A simple turbidimetric method for determination of exchangeable soil potassium

Abstract

It was found that sodium tetraphenylboron, NaB(C₆H₅)₄, can be used as a reagent for determination of K in acid sodium acetate extracts of soils. After extraction and filtration, sodium hydroxide and formaldehyde are added prior to the reagent to avoid interference of ammonium. At low concentrations of K in the extracts (<30 mg K/1) the white precipitate of potassium tetraphenylboron, KB(C₆H₅)₄, is colloidal and the concentration of K can be determined turbidimetrically with a simple instrument in the field or on the farm.     

Selection of soil physical quality indicators in relation to soil erodibility

Soil quality indices based on soil characteristics can be used to assess the sustainability of soil and to assist in soil management decisions. Principal component analysis (PCA) technique was used to identify dominant soil characteristics in relation to soil erodibility in watersheds of submontane Punjab (India). Soil physical and chemical characteristics were evaluated for four locations with four land uses at each location whereas runoff, soil loss and soil erodibility were determined at two locations under natural rainfall conditions and at four locations under simulated rainfall conditions. PCA was performed on 22 physical and chemical soil characteristics, which grouped these soil characteristics into five distinct principal components (PCs). These five PCs namely soil hydraulic factor, density factor, structural factor, sand factor and cation factor, explained 86% variability in data. These PCs also explained 86, 96 and 93% variability under natural rainfall conditions and 75, 76 and 77% variability under simulated rainfall conditions in relation to runoff, soil loss and soil erodibility, respectively. Soil total organic carbon content can be considered as dynamic soil physical quality indicator and can be used to monitor temporal and spatial changes in soil quality.     

The effect of pig slurry on exchangeable potassium in calcareous soils

Pig slurry in quantities of 200, 400, 500, 600, 800, and 1000 m³ ha^-1 year^-1 was added to two calcareous soils, which differed in concentration and type of clay minerals. The soils were cultivated with two successive crops of pepper and tomatoes grown in containers. A control was given no slurry. The soils were analysed after harvesting for exchangeable K⁺. Differences in exchangeable K⁺ were studied in relation to the concentration and type of clay minerals. The soil with the higher clay content and of the illite type retained K in the exchangeable form to a much greater extent than the soil with the low clay content. In the soil with the lower clay content, of the interstratified illitic — montmorillonite type, very little K was incorporated into the exchange complex. The exchange capacity being low, the amount of K added had little effect on the level of exchangeable K⁺.     

石灰性土壤交换性钙和镁测定方法的研究

石灰性土壤交换性盐基组成的测定,通行的方法是采用70%乙醇溶液反复洗盐,再经pH 8.50.1 mol L-1氯化铵-70%乙醇(CH3CH2OH)溶液进行多次交换处理,测定交换液中的K+、Na+、Ca2+、Mg2+浓度。但此方法常常受操作步骤繁琐,以及土壤中碳酸盐的溶解量因多次浸提而增加的困扰,最终导致测定结果偏高。基于上述原因,选择不同浓度、不同pH的NH4OAc和NH4Cl 10种交换剂,对比分析10种交换剂中的碳酸盐溶解度和土壤交换性钙镁含量。结果表明,pH=8.5 1 mol L-1氯化铵-70%乙醇(CH3CH2OH)溶液较适合石灰性土壤交换性盐基的测定。此新方法是先经70%乙醇(CH3CH2OH)溶液洗盐,再用pH8.5 1 mol L-1氯化铵(NH4Cl)-70%乙醇(CH3CH2OH)溶液进行一次性交换处理,然后测定交换液的K+、Na+、Ca2+、Mg2+浓度,简化了操作程序的同时有效抑制了土壤碳酸盐的溶解,降低了测定结果的偏差。     

Response of soil exchangeable and crop potassium concentrations to variable fertilizer and cropping regimes in long-term field experiments on different soil types

Annual potassium (K) balances have been calculated over a 40‐year period for five field experiments located on varying parent materials (from loamy sand to clay) in south and central Sweden. Each experiment consisted of a number of K fertilizer regimes and was divided into two crop rotations, mixed arable/livestock (I) and arable only (II). Annual calculations were based on data for K inputs through manure and fertilizer, and outputs in crop removal. Plots receiving no K fertilizer showed negative K balances which ranged from 30 to 65 kg ha^?1 year^?1 in rotation I, compared with 10–26 kg ha^?1 year^?1 for rotation II. On sandy loam and clay soils, the K yield of nil K plots (rotation I) increased significantly with time during the experimental period indicating increasing release of K from soil minerals, uptake from deeper soil horizons and/or depletion of exchangeable soil K (K_ex). Significant depletion of K_ex in the topsoil was only found in the loamy sand indicating a K supply from internal sources in the sandy loam and clay soils. On silty clay and clay soils, a grass/clover ley K concentration of ～2% (dry weight) was maintained during the 40‐year study period on the nil K plots, but on the sandy loam, loam and loamy sand, herbage concentrations were generally less than 2% K.     

Relationship between minimum exchangeable potassium and soil taxonomy

Abstract

Potassium is an essential element for plant growth and its importance in agriculture has been well recognized. With continuous cropping of a soil, exchangeable ? levels decrease to a minimum, steady‐state level if no ? is added. This minimum level is important to both modeling soil ? cycling and fertilizer ? recommendations, and it has been determined by field studies lasting from 2 to 10 years. Consequently, there is a need for estimation of minimum exchangeable ? levels for a wide range of soil types from soil physical and chemical properties. A literature survey provided 19 studies where minimum exchangeable ? had been measured and regression analysis was conducted on this data to determine predictive relationships. Minimum exchangeable ? is closely related to soil clay content (r² from 0.66 to 0.99), however, regression constants varied from study to study. Improved correlations were obtained between minimum exchangeable ? and clay content when all the soils (22A, r²=0.69) were divided into 3 groups according to the Fertility Capability Soil Classification (FCC) System and Soil Taxonomy (r² of 0.86, 0.82, and 0.68). Differences in regression constants between groups were consistent with changes in soil properties associated with ? levels and exchangeability. This analysis provided relationships to estimate minimium exchangeable ? level from soil clay content for a wide range of soil types, which should aid soil ? modeling and fertilizer ? recommendations.     

Effect of particle-size distribution on wind erosion rate and soil erodibility

Wind erosion is a serious problem, especially in arid and semi-arid regions. This study was conducted to assess the effects of wind speed as well as soil particle-size distribution on erosion rate (ER) using a wind tunnel. For this purpose, two clay loam soil samples (C2 and C10) in addition to a sandy clay loam (S2) were exposed to different wind velocities of 2, 9 and 18 m s^?1. The result showed that erosion rate increased significantly with increasing wind speeds. In addition, a critical diameter of 0.84 mm for soil particles was supported; for larger particles the changes in erosion rate were negligible. Furthermore, soil erodibility (K) was determined, which for S2, C2 and C10 was 57.73, 10.27 and 1.43, respectively. To predict soil erodibility, a power relationship as K = 3.382 MWD^?1.732 (R ² = 0.99) was established. The results indicated with increasing wind speed, the sensitivity of S2 remained constant, whereas C2 and C10 resisted wind speed. The finding of this research indicates the importance of particle-size distribution on wind erosion rate as well as soil erodibility.     

冻融条件下土壤可蚀性对坡面氮磷流失的影响

冻融作用与水力侵蚀的复合作用更容易使土壤发生侵蚀,进而加剧土壤养分的流失,为了揭示冻融作用下土壤可蚀性对坡面养分流失的影响,该文采用室内模拟降雨试验,研究了不同土壤含水率(SWC)下坡面的降雨产流产沙及养分流失特征,并分析了土壤可蚀性对坡面全氮(TN)和全磷(TP)流失的影响。结果表明:产流率与产沙率之间呈现正线性相关关系,相关方程斜率的绝对值可作为土壤可蚀性指标。径流中氮磷的流失主要受径流率控制,受土壤可蚀性影响较小(P0.05);而土壤可蚀性显著影响着泥沙中氮磷和总的氮磷流失(P0.01)。土壤可蚀性对黄土坡面氮素流失的影响与冻融作用有关,而土壤可蚀性对坡面磷素流失的影响与冻融作用无关,磷素的流失随着土壤可蚀性增加而增加。因此,在黄土地区,应当采取一系列的生态建设措施来控制水土流失,降低土壤可蚀性,从而减少坡面养分的流失。该研究结果为冻融条件下黄土坡面水-土和氮磷等养分流失机制提供了有效指导。     

Effects of 'Agri-SC' soil conditioner on soil structure and erodibility: some further observations

Abstract. In field and laboratory experiments the conditioner‘Agri-SC’has shown improvements in the structure of loamy sand soils in east Shropshire, UK. It resulted in statistically significant decreases in soil bulk density values and increases in soil porosity and aggregate stability. Further experiments are in progress on both loamy sand and silt loam soils.     

Effects of parent material and land use on soil erodibility

The objective of the present investigation was to find out the effect of different parent materials and land use on soil erodibility. Four types of parent materials such as andesite, basalt, alluvial, and gypsum, and three land use types such as grass, clover, and maize, all wide spread in Erzurum Province in Turkey, were tested. Aggregate stability and soil erodibility factors were determined. The susceptibility of soils against erosion decreased in the order of parent materials basalt > andesite > alluvial > gypsum. Likewise, the susceptibility of land use can be sorted as follows: grass > clover > maize.     

土地退化/恢复中土壤可蚀性动态变化

利用EPIC公式计算了不同开垦和退耕年限的土壤可蚀性K值,对黄土高原典型自然恢复区子午岭林区土地退化/恢复过程中土壤可蚀性的动态变化进行了系统的研究。结果表明：土地开垦后,土壤颗粒向粗骨化方向发展,有机碳含量降低,土壤可蚀性逐渐增强;土地退耕过程中,土壤有机碳含量逐渐增加,肥力水平提高,可蚀性逐渐减小;土壤中有机碳含量、全氮含量、水稳性团聚体含量以及团聚度与土壤可蚀性K值相关最为密切;土壤可蚀性的强弱本质上取决于土壤有机碳含量,恢复植被以提高土壤有机质含量,促进土壤团聚体的形成,增强土壤团聚度,是降低土壤可蚀性能的重要途径。     

Exchangeable potassium and potassium balances in organic crop rotations on a coarse sand

Abstract. Crops on sandy soils (<5% clay) are exposed to K deficiency due to the small release and high leaching losses of K. Reliable tools are needed to improve the K management in cropping systems with limited K input, such as organic farming where import of nutrients are restricted according to the EC regulations. We investigated K balances and exchangeable K (K_exch) changes in an organic crop rotation experiment. Potassium leaching decreased from 42 kg ha⁻¹ in 1998/99 to 21 kg ha⁻¹ in 2000/01 as an average of a crop rotation (spring barley, grass-clover, winter wheat and pea/barley) with manure application and without catch crops. In the same period, spring K_exch decreased from 5.0 to 3.0 mg K 100 g soil⁻¹ (0–20 cm). The retention of the straw K left in the field after harvest increased with decreasing levels of K_exch. The cereal crops did not respond to K application but in the pea/barley mixture the pea yield increased by 46%. The concordance between measured K balances and changes in K_exch was weak. Exchangeable K is suitable as a tool for K management on a rotational basis, and a K_exch above 3 mg 100 g soil⁻¹ in the autumn should be avoided to minimize K leaching.     

ESP值和黏粒含量对土壤表面封闭作用的影响

降雨导致土壤表面结皮形成封闭是自然现象,它能降低土壤入渗,增加土表径流,导致土壤侵蚀。该文系统地研究了不同性质土壤表面的封闭作用过程,分别确定封闭过程中的物理机械作用和化学作用。试验采用了具有不同土壤交换性钠百分率(ESP)值(2、5、10、20)和黏粒含量(10％、20％、40％、60％)的4种土壤进行降雨模拟试验,通过土壤表面播撒磷石膏(PG)(2000 kg/hm²)和PG与聚丙烯酰胺(PAM)(PG 2000 kg/hm²+PAM 20 kg/hm²)混合物的处理,分别抑制了土壤的化学封闭和物理封闭,论述了ESP值和黏粒含量对土壤化学封闭和物理封闭作用的影响,结果表明：在高ESP值土壤中,化学封闭作用占土壤封闭的主导作用;低ESP值土壤中,土壤的物理封闭作用增大。当黏粒含量较低时,土壤物理封闭作用较低;当黏粒含量较大时,土壤物理封闭作用显著增大。     

Filling the European blank spot—Swiss soil erodibility assessment with topsoil samples

Soil erodibility, commonly expressed as the K‐factor in USLE‐type erosion models, is a crucial parameter for determining soil loss rates. However, a national soil erodibility map based on measured soil properties did so far not exist for Switzerland. As an EU non‐member state, Switzerland was not included in previous soil mapping programs such as the Land Use/Cover Area frame Survey (LUCAS). However, in 2015 Switzerland joined the LUCAS soil sampling program and extended the topsoil sampling to mountainous regions higher 1500 m asl for the first time in Europe. Based on this soil property dataset we developed a K‐factor map for Switzerland to close the gap in soil erodibility mapping in Central Europe. The K‐factor calculation is based on a nomograph that relates soil erodibility to data of soil texture, organic matter content, soil structure, and permeability. We used 160 Swiss LUCAS topsoil samples below 1500 m asl and added in an additional campaign 39 samples above 1500 m asl. In order to allow for a smooth interpolation in context of the neighboring regions, additional 1638 LUCAS samples of adjacent countries were considered. Point calculations of K‐factors were spatially interpolated by Cubist Regression and Multilevel B‐Splines. Environmental features (vegetation index, reflectance data, terrain, and location features) that explain the spatial distribution of soil erodibility were included as covariates. The Cubist Regression approach performed well with an RMSE of 0.0048 t ha h ha^?1 MJ^?1 mm^?1. Mean soil erodibility for Switzerland was calculated as 0.0327 t ha h ha^?1 MJ^?1 mm^?1 with a standard deviation of 0.0044 t ha h ha^?1 MJ^?1 mm^?1. The incorporation of stone cover reduces soil erodibility by 8.2%. The proposed Swiss erodibility map based on measured soil data including mountain soils was compared to an extrapolated map without measured soil data, the latter overestimating erodibility in mountain regions (by 6.3%) and underestimating in valleys (by 2.5%). The K‐factor map is of high relevance not only for the soil erosion risk of Switzerland with a particular emphasis on the mountainous regions but also has an intrinsic value of its own for specific land use decisions, soil and land suitability and soil protection.     

山西褐土长期施钾和秸秆还田对冬小麦产量和钾素平衡的影响

在山西石灰性褐土一年一作条件下,通过16年的田间定位试验,研究了长期施钾和秸秆还田对小麦产量和土壤钾素平衡的影响。结果表明,只施用氮、磷肥,冬小麦年平均产量5.5 t/hm2,土壤钾素养分严重亏缺,年平均亏缺104.3 kg/hm2,与试验前的初始值比较,土壤速效钾和缓效钾含量分别下降23.6%和14.3%。在施用氮、磷肥的基础上每年施用钾肥(K2O 150 kg/hm2),平均增产10.2%以上;小麦秸秆还田平均增产6.6%以上,二者配合平均增产17.6%,年平均吸钾量提高32.0 kg/hm2。与试验初始值比较,土壤速效钾、缓效钾分别提高38.6%和11.0%。在施用氮、磷肥的基础上,长期施用钾肥和秸秆还田在显著增加冬小麦的经济产量、生物产量和吸钾量的同时,也减少年度间因气候因素等影响引起的产量变异,提高年度间产量和植物吸钾量的稳定性。     

Evaluation of differences in potassium availability in soils of the same exchangeable potassium level

Abstract

Potassium availability was determined by growing corn (Zea mays L.) in pots of soil in a controlled environment chamber. Comparison of K uptake rate per unit root area indicated differing degrees of K availability. The differences in availability among soils were not predicted by differences in cation exchange capacities. The K concentration in solution and the average rate of diffusion more nearly reflected differences in K availability, particularly when the kinetic rate factors of diffusion and mass flow were integrated with root growth and uptake factors in the Cushman mathematical model of K uptake. Utilization of this model demonstrated the importance of using rate factors for ion movement in soil along with plant factors of root growth in predicting K availability.     

闽西南崩岗土壤理化性质及可蚀性分异特征

崩岗是南方红壤区侵蚀沟在水力和重力交互作用下沟头遭受坍塌、陷蚀作用而形成的围椅状地貌,是该区域土壤侵蚀及生态系统退化的最高表现形式之一.为揭示崩岗侵蚀对土壤理化特性及可蚀性的影响,以福建省长汀县濯田镇黄泥坑崩岗群内植被盖度分别为2％,20％,95％的3个典型崩岗为研究对象,分别对崩岗系统内的集水坡面、崩壁、崩积体和沟口进行采样和理化特性的测定,并运用EPIC模型测算土壤可蚀性(K).结果表明:1)从集水坡面到崩壁、崩积体至沟口,3个崩岗的土壤砂粒质量分数、pH值和土壤密度呈升高趋势,粉粒、砂粒的质量分数和含水量呈下降趋势.2)1号和2号崩岗,集水坡面的土壤有机质质量分数最高,在崩壁最低;3号崩岗土壤有机质质量分数在崩壁处急剧下降,在崩积体中又明显上升.3)各崩岗中集水坡面、崩壁和崩积体的土壤颗粒组成、土壤密度和含水量差异较小,各土壤理化特性指标在沟口与集水坡面、崩壁和崩积体之间存在显著差异.4)崩岗系统内的集水坡面、崩壁、崩积体和沟口4个子系统的K值差异显著,1、2号崩岗呈现崩壁＞崩积体＞沟口＞集水坡面的变化规律,而3号崩岗则表现为沟口＞崩积体＞崩壁＞集水坡面的趋势.5)崩岗系统内的黏粒质量分数、pH值和有机质质量分数与土壤可蚀性关系密切,可以作为表征崩岗土壤可蚀性的有效指标.崩岗侵蚀造成土壤理化特性不断恶化,砂化严重,研究崩岗系统的土壤理化特性与可蚀性空间变化规律,对指导崩岗的恢复与重建具有重要意义.     

延河流域三种土壤可蚀性K值估算方法比较

土壤可蚀性因子K是表征土壤侵蚀作用的敏感指标。采用3种土壤可蚀性K值估算方法(Torri.D模型、EPIC模型、Shirazi公式法)对延河流域土壤可蚀性进行对比研究,以实测K值为依据,采用相关性分析和模型估算筛选出符合该区侵蚀特点的土壤可蚀性估算方法。结果表明:延河流域土壤中有机碳、黏粒、粉粒含量随植被覆盖度的变化由北向南逐渐增加,平均质量直径(D_(MW))表现为森林森林草原草原,K_(EPIC)和Kshirazi与D_(MW)呈正相关,而Torri.D模型估算K值(K_(Torri.D))与D_(MW)呈相反的变化趋势,即从草原到森林草原再到森林,土壤团聚体稳定性和抗侵蚀性逐渐增加。K_(Torri.D)的变化范围为0.068~0.147 5,高于真实K值(0.031 2~0.079 6),相比于其他两种方法,Torri.D模型平均绝对误差(MAE)、平均相对误差(MRE)和均方根误差(RMSE)更接近于0,而精度因子(Af)更接近1,具有更高的可信度,更加适用于延河流域土壤侵蚀敏感性评价和土壤流失量预测。     

Assessing the plant minimal exchangeable potassium of a soil

The plant minimal exchangeable K (E_Pl,min) defines the lower accessible limit of the most available pool of soil K to plants. It is also an index of long‐term K reserve in soils. However, its estimation by the classical method of exhaustion cropping is laborious. This study aimed at comparing E_Pl,min values obtained by the exhaustion cropping method with E_Pl,min values estimated by an alternative approach based on the cationic exchange capacity (CEC) of the infinitely high selective sites for K (i.e., always saturated with K) in the K‐Ca exchange (E_K‐Ca,min). A set of 45 soil samples, corresponding to the various fertilization K treatments of 15 long‐term K fertilization trials, was used in this study. The selected soil samples presented a wide range of texture, CEC, and exchangeable K. The plant minimal exchangeable K was found more or less independent of the K treatment, whereas E_K‐Ca,min increased when the soil exchangeable K content increased. The plant minimal exchangeable K was systematically lower than E_K‐Ca,min, showing that E_K‐Ca,min is at least partially available to the plant. Hence, E_K‐Ca,min is not a surrogate of E_Pl,min. Conversely, the plant minimal exchangeable K was strongly, positively correlated to soil CEC (measured at soil pH; r² = 0.90^***). This soil property can consequently be used as a proxy of E_Pl,min.     

红壤缓坡地径流与土壤可蚀性对土壤有机碳流失的影响

探明坡面径流和土壤可蚀性对土壤有机碳流失的影响,对于研究土壤有机碳固定和区域碳循环有重要作用。该文通过野外径流小区模拟降雨试验研究不同雨强(30~100 mm/h)和耕作条件下(翻耕和免耕)土壤有机碳流失过程及其与坡面径流和土壤可蚀性的关系。结果表明,坡面产流过程对泥沙态有机碳流失过程具有明显影响,除大雨强条件下泥沙态有机碳流失速率在10~30 min呈现短时间峰值外,各径流小区泥沙态有机碳流失过程与坡面产流过程总体变化趋势基本一致,均表现为产流开始后,其流失率随降雨历时延长而增加,而后逐步趋于平稳,但坡面产流过程对径流有机碳流失过程无明显影响;坡面径流率大小影响土壤有机碳流失,坡面径流率变化能解释80%土壤有机碳流失的变化,坡面径流率与土壤有机碳流失呈线性正相关关系,且坡面径流率对泥沙态有机碳流失的影响比其对径流有机碳流失的影响更明显;土壤可蚀性对土壤有机碳流失的影响是非线性的,且土壤可蚀性指标越大,土壤有机碳流失率越大,但土壤可蚀性对土壤有机碳流失的影响存在有限性。坡面径流和土壤可蚀性是土壤有机碳流失的重要影响因素。