Sustainable Optimization of Saffron Production through Zone-Specific Management of Soil Chemical Properties in Arid Regions: A Case Study of Gonabad

Introduction: Saffron (Crocus sativus L.), a perennial plant from the Iridaceae family, is among the world's most valuable agricultural products. It holds a prominent place in Iranian agriculture, particularly in Khorasan Razavi, where Iran dominates global production with over 90% of the world's supply. Gonabad County is a key production hub. Known as "red gold," saffron's value comes from the dried stigmas of its flowers, which contain bioactive compounds with antioxidant, anti-inflammatory, and antidepressant properties. However, cultivating saffron in arid and semi-arid regions presents significant challenges, including low rainfall (less than 200 mm annually), high temperatures (up to 40°C), low humidity, and low-fertility soils. These conditions often lead to yields below 5 kg/ha and compromised quality. Soil quality is a critical factor influencing saffron performance, directly affecting corm growth, flower production, and stigma quality. Key chemical properties of the soil, such as electrical conductivity (EC), sodium adsorption ratio (SAR), organic matter (OM), and pH, are pivotal for plant health. High soil salinity (EC > 4 dS/m) and sodicity (SAR > 13) cause osmotic stress, reducing water and nutrient uptake and disrupting physiological processes. In arid regions, saline water irrigation and high evaporation exacerbate salt accumulation. Conversely, balanced nutrient management and organic amendments can improve soil structure and increase water retention, significantly boosting saffron yield. Studies in Khorasan Razavi have shown a strong positive correlation (r=0.75) between the organic matter content and saffron yield.
Climatic factors and irrigation management closely interact with soil properties, affecting saffron phenology. Precise irrigation scheduling during critical growth stages can mitigate the effects of salinity and alkalinity. Advances in precision agriculture, such as geospatial tools for zoning and real-time soil sensors, enable targeted management, optimizing water and fertilizer use and potentially increasing yields by 20%.  Planting techniques and field management also play a crucial role. High planting density (150-200 corms/m²) and a planting depth of 15-20 cm can enhance yields by protecting corms from heat and drought stress. Corm requirements for planting vary from 1.5 to 10 tons/ha. Soil quality, particularly organic matter and salinity, profoundly impacts saffron growth. Organic matter levels above 1.5% strongly correlate (r=0.80) with higher saffron yields. High sodicity (SAR > 15) harms corm health and reduces stigma quality, underscoring the need for precise soil chemical management.
Gonabad County, with 150 mm annual rainfall, dedicates 3,400 hectares to saffron cultivation. This study aims to assess soil chemical properties in three distinct Gonabad zones (Central, Kakhk-Kalat, Paskalut) and their impact on saffron growth and yield. The goal is to develop a scientific framework for region-specific management strategies. It is hypothesized that significant differences exist in soil chemical properties among the zones and that high salinity and sodicity negatively correlate with saffron performance. This research, utilizing integrated field data and statistical modeling, seeks to improve saffron production in Gonabad and serve as a model for similar arid regions.
 
Materials and Methods: The study was conducted in Gonabad County. Three zones (Central, Kakhk-Kalat, Paskalut) were selected based on soil and water variations. Soil samples were analyzed for nitrogen, potassium, calcium, magnesium, bicarbonate, lime, gypsum, SAR, EC, organic matter, and pH. Geospatial tools facilitated zoning and sampling. Statistical analyses, including one-way ANOVA and Tukey's test, assessed differences in soil properties across zones, with Pearson correlation evaluating parameter relationships.
 
Results and Discussion: Analysis revealed significant differences (p<0.01) in soil EC, SAR, calcium, and magnesium across zones, with Paskalut showing the highest values (EC=5.44 mS/cm, SAR=7.29). These conditions correlate with reduced saffron yield. Paskalut had elevated sodium, calcium, and magnesium, indicating severe salinity and sodicity challenges. Conversely, pH, organic matter, and potassium showed no significant differences (p>0.05). Strong positive correlations (p<0.01) were found between EC and calcium (r=0.943), magnesium (r=0.950), and SAR (r=0.474 with sodium). Zone-specific strategies, like gypsum application in Paskalut and organic amendments in Central and Kakhk-Kalat, are critical. Precision agriculture tools can mitigate salinity and improve saffron yield.
 
Conclusion: This study emphasizes zone-specific soil management to enhance saffron productivity in Gonabad. Paskalut requires urgent interventions for high salinity and sodicity, including gypsum application and improved drainage. In Central and Kakhk-Kalat, increasing organic matter can boost soil fertility and saffron yield. An integrated governance framework, leveraging precision agriculture, is essential for sustainable saffron production and natural resource conservation in arid regions.