Water retention properties of a sandy soil with superabsorbent polymers as affected by aging and water quality

Hydraulic properties, specifically the water holding capacity of soils, play a key role in the ability of soils to sustain plant growth. Additions of hydrophilic polymers (superabsorbents) can improve the water holding capacity of sandy soils. This has led to practical applications of these materials particularly in arid regions and countries, where water is the limiting factor for plant production. The objectives of this study are to investigate how effective hydraulic properties of polymer‐soil mixtures are affected by addition of absorbents in different concentrations. Novel aspects are the investigation of aging under repeated wetting–drying‐cycles over an appreciable time in the field and a systematic investigation of the salt influence on the water uptake of polymers. We added the polymer Super AB, A‐200 (Iran Polymer Institute), to dune sand in ratios of 0.3%, 0.6%, and 1% w/w. We found that the effective water retention characteristics of the soil–absorbent mixtures were improved with respect to plant‐available water compared to the pure sand, and the improvement was related to the respective amount of absorbent in the mixture. The plant available water content (PAW) increased from 0.005 for the untreated sand to 0.06, 0.20, and 0.28 g g^?1, respectively, for the sand with the three polymer additions. Due to aging of the polymers, PAW decreased after 6 months of cyclic drying and wetting to about half of the value immediately after the initial treatment. We attribute this to the effect of salts. This is corroborated by the results from water uptake experiments by the pure polymers. Repeated cycles of water uptake showed that salts in the water greatly reduced the uptake capacity of the polymers after few cycles. The effect was strong for bivalent cations and less pronounced for monovalent cations.     

怀涿葡萄产区土壤过氧化氢酶活性空间分布规律及影响因素分析

为了探明影响土壤过氧化氢酶活性空间变异规律的葡萄品种、土壤物理、化学因素及其内在关系,本文利用GIS和地统计学分析方法研究了怀涿葡萄产区(河北省怀来、涿鹿两县)的83个表层土壤样品。结果表明:怀涿葡萄产区表层土壤过氧化氢酶活性表现出较强烈的空间相关性,其变异规律呈现出明显的区域差异分布特征,土壤过氧化氢酶活性的最佳空间拟合模型为指数模型;土壤中大量元素(除K外)、中量元素、微量元素、重金属元素和一些有益元素(V、I)均对土壤过氧化氢酶活性表现出了显著或极显著的活化作用。在当地传统的土壤葡萄体系管理模式下,土壤过氧化氢酶活性的空间变化规律与土壤不同空间位点的大多数化学元素含量变异分布特点密切相关;土壤过氧化氢酶活性与细粉粒含量呈显著正相关,与土壤黏粒含量呈极显著正相关,可以认为物理性黏粒尤其是黏粒和细粉粒含量是影响怀涿葡萄产区表层土壤过氧化氢酶活性空间变异特征的另一个重要因素。而葡萄品种和土壤pH对土壤过氧化氢酶活性影响较小,与土壤过氧化氢酶活性的空间分布规律关系不大。     

川中丘陵区土壤侵蚀对土壤特性和作物产量的影响

Roles of tillage erosion and water erosion in the development of within-field spatial variation of surface soil properties and soil degradation and their contributions to the reduction of crop yields were studied on three linear slopes in the Sichuan Basin, southwestern China. Tillage erosion was found to be the dominant erosion process at upper slope positions of each linear slope and on the whole short slope (20 m). On the long slope (110 m) and medium slope (40 m), water erosion was the dominant erosion process. Soil organic matter and soil nutrients in the tillage layer were significantly related to slope length and ¹³⁷Cs inventories on the long slope; however, there was no significant correlation among them on the short slope, suggesting that water erosion lowered soil quality by transporting SOM and surface soil nutrients selectively from the upper to lower slope positions, while tillage erosion transported soil materials unselectively. On the medium slope, SOM, total N, and available N in the tillage layer were correlated with slope length and the other properties were distributed evenly on the slope, indicating that water erosion on this slope was still the dominant soil redistribution process. Similar patterns were found for the responses of grain yield, aboveground biomass, and harvest index for slopes. These results indicated that tillage erosion was a major cause for soil degradation and grain yield reduction on the linear slopes because it resulted in displacement of the tillage layer soil required for maintaining soil quality and plant growth.     

采用土壤质量指数评估施肥对集约型稻麦轮作系统中土壤物理性质的影响

Soil quality assessment has been suggested as an effective tool for evaluating sustainability of soil and crop management practices.The objective of this study was to develop a sensitive soil quality index(SQI) based on bulk density(BD),water-holding capacity(WHC),water-stable aggregates(WSA),aggregate mean weight diameter(AMWD),total organic C(TOC) and C input to evaluate the important rice-wheat cropping system on an Inceptisol in India.A long-term experiment has been conducted for 18 years at the Indian Council of Agricultural Research-Indian Institute of Farming Systems Research,Modipuram,India.The treatments selected for this study were comprised of a no-fertilizer control and N,P and K fertilizers(NPK) combined with Zn and S fertilizers(NPK+ Zn+S),farmyard manure(NPK+FYM),green gram residues(NPK+GR) and cereal residues(NPK+CR),laid out in a randomized complete block design with three replications.Soil samples were collected and analyzed for BD,WHC,WSA and TOC.Correlation analysis revealed that both rice and wheat yields signi?cantly increased with the increases in AMWD,TOC and C input,but decreased with the increase in BD.The SQI values were then generated based on regression analysis of BD,WSA,AMWD,TOC and C input with rice and wheat yields for the 0–15 and 15–30 cm soil layers,respectively.Regression analyses between crop yields and SQI values showed a quadratic type of relation with the coeffcient of determination(R~2) varying from 0.78 to 0.89.With regard to soil sustainability,applying crop residues to both rice and wheat could maintain soil quality for a longer period,whereas the highest yields of both the crops were recorded in the NPK+Zn+S treatment.The regression equations developed in this study could be used to monitor soil quality in a subhumid tropical rice-wheat cropping system.     

Organic carbon accumulation in a 2000-year chronosequence of paddy soil evolution

Considerable amounts of soil organic matter (SOM) are stabilized in paddy soils, and thus a large proportion of the terrestrial carbon is conserved in wetland rice soils. Nonetheless, the mechanisms for stabilization of organic carbon (OC) in paddy soils are largely unknown. Based on a chronosequence derived from marine sediments, the objectives of this study are to investigate the accumulation of OC and the concurrent loss of inorganic carbon (IC) and to identify the role of the soil fractions for the stabilization of OC with increasing duration of paddy soil management. A chronosequence of six age groups of paddy soil formation was chosen in the Zhejiang Province (PR China), ranging from 50 to 2000 years (yrs) of paddy management. Soil samples obtained from horizontal sampling of three soil profiles within each age group were analyzed for bulk density (BD), OC as well as IC concentrations, OC stocks of bulk soil and the OC contributions to the bulk soil of the particle size fractions. Paddy soils are characterized by relatively low bulk densities in the puddled topsoil horizons (1.0 and 1.2 g cm^− 3) and high values in the plow pan (1.6 g cm^− 3). Our results demonstrate a substantial loss of carbonates during soil formation, as the upper 20 cm were free of carbonates in 100-year-old paddy soils, but carbonate removal from the entire soil profile required almost 700 yrs of rice cultivation. We observed an increase of topsoil OC stocks from 2.5 to 4.4 kg m^− 2 during 50 to 2000 yrs of paddy management. The OC accumulation in the bulk soil was dominated by the silt- and clay-sized fractions. The silt fraction showed a high accretion of OC and seems to be an important long-term OC sink during soil evolution. Fine clay in the puddled topsoil horizon was already saturated and the highest storage capacity for OC was calculated for coarse clay. With longer paddy management, the fractions < 20 μm showed an increasing actual OC saturation level, but did not reach the calculated potential storage capacity.     

紫色土坡耕地土壤物理性质空间变异对土壤侵蚀的响应

为了研究不同坡度和坡长的耕地上土壤侵蚀对土壤物理性质空间变异的影响,通过地形测量、137 Cs示踪、土壤物理性质分析等方法对川中丘陵紫色土区土壤物理性质对土壤侵蚀的响应进行了研究,结果表明：在中等坡度（16.60%～25.10%）的梯坡地上,耕作侵蚀处于主导地位,是导致耕层土壤物理性黏粒含量和容重在梯坡地上总体差异不大（CV＜6.3%）,且与137Cs含量不相关的主要原因;在已退耕还林的陡梯坡地上（35.60%）,水蚀占据主导地位,导致耕层土壤物理性黏粒含量和容重均与137Cs的含量显著相关。在长坡耕地上(10.10%),具有分选搬运能力的水力侵蚀占据主导地位,致使耕层土壤物理性黏粒含量与137Cs的含量具有显著的相关关系,而容重却与137Cs含量没有显著的相关关系。川中丘陵区坡耕地上,耕作侵蚀和水蚀共同作用于土层深度,使土层深度在坡顶、上坡最浅,在坡脚最深,顺坡向下逐渐增加。因此,在川中丘陵区不同坡长的坡耕地上,占主导地位的土壤侵蚀类型导致坡耕地上土壤物理性质出现相应的变化。     

耕翻和秸秆还田深度对东北黑土物理性质的影响

为了明确耕翻和秸秆还田深度对土壤物理性质的影响,在东北黑土区中部进行了6 a的耕翻和秸秆还田定位试验,设置了免耕（D0）、浅耕翻（0～20 cm）（D20）、浅耕翻+秸秆（D20S）、深耕翻（0～35 cm）（D35）、深耕翻+秸秆（D35S）、超深耕翻（0～50 cm）（D50）和超深耕翻+秸秆（D50S）7个处理开展研究,秸秆还田处理将10 000 kg/hm2秸秆均匀地还入相应的耕翻土层。结果表明,耕翻和秸秆还田深度是影响土壤物理性质的重要农艺措施。与初始土壤相比,免耕显著增加了0～20 cm土层土壤容重,减少了孔隙度、持水量、饱和导水率和>0.25 mm水稳性团聚体的含量（WAS>0.25）（P<0.05）,而对20～50 cm土层没有显著影响（P>0.05）。在0～20 cm土层,除了D50处理显著降低了WAS>0.25含量以外,D20,D35和D50处理对各项土壤物理指标均没有显著影响;而D20S和D35S处理则显著改善了该层各项土壤物理指标。在>20～35 cm土层,D35、D35S、D50和D50S处理显著改善了该土层各项土壤物理指标（除了2014年的容重）。在>35～50 cm土层,D50和D50S处理对各项土壤物理指标改善效果显著,特别是相应土层通气孔隙度和饱和导水率显著增加。研究结果表明耕翻配合秸秆对土壤物理指标的改善效果优于仅耕翻处理。综合评分结果也表明D35S和D50S处理分别对>20～35 cm和>35～50 cm土层土壤物理性质的改善效果最好,说明在质地黏重的黑土上深翻耕或者超深翻耕配合秸秆还田通过土层翻转秸秆全层混合施用能够显著改善全耕作层土壤的物理性质,增加耕层厚度,扩充土壤的水分库容,提高黑土的水分调节能力。     

Wind erosion and sand accumulation effects on soil properties in Horqin Sandy Farmland,Inner Mongolia

Rain-fed agriculture is widespread in Inner Mongolia, northern China, where wind erosion of farmland is very common because of sandy soil and dry, windy weather. However, very little is known about the effects of wind erosion on soil physical and chemical properties in this region. A field experiment was conducted in sandy farmland, where erosional and depositional gradients were established to evaluate the effects of wind erosion and leeward sand accumulation on soil texture, nutrient content, soil water, and soil temperature. The research showed that long term wind erosion could result in significant soil coarseness, infertility and dryness. Severe erosion reduced clay by 59.6%, organic C by 71.2%, total N by 67.4%, total P by 31.4%, available N by 64.5%, available P by 38.8%, and average soil water content by 51.8%, compared with non-eroded farmland in the study region. The sand fraction (particles > 0.05 mm), pH and ground-surface temperature increased by 6.2%, 3.7%, and 2.2 °C, respectively. Accumulated sand also caused a decrease in nutrients and soil water content. Under severe sand accumulation, clay was reduced by 2.0%, organic C by 19.3%, total N by 21.7%, total P by 13.7%, available N by 52.5%, and average soil water content by 26.6%. The sand fraction, pH, available P, and ground-surface temperature increased by 0.2%, 0.9%, 5.8% and 2.8 °C, respectively.     

Influence of four soil maintenance practices on Collembola communities in a Mediterranean vineyard

We studied the influence of four soil maintenance practices on Collembola communities in the soil of a Mediterranean vineyard: (a) postemergence herbicide with glyphosate; (b) postemergence and pre-emergence herbicides with glyphosate, terbuthylazine, diuron and oryzalin; (c) natural flora and (d) tillage to a depth of 10–15 cm. Total Collembola abundance, species diversity and species richness significantly varied between the four practices. Notably, the practice using postemergence and pre-emergence herbicides had significantly lower values. Identification of Collembola at species level allowed an interspecies comparison and revealed significant differences for the most common species between the four practices, with each practice being characterized by a different set of species. None of the species were found to be significantly more abundant in the plots treated with postemergence and pre-emergence herbicides.     

The effect of biochar with biogas digestate or mineral fertilizer on fertility,aggregation and organic carbon content of a sandy soil: Results of a temperate field experiment

Substitution of mineral fertilizers with organic soil amendments is postulated to improve productivity‐relevant soil properties such as aggregation and organic matter (OM) content. However, there is a lack of studies analyzing the effects of biochar and biogas digestate versus mineral fertilizer on soil aggregation and OM dynamics under temperate field conditions. To address this research gap, a field experiment was sampled four years after establishment on a sandy Cambisol in Germany where mineral fertilizer or liquid biogas digestate was applied with or without 3 or 40 Mg biochar ha^?1 (produced at 650°C). Soil samples were analyzed for soil organic carbon (SOC) content, pH, cation exchange capacity, bulk density, water‐holding capacity, microbial biomass, aggregate size class distribution, and the SOC content associated with these size classes. 40 Mg biochar ha^?1 significantly increased SOC content in all fractions, especially free particulate OM and the 2–0.25 mm fraction. The yield of small macroaggregates (2–0.25 mm) was increased by biochar, but cation exchange capacity, water‐holding capacity, and pH were not consistently improved. Thus, high‐temperature biochar applied to a sandy soil under temperate conditions is primarily recommended to increase SOC content, which could contribute to climate change mitigation if this C remains sequestered over the long‐term. Fertilizer type did not significantly affect SOC content or other measured properties of the sandy Cambisol, suggesting that replacement of mineral fertilizer with digestate has a neutral effect on soil fertility. Co‐application of biochar with digestate provided no advantages for soil properties compared to co‐application with mineral fertilizer. Thus, independent utilization of these organic amendments is equally suitable.     

Hydrological properties of a Mediterranean soil burned with different fire intensities

The influence of vegetation cover on soil hydrological properties and its response to the impact of different fire intensities, in a Mediterranean forest environment, has been evaluated. The study was carried out in the Permanent Experimental Field Station of La Concordia (Llíria–Valencia, Spain), on a set of nine erosion plots (4 × 20 m²). The Station is located on a calcareous hillside S–SE oriented, with soils of Rendzic Leptosol type and supporting Mediterranean shrubland vegetation. All runoff generated and sediment produced in every rain event was collected from each plot. The set up includes a system of sensors for the continuous monitoring of climatic parameters (air temperature and humidity, rain volume, intensity, etc.).In June 1995, a set of experimental fires was carried out to the Station. Three of the plots were burned with high intensity fire, three with moderate intensity and the remaining were left unaltered. Soil water content and water retention capacity (WRC) were measured in the different plots and in two different vegetation covers: under canopy (UC) and in bare soil (BS). The pF curves were also obtained for each fire treatment.A year after the fires (June 1995–June 1996), great differences, reaching 77.15%, in runoff generation between fire treatments and the control plots were observed.No significant differences were detected on water retention capacity between soils UC and BS in the burned plots. However, these differences appeared in the control plots, giving UC and BS values of 13% and 18%, respectively. Plots corresponding to the high intensity fire treatment showed values of WRC significantly higher than those of the moderate intensity and of the control treatments.The pF curves show that the values of water volume, at the different pressure points studied, were slightly greater on UC soil. Values obtained for BS samples are higher in the fire treatments, showing significant differences in respect to the control plots at pF 1 and 2. These differences were also observed for UC soil, but in this case at pF 2, 2.5 and 4.2.     

生物炭对沙质土水分蒸发和导水率的影响

Biochar, as a kind of soil amendment, has important effects on soil water retention. In this research, 4 different kinds of biochars were used to investigate the influences of biochar addition on hydraulic properties and water evaporation in a sandy soil from Hebei Province, China. Biochar had strong absorption ability in the sandy soil. The ratio of water content in the biochar to that in the sandy soil was less than the corresponding ratio of porosity. Because of the different hydraulic properties between the sandy soil and the biochar, the saturated hydraulic conductivity of the sandy soil gradually decreased with the increasing biochar addition. The biochar with larger pore volume and average pore diameter had better water retention. More water was retained in the sandy soils when the biochar was added in a single layer, but not when the biochar was uniformly mixed with soil. Particle size of the added biochar had a significant influence on the hydraulic properties of the mixture of sand and biochar. Grinding the biochar into powder destroyed the pore structure, which simultaneously reduced the water absorption ability and hydraulic conductivity of the biochar. For this reason, adding biochar powder to the sandy soil would not decrease the water evaporation loss of the soil itself.     

土壤含水率及物理性砂粒含量对风蚀模数影响的风洞模拟

为了探究土壤含水率及物理性砂粒含量对土壤风蚀模数的影响,在室内风洞中在5、6、9、12、15和18m/s风速下对不同含水率(0,1%,2%,3%,4%,5%,6%,7%,8%,9%和10%)的7种土壤(物理性砂粒质量分数的分别为20%、30%、40%、50%、60%、70%和80%)进行了10min吹蚀,在风洞轴线距出口1.2m处放置旋风式集沙仪分别测定垂直方向上10个不同高度的风蚀物收集量(高度分别为20、60、120、180、240、300、400、500、600和700mm),并利用MATLAB7.4.0(R2007)软件采用3次样条插值拟合法对旋风式集沙仪不同高度的风蚀物收集量进行积分,通过换算计算土壤风蚀模数E。结果表明,物理性砂粒质量分数低于40%的土壤在各种水分条件下集沙仪不同高度风蚀物收集量均很小。物理性砂粒质量分数≤20%时,风蚀物收集量在空间上符合指数函数变化规律;20%<物理性砂粒质量分数<40%风蚀物收集量在空间上利用指数函数和幂函数拟合相关性均很好,物理性砂粒质量分数高于40%后,风蚀物收集量在空间上呈现幂函数曲线变化规律。9m/s风速基本上是风蚀物空间动态发生变化的临界点;低于临界风速,风蚀物收集量与高度符合指数曲线变化规律;高于临界风速,二者符合幂函数曲线变化规律。集沙仪不同高度的总输沙量随风速的增加而增大,二者符合指数曲线变化关系。物理性砂粒质量分数低于40%的土壤,不会有风蚀现象发生;当物理性砂粒质量分数大于40%后,土壤容易发生风蚀,而且风蚀程度随物理性砂粒含量的增加而增大,尤其当土壤含水率低于3%时,极易发生风蚀。风速越大土壤风蚀模数越大,风蚀模数与风速按照指数曲线规律进行变化。阴山北麓旱作区冬春季节土壤地表含水率一般维持在3%～4%,土壤的物理性砂粒质量分数基本在50%～80%;单纯从土壤水分和土壤物理性砂粒含量考虑,阴山北麓旱作区大部分地区是沙尘暴的发生源。     

三峡山地不同坡位土壤的水分特征曲线及水力学性质

山地不同坡位的土壤水力学性质研究可为地表水文过程预测和坡地生态修复提供参考.通过采集三峡库区大老岭林区山地不同坡位的原状土样,测定饱和导水率、当量孔径、水分库容等水力学参数,利用V-G模型拟合土壤水分特征曲线,评价不同坡位土壤的渗透性能和持水能力.结果表明:坡顶土壤的入渗性能最好,平均饱和导水率为108.54 cm/d...     

东莞5种生态公益林枯落物及土壤水文效应

为了解东莞市内不同森林公园的森林地表枯落物和土壤水源涵养能力,于2020年7月选取东莞市5个森林公园5种30年的生态公益林作为研究对象,采用烘干法和浸水法对枯落物、土壤的持水能力及物理性质进行研究.结果表明:生态公益林林地枯落物层厚度变动为1.5～10.5 cm,生物量变化范围为0.32～5.73 t/hm2,最大持水...     

秸秆粉碎氨化还田对土壤体积质量及持水特性的影响

为尝试解决秸秆还田中秸秆分解缓慢、易诱发病虫害及与作物争氮等问题,通过室内土柱培养试验对比研究了秸秆粉碎程度及秸秆不同C/N值对自身分解速率、土壤体积质量、土壤持水特性的影响。结果表明：短期内秸秆粉碎程度对秸秆分解速率影响不大,但粉碎秸秆在试验后期分解速率明显高于长秸秆,氨化措施可显著加快秸秆的分解速率;粉碎秸秆对土壤体积质量的减小作用明显较长秸秆为好,在整个试验期,粉碎氨化秸秆处理的土壤体积质量均显著低于同时期其他处理;各处理土壤持水能力差异不大,但粉碎氨化秸秆能明显增强土壤耐旱性。该结果为探索一种能最大效益发挥秸秆改良土壤作用的秸秆还田新方式提供了一定的参照。     

Participatory soil and water conservation planning using a financial analysis tool in the West Usambara highlands of Tanzania

Despite decades of soil and water conservation (SWC) efforts in Tanzania, the adoption of the recommended SWC measures by farmers is minimal. In the past, SWC plans did not incorporate farmers' knowledge, and the economics of SWC was not given much attention at the planning stage. This research evaluated the applicability of two tools for participatory soil erosion mapping using farmers' indicators of soil erosion and financial analysis of SWC measures at the planning stage. The two tools were evaluated in Kwalei catchment in the West Usambara highlands, Tanzania. The participatory soil erosion‐mapping tool uses farmers' indicators of soil erosion to identify, classify and map soil erosion at the catchment level. The financial analysis tool involves farmers in a stepwise analysis of the costs and benefits of SWC measures before the implementation. The erosion‐mapping tool increased farmers' awareness on the severity of soil erosion problems, and they realised the need for SWC plans at both field and catchment scales. With the financial analysis tool farmers participated in the cost and benefits analysis and were able to select SWC options that were feasible under their socio‐economic situation. The two tools were able to demonstrate that farmers' participation in SWC planning increases the acceptance of SWC measures because they solve problems that are perceived by themselves. The financial analysis tool demonstrated how farmers could make selection of SWC measures that are feasible under their biophysical and economic condition if they are informed about the costs and benefits. Copyright © 2006 John Wiley & Sons, Ltd.     

Spatiotemporal distribution of soil moisture in gully facies

Gully erosion is one of the most important forms of land degradation in many regions of the world. Understanding the process of gully erosion therefore is important for better management of the watersheds prone to gully erosion. However, many different aspects of gully erosion, like hydrological behavior, are still not fully understood. The present study investigates the spatial distribution of soil moisture content (SMC), as one of the hydrological factors, at different depths and points across the cross section in the vicinity of the headcut of three gullies located in the Kalat County, Khorasan Razavi Province, Iran. SMCs were measured at depths of 10, 20, 30, 50, 70 and 100 cm at each seven points across the study cross sections one to three days after occurrence of three rain events. Two sampling points were symmetrically located at a distance of 50 cm outside the gully banks, two at the vertex of the sidewalls, two in the middle of the sidewalls and one at the center of gully cross section. SMCs were measured using a weighted method. Results of the study revealed a broad range of changes in SMCs at various depths and points. The minimum and maximum SMCs were found to be about 2% and 38%, respectively, for the study period and gullies under consideration. The coefficient of variation (CV) had drastic changes for various gullies and storm events from 2 to 107%. Results further indicated that SMC moved from the sidewalls towards the floor of the cross section. Accordingly, the maximum SMC for storm events was associated with the point located in the center of gullies, which indicated the role of gully system in draining soil moisture. The findings of this study will help watershed managers understand the important role of gully facies in changing water content of the soil that affects other ecohydrological processes.     

Influence of pebble mulch on soil erosion by wind and trapping capacity for windblown sediment

In the semiarid region of northwest China, pebble mulches have been used by farmers for over 300 years. However, very little studies were conducted on the effect of pebble mulch on soil erosion by wind. Results of a wind tunnel simulation and a field experiment showed that pebble mulch had two functions in controlling wind erosion: first, it could prevent soil from eroding by wind; second, it could trap dust carried by wind. According to the wind tunnel simulation experiment, pebble mulch reduced wind erosion rate (g m⁻² min⁻¹) by 84–96% at the different wind velocities (10–26 m s⁻¹) in comparison with the controls. In addition, the ratio between total soil loss from the pebble-mulched soil and the bare soil was 0.06. The field study indicated that pebble mulch could trap 1.6–1.8 times more windblown sediments than the control suggesting that pebble mulch might also be effective in controlling dust storms. The grain size distribution of eroded soil showed that a lower percentage of particles in the range of >1.0 mm fractions and a higher percentage in the range of <0.05 mm fractions occurred in the pebble-mulched treatments than in the controls, while windblown sediments trapped by pebble mulches had a lower percentage of grains in the range of >0.5 and <0.05 mm fractions than that trapped by the controls.     

Organic carbon and nitrogen in soil particle-size aggregates under dry tropical forests from Guanacaste,Costa Rica — Implications for within-site soil organic carbon stabilization

In this study we report results on the soil organic carbon (SOC) pool (0–50 cm) from a chrono-sequence of dry tropical forest (dTf) of increasing age and a yearly burned ancient pasture in the “Sector Santa Rosa” at the “Área de Conservación Guanacaste” (ACG) in northwestern Costa Rica, where intense human induced land-use modifications has occurred during the past century. The effects of land conversion on soil organic carbon (SOC) have mainly been conducted in the Atlantic humid forests while overlooking dTfs. We quantified the depth distribution of SOC concentration down to 50-cm and in physically separated mineral soil fractions, as these data are scanty from the dTf. Additional objectives were to identify the relationship with selected soil physical and chemical properties, including stabilized SOC fractions by means of multivariate ordination methods. Statistically significant differences were found for the main fixed factor ecosystem for all soil variables analyzed (ANOVA). SOC and N concentrations were significantly higher in the oldest dTf compared to the other dTfs. Soil physical properties like aggregate size distribution and bulk density changed with depth, and varied significantly among the three dTf stands sampled. The multivariate analysis, i.e. between-within class principal component analysis (PCA), revealed a significant ordination of dTfs (P < 0.0001). The SOC concentration decreased in particle size fractions of < 200 μm aggregates with increasing soil depth. The lowest and highest C concentrations were obtained in the fine sand (105–200 μm) and clay + silt (< 20 μm) fractions, respectively. Mineral-associated and stable SOC pool increased with depth, and poorly crystalline Fe oxides and ferrihydrite were the most important minerals for SOC stabilization at 40–50 cm depth. The highest SOC pool was found in the old-growth and > 80 years-old dTfs, i.e., 228.9 and 150.3 Mg C ha^− 1, respectively, values similar to those obtained in the Atlantic humid forests of Costa Rica. Comparatively to other studies, soils under dTf at Santa Rosa store a considerable amount of SOC with potentially large CO2 emissions if this ecosystem is not preserved.