The root system of lettuce was cut off because of seedling transplanting, and the fibrous roots were developed, which were distributed in shallow soil layer (20 ~ 30 cm). The absorption of water and fertilizer by lettuce mainly depends on the absorption capacity of fibrous roots. Pay attention to shallow fertilization depth when fertilizing, so as to facilitate root absorption and reduce fertilizer loss. If the fertilizer is applied too deeply, the roots can't be used. The root system of lettuce has a high demand for oxygen, which requires good permeability of soil, which is beneficial to the root system to absorb oxygen. The root system of lettuce develops well in loam rich in organic matter, and has strong water and fertilizer conservation ability; In the soil lacking organic matter, poor ventilation and poor soil, the root system is underdeveloped, the ability to absorb nutrients is weak, the expansion of leaf area is blocked, and the leaf bulbs are small, not full and of poor quality. Increasing the application of organic fertilizer and increasing the content of organic matter in soil have great influence on the root system and even the yield of lettuce, which should be paid attention to.
Lettuce should not be short of nitrogen at all stages. According to Garten's research, nitrogen deficiency will inhibit the differentiation of lettuce leaves and reduce the number of leaves at any time. Seedling stage is the main differentiation stage of leaves, and one leaf is differentiated every two days on average. Nitrogen deficiency at seedling stage will hinder the differentiation of leaves, reduce the number of leaves, reduce the leaf area at rosette stage, reduce the assimilation area, have small balls, light weight and low yield at fruiting stage. The results showed that even if nitrogen fertilizer was applied in the late seedling stage, it could not completely make up for the phenomenon of less leaf differentiation caused by lack of fertilizer in the seedling stage, and the number of leaves no longer increased, so the lack of nitrogen in the seedling stage had the most significant effect on the late yield. Lettuce seedlings must attach importance to nitrogen nutrition, strive to expand leaf area, improve photosynthetic capacity, increase dry matter production and promote leaf differentiation and development. Lack of phosphorus at seedling stage not only leads to less leaves, but also makes plants thin and short, leaves dark green, growth decline and yield decline. Potassium plays an important role in the formation of leaf bulb. Potassium can promote the formation of leaf bulbs, make them compact, promote the transport of nutrients made by rosette leaves to leaf bulbs, make them compact, enrich the weight of leaf bulbs, and have high clean vegetable rate. Therefore, potassium deficiency has little effect on leaf differentiation at any time, but affects leaf weight, especially at heading stage, which will significantly reduce lettuce yield. According to the experimental results, while keeping the proper balance of nitrogen and potassium, the lettuce must fully absorb nitrogen and phosphorus to transport the dry matter to the bulbs. The outer leaves are not heavy, but the bulbs are heavy. If there is more nitrogen and less potassium, more dry matter will be distributed to the leaves outside. Although the leaves outside are heavy and the bulbs are light, the bulbs are loose, showing a state of virtual length and slender leaves. According to the analysis, during the growth period of 120 days, lettuce with per mu yield 1500 kg absorbed 3.8 kg of nitrogen, 1.8 kg of phosphorus and 6.7 kg of potassium. Partial application of nitrogen fertilizer, while lack of potassium and calcium is easy to cause top burning disease and reduce production. Calcium deficiency in soil often causes "dry heartburn".
Because the growth period of lettuce is shorter than that of other vegetables, it is essential to apply fertilizer during the whole growth period, so it is necessary to apply fertilizer in time to meet its growth needs, and at the same time pay attention to the reasonable ratio of nitrogen, phosphorus and potassium.
(1) Seedbed fertilization.
Lettuce usually adopts seedling transplanting method. Every 65,438+00 square meters of seedbed, about 65,438+00 kilograms of fully decomposed and sieved organic fertilizer should be applied, and 0.3 kilograms of ammonium sulfate, 0.5 kilograms of calcium superphosphate and 0.2 kilograms of potassium sulfate should be added and fully mixed with the seedbed soil.
(2) Nutrient soil for seedling separation is prepared with reference to Chinese cabbage.
(3) Planting base fertilizer.
Per mu yield 1, 000 ~ 2,000 kg. Applying decomposed organic fertilizer or furrow application can increase soil organic matter and enhance soil permeability.
(4) topdressing.
Because a large part of lettuce is for human consumption, human feces should not be poured into fertilization. Fertilizer is suitable for fertilization. Top dressing for the first time: about 65,438+00 days after planting, slowly water the seedlings and apply about 5 kilograms of urea per mu. Second and third topdressing: topdressing once every 10 day after the first time, topdressing urea 5 ~ 10 kg per mu, and watering in coordination. After the lettuce is sealed, it is generally no longer fertilized and watered.