Effects of cropping practices and nitrogen application on nutrient uptake characteristics and root vigor of hybrid indica rice

To explore the effects of different planting methods and nitrogen application rates on nutrient absorption characteristics, root activity, and yield of hybrid indica rice, F You 498 was used as the experimental material in a two-factor split-plot design. The main plot consisted of carpet seedling machine transplanting, wet precision hole direct seeding, and manual transplanting, while the sub-plot included four nitrogen application rates (0 kg hm-2, 90 kg hm-2, 135 kg hm-2, and 180 kg hm-2). The effects on nitrogen, phosphorus, and potassium accumulation, root activity, yield, and yield components of hybrid indica rice under different treatments were studied. The results showed that the total nitrogen accumulation at the heading and maturity stages was highest in manually transplanted rice, followed by mechanical transplanting, and then direct seeding. The total phosphorus accumulation at the jointing stage and potassium accumulation at the heading stage were also highest in manually transplanted rice. The nutrient accumulation rate of nitrogen, phosphorus, and potassium before jointing was highest in direct-seeded rice, being 40.68%-63.64% and 19.42%-71.43% higher than in mechanical and manual transplanting, respectively. The nutrient accumulation rate peaked from jointing to heading stage under different planting methods. There was no significant difference in rice yield between manual and mechanical transplanting. However, compared to manual transplanting, direct seeding reduced rice yield by 8.09%-15.00%. The 1000-grain weight, grain number per panicle, and seed setting rate of manually transplanted rice were higher than those of mechanical transplanting and direct seeding, but the effective panicle number was significantly reduced, being 15.99%-41.77% and 23.19%-29.60% lower than those of mechanical transplanting and direct seeding, respectively. The dry matter accumulation of shoots and roots reached its maximum at the maturity and heading stages, respectively. Under manual transplanting conditions, the dry weight of shoots and roots at maturity was greater than that of mechanical transplanting and direct seeding. As the growth process advanced, the bleeding intensity of single stems and populations after heading gradually decreased, and the root activity of single stems and populations in mechanical transplanting was significantly higher than in manual transplanting and direct seeding. The optimal nitrogen application rate for machine-transplanted rice was in the middle to low range (90-135 kg hm-2), while for direct-seeded and manually transplanted rice, it was in the middle to high range (135-180 kg hm-2).