Field Crop 2025, Vol.8, No.6, 284-292 http://cropscipublisher.com/index.php/fc 285 for farmers and policymakers to enhance the productivity and environmental sustainability of rice cultivation in subtropical regions. The research results are expected to promote the wider application of mechanical direct seeding technology, thereby supporting the future construction of resilient and profitable rice production systems. 2 Overview of Mechanized Direct-seeded Rice Cultivation Technology 2.1 Basic principles and processes of mechanized direct seeding Mechanical direct seeding of rice is not a new concept, but in specific practice, it avoids the traditional seedling raising and transplanting steps and directly sows the rice seeds into the field with equipment. In terms of methods, they can roughly be divided into dry sowing and wet sowing. The tools used are adapted to local conditions, including precision row seeders and simplified drum-type equipment. Before planting, land preparation is essential. The depth and spacing of sowing should not be arbitrary either. All these need to be well coordinated with nutrient and weed management. If the sowing is accurate and the quantity is well controlled, the seedlings will emerge uniformly, there will be less seed waste, the input will be more efficient, and the returns will naturally not be bad (Sansen et al., 2019). However, not all regions remain unchanged. The differences between dry land and wetland require some adjustments in agricultural machinery and management in order for the technology to be truly implemented. 2.2 Comparison with traditional transplanting methods When comparing mechanical direct seeding rice (DSR) with traditional transplanting rice (PTR), many people first think of how much labor and water can be saved. Indeed, this approach can save 15% to 50% of labor, eliminate the steps of seedling raising and transplanting, and reduce costs by 8% to 19%. In terms of water conservation, DSR also has advantages. It can significantly reduce irrigation water and has low energy consumption, which is conducive to emission reduction. However, one should not only focus on its advantages. It has higher management requirements and is more sensitive to weeds, water conditions and climate change. Studies have pointed out that in the case of inadequate management, the output of DSR may be 2% to 12% lower than that of PTR (Xu et al., 2019; Devi et al., 2024). Of course, this gap can be bridged through more precise operations. From an environmental perspective, although direct seeding reduces methane emissions and is beneficial to the soil, if management fails to keep up, nitrous oxide emissions may increase instead. 2.3 Application bottlenecks in subtropical regions When it comes to promotion, especially in subtropical regions, things haven't gone so smoothly. A practical issue is that as the number of weeds increases, more pesticides are used, and the risk of herbicide resistance also rises. This requires a more complex integrated management plan to deal with. For instance, in low-lying areas or environments with frequent rainfall, it is not easy to keep the seedlings uniform and strong, and the problem of crop lodging occurs from time to time (Figure 1) (Jat et al., 2022). In addition, this method has high requirements for drainage. Once the fields are not unobstructed, the effect is often worse than that of traditional transplanting, and the yield cannot be significantly reduced. There is still a technical threshold for farmers. Many of them have never used live-streaming equipment and are not quite clear about how to fertilize and control weeds. Coupled with the lack of supporting training and services, it is naturally very difficult to promote. In terms of policy, mechanical subsidies and the lagging infrastructure construction are also major shortcomings. Therefore, although this technology has a promising future, for it to truly take root and blossom in subtropical regions, it still relies on more targeted research and policy support. 3 Effects of Sowing Date on Rice Growth and Development 3.1 Impact on germination and seedling stage If sowing is done when the temperature is suitable and the light conditions are sufficient, the possibility of uniform and strong seedlings will be much greater. The period from mid to late May is often regarded as the "window period" for rice, during which the emergence rate is high, the seedlings are full of vitality and grow fast. Conversely, once the sowing is delayed, the seedling environment may not be so ideal. Either the temperature is too low or the light is insufficient. The germination rate will decrease and the entire growth period will be shortened (Shanta et al., 2020). In some years, if late sowing encounters extreme weather conditions, such as
RkJQdWJsaXNoZXIy MjQ4ODYzNA==