Nutrient Uptake in Plants
There are 13 nutrients that are vital for plants to grow and thrive (Table 1). These can be divided into macro-nutrients, elements of which plants require large quantities, and micro-nutrients (elements that are required by the plant in smaller amounts). A micronutrient, though required in small doses, is not less vital for plant growth.
|Iron (Fe), Boron (B), Copper (Cu), Chlorine (Cl), Manganese (Mn), Molybdenum (Mo), Zinc (Zn)|
|Primary nutrients :Nitrogen (N), Phosphorus (P), Potassium (K)|
|Secondary nutrients:Calcium (Ca), Magnesium (Mg), Sulfur (S)|
Table 1: Plant nutrients
The availability and mobility of these 13 plant nutrients in the soil and in the plant itself is highly variable, and this has implications for responsibly managing plant nutrition, fertilization and irrigation.
MOBILITY OF NUTRIENTS IN SOIL
The mobility of plant nutrients in soil influences their uptake and their susceptibility to leaching, volatilization and runoff. For example: while nitrogen in the form of NO3- is highly mobile in soil, phosphorus (in the forms HPO42- and H2PO4-) is not. This means that nitrogen applications can be dispersed and still make it to plant roots, but must be managed carefully, to prevent leaching, whereas phosphorus must be applied closer to the seeds in order to be accessed by roots.
However, since phosphorus tends to remain in the upper layer of the soil, it might be lost in runoff when high precipitations occur. It is worth mentioning that nitrogen in the form of NH4+ is immobile in soil, so not only the nutrient, but also the chemical form in which it is applied can be significant.
MOBILITY OF NUTRIENTS IN PLANTS
Mobility of nutrients in the plants themselves influences how to read signs of nutrient deficiency in leaves. A deficiency of immobile nutrients can be seen in yellowing new leaves, whereas a deficiency in mobile nutrients can be seen in yellowing old leaves.
This is because mobile nutrients travel from old leaves to suffuse new growth, whereas immobile nutrients cannot be transferred between new and old growth, so deficiency symptoms will show up in the new growth.
Nutrients that are mobile in plants include the basic N-P-K primary macronutrients; nutrients that are immobile in plants include the secondary macronutrient, like calcium, magnesium and most of the micronutrients.
Managing nutrients responsibly involves not only the understanding of the quantities needed, but also how they move in soil and within the plant, and knowing to identify the deficiency or toxicity symptoms (Table 2).
|Nutrient||Uptake form||Mobility in Soil||Mobility in Plant||Role in Plant Growth||Sign of Deficiency|
|Nitrogen||NO3–, NH4+||Mobile in the form of NO3–, immobile in the form of NH4+||Mobile||Chlorophyll, amino acids, proteins||Yellowing in the middle of the leaf, reduced and red-brown new growth|
|Phosphorus||HPO42-, H2PO4–||Immobile||Somewhat mobile||DNA/RNA, ATP, cell membrane||Purple or reddish discolorations on leaves, poor growth, poor rooting, early fruit drop|
|Potassium||K+||Somewhat mobile||Very mobile||Plant metabolism, stress response, regulation of water loss||Yellowing of leaf margins and veins, crinkling or rolling leaves, poor growth|
|Calcium||Ca2+||Somewhat mobile||Immobile||Cell wall formation||Yellowing new growth, localized tissue necrosis|
|Magnesium||Mg2+||Immobile||Somewhat mobile||Photosynthesis, chlorophyll||Interveinal chlorosis (yellow leaves with green veins)|
|Sulfur||SO4–||Mobile||Mobile||Amino acids, proteins, oils, chlorophyll||Yellowing throughout the plant, necrotic tips on new growth|
|Boron||H3BO3, BO3–||Very mobile||Immobile||Cell wall, sugar transport, seed and fruit formation, hormone development||Cell wall, sugar transport, seed and fruit formation, hormone|
|Copper||Cu2+||Immobile||Immobile||Lignin production, photosynthesis, plant metabolism||Pale green, withered new growth, yellowing, wilting|
|Iron||Fe2+, Fe3+||Immobile||Immobile||Chlorophyll and enzyme production||Yellowing in new growth|
|Manganese||Mn2+||Mobile||Immobile||Photosynthesis, respiration, nitrogen assimilation||Interveinal chlorosis on new growth, sunken tan spots on leaves|
|Zinc||Zn2+||Immobile||Immobile||Chlorophyll, enzymes, proteins, growth hormones||Interveinal chlorosis on new growth|
|Molybdenum||MoO4–||Somewhat mobile||Immobile||Nitrogen cycle||Yellowing of leaf margins on new growth|
|Chlorine||Cl–||Mobile||Mobile||Opening and closing stomata (respiration)||Yellowing of leaf margins on old growth|
Table 2: Plant nutrient uptake and signs of deficiency
It is important to understand how nutrients behave in the soil and in the plants. The correct understanding will lead to the right nutrient managements decisions that can get you optimized yields and help you to reduce fertilizer costs and waste.
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