Preventing Wheat Frost Damage
Wheat frost occurs when the temperature at ground level suddenly drops below 0°C, falling below the minimum temperature that wheat can withstand at a certain stage of development, causing freeze damage. After wheat jointing, its cold resistance gradually weakens, making it prone to late frost damage. Wheat affected by frost damage may show symptoms such as stem injury, yellowing and twisting of leaves, severe cases may lead to plant wilting, and even cause freezing of the stamens and pistils in the ear, leading to flower degeneration, reduced fruiting rate, and ultimately affecting yield. Therefore, it is important to strengthen prediction, forecasting, and preventive measures. Common prevention methods include:
1. Irrigation: The role of irrigation in preventing frost includes:
- First, the water temperature during irrigation is higher than the soil temperature during frost occurrence (sometimes more than 10°C higher). Thus, pre-frost irrigation brings a significant amount of heat.
- Second, after irrigation, the moisture content in the soil increases the soil's thermal conductivity, allowing heat from deeper soil layers to rise.
- Third, due to water's much larger specific heat capacity compared to air and soil, irrigation reduces surface temperature fluctuations and prevents sudden temperature changes.
- Fourth, irrigation increases the humidity in the near-ground air layer, releasing latent heat during condensation.
In areas with sprinkler irrigation, spraying water during frost helps regulate the microclimate in the field and effectively prevents frost damage. Investigations have shown that irrigation before frost can increase ground temperature by 1-3°C (with a maximum of 4.1°C), and leaf surface temperature by 0.2-0.7°C, significantly reducing frost damage.
2. Smoking: Using straw for smoking to prevent frost has a long history in many regions. In areas where fuel is scarce, CHN chemical smoke agents (composed of ammonium nitrate, heavy oil, and sawdust) can be used. The primary functions of smoke in frost prevention are:
- First, burning forms a smokescreen that attracts radiated heat within the smoke, reducing ground radiation cooling and preventing excessive heat loss from the soil and plants.
- Second, the burning of smoke agents releases heat, increasing air temperature.
- Third, when water vapor condenses on smoke particles, latent heat is released, further raising the air temperature.
The timing of smoking is crucial; it should neither be too early nor too late. Generally, smoking begins when the leaf surface temperature drops to 1°C above the frost threshold. A unified ignition time must be announced to ensure quality and achieve good results.
3. Selecting Frost-Resistant Varieties: In regions prone to frost, late spring frost damage is common. Therefore, planting varieties that joint later and are more frost-resistant is recommended. Early-jointing varieties are more susceptible to frost damage, whereas late-jointing varieties exhibit stronger cold resistance and suffer less frost damage when late frosts occur.
4. Enhancing Cultivation Management to Improve Wheat's Frost Resistance: Strengthening cultivation practices can help improve wheat's ability to resist frost damage.
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