Chapter 10 Potassium Nutrition and
Potassic Fertilizer
钾不仅是植物生长发育的必需营养元素，而且是肥料三要素之一。许多植物需钾量很大，它在植物体重的含量仅次于氮。农业生产实践证明，使用钾肥对提高作物产量和改善品质均有明显的作用。
[目的与要求]
1．钾在植物体内的含量与分布
2．钾的营养功能
3．钾的缺素症状
4．钾肥的种类及施用技术
[了解]
土壤中钾的含量、分类和性质
[重点]
1．钾在植物体内的含量及营养功能
[难点]
作物对钾的吸收同化及钾在植物体内的运输
[课堂组织]
讲述、讨论和多媒体教具结合
[教学内容]
10.1 Content and Distribution of Potassium in Plant
In general, K20 content in plants is about 0.3~5% of dry weight.
Potassium is characterized by high mobility in plants at all levels (cells, tissues, long-distance transport) , which is easily transported from roots to shoots. Potassium transfers easily with growth center and is preferentially distributed in younger tissues.
There is a stable K concentration in cytoplasm, which is about 100~200 mM, the other K stores at the vacuole.
10.2 Nutrition Function of Potassium
Unlike N and P, K exists in plant as an ion(K+), and does not form stable complexes. Nutrition function of K+ involves :
Neutralizing the soluble and insoluble anion;
（1）Stabling pH between 7 and 8;
（2）Regulating osmotic pressure;
（3）Enzyme activation;
（4）Adaptation to stress
10.2.1 Enzyme activation
There are more than 60 enzymes which either completely depend on or are stimulated by K+.如： ATPase, pyruvate kinase （果糖激酶），6-phosphofructokinase （6-磷酸果糖激酶）
10.2.2 Protein Synthesis
It is now well established that K+ is required for protein synthesis in higher plants.K+ is involved in several steps of the translation process, including the binding of tRNA to ribosome.
The accumulation of soluble nitrogen compounds (aa, amide, and nitrate) when K+ is deficient. K nutrition function on protein synthesis shows a role on nitrogen fixation.
10.2.3 Photosynthesis
In higher plants K+ affects photosynthesis at various levels:
（1） Enhancing chlorophyll synthesis;
（2） Improving chloroplast structure;
（3） Increasing CO2 fixation;
（4） Improving carbohydrate transport.
10.2.4 Osmoregulation
K+ is the dominant osmotic substances. Cell extension is the consequence of the accumulation in the cells of K+.
10.2.5 Stomatal Movement
In most species K+ has the major responsibility for turgor changes in the guard cells during stomata movement. An increase in the K+ concentration in the guard cells results in the uptake of water from the adjacent cells and a corresponding increase in turgor in the guard cells and thus the stomata opening.
10.2.6 Improving organic acid metabolism
10.2.7 Improving the tolerance of plants to stress
Drought; High temperature; Cold; Disease; Salt; Lodging
10.3 Potassium and crop quality
（1）Suitable K can Improve crop quality:
（2）Increasing protein and ammonia acid composition
（3）Increasing sugars and starch content ;
（4）Enhancing vitamins in vegetables;
（5）Delaying storage period;
（6）Improving commercial quality;
Quality element!
10.4 Response of Plant to Potassium Deficiency or Excessive Potassium
Potassium deficiency does not immediately result in visible symptoms. At first there is only a reduction in growth rate (hidden hunger).Potassium deficiency symptoms generally begin in the old leaves.
Plants suffering from Potassium deficiency become flaccid, poor tolerant to drought, frost, fungal attract, and saline conditions.
缺素症状：
（1）植株生长缓慢,矮化;
（2）下部老叶叶缘先发黄，然后变褐、焦枯；
（3）有些作物叶片呈青铜色，向下卷曲，叶表叶肉突起，叶脉下陷；
（4）根系生长不良，色泽黄褐；
（5）种子、果实小，产量低，品质差；
（6）早衰。
图10－1水稻： 叶片披散，下部老叶沿叶尖、 图10－2玉米：yellowing, followed by tissue
叶缘焦枯，并逐渐扩散呈“V”型，老叶片 death，progressing inward along the margins
上有棕褐色斑点。 of older leaves.
图10－3葡萄：边缘黄化，并随缺钾加重而出现赤褐斑块，叶缘向内逐渐焦枯，果实色泽浅，粒少且小。
10.5 Potassium Fertilizer
Potassium mineral bed is the major source for manufacture of potassium fertilizer. Potassium chloride is the major sort of potassium fertilizer.
中国最大的钾镁盐湖——察尔汗盐湖(面积达5000多平方公里的大盐湖，是世界上海拔最高的内陆盐湖), 氯化钾储量为１.45亿吨，占中国已探明总储量的97％。
1958年，在察尔汗盐湖出现了,年产960吨钾肥的国产钾肥厂,迈出了中国钾肥发展的第一步。1989年原青海钾肥厂基本形成了年产25万吨的生产规模。1996年生产能力达５０万吨。
然而，与察尔汗盐湖1.45亿吨氯化钾储量和中国数百吨的钾肥年需求量，存在巨大的反差。 我国钾肥目前的市场需求在600万吨以上，而且这一数字还将以每年5%左右的速度递增。但目前我国的钾肥产量仅有50—60万吨，
自主建设的青海１００万吨钾肥项目建设工程渐近尾声。据《农民日报》2001.9.21报道：罗布泊钾盐储量1.74亿吨，被国家计委确定为国内两大钾肥生产的化工基地。
中国最大钾肥生产基地的第一步，一期建成20万吨硫酸钾厂，最终计划是年产220万吨钾肥。 这一产量将占中国年度进口钾肥总量的三分之一（中国农田里施用的钾肥90%是进口的）。
10.5.1 Properties of potassium fertilizer
10.5.1.1 Potassium chloride (氯化钾, K2O: 60% ）
The most common potassium fertilizer,90% of total K fertilizers in the world.
（1）High content
（2）呈白色或淡黄色；
（3）易溶于水，肥效迅速；
（4）有吸湿性，久贮结块；
（5）化学中性，生理酸性肥料。
（6）Cl-
10.5.1.2 Potassium sulfate (硫酸钾, K2O: 50-52%）
（1）白色或淡黄色结晶；
（2）易溶于水；
（3）吸湿性小；
（4）化学中性，生理酸性肥料。
10.5.1.3 Plant ash (草木灰)
（1）植物燃烧后的残灰；
（2）含钙、钾较多，其次是磷;
（3）以K2CO3为主，K2SO4次之；
（4）90%的钾为水溶性，是速性钾肥;
（5）水溶液碱性。
10.5.1.4 Biological potassium fertilizer (生物钾肥)
（1）微生物：钾细菌
（2）富钾植物
（3）稻草还田
10.5.2 Application
10.5.2.1 Potassium chloride
（1） 可作基肥和追肥，不宜作种肥；
（2）酸性土壤上配合施用有机肥或石灰，防酸化；
（3）一般作物尽量施用KCl，不用K2SO4，
对忌氯作物和盐碱地不宜多用。
10.5.2.2 Potassium sulfate
（1）可作基肥(10 kg/mu)、追肥、种肥(1.2-2.5 kg/mu)和根外追肥(2-3%)；
（2）施用于各种作物，尤其是喜硫作物：洋葱、韭菜、十字花科；
（3）不易施在还原性强的土壤上（水稻）。
10.5.2.3 Plant ash
（1）可作基肥、追肥及盖种肥。（一方面可供养分，另一方面可提高土温，还可减少病虫发生和危害。）
（2）草木灰呈碱性，不能与铵态氮肥、腐熟的人畜粪尿混合施用。
（3）盐碱土壤上涨生长作物的草木灰含大量NaCl，不宜做肥料。
10.6 Potassium in Soil
10.6.1 Potassium content and form in soil
Content:
Potassium (K) is the seventh most abundant element in the earth’s crust ranging from 0.5 to 2.5%. But the available K is only 1-2% of total K.
Forms:
Total K consists of four distinct forms in the soil, each of different availability to the plant:
(ⅰ) Mineral K---almost completely unavailable, 90~98%;
(ⅱ) Fixed K----slowly available, 1-10%;
(ⅲ) Exchangeable K----readily available, 1-2%;
(ⅳ) Soil solution K----readily available, 0.1-0.2%.
There is an equilibrium between the various forms which allows release of K from the less available forms to the more available forms or vice versa.Organic K is only a small part.
(ⅰ) Mineral K---almost completely unavailable, 90~98%;
Primary minerals, such as feldspars(长石) and micas(云母) are gradually broken down by weathering processes and release K ion slowly。
(ⅱ) Soil solution and exchangeable K
Soil solution K----readily available, 0.1-0.2%. It represents the most readily available form of K and is an immediate pool for plants uptake. It is also susceptible to leaching by water draining.
Exchangeable K----readily available, 1-2%. Which will rapid release K+ into solution after plant taking or leaching, or K+ move on to the exchange site after adding K fertilizers.
(ⅲ) Fixed K----slowly available, 1-10%;
Secondary minerals formed by weathering ， such as hydrous micas and illite clay(伊利石类粘土)， contain K which is part of their mineral structure.
图10－4土壤胶体对K+和NH4+固定和释放
10.6.2 Potassium transform in soil
K fixation(钾的固定)：土壤溶液中的钾或胶体表面吸附的钾进入粘土矿物晶层间，转化为非交换性钾的过程。
Affecting factors:
（1） 粘土矿物类型：2：1型易固定钾，1：1型不固定钾。
（2） 土壤水分：干湿交替促进钾的固定；
（3） 土壤pH：随pH降低，钾固定减少；
（4） NH4+抑制钾的固定。
钾的释放：
矿物风化，或通过人为的熏土、晒垡等措施，使晶层破裂。
钾的淋失：
淋失量与气候条件、土壤性质等有关。
10.7 Potassiic Fertilizer Application
10.7.1 Depending on soil properties
10.7.1.1 Providing K capacity
Be preferential to the low-K soils
10.7.1.2 Soil texture
The same amount of K potassium will give more yield in sandy soil than in clay；More amount is permitted to be applied once on clay;Split applications are recommendation on sandy soil.
10.7.1.3 Soil moisture
Affecting K diffusion
10.7.2 Depending on crop characteristics
10.7.2.1 Different demand for K in various crops
喜钾作物：
糖类：甜菜、马铃薯、甘薯、甘蔗，等；
纤维类：棉、麻，等；
蔬菜类：
10.7.2.2 Different demand for K in various cultivars
如，水稻需钾量： 矮秆＞高秆； 粳稻＞籼稻； 杂交稻＞常规稻
10．7．2.3 Different growth stage
Critical period：seedling
Maximum efficiency period：flower
10.7.3 Depending on fertilizer characteristics
Physiological acid fertilizer is suitable for using in calcareous soil;Physiological alkaline fertilizer is suitable for using in acid soil; Potassium chloride is suitable for using in paddy field, not saline soil
10.7.4 Rational application technique
10.7.4.1 Balance fertilization
（1）供氮、磷基础上施钾；
（2）有机肥多时，钾肥效果差。
10.7.4.2 Selecting proper k fertilizer
喜钾忌氯作物,
soils
10.7.4.3 Application technique
In generally applied as basal fertilizer;
Deep and place application
[思考题]
1、钾在植物体内的形态与分布特点
2、钾在植物体内的营养功能及其缺乏、过量的症状表现。
3、土壤中钾的形态与转化特点。
4、钾肥的主要种类、特点及施用。
5、钾可增加作物哪些抗逆性？为什么？
6、为什么KCl 不适于块根、块茎作物，却适于棉、麻？
7、草木灰的主要成分是什么？