开春以来，一些苗圃地苗木叶片不同程度地发生了黄化现象。据调查，土壤黏重，且以施用化学肥料为主的苗圃发病重；水质盐碱度高的地块发病重；种植密度大或是大苗遮挡下的弱小树体发病重；杨树平茬苗、柳树快繁苗和留床苗发病严重。另外，在污染严重企业周边，有的树种也表现出一定的黄化现象，甚至出现死苗。有一处土肥条件较好、规模生产的苗圃地也出现了黄化现象。 　　引起苗木黄化的原因很多，具体到实际情况，主要有以下几个方面： 　　1.与土壤的pH值过高有关。pH值愈高，土壤的碱性愈大，土壤中的铁元素在碱性条件下转化为根系不能吸收利用的不溶性铁，如氧化铁或沉淀为氢氧化铁，铁的溶解度降低，这时土壤分析并不表现缺铁，但土壤中的铁不能被植物利用，而成为无效铁。施入土壤的无机铁肥因氧化作用及土壤碱性作用最终会转化为氢氧化铁，使作物难以吸收利用。因此，生长在盐碱土壤上的苗木存在着潜在性缺铁，并易发生缺铁失绿症。当pH值大于8时，黄化症状愈加明显。 　　2.与栽培管理不当有关。苗木抗黄化的能力与苗木综合栽培管理水平密切相关。栽培管理水平较高，肥水管理得当，黄化现象较轻。前一年种植密度大或其他原因导致光照不足的苗圃，也会影响光合产物的产生，造成树体养分积累较少、根系发育不良、吸收能力减弱、树势不旺，一旦肥水管理不能弥补营养亏缺，也易出现黄化现象。 　　3.与天气条件影响有关。吴桥县去年夏季降水过多，一些树体根系上浮，恰遇今年4月份气候干旱，根系的吸收活力降低，影响了对铁和其他养分的吸收，造成黄化。 　　4.与土壤中缺乏铁元素有关。土壤中铁元素缺乏，造成植株缺铁性黄化。
Since the beginning of spring, some viability seedling leaves yellowing phenomenon happened in different degrees. According to the survey, heavy clay soil, and given priority to with applying chemical fertilizer nursery heavy disease; The onset of heavy water of high salinity land plots; Planting density or went under the shade of the weak tree heavy disease; Yang Shuping crop seedlings, willow and MiaoFa micropropagation seedling disease serious. In addition, the polluting enterprises around, some tree species also show some etiolation, appear even dead plants. There is a good soil conditions, scale of production has also appeared in the viability of blanching. Cause a lot of etiolated seedlings, specific to the actual situation, mainly has the following several aspects: 1. Related to the pH of the soil is too high. The more alkaline pH value, the higher the soil, the soil of iron in alkaline conditions into root system unable to absorb insoluble iron, such as iron oxide or precipitation of iron hydroxide, the solubility of iron is reduced, the soil analysis is not lack of iron, but can't be plants use iron in the soil, and become invalid iron. Into the soil inorganic iron fertilizer due to oxidation and alkaline soil will eventually translate into iron hydroxide, the use of crops to absorb. Therefore, grown in saline soil on seedling has the potential iron deficiency, and prone to iron deficiency disease of green. When the pH greater than 8 etiolation symptom more and more obvious. 2. Related to the improper cultivation management. Seedling ability of resistance to yellowing and seedling cultivation management level are closely related. The cultivation management level is higher, water management is proper, blanching is lighter. The year before planting density or other reasons lead to deficiency of nursery, may also affect the production of photosynthetic product, cause less nutrient accumulation of trees, tree root dysplasia, absorbing ability weakened, the potential is not flourishing, once the water management can not make up the nutrition deficiency, also easy to appear yellowing phenomenon. 3. Related to weather conditions. Wuqiao county last summer precipitation too much, some trees root floating body, when drought in April this year, the absorption of root vigor decrease, affect the absorption of iron and other nutrients, cause yellowing. 4. Related to the lack of iron in the soil. Soil fe deficiency, cause plant iron deficiency yellows.