IRRIGATION MANAGEMENT PBT-904 Dr. Rabia Amir Lecture 8

IMPORTANCE OF WATER FOR PLANTS Water is important for plants because of the following reasons: Seeds germination Photosynthesis Transport of nutrients and minerals from the soil to plants. Maintenance of the plant structure. Habitat in the form of ponds, rivers, lakes and sea

IRRIGATION AMOUNT The amount of applied irrigation water should be less than the soil water deficit in order to provide some soil water storage reserve for rainfall. For most soils the net irrigation application during early plant growth and the last few weeks before maturity should be only 30-50 percent of the soil water deficit. On most sandy soils the irrigation depth should be 80-100 percent of the soil water deficit during the crop's critical growth period . On medium to fine textured soils irrigation application depth should be 50-100 percent of the soil water deficit depending on the irrigation system's pumping capacity.

IRRIGATION MANAGEMENT STRATEGY Some general guidelines to consider in developing a water management plan and setting allowable soil water deficit limits are as follows:

IRRIGATION MANAGEMENT STRATEGY In Spring Always make sure the soil in the germination and early growth root zone is moist at the time of planting. www.scmao.com

IRRIGATION MANAGEMENT STRATEGY As the crop is nears its critical growth period Selected allowable soil water deficit should be reduced to minimize the risks of not meeting the crop's water needs www.scmao.com

As the crop nears maturity Soil water deficit generally can be allowed to increase to greater limits without causing stress to the crop

SOIL WATER MEASUREMENT Two common ways of estimating soil water deficit Feel/appearance method Use of soil water sensors

Feel/appearance method Collect soil samples in the root zone with a soil probe or spade Estimate water deficit for each sample by feeling the soil and judging the soil moisture Soil samples should be taken at several depths in the root zone and at several places in the field. Estimate the total soil water deficit in the root zone

Use of soil water sensors Soil tension can be measured by using tensinometer or electrical resistance blocks. Soil tension is expressed in centibars It can be measured at any point in the soil profile

SOURCES OF IRRIGATION WATER Ground water Extracted from springs By using wells Surface water Withdrawn from rivers, lakes or reservoirs non-conventional sources like treated wastewater

Flood Water Harvesting A special form of irrigation using surface water is spate irrigation. In case of a flood (spate) water is diverted to normally dry river beds using a network of dams, gates and channels and spread over large areas. Areas are located in semi-arid or arid, mountainous regions

Rain Water Harvesting Collection of runoff water from roofs or unused land and the concentration on cultivated land. This method is known as a water concentration method.

Methods of Irrigation Three principle methods of irrigation Surface, Sub surface and Aerial, Overhead or sprinkler irrigation.

Methods of Irrigation Surface irrigation Four variations under this method Flooding Bed or border method (flat beds), Basin method (ring and basin) and Furrow method (rides and furrows, broad ridges or raised beds)

Flooding Opening a water channel in a plot or field so that water can flow freely in all directions and cover the surface of the land in a continuous sheet.

Bed or Border Method Field is leveled and divided into small beds surrounded by bunds Small irrigation channels are provided between two adjacent rows of beds It requires leveled land It is suitable for crops plant in lines

Basin Irrigation Suitable where the size of the plot to be irrigated is very small e.g orchids It may be square, rectangular or circular shape Requires leveled land Not suitable for all types of soil Efficient in the use of water

Furrow Irrigation Water is allowed to flow in furrow opened in crop rows suitable for sloppy lands where the furrows are made along contours The length of furrow is determined mostly by soil permeability Row crops such as potatoes, cotton, sugarcane, vegetable etc. can be irrigated

Methods of Irrigation 2. Subsurface irrigation Subsurface irrigation or sub-irrigation may be Natural subsurface irrigation Artificial subsurface irrigation

Natural Sub surface Irrigation It is possible where an impervious layer exists below the root zone. Water is allowed in to series of ditches dug up to the impervious layer. It then moves laterally and wets root zone.

Artificial Subsurface Irrigation Perforated or porous pipes are laid out underground below the root zone. Water is led into the pipes by suitable means. The method involves initial high cost, but maintenance is very cheap.

There is a risk of soil getting saline or alkaline. There is risk of neighboring land damaged due to heavy seepage.

Subsurface irrigation Advantages Efficient in the use of water as evaporation is cut off almost completely The plant roots do not suffer from logging There is no loss of agricultural land in laying out irrigation system Implements can be worked out freely

1. Drip or Trickle Irrigation It involves slow application of water to the root zone. The drip irrigation system consist of Head Main line and sub line Lateral lines Drip nozzles

Advantages The losses by drip irrigation and evaporation are minimized. Precise amount of water is applied to replenish the depleted soil moisture at frequent intervals for optimum plant growth. The system enables the application of water fertilizers at an optimum rate to the plant root system. The amount of water supplied to the soil is almost equal to the daily consumptive use, thus maintaining a low moisture tension in soil.

Disadvantages The initial cost of the drip irrigation for large-scale irrigation is its main limitation. The cost of the unit per hectare depends mainly on the spacing of the crop. For widely spaced crops like fruit trees, the system may be even more economical than sprinkler.

2. Sprinkler or Overhead Irrigation It consists of application of water to soil in the form of spray, somewhat as rain. It is particularly useful for sandy soils because they absorb water too fast.

Advantages It ensures uniform distribution of water It is adaptable to most kinds of soil It offers no hindrance to the use of farm implements Water losses are reduced to a minimum extent More land can be irrigated Costly land leveling operations are not necessary The amount of water can be controlled to meet the needs of young seedling or mature crops.

Disadvantages The initial cost is rather very high. Any cost of power to provide pressure must be added to the irrigation charges. Wind interferes with the distribution pattern, reducing spread or increasing application rate near lateral pipe. There is often trouble from clogged nozzle or the failure of sprinklers to revolve. The cost of operations and maintenance is very high. Labor requirement for moving a pipe and related work approximately nearly one hour per irrigation. It is suitable for high value crops.

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