Crop period or Base period (B)
Delta of a crop(Δ): The total quantity of water required by the crop for its full growth may be expressed in hectare metre (ha.m) or simply as depth to which water would stand on the irrigated area if the total quantity supplied were to stand above the surface without percolation or evaporation. This total depth of water (in cm) required by a crop to come to maturity is called its delta (Δ).
Example 1: If rice requires about 10 cm depth of water at an average interval of about 10 days, and the crop period for rice is 120 days. Find out the delta for rice ?
Solution: Water is required at an interval of 10 days for a period of 120 days. It evidently means that 12 number of watering's are required, and each time, 10 cm depth of water is required. Therefore, the total depth of water required.
= 12 x 10 cm = 120 cm.
Hence Δ for rice = 120 cm.
The term duty means the "area of land" that can be irrigated with unit volume of irrigation water. Quantitatively, duty is defined as the area of land expressed in hectares that can be irrigated with unit discharge, that is, 1 cumec flowing throughout the base period, expressed in days.
If water flowing at a rate of one cubic meter per second, runs continuously for B days, and matures 200 hectares, then the duty of water for that particular crop will be defined as 200 hectares per cumec to the base of B days. Hence, duty is defined as the area irrigated per cumec of discharge running for base period B. The duty is generally represented by the letter D.
Relation between Duty(D) and Delta(Δ):
Let there be a crop of base period B days. Let one cumec of water be applied to this crop on the field for B days. Now, the volume of water applied to this crop during B days.
⇒Volume of water applied to crop (V)
= (1 x 60 x 60 x 24 x B) m3
= 86400 B (cubic metre)
By definition of duty (D), one cubic metre supplied for B days matures D hectares of land.
This quantity of water (V) matures D hectares of land or 104 D sq.m of area.
⇒ Total depth of water applied on this land = Volume/ Area
= 86,400 B/ 104 D
= 8.64 B/D metres
By definition, this total depth of water is called delta (Δ).
Δ = 8.64B/D (metres)
Δ is in cm, B is in days, D is duty in hectares/cumec
During the passage of water from these irrigation channels, water is lost due to evaporation and percolation. These losses are called Transit losses or Transmission or Conveyance losses in channels.
1. Rabi: 1st october - 31st march
2. Kharif: 1stApril to 30th September (Hot)
SOME IMPORTANT TERMS AND DEFINITIONS
TYPES OF IRRIGATION
Broadly irrigation can be classified as:
(1) Surface irrigation
(2) Sub-surface irrigation
(1) Surface irrigation:
(2) Sub-surface irrigation:
1. Free flooding
2. Border flooding
3. Check flooding
4. Basin flooding
5. Furrow irrigation method
6. Sprinkler irrigation method
7. Drip irrigation method
Reclamation of water logged and saline soil. An agriculture land is said to be water logged, when its productivity gets affected by the high water table. If root zone of plant gets flooded with water, air will not be available to plant root zone and reduces the yield.
Plant requires nutrients like nitrate, sand these are formed by aerobic bacteria. So if air is not available, bacteria will not survive so that no food for plants and results in less yield. Due to water logging, salts will be accumulated in the root zone and these soils become saline.
Causes of Water logging:
1. Over and intensive irrigation
2. Seepage of water from adjacent high lands
3. Seepage through the canal
4. Impervious obstruction
5. Inadequate natural drainage
6. Inadequate surface drainage
7. Excessive rains
8. Submergence due to floods
9. Irregular or flat topography
Water logging Control
1. Lining of canals & water courses
2. Reducing intensity if irrigation
3. Introducing crop rotation
4. Optimum use of water
5. Providing intercepting drains
6. Provision of efficient drainage system
7. Improving the natural drainage of the area
8. Introduction of lift irrigation
The phenomenon of salts coming up in solution and forming a thin (5 to 7.5 cm) crust on the surface, after the evaporation of water is called Efflorescence. Land affected by efflorescence is called Saline soil.
In this process the land is flooded with adequate depth of water. The alkali salts present in the soil get dissolved in this water which percolate down to join the water table or declined away by subsurface drains.
LR (leading requirement)
Di = Cu + Dd
⇒ Dd = Di – Cu
Ci = salt content of irrigation water
Cd = salt content of leach water
ECi = electrical conductivity of irrigation water
ECd = electrical conductivity of drainage water