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Fertilization Techniques for Main Vegetables in Protected Fields
The common features of fertilizer requirements:
1. Nutrient demand: Vegetables typically have a high biological yield, which means they require more nutrients per hectare compared to staple crops like cereals. For example, the average nitrogen uptake by vegetables is 4.4 times higher than that of wheat, while phosphorus is 0.2 times and potassium is 1.9 times higher. Additionally, calcium intake is 4.3 times greater, and magnesium is 0.5 times higher in vegetables.
2. Nutrient content in plant parts: The levels of nitrogen, phosphorus, and potassium in the stems and leaves of vegetables are significantly higher than in rice and wheat—6.52, 7.08, and 2.32 times, respectively. In contrast, the nutrient content in the seeds or edible parts of vegetables is lower compared to rice and wheat, with nitrogen at 2.04 times, phosphorus at 1.49 times, and potassium at 6.91 times. This indicates that vegetable harvests remove more nutrients from the soil, increasing the need for regular fertilization.
3. Special nutrient needs: Certain vegetables have specific nutritional requirements. They often prefer nitrate nitrogen, have a high demand for potassium and calcium, and are more sensitive to boron and molybdenum. These factors must be considered when designing fertilization strategies to ensure optimal growth and quality.
Protected area soil characteristics:
1. Soil nutrient status: According to soil surveys conducted in greenhouses across eight cities in Shandong Province, including Jinan, Tai’an, Jining, Linyi, Rizhao, Heze, Zibo, and Weifang, the nutrient levels inside greenhouses were significantly higher than those outside. In the top 0–20 cm soil layer, the average organic matter content was 17.0 g/kg inside greenhouses, compared to 12.5 g/kg outside. Available nitrogen was 126.15 mg/kg inside versus 60.11 mg/kg outside, while available phosphorus was 196.68 mg/kg inside versus 68.45 mg/kg outside. Available potassium was 381.41 mg/kg inside and 180.44 mg/kg outside. Overall, phosphorus levels were highest, followed by nitrogen, potassium, and then organic matter. However, due to varying planting cycles, fertilizer application rates, and types of fertilizers used, the nutrient balance in protected soils can be uneven, requiring careful management through balanced fertilization.
2. Salt accumulation and acidification: A significant portion of greenhouse soil samples showed signs of salinization. Approximately 26.09% of the samples had salt concentrations above 0.2 dS/m, which is 3.78 times higher than outside the greenhouse. The maximum salt content reached up to 1.2%, with an average of 0.27%. Nitrate (NO₃â»), potassium (Kâº), calcium (Ca²âº), magnesium (Mg²âº), chloride (Clâ»), and sulfate (SO₄²â») ions all accumulated in the soil, contributing to increased salinity. This is largely due to improper fertilization practices. Additionally, soil pH in the 0–20 cm layer was found to be 0.46 units lower inside greenhouses compared to outside, indicating a clear trend of acidification. Proper soil management and monitoring are essential to mitigate these issues.