How should weak winter wheat seedlings be managed?
After winter wheat emerges, due to the influence of natural conditions and cultivation measures, various types of weak seedlings often form. Weak seedling conditions should be managed according to the specific cause, as described below one by one:
1. Weak seedlings caused by soil drought mostly occur in wheat fields with insufficient subsoil moisture or where moisture is lost through ventilation. Their characteristics are: slow emergence of tillers, grayish-green leaf color, short and small central leaves, slow or stalled growth (what people call “shriveled-heart seedlings”), and middle and lower leaves gradually turning yellow and drying up, with few and fine roots. Key management points: combined with watering, apply 15 kg of ammonium bicarbonate per mu.
2. Weak seedlings caused by soil nitrogen deficiency are thin and weak, standing upright, with reduced tillering, narrow and short leaves, and lower leaves that begin turning yellow and drying from the leaf tip and gradually spread to the upper leaves. Key management points: use 7-8 kg of urea per mu, or 20-25 kg of ammonium bicarbonate, applied in furrows between rows or watered on after mixing with water.
3. Weak seedlings caused by soil phosphorus deficiency show poor root development, few and weak secondary roots, dark green dull leaf color, purple-red leaf tips and leaf sheaths, stunted and small plants, and reduced tillering. Key management points: combined with watering and hoeing, apply 20-30 kg of superphosphate per mu in furrows opened between rows; the earlier the application, the better the effect.
4. Weak seedlings caused by waterlogged compacted soil or salt-alkali damage usually show poor root development, weak absorption capacity, and slow emergence of tillers, often accompanied by nutrient deficiency symptoms; in plots with severe salt-alkali damage, patches of purple-red “little old seedlings” often appear, the basal 1-2 leaves of the seedlings turn yellow and dry up, and in severe cases the seedlings die in spots and patches. Key management points: combined with deep intertillage, open furrows and apply a mixed nitrogen and phosphorus fertilizer; in plots with severe salt-alkali damage, irrigate after topdressing to press down salts, and promptly hoe and loosen the soil to break up crusting.
5. Weak seedlings caused by hard compacted soil are due to lack of soil moisture and air, making root extension difficult, causing wheat leaves to be yellow and short and tillers to fail to appear on time. Key management points: first water promptly, then deep intertill and loosen the soil to break up the hard layer.
6. Weak seedlings caused by excessively wet soil usually show pale purple leaf color, slow emergence of tillers, and in severe cases leaf tips turning white and drying up. Key management points: first deep intertill promptly to disperse moisture and improve aeration, then apply a small amount of quick-acting chemical fertilizer to promote early seedling growth.
7. Weak seedlings caused by excessive seeding rate show: seedlings crowded together, plants thin and weak, slender. Key management points: first promptly thin the seedlings, especially at the field edges, borders, and the “clumped seedlings” within the field, which should be thinned early and severely, then combined with watering, apply a small amount of quick-acting nitrogen and phosphorus fertilizer to compensate for excessive consumption of soil nutrients and promote the wheat seedlings to turn from weak to strong.
8. Weak seedlings caused by sowing too deep show: slow emergence, slender leaf sheaths, delayed tillering, and no secondary roots. Key management points: first scrape away soil to clear the crown, then topdress promptly (apply 15 kg of ammonium bicarbonate per mu) to promote root and seedling development.
9. Weak seedlings caused by sowing too shallow are due to the tillering node being too close to the soil surface, with poor moisture and nutrient conditions, inhibiting root growth and tiller bud development, thus usually showing reduced roots and tillers, yellow and weak plants, and susceptibility to freezing injury and death. Key management points: combined with hoeing, earth up around the roots; when aboveground growth has basically stopped, break the ridge and cover with soil. The soil cover thickness should be such that the tillering node is about 3 cm below the soil surface; if using imported soil cover, that is, covering sand with clay or covering clay with sandy soil, the soil can also be improved.
10. Weak seedlings caused by sowing too late are mostly due to a short pre-winter growth period and insufficient accumulated temperature, resulting in thin and weak wheat seedlings and few tillers. Key management points: focus on hoeing and supplemental fertilizer and water, apply 15 kg of ammonium bicarbonate per mu at the three-leaf stage; for wheat fields with poor soil moisture and rapid water infiltration, irrigate with tillering water promptly after the three-leaf stage (but for plots with suitable moisture or heavy clay soil and poor water permeability, do not water before winter), and for the last hoeing before freezing, pay attention to earthing up around the roots to protect the seedlings for safe overwintering.