺ in clay correlated significantly with CDR and WSA sizes 1.0–0.5 mm and 0.5–0.25 mm (r=0.45,* 0.51,* and 0.60*), respectively, but negatively correlated with clay flocculation index (CFI) (r=?0.45*). Also, available P in clay correlated respectively with CDR and CFI (r=0.45*, ?0.45*), whereas K⁺ in silt correlated significantly with WDSi (r=0.64*), CFI (r=0.62*), and CDR (r=?0.65*). Principal component analysis revealed that elemental contents in the silt fraction can play very significant roles in the microaggregate stability.     

Impact of Soil Management on Organic Carbon Content and Aggregate Stability

Abstract

Soil cultivation influences organic carbon storage and soil structures. To evaluate the impact of different soil‐management practices on soil organic carbon (SOC) pools and aggregate stability in black soils, SOC in whole soil, various size aggregates, and density‐separated fractions from three long‐term experiments (20 years) was examined. The three soil‐management systems were grassland (GL), bare land (BL), and croplands. The croplands had two treatments: nitrogen and phosphorus fertilizer application (NP) and NP together with organic manure (NPM). The SOC in the 0‐ to 10‐cm layer decreased in the order NPM>GL>NP>BL and also declined with the soil depth. The SOC of GL increased by 9.7% as compared to NP after 20 years of natural vegetation restoration. The SOC of NPM increased by 11% over NP after 13 years of organic manure application. The percentages of water‐stable aggregate (>0.25 mm) (WSA_>0.25mm) decreased in the order GL>BL>NPM>NP in the top 0‐ to 20‐cm horizon. WSA_>2mm, the most important fraction for carbon (C) storage in GL and NPM, accounted for 33 and 45% of the whole soil for GL in the depths of 0–10 and 10–20 cm, respectively, and 25 and 18% for NPM in the same soil layers. A significant positive correlation was found between the C stored in WSA_>2mm and total SOC (r=0.81, P<0.05) and between the mean weight diameters (MWD) of aggregates and total SOC (r=0.78, P<0.05). Water‐stable aggregate_0.25–2mm was the largest fraction of WSA_>0.25mm, ranging from 54 to 72% for the 0‐ to 10‐cm layer and 46 to 71% for the 10‐ to 20‐cm layer; thus these aggregates would play a major role in soil sustainability as well as the resistance to soil erosion. The organic carbon (OC) of heavy fraction (HF) accounted for 94–99% of the OC in the WSA_0.25–2mm, whereas free particulate organic matter (fPOM) and occluded particulate organic matter (oPOM) contributed a minor fraction of the OC in the WSA_0.25–2mm, suggesting that C sequestration in HF could enhance the stability of aggregates and C pools in black soil.     

Water-stable aggregates, glomalin-related soil protein, and carbohydrates in a chronosequence of sandy hydromorphic soils

The conversion of pasture to cropland leads to a decline of aggregation in topsoils and to a decrease of aggregate-binding agents such as carbohydrates and glomalin-related soil protein (GRSP). Till now, studies on soil aggregation focused either on carbohydrates or on GRSP as a binding agent in aggregates. In this study we analyse the development of the relationship between carbohydrates, GRSP, TOC and aggregate-stability following land-use change. Furthermore, we discuss the contents of carbohydrates, GRSP and TOC in each of the aggregate fractions. For these purposes, a chronosequence of sites, which were converted from pasture to cropland at different periods in history, was established. To get further insight into the impact of different types of land-use, also soils under forest, either afforested or permanent, were studied. The mean-weight diameter (MWD) of water-stable aggregates, the carbohydrate, and the GRSP content were determined in 49 soils. It was found that the MWD of the water-stable aggregates decreased monoexponentially (R² = 0.66) by 66% during the first 46 years after conversion of the soils from pasture to cropland. During the same period, the carbohydrate content decreased very rapidly after the land use change by 64% and the GRSP content decreased more slowly by 57%. The MWD of the forest soils were in the same range as those of the permanent pasture soils although they exhibit significantly higher TOC contents, which indicate that other stabilization mechanisms are dominant in forest soils, less important in the chronosequence soils. TOC, carbohydrates and the GRSP contents were sigmoidally correlated with the MWD. Among the four water-stable aggregate fractions TOC and carbohydrates exhibited high contents in the macroaggregates and were less present in the microaggregates. GRSP, in contrast, was more equally distributed among the four water-stable aggregate fractions.