Foliar applicationFoliar application

Chapter 6

A A foliar fertilizerfoliar fertilizer is one that is applied to the is one that is applied to the surface of the plant. surface of the plant.

Foliar uptake is important to aquatic plants and Foliar uptake is important to aquatic plants and when nutrients are sprayed on foliage in when nutrients are sprayed on foliage in horticulture and agriculture.horticulture and agriculture.

Foliar fertilizer

陆 生 植 物 可 以 通 过 气 孔 吸 收 气 态 养 分 ， 如CO2 、 O2 以及 SO2 等。

Leaves and other aerial plant organs are well able to take up nutrients in gaseous form such as CO2, O2, and SO2 via the stomata.

Gas nutrients uptake by the leaves

干重 (mg/ 株 ) 含硫量(Smg/ 株)

处 理

叶 根 叶 根

不供硫 0.8 1.5 1.9

2.0 11.4 1.9叶片供 SO2

根部供 SO42- 2.0 7.4 4.9

6.4

0.61

0.6

地上部供给 SO2 或根系供给 SO42- 烟草

干物质产量及含硫量 The effects of supply SO2 and SO4

2- on the biomass and S content of tabacum

陆生植物因叶表皮细胞的外壁上覆盖有蜡质及角质层，对矿质元素的吸收有明显障碍。

The process of nutrients uptake by leaf cells is the same as that of nutrient absorption by plant root cell.

The uptake of nutrients in ionic forms from solution is limited as the outer epidermal cells of the leaf are covered by the cuticle( 表皮 ) which occurs in all terrestrial （陆生） plant species. The cuticle consist of two components cutin( 角质） and wax（腊质） .

Uptake of mineral nutrients by the leaves

叶表皮细胞外壁的示意图叶表皮细胞外壁的示意图

角质（ cutin)

半角质 (hemicutin)

果胶 (pectin)

蜡质 (wax)

角质角质层

初生壁

次生壁

质膜细胞质symplasm

蜡质覆盖

带除垢剂的小水滴小水滴蜡质小秆

外质连丝外质连丝

cuticle

Cell wall

细胞膜 cell membrane

ectoesmata

Waxes represents the water proofing Waxes represents the water proofing

component of the cuticle. Due to their component of the cuticle. Due to their hydrophobic nature waxes impede the hydrophobic nature waxes impede the diffusion of hydrophilic ions.diffusion of hydrophilic ions.

So the leaves are not constructed for So the leaves are not constructed for the uptake of hydrophilic ions dissolved the uptake of hydrophilic ions dissolved in water. Nevertheless uptake of aqueous in water. Nevertheless uptake of aqueous plant nutrients at least in small plant nutrients at least in small quantities.quantities.

Uptake of mineral nutrients by the leaves

Advantage of foliar nutrition1. Nutrients can be absorbed quickly

2. Foliar application is particularly useful under conditions where nutrients uptake from the soil is restricted.

3. Avoids the problem of nutrient fixation in the soil . Such as iron, Mn, Zn and Cu, which are frequently fixed by the soil particles.

The characteristics of foliar nutrition

4.Nutrients sprays are particularly used for 4.Nutrients sprays are particularly used for fruit trees, especially in grass-grown orchards.fruit trees, especially in grass-grown orchards.

5.Physiological disorders, such as “bitter pit” 5.Physiological disorders, such as “bitter pit” in apples, which results from Ca deficiency, in apples, which results from Ca deficiency, can be alleviated to some extent by spraying can be alleviated to some extent by spraying the fruit with a solution of Ca salt. the fruit with a solution of Ca salt.

The characteristics of foliar nutrition

Advantage of foliar nutrition

The effect of foliar spraying of Cu on the wheat growing in Cu deficit soil

Treat ears/m2 seeds/ear seed weight （ g/m2 ）

No CuSoil dress CuSO4(kg/ha) 2.5 10.0

Foliar spraying Cu12%,2CuSO4(kg/ha)

elongation stage elongation stage and heading stage

37.0 0.14 0.03

28.8 2.3 1.0 58.5 2.9 2.3

63.8 17.1 14.0 127.4 52.0 79.3

Disadvantages Rate of application is limited (if it is too high, the leaf will be harmed). It should be remembered that in general leaves are only able to take up a relatively small quantity of nutrients in comparison with plant demand, especially for macronutrients. So, It cannot replace the need for the application of nutrients to the soil.

Uptake of mineral nutrients by the leaves

矿质养分的种类矿质养分的种类 (kinds of nutrients)(kinds of nutrients) 叶片对钾的吸收速率依次为：叶片对钾的吸收速率依次为： KCl>KNOKCl>KNO33> K> K22HPOHPO44 ；；对对氮的吸收为尿素氮的吸收为尿素 >> 硝酸盐硝酸盐 >> 铵盐。铵盐。

矿质养分的浓度矿质养分的浓度 (nutrient concentration)(nutrient concentration) 在一定浓度范围内，矿质养分进入叶片的速率和数量随浓在一定浓度范围内，矿质养分进入叶片的速率和数量随浓度的提高而增加，但浓度过高会灼伤叶片度的提高而增加，但浓度过高会灼伤叶片 (scorching and (scorching and burning)burning) 。。

Notices

植物种类和生长环境植物种类和生长环境Kinds of plant and grown conditionsKinds of plant and grown conditions

Because Dicotyledonous leaf is big and the cuticle Because Dicotyledonous leaf is big and the cuticle is thin, the nutrient uptake by the leaf is easily; is thin, the nutrient uptake by the leaf is easily;

Reverse is the monocotyledonous.Reverse is the monocotyledonous. The crops grown in the field is different from the The crops grown in the field is different from the

same crops grown in the greenhousesame crops grown in the greenhouse

Notices

叶片对养分的吸附能力叶片对养分的吸附能力Capability of ion sorption on leafCapability of ion sorption on leaf

Nutrients uptake by the leaf is more effective the Nutrients uptake by the leaf is more effective the longer the nutrient solution remains in the form a longer the nutrient solution remains in the form a fine film on the leaf surface.fine film on the leaf surface.

In order to obtain thin surface films which adhere In order to obtain thin surface films which adhere to the leaf surface , foliar spray solutions are often to the leaf surface , foliar spray solutions are often supplemented with surfactants(supplemented with surfactants( 表面活性剂）表面活性剂） . .

Notices

温度 温度 (Temperature)(Temperature)

On the hot clear days when evaporation is high On the hot clear days when evaporation is high the water from the foliar spray can easily the water from the foliar spray can easily evaporate, so spraying on cool cloudy days or evaporate, so spraying on cool cloudy days or in evening, early morning to let the thin film in evening, early morning to let the thin film last for longer time on the leaf.last for longer time on the leaf.

Notices

喷施次数与喷施量喷施次数与喷施量Spray times and rateSpray times and rate

Spray times Spray times To the macronutrients, iron and Ca, To the macronutrients, iron and Ca,

several application must be made. several application must be made. To other micronutrients, a foliar spray To other micronutrients, a foliar spray

applied once or twice and correctly timed, applied once or twice and correctly timed, is adequate to meet the demand of the is adequate to meet the demand of the crop.crop.

Notices