Soil physical properties of afforested and arable land

Abstract. The effects of tree crops on the soil physical properties of former agricultural land were compared with those of ley in a rotation with cereals on adjacent sites. Five sites in southern Sweden were investigated focussing on soil water retention characteristics, dry bulk density, macroporosity and saturated hydraulic conductivity. Three of the sites were on light textured soils and two on clay soils. The tree crops were 30 to 35-year-old hybrid aspen, Populus deltoides , and silver birch, Betula pendula , and the ley crops were one to five years old.
The light-textured soils under tree crops showed bimodal pore size distributions in the macropore region, whereas under ley crops they showed unimodal distributions. Dry bulk densities were generally smaller and the macroporosities larger under tree crops compared with leyicereal crops. Saturated hydraulic conductivities tended to be larger under tree crops. Slopes of the linear regression lines between saturated hydraulic conductivity and each of the parameters dry bulk density, porosity and macroporosity were steeper in the soil under agricultural crops than under tree crops.
Observed differences in physical properties were considered to be an effect of land use, which had brought about changes in aggregate stability, pore size distribution and pore continuity.     

Soil physical and chemical changes due to tillage and their implications for erosion and productivity

A seven-year tillage trial was conducted in central New South Wales, Australia to measure the effect and extent of conservation tillage practices on soil physical and chemical properties. Three tillage treatments, traditional tillage (TT), reduced tillage (RT) and direct drilling (DD) were imposed on hardsetting red-brown earths at Cowra and Grenfell. A fourth treatment, direct drilling without grazing (NT) was imposed at Cowra only.

At Cowra there was a significant trend of reduced total runoff in the DD and NT treatments but not in the RT treatment. Runoff significantly increased in the TT treatment.

At Grenfell, runoff decreased in all treatments but only significantly in the DD and RT treatments. Similar trends in total sediment loss were measured at both sites.

Associated physical measurements of saturated hydraulic conductivity, sorptivity and bulk density confirmed that the changes in runoff were due to the creation of macroporosity greater than 0.75 mm diameter. The relationship between macroporosity, organic carbon and aggregate stability is discussed. Conclusions were that in these soil types runoff and sediment loss were affected more by destruction of macroporosity due to cultivation than changes in organic carbon from residue retention. To achieve these soil improvements using conservation tillage a continuous cropping period of four years was necessary to obtain significant and consistent trends.

Soil chemical data showed that total nitrogen increased with conservation tillage practices. Available phosphorus changes due to tillage were not observed because of more than adequate fertiliser applied. Soil pH decreased significantly in the DD and NT treatments at Cowra only. The implications of these chemical changes are discussed.     

应用土壤质地预测干旱区葡萄园土壤饱和导水率空间分布

田间表层土壤饱和导水率的空间变异性是影响灌溉水分入渗和土壤水分再分布的主要因素之一,研究土壤饱和导水率的空间变化规律,有助于定量估计土壤水分的空间分布和设计农田的精准灌溉管理制度。为了探究应用其他土壤性质如质地、容重、有机质预测土壤饱和导水率空间分布的可行性,试验在7.6 hm2的葡萄园内,采用均匀网格25 m×25 m与随机取样相结合的方式,测定了表层(0～10 cm)土壤饱和导水率、粘粒、粉粒、砂粒、容重和有机质含量,借助经典统计学和地统计学,分析了表层土壤饱和导水率的空间分布规律、与土壤属性的空间相关性,并对普通克里格法、回归法和回归克里格法预测土壤饱和导水率空间分布的结果进行了对比。结果表明:1)土壤饱和导水率具有较强的变异性,平均值为1.64 cm/d,变异系数为1.17;2)表层土壤饱和导水率60%的空间变化是由随机性或小于取样尺度的空间变异造成;3)土壤饱和导水率与粘粒、粉粒、砂粒和有机质含量具有一定空间相关性,而与土壤容重几乎没有空间相关性;4)在中值区以土壤属性辅助的回归克里格法对土壤饱和导水率的预测精度较好,在低值和高值区其与普通克里格法表现类似。研究结果将为更好地描述土壤饱和导水率空间变异结构及更准确地预测其空间分布提供参考。     

Determining soil saturated hydraulic conductivity and sorptivity from single ring infiltration tests

The difference between the cumulative infiltration occurring during three‐dimensional axisymmetric and one‐dimensional vertical flow is a linear function of time. The slope of this line is a function of the source radius, initial and final volumetric soil water contents and the soil sorptivity. This allows the determination of the sorptivity and saturated conductivity of the soil from data of axisymmetric flow in a single ring of small diameter under negligible head of water. The method is based on the optimization of the sorptivity and saturated conductivity on the one‐dimensional vertical cumulative infiltration inferred from axisymmetric flow data. To examine the reliability of the method to determine these parameters, numerical three‐ and one‐dimensional data are generated on soils with known hydrologic properties from the literature. The linearity versus time of the difference of the two types of flow is verified. Several physically based expressions for the vertical cumulative infiltration as a function of time are considered. The optimized values of the sorptivity and saturated conductivity are compared to the their real known values. Despite the large errors on the optimized parameters, namely the saturated conductivity, the error on the vertical predicted cumulative infiltration is limited to 10%. This makes possible the application of this method on a large scale for hydrological modelling purposes.     

蓄水坑入渗表层土壤体积质量和饱和导水率的变化

表层土壤体积质量和导水率是影响土壤入渗及水分运动的重要物理参数。该文采用土壤切片技术和数字图像分析技术,分析了蓄水坑灌条件下入渗水头对砂壤土表层土壤体积质量的影响,进行了不同入渗水头、土壤体积质量对砂壤土表层土壤饱和导水率的试验研究,并对蓄水坑侧向水平入渗湿润锋变化的试验结果与数值模拟结果进行对比分析。结果表明：该研究试验条件下（土壤体积质量为1.345 g/cm3）,入渗水头对土壤体积质量和表层土壤饱和导水率有较明显的影响。随着入渗水头的增大,其作用下的表层土壤体积质量趋于增大,土壤结构趋于密实,表层土壤的饱和导水率趋于减小;表层土壤饱和导水率与入渗水头和土壤体积质量之间呈乘幂关系,且表层土壤饱和导水率对土壤体积质量的变化较为敏感,当土壤体积质量达到某一程度时（1.466 g/cm3）,入渗水头对表层土壤饱和导水率的影响甚微。研究成果揭示了入渗水头影响蓄水坑土壤入渗的微观机制,为进一步研究蓄水坑灌法提供了理论依据。     

Impact of land‐use changes on soil hydraulic properties of Calcaric Regosols on the Loess Plateau,NW China

Vegetation restoration efforts (planting trees and grass) have been effective in controlling soil erosion on the Loess Plateau (NW China). Shifts in land cover result in modifications of soil properties. Yet, whether the hydraulic properties have also been improved by vegetation restoration is still not clear. The objective of this paper was to understand how vegetation restoration alters soil structure and related soil hydraulic properties such as permeability and soil water storage capacity. Three adjacent sites with similar soil texture, soil type, and topography, but different land cover (black locust forest, grassland, and cropland) were selected in a typical small catchment in the middle reaches of the Yellow River (Loess Plateau). Seasonal variation of soil hydraulic properties in topsoil and subsoil were examined. Our study revealed that land‐use type had a significant impact on field‐saturated, near‐saturated hydraulic conductivity, and soil water characteristics. Specifically, conversion from cropland to grass or forests promotes infiltration capacity as a result of increased saturated hydraulic conductivity, air capacity, and macroporosity. Moreover, conversion from cropland to forest tends to promote the creation of mesopores, which increase soil water‐storage capacity. Tillage of cropland created temporarily well‐structured topsoil but compacted subsoil as indicated by low subsoil saturated hydraulic conductivity, air capacity, and plant‐available water capacity. No impact of land cover conversion on unsaturated hydraulic conductivities at suction > 300 cm was found indicating that changes in land cover do not affect functional meso‐ and microporosity. Our work demonstrates that changes in soil hydraulic properties resulting from soil conservation efforts need to be considered when soil conservation measures shall be implemented in water‐limited regions. For ensuring the sustainability of such measures, the impact of soil conversion on water resources and hydrological processes needs to be further investigated.     

Anisotrope Variation der gesättigten Wasserleitfähigkeit einer unterschiedlich beweideten Salzmarsch im Deichvorland

Anisotropic variation of saturated hydraulic conductivity of a variously grazed salt marsh soil Undisturbed core samples were taken in horizontal and vertical direction from a variously grazed salt marsh soil for investigation of the anisotropic variation of saturated hydraulic conductity K_sat, bulk density, and pore size distribution. The results show that saturated hydraulic conductivity varies significantly anisotropically. The average Kv/Kh ratio is 0.38 for the soil profile and 0.44 for the surface soil. This anisotropy of K_sat is mainly attributed to the stratified structure of soil due to the sedimentation conditions in the salt marsh environment and decreases if soil structure development through pedological processes progresses. Furthermore. K_sat decreases significantly if the stocking rate of grazing is larger than 1.0 sheep unit/ha and the effect is more pronounced near the dike. However, both the Kv and Kh are affected by grazing in the same manner, so that the anisotropy of K_sat is independent from grazing. Bulk densitiy and macroporosity are affected by grazing but not by the direction of sampling. There are significant correlations between K_sat and > 50 μm as well as > 10 μm pore volume. The correlation between K_sat and total porosity is however not significant. The anisotropy of K_sat implicates the favouring of the lateral water flux and in the hydrological research and modelling of the salt marsh ecosystem the anisotropy of K_sat should be taken into account.     

The effect of dairy sewage sludge amendment on repellency and hydraulic conductivity of soil aggregates from two depths of Eutric Cambisol

Appropriate management of sewage sludge is an important worldwide issue due to the still growing amount of wastewaters. In the study we examined to what extent the addition of dairy sewage sludge compared with mineral fertilization affects porosity, repellency index, and hydraulic conductivity of variously sized aggregates from two soil depths of Eutric Cambisol derived from loess: 5–15 cm and 25–35 cm. The repellency index was calculated as a ratio of ethanol and water sorptivity. Data on water and ethanol sorptivities of initially air‐dry soil aggregate fractions were obtained from steady state flow measurements using an infiltration device. Hydraulic conductivity was determined by measuring water infiltration at five pressure heads: –8, –6, –4, –2, and 0 cm of water column with the same device as for sorptivity determination. Addition of sewage sludge to the soil decreased the soil repellency index by an average of 27% in topsoil and 32% in subsoil for both aggregate sizes, respectively, and increased hydraulic conductivity about four times in both layers. Smaller aggregates (15–20 mm diameter) from soil amended with sewage sludge, in comparison with larger ones (30–35 mm diameter), had a higher repellency index by 36 and 24% in topsoil and subsoil, respectively. As for aggregates from soil with mineral fertilization, those differences were smaller and equal to 15% in subsoil, in topsoil smaller aggregates even had slightly lower repellency index (by 5%). Aggregates taken from the upper soil layer were more water repellent and had smaller hydraulic conductivity than those taken from subsoil, regardless of soil treatment and aggregate size.     

A dual‐porous,inverse model of water retention to study biological and hydrological interactions in soil

The deterministic modelling of bio‐hydrological processes in soil requires a void structure model that is explicitly dual‐porous containing fully and separately characterized macroporosity and microporosity. It should also contain information that relates the positioning of microporosity relative to macroporosity. An example of such a process is the production of nitrous oxide, in which bacteria in microporous ‘hot‐spots’ are supplied with nutrients and gases through a macroporous pathway. We present a precision void‐structure model that satisfies these two criteria, namely explicit macroporosity and microporosity, and their positional relationship. To demonstrate the construction of the model, we describe the modelling of a single soil, namely Warren soil from Rothamsted Research's Woburn Experimental Farm in Bedfordshire, UK, although the modelling approach is applicable to a wide range of soils and other dual porous solids. The model is capable of fitting several fundamental properties of soil, namely water retention, aggregate size distribution, and porosity of the microporous and macroporous zones. It comprises a dendritic critical percolation path, around which are clustered the microporous regions. The saturated hydraulic conductivity of the dual‐porous network is of the correct order of magnitude for a soil of the same density and texture as the Warren sample. Finally, we demonstrate how the preferential flow pathway in the resulting structure differs from the critical percolation pathway, and that only 4.6% by volume of the unclogged macroporosity contributes to the fluid flow through the structure.     

推求土壤水分运动参数的简单入渗法──Ⅱ.实验验证

预报土壤中水分流动需要的土壤导水特性可通过观察水平土柱的入渗过程来确定,这一观测过程的分析是基于对Ｒｉｃｈａｒｄｓ方程求积分解。土壤水分特征曲线中的参数由观测的水平土柱和特征湿润长度和吸力为确定,非饱和土壤导水率由已确定的特征曲线中的参数和测定的饱和导水率导出。供试土壤有三种,它们的质地从砂壤到粘壤。由这种方法所确定的这三种土壤的水分特征曲线与实测的特征曲线符合良好,所确定的砂壤的非饱和导水率与实     

Effect of compaction on pore functions of soils in a Saalean moraine landscape in North Germany

Soil compaction and related changes of soil physical parameters are of growing importance in agricultural production. Different stresses (70, 230, 500, and 1000 kPa) were applied to undisturbed soil core samples of eight typical soils of a Saalean moraine landscape in N Germany by means of a confined compression device to determine the effect on (1) total porosity/pore‐size distribution, (2) saturated hydraulic conductivity, and (3) air conductivity to assess the susceptibility towards compaction. Different deformation behaviors after exceeding the mechanical strength particularly resulted from a combination of soil characteristics like texture and initial bulk density. The saturated hydraulic conductivity, as an indicator for pore continuity, was largely affected by the volume of coarse pores (r² = 0.82), whereas there was no relationship between bulk density and saturated hydraulic conductivity. Since coarsely textured soils primarily possess a higher coarse‐pore fraction compared to more finely textured soils, which remains at a high level even after compaction, only minor decreases of saturated hydraulic conductivity were evident. The declines in air conductivity exceeded those in hydraulic conductivity, as gas exchange in soils is, besides the connectivity of coarse pores, a function of water content, which increases after loading in dependence of susceptibility to compaction. A soil‐protection strategy should be focused on more finely textured soils, as stresses of 70 kPa may already lead to a harmful compaction regarding critical values of pore functions such as saturated hydraulic conductivity or air capacity.     

Variations in Soil Physical Properties in a Cleared Forestland Continuously Cultivated for Seven Years in Eastern Nsukka,Nigeria

In this study, soil physical properties were evaluated in the top 40 cm of cleared forestland that had been subjected to continuous cultivation for 7 years to ascertain selected crop or crop combinations that influenced the soil physical properties the most. There was no significant effect of crop treatment on particle‐size distributions over 6 years of cultivation. In year 7, clay values were significantly (p = 0.05) greater in plots grown with solely cassava (SC) and solely maize (SM) than in the plots grown with solely pigeon pea (SP). The soil depth effects over the 7 years were significant on the clay content. The mean values of bulk density, pore‐size distribution, and hydraulic conductivity obtained from each plot fluctuated over the years. The bulk density values in 1998 ranged from 1.29 to 1.43 g cm³, but from 1999 to 2004, the range was from 1.12 to 1.40 g cm³. Thus, bulk density generally decreased when compared with their respective values in 1998. The greatest decrease of ≈ 22% was in 2000. More than 70% of the macroporosity values were significantly less than their respective values in 1998. The greatest decease of 72% was obtained from SM plots in 2001. All the microporosity were significantly more than the 1998 values. All the increases were >100% of the original values. These increases were reflected in the variations of total and saturated hydraulic conductivity (Ks) values. However, in 2004, Ks values decreased in the plots grown to C + P, SP, and SM. Generally, the C + M + P mixture appeared to be the most consistent in improving micro‐ and total porosities and Ks among the crop treatments.     

Different responses in bulk density and saturated hydraulic conductivity to soil deformation by logging machinery on a Ferralsol under native forest

Ferralsols have high structural stability, although structural degradation has been observed to result from forest to tillage or pasture conversion. An experimental series of forest skidder passes in an east Amazonian natural forest was performed for testing the effects of mechanical stress during selective logging operations on a clay‐rich Ferralsol under both dry and wet soil conditions. Distinct ruts formed up to 25 cm depth only under wet conditions. After nine passes the initially very low surface bulk density of between 0.69 and 0.80 g cm^?3 increased to 1.05 g cm^?3 in the wet soil and 0.92 g cm^?3 in the dry soil. Saturated hydraulic conductivities, initially >250 mm h^?1, declined to a minimum of around 10 mm h^?1 in the wet soil after the first pass, and in the dry soil more gradually after nine passes. The contrasting response of bulk density and saturated hydraulic conductivity is explained by exposure of subsoil material at the base of the ruts where macrostructure rapidly deteriorated under wet conditions. We attribute the resultant moderately high hydraulic conductivities to the formation of stable microaggregates with fine sand to coarse silt textures. We conclude that the topsoil macrostructure of Ferralsols is subject to similar deterioration to that of Luvisols in temperate zones. The stable microstructure prevents marked compaction and decrease in hydraulic conductivity under wetter and more plastic soil conditions. However, typical tropical storms may regularly exceed the infiltration capacity of the deformed soils. In the deeper ruts water may concentrate and cause surface run‐off, even in gently sloping areas. To avoid soil erosion, logging operations in sloping areas should therefore be restricted to dry soil conditions when rut formation is minimal.     

Is mechanical soil aeration a strategy to alleviate soil compaction and decrease phosphorus and suspended sediment losses from irrigated and rain‐fed cattle‐grazed pastures?

Agriculture is a major source of phosphorus (P) and suspended sediment (SS) losses to aquatic ecosystems promoting eutrophication. Mechanical soil loosening equipments such as topsoil looseners or aerators have been reported to improve the physical quality and infiltration of soils susceptible to livestock damage resulting from treading. We hypothesized that soil aeration would significantly decrease the volume of surface runoff and consequent losses of P and SS compared with non‐aerated soil (control) in cattle‐grazed pasture on a poorly structured silt‐loam soil. Hydrologically isolated plots (2 m long × 1 m wide × 0.15 m deep) were installed in aerated and control plots to collect surface runoff following irrigation or rainfall and analysed for P and SS losses for 1 year. Soil physical properties [% macroporosity, bulk density, saturated hydraulic conductivity (K_sat) and unsaturated hydraulic conductivity (K_unsat at ?1kPa)] were measured in the aerated and control treatments and taken before each irrigation event (n = 12). Six months after mechanical aeration was employed, but before cattle grazing commenced, no significant differences in soil physical quality were found between aerated and control treatments, with the exception of a minor increase in K_unsat for the control plots. This lack of treatment difference continued after grazing and was largely attributed to the re‐settling of the poorly structured and dispersive soil. Flow‐weighted mean concentrations and annual loads of dissolved reactive P (DRP) on the mechanically aerated soil (2.24 kg DRP/ha) were approximately double those from the control treatment (1.20 kg DRP/ha). However, no significant differences were observed between treatments for surface runoff volumes and losses of total P and total SS, which may reflect the similar soil physical conditions exhibited between treatments throughout most of the trial. As observed elsewhere, time (days) since grazing or fertilizer application was found to influence P and/or SS losses. We conclude that aeration did not decrease P and SS losses. Any changes in soil physical properties such as macroporosity were short‐lived and therefore unlikely to influence surface runoff and subsequent P and SS losses for this soil type.     

黄土高原生态工程区土壤容重及饱和导水率的分布特征

土壤水力性质是影响水分运动、溶质运移以及流域水文模型模拟的重要参数。近年来,黄土高原实施的退耕还林(草)工程、治沟造地工程等重大生态工程,影响了该区域的地形地貌、土壤水力性质等。深入研究流域尺度土壤容重(Bulk Density,BD)与饱和导水率(Ks)的动态变化特征,对于理解重大生态工程影响下的水文过程演变规律具有重要意义。本研究以黄土高原重大生态工程影响的典型小流域为对象,采用80m×80m的网格布点(89个样点),分别于2016年9月(夏末)、11月(初冬)和2017年3月(初春)采集土壤表层(0～5 cm)环刀样品,分析BD和Ks的动态分布特征及其影响因素。结果表明:BD在0.93～1.61 g/cm3之间变动,Ks介于0.01～7.30 cm/min;BD呈弱变异性,变异系数(Coefficient of Variation,CV)为10%,而Ks呈强变异性(CV=166%)。坡面BD显著小于沟底(P0.05),而Ks则显著大于沟底(P0.05)。坡面林地和草地BD表现出显著的季节性差异(P0.05),而Ks在林地、灌木和草地之间均表现出显著的季节性差异(P0.05)。地形对流域内的土壤水力参数分布有显著影响,外界环境(温度)变化是决定BD和Ks呈季节性动态变化的重要因素。多因素方差分析表明土地利用类型对BD与Ks均有显著影响;采样时间对Ks有显著影响,对BD无显著影响。相关结果可为揭示重大生态工程区小流域土壤水力参数的动态变化规律及其主控因素提供数据支撑和理论参考,有助于小流域水文过程的模型模拟研究与精细调控。     

土壤容重对红壤水分溶质运移特征影响的试验研究

通过测定南方第四纪红壤不同土壤容重条件下,土壤水分水平入渗过程和溴化钾溶液穿透曲线,分析了土壤容重对入渗速率、土壤饱和导水率的影响;根据CDE模型、运用CXTFIT软件对溴离子的穿透曲线(BTC)进行拟合.并求其运移参数.结果表明:土壤水分运移速率和土壤饱和导水率随着红壤容重增大而减少;随着容重增大,Br-的水动力弥散系数D增大,阻力因子R也增大.     

Soil properties after change to conservation agriculture from ridge tillage in sandy clay loams of mid‐altitude Central Malawi

A comparative study was carried out of annual ridge tillage (RT) and short‐term effects of conservation agriculture (CA) on soil properties in fields of small‐scale farmers. Soil samples were collected at depths of 0–10 and 10–20 cm from a total of 12 fields which had been under CA for two and four seasons, respectively, and from adjacent RT fields for direct comparisons. CA fields were converted from fields previously under continuous RT. Soil organic carbon, total nitrogen and available phosphorus were greater in CA fields while extractable potassium, pH and salt content were moderated under CA. Conversion of long‐term RT to CA did not significantly influence bulk density and aggregate stability (geometric mean diameter) although structural stability was greater under CA practices. Total porosity, macroporosity and matrix porosity, and volumetric water content at saturation, field capacity and permanent wilting point did not substantively respond to tillage effects. Relative water capacity and air–water storage parameter, θ_fc/POR_t, were significantly greater after 4 yr of CA. Soils under CA showed greater values for field‐saturated hydraulic conductivity compared with RT fields. With the highest loadings in a principal component analysis, this work suggests that variables related to volumetric water content and aeration of the soil matrix, organic carbon, available phosphorus and soil texture were the most useful indices for future field comparison of RT and CA practices.     

灰色关联及非线性规划法构建传递函数估算黑土水力参数

土壤水分特征曲线和饱和导水率是重要的水力参数,为了简便准确获取这些参数,以松嫩平原黑土区南部为研究区域,采集136个采样点土样用于测定不同土层土壤水分特征曲线、饱和导水率以及土壤理化性质,并运用灰色关联分析确定影响土壤水力参数的主要土壤理化性质,采用非线性规划构建土壤分形维数、有机质、干容重、土壤颗粒组成与土壤水分特征曲线、饱和导水率之间的土壤传递函数,并通过与现有土壤传递函数对比分析进行精度验证。结果表明:1)土壤分形维数是估算土壤水分特征曲线模型参数和饱和导水率的主要参数之一,同时,干容重和有机质含量也在不同土层土壤传递函数中起到重要的作用;2)通过验证分析,不同土层各参数平均绝对误差接近于0,均方根误差值也都较小,其中在不同土层土壤传递函数估算的土壤含水率均方根误差分别为0.022、0.017cm~3/cm~3;3)对比分析其他已存的土壤水分特征曲线和饱和导水率的土壤传递函数,该文构建的土壤传递函数均方根误差值均较小,决定系数值都在0.66以上,表明估算精度较高,均好于其他方法估算精度,具有良好的区域适应性。综上,所构建的土壤水分特征曲线和饱和导水率土壤传递函数可以用于松嫩平原黑土区土壤水力参数估算。     

Tillage and straw management for modifying physical properties of a subarctic soil

Conservation tillage practices are intended to minimize soil erosion. Yet little is known concerning changes in physical properties of subarctic soils subject to tillage practices. This study ascertained whether physical properties of a newly cleared subarctic soil are altered after 7 years of continuous barley (Hordeum vulgare L.) using different tillage and straw management strategies. Tillage and straw treatments were established in 1983 near Delta Junction, Alaska, and consisted of conventional fall and spring disk, fall chisel plow, spring disk, and no-tillage. Tillage plots were split by straw management practices, which included straw and stubble, stubble only, and no straw or stubble. Soil samples were collected from the upper 0.15 m of the profile in the spring of 1990 to assess water content, bulk density, saturated hydraulic conductivity, dry aggregate and mechanical stability, penetration resistance, water retention, and particle size distribution. Percent non-erodible aggregates, mechanical stability, and penetration resistance were greater for no-tillage compared to conventional tillage, chisel plow, and spring disk. No-tillage soils were also typically wetter, denser, and had a greater hydraulic conductivity. The spring disk treatment was least susceptible to erosion and also conserved soil water compared with chisel plow. Straw maintained on the surface conserved water and promoted soil stability.     

Effect of Continuous Rice–Wheat Rotation on Soil Properties from Four Agro‐ecosystems of Indian Punjab

In Indian Punjab, rice–wheat is a dominant cropping system in four agro‐ecosystems, namely undulating subregion (zone 1), Piedmont alluvial plains (zone 2), central alluvial plains (zone 3), and southwestern alluvial plains (zone 4), varying in rainfall and temperature. Static and temporal variabilities in soil physical and chemical properties prevail because of alluvial parent material, management/tillage operations, and duration of rice–wheat rotation. A detailed survey was undertaken to study the long‐term effect of rice–wheat rotation on soil physical (soil separates, bulk density, modulus of rupture, saturated and unsaturated hydraulic conductivities, soil water content, and suction relations) and chemical (organic carbon, pH, electrical conductivity) properties of different textured soils (sandy clay loam, loam, clay loam, and silty clay loam) in these four zones of Punjab. Soil samples (of 0‐ to 30‐cm depth) from 45 sites were collected during 2006 and were analyzed for physical and chemical properties. The results showed that sand content and pH increased whereas silt and organic carbon decreased significantly from zones 1 to 4. Compared to other textures, significantly greater organic carbon, modulus of rupture, and pH in silty clay loam; greater bulk density in clay loam, and greater saturated hydraulic conductivity in sandy clay loam were observed. Irrespective of zone and soil texture, in the subsurface soil, there was a hard pan at 15–22.5 cm deep, which had high soil bulk density, modulus of rupture, more silt and clay contents (by 3–5%) and less organic carbon and hydraulic conductivity than the surface (0–15 cm) layer. These properties deteriorated with fineness of the soil texture and less organic carbon content. Continuous rice–wheat cropping had a deleterious effect on many soil properties. Many of these soils would benefit from the addition of organic matter, and crop yields may also be affected by the distinct hardpan that exists between 15 and 22.5 cm deep.