مجله مدیریت اراضی
سال هشتم شماره 2 (پاییز و زمستان 1399)

Citrus fruits are of special economic importance; hence, the factors affecting their production need special attention. The citrus decline disorder is the cause of serious losses to the citrus industry due to the economic failure or total degradation of citrus orchards in the south of Iran. Even though the causal agents of the disorder in these regions are not yet fully known, a combination of environmental stresses and biological agents, depending on the affected region, seem to play roles in the spread of the disorder. Whatever the major causal agents, it is well established that the affected trees lose their hairy roots that are responsible for water and nutrient uptake. Drawing upon literature reports, field investigations, observational experiments, and the past experience of the present authors, the present paper proposes a number of remedial and preventive practices to mitigate, or even eradicate, the citrus decline disorder. Some of the most important strategies proposed include well managed irrigation regimes, timely application of proper fertilizers, reducing environmental stresses, orchard sanitation, and proper horticultural practices. Although such recommended practices as reducing environmental stresses may not be easily applicable under certain conditions, most seem readily practical.

The global food crisis due to the plunging production and rising prices in recent years, particularly in 2008, calls for solutions to ensure food security in most developing countries. The situation is worsened by the rising demands for food and water as consequences of the population explosion and cropland decline in these countries. By 2050, the world population is projected to rise to 9.2 billion and Iran will be one of the top 20 most populated countries in the world. According to a FAO report, agricultural production must be increased by about 70% during the years running up to 2050 in order to meet the projected food requirements. Finally, study has shown that more than 60% of the present population in Asia (particularly in South and South-West Asia) and a quarter of the African population suffer from malnutrition. The present paper explores the literature on sustainable land management and some of its components such as conservation agriculture, proper crop rotation, and proper management of soil organic content as the cornerstones of agricultural production toward food security.

Phosphorus (P) is a macronutrient of high consumption required by plants. Most agricultural soils around the world are poor in phosphorus and P fertilizers are used as a remedy. Not only are the fertilizers low in use efficiency but their application has also exacerbated the eutrophication of water bodies and the associated environmental pollution. This is while P fertilizers are extracted from the finite and non-renewable phosphate rock reserves, causing their rising prices over time as more P fertilizers will be needed to produce more food for the growing global population. P fertilizer management is, therefore, a key parameter in agricultural production. This is why a lot of attention has been recently paid to the application of sustained/controlled-release P fertilizers (SRF/CRF) in order to improve upon P use efficiency and plant growth at reduced environmental costs. The designation SRF/CRF is due to the lower water solubility of such fertilizers compared to conventional ones so that nutrients are supplied to plant roots over longer periods of time. Unlike SRFs, CRFs are characterized by well-controlled nutrient release rate, pattern, and duration. The methods used to manufacture P SRF include: 1) Coating the fertilizer with such materials as: a) polymers (including biodegradable polymers like chitosan, water-superabsorbent polymers, PVDC copolymers, polyolefins, polyurethanes, urea-formaldehyde resins, polyesters, and alkyd resins), b) sulfur, c) sulfur-polymers, d) organic acids, e) paraffin, f) clays, and g) fly ash; 2) Preparing SRFs from materials with a low solubility or a low mineralization rate; 3) Conversion of phosphate rock into P SRF using such different methods as partial acidification and phosphate solubilizing microorganisms; 4) Manufacturing P SRFs via nanotechnology-based techniques; 5) Producing P SRFs using phosphate-loaded layered double hydroxides, biochar, and hydrsochar; and 6) Using fly ash to manufacture SRF. The present article examines these methods and the effects of each on P use efficiency and the growth of different plants. It is generally concluded that P SRFs or CRFs improve P use efficiency and plant growth.

Environmental protection and natural resource conservation aimed at ensuring food security through healthy, organic food production form major items of Iran's development plans. The involvement of too many public agencies and authoritative sources has over recent years led to legal challenges hindering the realization of development and economic goals. This situation has, in turn, caused the Farm and Garden Land Conservation Act to face not only legal challenges in its implementation but, in certain cases, to conflicts with other laws. Despite its amendment in 2006, the law still requires substantial modifications and radical revisions in such areas as punitive measures for violation of law or methods to restore degraded or encroached land, and selection of trustees to carry out legal verdicts when they are approved for implementation. The present descriptive-analytical study explores the legal challenges facing the above Act and the duplicate roles and interventions by multiple government bodies. It is maintained that, as an attempt to resolve the mentioned challenges, conflicts, and parallel work, it is necessary to adopt a new approach that integrates the highly dispersed and diverse laws into a unit hole and one that grants authority to an independent institution or agency to make decisions about and to carry out law enforcement outside the urban and rural legislative units. These provisions are expected to reduce illegal land use changes and to witness proper law enforcement across the state.

A major concern in our modern world is the emission of the greenhouse gases carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4) into the atmosphere and their effects on climate change. Due to their significant impacts on carbon and nitrogen dynamics, agricultural activities have both direct and indirect effects on soil greenhouse emissions. Nitrous oxide is a potent greenhouse gas with a global warming potential of 298 times that of carbon dioxide. Most N2O emissions are agriculturally-induced, occurring due to nitrification and denitrification processes in soils and strongly affected by various environmental and soil management factors. The present review paper attempts to evaluate the capability of different agronomic management practices in mitigating nitrous oxide (N2O) emissions from agricultural soils. Proper management of crop residues, application of new methods of conservation tillage and irrigation techniques, and inclusion of legume crops in crop rotation programs are reportedly among the measures effective in reducing nitrous oxide emissions. Moreover, the use of nitrification and urease inhibitors as well as sustained-release fertilizers to improve nitrogen use efficiency might lead to reduced nitrous oxide formation and emission. From a different perspective, the use of novel technologies to identify the sources of nitrous oxide is of great importance in the selection and application of proper farm operations aimed at preventing further greenhouse emissions. It is expected that the agronomic management strategies proposed herein might have significant contributions to reducing nitrous oxide emission from soils, abating or preventing global climate change and the associated global warming, and achieving sustainable agricultural production.

The method potassium (K) fertilizer is applied in agricultural soils with a high K fixation capacity has a considerable effect on its use efficiency. To determine the effects of K fertilizer topdressing on irrigated wheat (Triticum aestium L.), experiments were performed during the years 2010, 2011, and 2013 under both field and experimental conditions in West Azerbaijan Province characterized by loamy soils as the dominant soil series with available K (Kava.) levels below 250 mg kg-1 (critical level). The experiments were arranged in a randomized complete block design with three treatments and four replications. Wheat was grown in early spring with varying topdressing K fertilizer levels (control, 100, and 200 kg ha−1 KCl) applied at the stem elongation stage. The results indicated that K fertilizer had no significant effects on either grain yield or its components. K concentration and uptake by the grain and straw were not affected by the treatments in which apparent K recoveries were measured below 7%. In contrast, soil Kava was significantly affected by K topdressing application. Lab tests revealed that more than 90% of the applied K fertilizer accumulated in the first six cm of the topsoil without being transferred to subsoil layers. A K fixation capacity of 45.5–54.5% with an average value of 51% was recorded for the soils in the region. Finally, it was concluded that both K sorption and fixation phenomena prevented K transfer from the surface layer to the plant root zone in the soils studied; hence, K topdressing in similar loamy soils would not be effective in meeting wheat K requirements.

Soil erosion and sedimentation measurements and evaluation of the temporal and spatial data thus obtained are crucial for advancing the knowledge on soil erosion, evaluating relevant models, and designing soil erosion experiments. Extensive temporal changes in erosion and sediment yields, particularly in small watersheds, require special technical provisions to ensure accurate records. Based on the existing records, maximum events, or even a single one (with a high return period), play an important role in altering average sediment yields in river basins. It is, therefore, necessary to collect long-term data in order to derive a reliable average value for sediment yield under natural conditions. The present paper explores such technical considerations in measuring sediment yields in small experimental watersheds. For this purpose, two simple and automatic sediment samplers and a flow divider are introduced for measuring suspended sediments. It is also shown that concrete tanks and small reservoir dams need to be constructed at the outlets of the experimental watersheds. Finally, different methods used for measuring total load (including bed and suspended loads) are described.

Land use change due to human activities is one of the most important issues in regional planning and development. Damghan urban basin has in recent years undergone many changes of the sort, including intensely increased urban population, physical expansion of urban and rural settlements, and disappearance of green spaces converted into residential areas. These changes have resulted in many flooding and inundation events within the urban area. The satellite technology can be exploited to identify such changes and the areas affected. For the purposes of this study, use was made of the ETM+ images of 2003 and the OLI images of 2015 obtained from Landsat to calculate the inundation conditions in Damghan urban basin using the USISM method. The ETM+ results showed a kappa coefficient of 75% and an overall accuracy of 0.67% while those of OLI images were 80% and 0.74%, respectively. The images revealed that green spaces had been converted to residential and commercial sites at a rate of 28% in 12 years. Meanwhile, agricultural land was found to have increased during the same period but barren lands to have decreased.