Sustainable crop production (salinity) Flashcards
5 causes of salinity
- lack of water
- excessive ET
- poor drainage
- irrigation water quality
- human activity
how does lack water cause salinity
in arid and semi-arid regions lack of water leads to the accumulation of salts. this means there is hardly any salinity near costal areas due to high rainfall
what are the major cations for salinity (4)
Na+ sodium
Ca2+ calcium
Mg2+ magnesium
K+ potassium
these are the major cations needed for soil
what are the major anions for salinity (5)
Cl- chloride So4- sulfate HCO3- bicarbonate CO3 2- carbonate NO3- nitrate
how does high ET cause salinity
high potential ET of arid regions increase salinity as water is evaporated and salt is left behind
how does poor drainage cause salinity
drainage helps leach salts out of the soil profile however if the water table is high (groundwater) OR the soil has low water permeability (compaction), the salt will remain in the soil solution
inadequate leaching
how does irrigation quality cause salinity
using water with high levels of soluble salts, high EC water or using excess water
how does human activity cause salinity
changes in the hydrological cycle can lead to salinity in the soil. rising groundwater table due to land clearing, excess irrigation
what are the 4 sources of salt
- fossil salts
- mineral weathering
- atmospheric deposition
4, local salt accumulation
what is a fossil salt
salts that were in marine sediments or prior salt deposits
what is mineral weathering
weathering of minerals and ions. this is a natural process and leaching removes these salts however in arid areas where there is a lack of water they cannot be leached out of systems
what is atmospheric deposition (salts)
over ocean aerosols of salts are carried with wind and deposited on salt (dry or through rain), significant in geological time
what is local salt accumulation
product of geomorphic landscape. eg in low lying areas (Sydney basin) accumulates all surrounding salts, these areas usually have high groundwater tables
what are the two natures of salinity when describing a location
primary and secondary
what is primary salinity
areas that are naturally saline due to landscape and climate (ie low rainfall less than 350 mm/year)
what is secondary salinity
areas that are now saline due to land degradation (previously non-saline)
how much of the worlds irrigated land has become secondary saline
1/3
AUS affected largely due to land clearing
what is dryland salinity and what are the two forms
salinity in non irrigated areas, this is the main form of salinity in AUS context
- seepage
- scalds
what is saline seepage
grounndwater rise due to modication of native vegetation, usually occurs in drainage depressions, extended series of wet seasons, poor drainage of subsoil
what is saline scalds
when top soil is removed to expose subsoil naturally high in salts
what is sodicity
salts bound to clay exchange sites (clay particles) that repells water when in contact, affects physcial behaviour ie structure and stablility
what is salinity
free salts in soil that affect water and vegetation quality
what is EC
electrical conductivity measure of distance between 2 points
how to convert 1:5 EC to more accurate Saturated ECe
dependant on soil texture
sand x 17
loam x 10
clay x 7
what is TDS
ECe is a proxy of TDS
total dissolved salts sum of cation and anions in solution
how do you calculate TDS from Ece
multiply by a conversion factor
mg L-1 = ECe x 640
if greater than 5 ds m-1 X 800
how does salinity affect water availabilty
affects Osmotic potential (negative), will draw water out of the plant instead to entering the plant cells if highly saline (reverse)
what is moderate salinity
ECe between 2-6 (below is okay and above is bad)
how to reverse effects of salinity seepage
inverse of cause of salinity maximize crop water use, rotation agroforestry perennial crops native vegetation
site treatment with very high salinity
fence off site to stop degretation, planting salt tolerant trees and shrubs, drainage or pumping of grounwater table
how to calculate percent base saturation
percentage of CEC occupied by base cations,
(Ca+Mg+K+Na/CEC) * 100
in neutral soils all exchnagesites will be occupied by these = 100%
how to calculate exchangeable sodium percentage
ESP = (Na/CEC )*100
sodic soils have ESP greater than 6
what is sodium adsorption ratio
amount of sodium relative to Mg and Ca
SAR = na/ srt ca+mg
if measureing mmol(+) then divide denominator by 2
