Water Requirements of Crops in Irrigation Engineering – Complete Guide for JKSSB Aspirants

📖 Introduction

In agriculture, water is not just a resource—it’s the lifeline of crop production. From germination to harvesting, every phase of a crop’s lifecycle demands specific quantities of water. In the field of Irrigation Engineering, calculating and managing the water requirement of crops ensures optimal use of water resources while maximizing agricultural yield.

For JKSSB aspirants, this topic is frequently covered under Civil Engineering (JE, AE) and Agriculture Engineering exams. Questions are often conceptual or numerical, so understanding both theory and practice is key.

💧 What is the Water Requirement of Crops?

The Water Requirement (WR) of a crop refers to the total amount of water required from the time of sowing to harvesting to fulfill the following needs:

• Evapotranspiration (ET) – water lost through evaporation from soil and transpiration from plants.
• Soil moisture preservation – maintaining the root zone moisture for healthy growth.
• Percolation & leaching – excess water movement to deeper soil layers or removal of salts.
• Germination and metabolic needs – aiding biological and physiological functions.

✅ Definition

“Water requirement is the total quantity of water required by a crop from sowing to harvesting for its normal growth under field conditions.”

🔍 Why is Understanding Water Requirement Important?

• Efficient irrigation planning
• Water conservation
• Higher crop productivity
• Avoidance of over-irrigation and under-irrigation
• Prevention of soil salinity and waterlogging

🧾 Components of Crop Water Requirement

The total water requirement includes the following components:

1. Consumptive Use (CU)
   ➤ Also called evapotranspiration, it is the water consumed by the plant for growth and lost to the atmosphere.
2. Application Losses
   ➤ Water lost during application due to seepage, deep percolation, and conveyance losses.
3. Special Requirements
   ➤ Additional water needed for:
   • Germination
   • Frost protection
   • Leaching salts (especially in saline soils)

🧮 Formula for Water Requirement

WR=CU+Losses+Special Needs\text{WR} = \text{CU} + \text{Losses} + \text{Special Needs}WR=CU+Losses+Special Needs

Where:

• WR = Water Requirement
• CU = Consumptive Use
• Losses = Application, seepage, deep percolation
• Special Needs = Cultural operations (germination, leaching)

🌱 Types of Water Requirements

🌦️ Factors Affecting Crop Water Requirements

📋 Crop-wise Approximate Water Requirements

🔢 Estimating Water Requirement – Methods

1. Blaney-Criddle Method

• Uses temperature and crop coefficient
• Easy and suitable for regions with limited data

2. Penman-Monteith Method

• Based on temperature, wind, humidity, radiation
• Very accurate (FAO recommends it)

3. Pan Evaporation Method

• Uses evaporation pan data and crop coefficient

4. CROPWAT Model

• FAO’s software to compute crop water needs and irrigation schedules

🧠 JKSSB Exam Relevance

For JKSSB Civil and Agriculture Engineering exams, this topic may appear as:

• Conceptual MCQs (e.g., “What is Net Irrigation Requirement?”)
• Numerical problems (e.g., Calculate GIR given efficiency and NIR)
• Theory questions (e.g., Discuss factors affecting crop water requirement)

🔚 Conclusion

Understanding the water requirements of crops is essential for efficient irrigation management. It ensures optimal water use, enhances crop yield, and supports sustainable farming practices. For JKSSB aspirants, this is a scoring topic with practical importance in both academic and professional fields.

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Sahil Digra

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