Bulk density by Proctor test as a function of texture for agricultural soils in Maputo province of Mozambique

Soil degradation processes may be of various kinds, including soil compaction. The present study was carried out with the objective of assessing the sensitivity of agricultural or recently abandoned soils in Maputo province of Mozambique to compaction. The assessment is based on the maximum of bulk density attained using the Proctor test (MBD).

In this study the soil texture is expressed by silt plus clay (S + C) or clay (C). The relations between the soil texture and MBD, and between soil texture and critical water content (CWC—soil water at which MBD is attained) were determined. Selected soils range from 10 to 74% of S + C and 9 to 60% of C.

The results suggest there is a relationship between the considered parameters, being that between S + C and MBD or CWC, the best. For MBD the relationship is represented by two quadratic equations with the boundary in between these being a S + C value of 25% and C value of 20%.

Based on the obtained results, one can conclude that the selected parameters may be a useful basis for estimation of the sensitivity to compaction of the Maputo province's soils. It is recommended that similar studies be carried out for soils under forest land and for soil of other provinces to establish the national physical degradation hazard as a function of soil parameters determined routinely and at low cost. The suggested parameters are texture and soil organic matter (SOM).     

土壤紧实度与土块分配对水稻生长的影响及耕作方法的调节

本文就苏南地区二种粘质水稻土的土壤紧实度和土块组成对水稻生长的影响进行了研究,并对不同方法耕作后耕层土块的组成状况进行了观测,结果指出:土壤紧实度和土块/细土比例的不同对水稻生长有明显的影响,土壤紧实度对水稻生长的影响是通过土壤对根的机械阻力,抑制土壤养分的转化及水分物理特性的改变所致;而土块组成的影响可能主要是影响土壤养分的转化。研磨细了的土壤转化成NH₄-N的量最高,土块大于1厘米者对NH₄-N的产生受到严重抑制,因此认为,春耕后耕层中小于1厘米的土块是评定春耕质量的一个重要指标,耕层土块大于8厘米时妨碍栽秧操作,8-4厘米者影响次之,1-4厘米者对栽秧无影响。对于要获得较小土块组成的耕作质量,旋转耕作效果最好,机耙最差,但土壤经过充分晒垡后,各种耕作方法均可获得较好的相同效果,这时,对合适机具的选择主要可从经济效益考虑。渍水条件下土垡经过挤压受损后,可使土块膨软,这或对土壤养分的释放有利,故一般用于春耕机具,只考虑其切割效果而不同时考虑挤压作用是不足的。     

Infiltration of water into two nigerian soils under secondary forest and subsequent arable cropping

Infiltration rates into two tropical-forest soils of western Nigeria under bush fallow (natural regrowth) were found to be high, equilibrium rates about 20–25 cm/h, even after precautions were taken to ensure only vertical flow from the double-ring infiltrometer system. Horizontal flow was difficult to restrain apparently due to the presence of horizontally oriented micro-fauna channels.Ploughing and tillage operations destroyed the micro-fauna channels in the plough layer and greatly reduced the tendency for horizontal flow from a normal double-ring infiltrometer system during arable cropping. Micro-fauna activity also declined in the cultivated soils and had little effect on infiltration.When the land was shifted to arable cropping, the weak granular aggregation of the surface soil deteriorated, and by the end of the first cropping year crusts began to decrease the infiltration capacity. Crusting became more severe during the second cropping year with a further reduction in the infiltration capacity and caused the development of rather serious soil erosion. The soil body beneath the crust remained hydraulically stable for a longer period but it also began to deteriorate during the second cropping year in the Oba soil probably due to its susceptability to tillage compaction and plough pan formation.     

A concept of compaction

Bulk density data of about 150 soil profiles from America, Europe and Asia were used to obtain the regression curve of void ratio ? as a function of vertical stress σ_z. For virgin soils straight lines were obtained if a linear scale was used for ? and a logarithmic scale for σ_z. The slope of these lines was steepest for forest zone soils, less steep in soils of high-grass zones and flattest in short-grass soils. This difference is attributed to varying amounts of loosening by bio- and cryoturbation. Thus the compaction state of virgin soils is that of normal compaction caused by pedogenic processes which are superimposed on previous strong overconsolidation due to desiccation. Against this background agricultural land use creates overconsolidation in the upper soil layers, which is particularly pronounced when the previous bioturbate action has been strong. Young soil deposits cannot develop normal compaction, because of the lack of previous drying of the whole profile.     

A model for estimating crop yield losses caused by soil compaction

A computerized empirical model for estimating the crop yield losses caused by machinery-induced soil compaction and the value of various countermeasures is presented, along with some examples of estimations made with it. The model is based mainly on results of Swedish field trials, and predicts the effects of compaction in a tillage system that includes mouldboard ploughing. It is designed for use at farm level and predicts four categories of effects: (1) Effects of recompaction after ploughing. The calculations are based on the wheel track distribution in the field and the relationship between “degree of compactness” of the plough layer and crop yield. (2) Effects of plough layer compaction persisting after ploughing. Crop yield losses are estimated from traffic intensity in Mgkm ha⁻¹ (Mgkm = the product of the weight of a machine and the distance driven), soil moisture content, tyre inflation pressure and clay content. (3) Effects of subsoil compaction. The calculations are similar to those presented under point (2), but only vehicles with high axle load are considered. These effects are the most persistent. (4) Effects of traffic in ley crops. The estimations are based on wheel track distribution, soil moisture content and several other factors.     

土壤中黑碳对农药敌草隆的吸附-解吸迟滞行为研究

采用批处理振荡法和连续稀释法分别测定了敌草隆在人工添加黑碳土壤和自然形成的不同有机质和黑碳含量的土壤中的吸附一解吸行为。吸附结果表明，人工添加黑碳的土壤对敌草隆的吸附强度和吸附容量以及吸附等温线的非线性均随土壤黑碳添加浓度的增加而逐步增大；自然土壤的吸附容量和吸附强度随土壤总有机质含量增加而增加，但吸附等温线的非线性则与土壤中黑碳对有机质的相对含量有关，黑碳比例越高，等温线非线性越大。解吸实验结果表明，无论是人工添加黑碳的土壤还是自然土壤，对敌草隆的解吸迟滞作用均随土壤黑碳含量增高而愈明显。     

横坡和顺坡耕作对紫色土土壤团聚体稳定性的影响

通过径流小区试验,分析探讨了紫色土横坡和顺坡两种耕作模式下表层(0~20 cm)土壤水稳性团聚体及有机碳含量的特征,为紫色土区坡耕地的有效改造和综合利用提供科学依据。试验结果表明,横坡耕作下土壤水稳性指数K值比顺坡耕作高38.99%,而土壤分散性D值为顺坡耕作的1.64倍,横坡耕作抗蚀性大于顺坡耕作。横坡耕作>0.25 mm水稳性团聚体含量比顺坡耕作增加3.62%,>5 mm、5~3 mm、3~2 mm水稳性团聚体含量横坡耕作均高于顺坡耕作,横坡耕作显著提高>2 mm水稳性团聚体含量。横坡耕作下团聚体结构体破坏率较顺坡耕作减少3.05%,团聚体平均重量直径为顺坡耕作的1.39倍。2种耕作模式下0.5~2 mm团聚体有机碳含量均最高,>0.25 mm不同粒级团聚体有机碳含量百分数均随粒径的减小而减小,均在0.5~0.25 mm粒级下达到最小。横坡和顺坡耕作模式下2~1 mm团聚体有机碳含量无显著差异。横坡耕作较顺坡耕作能够显著增加紫色土>2 mm水稳性团聚体含量,且对有机碳的固持作用更好,有利于土壤结构的改善。     

土壤导热率测定及其计算模型的对比分析

土壤导热率是重要的热参数之一,为了获得预测导热率的准确方法,该文对比分析了确定土壤导热率的热脉冲直接测定法和模型间接推求法。根据热脉冲原理在相同体积质量下,测定了不同质地和含水率土壤的导热率值。结果表明在相同含水率条件下,砂粒含量越高,土壤的导热率越大,土壤导热能力越强。利用Horton经验公式对实测值进行了拟合,结果显示Horton经验模型基本可以反映土壤导热率变化特征,并得到了Horton公式经验系数。利用实测值与Campbell模型计算值进行了比较,结果显示Campbell模型计算结果偏差较大,并对其进行了修正。并且用实测值与Johansen模型及其2种改进模型(Coté-Konrad模型和Lu-Ren模型)的计算值进行了对比分析,结果表明Johansen模型计算结果与实测值偏差较大,2种改进型模型的计算结果与实测值更接近。该研究表明土壤导热率可以利用土壤质地、含水率、孔隙度和体积质量进行计算,3种理论模型的计算值与实测值的相关系数均值分别为:0.643、0.937、0.943,推荐使用Coté-Konrad模型和Lu-Ren模型计算土壤导热率,Lu-Ren模型比Coté-Konrad模型的适用范围更广。     

A method for predicting soil susceptibility to the compaction of surface layers as a function of water content and bulk density

Identifying the vulnerability of soils to compaction damage is becoming an increasingly important issue when planning and performing farming operations. Soil compaction models are efficient tools for predicting soil compaction due to agricultural field traffic. Most of these models require knowledge of the stress/strain relationship and of mechanical parameters and their variations as a function of different physical properties. Since soil compaction depends on the soil's water content, bulk density and texture, good understanding of the relations between them is essential to define suitable farming strategies according to climatic changes. In this work we propose a new pedotransfer function for 10 representative French soils collected from cultivated fields, a vineyard and forests. We investigate the relationship between soil mechanical properties, easily measurable soil properties, water content and bulk density. Confined compression tests were performed on remoulded soils of a large range of textures at different initial bulk densities and water contents. The use of remolded samples allowed us to examine a wide range of initial conditions with low measurement variability. Good linear regression was obtained between soil precompression stress, the compression index, initial water content, initial bulk density and soil texture. The higher the clay content, the higher the soil's capacity to bear greater stresses at higher initial water contents without severe compaction. Initial water content plays an important role in clayey and loamy soils. In contrast, for sandy soils, mechanical parameters were less dependent on initial water content but more related to initial bulk density. These pedotransfer functions are expected to hold for the soils of tilled surface layers, but further measurements on intact samples are needed to test their validity.     

Fine-earth translocation by tillage in stony soils in the Guadalentin, south-east Spain: an investigation using caesium-134

Tillage erosion is increasingly recognised as an important soil erosion process on agricultural land. In view of its potential significance, there is a clear need to broaden the experimental database for the magnitude of tillage erosion to include a range of tillage implements and agricultural environments. The study discussed in this paper sought to address the need for such data by examining tillage erosion by a duckfoot chisel plough in stony soils on steep slopes in a semi-arid environment. Results of the investigation of coarse fraction (rock fragment) translocation by tillage in this environment have been presented elsewhere and the paper focuses on tillage translocation and erosion of the fine earth. Tillage translocation was measured at 10 sites, representing both upslope and downslope tillage by a duckfoot chisel plough on five different slopes, with tangents ranging from 0.02 to 0.41. A fine-earth tracer, comprising fine earth labelled with ¹³⁴Cs, was introduced into the plough layer before tillage. After a single pass of the plough, incremental samples of plough soil were excavated and sieved to separate the fine earth from the rock fragments. Translocation of the fine-earth tracer was established by analysing the ¹³⁴Cs content of the samples of fine earth. These data were used to establish translocation distances for each combination of slope and tillage direction. Translocation distances of the fine earth were not significantly different from translocation distances of the coarse fraction. For all sites, except uphill on the 0.41 slope, translocation distances were found to be linearly related to slope tangent. The soil flux due to tillage for each site was calculated using the translocation distance and the mass per unit area of the plough layer. For slopes with tangents <0.25, the relationship between soil flux and tangent was linear and the soil flux coefficient derived was 520–660 kg m⁻¹ per pass. This is much larger than the coefficients found in other studies and this high magnitude is attributed to the non-cohesive nature and high rock fragment content of the soil in this investigation. A second contrast with previous studies was found in non-linearity in the relationship between soil flux and tangent when steeper slopes were included. This was a product of variation in plough depth between the steepest slopes and the remainder of the study area. On the basis of the study it is suggested that an improved understanding of tillage erosion may be obtained by considering the dual processes of tillage detachment (mass per unit area of soil subject to tillage) and tillage displacement (equivalent to translocation distance per pass) in assessing, comparing and modelling tillage translocation. An improved model is proposed that recognises the complexity of soil redistribution by tillage, provides a framework for process-based investigation of the controls on tillage fluxes, and allows identification of potential self-limiting conditions for tillage erosion.     

深翻－旋耕轮耕与有机肥配施对黑土农田土壤物理性质的影响

针对东北松嫩平原中南部黑土区玉米带农田长期旋耕导致耕层变浅、容重增大等问题,开展深翻-旋耕轮耕模式改善土壤物理性质的研究。试验设置连年旋耕配施化肥（RT）、连年旋耕配施化肥与有机肥（RM）、深翻－旋耕轮耕配施化肥（DT）和深翻－旋耕轮耕配施化肥与有机肥（DM）4个处理,分析0 ~ 45 cm土壤含水量、容重、紧实度、团聚体的变化及10 cm、20 cm、30 cm各深度处土壤温度变化情况。结果表明,与RT处理相比,DT处理能够显著提高玉米苗期和拔节期20 cm、30 cm深度土壤温度,增加玉米各生育时期15 ~ 45 cm土层土壤含水量,并且显著降低土壤容重和紧实度,提高了30 ~ 45 cm土层 > 0.25 mm水稳性团聚体的比例;同时DM处理能够增加苗期、收获期各土层含水量,且对0 ~ 45 cm土壤容重均有显著降低作用;而RM处理仅使0 ~ 15 cm土层容重有降低,但并不显著,且对深层土壤容重无明显影响。相关分析表明,在0 ~ 15 cm土层中,土壤含水量、紧实度、容重与温度呈负相关关系（P < 0.05）;在0 ~ 45 cm土层中,土壤容重与土壤紧实度呈极显著正相关关系（P < 0.05）。DM的耕作模式能降低土壤容重和紧实度,有效提高土壤温度、土壤含水量以及 > 0.25 mm 水稳性团聚体的比例,能够较好的改善土壤耕层物理性质。     

土壤中镍生态阈值的影响因素及预测模型

利用实验室获得的毒理学数据建立土壤生态阈值需通过老化-淋洗因子校正以消除外源添加的人工污染与野外实际污染的差异。该文利用基于中国土壤的17个物种的镍毒理学数据建立镍土壤生态阈值并利用老化-淋洗因子对数据进行校正。结果表明淋洗效应在pH值大于8.5的土壤中尤为显著,除个别土壤外,淋洗因子(LF)值均大于2;老化效应在碱性土壤(pH值>7.0)中更为显著,且老化因子(AF)值随着土壤pH值的升高而增大。pH值、有机碳含量(OC)、阳离子交换量(CEC)可分别控制镍生态阈值变异的86.2%、9.0%和4.1%。土壤pH值是影响土壤镍生态阈值的最重要因子,基于土壤pH值和OC的2因子预测模型能较好地预测土壤镍生态阈值,其相关性达到95.2%,利用该研究获得的两因子模型并依据土壤性质参数可预测不同类型土壤中的镍生态阈值。     

Use of in-growth soil cores in mesh bags for studies of relations between soil compaction and root growth

Using in-growth soil cores in cylindrical mesh bags, the effects of 3 soil compaction treatments on growth of crop roots were studied in a sandy soil. The bags were inserted after crop emergence in holes (70 mm diameter; 60 cm depth) augered in the soil in crop row interspaces. In 1984 (with rapessed), at all sampling dates, root biomass in the inserted cores decreased with increased compaction of the plough layer (0–25 cm) as well as the subsoil (25–60 cm). Root biomass in the subsoil was low. In 1985 (with wheat), the effects of compaction in the subsoil were similar, although root biomass was greater than in 1984. However, in the plough layer there were significant differences in root biomass on only one sampling date. The mesh bag technique should be a useful complement to other field methods in studies of relations between physical soil characteristics or tillage treatments and root growth.     

Estimation of density—Moisture—Stress functions from uniaxial compression of unsaturated, structured soils

A quasi-theoretical soil compaction model is presented which gives good estimates (r²=0.980−0.995, P<0.001) of the complete density-stress compression line for soils of variable initial moisture content under static loads from 0 to 1.0 MPa. The 3 unknown parameter coefficients of the generalized model equation are shown to be highly correlated to several soil properties such as moisture content, pre-compression (initial) void ratio, texture, organic matter content ans the Atterberg consistenct limits. A 3-tier classification for partition consisteny limits. A-tier claasificaton for pationing soils into groupings of response to compressive stress is proposed for soil compaction modeling. This categorization is based on soil plasticity and the existence of a “compaction threshold“ sensitivity threshold” in most soils.     

黄土高原几种质地土壤的水分扩散率

本文采用水平土柱入渗法,测定了四种不同质地、不同孔隙度土壤的水分扩散率。结果表明,粘粒含量较多和孔隙度较小的土壤,单位时间内入渗水量较少,渗到既定距离需要的时间较长。各种质地土壤的扩散率D都随含水量增加而增加。当饱和度相同时,质地愈粘重,扩散率愈小。扩散率和孔隙度呈正相关。本文建立了土壤扩散率D和饱和度c的幂函数方程。将其运用到非饱和水分运动方程中,以有限差分数值计算法,所得土壤含水量的计算值和实测值比较接近,说明这些经验公式有一定的可靠性。     

Ecological safe management of terraced rice paddy landscapes

Ecological safe management of rice paddy landscapes is in focus of a joint research project comprising five German working groups and Chinese partners. The project is aiming at characterizing the scale-depending structures and processes of agricultural landscape of terraced paddy fields in southeast China. The specific objectives were the enlightenment of the linkage between remote sensible information and the spatial distribution of soil features, as well as soil structural processes and their relation to vertical and lateral water losses and solute leaching.The experimental watershed is located in southeast China. The soils which either developed from quaternary clay or red sandstone exhibit a (man-made) layered structure with three hydraulic-functional horizons: puddled layer, plough pan and the (water unsaturated) subsoil.The analysis of soil texture and selected chemical parameters on the catenary and catchment scale confirmed that even in old terraced and thoroughly modified landscapes, the original structures (unaffected by man) of catenary soil property distributions persist. Thus, the application of co-regionalization techniques incorporating topographical attributes as explaining variables was found to be suitable to characterize soil property distributions on both the catenary and the catchment scale.On-site field scale investigations revealed that paddy soils exhibit a dynamic soil–water system which is driven by the mechanical seed bed preparation (puddling) on the one hand and drying and wetting cycles including ponded/flooded periods on the other. It was found that the hydraulic properties depend mainly on the duration of cultivation as a rice paddy. In contrast to earlier studies, we found that a further decrease in the saturated hydraulic conductivity of the plough pan may still occur after 20 years. Even in older rice paddies, however, water losses may be significant mainly because of ineffective functioning of the surrounding bunds.Pedon and aggregate investigations demonstrated the pronounced dual porosity nature of the paddy soils with a macropore network consisting of cracks and biopores penetrating both the plough pan and the bunds. The shrinkage potential of the puddle layer was higher in older paddy fields than in younger ones while it was vice versa for soil from the plough pan. Swelling and shrinkage affected also the living conditions for soil microorganisms especially after drainage when the habitable pore space was significantly reduced. Pore scale and micro-biological investigations revealed that drainage induced stress reduced micro-biodiversity and decreased abundances of soil inhabiting microorganisms.In addition to newly proposed management strategies with recurrent wetting and drying cycles, we suggest maintaining (saturated) equilibrium conditions over longer periods to reduce soil structural dynamics and the risks of water losses and chemical leaching involved with preferential flow.     

Anisotropy of the properties of some anthropogenically transformed soils of podzolic type

It is shown that the horizons and profiles of anthropogenically transformed soils of podzolic type—light typical agrozems, typical texture-differentiated soils developed from glaciolacustrine loamy sands and clays and from noncalcareous mantle loams, agrosoddy deeply podzolic soils developed from noncalcareous mantle loams, and agrosoddy shallow-podzolic soils developed from noncalcareous mantle loams and from calcareous loams underlain by ancient glaciolacustrine loams and clays—are characterized by some anisotropy of most of their properties. The highest anisotropy is typical of the field water content, bulk density, and total porosity. The coefficients of anisotropy (gradients) calculated for the separate horizons as the ratios between the values of the properties measured in the horizontal and vertical directions (k = P_horiz/P_vertic) of these properties are much higher than those of other soil properties. The coefficient of anisotropy of the soil profile (K) is suggested as the coefficient of correlation between the values of a given property determined in the horizontal and vertical soil sections. For the considered properties, K varies from 0.4 to 0.6. For other soils properties, such as the solid phase density, the electrical resistance determined in a laboratory and in the field, and the organic carbon content, the coefficients of anisotropy are close to 1.0. The clay content has an intermediate anisotropy. The values of anisotropy and its direction (gradient) should be taken into account upon the assessment of the soil physical properties and the processes controlling them; this is particularly important in the study of soil transformation. The revealed regularities of the soil anisotropy make it possible to suggest a new interpretation of the data on the distribution of water and energy in soil profiles.     

Acoustic determination of air-filled porosity and relative air permeability of soils

Two acoustic techniques for determining the air-filled porosity and air permeability of soil surfaces, and the near-surface variation of these properties with depth, have been applied to several soils in situ. The techniques depend upon an inversion process using data on sound propagation near to the soil surface and through the soil surface. The measured difference in acoustic spectra received by two vertically separated microphones above the ground surface and by probe microphones beneath the surface were matched theoretically to deduce the porosity of air-filled connected pores and an effective air permeability which depends on pore shape and size distribution. This modified permeability parameter and the acoustically deduced porosity varied realistically with surface sealing and compaction. The acoustically deduced porosities were within 10% of those obtained conventionally. Changes in acoustically deduced parameters occurred with changes in moisture content both in soil bin and field experiments. The acoustic techniques were successful in monitoring surface sealing and near-surface layering on a fine scale.