JWSS - Journal of Water and Soil Science

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Methods of seedbed preparation affect establishment, growth and yield of crops via manipulating physical and chemical properties of soil. These effects on wheat-mungbean double-cropping have not been studied in Isfahan. Therefore, the influences of various seedbed preparation methods on soil physical properties and nutrients content and on establishment of mungbean (experimental line 1-61-16) were studied in a wheat-mungbean double-cropping system during 1996 at the Agricultural Research Station, Isfahan University of Technology. Two residue management treatments (burned and unburned) along with four tillage systems (moldboard plow, disk, khishchee and no-till) were laid out in a strip plot design within a randomized complete block design with four replications. Bulk density and penetrability of soil at various depths were not affected by residue management at emergence. However, at the time of flowering, bulk density at 0-15 cm soil depth was lower and soil penetrability at 3-15 cm depth was higher in unburned treatment due to mineralization. Rate and coefficient of emergence of seeds were lower in unburned residue treatment. Soil bulk density at 0-30 cm depths was lower and penetrability at 3-21 cm depth was higher with moldboard plowing at both emergence and flowering time. In addition, lower soil N, P and K content at 0-15 cm depth at emergence and flowering time was obtained with moldboard plowing. Rate and coefficient of emergence were strongly lower in no-till treatment. Based on these results and considering sustainable agricultural goals, incorporating residue with disk tillage might be advantageous under conditions similar to this experiment.

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Tillage system effect, Conventional (CT) vs. No-Till (NT), on soil physical properties and Br transport was studied at two locations in North Carolina. The soil types were a Typic Paleudults at Coastal Plain (site 1) and a Typic Kanhapludults at Piedmont (site 2). Bulk density (BD), total porosity (TP), macroporosity (MP), and saturated hydraulic conductivity (K_s) .were measured in plant row (R), and trafficked (T) and untrafficked (N) interrows. A rainfall simulator was used to apply two early season rainfalls to 1 m² plots where KBr suspension was surface applied for Br leaching study. The first simulated rainfall event (30 min) consisted of a low (1.27 cm h^-1) or a high (5.08 cm h^-1) rate applied, 24 h after Br application. One week later, the high rainfall rate was repeated on all plots.

 Soil samples were taken two days after applying first and second simulated rainfall (a week between them) and the end of season from different depths for measuring Br concentrations. Soil physical properties were affected by both tillage system and position.

Bulk density was higher in NT versus CT and in T position versus Rand N positions. Total porosity was lower in NT versus CT but MP was significantly higher in NT. Saturated hydraulic conductivity was about 90% lower at T position versus N and R positions. Coefficient of variation was quite large, making it difficult to obtain statistical differences between tillage systems. The surface l0-cm of soil contained the highest Br concentration for depth treatments with treatment differences occurring primarily in 0 to 25 cm depth. In first and second sampling dates, more Br leached under NT versus CT system. However, there was no significant difference between the two tillage systems in Br leaching at the end of the growing Season. In site 1, Br leached more due to the coarse texture and high Ks of the soil.

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The effects of three kinds of organic matter on the physical characteristics of two soil series (Coarse Loamy, Mesic, Typic, Xerofluvents and Fine Mixed, Calcixerollic, Xerochrepts) were studied along with the measurement of maximum dry bulk density (MDBD) and the corresponding critical moisture content (CMC). Soil samples were taken from a depth of 0-20 cm and the percentage of organic matter and soil texture were determined. Three kinds of organic matters (peat, farmyard manure and filter press apple) were mixed with the soils at four levels (0, 4, 8 and 12% by mass), and were compacted using 10, 20 and 30 proctor hammer blows. The compaction tests on soils were carried out at different moisture contents. The present experiment, using factorial design, was randomly conducted in three replications. The results of this study showed that while the mean MDBD declined significantly (P<0.01) from 1.53 to 1.28 gr.cm^-3, the mean CMC increased from 23.32 to 33.28% as the organic matter increased from 0.12%. In all the experiments, CMC decreased with increasing compaction efforts, so that the effect of mixed organic matter and soil in terms of MDBD reduction and CMC increase was decreasing in the order, peat, farmyard manure and filter press apple. The clay loam soil showed lower values of MDBD but higher values of CMC as compared to the sandy loam. The significant interaction effect observed between incorporation of organic matter and soil compaction were meaningful. Finally an equation as to the relationship between MDBD and CMC was proposed for the purpose of mixing the three organic materials with soil.

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A field experiment was conducted to investigate the effects of sewage sludge and of time lapse after sludge application on soil physical properties. Four sewage sludge treatments (0, 25, 50, and 100 ton/ha) in a complete randomized block design with three replications were applied and mixed to a depth of 20 cm. Wheat was planted and soil physical properties were measured 23, 85, 148, and 221 days after sewage sludge application. Sewage sludge application significantly increased MWD, hydraulic conductivity, final infiltration rate, moisture percentage at 1/3 and 15 bars, and plant available soil moisture, while it significantly decreased soil bulk density. In general, the best results obtained with the 100 ton/ha sewage sludge treatment. Time lapse after sewage sludge application caused soil physical properties to approach the values of the control. However, even 221 days after sludge application, the 50 and 100 ton/ha treatments had significantly different values compared with the control treatment. The results in this research show that sewage sludge can help to improve soil physical conditions and this effect persists over long periods. This effect is specially important with plant available soil moisture and infiltration.

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Soil tilth is crucial to seedling emergence, plant growth, and crop yield. Soil tilth of unstable soil is very susceptible to change. Internal forces originating from matric suction can change soil physical properties. A laboratory study was conducted on pots of a surface silty clay loam soil of Khomeinishahr series (fine-loamy, mixed, thermic Typic Haplargids, USDA), located in Research Farm of Isfahan University of Technology. Soil surface subsidence, bulk density, cone index, and tensile strength were measured after first flood irrigation. Results showed that the seedbed (0-20 cm) with a bulk density of 1.2 Mg.m^-3 will be changed to a massive soil with high values of bulk density, cone index, and tensile strength after soil wetting. Slaking, slumping and coalescence of the soil caused soil surface to subside about 1.5 cm in 20 cm soil layer. After irrigation, cone index and tensile strength increased abruptly with decreasing of moisture content. It is shown that the dominant source of strength (cone index and tensile strength) gain during drying is the effective stress due to matric suction. In the absence of external loads, physical state (tilth) of the soil returned back to the original state. Therefore, soil slaking and slumping and rearrangement of particles along with the internal forces are the factors leading to soil hardness.

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To obtain soil-moisture characteristic curve experimentally is time-consuming and usually subject to considerable errors. So, many investigators have tried to predict soil-moisture characteristic curve by different models. One of these models predicts soil moisture characteristic curve based on soil particle size distribution and bulk density. In this model, soil particle size distribution curve is divided into a number of segments, each with a specific particle radius and cumulative particle mass greater than that of the radius. Using these data, soil-moisture characteristic curve was estimated. In this model, a scale factor, α, is used which may be considered as a constant, or obtained by logistic or linear procedures. The average values of α for clay, silty clay, sandy loam, two loam soils, and two silty clay loam soils were 1.159, 1.229, 1.494, 1.391, 1.393, 1.253 and 1.254, respectively. For most conditions, soil particle size distribution curve is not available, but only the percentages of clay, silt, and sand could be obtained using soil textural data, which is not enough to draw a precise soil particle size distribution curve. In this situation, a precise soil particle size distribution curve must be initially developed on the basis of which the soil moisture characteristic curve can be predicted. In this study, using soil textural data of seven different soils, soil moisture characteristic curve of each was estimated. In these estimations, logistic and linear methods were used to obtain the α value. Then, the results were compared with those of measured soil moisture characteristic curve. For estimation of soil particle size distribution curve, two extreme values for soil particle radius, 125 and 999 m, were used. The results indicated that using particle radius of 999 µm is more appropriate. On the other hand, it was found that for clay, silty clay, and sitly clay loam texture, it is more appropriate to employ a linear equation to determine for estimating soil-moisture characteristic curve while the logistic equation can be more appropriately used for loam and sand loam textures.

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  Soil particle size distribution and bulk density are used for estimating soil-moisture characteristic curve. In this model, soil particle size distribution curve is divided into a number of segments, each with a specific particle radius and cumulative percentage of the particles greater than that radius. Using these data, soil-moisture characteristic curve is estimated. In the model a scale factor, a , is used which may be considered as a constant, or obtained by logistic or linear procedures. F or most conditions, soil particle size distribution curve is not available, but only the percentages of clay, silt and sand could be obtained using soil textural data. In this situation, at first a precise soil particle size distribution must be developed, based on which the soil-moisture characteristic curve can be predicted. According to the previous studies, using particle radius of 999 µ m is more appropriate than radius 125 µ m. Also, adjusted coefficients for estimating soil particle size distribution curve for radii 1 to 20  µ m was obtained. In this study, using the soil textural data of 19 different soils from UNSODA database, soil-moisture characteristic curve of each was estimated with logistic and linear methods based on initial and adjusted soil particle size distribution estimation. The estimated values were compared with the measured data. The results indicated that for most soils, using the combination of logistic and adjusted particle size distribution estimation procedures is more appropriate than the previous methods.

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  Tillage is one of the important managing factors that can destroy or improve soil structure. Soil structure is affected by the machines and shape of the wheels. Field experiments were conducted at Hamadan Agricultural Research Station on a coarse loamy mixed mesic Calcixerolic Xerocrepts soil to measure and evaluate the effects of tillage and wheel-induced compaction on selected soil physical properties. Treatments included tillage methods (Moldboard Plow and Chisel Plow, (MP, CP)) performed using three customary tractors in Iran [John Deer (J), Romany (R) and Massey Ferguson ( MF) ]. Traffic zone and non traffic zone were other treatments. A split-plot design with three replications was used in a completely randomized arrangement of treatments. Soil samples were taken at the end of wheat growth season in traffic and non- traffic zone and from four layers and compared for bulk density (BD), cone index (CI), and mean weight diameter (MWD). The influence of both tillage methods on BD in most soil depths was not significant, meanwhile, BD was higher in the deeper layers. Wheel traffic did not affect BD significantly, but its effect decreased by increasing the depth. Commonly, conservation tillage increased structural stability as evaluated by MWD. Cone index illustrated the same trend as for BD, with some variation because of it higher sensitivity, so it was significantly was increased in CP rather than in MP for the traffic zone. Such a difference was not observed in non-traffic zone. The CI was also significantly increased in traffic zone compared with non-traffic zone. J significantly increased CI in two first layer in comparing with MF, but there was not significant difference between J and R. The MWD was increased by chisel plow in non-traffic zone and this increment was significant in fourth soil layer (22.5- 30 cm). Wheel traffic caused the increase of MWD in the second layer and significant difference was not observed in other layers. Overall, R caused less destruction in soil structure and tillage methods changed some of soil physical properties.

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  Applying of intensive cultivation especially in marginal and sensitive regions, after conversion of rangelands to cropland farms, commonly causes reduction in soil quality, and thus an increase in soil degradation, erosion and runoff. This study was conducted to evaluate the land use change effects on some soil physical and chemical properties such as mean weight diameter (MWD), soil organic matter (SOM), bulk density (BD) and saturated electrical conductivity (ECe). For the experiment, soil samples were collected from 8 regions (rangeland and cultivated range) from west and southwest of Isfahan. Samples were taken from two soil layers 0-15 and 15-30 cm. Results showed that after conversion of range to cultivated lands, in some regions, SOM content was increased about 39% but in some regions decreased about 26%. This is due to the initial conditions of the regions. The ECe also increased by 41% due to this conversion. However, no changes were observed to the MWD, BD and pH in different treatments. Although there were little change to the physical and chemical properties of soil as a result of this conversion, those properties which were changed, could have a degradation effect and lower the soil quality.

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Soil bulk density measurements are often required as an input parameter for models that predict soil processes. Nonparametric approaches are being used in various fields to estimate continuous variables. One type of the nonparametric lazy learning algorithms, a k-nearest neighbor (k-NN) algorithm was introduced and tested to estimate soil bulk density from other soil properties, including soil textural fractions, EC, pH, SP, OC and TNV. As many as eight nearest neighbors, based on cross validation technique were selected to perform bulk density prediction from the attributes of 136 soil samples. The nonparametric k-NN technique mostly performed equally well using Pearson correlation coefficient (r=0.86), root-mean-squared errors (RMSE=2.5) maximum error (ME=0.15), coefficient of determination (CD=1.3), modeling efficiency (EF=0.75) and coefficient of residual mass (CRM=0.001) statistics. It can be concluded that the k-NN technique is an alternative to other techniques such as pedotransfer functions (PTFs).

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Hardsetting phenomenon is an indicator of poor soil physical quality. Hardsetting soils are soils with high rate of mechanical strength increase upon drying and are hardened and/or compacted when dry out. It is difficult to till such soils. Hardsetting soils have additional limitations such as poor aeration at wet conditions, low infiltrability and high runoff and erosion. Most of Iran soils have low organic matter content and it is expected that hardsetting phenomenon occurs in some of these soils. This study was conducted to investigate the hardsetting phenomenon on 9 soil series collected from Hamadan province. Three types of mechanical strength consisting tensile strength (ITS), unconfined compressive strength (UCS), and penetration resistance (PR) were measured on the repacked soil samples prepared in the lab. The ITS, UCS and PR tests were done on the soil cores which had been prepared at bulk density (BD) equal to 90% of critical BD for root growth (0.9BDcritical). The effects of intrinsic properties on the hardsetting phenomenon were studied, too. Based on the suggested definition in “International Symposium on Sealing, Crusting and Hardsetting Soils” to International :::union::: of Soil Science, in which a hardsetting soil has air-dry tensile strength ≥ 90 kPa, one soil (medium-textured) out of the studied soils showed the hardsetting phenomenon at 0.9BDcritical. It might be concluded that medium-textured soils are more susceptible to hardsetting. For all of the studied soils, the ITS increased with the increase in clay content. The increasing impacts of clay and carbonate contents were also observed for the UCS and PR, respectively. Calcium carbonate could act as a cementing agent in between the soil particles and brings about the soil susceptibility to hardsetting. Moreover, the decreasing trend of all soil mechanical strengths was observed with water content increase. Slope (b) of the exponential model (fitted to the soil mechanical strength characteristic curve), as an index of hardsetting, had positive correlation with the sand content and negative correlation with the silt content. Overall, texture and calcium carbonate content are major and effective properties in terms of hardsetting phenomenon in Hamadan soils.

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Increase in soil bulk density and reduces in porosity and infiltration rate are the most common disturbances during timber harvesting and ground-base skidding. The present study was conducted to study soil physical properties e.g., soil bulk density, moisture, porosity and soil hydrological properties e.g., soil infiltration from ground-base skidding in twenty years since logging. After initial survey, four abandonment skid trails were selected with similar pedologic, climatic conditions and physiographic and different age in Necka-Zalemrod catchment in east of Mazandaran province. Results indicated that impacts of machinery traffices in high traffic intensity have remained yet 20 years since logging. Means soil bulk density, porosity and void ratio were 42.4 greater, 24.6 and 46.7 percent, respectively, lower than the undisturbed areas. The least infiltration rate was recorded in 1-5 years old skid trail, so the reduction of water was not considerable within 18 minutes after experiment into soil in inner ring in this skid trail. Results in each skid trail firmed that in low traffic intensity soil physical and hydrologic properties was tent to “normal” recover in compare to the undisturbed areas.

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There chemical and organic matter content in garbage leachate that may affect soil physical and hydraulic properties. The main objective of this study was to evaluate the influences of the leachate of Isfahan Organic Fertilizer Factory (IOFF) on some soil physical and hydraulic properties in a soil chemically enriched by Zeolite. The treatments include two soil textures (clay loam and sandy loam) and three levels of zeolite (0, 5 and 10 percent). The treatments were applied on lysimeters scale. The results showed that irrigation with the leachate caused a reduction of infiltration and hydraulic conductivity in the clay loam soil. The hydraulic conductivities in clay loam soil without zeolite (B0) before and after irrigation with leachate were 1.73 and 0.36 m/day, respectively. In contrast, there were no changes in the sandy loam soil’s infiltration and hydraulic conductivity. The hydraulic conductivities in the sandy loam soil with 5 percent zeolite (A5) before and after irrigation with leachate were 3.17 m/day. Furthermore, zeolite had a decreasing effect on those processes. The results show that irrigation with leachate caused reduction of bulk density in two types of soil and all levels of zeolite.

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Improper use of rangelands may lead to their destruction. Therefore, the conversion of these degraded rangelands to agricultural lands and other land uses may improve their soil quality. The purpose of the present study was to evaluate the impact of cultivation in the degraded rangelands on some soil characteristics in Safashahr region of Fars province. Four land uses including the rangeland with sparse vegetation (degraded rangeland), the rangeland converted to agricultural land over 17 years, the agricultural land converted to apple orchard for 4 years and also to an apple orchard for 40 years were selected. Samples were randomly taken from each land use at two depths (0-20 and 20-50 cm) with five replications. The results revealed that land use change significantly increased organic matter and MWD in both soil depths. Bulk density and water dispersible clay increased in agricultural land and new orchard while a decrease was observed for old apple orchard. It is suggested the traditional farming to be replaced with new cultivation methods like minimum tillage and no tillage. Overgrazing of the rangelands must also be avoided.

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Considering soil compaction problem in sugarcane fields due to using heavy harvester and haulout equipment under unsuitable moisture conditions, this research aims to assess soil compaction in sugarcane fields located in Da'balKhazaei Plantation unitofSugarcane Development and By-product Company, Ahvaz. Undisturbed soil samples from the furrow (wheel tracks) were collected for measuring soil water content and bulk density. Considering the changes in soil texture of sugarcane fields, for expressing the degree of soilcompactness, in addition to soil bulk density (BD), relative bulk density (BD divided by reference BD) was also determined. The change in soil mechanical resistance with depth was determined by a cone penetrometer. Results showed that most of soil BD values measured in the sugarcane fields were in the range of small root development scale (high limitation). Comparingthe calculated RBD values with optimum value (0.85), it was observed that most of the values were higher than the optimum values recommended for root growth. This shows excessivesoil compaction in the sugarcane fields. The values of cone indices measured in soil profiles indicated that most of the values were higher than either limiting (2 MPa) or critical (3 MPa) values for root growth. Therefore, for improving soil physical fertility and achieving sustainability in crop production, management of farm machinery traffic in sugarcane fields, especially at the harvest time, needs to be reconsidered.

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