Plant Nutrition
Outline:
- Essential Elements
- Nutrient Cycle
- Essential Elements
- Plants require 16 essential elements for plant growth.
These nutrients may be broken into two groups:- those needed in large amounts (macronutrients)
- those needed in small amounts (micronutrients).
- Macronutrients:
- C, H, O : come from air and water
- N, P , K : primary macronutrients
- Ca, Mg, S : Secondary macronutrients
- Micronutrients:
Zn, Cu, Fe, Mn, B, Cl, Mo
- Macronutrients:
- those needed in large amounts (macronutrients)
- Deficiency symptoms usually show up as visual signs in the plant. Whether the symptoms appear in new growth or older growth depends on the mobility of the nutrient in the plant.
- Mobile elements in Plants:
- can be translocated within plants from older to actively growing tissue.
- N, P, K, Mg
- deficiency symptoms occur in the older growth
- Immobile elements in Plants:
- not translocated within the plant.
- Ca, S, B, Fe, Zn, Cu, Mn
- deficiency symptoms occur in the new growth
- Mobile elements in Plants:
- Plants require 16 essential elements for plant growth.
- Nutrient Cycle:
- Sources of Elements in the Soil
- Organic matter:
Most soil nutrients are contained in the soil organic matter. To make these nutrients available the organic matter must be decomposed.. - Soil minerals (includes clay minerals)
These are the nutrients that are in the parent materials. These nutrients may become available through weathering, however this is a very slow process. There are also nutrients in the clay minerals. This includes Mg and K that are in the 2:1 clay minerals. - Adsorbed nutrients
These are the nutrients that are held on the soil colloid. This is the major source of nutrients for the plants, and is the source that is most easily controlled by man.
- Organic matter:
- Relation of C/N ratio in organic materials to decomposition and soil N
As organic matter decomposes, plant nutrients are released into the soil. If the organic matter has a high C:N ratio the organic matter does not readily and the nutrients are not available for plant growth. - The Nutrient cycle shows the different ways the system may be controlled.
- Plant uptake; movement of nutrients into the plant. This is an active on going process.
- Nutrient loss from the plant; plant may exchange some nutrients or just lose them.
- Addition of residues. This is Organic matter addition; it may be either plant or animal residue.
- Immobilization; conversion of available forms to unavailable forms. May be controlled by the C:N ratio.
- Mineralization; conversion of unavailable forms to available forms. Also is controlled by the C:N ratio. This is also decomposition.
- Precipitation: soluble to insoluble. This is controlled by by the soil pH. Certain nutrients are only available at set p ranges.
- Dissolution: insoluble to soluble. This is a function of pH.
- Volatilization; biological reaction controlled by micros denitrification and CO2 production are controlled by this.
- Biological fixation; N being fixed by micros.
- Gases are used to produce some fertilizers. N is the big one.
- Erosion; Any erosion may lead to the remove of the nutrients.
- Leaching; Common way to lose nutrients. There is a difference depending on the charge that is on the ion.
- Deposits; large concentrations of given element that may be mined for fertilizer. These are things like nitrates, phosphates, limestone, potassium etc....
- Fertilizer; material that contains one or more of the essential elements for plant growth.
- Nutrient Needs
The amount of nutrients taken up by plants is in this order:
N> K> Ca >P> Mg> S>micronutrients
Forms of nutrients taken up by the plant. - plants will only take up a nutrient if it is in some ionic form. The different plant nutrients, depending upon their ionic charge will either be held on the colloid or leached off.N NH4+ , NO3- P H2PO4-, HPO4-2 K K+ Ca Ca +2 Mg Mg+2 S SO4 -2 Fe Fe +2 Mn Mn +2 B H2BO3- Cu Cu+2 Zn Zn+2 Cl Cl- Mo MoO4-2 - Soil /Plant Relations
Uptake of the essential elements is controlled by the availability of the nutrients and by the proximity to the root surface.
Nutrients are supplied to the root surface in 3 ways:- Root Interception:
- root moves through the soil and comes into contact with the nutrient on the colloid.
- generally not very important because the root only comes into contact with 1-2% of the total soil volume.
- Mass flow:
- nutrients move to the root with water.
- most important with nutrients that will easily flow with the water. N may be taken up by mass flaw
- Diffusion:
- concentration gradients are set up around the root surfaces and the soil farther away. In response to this gradient the nutrients move towards the plant root. For most cations this is the most important form of movement.
- for nutrients like P and K this is the most important form of uptake.
- the addition of fertilzer will increase the gradient and increase uptake.
- concentration gradients are set up around the root surfaces and the soil farther away. In response to this gradient the nutrients move towards the plant root. For most cations this is the most important form of movement.
- Root Interception:
- Nutrient absorption:
N utrient uptake by plant roots is not a passive process and requires a plant-soil interaction.
The high microbial activity around the root (rhizosphere) helps uptake. Chemical carriers (proteins) transport ions across the cell membranes. Ion Diffusion also a part of nutrient uptake.
- Sources of Elements in the Soil