نشریه پژوهشهای خاک (علوم خاک و آب)
سال سی و ششم شماره 4 (زمستان 1401)

This study was conducted to investigate the effect of silicon on wheat yield and water use efficiency (WUE) in water stress conditions. The study site was Research Farm of Soil and Water Research Institute in Karaj. The experiment was conducted as a randomized complete block design with split plots, in 2018-219 season. The main factor was irrigation at two levels of full irrigation and stress (40% less than wheat water requirement), and the secondary factor including foliar application of potassium silicate at three levels (zero, 2.5 and 5 kg/ha) at three growth stages (shooting, flowering, and grain filling) and soil application of potassium silicate (zero and 20 kg/ha). The results showed that soil and foliar application of potassium silicate increased grain yield, thousand-grain weight, number of seeds per spike, spike length, and height of wheat plant. Reducing irrigation from 100% to 60% of wheat water requirement caused a decrease in grain yield by 8.3%, but the application of potassium silicate compensated for this decrease, such that under drought stress, wheat grain yield with application of 0.005 potassium silicate increased by 30.6% compared to the non-application of silicon. The highest WUE was obtained under water stress conditions and application of 5‰ potassium silicate increased the WUE by 31% compared to non-application. Therefore, in the conditions of water stress, compared to the farmers' practices, foliar application of potassium silicate with a concentration of 5‰ can be recommended during the growth stages of wheat.

To evaluate the effect of calcium nitrate on some growth characteristics of selected pomegranate (Punica granatum) genotypes, a factorial experiment was carried out based on randomized complete block design (BCRD) with 3 replications at Chahafzal Station of the National Salinity Research Center of Iran, in 2019-2020. Two factors were studied: genotypes at 6 levels (Post-Siyah Ardakan, Rabab Neyriz, Chah Afzal, Narak Lasjerd Semnad ,Vahshi Babolsar, and Malas Yazdi) and calcium nitrate at 3 levels (0 (control), 50 and 100 kg/ha), using irrigation water salinity of 9±0.5 dS/m.  The results showed that type of genotype and levels of calcium nitrate affected morphological and physiological characteristics and concentration of nutrient elements in leaves. The highest and lowest necrotic leaves (12% and 2%), leaf surface ratio (1845 and 879 mm2/g dry weight), relative water content (80.83% and 52.40%), total chlorophyll (11.4 and 6.45 mg/g fresh weight), potassium content (0.378% and 0.322%) and lowest and highest sodium content (1.88% and 2.75%), relative ions leakage (14.85% and 30.02%) and sodium to potassium ratio (0.118 and 0.197) was observed in Chah Afzal with 100 kg/ha of calcium nitrate and Rebab Niriz without calcium nitrate application, respectively. Overall, Chah-Afzal was recognized as the most tolerant genotypes to saline condition. This genotype showed more suitable growth than the other genotypes by maintaining its growth characteristics and increasing potassium uptake compared to sodium. Also, the results showed that application of 100 kg/ha of calcium nitrate at the beginning of the growing season significantly improved the growth characteristics and reduced the harmful effects of sodium in all studied genotypes.

The Smooth Flat Seville (Citrus spp. hybrid of uncertain origin) has been reported as one of the rootstocks tolerant to soil lime and Tristeza disease. Therefore, the present study aimed to evaluate the growth trend and tolerance of this rootstock to the calcareous soils of east Mazandaran Province, Iran. An experiment was conducted for two years in a randomized complete block design in seven soils with calcium carbonate equivalent ranging from 2% to 45%. Measurements included vegetative growth trend, dry weight, chlorosis rate, fluorescence index (Fv/Fm), chlorophyll and nutrient concentration in leaves and roots. The results showed that the highest average dry weight of aerial parts was obtained from soils with total lime of 9%. There was no significant difference in the chlorosis rate of the leaves of seedlings on this rootstock in different soils. The average of Fe concentration in the roots was 11.1 times the average concentration in the leaves, indicating accumulation and deposition of iron in the roots. In most soils, the amount of manganese available for citrus trees was excessive, but the mean concentration of leaf was less than adequate. The overall mean Mn concentration in the roots was about 4.6 times more than its mean concentration in the leaf. From macroelements, magnesium and sulfur had the highest and lowest transfer efficiency and, from microelements, active Fe and total Fe had the highest and lowest transfer efficiency, respectively. According to the results of this research, chlorosis rate of the seedlings in different soils did not differ significantly, which shows this rootstock is tolerant to soil lime. Therefore, Smooth Flat Seville can be a good substitute for orange rootstock in calcareous soils (especially with medium and high lime).

The present research aimed to study the effects of S application with and without cow manure on growth indices of young sour orange (SO) seedlings and on some chemical and biological properties of a non-calcareous soil (pH= 6.8). In this experiment, eight different treatments, including the application of S at four levels (0, 10, 20, and 30 g-S per kg-soil) with or without cow manure were used. Eight months after planting, seedlings were harvested, and shoot weight and the concentration of nutrients including phosphorus, potassium, calcium, iron, and zinc in the leaves of the seedlings were measured. Additionally, at the end of the experiment, the soils around the SO root were sampled and some biological and chemical properties including the activity of phosphatase enzymes, microbial respiration, pH, electrical conductivity (EC), and the cation exchange capacity were determined. The results showed that the combined application of S and cow manure had a more pronounced effect on the growth indices of SO seedlings and soil quality indices than S and cow manure applied alone. Also, application of 10 g S had positive effects on the shoot’s weight and the concentration of P, Ca, Fe, and Zn in SO leaves and these positive effects were more pronounced in the combined application of S with cow manure. Also, with increasing the level of S application, soil pH decreased, and this decrease was more in the combined application of S and cow manure conditions. Additionally, the available amount of P, K, Ca, sulfate, Zn and Fe in the soil was affected by the level of sulfur application. Application of 10 g of S increased soil EC, although increasing the level of S application did not lead to a further increase in this parameter. The highest activity of alkaline and acidic phosphatase enzymes was obtained in the application of 10 g of S in combination with cow manure. In general, the results of this study showed that application of more than 20 g of S had an inhibitory effect on the growth of SO shoots and biological parameters under study.

Estimating the amount of soil organic carbon on a regional scale determines the potential of a landscape soil as a carbon storage site. This study was carried out in the Fandoqloo Region, Ardabil Province, Iran, and aimed to introduce: (i) the most suitable soil and environment characteristics as ancillary data for estimating soil organic carbon density (SOCD) and (ii) the most appropriate method for mapping SOCD among ordinary kriging (OK), co-kriging (CoK) and regression-kriging (RK) models. To fulfil the objectives, geographic information systems' database of the study area was developed by introducing soil, topographic and satellite data in the first step. Next, using Latin Hypercube (LHC) techniques and soil, land use, and geology maps and 140 sites were determined in the study area for collecting surficial (0-15 cm) compound soil samples. Results indicated that the land use type significantly affected SOCD (P ≤ 0.01) and SOCD of rangelands was higher than of croplands. Soil total nitrogen and mean weight diameter (MWD) were significantly (P ≤ 0.001) correlated with SOCD and could be applied as ancillary data for estimation of SOCD. Statistical indices revealed that application of co-kriging along with total soil nitrogen as ancillary data improved SOCD mapping compared with ordinary kriging. In general, this research indicated that regression-kriging was the most efficient method for mapping SOCD and total soil nitrogen, MWD, normalized difference vegetation index (NDVI) and plane curvature were significant soilscape characteristics that affect SOCD distribution.

Soil quality can be studied from two aspects: intrinsic soil quality and dynamic soil quality. The intrinsic aspect of soil quality is influenced by soil-forming factors, but the dynamic aspect of soil quality includes the characteristics of soil that change depending on the type of management and indicate the state of soil health. In this research, soil quality of a part of Qazvin lands, in Iran, was calculated using two cumulative soil quality indices and Nemro quality index. The results showed that the cumulative quality index was consistent with the spherical model and the numerical quality index was consistent with the exponential model, and the coefficient of determination of both indices was 0.87, which indicates a good correlation between the fitted model and observation points. Compared to the Inverse Distance Weighting (IDW) method, for both soil quality indicators, the normal kriging method had a lower value of the mean skewness error and root mean squared error (RMSE). Soil quality maps of the studied area were drawn with the help of two indices of cumulative quality and numerical quality based on the conventional kriging method. The pattern of soil quality was almost the same for both indicators. Based on the cumulative quality index, the soil in the northern and northwestern parts of the study area had the lowest soil quality values (0.4 and 0.3) while the southern and southeastern parts had the highest values (0.7 and 0.5), respectively. Two soil quality indices showed a positive and significant relationship with organic carbon, cation exchange capacity, nitrogen and potassium, but these relationships with bulk density and soil acidity had a negative and significant relationship. It can be concluded that the soil quality of the region is affected by the dynamic characteristics of the soil and it is important to pay attention to maintaining these characteristics.