نشریه پژوهشهای خاک (علوم خاک و آب)
سال سی و هفتم شماره 1 (بهار 1402)

Water and nitrogen are among the main factors affecting crops yield. In order to investigate the effect of different levels of irrigation and amounts of nitrogen on some traits affecting yield of spring corn, a research was carried out in the form of split plots and use of a completely randomized block design with three replications in the research farm of the Islamic Azad University, Ahvaz branch.  Treatments included irrigation at three levels (irrigation after 60, 95, 130 mm of evaporation from class A evaporation pan, and the total volume of irrigation water in each treatment was, respectively, 6435, 5620 and 5140 m3/ha) and amounts of nitrogen consumption at three levels (including 80, 150, and 220 kg.N.ha-1), which were placed in the main and sub plots, respectively. The results showed that irrigation treatment had a significant effect on traits such as leaf area index, leaf relative water content, grain yield and its components, and harvest index. Also, application of nitrogen fertilizer significantly affected the characteristics of leaf area index and cob leaf nitrogen, yield and yield components, biological yield and harvest index. The highest seed yield from the irrigation treatment was obtained after 60 mm of evaporation and 220 kg.ha-1 of nitrogen fertilizer with an average of 763.2 g.m-2, which had no statistically significant difference with the treatment of 60 mm of class A evaporation pan and 150 kg/ha of nitrogen fertilizer; threfore, this treatment is suggested for the climatic conditions of Khuzestan

Optimum soil water content (OSWC) for tillage is the moisture at which, if tillage is done, the maximum amount of crushing (friability) is created in the soil with minimum energy consumption. The purpose of this research was to determine the OSWC for tillage operations under different agricultural land uses in Jiroft Plain, Iran, and to evaluate the effectiveness of the decision tree model in this regard for the region. For this purpose, soil samples (90 samples) were taken intact from 0 to 20 cm depth and some of its physical and chemical characteristics were determined. To determine the soil water characteristics curve, the soil water contents at matric suctions of 10, 30, 50, 100, 300, 500, 1000 and 1500 kPa were measured using a pressure plate device. The results showed that the type of cultivation did not have a significant effect on the physical and chemical characteristics of the soil, including the optimum weighted humidity. OSWC prediction was done with decision tree. In this research, three prediction accuracy criteria, namely, coefficient of determination (R2), root mean square error (RMSE), and normalized root mean square error (NRSME) were used to evaluate the model performance. The results showed that use of decision tree for predicting the OSWC was appropriate due to having a lower NRMSE (0.017) and a high R2 (0.75). Also, the results of OSWC modeling showed organic matter as the most influencing variable, followed by the equivalent calcium carbonate percentage, electrical conductivity, apparent density, and percentage of sand and silt.

Today, various methods are used to reduce the negative effects of high concentration of heavy metals in the soil. In this regard, the use of biochar is a relatively cost effective and new method to reduce the toxicity and mobility of heavy metals. In this study, in order to investigate the effect of biochar on improving peppermint plant growth in cadmium-contaminated soil, a pot experiment was conducted using a factorial design in the form of a completely randomized design. Treatments included three factors of cadmium (Cd) levels (50 and 100 mg/kg), the type of organic matter (spruce sawdust, sawdust biochar prepared at 300 and 600 °C, wheat straw, wheat straw biochar at 300 and 600 °C) and the amount of organic matter (zero, 2%, and 4 % by weight). Growth characteristics and performance of peppermint plant essential oil were determined. The results showed that with increasing Cd level, there was  a reduction in chlorophyll a 37.6%, chlorophyll b 54.9%, total chlorophyll 42.9%, carotenoid level 31.6%, photosynthesis rate 40.5%, essential oil percentage 34.8%, and essential oil content showed 83.3% reduction. The results indicate the positive effects of biochar in reducing the negative effects of Cd. Comparison of Cd treatment alone with Cd treatments along with biochar showed that herbal biochar had a greater ability to reduce the negative effects of Cd than other treatments. In most cases, wheat straw biochar at two temperatures of 300 and 600 degrees at the level of 2% and 4% was superior in improving plant growth and performance. The highest percentage of essential oil belonged to wheat straw biochar at 600 oC and level of 2% and 50 mg/kg of Cd with 86% increase compared to the control, with an increase of 20% in the weight of aerial parts. The amount of N, K, and P absorption in this treatment increased by 100%, 73%, and 76%, respectively, compared to the control. The obtained results show the ability of straw and wheat stubble biochar to increase and improve plant growth compared to other organic materials used in this study.

The aim of this study was to investigate the effect of chromium heavy metal on soil enzymatic activities and some physiological and morphological indices of portulaca oleracea L., with the local name of Khorfeh. The study was carried out based on a completely randomized design with three replications. Soil samples were infected with different concentrations of chromium (0, 25, 50, 75, and 100 mg kg-1 soil). After reaching equilibrium in the soil, Khorfeh plants were grown. The activity of dehydrogenase, phosphatase, and urease, and some physiological and morphological characteristics of plants was determined under chromium stress, then, the correlation between them was determined. The results showed that soil enzyme activities decreased with increasing chromium concentration in the soil. Root and shoot dry weights had the most negative correlation with chromium concentration. The role of soil enzyme activity in the evaluation of chromium contamination status was determined by the biochemical index of soil fertility, which showed the most negative correlation with shoot dry weight. The correlations between Cr concentration in soil and all the physiological indices of plants were above 0.9%. The dehydrogenase activity in relation to plant physiological indices showed similar behavior to the biochemical index of soil fertility. In general, according to the results of this study, the physiological indices of the plant with higher sensitivity than its morphological indices could indicate Cr contamination in the plant.

Due to the pollution of water resources by various pollutants such as nitrate, the use of amendments such as biochar can be considered as an approach to solve this environmental problem. To investigate the effect of barberry stem biochar on nitrate leaching, a research was conducted using a factorial and completely randomized design in 2021, in the soil laboratory of the Faculty of Agriculture, University of Birjand, Birjand, Iran. Experimental factors were particle size of biochar at two levels (less than 1 mm, more than 2.8 mm) and biochar volume in three rates (1, 2, and 3 mm on weight basis). Biochar was produced during the thermal decomposition process under limited oxygen conditions (400 0C for 6 h). The pots were subjected to wet cycles (field capacity plus 20%) and drying (permanent wilting moisture) and the nitrate concentration in the drained water from irrigation was measured in two stages with an interval of six weeks. The highest and lowest nitrate leaching rates in the samples were observed in the control treatment without biochar and biochar with particle size less than 1 mm at the rate of 1% by weight, respectively. The results of this study showed that addition of the biochar to the soil significantly reduced nitrate leaching compared to the control without biochar. At the two measuring times, biochar treatments with particle size of less than 1 mm and 1%, 2% and 3%, biochar with natural particle sizes of 1%, 2%, and 3% showed decrease in nitrate leaching by, respectively, 83.6%, 82.4%, 76.8%, 81.7%, 64.2%, and 60.2 % compared to the treatment without biochar. Moreover, the results showed that biochar particles less than 1 mm had more effects on reducing nitrate leaching than biochar particles more than 2.8 mm. According to the results of this study, it seems that application of barberry branch waste biochar left after harvesting can reduce nitrate leaching and the risk of transmitting contamination to other soil.

Organo-clays, like organo-montmorillonite, have attracted interest in different sciences, due to their wide range of applications. In this study, three types of organo-montmorillonite clay were produced based on Cation Exchange Capacity (2 HMM, 1HMM, 0.5 HMM), using different amounts of hexadecyl trimethyl ammonium bromide surfactant. To analyze their properties, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and field emission scanning electron microscope (FE-SEM) were employed and clays’ dispersive capability was investigated. Results of XRD showed that the basal spacing of the treated organo-clay increased. Results of FTIR spectra also illustrated that the newly identified bands in organo-montmorillonite were due to organic surfactants. SEM morphological study of clays depicted that although the montmorillonite clay was in agglomerative form, treating with organic surfactants altered it to the shorter layers with porous surfaces. Results of XRD indicated that treatment on organo-montmorillonite changes the surface properties from hydrophilic to hydrophobic, and this affects the absorbance of organic pollutants and enzymes. This study has an important role in preparing the cheap organo-clays, employing such additives to decrease the environmental pollutants and increase the biological activities of the soil, specifically to activate the soil enzymes. Effects of applying the organo-clay on L-arginine ammonification process were then determined. Experiments were carried out using a completely randomized design with factorial arrangement employing three clay types (montmorillonite, montmorillonite intercalated with hexa decyl trimethyl ammonium bromide, and the control) for five durations (1, 3, 7, 14, and 21 days) with three replications. Results indicated that the highest ammonification of L-arginine, as an estimate of the soil microbial biomass, was in the soil samples that were treated with montmorillonite intercalated with hexa decyl trimethyl ammonium bromide (HMM) surfactant. Results indicated that the change in the soil. Environment surrounding the enzymes with the organic surfactant increased activity and stability of enzymes in soil during the 21-day incubation period.