What issues should be noted for winter irrigation of wheat?
Winter irrigation is one of the effective practical experiences for increasing winter wheat yields. To carry out winter irrigation correctly, the following three factors must be considered: temperature, soil moisture, and seedling condition.
The suitable temperature for winter irrigation requires an average daily temperature of about 3°C. If winter irrigation is too early, the temperature is still high, evaporation is large, and it cannot achieve the effect of irrigation and moisture enhancement; at the same time, it can also cause excessive growth of wheat seedlings, making them not cold-resistant. If winter irrigation is too late, the temperature is relatively low, the soil freezes, water cannot infiltrate downward, and ice-crust heaving often occurs, which can cause the wheat seedlings to freeze or suffocate to death. Whenever the average daily temperature at the time of winter irrigation is below 0°C or close to 0°C, there will be varying degrees of freezing damage after irrigation. After winter irrigation, when a cold wave arrives and the temperature drops below 0°C, the soil temperature of winter-irrigated fields is higher than that of non-winter-irrigated fields, which is greatly beneficial for ensuring the safe overwintering of wheat seedlings.
From the perspective of soil moisture, if it is below 70% of field capacity, winter irrigation should be carried out; if it is above 70%, winter irrigation can be appropriately delayed or not carried out, but measures to loosen the soil and preserve moisture should be strengthened to increase soil temperature and promote wheat roots to grow downward, so as to cultivate strong seedlings.
The seedling condition at the time of winter irrigation is also an important condition for considering whether to carry out winter irrigation. Vigorous seedlings generally do not lack water or fertilizer, so there is no need for winter irrigation. Weak seedlings (especially late-sown wheat and single-stem solitary seedlings) are also not suitable for winter irrigation, in order to prevent silted seedlings, ice-crust heaving, and freezing damage to wheat seedlings, or even dead seedlings. For such weak seedlings, winter water can be changed to tillering water, using water to regulate fertilizer and fertilizer to promote seedlings, so that the wheat seedlings turn from weak to strong. In low-lying wet wheat fields, soil aeration is poor, and after winter irrigation the wheat seedlings are prone to turning red, turning yellow, or even suffocating to death. For such wheat fields, when pre-sowing irrigation has been applied and sowing was done with sufficient soil moisture, strengthening intertillage and moisture-preservation measures after tillering means winter irrigation does not need to be considered.
The amount of winter irrigation water must not be too large, so as to avoid standing water on the ground, which under low temperatures can form an ice shell, causing the aboveground part of the plants to freeze, the root system to suffocate, and tillers to die, thus reducing yield.
After winter irrigation, it is necessary to timely harrow and loosen the soil to avoid soil compaction and cracking damage. Late-sown wheat must be given special attention. In addition to preserving moisture, preventing soil compaction and cracking, and improving aeration, harrowing and loosening the soil can also increase the soil temperature at 0-10 cm by about 1°C, which is beneficial for promoting seedling growth.