Meniscus Lenses: The Positive Meniscus can increase the NA of the system while only adding slightly to the total spherical aberrations. The Negative Meniscus Lens is used to increase the focal length of another lens while maintaining the angular resolution of the optical assembly. This lens shape is best used when one conjugate is relatively far from the lens. The meniscus lens plays a divergent role in the optical path, and is commonly used in photographic system, objective lens system and laser measuring system.
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The "four essentials" are:
One must be deep. Although the chemical properties of urea are relatively stable, it can be converted to ammonium carbonate in a certain period of time under the action of urease in the soil. Further decomposition of ammonium carbonate produces ammonium bicarbonate and ammonium hydroxide, both of which are unstable and quickly decompose into ammonia and carbon dioxide, which have great volatility, so urea and ammonium bicarbonate, ammonia and other fertilizers The same, but also deep application. This is especially true in calcareous soils and alkaline soils. Urea deep application generally increases the utilization rate of surface application by 15-20%. Deep application of urea in dryland can weaken or eliminate ammonia fumigation and burning seedlings; deep application in paddy fields can prevent nitrogen nitrate leaching and prevent deamination loss caused by denitrification. The farmer said: "The fertilizer is deep into the soil, and the top of the acre is two acres." It makes sense.
Second, we must apply in advance. Because urea needs to be decomposed and transformed by urease in soil, it can be absorbed and utilized by crop roots. Compared with ammonium bicarbonate, ammonium sulfate, ammonium chloride, etc., the fertilizer effect is slow. The speed of urea fertilizer is related to soil organic matter content, ground temperature and moisture content. Among them, temperature factor plays a key role. According to the study, when the temperature is 10 °C, urea conversion takes 7 to 10 days; at 20 °C, it takes 4 to 5 days; at 30 °C, it takes only two days. Therefore, urea should be applied in the summer and autumn high temperature seasons 2 to 3 days earlier than other nitrogen fertilizers; urea should be applied to winter wheat, winter rape and other winter crops at the end of autumn and spring, 6 to 8 days in advance.
Third, we must apply the right amount. Urea has a high nitrogen content and should be used in a smaller amount than other nitrogen fertilizers. Excessive application not only causes waste, but also easily causes crops to be mad, lodging, pests and diseases and burning seedlings. The specific application amount should be calculated according to the crop demand and the amount of ammonia. For example, if you need to apply 20 kg of ammonium bicarbonate, change to 7.5 kg of urea; if you need to apply 15 kg of ammonium nitrate, you can only use 10.7 kg of urea. Experienced farmers said: "Urea and ammonium bicarbonate are not the same.
The fourth is due to the soil. Urea is different from ammonium bicarbonate and ammonium sulfate. After it is applied to farmland, it exists in the molecular state of soil water. Only about 20% can be adsorbed by soil colloid, and this adsorption is not strong, so urea is in the soil. Medium mobility is the most easy to lose. Therefore, urea should be used as the base fertilizer for paddy field. It should be turned into the soil 5 to 7 days before the irrigation; if it is immediately poured after application, the fat loss will be much. If urea is used as top dressing in paddy field, only shallow water layer should be left when fertilizing, and weeding and weeding should be combined after application, and no water should be poured into the field within 2~3 days. If urea is applied in the dry land, it can be properly watered after the surface layer is applied, so that the water can be infiltrated to a depth of 20 to 30 cm, which can play a deep application. This method is adopted for dense crops such as wheat and millet. The fertilizer effect is equivalent to the deep ditch. However, it is forbidden to flood the water after application, so as to avoid urea leaching and reduce fertilizer efficiency. The degree of urea leaching is also related to soil texture. Generally, clay soil and organic-rich soil, urea is not easy to leaching, and urea is easy to leaching on sandy soil.
"Four Don't" is:
Do not mix with alkaline fertilizer or apply at the same time. Urea is applied at the same time as acid fertilizers such as calcium superphosphate and potassium sulfate, and does not lose fertilizer efficiency. However, if it is mixed with or applied with alkaline fertilizers such as grass ash, lime, fly ash, calcium magnesium phosphate, steel slag and phosphate, it will aggravate urea. Nitrogen in the ammonia volatilization loss. Under normal circumstances, urea should be staggered with alkaline fertilizer, summer and autumn high temperature season should be staggered for 3 to 4 days, winter and spring and cold season should be staggered for 7 to 8 days.
Second, do not apply as a seed fertilizer. Under normal circumstances, urea can not be used as seed dressing fertilizer. This is because high concentrations of urea can destroy protein structure, degrade proteins, and affect seed germination. And the biuret contained in urea also has toxicity and inhibition to seeds. According to the test, urea containing more than 1% of biuret and 2.5~5 kg of seed for acre will seriously inhibit seed germination and damage seedling growth. If it is not possible to mix with urea, the amount of seed dressing should not exceed 2.5 kg, except that the dry fertilizer is mixed.
3. Do not water immediately after application, otherwise it will be severely leached, and its leaching is no less than ammonium nitrate. Under normal circumstances, summer and autumn high temperature season should be re-watering 2~3 days after urea application, watering should be better after 7-8 days in winter and spring cold season, because the urea is basically converted. Urea application in paddy fields should also be controlled in the case of thin water layers or "flower water". Urea cannot be applied before the arrival of heavy rain, otherwise it will be excessively leached and wasteful.
4. Do not apply too much foliar fertilizer. Among all nitrogen fertilizers, urea foliar spray has the best effect, and its absorption rate can reach about 90%. Tests have shown that foliar application of urea also promotes the absorption of more nitrogen in the roots of crops. However, the urea concentration on the foliar spray should not be too large, otherwise it will burn and poison the leaves, seriously affecting photosynthesis efficiency and normal crop growth. Under normal circumstances, the spraying concentration varies from crop to crop: wheat, barley, rice, corn, cotton with 1.5~2% urea solution, vegetable melon with 0.5~1%, seedbed seedling with 0.2~0.3%; fruit tree The concentration of mulberry trees can be slightly larger. The test has repeatedly proved that urea containing more than 1% of biuret cannot be used for foliar spray fertilizer.
Author: Han Xiaojun Wang Xiangming Qi Jinwei Source: Dong'e County Farm Bureau
*Material BK7,CaF2 crystal,MgF2,Ge,BaF2 lens,ZnSe or other optical materials
*Dimension Tolerance +0.0 - -0.1mm
*Center Thickness +/-0.1mm
*Focal Length Tolerance+/-1%
*Surface Quality:60/40
*Surface Figure:lambda/2 at 633nm on plano side
*Clear Aperture >90%
*Chamfer 0.25mm at 45 degree typical
*Coating Optional
Four and four do not apply urea
Urea, with a nitrogen content of up to 46%, is a “Hercules†in solid nitrogen fertilizer. Compared with other nitrogen fertilizers, it is easy to transport and easy to store. It has a wide range of applications, suitable for all kinds of soils and various crops; It can also be used as top dressing, and it is also the most ideal fertilizer for top dressing. However, in order to give full play to the role and economic benefits of urea, it is necessary to make "four essentials" and "four do not" when applying urea.
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