(a) Cultivation Season
Due to the longer growth cycle of Sagittaria, transplants are widely used across the country to enhance multiple cropping. Spring nursery is commonly practiced, with planting carried out in stages. In the Yangtze River basin, seedlings are typically nurtured from mid-April to May and then planted in Daejeon between mid-June and early July. This is referred to as "early water sagittaria," which can be harvested in autumn. Alternatively, it can be planted after the harvest of early indica rice, white rice, or mat grass. Once those crops are collected, planting occurs between late July and August, known as "late water sagittaria," which is harvested in winter and spring.
(b) Seedling Raising Methods
1. Selection of Bulbs: To ensure strong seedlings, high-quality bulbs must be chosen. These should exhibit characteristics of the variety being cultivated, have a moderate size, and be fully mature. The top buds should be about 0.6–1 cm thick.
2. Preparation of Seedbeds: Choose fertile soil that is well-drained and suitable for irrigation. For early water sagittaria, apply 3,000–4,000 kg of organic fertilizer per 666.7 m², plow deeply to 20–25 cm, and create long seedbeds 1.3–1.6 m wide with 30 cm aisles.
3. Planting: Typically done between late April and early May when temperatures exceed 15°C. Top buds are inserted 9–12 cm apart along rows and spacing. Planting density depends on seedling age and soil fertility. Thicker soils allow for more spaced planting, while thinner soils require closer spacing. The top bud should be placed so that one-third is above the soil surface. Insert 1.5–2 cm into the soil, and maintain 2–3 cm of shallow water for 7–10 days to promote root development. Once the coleoptile opens and the first leaf emerges, a thin layer of water is added.
If different sizes of buds are used, they should be planted separately for easier management.
4. Seedling Management: During the sprouting stage, keep 2–3 cm of shallow water to warm the soil and encourage root growth. In case of frost, use deep water at night and shallow water during the day. After 7–10 days, hairy roots begin to grow, and a light application of decomposed manure water (1,000 kg/666.7 m² of 20% solution) can be applied. Weeding begins around 10 days after planting, and pest control is essential.
When seedlings reach 25–30 cm tall with 3–4 leaves, they are ready for transplanting. If the field is not yet prepared, they can remain in the nursery for up to 90 days. As summer heat rises (above 25°C), irrigation depth increases to 6–10 cm. Prevent overgrowth and nutrient deficiency by adjusting water and fertilizer, applying appropriate phosphorus and potassium. Regularly remove old leaves, keeping only 3–4 new central leaves.
(c) Field Planting
1. Soil Preparation and Fertilization: Choose soil with more than 1.5% organic matter and a thick paddy layer. Plow 20 cm deep and apply 66 kg/m² of fertilizer or manure per 666.7 m². Apply 15–20 kg of urea and 30–40 kg of superphosphate as base fertilizer. Water the field to a depth of 2–3 cm before planting.
Base fertilizer provides essential nutrients and improves soil structure, promoting rapid bulb expansion. It is crucial for achieving high yields.
2. Timely and Reasonable Planting: The timing of planting varies with climate and crop schedule. Early varieties should not be planted too early; seedlings should be at least 45 days old, 25–30 cm tall, with 4–5 green leaves. Late varieties should be planted as soon as possible after the previous crop is harvested, as later planting reduces yield due to shorter growing seasons. In the Yangtze River basin, planting should not be delayed beyond late August.
Planting requires shallow water and proper spacing. Early varieties need wider spacing (40–45 cm), while late varieties require narrower spacing (35 cm). Adjust based on soil fertility and plant type. Before planting, remove outer leaves, leaving 25–30 cm of central leaves and petioles to reduce water loss and prevent wind damage. Plant at 9–12 cm depth, ensuring stability. Add a few extra seedlings at the field edges to account for losses. Maintain 2–3 cm of shallow water after planting.
(d) Field Management
1. Water Management: Shallow water and drought prevention are key. During hot and rainy periods, drainage should be considered to avoid leggy growth. In dry conditions, cold water irrigation is needed to prevent disease. In early growth stages, maintain 3–6 cm of shallow water. During the rainy season, control overgrowth by reducing water levels in mid-July to improve plant robustness. Water depth should be adjusted based on seedling condition.
As temperatures rise, increase water depth to 12–20 cm during hot periods. Cold water irrigation at night or early morning helps maintain plant health and microclimate. By mid-August, return to 8–10 cm, and by September–October, maintain 3–5 cm. Keep the soil moist until harvest.
2. Fertilization: Fertilizer application should follow a "promote, control, promote" strategy, using balanced nitrogen, phosphorus, and potassium. Studies show that applying 50 kg of P fertilizer increased yield by 15%. Potash improves quality, making bulbs large, purple-blue, and resistant to storage. Apply 13 kg of potassium chloride per 666.7 m². Apply early and combine with nitrogen and phosphorus.
For early water sagittaria, start fertilizing 10–14 days after planting, using 1,500 kg of decomposed manure water or 30 kg of ammonium bicarbonate plus 10 kg of urea. Later, apply 2,500 kg of decomposed human excrement or 30 kg of urea plus 100 kg of wood ash. Late varieties usually receive one topdressing after 25–30 days.
3. Weeding and Leaf Removal: After planting, conduct weeding and remove old leaves to improve light and air circulation. Remove outer yellow leaves, leaving 4–5 new ones every 15–20 days, 2–4 times total. This enhances photosynthesis and reduces pests. Continue until temperatures drop below 25°C. Protect leaves and roots from damage.
(e) Pest and Disease Control
1. Diseases: Sagittaria is prone to three main diseases:
(1) Smut: Appears as blisters on leaves and petioles, causing discoloration and reduced yield. Control by rotating crops, using disease-free bulbs, removing infected leaves, and applying fungicides like triadimefon and mancozeb.
(2) Asthma Streak: Causes gray-brown spots on leaves. Control through early weeding, destroying diseased tissue, and applying copper-based fungicides.
(3) Brown Spot: Produces dark spots on leaves. Similar to smut in control methods.
2. Pests:
(1) Lotus Root Tube Mites: Harm young leaves, causing curling. Control with insecticides like dimethoate and deltamethrin.
(2) Sagittaria Bore Insects: Larvae bore into petioles, damaging leaves. Clear stubble and spray insecticides.
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