Seedling quality regulation of rice potted-seedling in mechanical transplanting

Abstract: Rice potted-seedling of mechanical transplanting, which adopt a new type of transplanter with a certain line of planting distance, is a major technological innovation on rice production. In recent years, the technology has increased production significantly in Jiangsu, Heilongjiang, Anhui, and Jiangxi, etc. In order to promote the technology, Yangzhou University has been conducting research on rice potted-seedling in mechanical transplanting, with several units cooperating. This paper selected Wuyunjing24 as experimental material to investigate the effects of seedling quality caused by different sowing densities, irrigation management and twice chemical regulations of rice potted-seedlings in mechanical transplanting. The results indicated: 1) as the number increased, the quality of potted-seedings tended to be inferior; it was mainly reflected in the delicate seedlings, the reduction of dry weight, poor plumpness, poor root development, et al. High sowing density consumed a large number of seeds, so the seedling populations received restrictive ventilation and light, and also the competition among the individual plants became intense in each bowl of the nursing tray, and those resulted in poor quality which was not conducive to high yield. Seedlings of a low sowing density had enough space to absorb nutrition, and the seedling quality was optimized. The soil in the potted-tray, however, would have intensive lumpy forms in low probability, which was difficult to cooperate with the rice transplanter. Besides, the thin planting and high leakage rate made it hard to meet the requirements of high yield. The suitable sowing amount of the normal japonica rice, Wuyunjing24, with a large fringe, was 45-60 g in each potted tray, and on average, there were 3-4 strains of plants per plastic hole. 2) Regarding the water management, the dry rice seedling had more tiller and higher chlorophyll content than the seedlings in the moist environment. Dry management delayed the stagnant growth period of tiller, and the degradation rate of chlorophyll was low, which improved the seedlings' ability to maintain green. Under the experimental conditions, the seedling ages could be extended to 35 days. 3) Twice chemical regulations, by analyzing the seedling plumpness through the orthogonal design of seedling-strengthening agent, MET, water management, sowing densities, was determined as the optimal combination. Timely and appropriate twice chemical regulations could approve seedling plumpness and quality significantly, and it could achieve the uniformity of seedlings in height. To achieve seedling of the best quality, the optimal method was that in the condition of 45 g per potted tray under dry management, mixing up 100 kg subsoil with a 0.5 kg seedling-strengthening agent, and spraying 0.06g MET per tray in the two-leaf period.