Types of fertilizers suitable for application under low-temperature conditions in winter
In the cold winter environment, the vitality of crop roots decreases, the efficiency of nutrient absorption declines, and the activity of soil microorganisms weakens, resulting in a slower conversion rate of fertilizers. Therefore, when choosing fertilizers, one should follow the core principle of "promoting absorption, reducing loss, protecting roots, and stabilizing growth", and prioritize the selection of types that can quickly supply nutrients, enhance the cold resistance of crops, and adapt to the low-temperature soil environment. This can be divided into the following four categories, taking into account both practicality and scientificity.
1. Quick-acting nitrogen fertilizer: Provides immediate nutrient supply to crops, preventing nutrient deficiency.
At low temperatures, the photosynthetic efficiency of crops decreases. If nitrogen supply is insufficient, the leaves may turn yellow and the growth may be slow. Moreover, the absorption and utilization rate of slow-release nitrogen fertilizers by crops significantly decreases. Therefore, quick-release nitrogen fertilizers should be prioritized to ensure that nutrients are quickly absorbed by the root system and to maintain basic physiological functions.
The suitable varieties mainly use urea, ammonium sulfate and ammonium nitrate. Among them, ammonium sulfate is a physiological acidic fertilizer. It not only can quickly replenish nitrogen but also can supplement sulfur elements, enhancing the cold resistance of crops. It is especially suitable for winter crops such as wheat and rape. Urea needs to be converted into ammonium nitrogen by soil microorganisms before being absorbed. The conversion period is prolonged under low temperatures. When applying, it is recommended to do so 3-5 days in advance and combine with watering to promote conversion and absorption, avoiding fertilizer residue loss. Although ammonium nitrate has strong quick-acting properties, its stability is poor. It should avoid being mixed with alkaline fertilizers and should not be over-applied to prevent excessive growth of crops and reduce their cold resistance.
II. Phosphorus and Potassium Fertilizers: Enhance the cold resistance of crops and promote root development
Phosphorus and potassium are the key nutrients for enhancing the adaptability of crops. Applying phosphorus and potassium fertilizers in low-temperature environments can not only promote the growth of crop roots (especially fibrous roots and lateral roots), enhance the roots' tolerance to low temperatures and their ability to absorb nutrients, but also increase the cell fluid concentration, reduce the damage to cells caused by low-temperature freezing, and prevent crops from experiencing abnormal growth due to nutrient imbalance.
Phosphate fertilizer: Preferentially choose superphosphate calcium, potassium dihydrogen phosphate (a phosphorus and potassium dual fertilizer), and monopotassium phosphate. Superphosphate calcium not only replenishes phosphorus but also contains calcium and sulfur, etc. as trace elements, which can improve the micro-environment of the soil and enhance the cold resistance and lodging resistance of crops. It is suitable for spreading or applying in trenches around the roots of overwintering crops; Monopotassium phosphate is an acidic fertilizer. It has a high solubility at low temperatures, a stable nutrient release rate, and is not easily combined and fixed with calcium and magnesium elements in the soil. It is suitable for all types of soil, especially for alkaline soils in northern regions.
2. Potassium fertilizer: The main types are potassium sulfate and potassium dihydrogen phosphate. Potassium sulfate does not contain chlorine and has no adverse effect on the root system of crops. It can promote the accumulation of sugar and starch in crops and enhance the cell's frost resistance. It is suitable for crops that are sensitive to chlorine or have relatively weak chlorine tolerance, such as vegetables, fruit trees, wheat, and rape. Potassium dihydrogen phosphate (with 52% phosphorus and 34% potassium) combines the advantages of phosphorus and potassium. It is mainly applied through foliar spraying and can be quickly absorbed by the leaves, avoiding the problem of insufficient root absorption under low temperatures. It is often used before the winter of fruit trees, during the seedling stage of vegetables, and before the green-up of overwintering crops, showing significant improvement in cold resistance.
III. Trace Element Fertilizers: Addressing Nutrient Shortcomings and Enhancing Resistance Foundations
In winter under low temperatures, although the demand of crops for trace elements such as calcium, magnesium, boron and zinc is lower than that for nitrogen, phosphorus and potassium, the deficiency of these elements will directly lead to a decrease in the crop's cold resistance (for example, calcium deficiency can cause root rot, and boron deficiency affects nutrient transportation). Moreover, the activity of trace elements in the soil weakens as the temperature drops, and problems such as "the crop needs them, but the soil has them but it's difficult to absorb" may occur. Therefore, targeted supplementation is necessary.
Calcium fertilizer: Nitric calcium and calcium chloride are preferred. Nitric calcium has a high solubility and quick absorption, and can be applied by foliar spraying or drenching. This helps prevent fruit cracking (such as in winter greenhouse tomatoes and strawberries) and root necrosis due to calcium deficiency in crops. Calcium chloride is highly effective but the concentration needs to be controlled to avoid stimulating the roots with high concentrations, making it suitable for emergency supplementation.
Magnesium fertilizer: Mainly composed of magnesium sulfate. Magnesium is a crucial element for the synthesis of chlorophyll. Supplementing magnesium at low temperatures can prevent the loss of green color in crop leaves and the decline in photosynthetic efficiency. It can be combined with nitrogen fertilizer for topdressing, or sprayed on the leaves of fruit trees and vegetables.
Boron and zinc fertilizers: Use borax and zinc sulfate. Boron can promote the development of crop roots and nutrient transportation, while zinc can enhance the cold resistance of crops and prevent stunted growth. Both are mainly applied through foliar spraying. The dosage is small and absorption is fast, avoiding fixation in the soil during application. They are particularly suitable for winter wheat, rape, and greenhouse fruits and vegetables.
4. Composted Organic Fertilizer: Improves soil environment and provides long-lasting nutrients to nourish the roots.
The low temperatures in winter not only affect the growth of crops, but also lead to soil compaction and decreased air permeability. Composted organic fertilizer, on the other hand, has the dual functions of "improving the soil" and "providing long-term fertilizer supply". It can not only increase the organic matter content in the soil, improve the soil aggregate structure, enhance the soil's ability to retain heat, water and nutrients, creating a warm and loose environment for the roots to grow, but also slowly release nutrients, avoiding the damage caused by excessive quick-release fertilizers. It reserves nutrients for the crops to survive the winter and return to green in spring.
Suitable varieties include decomposed livestock and poultry manure (chicken manure, sheep manure), compost, and composted manure. It is important to note that only "fully decomposed" organic fertilizers should be selected. Uncomposted organic fertilizers will continue to ferment and release heat in the soil, which may burn the roots of the crops and also cause diseases and pests. When applying, it is recommended to use "ditch application" or "hole application", placing the organic fertilizer 10-15 centimeters below the roots of the crops to avoid direct contact with the roots. At the same time, a small amount of quick-release phosphorus and potassium fertilizers can be combined to achieve a combination of "long-term effect + quick effect", improving the fertilization effect, especially suitable for fruit trees, seedlings, and overwintering field crops.
