مجله مدیریت اراضی
سال هشتم شماره 1 (بهار و تابستان 1399)

Sustainable agricultural development and soil resources conservation presuppose adequate knowledge of soil properties, land yield potential, and land use to facilitate the production of such essential agricultural products as wheat. Along these lines, the present study was conducted to identify the land limiting factors, as well as the severity of each factor, in four selected regions in Iran covering an area of about 60,000 ha. Moreover, the relationship between wheat actual yield and land yield potential in the study areas was established. Finally, the results of land suitability investigations and land yield potential estimations were duly analyzed. It was found that the mean effect of intrinsic soil properties on wheat yield reduction was about 2388 kg.ha‒1 (28.74%). Also, a difference of about 2192 kg.ha‒1 (26.37%) was found between land yield potential and average farm yield in the study areas, which is relatively high and indicates both the lack of a proper management system and the failure to exploit land yield potential toward optimum crop production. A point of interest in the study areas was that the difference between actual yield by some leading farmers and the land yield potential in soils highly suitable (S1) for irrigated wheat production was low but that it was high in soils with moderate to low suitability. It was, therefore, concluded that it would be necessary to extend proper agricultural management practices among leading farmers in each area to enhance their crop yield and land productivity in that area. Once implemented, optimal management practices will expectedly improve irrigated wheat farm yield by as much as 85% the local land yield potential.

Agroforestry systems have been introduced for sustainable development in response to the growing demand for food and the increasing need for proper exploitation of agricultural land. In the agroforestry system, rows of trees or shrubs established around farms create the microclimate conditions favorable to crop production. In this study, changes in the areas of cultivated land under an agroforestry system in Jiroft Plain, Iran, were studied using Landsat satellite images taken over a period of 22 years. For this purpose, the supervised classification method was used to identify two categories of land cover including cultivated land and bare land via Landsat TM sensor images as well as three categories of land cover including cultivated land, tree cover, and bare land via Landsat 8 images. The land cover changes over the 22-year study period were subsequently analyzed using the post-classification approach. Results revealed that windbreaks had been planted over 5.1% of the bare land and 15.4% of the agricultural land while 26.9% of the bare land had been transformed into farmland such that the area of agricultural land had risen from 556 ha in 1992 to 741 ha in 2014. Our findings indicate that proper management of the agroforestry system in the study area has led to the creation of conditions favorable to enhanced crop production. In order to make the most of the agroforestry system, high spatial resolution images should be used as tools toward determining the best tree species for use as windbreak and the best direction for their establishment both to achieve land conservation objectives and to create the conditions required for improved crop production.

Enhancements in crop yield and quality depend on proper use of chemical fertilizers, the most important tool for which is a comprehensive understanding and accurate knowledge of the fertility status of the soil under cultivation. The present study presents a review of the fertility of soils under wheat cultivation in Qazvin Plain in an attempt to formulate extension guidelines for facing the challenges due to soil limitations hindering satisfactory wheat yield. For this purpose, use was made of 43120 soil analytical data obtained from 2695 samples collected from Qazvin Plain to study the 12 soil physicochemical properties of soil texture, pH, and EC as well as lime, organic carbon, phosphorus, potassium, iron, copper, manganese, and boron contents. The results showed that, while a major portion of the soils studied was loam, more than 78% were alkaline in nature with pH values of 7 to 8. Also, the soils were found to suffer from such limitations as deficient available K, manganese, copper, and boron. Given an electrical conductivity of less than 2 dS m-1 obtained for the soil saturation extract, 47.1% of the soils in the plain were identified as non-saline. Calcium carbonate accounted for more than 96% of the soils as affected by lime. Moreover, the soils were drastically deficient in organic content as revealed by the organic carbon index that indicated an organic carbon content of less than 1% in 93.5% of the soils examined. Critical phosphorus and potassium levels were measured at 15 and 300 mg kg-1, respectively, indicating 27% of the soils in need of phosphorus fertilizer application but more than 80% in no need of potassium fertilizers. The critical levels of iron, zinc, manganese, boron, and copper were measured at 5, 1, 5, 1, and 1mg kg-1, respectively, such that about 74% of the studied areas suffered from iron deficiency, 64% from zinc deficiency, 17% from manganese deficiency, 27% from boron deficiency, and about 30% from copper deficiency. Thus, soil micronutrients were not uniformly distributed across the wheat farms. It is, therefore, essential to formulate recommendations duly based on plant needs and to avoid uniform application of the same fertilizers on all soils with different deficiencies in order to achieve desirable yields at lower production costs.

Improved product quality, sustainable cultivation systems, and reduced production costs are among the objectives of modern agriculture despite the global and local climate changes that have faced crops with a variety of stresses. Biostimulants seem to be capable of helping plants in their struggle against these stresses toward the goals of modern agriculture. These compounds include humic substances, seaweed extracts, amino acids, microbial inoculants, and minerals such as useful elements and inorganic salts including phosphates and antiperspirants. While application of biostimulants has witnessed a dramatic increase in the world and in Iran over the past few years, it must be noticed that they might have different effects on different species and even on different varieties of a given plant species. Their application for agricultural and horticultural purposes must, therefore, be duly modified in accordance with local and regional research findings. It is the objective of this paper to provide a better understanding of plant biostimulants based on scientific findings and practical experience in agriculture and horticulture. It will be shown that plant biostimulants are capable of improving crop production, enhancing plant resistance to abiotic stresses, and elevating crop quality. Future research in this area should aim at the determination of the mechanism(s) underlying the activities of such materials since a better understanding of their activities and effects will be necessary for achieving sustainable agricultural production systems.

While excessive chemical input into agricultural lands has caused environmental problems, deteriorating crop quality, disease and pest resistance in plants, and declining soil fertility, concerns about food security and enhanced quality of agricultural products have been steadily rising in most human communities. Meanwhile, more than 60% of Iran's agricultural land is located in arid and semi-arid areas that are poor in organic matter. It is, therefore, of utmost importance to improve soil fertility by application of organic matter to soil. A major portion of the vermicompost research in the past was focused on the effects of this organic fertilizer on the performance and yield of different farm, horticultural, ornamental, and medicinal crops; mitigation of plant stresses; and soil physicochemical properties. Based on the results obtained, application of vermicompost, either alone or in combination with chemical fertilizers, at 5‒10 t/ha for medicinal plants, 20‒30% of pot volume for ornamental plants, 20‒60 t/ha for crop plants, 40‒80 t/ha every two or three years for vegetables and summer fruits, and 30‒60 t/ha every three years for fruit trees has been recommended. Application of vermicompost fertilizer seems not only to improve soil physicochemical properties but also to reduce significantly the amount of chemical fertilizers used, thereby contributing positively to sustainable crop production.

Bioavailability of micronutrients in soils and their uptake by plants depend on soil properties (e.g., pH and carbonate content) and the interactions between plant roots and soil microorganisms. The low bioavailability of iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn), as a major factor limiting plant nutrition, in calcareous soils is due to the low organic content, high pH levels, and precipitation by carbonates in such soils. Study has shown that, under nutrient deficiency conditions, plant roots release low-molecular-weight organic acids (LMWOA) such as citric, oxalic, and malic acids to increase the solubility of micronutrients like Fe, Mn, Cu, and Zn in the rhizosphere. The LMWOAs exuded into the rhizosphere are known to enhance the mobility and bioavailability of such micronutrients and their uptake by plants. In addition, LMWOAs are involved in metal detoxification and improvement of microbial activity in soils. The present study investigates the role LMWOAs play in the bioavailability of such micronutrients as Fe, Mn, Cu, and Zn.

Salinity of irrigation water is a major limiting factor for the development of irrigated agriculture in arid and semi-arid regions. Moreover, application of saline water might increase soil salinity and mitigate its fertility in the absence of scientific principles and proper management. The present experiment was carried out using a complete block design with five irrigation treatments at the Date Palm and Tropical Fruits Research Center during the period 2017‒2018. The treatments included one irrigation with water abstracted from the Karun River; one with saline water of 5 dS/m; one with saline water of 8 dS/m; two with the Karun River water and one with saline water of 5 dS/m; and finally two with the Karun River water and one with saline water of 8 dS/m, all conducted in triplicates. The results showed that salinity of irrigation water led to significantly reduced leaf number, leaf length, leaf width, leaflet number, leaflet length, and trunk perimeter at the 5% probability level. Maximun and minimun values of plant vegetative properties were obtained under irrigation with water from the Karun River and that with saline water of 8 dS/m, respectively, such that the mean number of leaves and leaflets decreased by 73.0 and 69.2%, respectively. Compared to the irrigation treatment with the water from the Karun River, the one with two irrigations with the Karun River water and once with saline water of 5 dS/m did not lead to any significant reductions in such vegetative characteristics as numbers of leaves and leaflets of the date palm seedlings at the 5% probablity level. It may be concluded that date palm seedlings may be safely irrigated with saline water of up to 5 dS/m if irrigation management is properly implemneted.

Increasing nutrient inputs into terrestrial ecosystems affect not only plant communities but also the associated soil microbial ones. Studies carried out in predominantly unmanaged ecosystems have found that increasing nitrogen (N) inputs generally decrease soil microbial biomass while less is known about their long-term impacts on managed systems such as agroecosystems. The objective of this study was to analyze the responses of soil microorganisms to mineral fertilizers using data from long-term fertilization trials in cropping systems. A meta-analysis based on 107 datasets from 64 long-term trials from around the world revealed that mineral fertilizer application led to a 15.1% increase in the microbial biomass (Cmic) above the levels observed in unfertilized control treatments. Mineral fertilization also increased soil organic carbon (Corg) content, suggesting that Corg is a major contributor to the overall increase in Cmic under mineral fertilization. The magnitude of the effect of fertilization on Cmic was found to be pH-dependent. While fertilization tended to reduce Cmic in soils with a pH below 5 in the fertilized treatment, it had a significantly positive effect at higher soil pH values. Duration of the trial also affected the response of Cmic to fertilization, with increases in Cmic most pronounced in studies with a duration of at least 20 years. The input of N per se does not seem to negatively affect Cmic in cropping systems. Application of urea and ammonia fertilizers can, however, temporarily increase pH, osmotic potential, and ammonia concentrations to levels inhibitory to microbial communities. Even though impacts of fertilizers are spatially limited, they may strongly affect soil microbial biomass and community composition in the short term. Long-term repeated mineral N applications may alter microbial community composition even with small changes in pH. The way specific microbial groups respond to repeated applications of mineral fertilizers, however, varies considerably and seems to depend on environmental and crop management related factors.