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Enhancing the frost resistance of fruit and berry crops and their preparation for wintering
Leaf Surface Diagnosis
In modern high-performance agriculture, it is not enough to simply apply fertilizers “according to schedule.” A plant is a living organism, and its needs constantly change depending on the weather, soil type, and stage of development. One of the most accurate ways to assess the real nutritional status is leaf surface diagnosis.
Leaf (tissue) diagnosis is a critically important tool of precision agriculture that allows you to determine the current nutritional status of the crop, eliminate hidden deficiencies, and avoid irreversible yield losses.
Why Is Leaf Diagnosis Necessary?
Leaf diagnosis answers the most important question: “How many nutrients has the plant actually absorbed and used?”
Leaf diagnosis is carried out to determine the plant’s need for foliar feeding; however, it is unreliable as the sole basis for developing a fertilization system – it must be combined with agrochemical soil analysis, which helps design a high-quality nutrient management plan.
Unlike soil analysis, which only shows the reserve of elements in the soil, leaf analysis reflects the real picture of nutrient uptake, taking into account all agronomic and climatic factors:
Early Detection: Reveals nutrient deficiencies long before visual symptoms appear. When you see yellow leaves (chlorosis), it already means yield losses are irreversible. Diagnosis, in turn, allows timely intervention.
Detection of Blockages: Helps understand why a plant cannot absorb nutrients even when they are present in the soil. For example, a high pH can block zinc uptake, while low temperatures can restrict phosphorus absorption.
Investment Efficiency: Ensures the application of the exact nutrient that is critically deficient, in the correct form and dosage. This prevents unnecessary costs for unneeded fertilizers.
How to Properly Collect Samples: The Key to Reliability
The quality of results depends 90% on proper sampling. Each crop has its own “diagnostic” leaves, which are usually collected in the morning, avoiding rainy or hot weather. The time between sampling in the field and laboratory analysis should not exceed 1–3 hours. Improper sampling leads to inaccurate data and wrong decisions.
Determining the Critical Growth Stage
Samples should be collected during key growth stages of the crop. For example, for maize – the 5–7 leaf stage and before tasseling; for wheat – the end of tillering and stem elongation; for rapeseed – 4–6 leaves in autumn and stem elongation in spring.
| Crop | Optimal Stage for Diagnosis | Purpose |
|---|---|---|
| Winter wheat | End of tillering (spring) and stem elongation | Assess need for N, S, Cu, and Mn before the intensive growth phase |
| Maize (corn) | 5–7 leaf stage | Critical period for Zn application and evaluation of initial nutrition |
| Rapeseed | Autumn 4–6 leaves and stem elongation in spring | Assess reserves of B and S for overwintering and reproductive organ formation |
| Sunflower | 4–6 leaf stage and star stage | Assess need for B and N for head initiation |
Before analysis, leaves should be cleaned from dirt, soil, and pesticide residues. They are washed with a 2% solution of a phosphate-free detergent and rinsed with distilled water.
Regular sampling (e.g., every 10–14 days during the period of intensive growth) allows monitoring of nutrient dynamics.
Sample Selection (Which Leaves to Cut?)
The choice of leaves depends on the mobility of the nutrient within the plant:
Mobile elements (N, P, K, Mg): Their deficiency appears on older (lower) leaves, so for analysis, the youngest fully developed leaves are collected.
Immobile elements (Ca, B, Fe): Their deficiency appears on young (upper) leaves, so these are collected for analysis as well — the youngest fully developed leaves that are no longer in the bud stage.
Representativeness
Samples should be collected from uniform, typical plants across the field. Avoid edges, headlands, and obviously diseased or damaged plants. Collect approximately 30–50 leaves per composite sample representing an area of up to 20–30 hectares.Preparation for Analysis
Leaves must not be wet from rain or dew. If spraying was carried out, sampling should be done only after 48–72 hours. Samples must be placed in paper bags (not plastic) to prevent rotting and data distortion.
Before analysis, leaves are cleaned of dirt, soil, and pesticide residues by washing with a 2% phosphate-free detergent solution and rinsing with distilled water.
Interpretation of Results: From Diagnosis to Decision
Laboratory results are provided in mg/kg of dry matter. Your task is to compare these results with the optimal reference ranges for the specific crop and growth stage.
Methods of Leaf Diagnosis
Several methods of leaf diagnosis are used in agronomy to assess plant nutrition: laboratory (chemical) analysis, visual diagnosis, and rapid (field) methods.
Laboratory (Chemical) Analysis
This is the most accurate and reliable method – the foundation for decision-making in precision agriculture. The method involves collecting leaf samples from the field during critical growth stages to determine the content of nitrogen and ash elements after ashing with a mixture of acids and hydrogen peroxide.
It helps determine the exact concentration of all key nutrients (macro- and micronutrients) in plant tissues, measured in mg/kg of dry matter or as a percentage.
Advantages include high accuracy, the ability to simultaneously measure dozens of elements, and detection of hidden deficiencies before visual symptoms appear. However, it requires time for sampling, transportation, and laboratory processing (several days to a week).
Rapid (Field) Methods
These are quick techniques that provide real-time information directly in the field using portable instruments.
Chlorophyllometry (SPAD meter): A device that measures the intensity of the green color of leaves, indicating chlorophyll content. It provides an indirect assessment of nitrogen and other nutrients critical for photosynthesis (e.g., magnesium, iron). This method is fast, gives instant results, and allows dynamic monitoring.
Nitrate Testing: Measures the concentration of nitrate nitrogen in plant sap, determining the current nitrogen availability. It allows rapid evaluation and decision-making for nitrogen fertilization.
Visual Diagnosis
This is the simplest but least reliable method, based on visual inspection of plants. Nutrient deficiencies are identified by characteristic symptoms (chlorosis, necrosis, leaf deformation, discoloration). Typically, only acute deficiencies can be identified, and symptoms appear when yield losses have already occurred.
For accurate and efficient crop management, it is recommended to combine laboratory analysis (for strategic planning and hidden deficiency detection) with rapid methods (for real-time nitrogen monitoring).
From Diagnosis to Success: Nutrient Correction
After receiving the laboratory report, the agronomist compares the actual data with optimal reference ranges for the specific crop and growth stage.
Low nutrient levels require immediate corrective foliar feeding – boron, zinc, and manganese are applied quickly and precisely.
Excessive levels indicate potential toxicity (e.g., boron) or blockage of other nutrients. In this case, further nutrient management strategy must be adjusted.
Conclusion
Leaf diagnosis is not a luxury but a strategic necessity for the modern agronomist. It transforms the fertilization process from guesswork into precise engineering, ensuring that the plant receives its “fuel” at the right time and in the right amount.
Do not wait for visible signs of deficiency – listen to your plants through laboratory analysis.
