Lettuce yields are high, and its growth requires various nutrients such as nitrogen, phosphorus, and potassium simultaneously. Different growth stages have varying demands for these nutrients, so often, we need to use a combination of different water-soluble fertilizers and foliar sprays.
The early growth stage is the peak period for lettuce nutrient absorption, during which the lettuce grows rapidly, with nitrogen uptake accounting for over 80% of the entire growth cycle. It is advisable to use high-nitrogen foliar fertilizers, such as Sheride's DeCui (Rare Earth Peptide Nitrogen Fertilizer). A nitrogen deficiency during the early growth stage leads to fewer leaves and smaller plants, with dark green foliage and a decline in growth vigor. The early growth stage is also the critical period for phosphorus nutrition, so a high-phosphorus foliar fertilizer should be used. A potassium deficiency during the growth and heading stages does not significantly affect leaf differentiation but impacts leaf weight. Therefore, when heading lettuce begins to form heads, it is crucial to maintain a proper balance of nitrogen and potassium nutrients while absorbing sufficient nitrogen and phosphorus, to quickly transport assimilates to the head, improve the net vegetable yield, and product quality. If nitrogen is excessive and potassium is insufficient, the outer leaves may grow excessively, leading to elongation and a narrower leaf shape, with the head also becoming elongated. This stage is suitable for balanced water-soluble fertilizers. A rational combination of various element fertilizers is necessary to achieve ideal returns.
Lettuce is a crop with a high demand for calcium, requiring approximately 1kg of calcium for every 1000kg produced. The absorption of calcium exceeds that of phosphorus, especially during the heading stage, where physiological calcium deficiency due to factors like weather and fertilization can easily occur, leading to physiological diseases such as dry heart and cracked heads. Calcium fertilizers have poor mobility in the soil and plant, with basal application being the primary method. During the peak fruiting period of lettuce, the calcium demand of the plant rapidly increases. At this time, it is necessary to supplement calcium through foliar sprays of calcium-rich foliar fertilizers, such as Sirede's chelated calcium. As for trace elements, lettuce responds differently to various elements. Its reaction to iron is particularly pronounced, while its response to manganese, boron, zinc, and molybdenum is more general. Iron deficiency in lettuce can block the synthesis of chlorophyll, resulting in uniformly yellowing leaves, with the top leaves becoming more severely yellow. To address iron deficiency in lettuce, a 0.2%-0.5% iron sulfate solution can be applied via foliar spray. Spraying manganese solution (MnCl2) can increase the plant height, number of leaves, stoma count, chlorophyll content, soluble sugar content, soluble protein content, and proline content in lettuce. Spraying selenium solution can enhance the chlorophyll, amino acids, and vitamin C content in lettuce leaves. Additionally, the use of amino acid-containing foliar fertilizers can improve lettuce yield and quality.