International Journal of Horticulture, 2024, Vol.14, No.6, 355-367 http://hortherbpublisher.com/index.php/ijh 359 3.3 The relationship between sunlight duration and photosynthetic efficiency Photoperiod directly affects biomass production in rapeseed. Longer daylight hours enhance photosynthetic activity, increase biomass accumulation, and improve yield potential. A study on rapeseed production in the Yangtze River Basin, China, indicated that factors like photoperiod during growth stages significantly impact biomass and leaf area index (Xu et al., 2021). In high-altitude regions, extended daylight hours have been shown to substantially boost rapeseed yield by increasing the number of siliques and seed weight (Xiong et al., 2022). Additionally, research suggests that early sowing (e.g., mid-October) can extend the photosynthetic period, significantly enhancing biomass accumulation and yield. In contrast, delayed sowing shortens the growth duration, thus reducing yield (Kaur et al., 2018). Therefore, optimizing sowing dates to align with periods of maximum sunlight is a strategy to improve biomass production and overall yield. In areas with shorter daylight, supplemental lighting or selecting high photosynthetic efficiency varieties can mitigate limitations caused by insufficient light (Li et al., 2022). 4 Soil Fertility and Nutrient Management 4.1 Suitability of soil types for rapeseed growth Soil texture significantly influences root development in rapeseed. In the Yangtze River Basin, subsoil tillage (Sub-T) has been shown to reduce soil bulk density and penetration resistance, which in turn promotes root and shoot growth of rapeseed. This method enhances the concentration of moisture, total nitrogen, organic matter, and available nutrients in the soil, thereby improving root bleeding sap and root hormone levels, which are crucial for robust root development (Wang et al., 2021). Additionally, poorly drained clay soils in this region negatively affect rapeseed growth, highlighting the importance of soil texture in crop productivity. Soil pH is another critical factor affecting nutrient availability for rapeseed. Biochar application has been found to significantly increase soil pH, which in turn enhances the availability of phosphorus, organic carbon, and other essential nutrients (Jin et al., 2019; Liu et al., 2022). In upland red soils, biochar amendments improved soil pH and nutrient availability, leading to increased rapeseed yield, although these benefits diminished over time. Similarly, the combined application of biochar with organic and inorganic fertilizers improved soil pH and nutrient availability, promoting rapeseed growth in purple soils. 4.2 Roles of key nutrients Nitrogen (N) is a vital nutrient for rapeseed, significantly impacting plant vigor and yield. Studies have shown that nitrogen application enhances leaf chlorophyll content, leaf area, and the quantum yield of photosystem II, which are essential for photosynthesis and plant growth (Zangani et al., 2021). Optimal nitrogen rates have been identified to maximize rapeseed yield, with higher nitrogen levels leading to increased seed and oil yield (Grzebisz et al., 2020; Zangani et al., 2021). However, excessive nitrogen can lead to nutrient imbalances and reduced efficiency in nutrient uptake (Khan et al., 2020). Phosphorus (P) and potassium (K) play crucial roles in the flowering and seed formation of rapeseed. Phosphorus application has been shown to increase leaf stomatal conductance and the quantum yield of photosystem II during the early flowering stage, thereby enhancing seed yield and quality (Zangani et al., 2021). Potassium, along with phosphorus, is essential for nutrient uptake and overall plant health. Studies have demonstrated that the combined application of phosphorus and potassium significantly improves rapeseed yield and nutrient status (Grzebisz et al., 2020; Zangani et al., 2021). 4.3 Effects of trace elements on quality and disease resistance Micronutrients such as sulfur (S) and boron (B) are critical for improving the oil quality of rapeseed. Sulfur is essential for the biosynthesis of glucosinolates and sulfur-containing amino acids, which are important for oil quality (Basumatary et al., 2021; 2022). The combined application of sulfur and boron has been shown to enhance the oil content and protein quality of rapeseed seeds, thereby improving the overall quality of the crop.
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