problem soils and their mitigation efforts

2. PROBLEM SOILS
 problem soils are an important ecological entity for arid, semi-arid
or humid climate of our country.
 In India saline and sodic soils occupy nearly 8.6Mha and is the
present serious threat to our ability to produce enough food grains
for expanding needs.
 The other main problem is acid and acid sulphate soils, spread in
one-third of cultivated land.
 Problem soils are either deficient in plant nutrients or the nutrient
availability is inhibited by the antagonistic effect of the nutrient
element present in excessive amounts as soluble or exchangable
ions.

3. CHARACTERISATION OF PROBLEM SOILS
Saline soils:
* They contain excess neutral soluble salts like chlorides and
sulphates of sodium, calcium and magnesium. In these soils EC
exceeds 4dSmˉˡ, pH is less than 8.5 and ESP is usually less than 15.
* Saline soils are in a flocculated state and hence fairly
permeable.Plant growth is affected by osmotic effect due to
accumulation of soluble salts in the soil surface horizone and lesser
availability of nutrients due to competitive uptake.

4. Sodic soils:
* Sodic soils also called Alkali soils are those in which PH
exceeds 8.5 and ESP is more than 15.
* There is the presence of carbonates and bicarbonates of
sodium among the soluble salts.
* Due to high pH and ESP, Alkali soils develop poor physical
properties.
* The dispersed clay particles block the soil pores resulting in
very low infiltration rate , crusting and hardening of soil surface upon
drying. Thus water and air movement remains restricted.

5. Acid and Acid sulphate soils:
* Acid soils are generally characterised by low pH .
* They contains excessive amounts of dissolved ions
of Al,Fe, Mn and Cu.
* Acid soils are deficient in Ca and Mg .
* Acid sulphate soils are rich in pyrite which on
oxidation form sulphuric acid .These soils have pH <4.
* Crops on these soils suffer mainly due to Al toxicity and
nutrient deficiency

6. RECLAMATION OF SODIC AND SALINE SOILS
Sodic soils:
Chemical reclamation:-
# Gypsum is most commonly used , here , exchangeable sodium is replaced
with Ca.
Gypsum requirement can be calculated as follows:
Gypsum requirement = ESP Initial – ESP Final x CEC
per 100 g of soil 100
# Pyrite (FeS₂) as soil amendment to sodic soil has been used for fodder crops.
# Mineral acids such as sulphuric acid,nitric acid,etc have also been used to some
extent.
# Byproducts of gypsum from industries manufacturing citric acid ,phosphoric
acid,oxalic acid,etc can also be used for reclaiming sodic soils.

7. Crops and cropping system:-
# Choice of crops and cropping sequences to be followed while reclamation is
important.
# Since rice prefers standing water it is the acceptable crop during karif.
shallow rooted crops like wheat, barley and berseem could be grown in rabi during
initial phases of reclamation.
# After 3-5 years relatively deep rooted crops like sorghum, pearl millet,
rapeseed , oil seeds and cotton can be grown.
Biological reclamation :-
# Application of FYM increases solubility of applied gypsum and hastens the
reclamation process besides providing plant nutrients and improving soil physical
condition .

8. # Use of green manure crops like Sesbania aculeata (dhaincha) for
reclamation of alkali soils has been a practice since long .
# Decomposition of organic residue of biological amendments
release carbondioxide and other organic acids which enhance the
solubility of native CaCO₃ and this provide calcium for the removal
of exchangeable sodium.
# Leptochloa fusca (karnal grass),chloris gayana (rhodes grass),
Panicum maximum (gatton panic) have been found tolerant and
better than other grasses for improving sodic soils.

9. Cultural practices:-
# Deep ploughing,subsoiling,sanding and profile inversion have been
used to improve problem soils
.
# First three methods increase soil permeability.Profile inversion
covers an undesirable soil layer with better material from a lower
layer.Mulching helps in minimising salt problem by reducing
evaporation.
Stand establishment :-
# Increasing the seed rate and increasing the number of seedlings per
hill and transplanting relatively aged seedlings can aid in establishing
required crop stand.
# Seeds have to be placed in the area where salt concentration is less.

10. Soil ferStioliitly f emratinliatyg emmaennatg:-ement
# Addition of organic manures besides supplying nutrients,improve
physical,chemical and biological characteristics of the soil.
# Among the green manure crops Sesbania aculeata has been found to
be more beneficial for alkali soils.
# Acid farming fertilizers ( Ammonium sulphate, urea) are better suited
for sodic soils.
# Application of Ca and Zn can increase the yield of rice and barseem.

11. Irrigation water management
• The water intake of alkali soils is very low.
• Flowing irrigation is better in these soils.It is desirable to change
water every week if availability of water is not a problem.
• Since the soil gradually dries out after each irrigation ,salt
concentration increases and then drops following the next irrigation.
• Hence,high frequency irrigation with shallow depth of irrigation is
more ideal than low frequency with high depth of water application
at each irrigation.

12. Saline soils
leaching
# reclamation of saline soils involves leaching of excess soluble salts to
reduce root zone salinity ,lowering of water table below the critical
depth,crops and cultivar selection and agronomic practices to keep root
zone environment at minimum salt level.
# Efficiency of leaching per unit of applied water depends upon soil
type,soil profile characteristics,depth of applied water, method of
application,absorption and exchange reactions during leaching and
initial wetness of the soil

13. • water requirement for leaching is in the order:peat
>clay>loam>sandy loam.
• Sub surface drainage provides an efficient means for lowering water
table and to prevent secondary salinisation.
Crop and cropping sequences
• In Arid and semi arid regions of north western india
cotton,sorghum,pearlmillet etc should be grown during karif and
wheat ,barley ,mustard and sunflower during rabi depending on the
availability of irrigation water.
• Recommended cropping sequences for saline soils are pearlmillet-barley
,pearlmillet-wheat,pearlmillet-mustard and sorghum-wheat
or barley .

14. Cultural practices
• For alkali soils,the major requirement is to provide very slight slope or no
slope at all in the direction of water flow.
• Provision should be made to drain off excess water if it stays for more than
one or two days.
• Cultural and stand establishment practices discussed under sodic soils holds
good in the case of saline soils also.
Soil fertility management
• Owing to low organic matter content ,nitrogen deficiency is common in
saline soils .
• Integrated plant nutrient systems are essential for stable crop production .
• Potassium fertilisers increased crop yield on moderately saline soils by
improving their tolerants to sodium ,calcium and magnesium
concentrations.
• Split application of nitrogen fertilisers reduce nitrogen losses through
• Volatilisation and denitrification.

15. Water management
Light and frequent irrigations are desirable than heavy irrigation
water application at lower intervals.
.
Cyclic use of canal and saline water is more beneficial than mixing
these two to minimise adverse effect of salinity.
RECLAMATION OF ACID AND ACID SULPHATE SOILS
Liming
• Application of lime is recommended for reclaming acid soils.
• It improves the base saturation,inactivates iron ,manganese and
aluminium in soil solution leading to reduce phosphorus fixation
• Lime should be applied once in five years depending on soil pH.
• As flooding alleviates acidity,rice is the choice on acid sulphate
soils in warm regions.

16. ChoiCceh ooifc ecr oofp csr aonpds caunldti vcaurltsivars
• Many of the major food and vegetable crops are sensitive to acid soils.
• Rice is relatively tolerant to soil acidity,since flooding the field raise soil pH
to near neutrality.
• Millets and oats among cereals,groundnut among the legumes,tea and
potato among others can be grown on acid soils.
Soil fertility management
• Leaching losses of nitrogen fertilisers can be reduced by split by split
applications.
• P deficiency due to its high fixation has to be tackled through application of
adequate amount of suitable type of fertilizer following responsive cropping
system and placement of the fertiliser.
• Use of completely water soluble sources like SSP ,TSP,DAP should be
avoided.

17. • Potassium sulphate is preferred over murate of potash because the
chloride ions have adverse effect on dry matter and starch content of
potato tubers.
• Potassium chloride is the common source of potassium except for
chloride sensitive crops like tobacco,tomatoes and pineapple.
• Judicious use of lime and organic residue incorporation can overcome
trace element deficiencies in acid soils.
• Molybdenum deficiency can be corrected by application of small
amounts of sodium or ammonium molibdate.