Detailed Explanation of Key Points of Fertilization Technology for Machine-Transplanted Rice

The total amount of fertilizer applied to machine-transplanted rice is roughly equivalent to that for manually transplanted rice. However, how it is applied at each stage differs between machine-transplanted rice and ordinary hand-transplanted rice. The main reason is that machine-transplanted rice has lower tillering node positions and a longer tillering period. To keep the number of panicles in the population within an appropriate range, the focus of fertilizer management should be on improving the timing of tillering fertilizer application, so as to regulate and utilize the optimum tillering node positions and control the mid-season population, while increasing the application of panicle fertilizer to promote spikelet differentiation and strive for large panicles.

The characteristics of machine-transplanted rice and hand-transplanted rice determine that the ratio of basal fertilizer to tillering fertilizer within the basal and tillering fertilization for machine-transplanted rice must be significantly different. For ordinary hand-transplanted rice, basal fertilizer accounts for about 70% of the basal and tillering fertilizer, and tillering fertilizer accounts for 30%; whereas for machine-transplanted rice, basal fertilizer should account for 30%-40% of the basal and tillering fertilizer, and tillering fertilizer should account for 60%-70%. This is because machine-transplanted rice has a long seedling recovery period, mechanical transplanting causes severe root damage, and new roots grow slowly. Too much basal fertilizer cannot be utilized by the seedlings, which will lead to fertilizer burn and stunted seedlings, and frequent irrigation and drainage after transplanting will also cause serious fertilizer loss, reducing fertilizer use efficiency. Based on experimental results, generally the first green-turning tillering fertilizer is applied 7 days after transplanting when the second new leaf emerges, combined with the use of a small-seedling herbicide for chemical weed control. The method is to mix urea with a paddy field small-seedling herbicide and moist fine soil, pile and cover for 3-5 hours, then broadcast it in the evening after the field is flooded to a depth of 5-7 cm. After application, keep the field water layer at 5-7 days, and at the same time open a level water gap to prevent rainwater from submerging the rice heart, causing herbicide stunting or even herbicide damage, so as to improve the chemical weed control effect. For fields that have already been treated with a chemical sealant for weed control before transplanting, herbicides must not be used again, to prevent continuous use from causing herbicide damage. Apply tillering fertilizer once more 12-14 days after transplanting; about 18 days after transplanting, apply fertilizer once more depending on seedling conditions, generally ensuring that the vigor can decline in time after the effective tillering leaf age stage. It is essential to avoid applying tillering fertilizer too much or too late, which would cause the population to become too large and affect the panicle-setting rate and the formation of large panicles.

Panicle fertilizer is beneficial both for consolidating the number of panicles and for striving for large panicles, but it is necessary to prevent excessive growth of leaf area so as to form a well-configured canopy structure; it can both expand the sink to form a greater total number of spikelets and strengthen the "source" and smooth the "flow" to form a higher grain-leaf ratio, which helps improve the seed-setting rate and 1000-grain weight. Panicle fertilizer is generally applied twice: flower-promoting fertilizer and flower-preserving fertilizer.

Flower-promoting fertilizer mainly promotes the differentiation of rice panicle branches and spikelets and increases the number of spikelets per panicle. It is generally applied at the initial stage of panicle differentiation, that is, when the leaf age remainder is about 13.5 leaves. The specific application time and amount should be determined according to seedling conditions; if the leaf color fades normally, apply 8-12 kg of urea per mu; if the leaf color is darker and does not fade, the application can be postponed and the amount reduced; if the leaf color is lighter, the flower-promoting fertilizer can be applied 3-5 days earlier and the amount appropriately increased; if the leaf color is darker, it may also be omitted.

Flower-preserving fertilizer is generally applied 18-20 days before heading, that is, when the leaf age remainder is 1.5-1.2. The specific application period should be determined by dissecting more than 10 single stems and checking the leaf age remainder. When the leaf age remainder of 50% of the effective stems and tillers does not exceed 1.2, it is the suitable time for topdressing flower-preserving fertilizer. The amount is generally 7.5 kg of urea per mu. For those with light leaf color and small population growth, more can be applied, but it should not exceed 10 kg/mu; on the contrary, apply less or not at all.