(1) It acts as a solvent for the nutrients. Water forms the solution of the nutrients, and this solution is absorbed by the roots. Thus, water acts as the nutrient carrier.
(2) The irrigation water supplies moisture which is essential for the life of bacteria beneficial to the plant growth.
(3) irrigation water supplies moisture which is essential for the chemical action within the plant leading to Its growth.
(4) Some salts present In soil react to produce nourishing food products only in the presence of water.
(5) Water cools the soil and the atmosphere, and thus make more favorable environment for healthy plant growth. Irrigation water, with controlled supplies, washes out or dilutes
(6 Irrigation water, with controlled supplies, washes out or dilutes stilts the the soil
(7) Ii reduce the hazard of soil piping
(8) It softens the tillage pans Crop Periods Crop period: Crop period is the time, in days, that a crop takes from the Instant of its sowing to that of its harvesting Base period Base period for a crop refers to tug whole period of cultivation from the time when irrigation water is first Issued for preparation or the ground for planting the crop to its last watering before harvesting. Crop Potation The term rotation of crops is somewhat self explanatory it implies that nature of the crop sown in a particular field is changed year after year Necessity for rotation: The necessity for rotation arises from the fact that soil gradually losses its fertility if the same crop is sown every year and the field has to be allowed to lie fallow in order to regain its fertility. The effect of fallow is obtained by rotation of crops.
All crops require similar type of nutriest for their growth but all of them do not take in the same quantities or proportions; some crop favours certain plant nutrients and take them more than the others. Thus if a particular crop is grown year after year, the soil gets deficient in the plant food favored by that crop. If different crops were to be raised there would certainly be more balance fooding and soil deficient in one particular type of nutrient is allow to recoupe.
Crop diseases and insect pests will multiply at an alarming rate, if the same crop is to be grown continuously. Rotation will check this disease.
A leguminous crop (such as gram) if introduced in rotation will increase nitrogen content of the soil thus increasing its fertility.
There could be deep rooted crops and shallow rooted crop in rotation and so they shall draw there food from different dept of soil. The soil will thus be better utilized. Rotation of crops the long run is beneficial to the farmer and soil both as there would be a rotation of cash crops, fooder crops and soil renovating crop The following rotations have been found useful:
(i) Introduction of groundnut in the usual cotton jowar rotate as per the experiments in Central Provinces Hyderabad
(ii) In Northern Pakistan, cotton Ii known to have improved when it follow. Berseen on fields manured with phosphate.
(iii) In Central Pakistan, Bajra when rotated with cotton has proved to be superior to Jowar being rotated with cotton
(iv) Cotton gives good result after gram or fallow
(v) Wheat does well after-sugarcane and gowar
In general the rotation of the crops can be summarized as given below:
1. Wheat great millet gram
2 Rice gram
3. Cotton wheat gram
4 Cotton wheat-sugarcane
5, Cotton great millet gram
The reason for gram being one In rotations Is Its being leguminous crop giving nitrogen to the field. Duty of Water Duty represents the irrigating capacity of a unit of water. It is the relation between the area of a crop irrigated and the quantity of irrigation water required during the entire period of the growth of that crop. For example, if 3 cumecs of water supply is required for a crop sown in an area of 5100 hectares, the duty of irrigation water will be 5100/3—1700 hectares/cumec, and the discharge of 3 cumecs will be required throughout the base period. Delta Delta is the total depth of water required by a crop during the entire period the crop is in the field and is denoted by the symbol £. For example, if a crop requires about 12 waterings at an interval of 10 days, and a water depth of 10 cm in every watering, then the delta for that crop will be 12 x 10120 cm-1.20 metres. If the area under that crop is L hectares, the total quantity will be 1.20 x/l — 1.2 hectare-metres in a period of 120 days Factors Affecting Duty The duty of water of canal system depends upon. a variety of the, factors. The principal factors are:
1. Methods and system of irrigation;
2. Mode of applying water to the crops;
3. Methods of cultivation;
4. Time and frequency of tilling;
5. Types of the crop;
6. Base period of the crop;
7. Climatic conditions of the area;
8. Quality of water
9. Method of assessment
10. Canal conditions;
11. Character of soil and sub-soil of the canal;
12. Character of soil and sub-soil of the irrigation fields. 1. Method and Systems of Irrigation: In the perennial irrigation system, soil is continuously kept moist, and hence water required for initial saturation is less. Also, due to the shallow depth of the water table, deep percolation losses are less. In the inundation irrigation, there is wasteful use of water. Hence, the perennial irrigation system has more duty than the inundation irrigation. The flow irrigation system has lower duty due to the conveyance losses in the network of the canals, while the lift irrigation in has higher duty because the commanded area of each well is very near to it. Tank Irrigation high duty d to rigid control. 2. Mode of Applying Water: The flood irrigation system has lesser duty than the fu system. Sub-irrigation system gives still higher duty. The basin irrigation and uncontrolled flooding give less duty. 3. Method of Cultivation: TI the land is properly ploughed and made quite loose before irrigating, the soil will have high water retention capacity in its unsaturated zone. Thus, the number of watering can be reduced increasing .the duty. The old and conventional methods of cultivation give less duty in comparison to the modem methods. 4. Time and frequency of Tilling: Frequency of cultivation reduces the loss of moisture through weeds. Soil structure affects the plant growth to a very great extent. A good structure (i.e. the good arrangement of soil particles in relation to one another) is called good fifth of soils. When the soil is in good filth, evaporation losses from the surface of soil is less, soil becomes properly aerated, and hence the yield of crop is also better. 5. Type of the crop: The duty varies from crop to crop as is clear from table 6. Base Period of the Crop: If the base period of the crop is more, the amount of water required will be high, hence duty will be low and vice-versa. 7. Climatic Conditions of the Area: The climatic conditions which affect the duty are (i) temperature, (ii) wind. (iii) humidity, and (vi) rainfall. Due to high temperature and wind, evaporation losses will be more, and duty will be less. A humid atmosphere reduces the losses. Rainfall during the crop period will reduce the irrigation-water requirement and the duty will thus be higher. In this context there are two popular terms: (1) Duty inclusive of rainfall, i.e. duty be considered by taking rainfall into account, (ii) Duty exclusive of rainfall, that is the duty has been considered by not considering the rainfall in the area. 8. Quality of water: If the harmful salt-content and alkali content of the water is more, water will have to be applied liberally so that the-salts are leached off. This will, in turn, reduce the duty. More fertilizing matter in water will cause less consumption of water, and increase duty, 9. Method of Assessment: Volumetric method of assessment always leads to a higher duty. This is because i.e. the farmer will use water economically. If, however, the meth of assessment is based on the area under cultivation, the farmer will have a tendency to use more water, and the duty will be low. 10. Canal Conditions: In an earthen canal, the seepage and percolation losses will be high, resulting in the low duty. If, however, the canal is lined, the losses will be less, and duty will be high. If the high canal is so aligned that the irrigated areas are concentrated along it, the V/ duty will be higher. The dispersion of the irrigated areas with respect to the canal tends to reduce the duty. 11. Character of Soil and Sub-soil of the Canal: If the canal is unlined, and if it flows through coarse grained, permeable soils, the scepage and percolation losses will be high. If the canal flows through fine grained soil, such losses will be less and hence the duly will be higher. 12. Character of Soil and sub-soil of the Irrigation Field If the soil and sub-soil of the field is coarse-grained, percolation losses will be high. However, if there is hard pan at depth I to 2 metre below surface, the percolation loss reduces. The duty is also affected by the topography of the land. If the field is not level, the lower portions get more water, while higher portions may remain drier. In order to supply water to the higher places, more water will be used, and the duty will be reduced. Factors Affecting Duty The duty varies with the place of its measurement, because of continuous conveyance losses as the water flows. The duty of water goes on increasing as the water flows. For example, let C be the head of the field, B be the head of the water course or the field channel, and A be the head of the distributary. Let the area of the field be 1700 hectares, and let cumec water be required to be delivered at point C, for the growth of the crop. Thus, the duty at the head of the field will be 1700 hectares/cumec. Assuming the conveyance losses between B and C to be 0.1 cumecs (Say) the discharge required at B will be 1.1 Cumes and hence duty of water measured at B will be 1700/1.1 = 1545 hectares/cumec only. Again, if the losses between A to B are taken to be equal to 0.2 cumec, the discharge required at the head of the distributary will be 1.1+ 0.2—1.3 cumecs, Le. if 1.3 cumecs are discharged at A, then 1 cumec will reach at the head of the field. Hence the duty of water at A will be 1308/1.3 hectares cumec only.
Thus, duty at the head of the water course (at B) is lesser than the duty at the head of the field, and is greater than the duty at the head of the distributary. The duty at the head of the water-course is called the outlet duty. Thus measurements of duty are taken at four points noted below
(i) At the head of main canal—known as Gross Quantity.
(ii) At the head of a branch canal—known as Lateral Quantity.
(iii) At the outlet of a canal—known as Outlet Factor,
(iv) At the head of land to be irrigated—known as Net Quantity. Relation Between Duty and Delta We shall derive the relationship between duty and delta, in both the systems of units.
(a) F.P.S. system
Let D duty in acres/cusec
A = total depth of water supplied (in ft.)
B base period in days.
(i) If we take a field of area D acres, water supplied to the
field corresponding to the water depth t will be = z2 x D acre-
feet — A x D x 43560 cuft.
(ii) Again, for the same field of D acres, one cusec of water is required to flow during the entire base period. Hence, water supplied to the this field = (1) x (B x 24 x 60 x 60 ) cu.ft,
No comments:
Post a Comment