Soil Science - Basic Knowledge
S O I L S C I E N C E
As a tree grower we should have some basic knowledge about the chemical composition of our farm soil enabling us to select correct plant that suits our soil type. Some basic soil types, some problematic soils and their remedy methods are listed here.
Those who have already tested their farm soil and got test reports can verify their soil status with the following 'Soil quality parameter chart.'
S.No. ........ Parameter
1. pH range
Acidic : Below 6.5
Neutral : 6.5 to 7.5
Alkaline : above 7.5
2. E.C Electrical Conductivity should be less than 1.
3. Carbonate status:
P.E - Profuse effervescence
M.E - Medium effervescence
N.E - No effervescence
4. N.P.K
HighStatus ... MediumStatus........... LowStatus
N 148 ............ 113 to 148 .......... Below 113 Kgs per acre
P above 9 ...............4.5 to 9 .............Below 4.5 Kgs per acre
K above 113 ............ 48 to 113 .............Below 48 Kgs per acre
N Nitrogen – Essential for life
P Phosphate – P2O5 – Phosphate Pentoxide ( Key to yield)
K Potash – K2 O – Potassium oxide ( Chemical Policeman)
( Na – Sodium is the thief.)
5. O.C Organic Carbon 0.5 – Good, 1 – Excellent6. O.M Organic Matter Always double of O.C
Soil weight of 6” depth x 1 Acre area = 10 Lakh Kgs. In that mass if you add 200 tons of dry matter,You will get 20 tons of Organic matter (OM), that will give 10 tons of Organic Carbon (OC) that’s called 1% OC
7. C.E.C Cationic Exchange Capacity. It should be above 50. Achieving 100 is a must. Heavy dose of organic input and Humic acid will enhance CEC considerably.
8. Essential elements: Carbon, Hydrogen and Oxygen (available from air & water)
9. Major Nutrients: N P K
10. Secondary Nutrients: Ca, Mg and S
Ca – Calcium is the king among the nutrients. Among Ca, Mg, Na & K, more than 50% should be Ca. Ca content should be 1/3 to 1/2 of C.E.C. In other words Ca should be 50% of CEC. If Ca is low, then apply Calcium Carbonate. Application of Mono calcium Phosphate and Super Phosphate should be increased.
Mg - Magnesium should be 25% of CEC. Ca and Mg should be in the ratio of 3:1. If Mg is low, then apply MgSo4.
Na, K and other Mineral balance 25% of CEC.
10 a) Micro Nutrients: Cu, Zn, Mn, Fe, Boron, Chlorine, Fluorine Etc.,
Cu - above 1.2 ppm or Kgs / Acre. If lower, then apply Cu So4.
Zn - above 1.2 ppm or Kgs / Acre. If lower, then apply Zn So4.
Mn - above 3.8 ppm or Kgs / Acre. i.e half the value of Fe. If lower, then apply Mn So4.
Fe - above 6 ppm or Kgs / Acre. i.e double the value of Mn. If lower, then apply Fe So4.
11. B.S.P: - Base Saturation Percentage should be above 80%.
Ratio between – (Ca + Mg + Na + K / (CEC) x 100 = 80%
12. E.S.P - Exchangeable Sodium Percentage.
Safe level below10
Moderate level 10 to 15.
Toxic level >15.
( Na / CEC) x 100 = below 10%
13. Types of Soil : Sand, Loamy Sand, Sandy Loam, Sandy Clay Loam, Clay loam, Sandy Clay, Silty Clay and Clay.
14. Ideal Soil Texture : Sand 33% : Silt 33% : Clay 33%
15. Acidic soil and its remedies: ( ‘அமில நிலம் ’ in Tamil)
Acidity due to Lower Ph because of low Ca.
pH range below 6.5 is Acidic.
Apply recommended dose of Calcium 10 days before applying any basal fertilizers then plough well to properly mix the Ca in the soil and irrigate.
16. Alkaline soil and its remedies: ( ‘களர் நிலம் ' in Tamil) Alkalinity due to higher pH because of the presence of Na.
Soil pH above 8 to 8.9 is Alkaline.
E.C below 4
E.S.P Below 10% (For Sodic Soil above 15%)
Growth of sensitive deep rooted crops will be moderately affected.
Apply liberal Qty. of FYM, raise Green Manure crops and plough them back into soil to increase O.C thereby increasing the drainage capacity of the soil.
Basal application of 300 Kgs of Gypsum per Acre for every crop. Apply more depending upon the alkalinity of the soil.
Use only Fertilizers like DAP, Zn So4, Am So4, K2 So4 (Pottassium Sulphate) Etc.
17. Sodic soil and its remedies: Presence of Na above 15 in Alkaline soil.
Soil pH above 9
E.C below 4
E.S.P above 15% (For Alkaline soils below 10%)
Sodium Carbonate in the Soil reacts with salts and Fertilizers and the end products get deposited as white patches above the soil.
Because of higher pH, nutrients in the soil are less. Since the soil subsurface is harder, plant roots can’t able to penetrate it.
Remedy for Sodic Soil:
Raise Daincha or Sunhemp and plough it back into soil (incorporate).
Cultivate Sun Flower Crop every year. It was proved that the Sun Flower plant absorbs Na from the soil and stores them in its parts. After harvest, the total plant with dried leaves should be removed.
Apply 5 Tons of press mud from Sugar mill.
Use only Fertilizers like DAP, Zn So4, Am So4, K2 So4 (Pottassium Sulphate) Etc.
Apply liberal Qty. of M.N nutrients especially Zn. (Zn So4 @ 40Kgs per Hect. as basal is necessary.
25% more N as Basal is necessary.
Raise Saline resistant varieties (Such as Trichy 1, Co 43 in Paddy)
For Paddy, transplant only matured plantlings of 35 to 40 days age. Plant 3 to 5 saplings per Kuthu. Sodic condition can be rectified using Chemicals such as Gypsum, Sulphur or Pairates.
Role of Gypsum (Ca So4) in the reclamation of Sodic Soil:
Contents of Gypsum: S 18% + Ca 23% + P2 O5 5%
Regular application of Gypsum (Ca So4) @ 200 Kgs per Acre will give good yields because of it’s S and Ca contents.
It neutralizes the harmful Na in the soil and reduces the E.S.P.
For Sodic soil reclamation :
1) Deep plough the field twice especially by Disc plough. It breaks open the hard soil pan lies in the subsurface and brings out the Na rich soil to the surface.
2) Evenly spread Gypsum (Ca So4) 2 Tons – leading in good quality water (leaching) – puddling by cage wheel ( தொலியடிப்பு ) - maintain Water level at 6’’ and wait for 2 days. - Ca So4 in Gypsum reacts with Na ( Sodium Bicarbonate ) in the soil and becomes Na So4 – Drain out the frothy Na So4 solution from the field. – Irrigate immediately - puddling by cage wheel ( தொலியடிப்பு) 2nd time – Drain out the frothy Na So4 solution from the field.
3) Raise Daincha and incorporate. 4) Afetr that raise ‘Horse Gram’ ( “கானம் ” in Tamil) and don’t take seeds in the first year – allow the seeds to drop and the plant to wither – after the rains i.e. in the next season take seeds.
Saline soil and its remedies: ( ‘ உவர் நிலம்’ in Tamil)
Normal Ph range, but with more E.C, because of Sulphates and Chlorates of Ca, Mg, Na and K.
Soil with high soluble salts, hence E.C above 4
Density of the cell sap in the root system is lower than the density of the salts in the soil resulting in reverse osmosis. (i.e) water / cell sap will ooze out of the cell wall and into the soil.
Cultivate Saline (Uvar) tolerant varieties such as Paddy , Ragi, Cotton, Sugar cane and Chillies,
Apply liberal Qty. of FYM, raise Green Manure crops and plough them back into soil to increase O.C thereby increasing the drainage capacity of the soil.
Level the field evenly - Irrigate Soft water ( free from Bicarbonates) copiously – maintain water level – then drain out the water completely - the unwanted salts dissolves in the water and flows out.
Provide adequate channels to let in rainwater and water from the irrigation tank. Salts will be washed off during heavy rains. Drain out the salt dissolved water from the field. We can reduce the salt content of the soil by increasing the drainage capacity of the field.
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