دوماهنامه
نوع مقاله : مقالات پژوهشی
نویسندگان
1 دانشیار بخش تحقیقات خاک و آب، مرکز تحقیقات و آموزش کشاورزی و منابع طبیعی استان مرکزی (AREEO)، شیراز، ایران
2 استادیار موسسه تحقیقات خاک و آب، سازمان تحقیقات، آموزش و ترویج کشاورزی (AREEO)، کرج، ایران
3 استادیار بخش تحقیقات خاک و آب، سازمان تحقیقات، آموزش و ترویج کشاورزی (AREEO)، مرکزی، ایران.
کلیدواژهها
عنوان مقاله English
نویسندگان English
Introduction
Rapseed (Brassica napus L), particularly the low erucic acid and glucosinolate cultivars known as canola, is the third largest oilseed crop in the world after soybean and oil palm. In Iran, canola cultivation covers approximately 173 thousand hectares, making it the largest cultivated area among oilseed crops. Golestan and Khuzestan provinces have the largest cultivated areas. Balanced fertilization is crucial for optimizing canola yield, especially under adverse environmental conditions. Plant tissue analysis serves as a fundamental tool for diagnosing nutrient status and exploits the principle that tissue nutrient concentration reflects soil nutrient availability. Advanced diagnostic methods, such as deviation from optimum percentage (DOP) and nutrient balance index (NBI), provide quantitative measures of nutrient adequacy and imbalance. The DOP method ranks nutrient deficiencies by comparing observed tissue concentrations with those in high-yielding populations. Meanwhile, the NBI integrates multiple nutrient statuses into a single measure (Σ|DOP|) and provides a comprehensive assessment of overall nutrient health.
Materials and Methods
The study was conducted in four provinces: Alborz, Markazi, Golestan, and Ardabil (Moghan region), to reflect the diverse agro-ecological conditions of the country. Thirty farms were randomly selected in each province.
Alborz province (Karaj region) is located at latitudes 35°48'N and 51°10'E. Markazi province (Arak city) is located at latitudes 34°5'30'N and 49°41'30'E. East Golestan Province (Gonbad Kavus region) is located at coordinates 37°16'N and 55°12'E, while Ardabil Province (Parsabad and Moghan regions) is located at coordinates between 39°12'N and 39°42'N and 47°10'E and 48°21'E.
Soil samples were collected from the fields before planting. Plant tissue samples were taken at the biganing of stem elongation stage (two-digit growth code 30), which is a sensitive stage for identifying and eliminating nutrient deficiencies before canola flowering. Plant samples were collected as whole plants from 20 random points per hectare, and 20 plants were sampled from each point. Total nitrogen (N), phosphorus (P), potassium (K), and micro nutrients zinc (Zn), manganese (Mn), iron (Fe), copper (Cu), and boron, were measured in plant tissue. Grain yield was measured at maturity. To assess nutrient status and identify yield-limiting factors, the key diagnostic index, deviation from optimal percentage (DOP), quantifies the deviation in nutrient concentrations from the optimal values observed in high-yielding populations. The NBI index was also used in this study.
Results and Discussion
In terms of soil properties, there was significant variation in pH, salinity, organic carbon, and nutrient availability across the studied provinces.
In Alborz province, the average organic carbon content was low (0.81%) and the frequency of nutrient deficiencies was high, including nitrogen (N, 73%), phosphorus (P, 47%), potassium (K, 20%), sulfur (S, 87%), magnesium (Mg, 37%), iron (Fe, 83%), copper (Cu, 20%), zinc (Zn, 50%), manganese (Mn, 43%), and boron (B, 60%). In Markazi Province, with an average salinity of 1.47 dS/m, severe deficiencies of nitrogen (90%), phosphorus (75%), and potassium (37%) were observed. In Golestan Province, non-saline soils in this region with an average organic carbon percentage of 1.4% showed deficiencies of nitrogen (27%), phosphorus (94%), potassium (32%), magnesium (100%), iron (32%), copper (22%), manganese (31%), and zinc (81%). In Ardabil Province, high clay content (40%) and salinity (2.4 dS/m) led to deficiencies of phosphorus (50%), potassium (1%), sulfur (99%), magnesium (99%), iron (50%), copper (3%), zinc (87%), and manganese (10%).
DOP standards for nutrient concentrations in canola shoots during stem elongation were determined as follows: nitrogen 3.61%, phosphorus 0.46%, potassium 2.8%, sulfur 0.513%, magnesium 44.00%, calcium 1-2%, iron 226 mg/kg, copper 1.8 mg/kg, manganese 78.5 mg/kg, zinc 45.8 mg/kg, and boron 54 mg/kg.
The nutrient balance index (NBI), calculated as the sum of absolute DOP values, was inversely correlated with yield, confirming that greater nutrient imbalances resulted in reduced yield. Statistical analyses confirmed that NBI thresholds between 133 and 146 corresponded to significant yield reductions (p<0.01). based on these thresholds, yield decreased by 12 to 18% for each unit increase in NBI. It is noteworthy that when NBI exceeds a certain threshold (NBI breakpoint) (BPC), yield reduction becomes more evident. Below this threshold, yield is less affected by NBI. Alborz province had the highest BPC (146), followed by Ardabil (139), Markazi (138), and Golestan (133) provinces, respectively. Farmers and advisors can use this range as a guide for fertilizer recommendations.
Conclusion
This study shows that the variability of canola yield in agro-ecological regions of Iran is primarily due to the deficiency of region-specific nutrients, especially phosphorus and zinc, combined with soil alkalinity, low organic carbon, and mineralogical characteristics. By implementing region-specific nutrient management strategies, yield gaps can be closed, and sustainability in semi-arid oilseed systems can be promoted. The Balance Index integrates vital nutrient ratios (such as phosphorus:zinc, magnesium:potassium) to detect imbalances.
کلیدواژهها English
