Effects of Long-Term Winter Planted Green Manure on Distribution and Storage of Organic Carbon and Nitrogen in Water-Stable Aggregates of Reddish Paddy Soil Under a Double-Rice Cropping System

In agricultural systems, maintenance of soil organic matter has long been recognized as a strategy to reduce soil degradation. Manure amendments and green manures are management practices that can increase some nutrient contents and improve soil aggregation. We investigated the effects of 28 yr of winter planted green manure on soil aggregate-size distribution and aggregateassociated carbon（C） and nitrogen（N）. The study was a randomized completed block design with three replicates. The treatments included rice-rice-fallow, rice-rice-rape, rice-rice-Chinese milk vetch and rice-rice-ryegrass. The experiment was established in 1982 on a silty light clayey paddy soil derived from Quaternary red clay（classified as Fe-Accumuli-Stagnic Anthrosols） with continuous early and late rice. In 2009, soil samples were collected（0-15 cm depth） from the field treatment plots and separated into water-stable aggregates of different sizes（i.e., 〉5, 2-5, 1-2, 0.5-1, 0.25-0.5 and 〈0.25 mm） by wet sieving. The long-term winter planted green manure significantly increased total C and N, and the formation of the 2-5-mm water-stable aggregate fraction. Compared with rice-rice-rape, rice-rice-Chinese milk vetch and rice-rice-ryegrass, the rice-rice-fallow significantly reduced 2-5-mm water-stable aggregates, with a significant redistribution of aggregates into micro-aggregates. Long-term winter planted green manure obviously improved C/N ratio and macro-aggregate-associated C and N. The highest contribution to soil fertility was from macro-aggregates of 2-5 mm in most cases.

Relationship Between Water-Stable Aggregates and Nutrients in Black Soils After Reclamation

Water-stable aggregates, which are an index for the evaluation of the structural properties of the soil, are affected by many factors. Zhaoguang Farm, Longzhen Farm, and Jiusan Farm were chosen as the representative study sites in the region of black soils, a typical soil resource in Northeast China. The variation in the content of 〉 0.25 mm water-stable aggregates and its relationship with the nutrients in black soil were investigated after different years of reclamation. The results showed that the 〉 0.25 mm water-stable aggregates were more in the surface than in the subsurface soil and they changed in the following order： Longzhen Farm 〉 Zhaoguang Farm 〉 Jiusan Farm. The water-stable aggregates decreased sharply at the initial stage of reclamation and then became stable gradually with time. They were significantly correlated with the contents of organic C, total N, total P, and CEC in black soil, with the correlation coefficients r being 0.76, 0.68, 0.61, and 0.81 （P 〈 0.01）, respectively; however, their relationships with available P, available K, and total K were unclear. These showed that organic matter was the cementation of soil water-stable aggregates. Increasing decompositions and decreasing inputs of organic matter after reclamation were responsible for the amount of reduction of the water-stable aggregates. Thus, to maintain good soil aggregate structure, attention should be paid to improvement of soil nutrient status, especially the supply of organic C and N.

Light Fraction Carbon and Water-Stable Aggregates in Black Soils

The distribution of light fraction carbon （LF-C） in the various size classes of aggregates and its relationship to water- stable aggregates as well as the influence of cultivation on the organic components in virgin and cultivated black soils were studied by wet sieving and density separation methods. The total organic carbon （TOC） and LF-C were significantly higher （P≤ 0.05） in the virgin soils than in the cultivated soils. The LF-C in aggregates of different size classes varied from 0.9 to 2.5 g kg^-1 in the cultivated soils and from 2.5 to 7.1 g kg^-1 in the virgin soils, whereas the ratio of LF-C to TOC varied from 1.9% to 7.3% and from 5.0% to 12.2%, respectively. After being incubated under constant temperature and controlled humidity for three months, the contribution of LF-C to TOC sharply decreased to an amount （1.7%4.5%） close to the level in soils that had been cultivated for 20 to 25 years （1.3%-8.8%）. As a result, the larger water-stable macro-aggregates （especially 〉 1 mm） decreased sharply, indicating that the LF-C pool in virgin soils declined quickly after cultivation, which reduced the water stability of soil aggregates.

Influences of Seasonal Freezing and Thawing on Soil Water-stable Aggregates in Orchard in High Cold Region,Northeast China

Soil aggregate stability,as an important indicator of soil functions,may be affected by seasonal freezing and thawing(SFT)and land use in high cold and wet regions.Therefore,comprehensive understanding the effects of SFT on aggregate stability in orchards during winter and spring is crucial to develop appropriate management strategies that can effectively alleviate the degradation of soil quality to ensure sustainable development of orchard ecosystems.To determine the mechanism of degradation in orchard soil quality,the effects of SFT on the stability of water-stable aggregates were examined in apple-pear orchards(Pyrus ussuriensis var.ovoidea)of four different ages(11,25,40,and 63 yr)on 0 to 5%slopes before freezing and after thawing from October 2015 to June 2016 in Longjing City,Yanbian Prefecture,Northeast China,involving a comparison of planted versus adjacent uncultivated lands(control).Soil samples were collected to investigate water-stable aggregate stability in three incremental soil layers(0–20,20–40 and 40–60 cm).In the same samples,iron oxide,organic matter,and clay contents of the soil were also determined.Results showed that the destructive influences of SFT on water-stable aggregates were more pronounced with the increased orchards ages,and SFT exerted severe effects on water-stable aggregates of older orchards(40 and 63 yr)than juvenile orchards.Undergoing SFT,the soil instability index and the percentage of aggregate destruction increased by mean 0.15 mm and 1.86%,the degree of aggregation decreased by mean 1.32%,and the erosion resistance weakened,which consequently led to aggregate stability decreased.In addition,soil free,amorphous,and crystalline iron oxide as well as soil organic matter and clay contents are all important factors affecting the stability of water-stable aggregates,and their changes in their contents were consistent with those in the stability of water-stable aggregates.The results of this study suggest that long-term planting fruit trees can exacerbate the damaging effects of SFT on aggregate stability and further soil erosion increases and nutrient losses in an orchard,which hider sustainable use of soil and the productivity orchards.

Contents of soil organic carbon and nitrogen in water-stable aggregates in abandoned agricultural lands in an arid ecosystem of Northwest China

Soil organic matter content in water-stable aggregates（WSA） in the arid ecosystems（abandoned agricultural lands especially） of China is poorly understood. In this study, we examined the WSA sizes and stability, and soil organic carbon（OC） and nitrogen（N） contents in agricultural lands with abandonment ages of 0, 3, 12, 20, 30 and 40 years, respectively, in the Minqin Oasis of Northwest China. The total soil OC and N contents at depths of 0–20, 20–40 and 40–60 cm in abandoned agricultural lands were compared to those in cultivated land（the control）. Agricultural land abandonment significantly（P0.25 mm） as the age of agricultural land abandonment increased. The effect of abandonment ages of agricultural lands on MWD was determined by the changes of OC and N accumulation in WSA sizes ＆gt;2 mm. The total OC and N contents presented a stratification phenomenon across soil depths in this arid ecosystem. That is, both of them decreased significantly at depths of 0–20 and 40–60 cm while increased at the depth of 20–40 cm. The WSA sizes ＆lt;0.053 mm had the highest soil OC and N contents（accounting for 51.41%–55.59% and 42.61%–48.94% of their total, respectively）. Soil OC and N contents in microaggregates（sizes 0.053–0.25 mm） were the dominant factors that influenced the variations of total OC and N contents in abandoned agricultural lands. The results of this study suggested that agricultural land abandonment may result in the recovery of WSA stability and the shifting of soil organic matter from the silt＋clay（＆lt;0.053 mm） and microaggregate fractions to the macroaggregate fractions. However, agricultural land abandonment did not increase total soil OC and N contents in the short-term.

The Effects of Different Ratios of Feldspathic Sandstone and Sand Compound Soil on Water-stable Aggregates in 4 Years Crop Planting

To study the formation process of feldspathic sandstone and sand compound soil in the Mu Us Desert,1∶ 1,1∶ 2 and 1∶ 5 ratios of feldspathic sandstone and sand were mixed to obtain compound soil to plant crops,and analyze the rules of changes in water-stable aggregates of the compound soil among the 4 years crops growing process. The results showed,before crop planting,the order of mass percent of> 0. 25 mm and 0. 25-2. 00 mm water-stable aggregates in three kinds of compound soil was 1∶ 1 > 1∶ 2 > 1∶ 5,showing that the overall content was low; the mass percent of > 0. 25 mm water-stable aggregates remained at 18. 38%-28. 22%; the mass percent of 0. 25-0. 50 mm,0. 50-2. 00 mm,2. 00-5. 00 mm,and > 5. 00 mm water-stable aggregates was close with each other in each kind of compound soil. After4 years of planting,the mass percent of > 0. 25 mm water-stable aggregates in 1∶ 2 compound soil increased significantly and exceeded other2 kinds of compound soil,reached 32. 34%; the main components of > 0. 25 mm water stable aggregates in 1∶ 1,1∶ 2,and 1∶ 5 compound soil were 0. 25-0. 50 mm( 53. 54%),0. 25-0. 50 mm( 59. 43%),0. 05-2. 00 mm( 52. 16%),aggregates; 0. 25-2. 00 mm aggregates increased significantly in all three kinds of compound soil,with the highest increase in 1∶ 2 compound soil; the organic matters of 1∶ 2 compound soil were significantly correlated with 0. 25-0. 50 mm and 0. 25-2. 00 mm water-stable aggregates. The results showed that the ratio of 0. 25-2. 00 mm aggregates in the three kinds of compound soil was increased after 4 years of crop planting and 1∶ 2 compound soil was most favorable for the formation of aggregates.

Accumulative Effect of Soil Organic Carbon and Nitrogen in Water-Stable Aggregates and Soil Stability Characteristics of Robinia pseudoacacia Plantation in the Loess Hilly-Gully Region

Soil water-stable aggregates (WSAs) are the basic unit of soil constitution and can contribute to remaining the stable soil constitution. The objective of this study was to clarify the distribution and stability of WSAs and the soil organic carbon (SOC), the total nitrogen (TN), and the total phosphorus (TP) concentrations in 0 - 20 cm and 20 - 40 cm soil layers under the different ages of Robinia pseudoacacia plantations. The 20, 25, 40, and 50 years-old Robinia pseudoacacia plantations were selected. Stepwise regression analysis showed that >5 mm and 1 - 2 mm WSAs, SOC concentration in 2 - 5 mm WSAs, and TN and TP concentrations in < 0.25 mm WSAs were dominant independent variables affecting aggregate stability and that SOC in 0.25 - 0.5 mm WSAs, TN in <0.25 mm and 1 - 2 mm WSAs and TP in 2 - 5 mm WSAs were dominant independent variables affecting SOC, TN, and TP concentrations in bulk soils.

Role of Organic Matter in Formation and Stability of Aggregates in Mulberry Plantation Soils

The role of organic matter in the formation and stability of soil aggregates in mulberry plantation in the Hang-Jia-Hu Plain, northern Zhejiang Province, was evaluated in this study. A positive correlation was found between water-stable aggregate contents and organic matter contents in the mulberry plantation soils, which supported the hypothesis that organic matter was the main cementing agent in formation of aggregates. A close correlation was also found between stability of aggregate and organic matter contents. Regression analysis showed that total nitrogen content was also an indicator of water-stable aggregate content and stability. The aggregate size distribution indicated that the water-stable aggregates 1--0.25 mm in diameter were the major component of the aggregates in the mulberry plantation soils. The organic matter contents of aggregates ranging from 5 to 0.25 mm in diameter increased with the decrease of aggregate sizes, and the aggregates 1-0.25 mm in diameter had the maximum organic matter content.

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 plan-tations 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 carbohy-drate 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 con-tent 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 car-bohydrate 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.

Short-Term Impacts of No Tillage on Aggregate-Associated C in Black Soil of Northeast China

In order to get a good indicator to evaluate the impacts of no tillage （NT） on soil structure and soil quality, we studied the dynamics of total soil organic carbon （SOC） and aggregate-associated SOC, and their relationships in the plow layer （30 cm） in black soil of Northeast China under NT practice. The tillage experiment was established in Dehui County, Jilin Province, China, in 2001. The total SOC and aggregate-associated SOC under 5-yr tillage treatments were measured. NT practices did not lead to the increase of average SOC content at 0-30 cm depth, but it did significantly increase SOC at the top soil （0-5 cm）. In NT plots, the change of SOC in 〉 1 000 μm aggregate was the same with that of total SOC, but the effect of NT on SOC in 〉 1 000 lain aggregate was greater than the effect on total SOC, suggesting that 〉 1 000 μm aggregate had more sensitive response to the impact of tillage practices. Also, significant positive correlation occurred between total SOC and SOC in 〉 1 000 μm aggregate in black soil. Consequently, in the short term soil macroaggregate 〉 1 000 μm could be used as an indicator to evaluate the impacts of tillage practices on soil structure in black soil of Northeast China.

How freezing and thawing processes affect black-soil aggregate stability in northeastern China

Laboratory experiments were carried out to investigate the effect of freezing and thawing processes on wet aggregate stability （WAS） of black soil. Wet aggregate stability was determined by different aggregate size groups, different water contents, various freeze-thaw cycles, and various freezing temperatures. The results showed that, when at suitable water content, aggregate stability was enhanced, aggregate sta-bility will be disrupted when moisture content is too high or too low, especially higher water content. Temperature also had a significant ef-fect, but moisture content determined the suitable freezing temperatures for a given soil. Water-stable aggregate （WSA〉0.5）, the total aggre-gate content, and mean weight diameter decreasing with the freeze-thaw cycles increase, reached to 5 percent significance level. The reason for crumbing aggregates is the water and air conflict, thus raising the hypothesis that water content affects the aggregate stability in the process of freezing and thawing.

Effect of Rotational Tillage on Soil Aggregates, Organic Carbon and Nitrogen in the Loess Plateau Area of China

In rain-fed semi-arid agroecosystems, continuous conventional tillage can cause serious problems in soil quality and crop production, whereas rotational tillage （no-tillage and subsoiling） could decrease soil bulk density, and increase soil aggregates and organic carbon in the 0-40 cm soil layer. A 3-year field study was conducted to determine the effect of tillage practices on soil organic carbon （SOC）, total nitrogen （TN）, water-stable aggregate size distribution and aggregate C and N sequestration from 0 to 40 cm soil in semi-arid areas of southern Ningxia. Three tillage treatments were tested： no-tillage in year 1, subsoiling in year 2, and no-tillage in year 3 （NT-ST-NT）; subsoiling in year 1, no-tillage in year 2, and subsoiling in year 3 （ST-NT-ST）; and conventional tillage over years 1-3 （CT）. Mean values of soil bulk density in 0-40 cm under NT-ST-NT and ST-NT-ST were significantly decreased by 3.3% and 6.5%, respectively, compared with CT, while soil total porosity was greatly improved. Rotational tillage increased SOC, TN, and water-stable aggregates in the 0-40 cm soil, with the greatest effect under ST-NT-ST. In 0-20 and 2（}-40 cm soils, the tillage effect was confined to the 2-0.25 mm size fraction of soil aggregates, and rotational tillage treatments obtained significantly higher SOC and TN contents than conventional tillage. No significant differences were detected in SOC and TN contents in the 〉 2 mm and 〈 0.25 mm aggregates among all treatments. In conclusion, rotational tillage practices could significantly increase SOC and TN levels, due to a fundamental change in soil structure, and maintain agroecosystem sustainability in the Loess Plateau area of China.

Impact of Land Use and Soil Fertility on Distributions of Soil Aggregate Fractions and Some Nutrients

The size distribution of water-stable aggregates and the variability of organic C,N and P contents over aggregate size fractions were studied for orchard,upland,paddy,and grassland soils with high,medium,and low fertility levels.The results showed that > 5 mm aggregates in the cultivated upland and paddy soils were 44.0% and 32.0%,respectively,less than those in the un-tilled orchard soil.Organic C and soil N in different size aggregate fractions in orchard soil with high fertility were significantly higher than those of other land uses.However,the contents of soil P in different size aggregates were significantly greater in the paddy soil as compared to the other land uses.Soil organic C,N and P contents were higher in larger aggregates than those in smaller ones.The amount of water-stable aggregates was positively correlated to their contribution to soil organic C,N and P.For orchard and grassland soils,the > 5 mm aggregates made the greatest contribution to soil nutrients,while for upland soil,the 0.25-0.053 mm aggregates contributed the most to soil nutrients.Therefore,the land use with minimum disturbance was beneficial for the formation of a better soil structure.The dominant soil aggregates in different land use types determined the distribution of soil nutrients.Utilization efficiency of soil P could be improved by converting other land uses to the paddy soil.

Soil Aggregate Stability and Iron and Aluminium Oxide Contents Under Different Fertiliser Treatments in a Long-Term Solar Greenhouse Experiment

Soil in greenhouses is likely to suffer a gradual decline in aggregate stability. Determination of the effects of different fertiliser practices on soil aggregate stability is important for taking advantage of solar greenhouses. Soil aggregate stability and iron （Fe） and aluminium （A1） oxide contents were investigated in a 26-year long-term fertilisation experiment in greenhouse in Shenyang, China, under eight fertiliser treatments： manure （M）, fertiliser N （FN）, fertiliser N with manure （MN）, fertiliser P （FP）, fertiliser P with manure （MP）, fertiliser NP （FNP）, fertiliser NP with manure （MNP）, and control without any fertiliser （CK）. A wet sieving method was used to determine aggregate size distribution and water-stable aggregates （WSA）, mean weight diameter and geometric mean diameter as the indices of soil aggregate stability. Different fertiliser treatments had a statistically significant influence on aggregate stability and Fe and A1 oxide contents. Long-term application of inorganic fertilisers had no obvious effects on the mass proportion of aggregates. By contrast, manure application significantly increased the mass proportion of macroaggregates at the expense of microaggregates. All treatments, with the exception of FNP, significantly increased the stability of macroaggregates but decreased that of microaggregates when compared with CK. Aggregation under MP and MN was better than that under M and MNP; however, no significant differences were found among inorganic fertiliser treatments （i.e., FN, FP, and FNP）. A positive relation was found between pyrophosphate-extractable Fe and WSA （r=0.269）, but no significant relations were observed between other Fe and Al oxides and aggregate stability.

Effects of Long-Term Fertilization on Organic Carbon and Nitrogen Dynamics in a Vertisol in Eastern China

Mineral fertilizers and organic amendment can affect the various soil organic matter (SOM) pools and the distribution of organic carbon (OC) and nitrogen (N) in these pools. It is unknown how OC and N are distributed in different SOM pools under different long-term fertilization regimes. Therefore, this study aimed to examine the effects on OC and N concentrations in various SOM pools after 33 years of application of chemical fertilizer and organic amendment in Anhui Province in the Huang-Huai-Hai Plain, eastern China. This long-term experiment consisted of five fertilization treatments measuring changes in the OC and N concentrations in the soils and different SOM fractions of each experiment plot. Organic amendment increased the OC and N concentrations in the mineral-associated fraction, the coarse mineral-associated fraction and the aggregates compared with the values obtained without fertilizer application. Mineral fertilizer application alone increased the abovementioned indexes, but this increase was small. There was a small but significant increase in the OC and N concentrations in the free particulate fraction, and the change in magnitude had no obvious effect on the total OC (TOC) and total N (TN) concentrations in soils. More than 80% of the water-stable aggregate-associated C was stored in macroaggregates >2 mm in size. More than 60% of the TOC and TN accumulated within mineral associations in the soil, and organic amendment increased this proportion to 80%. These results suggest that the OC in Vertisols is dominated by mineral-associated OC and that the effect of organic amendment on mineral-associated OC is obvious.

Effects of perfluoroalkyl and polyfluoroalkyl substances(PFAS)on soil structure and function

Soils are impacted globally by several anthropogenic factors,including chemical pollutants.Among those,perfluoroalkyl and polyfluoroalkyl substances(PFAS)are of concern due to their high environmental persistence,and as they might affect soil structure and function.However,data on impacts of PFAS on soil structure and microbially-driven processes are currently lacking.This study explored the effects of perfluorooctanesulfonic acid(PFOS),perfluorooctanoic acid(PFOA)and perfluorobutanesulfonic acid(PFBS)at environmental-relevant concentrations on soil health,using a 6-week microcosm experiment.PFAS(even at 0.5 ng g-1 for PFBS)significantly increased litter decomposition,associated with positive effects on-glucosidase activities.This effect increased with PFAS concentrations.Soil pH was significantly increased,likely as a direct consequence of increased litter decomposition affected by PFAS.Soil respiration was significantly inhibited by PFAS in week 3,while this effect was more variable in week 6.Water-stable aggregates were negatively affected by PFOS,possibly related to microbial shifts.PFAS affected soil bacterial and fungal abundance,but not microbial and certain enzyme activities.Our work highlights the potential effects of PFAS on soil health,and we argue that this substance class could be a factor of environmental change of potentially broad relevance in terrestrial ecosystem functioning.

化肥与不同有机物料配施对土壤有机碳组分及土壤水稳性团聚体的影响

【目的】通过探究化肥与不同有机物料配施对土壤水稳性团聚体和有机碳组分的影响,为增加土壤碳固存,改善土壤结构,指导有机物料合理利用提供科学依据。【方法】进行化肥与有机物料配施试验,以玉米为供试作物,设置5个处理,分别为单施化肥(CK)、化肥+羊粪(AF)、化肥+木薯渣(PF)、化肥+木本泥炭(MF)、化肥+味精废浆料(IF),测定不同处理下土壤有机碳组分和水稳性团聚体含量。【结果】与CK相比,各施用不同有机物料处理的土壤总有机碳(TOC)含量提高了7.93%~24.67%,可溶性有机碳(DOC)、易氧化有机碳(ROC)、微生物生物量碳(MBC)含量均有增加;其中,IF处理的TOC、ROC含量最高,MBC含量最低;AF处理的DOC含量最高;MF处理的MBC含量最高,而TOC、DOC、ROC含量均最低。不同有机物料处理的活性碳组分在总有机碳中的分配比率均有差异,相比CK,仅有AF处理的DOC/TOC有所增加,而各施用有机物料处理的ROC/TOC和MBC/TOC均有增加。施用有机物料明显增加了1~2 mm和0.5~1 mm粒级的土壤水稳性团聚体含量,有利于>0.25 mm粒径大团聚体的形成,且各处理的土壤水稳性团聚体在2~5 mm粒级内占比最高。施用有机物料后,土壤水稳性大团聚体含量提高了17.64%~30.48%,土壤水稳性团聚体的平均重量直径(MWD)表现为AF>PF>IF>MF>CK的变化趋势。相关性分析表明,DOC与土壤水稳性团聚体大团聚体含量(MR>0.25)、MWD和GMD之间呈显著正相关,说明DOC含量越高,土壤团聚体稳定性越强。【结论】施用味精废浆料对土壤有机碳的提升效果最好,施用羊粪后土壤水稳性团聚体稳定性最好。

Soil Fertility Indices of Citrus Orchard Land Along Topographic Gradients in the Three Gorges Area of China

In the Three Gorges Area of China, soil erosion and the resultant non-point source pollution and ecological degradation have endangered agricultural ecosystems and fresh water reservoirs. Although efforts have been undertaken to reduce soil and water losses from slope land used for citrus production, information on the effects of management practices on soil fertility indices is either limited or nonexistent. This study was conducted to compare the effects of 10 years of various management practices, citrus intercropped with white clover (WC), citrus mulched with straw (SM), citrus intercropped with contour hedgerows (CH), citrus orchard land with impermeable membrane (IM), and citrus intercropped with wheat (Triticum aestivum) and peanut (Arachris hypogaea) (WP), as treatments on soil fertility indices with that of the conventional citrus management (CM). Results showed that the soil organic carbon, total and available nitrogen, available potassium, and water-stable aggregate (> 0.25 mm) contents at the 0–5 cm depth were higher for the WC and SM treatments than the CM treatment. There was also spatial variation in soil fertility along slopes of the WC and SM treatments. The soil total and available nitrogen, phosphorus, and potassium, and water-stable aggregate (> 0.25 mm) contents at both the 0–5 and 5–20 cm depths were higher for the CH and IM treatments than the CM treatment. The average soil available nitrogen and available potassium contents were higher for the WP treatment than the CM treatment, but the WP treatment had little effect on the soil organic carbon, total nitrogen, and water-stable aggregate (> 0.25 mm) contents. These suggested that white clover intercropping and straw mulching were the most effective approaches to improve soil fertility in citrus orchard land of the Three Gorges area.

Effects of key design parameters of tine furrow opener on soil seedbed properties

The structural parameters of tine furrow openers have significant effects on soil property of seed furrow in no-till planting,thereby affecting crop growth and yields.In order to analyze the effects of key parameters of tine furrow openers on soil properties(soil bulk density,soil water-stable aggregates(WSA),and soil disturbance)of the surface soil layer of 0-10 cm and surface straw disturbance,the tine furrow openers with different structural parameters,including cutting edge thickness,cutting edge curve,penetration clearance angle and rake angle,were designed and tested under no-till conditions.Orthogonal test and single factor test were performed to analyze the effects of different parameters.Results showed that the rake angle,cutting edge thickness and cutting edge curve had significant effects on cross-sectional area of furrow(Af)and disturbance of surface straw;the rake angle had a significant effect on soil bulk density.Soil types and operating depth had significant effects on soil disturbance caused by tine furrow openers.The concave type tine furrow opener produced the lowest soil disturbance and soil bulk density of seed furrow,the highest surface straw disturbance and the greatest content of WSA(>0.5 mm).With increasing rake angles of tine furrow opener,the width of seedbed(Wsb)and the Af decreased first and then increased,respectively,while the width of soil throw(Wst)and the height of ridge(Hr)increased.The Wsb and Af created by tine furrow opener with 60°rake angle were significantly lower than that with others,respectively.The tine furrow opener with rake angle ranged from 45°to 60°created the lowest soil bulk density.As the penetration clearance angle increased,the content of WSA(>0.5 mm)decreased,but the effect of penetration clearance angle on the content of WSA(<0.5 mm)was not significant.The cutting edge thickness(<2 mm)had no significant effects on soil properties of seedbed.This study could provide a reference for optimal design of the tine furrow opener to create more suitable seedbed environment,and promote the application of the light no-till planters.