Sustainable crop production (salinity)

Question 1

5 causes of salinity

Answer 1

1. lack of water
2. excessive ET
3. poor drainage
4. irrigation water quality
5. human activity

Question 2

how does lack water cause salinity

Answer 2

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

Question 3

what are the major cations for salinity (4)

Answer 3

Na+ sodium
Ca2+ calcium
Mg2+ magnesium
K+ potassium

these are the major cations needed for soil

Question 4

what are the major anions for salinity (5)

Answer 4

Cl- chloride 
So4- sulfate 
HCO3- bicarbonate 
CO3 2- carbonate 
NO3- nitrate

Question 5

how does high ET cause salinity

Answer 5

high potential ET of arid regions increase salinity as water is evaporated and salt is left behind

Question 6

how does poor drainage cause salinity

Answer 6

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

Question 7

how does irrigation quality cause salinity

Answer 7

using water with high levels of soluble salts, high EC water or using excess water

Question 8

how does human activity cause salinity

Answer 8

changes in the hydrological cycle can lead to salinity in the soil. rising groundwater table due to land clearing, excess irrigation

Question 9

what are the 4 sources of salt

Answer 9

1. fossil salts
2. mineral weathering
3. atmospheric deposition
   4, local salt accumulation

Question 10

what is a fossil salt

Answer 10

salts that were in marine sediments or prior salt deposits

Question 11

what is mineral weathering

Answer 11

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

Question 12

what is atmospheric deposition (salts)

Answer 12

over ocean aerosols of salts are carried with wind and deposited on salt (dry or through rain), significant in geological time

Question 13

what is local salt accumulation

Answer 13

product of geomorphic landscape. eg in low lying areas (Sydney basin) accumulates all surrounding salts, these areas usually have high groundwater tables

Question 14

what are the two natures of salinity when describing a location

Answer 14

primary and secondary

Question 15

what is primary salinity

Answer 15

areas that are naturally saline due to landscape and climate (ie low rainfall less than 350 mm/year)

Question 16

what is secondary salinity

Answer 16

areas that are now saline due to land degradation (previously non-saline)

Question 17

how much of the worlds irrigated land has become secondary saline

Answer 17

1/3

AUS affected largely due to land clearing

Question 18

what is dryland salinity and what are the two forms

Answer 18

salinity in non irrigated areas, this is the main form of salinity in AUS context

1. seepage
2. scalds

Question 19

what is saline seepage

Answer 19

grounndwater rise due to modication of native vegetation, usually occurs in drainage depressions, extended series of wet seasons, poor drainage of subsoil

Question 20

what is saline scalds

Answer 20

when top soil is removed to expose subsoil naturally high in salts

Question 21

what is sodicity

Answer 21

salts bound to clay exchange sites (clay particles) that repells water when in contact, affects physcial behaviour ie structure and stablility

Question 22

what is salinity

Answer 22

free salts in soil that affect water and vegetation quality

Question 23

what is EC

Answer 23

electrical conductivity measure of distance between 2 points

Question 24

how to convert 1:5 EC to more accurate Saturated ECe

Answer 24

dependant on soil texture
sand x 17
loam x 10
clay x 7

Question 25

what is TDS

Answer 25

ECe is a proxy of TDS

total dissolved salts sum of cation and anions in solution

Question 26

how do you calculate TDS from Ece

Answer 26

multiply by a conversion factor
mg L-1 = ECe x 640
if greater than 5 ds m-1 X 800

Question 27

how does salinity affect water availabilty

Answer 27

affects Osmotic potential (negative), will draw water out of the plant instead to entering the plant cells if highly saline (reverse)

Question 28

what is moderate salinity

Answer 28

ECe between 2-6 (below is okay and above is bad)

Question 29

how to reverse effects of salinity seepage

Answer 29

inverse of cause of salinity 
maximize crop water use, rotation
agroforestry
perennial crops
native vegetation

Question 30

site treatment with very high salinity

Answer 30

fence off site to stop degretation, planting salt tolerant trees and shrubs, drainage or pumping of grounwater table

Question 31

how to calculate percent base saturation

Answer 31

percentage of CEC occupied by base cations,
(Ca+Mg+K+Na/CEC) * 100
in neutral soils all exchnagesites will be occupied by these = 100%

Question 32

how to calculate exchangeable sodium percentage

Answer 32

ESP = (Na/CEC )*100

sodic soils have ESP greater than 6

Question 33

what is sodium adsorption ratio

Answer 33

amount of sodium relative to Mg and Ca

SAR = na/ srt ca+mg
if measureing mmol(+) then divide denominator by 2