نشریه پژوهشهای خاک (علوم خاک و آب)
سال سی و سوم شماره 4 (زمستان 1398)

Despite the relatively long history of conservation tillage in the world, this technology is still new in Iran; therefore, evaluating effects of conservation tillage on soil properties and crops yield is necessary. Thus, this study was conducted using a randomized complete block experimental design with five treatments and four replications in Darab region of Fars province for four years (2010-2014). Treatments were T1) reduced tillage with 15 cm tilling depth, T2) wheat and sesame direct seeding, T3) sesame direct seeding for four years, wheat direct seeding for the first two years and the fourth year, and conventional planting in the third year, T4) wheat direct seeding for four years, sesame direct seeding for the first two years and the fourth year, and conventional planting in the third year, and T5) conventional tillage using moldboard plough (tilling depth of 25 cm), disk harrow, and land leveler. Soil moisture content, soil aggregates, soil bulk density, percentage of residue inversion, fuel consumption, field capacity, and wheat yield were measured. Results showed that conservation tillage methods increased soil moisture content by up to 18%, but soil bulk density was not affected by tillage methods. Conservation tillage methods decreased fuel consumption compared to the conventional tillage by up to 77% and increased effective field capacity for seed bed preparation and planting for up to 2.8 times. Wheat yield significantly decreased in the conservation tillage methods compared to the conventional tillage by 21%; therefore, soil needs more time to get adapted to the conservation tillage conditions in Darab region. Economic evaluation also showed that conventional tillage was the first option for the seed bed preparation in the wheat-sesame cropping system in Darab region, and the reduced and no-till were the second and third priorities, respectively.

Nitrogen use efficiency (NUE) is a critically important indicator for judging the wise use of N fertilizer in crops. It can be affected by management factors or soil properties. This study was conducted to estimate NUE in wheat based on large scale fields (20 wheat farms) trials and determining the role of soil factors, in Khorasan Razavi province. Two levels of N as urea (0 and conventional) were applied in each of the fields. In the fields, grain yield (conventional) was divided into low yield population (LYP, GY< 5 Mg ha-1) and high yield population (HYP, GY ≥ 5 Mg ha-1) categories. Then, apparent recovery efficiency (ARE), physiological efficiency (PE), agronomic efficiency (AE) and Partial Factor Productivity (PFP) were calculated for N in both yield populations. The results showed that nitrogen efficiency indices in both yield populations were much lower than optimum level. However, AE (8.2 kg/kg), ARE (25%), and PFP (46 kg /kg) in the HYP were more than in the LYP, but there was no difference between PE in both yield populations. There was a significant correlation between AE and soil organic carbon (r = -0.97, P <0.01,   also ARE with soil organic carbon (r = -0.82, P<0.05) and soil clay content (r = 0.68, P <0.05) for LYP in contrast to the HYP). While PFP exhibited positive correlation with soil organic carbon (r = 0.86, P <0.01) and negative correlation with soil electrical conductivity (r = -0.77, P <0.05) for LYP, this relationship was weaker with soil organic carbon in HYP. None of soil factors had a significant effect on PE. These results show that soil factors such as organic carbon, salinity, and clay content of soil had a decisive role in AE, ARE, and PFP in the LYP. In contrast, soil factors had no effect on nitrogen efficiency indices in the HYP (with the exception of the effect of soil organic carbon on PFP).

In order to increase the storage of nitrogen, zinc and boron of peach trees and its effect on flowering and fruit set, an experiment was conducted in a randomized complete block design with seven treatments and four replications for three years (2015-2018) on 56 trees with the same age and size trees in the east of Mazandaran. Treatments included: 1) control, 2) Urea (10 gL-1), 3) Urea (10 gL-1) + Zinc sulfate (5 g.i-1), 4) Urea (10 g.l-1) + Zinc sulfate (5 g.l-1) + Boric acid (5 g.l-1), 5) Urea (15 gL-1) + Zinc sulfate (5 gL-1) + Boric acid (5 gL-1), 6) Urea (20 g.L-1) + Zinc sulfate (5 gL-1) + Boric acid (5 gL-1), and 7) Urea (25 g.L-1) + Zinc sulfate (5 gLl-1) + Boric acid (5 g.L-1).   The results showed that urea was quickly absorbed by leaves, so that nitrogen concentration in leaf tissue increased shortly after spraying. The measuring trend of nitrogen concentration at different times in foliar spray treatments showed that nitrogen concentration in leaf tissue increased initially and then began to decrease again. Therefore, in treatments 7, nitrogen concentration at 4, 24, and 48 hours after spraying increased from 2% before spraying to, respectively, 3.15%, 3.07%, and 2.06%. That indicates the absorption and then removal of nitrogen from the leaf tissue. Zinc concentrations in the leaves increased in all treatments by foliar spray of zinc sulfate, and this trend of absorption and increase of zinc concentration in the leaf tissue lasted for 48 hours after spraying. Boric acid foliar spray also increased the concentration of boron in the leaf tissue, such that the concentration of boron in the leaf tissue reached the maximum after 4 hours, and then decreased gradually. Results showed that fallspray treatments were effective in increasing fruit set and reducing abscising fruitlets, and this increase in fruit set was statistically significant. However, treatment seven that accelerated leaf loss had the highest effect on fruit formation, and was about 50% higher than the control. Therefore, to increase the fruit set and reduce the flower and fruitlets drops, applying treatment 7 in autumn, when 10-15% of the leaves are yellow, is recommended.

In order to investigate the role of mycorrhiza inoculation and Biochar application on the phosphorus availability, growth, and yield of sorghum and some chemical properties of soil, a pot experiment were conducted as a factorial experiment in completely randomized design, with three replications. In this research, application effects of biochar (0 and 1.5 % by weight), mycorrhiza (inoculation and non-inoculation of mycorrhiza fungi) and phosphorous (four levels of triple superphosphate: 0, 55, 110, and 165 mg .kg-1 soil) on sorghum were studied. The results showed that phosphorus and biochar application significantly (P<0.01) increased foliage and roots weights, roots volume, and also nitrogen, phosphorous and potassium uptake. Furthermore, the application of phosphorus in combination with biochar and inoculation of plant roots with mycorrhiza increased the above-mentioned traits to a higher level. Application of phosphorus or biochar alone increased soil salinity, but their combined application together with the plant root inoculation using mycorrhiza decreased it. Application of phosphorus decreased soil organic carbon, whereas biochar and mycorrhiza significantly increased it. The maximum dry foliage (24.4 g.pot-1) and the maximum phosphorous uptake (79.9 mg.pot-1) were obtained from combined application of mycorrhiza, biochae and 55 mg.kg-1 triple superphosphate. The results showed that biochar and or mycorrhiza application affect the amount of phosphorus consumed[H1] , but it should be noted that prolonged use of biochar could increase soil salinity.

Soil compaction is a worldwide environmental problem. Investigations on soil compaction have focused mainly on its effects on soil physical parameters and plant growth. There is an essential need to identify the effect of soil compaction on soil organisms and biological process, especially in arid and semiarid regions such as Iran. The main objective of this research was to investigate the effect of soil compaction and organic matter on soil respiration and microbial biomass carbon, urease activity, and soil nitrification. Therefore, a factorial experiment was conducted based on completely randomized design with three replications in greenhouse conditions. Treatments included different compaction levels (0, 10, and 20 %) and organic matter addition (0 and 2 %W/W from the bagasse compost). The results indicated that the effects of soil compaction and organic matter on soil respiration, microbial biomass carbon, urease activity, and soil nitrification rate were significant. Also, the interaction effect of soil compaction and organic matter on the measured biological properties were significant (p<0.01). Furthermore, the results showed that the value of all measured biological properties decreased with increasing soil compaction, whereas, increasing soil organic matter improved those properties and the amount of microbial respiration, microbial biomass carbon, urease activity and soil nitrification significantly increased. Therefore, increasing organic matter or plant residues is an important management approach that can improve soil characteristics and performance.

Soil is one of the natural and capital resources of each country that should be seriously considered in land-use planning at national and local scales.   The purpose of this study was to investigate the effect of land use on organic matter content and soil particle size distribution in Bardeh watershed. To fulfil the objective, 140 composite and random surficial soil samples were taken from a depth of 0-5 and 0-20 cm. Geostatistical analysis of the spatial structure of soil characteristics showed that their distributions followedan exponential model and had medium to intermediate spatial dependencies. The results also showed that there were significant Pearson correlation coefficients between reflection in visible, infrared, and thermal bands with soil texture components. In order to map different variables, the interpolation and zoning were done by Kriging method. The maps of different soil properties showed that the distribution pattern of organic matter and particle size distribution were mainly due to the variability of soil inherent factors (such as soil material) and partly by management practices (such as soil management). Lastly, using Landsat 8 images, the soil properties were compared with radiation, reflection and degree. Radiation heat was investigated using regression models. The results showed that at the two depths of sampling 0-5 and 0-20 cm, and in different applications, the coefficient of variation did not show a significant difference.  Correlation coefficients showed that the strongest relationship existed between the percentage of organic matter, clay, silt, sand, with the reflection in the visible light range and near infrared and the long-wave infrared panchromatic wavelength of the electromagnetic spectrum. Comparison of the power of correlation between the bands reflection and the percentage of organic matter in the section (NIR) shows greater correlation. Validation showed that the maps obtained by geostatistics and remote sensing well characterized the distribution of features.

Soil organic matter is one of the most important physical properties of soil, and is affected by such factors as vegetation, soil properties, and the climate of the region. In order to determine the amount of soil organic matter, after studying satellite images and resource assessment and land capability maps, a part of Semirom region was selected for conducting field studies, and Landsat 8 OLI image was cut in accordance with the border of the study area. Sampling points were chosen through identification of the region and using maps, official statistics, and false-color composite images of the area. Accordingly, 50 soil samples were taken from the surface soil (0-20 cm) and the amount of organic matter, electrical conductivity and pH were measured. To investigate the efficiency of satellite images in determining the amount of soil organic matter, Normalized Difference Vegetation Index (NDVI) and Soil Adjusted Vegetation Index (SAVI) were estimated using satellite images and Terrest and ArcGIS 10.5 softwares, and the corresponding maps were developed. The relationship between the organic matter and vegetation indexes was examined using linear regression analysis and correlation coefficient. The results indicated significant correlation higher than 70 % between the organic matter and the vegetation indices. It could be concluded that remote sensing and satellite images can serve as tools for overcoming the limitations of traditional methods and are appropriate for monitoring the quality of soil. Remote sensing allows for displaying the results in terms of temporal and spatial scales, and is especially appropriate for extensive areas.

Soil degradation is one of the most important issues facing humanity.Since land use change affects soil properties, this study aimed to investigate the effects of land use on some soil physical and chemical attributes. Experiment was conducted at 25 experimental locations on a relatively regular network design with 5×5 meter distance intervals in each three studied land uses including annual cultivated field (ACF), perennial alfalfa field (PAF) and orchard field (OF) in Bajgah region, Fars Province.  Soil samples were collected from 0 to 20 cm depth, air dried, and passed through a 2 mm sieve and some physico-chemical properties were determined. Clay content, fractal dimension (D), soluble sodium (Na), potassium (K) and magnesium (Mg), sodium adsorption ratio (SAR) and soil cation exchange capacity (CEC) in PAF in comparison with ACF showed significant decreases of 15.9%, 1.05%, 70.1%, 50.1%, 36.5%, 69.5%, and 12.9%, respectively. However, values of sand, silt, electrical conductivity (EC), soluble calcium (Ca) and calcium carbonate equivalent (CCE) in the soil of PAF in comparison with ACF showed significant increases of 32.8%, 8.85%, 37.4%, 29.7%, and 15%, respectively. There were no significant differences between the mean values of bulk density (BD, respectively with 1.24 and 1.27 g cm-3), saturation moisture (0.28 and 0.27 cm-3), structural stability index (SI, 2.54 and 2.52%), pH (8.03 and 8.03), organic matter (OM, 2.44 and 2.39%) and carbon sequestration (CS, 352 and 352 ton ha-1) between the ACF and PAF land uses. Land use change from ACF to OF caused a significant decrease of 3.36%, 34.8%, 2.46%, 6.07%, 1.0, and 16.7% in silt, clay, D, saturation moisture, pH, and CEC, respectively. However, ACF to OF land use change caused significant increases of 404%, 83.5%, 68.8%, 53.7%, 57.1%, 107%, 65.7%, 58.7%, 81%, and 33.3% in sand, SI, EC, OM, Cs, soluble Na, K, and Ca, SAR, and CCE, respectively. There were no significant differences between BD and soluble Mg in the soils of ACF and OF. Generally, land use change affected many soil physical and chemical properties influencing soil quality. Therefore, proper land management is essential to protect soil resources.

Presence of metals in soils in various chemical forms can affect their role in development of nutritional effects or contamination. Considering the proven effects of the Khuzestan Steel Company on contamination of surrounding soils, the purpose of this study was: (1) to investigate the chemical distribution of iron and manganese in soils taken from the vicinity of the Khuzestan Steel Company, and (2) to determine the correlation of the chemical forms of these elements with some soil characteristics and concentrations in the aerial parts of the garden cress plant. After preparation of the soil sample, physical and chemical properties were determined by standard methods. Sequential extraction was performed by modified BCR method. The data were used to calculate the risk assessment code in the soil, reduced partition index, the ratio and risk index in the plant and the bioavailability factor. Based on the results for iron, the soluble, exchangeable, and acid extractable fractions constituted 0.13% of the total iron concentration in the soil, including 44.1%, 0.9% and 54.8% as, respectively, reducible, oxidizable, and residual fractions. Therefore, the highest amount of iron in the soil was in the residual and reducible fractions, which are stable and relatively stable parts of solid phase in the soil. In case of manganese, soluble, exchangeable and carbonate fraction constituted 12.3 percent of total manganese concentration in the soil, including 51.5%, 0.7% and 45.4% as, respectively, reducible, oxidizable and residual fractions. Iron had lower amounts in soluble, exchangeable, and carbonated forms as compared to manganese, therefore, all calculated indices for iron showed no contaminated situation. In case of manganese, the conditions were different and the share of soluble, exchangeable, and carbonate was significant. Due to the positive and significant correlation of this part with concentration of element in the plant, hazard quotient was also increased in plant. Concerning both elements, the bio-concentration factor was lower than its permitted value, but due to the high concentrations of these elements in the soil and the normal vegetation of this region, it seems necessary to pay attention to the type of cultivated plant.

Slope aspect, vegetation type, and depth of sampling are factors affecting soil chemical properties. These factors affect soil quality by increasing or decreasing organic matter content. However, the simultaneous effects of plant type and aspect on some soil properties have rarely been studied. For this purpose, the effect of aspect, plant type, and depth of sampling on soil chemical properties were studied based on factorial experiment in a completely randomized design with 6 replications, in the Gonbad Paired Watershed Research Station. Soil sampling was done in August 2016 and chemical properties were measured. The soil pH was higher in the southern slopes than in the northern slopes. The pH of the soil under Astragalus parrowianus was significantly lower than that of Bromus tomentellus. In the northern slope, CEC of soil under Astragalus parrowianus was higher compared to that under Bromus tomentellus and inter-plant position, while in the southern slope, soils in the inter-plant position had significantly lower CEC in comparison with those under Bromus tomentellus and Astragalus parrowianus plants. At all plant and inter-plant positions, the CEC and organic matter content were significantly lower in the southern slope than in the northern slope. At the first and second depths of the northern and southern slopes, soil under Astragalus parrowianus plants had significantly higher organic matter and calcium carbonate compared to the Bromus tomentellus and inter-plant position. Also, at the first depth of the northern slope, soil under Bromus tomentellus plants had significantly higher organic matter and calcium carbonate compared to the inter-plant position. Generally, influence of the factors of aspect and vegetation type was more than that of the depth of sampling.

Increasing anthropogenic disturbances, especially on land use change, is the major cause of soil quality deterioration in the world. Soil organic carbon has recently gained prominence in assessment of soil quality since it affects chemical, physical and biological aspects of the soil. This study was carried out to investigate the impact of land use change on some carbon fractions and carbon management index (CMI) in Tootkabon area, Guilan province. Three land uses (forest, dry farming, and rangeland) and three slope positions were selected. Soil sampling was done randomly from 0-15 cm depth of each land use and slope position. Particulate organic matter (POM) was measured in both bulk soil and aggregate particles and mineral associated organic matter (MOM) and extractable carbohydrate were measured in bulk soil. Carbon management index and carbon pool index were calculated using forest soil as a reference. Results showed that the highest and lowest amounts of particulate organic matter, mineral associated organic matter, and carbohydrate, and carbon pools were obtained in, respectively, forest and rangeland. Results also showed that the particulate organic matter in forest was increased by, respectively, 105% and 423% compared to dry farming and rangeland.[H1]  The highest percentage of particulate organic carbon was stored in macro aggregates, thus, the factors that control the stability and degradation of these aggregates can control soil organic carbon storage. Results showed that carbon pool index in dry farming and rangeland was decreased by, respectively, 45% and 82% compared to forest; and carbon management index in dry farming and rangelands was declined by 67% and 80.2%, respectively.

There are different methods for assessing the bioavailability of micronutrients in soil and water. One of the new techniques in this regard is diffusive gradient in thin films (DGT). This method acts on ion transport in the diffusion layer and absorption in the resin layer. The aim of this study was to evaluate the performance of DGT for soil Zn and Cu determination and to compare it with Zn- and Cu-DTPA measured for the bioavailability of these elements in maize (Zea mays L.). For this purpose, DGT was placed in 10 soils with different properties that had saturated moisture for 24 h. Also, maize cultivation was done in these soils and, finally, the amount of elements absorbed by the plant was compared with the amount of zinc and copper measured by DGT and DTPA methods. The results showed that there was a linear relationship between Zn and Cu changes in the plant and the concentration of these elements in soil measured by DGT. Zn measured by DGT method (CEDGT) had higher correlation with Zn uptake compared to the DTPA method (r2 = 0.8 for DTPA, r2 = 0.82 for CE) and in the 10 different soils, CE represented 82% of the changes related to the plant Zn uptake. In the case of Cu, the correlation between Cu measured by DTPA and its uptake by maize had a correlation coefficient of 0.75, whereas Cu measured by (CEDGT) had r2 = 0.78. The results of this study showed that DGT is relatively more accurate than the DTPA method for predicting uptake of these elements in maize leaves.