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Nutrient Uptake in Plants

INTRODUCTION

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.

Micro-nutrientsMacro-nutrients
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).

NutrientUptake formMobility in SoilMobility in PlantRole in Plant GrowthSign of Deficiency
NitrogenNO3, NH4+Mobile in the form of NO3, immobile in the form of NH4+MobileChlorophyll, amino acids, proteinsYellowing in the middle of the leaf, reduced and red-brown new growth
PhosphorusHPO42-, H2PO4ImmobileSomewhat mobileDNA/RNA, ATP, cell membranePurple or reddish discolorations on leaves, poor growth, poor rooting, early fruit drop
PotassiumK+Somewhat mobileVery mobilePlant metabolism, stress response, regulation of water lossYellowing of leaf margins and veins, crinkling or rolling leaves, poor growth
CalciumCa2+Somewhat mobileImmobileCell wall formationYellowing new growth, localized tissue necrosis
MagnesiumMg2+ImmobileSomewhat mobilePhotosynthesis, chlorophyllInterveinal chlorosis (yellow leaves with green veins)
SulfurSO4MobileMobileAmino acids, proteins, oils, chlorophyllYellowing throughout the plant, necrotic tips on new growth
BoronH3BO3, BO3Very mobileImmobileCell wall, sugar transport, seed and fruit formation, hormone developmentCell wall, sugar transport, seed and fruit formation, hormone
CopperCu2+ImmobileImmobileLignin production, photosynthesis, plant metabolismPale green, withered new growth, yellowing, wilting
IronFe2+, Fe3+ImmobileImmobileChlorophyll and enzyme productionYellowing in new growth
ManganeseMn2+MobileImmobilePhotosynthesis, respiration, nitrogen assimilationInterveinal chlorosis on new growth, sunken tan spots on leaves
ZincZn2+ImmobileImmobileChlorophyll, enzymes, proteins, growth hormonesInterveinal chlorosis on new growth
MolybdenumMoO4Somewhat mobileImmobileNitrogen cycleYellowing of leaf margins on new growth
ChlorineClMobileMobileOpening 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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