International Journal of Horticulture, 2024, Vol.14, No.6, 355-367 http://hortherbpublisher.com/index.php/ijh 360 Trace elements also play a significant role in enhancing disease resistance in rapeseed. Micronutrients such as magnesium (Mg) have been found to improve the nutritional status of plants, thereby enhancing their resistance to diseases (Geng et al., 2021). Improved magnesium nutrition not only increases seed yield and quality but also enhances the uptake of other essential nutrients like nitrogen and phosphorus, contributing to better plant health and disease resistance. 5 Planting Density and Field Management 5.1 Impact of planting density on yield Optimal planting density is crucial for maximizing rapeseed yield. Studies have shown that the highest yields are often achieved at moderate planting densities. For instance, a planting density of 22.5×104 plant/ha combined with high fertilization rates resulted in the highest seed oil and protein yields (Tian et al., 2020). Similarly, the CROPGRO-Canola model simulations indicated that an optimal planting density of 45-75 plants/m2, along with appropriate nitrogen rates, maximizes yield (Wang et al., 2022). Another study found that a density of 30.0×104 plants/ha with 144 kg N/ha was optimal for high yield and nitrogen utilization efficiency (Zhao, 2022). Overcrowding can negatively impact plant health and yield. High planting densities can lead to reduced photosynthetic rates, lower pod numbers per plant, and increased competition for resources, ultimately reducing individual plant yield (Li et al., 2018). Additionally, excessive density can increase the lodging index, which negatively affects seed oil content and overall plant stability. Overcrowding also reduces biomass accumulation and root-to-shoot ratios, leading to lower survival rates after mechanized transplanting (Zuo et al., 2022). 5.2 Key measures for weed and pest management Effective weed control is essential for optimizing rapeseed yield. Integrated weed management strategies, including timely planting and appropriate planting densities, can significantly reduce weed pressure. Higher planting densities have been shown to inhibit weed growth by reducing the space available for weeds to establish (Li et al., 2018). Additionally, the use of mulching can suppress weed growth by creating a physical barrier and altering soil conditions unfavorable for weed germination (Feng et al., 2020). Combining biological and chemical pest control methods can effectively manage pest populations in rapeseed fields. Biological control involves using natural predators or parasites to reduce pest numbers, while chemical control uses pesticides. Studies have shown that integrated pest management (IPM) strategies, which combine these methods, can improve yield and reduce the reliance on chemical pesticides, thereby minimizing environmental impact (Zhang et al., 2020). Effective pest control is crucial for maintaining plant health and maximizing yield potential. 5.3 Mulching and soil moisture management Mulching is a crucial practice for managing soil moisture and improving rapeseed yield, especially in regions with fluctuating climate conditions. Feng et al. (2020) conducted a field experiment during rainy and drought seasons in Southwest China to analyze the effects of different cultivation methods and fertilization strategies on rapeseed growth and resource use efficiency. The results showed that yields were lower in the rainy season than in the drought season. However, the combination of slow-release fertilizer with straw mulching or ridge-furrow rainfall harvesting systems effectively increased rapeseed yield and oil content by 7.71% to 29.93% (Figure 2). Additionally, these combinations significantly improved water and fertilizer use efficiency while reducing total water consumption. Additionally, subsoil tillage (Sub-T) can improve soil properties such as bulk density and penetration resistance, further promoting root and shoot growth and increasing yield by up to 16.5% (Wang et al., 2021). These practices are particularly beneficial in poorly drained soils, such as those found in the Yangtze River Basin, where they can provide lasting improvements in soil conditions and crop yield.
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