chapter 5 a & b Flashcards
potential of soil to supply nutrients in amounts, forms, and proportions required for the normal growth of plants
soil fertility
3 important things in soil fertility
content, balance, availability
4 factors that affect plant growth
genetic factors: tolerance to pest and diseases, soil acidity, elemental toxicity
environmental factors: sunlight, weather, avail of water, soil fertility, solum thickness
earth’s crust: 95% igneous, 5% sedimentary and meta
hydrosphere: 98% sea 2% fresh
atmosphere: 78% nitrogen, 20% oxygen
forms of available nutrients in soil
readily: soluble & exchangeable- fertilizers
moderately: elements in readily mineralized form- compost
difficulty: slowly decomposable sources of nutrients- fresh OM, fixed form (bodies of micro-org) P, K, NH4
arnon’s criteria
- deficiency of element makes it impossible for plant to complete life cycle
- deficiency can be corrected only by supplying limiting element
- element must be directly involved in nutrition of plant
absorbed by plants in large amount
macro nutrients
absorbed by plants in small amount
micro nutrients
non-mineral nutrients
hydrogen, carbon, oxygen
macro nutrients
primary: N, P, K
secondary: Ca, Mg, S
micro nutrients
boron, copper, iron, chloride, manganese, molybdenum, zinc
nitrogen is essential component of plant material especially
protein molecule
when N is deficient
root system and plant growth is stunted
older leaves turn yellow
crop is low in crude protein
too much N
delay maturity
excessive growth
N fertilizer is produced by
haber-bosch process
gradual increase of P, N, and other plant nutrients in an aquatic ecosystem
eutrophication
process that increase N content
fixation
mineralization: nitrification, ammonification
process that decrease N content
denitrification
volatilization
immobilization
leaching
in what form of N is taken by plant
nitrate (NO3-)
conversion of atmospheric N to plant available form
fixation
biological process of N fixation
biological N-fixation by legume crops and microorganisms
nitrogen fixation requires
energy, enzymes, and minerals
microorganism fixing N2
cyanobacteria
green sulfur bacteria
azotobacteraceae
rhizobia
frankia
microbes decompose organic N from manure
OM and crop residues to ammonium
mineralization
rate of mineralization vary with
soil temp
moisture
aeration (amount of oxygen)
mineralization readily occurs in
warm well-aerated and moist soils
process of degradation f organic nitrogenous constituents of freshly added residues as well as those in SOM, which produces ammonia
ammonification
under aerobic condition, ammonia produced is
rapidly converted to nitrate by bacteria
under anaerobic condition, such as paddy paddy fields
mineralization favors the accumulation of NH4-
microorganism convert ammonium to nitrate to obtain energy
nitrification
2 groups of bacteria in nitrification
nitrosomonas
nitrobacter
N is lost through conversion of nitrate to gaseous forms of N, such as nitric oxide, nitrous oxide, and nitrogen gas
denitrification
denitrification is common
poorly drained soils
soil is saturated and bacteria use nitrate as oxygen source
denitrification
loss of N through conversion of ammonium to ammonia gas, which is released to atmosphere
volatilization
volatilization losses increase at
higher soil pH and conditions that favor evaporation (hot and windy)
volatilization losses are higher for
manures and fertilizers that ae surface applied and not incorporated (by tillage or rain) into the soil
reverse of mobilization
nitrate and ammonium are taken up by soil organism and becomes unavailable to crops
immobilization
rate of leaching depends on
soil drainage
rainfall
amount of nitrate present in soil
crop uptake
