Key Points of Topdressing Techniques and Yield-Increasing Methods for Dry-Raised Rice Seedlings

The seedbed for dry-raised rice seedlings is carefully and rigorously fertilised. Its total nutrient supply can fully meet the fertiliser requirements for the growth of dry-raised seedlings, and the nutrients are comprehensive with a high content of readily available fertiliser. However, because the seedbed soil is in a relatively dry or semi-dry state, the mobility of nutrients is poor, leading to insufficient nutrient uptake by the roots and a disguised nutrient deficiency; secondly, because dry-raised seedlings have less free water flowing within their bodies and weaker transpiration, the transport and distribution of fertiliser nutrients within the plant are impeded, which can also cause a disguised nutrient deficiency.

After dry-raised rice seedlings reach the four-leaf stage, as leaf age increases, the growth of above-ground stems, leaves and tillers continuously increases, and the daily increment of required nutrient elements also continuously increases. Fertiliser supply becomes relatively insufficient, and the contradiction of nutrient deficiency is exposed. When cultivating medium or large seedlings, symptoms of yellowing and loss of vigour in dry-raised seedlings often appear, so fertiliser must be topdressed at the right time and in the right amount.

1. The leaf colour of dry-raised seedlings is generally relatively dark green, and nutrient deficiency is not easily detected in the early stage. When leaves begin to turn yellow, it indicates that the degree of nutrient deficiency is more severe than that of wet-raised seedlings with the same leaf colour.

2. The type of fertiliser used for dry-raised seedlings should take into account the dry characteristics of the seedbed. High-quality urea is the best choice; other volatile fertilisers must not be applied. At the same time, it must not be broadcast directly; instead, it should be applied by spraying with fertiliser water to prevent leaf burn or seedling damage caused by excessively high fertiliser concentration. If chemical fertiliser is to be broadcast directly, it must be immediately rinsed with water after broadcasting.

3. Nutrient deficiency in dry-raised seedlings is caused by water shortage, so when topdressing, too much fertiliser should not be applied at one time. A 1%-2% urea solution should be sprayed to avoid seedling burn, and also to allow the fertiliser to enter the soil and improve fertiliser efficiency. However, applying fertiliser solution is the same as watering: it should be done in the evening, preferably simultaneously with water replenishment. The amount of fertiliser and water used must be strictly controlled to prevent weakening the physiological effects of dry-raised seedlings.

To give full play to the yield-increasing advantages of dry-raised rice seedlings, shallow transplanting and sparse planting must be carried out. The following work should be done well at transplanting:

1. Fertilisation and land preparation.

After the transplanting field is ploughed up, apply 1500-2000 kg of organic fertiliser per mu as base fertiliser, and apply 15-20 kg of ground phosphate rock as middle-layer fertiliser, 10 kg of potassium fertiliser and 10-15 kg of urea per mu. For zinc-deficient fields, apply an additional 0.5-1 kg of zinc sulfate. For wheat fields and poor fields, apply appropriately more; for broad bean fields and fertile fields, apply appropriately less. During land preparation, first dry-plough and dry-harrow, and finally flood and level the field, achieving a level field and fine soil. After the field is levelled, let it settle for 1-2 days, which helps shallow-transplanted seedlings avoid lodging.

2. Skillful pulling of dry-raised seedlings.

Dry-raised seedlings have short new roots and brittle old roots, so pulling seedlings is labour-saving. Do not water or irrigate 2-3 days before pulling seedlings, otherwise it will weaken the “explosive effect” of dry-raised seedlings after transplanting, and the seedlings will still lodge or need replacing after transplanting. Water thoroughly the evening before pulling seedlings. When pulling seedlings, use an iron shovel or nail rake to dig deep into the seedling field first, then pull the seedlings. It is even better if the seedling roots carry a small amount of soil when transplanted.

3. Transplanting in shallow water.

When transplanting, the water layer in the field must not exceed 2 cm. It is sufficient that the transplanted seedlings do not lodge or float. The general transplanting depth is 2 cm. If transplanted too deep, the young leaves of the seedlings remain submerged in water for a long time, which easily leads to seedling death; the mud temperature around the roots is low, tillering and tiller development are slow, and the tillering node position is high, making it difficult to form large panicles and large grains.

4. Reasonable sparse planting.

Sparse planting of dry-raised seedlings should be comprehensively considered based on the biological characteristics of the variety, soil fertility, climatic conditions, yield level and other factors, with the aim of achieving high quality and high yield. If transplanting is too dense, during the tillering stage the large tillers are not strong while small tillers keep emerging, causing the field population to be too large, poor ventilation and light penetration, and severe disease. It is also unfavourable for defending against “overcast damage” weather and “low temperatures during the heading and flowering stage”, resulting in a low seed-setting rate. According to different sparse planting experiments conducted by the agricultural technology department and the municipal meteorological bureau of Dali City: for hybrid rice in Dali City, a plant-row spacing of (4*5) cun, 30,000 hills per mu, and 30,000-50,000 seedlings per mu. For japonica rice, 3*5 (cun), 40,000 hills per mu, and 40,000-70,000 seedlings per mu are suitable. For high-fertility fields and areas with good heat conditions, planting can be sparser; for cold-waterlogged fields and areas with poor heat conditions, planting can be appropriately denser.