Water Requirement for Different Crops and Related Problems

Md. Nurul KadirLecturerDepartment of Agricultural Engineering

Sher-e- Bangla Agricultural University, Dhaka

04/18/2023

Water Requirement

Water requirement (WR) may be defined as the quantity of water, regardless of its source, required by a crop or diversified pattern of crops in a given period of time for its normal growth under field condition at a place.

In short, Crop water requirement (CWR) is defined as the depth of water (mm) needed to raise crop in a given period.

It comprises of the water lost through evaporation from crop field, water transpired and metabolically used by crop plants, water lost during application which is economically unavailable and the water used for salt leaching and so on.

Determination of crop water requirement is used for the planning, design, and operation of both rain fed and irrigated agriculture.

Therefore, WR or CWR = ET or CU + application losses + special needs

Also, WR or CWR = Irrigation requirement (IR) + Effective rainfall (ER) + Soil profile contribution (S)

04/18/2023Md. Nurul Kadir Lecturer, Dept. of Agril. Engg. SAU

Dhaka

04/18/2023Md. Nurul Kadir Lecturer, Dept. of Agril. Engg. SAU Dhaka

Factors Affecting Water Requirements of Crop

1. Sunshine2. Temperature3. Humidity4. Wind speed5. Depth and distribution of rooting6. Size of the crop canopy (top portion)7. Thickness of stem8. Texture of soil9. Organic matter in the soil10. Type of crop grown11. Rainfall pattern12. Method of irrigation13. Quantity and type of fertilizer used

Climatic factor

Evapotranspiration

04/18/2023 Md. Nurul Kadir Lecturer, Dept. of Agril. Engg. SAU Dhaka

Terminology

EvaporationProcess of water movement, in the vapor form, into the atmosphere from soil, water, or plant surfaces

TranspirationEvaporation of water from plant stomata into the atmosphere

EvapotranspirationSum of evaporation and transpiration

Consumptive use (CU)Consumptive use is the total amount of water needed to grow a crop (the sum of the water used in evapotranspiration plus the water stored in the plant's tissues). The term consumptive use is generally used interchangeably with evapotranspiration because the amount of water retained in plant tissue is negligible compared to the amount of evapotranspiration.

Evapotranspiration

04/18/2023Md. Nurul Kadir Lecturer, Dept. of Agril. Engg. SAU Dhaka

Factors affecting ET1. Solar radiation 2. Temperature 3. Wind velocity 4. Relative humidity 5. Plant characteristics and growth stages 6. Soil water regime

Evaporation essentially occurs on the surfaces of open water such as lakes, reservoirs, or puddles, or from vegetation and ground surfaces. Transpiration involves the removal of water from the soil by plant roots, transport of the water through the plant into the leaf, and evaporation of the water from the leaf interior into the atmosphere.

Evapotranspiration

04/18/2023Md. Nurul Kadir Lecturer, Dept. of Agril. Engg. SAU Dhaka

04/18/2023Md. Nurul Kadir Lecturer, Dept. of Agril. Engg. SAU Dhaka

Irrigation Water Requirement (IWR):For irrigated crops, another main concept is the irrigation water requirement (IWR), defined as the net depth of water (mm) that is required to be applied to a crop to fully satisfy its specific CWR. The IWR is the fraction of CWR not satisfied by rainfall, soil water storage, and groundwater contribution.

Net Irrigation Requirement : It is the amount of irrigation water requirement to bring the soil moisture level in the effective root zone to field capacity. Thus it is the difference between the field capacity and the soil moisture content in the root zone before starting irrigation.

04/18/2023

Md. Nurul Kadir Lecturer, Dept. of Agril. Engg. SAU

Dhaka

The root zone

04/18/2023Md. Nurul Kadir Lecturer, Dept. of Agril. Engg. SAU Dhaka

Gross Irrigation Requirement : the total amount of water applied through irrigation is termed as “gross irrigation requirement”. In other words, it is the net irrigation requirement plus losses in water application and other losses.

Gross Irrigation Requirement =

For example, if the net amount of irrigation is 8 cm and the field efficiency is 75%, the gross amount of water to be applied to the field is, = 10.66 cm

04/18/2023

Md. Nurul Kadir Lecturer, Dept. of Agril. Engg. SAU

Dhaka