ssc - role of soil in plant nutrition (unit 5)

how many of 17 essential elements come from soil

14

law of the minimum

if one growth factor is deficient, plant growth is limited

structural components of soil (3)

carbon, hydrogen, oxygen

primary macronutrients (3)

nitrogen, phosphorus, potassium

secondary macronutrients (3)

calcium, magnesium, sulfur

micronutrients (8)

iron, manganese, boron, zinc, copper, chlorine, molybdenum, nickel

cations

boron (pH dependent), calcium copper, hydrogen, magnesium, manganese, nickel, nitrogen (ammonium), potassium, zinc

anions

borons (pH dependent), chloride, molybdate, nitrogen (nitrate), phosphate, sulfate

contributors to soil solution

exchange sites on clay and OM, OM and microorganisms, weathering of rocks, atmosphere and precipitation, fertilizer

carbon plant concentration

45%

hydrogen plant concentration

6%

oxygen plant concentration

43%

mass flow

dissolved nutrients move to the root in soil water

diffusion

nutrients move from higher concentration in bulk soil solution to lower concentration at the root

root interception

roots get nutrients by physical contact, mycorrhizae help

passive uptake (ion absorption)

diffusion, ion exchange

active uptake (ion absorption)

ion carriers, selective/competitive

forms of plant-available nitrogen

nitrate NO 3-

ammonium NH 4+

nitrate NO 3- more likely to be lost from

leaching

ammoniun NH 4+ more likely to be lost from

volatilization

symbiotic biological N fixation

bacteria fix N2 into plant available forms, get sugar in return

nitrogen fixing crops

legumes

mineralization

biological conversion of unavailable organic N to plant-available inorganic N

ammonification (step of mineralization)

organic N to ammonium. needs warm temp, good soil moisture, oxygen. makes soil more basic

nitrification (step of mineralization)

ammonium to nitrite, nitrite to nitrate. needs warm temp, well-drained soil. makes soil more acidic.

immobilization

biological conversion of plant available N into unavailable organic N

what happens to ammonium

immobilized by plants and microorganisms, bound to cation exchange sites, lost to volatilization, oxidized to nitrate to acidify soil

what happens to nitrate

immobilized by plants and microorganisms, leaching, denitrification, acidifies soil

nitrogen gain

fertilizer, net mineralization, nonsymbiotic fixation, organic amendments, rainfall, symbiotic nitrogen fixation

nitrogen losses

crop uptake, denitrification, erosion and runoff, leaching, volatilization

function of phosphorus

energy transfer, growth regulations

symptoms of p deficiency

small size, dark color, reddish-purple pigment

forms of phosphorus

adsorbed as an anion, bound with Al and Fe, organic

what happens to P at lower pH

more Fe, Al fixation

what happens to P at higher pH

more Ca fixation

eutrophication

too much N P K cause algal blooms

P loss from soil

runoff, erosion, leaching

role of potassium

photosynthesis, water regulation, protein synthesis, drought tolerance, disease resistance

symptoms of K deficiency

stunted growth, poor root systems, delayed maturity

nitrogen cycle mediated by _______

microbes

phosphorus cycle mediated by __________

equilibrium chemistry, pH

function of calcium (secondary macro)

structural component of cell walls

function of magnesium (secondary macro)

component of chlorophyll, important in oil-seed crops

function of sulfur (secondary macro)

component of amino acids required for proteins

factors affecting micronutrient availability

OM, compaction, pH, water content, temp, crop type

purpose of soil testing

assess pH, plant-available nutrients, determine need for lime, fertilizers, avoid losses and environmental damage

composite samples

combining smaller samples into one sample for the field

grid sample

field sampled at regularly spaced grid points

nutrient management factors

amount, timing, source, placement