Lecture No 15 Soil irrigability.pptxkick

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1. Land Irrigability Classification and Soil Productivity Rating Dr. V. Arunkumar Assistant Professor (SS&AC) AC & RI, Vazhavachanur

2. LAND IRRIGABILITY CLASSIFICATION (LIC) Soils are classified according to their suitability for sustained use under irrigation based on soil properties. Predicting the behaviour of soils under greatly altered water regimes brought about by introducing irrigation. Physical factors (topography, drainage and water quality) Socio-economic factors (development, costs, etc.,).  

3. System used for Selection of irrigable lands, Estimation of water requirements Development costs and benefits from irrigation. Separation of land irrigability classes are made on specified limits of soil properties and other physical parameters.

4. In LIC special attention is paid to three factors viz., - drainability of land, - predicted effect of irrigation water on salinity and alkalinity status of soils - the cost of inputs for land development. Generally all soils / lands are not equally suited for irrigation on a sustainable basis.

5. LAND IRRIGABILITY CLASSIFICATION (LIC) Suitability criteria Available water holding capacity (AWHC) Effective rooting depth Intake characteristics of soils.  FAO and Iranian workers developed a system Based on limitations of different land characteristics Texture Depth Permeability Salinity Topography

6. The soil unit are grouped into six suitability classes Class 1 to 3 Arable, suitable for irrigated agriculture with negligible (for class 1) to moderate (for class 3)limitation Class 4 Restricted – arable with severe limitations of soil. Land not irrigable except under special conditions. Class 5 Undetermined arable land that have severe limitations of soil Salinity/ drainage for irrigated agriculture. Class 6 Non – arable; unsuitable for irrigation.

7. The soil unit are grouped into six suitability classes Class 1(A) Lands that have few limitations Nearly level (<1%) Deep (>90 cm) Favourable permeability (5.0- 50 mm/ hr ) Texture ( sl , cl) surface 30 cm Moisture holding capacity (12 cm) The soils in this class are nearly level, have deeper rooting zones, have favourable permeability, texture, available moisture holding capacity.

8. Class 2(A-B) Lands that have moderate limitations for sustained use under irrigation - 1-3 % slope 45-90 cm depth Permeability (1- 3.5 mm/ hr ) Texture (loamy sand, clay) Moisture holding capacity (9-12 cm) Limitations may be 1. Very gentle slopes 2. Less than ideal depth, texture permeability 3. Moderate salinity or alkali 4. Somewhat unfavourable topography or drainage conditions

9. Class 3(C) Lands that have severe limitations for sustained use under irrigation - 3-5 % slope favourable soil depth (22.5 -45 cm) Permeability (0.3-1.3 mm/ hr ) (130-250mm/ hr ) Texture (sand, clay) Moderate severe salinity or alkalinity (8-12 d Sm -1 ; ESP > 15) Unfavourable drainage (poor or excessively drained) Moisture holding capacity (6-9 cm) Limitations are 1. Gentle slopes 2. Unfavourable soil depth, texture, permeability 3. Moderately severe salinity or alkalinity 4. Unfavourable topography

10. Class 4(D) Marginal lands for sustained use under irrigation - 5-10 % slope Soil depth (7.5-22.5 cm) permeability (0-3 mm/ hr ) (>250mm/ hr ) Texture (sand, clay) Very severe salinity (12-16 mmhos /cm) alkalinity (ESP > 15) Moisture holding capacity (2-6 cm) Limitations are 1. Moderately steep slopes 2.Very unfavourable soil depth, texture, permeability 3. Severe salinity/alkali when in equilibrium with irrigation water 4. Very unfavourable topography

11. Class 5 Lands that are temporarily classed as not suitable for sustained use under irrigation pending further investigations Class 6(E) Lands not suitable for sustained use under irrigation - >10 % slope Soil depth (<7.5 cm) permeability Texture (any texture) Salinity and alkalinity (ESP > 15)

12. Major limitation Soil unit with all characteristics of class 1 and only one characteristic of class 3 will grouped under class 3 While another soil unit with all the characteristics of class – 3 will also come under class – 3 Though the two soils may respond in an entirely different manner on irrigation.

13. Land irrigability sub classes land irrigability units that have same kinds of dominant limitations for sustained use under irrigation when lands are placed in a class lower than 1 Groups of land irrigability units with some dominant limitation s – Soil t – Topography d – Drainage

14. How to denote sub class Lands with one or more limitations may be indicated with relevant letters after class like ‘ Class 2 st ’ land irrigability class 2 limitations are soil and topography .

15. Land irrigability units Grouping of lands that are nearly alike in suitability for irrigation H aving similar crop adaptation, yield potential and soil and water management needs. Detailed information regarding crops adopted (a), water requirement (b), method of irrigation (c), cost and benefits of land development (d), land treatment (t) are to be suggested in formulating irrigation projects.

16. LAND CAPABILITY CRITERIA

17. The US Bureau of Land Reclamation (1953) land class is defined as a category of land having comparable physical and chemical attributes which affect the suitability of land for irrigation six classes class. I land has highest class – 6 land has the lowest payment capacity. The land classes in this system are not uniform everywhere. Example : Salinity may not be considered as a limitation in lands that have suitable permeability and adequate drainage.

18. Capability Index- Ci - Sys (1976) a) Soil physical and chemical properties: Such as texture, AWHC, salinity, CaCO 3 and gypsum contents. b) Drainage condition as deduced from the internal drainage, permeability and intake rates. c) Topographical conditions as influenced by slope (degree and length)

19. Capability Index- Ci - Sys (1976) The rating to each soil unit is assigned as per the table furnished below and the overall capability index (Ci) is calculated as: Capability index ( Ci )= A.B.C.D.E.F.G Where A=rating for soil texture (taken as 100 for the best texture - loam) B=rating for soil depth (taken as fraction of 1) C=rating for CaCO 3 (taken as fraction of 1) D=rating for gypsum status (taken as fraction of 1) E=rating for salinity/alkalinity status(taken as fraction of 1) F=rating for drainage condition (taken as fraction of 1) G=rating for topography (slope) (taken as fraction of 1)

20. Capability index ( Ci )= A.B.C.D.E.F.G A soil with loam structure, very deep, 5 to 10 % CaCO 3 , 2 to 5 % gypsum, 4 to 8 % (dSm -1 ) salinity, well drained, >1% slope, Ci can be calculated as Ci= 100 x 1 x 0.9 x 0.8 x 0.9 x 1 x 1= 64.5 = 65

21. According to overall capability index (Ci) value, the soil suitability class for each of the soil mapping unit is determined. The following classes and sub classes are defined: Class Suitability Ci rating S 1 Very suitable to suitable  80 S 2 Moderately suitable 60-80 S 3 Marginally/slightly suitable 40-60 N 1 Almost unsuitable 20-40 N 2 Unsuitable <20   Subclasses: s- limitations of physical soil properties n- limitations due to salinity/alkalinity d- drainage or wetness limitations t -topographical limitations Ratings based on kind and degree of limitation for surface irrigation S2s – moderately suitable land (S2) with limitation of physical soil properties (s).

22. SOIL PRODUCTIVITY RATING Rating citrus growing soils in California for tax purpose. First of index appeared in 1930’s and updated in 1978 Soil productivity is the capability of soils to produce a certain amount of crop yield per unit area per annum. Potential productivity It is the productivity of soil when all possible improvements have been made. It is the future productivity of the soil after eliminating all the constraints, which restricts the yield potential.

23. Riquier index Determination of productivity index Productivity is a function of the intrinsic properties of soil, determined in the process of describing the soil profile in situ and by laboratory analysis, wherein soil moisture and temperature are included; and environmental factors such as slope, vegetation and climate will be used to determine what set of management practices are necessary.

24. Factors are determining soil productivity nine soil/site factors were used in computing soil Productivity Index (PI). Soil Productivity = H x D x P x T x N (or) S x O x H x M Moisture (H ) Drainage (D ) Effective depth (P) Texture / structure (T) Base saturation (N) Soluble salt concentration (S) Organic matter content (O) Mineral exchange capacity / nature of clay (H) Mineral reserves (M)

25. A soil is considered more fertile if Soil Depth - P Base saturation N Texture and structure – T Rich in OM, high CEC and more mineral reserves Each factor is rated on scale from 0 to 100, the actual percentage being multiplied by each other. The resultant index of productivity also lying between 0 and 100 % is set against a scale placing soil in one or other of following five productivity classes.

26. PRODUCTIVITY RATING SI. No. Class Rating % 1. Excellent 65-100 2. Good 35-64 3. Average 20-34 4. Poor 8-19 5. Extremely poor 0-7

27. Potential productivity Potential productivity rating (P’) After effecting all the possible soil improvement factors, the potential productivity rating was worked out and grades were assigned ( Riquier et al., 1970). It is the future productivity of that soil taking into account of physical and chemical characteristics as modified by conservation practices or improvements.

28. The limiting factor requiring soil management H (dryness) Requires irrigation D (Poor drainage) Requires drainage P (Shallowness) Deepening T (Poor structure or texture) Improvement of structure / texture N (Low nutrient content) Requires fertility management C (Salinity) Requires desalting O (Low organic matter) Requires application of organic matter

29. Co-efficient of improvement The ratio of P : P’ indicating the extent to which productivity can be improved is called the co-efficient of improvement. CI = Potential productivity rating Present Productivity rating If the ratio is 2.5 means, the productivity can be improved by 2.5 times more.

30. STORIE INDEX Earl storie (1964) proposed storie index for evaluation of soil. Storie index of soil rating is a function of 4 major factors. A - Rating on character of physical profile B - Rating on the basis of surface texture C - Rating on the basis of slope X - Rating of conditions other than those in factors A, B and C like drainage, nutrient (fertility) levels and erosion etc.

31. STORIE INDEX RATING OR SOIL SUITABILITY RATING Storie index of soil rating is a function of four major factors viz., Rating = A x B x C x X A - Rating on character of physical profile B - Rating on the basis of surface texture C - Rating on the basis of slope X - Rating of conditions other than those in factors A, B and C like drainage, nutrient (fertility) levels and erosion etc.

32. Properties Values Profile (A) – 60/100 Surface texture (B) – 95/100 Slope (c) – 90/100 Drainage (X) – 100/100 Erosion (X) – 95/100 Fertility (X) – 95 /100 Therefore, soil rating = 46.2

33. Grade1 (excellent) Soil that rate between 80 and 100 per cent and which are suitable for wide range of crops. Grade2 (good) Soils that rate between 60 and 79 per cent and which are suitable for most crops. Yields are generally good to excellent. Grade3 (fair) Soils that rate between 40 and 59 per cent and which are generally of fair quality with less wide range of suitability than grades 1 and 2. Soils in this grade may give good results with certain specialized crops.

34. Grade4 (poor) Soils that rate between 20 and 39 per cent and which have a narrow range in their agricultural possibilities. For ( eg ) a few soils in this grade may be good for rice, but opt for many other crops. Grade5 (very poor) Soils that rate between 10 and 19 per cent are of very limited use except for pasture, because of adverse conditions such as shallowness, roughness, and alkali content. Grade6 (non agricultural) Soils that rate less than 10 per cent which include tidelands, river wash soils of high alkali content and steep broken land.

35. Thank you