eChapters

Water is a very essential component for human civilization, living organisms, and natural habitats. It ma.kes up a major part of plant biomass (about 90% of plant cytoplasm; Singh, 2014). Irrigation, the largest water user sector, is currently under pressure to produce more with higher quality by using limited water to feed the increasing population of the country. The highest proportion of water is consumed by agricultural crops, which is called the blue water footprint, and it is assumed that the water scarcity will increase in the future in view of the changing climate. India has 18% of the world population; however, the water resources are only 4%. Even with all the planning and development, the country has not even been able to provide sufficient drinking water to all at the end of the 20th century. The water sector is facing a number of challenges regarding the availability, accessibility, use, and sustainability of its fresh water resources. Further, the distribution of water in the country is also uneven over space and time. Unfortunately, Rajasthan is the driest state in the country and has been water scarce (with per capita water availability below 1000 m3/year) since 1991. The efficient use of water in agriculture/ horticulture without affecting crop productivity or quality by adopting water saving irrigation techniques is the foremost need. Fruit crops, which have gained commercial attention in recent years, are an important component of Indian agriculture. Due to low irrigation and water use efficiencies, irrigation managers are looking for the introduction of effective water-saving devices and practices for water management in fruit crops.

5.1. Irrigation requirement of field crops

Water is an extremely essential component in plant growth and development. It is of utmost importance for photosynthesis, cell division, cell growth / elongation, respiration, nutrient uptake, mineral utilization and much other metabolic process, which directly affect the quantity and quality of the produce. Hence quantity and quality of water play a vital role in performance of a crop. A well distributed water supply, throughout the growth of plant is essential. Rainfall is the major source of water for the crops. Rainfall recharges the surface water resources such as rivers, streams and ponds and also the ground water resources like wells.

Pumps play a critical role in irrigation systems by providing the necessary force to move water from its source (such as a well, river, or reservoir) to the f ields where crops are grown. The selection and proper operation of irrigation pumps are crucial for the efficiency and success of agricultural practices. Here’s a detailed overview of pumps used in irrigation:

Types of Irrigation Pumps

Centrifugal Pumps

Principle of Operation: Centrifugal pumps are the most common type used in irrigation. They work by converting mechanical energy into kinetic energy in the form of fluid flow. Water enters the pump through the center (eye) of a rotating impeller and is accelerated outward.

8.1 Introduction

For maximization of yield of crops, it is essential to provide irrigation to crops. When either the natural sources like rainfall, dew, snowfall and other forms of precipitation or when the capillary rise of groundwater is not sufficient to meet the crop water demand, then there is need to supply irrigation. This irrigation water is a precious resource and need to be used cautiously. There are three important things need to be understood for optimum utilization of irrigation water with basic purpose to maximize the yield and returns. 

7.1 Introduction

For maximization of yield of crops, it is essential to provide irrigation to crops. When either the natural sources like rainfall, dew, snowfall and other forms of precipitation or when the capillary rise of groundwater is not sufficient to meet the crop water demand, then there is need to supply irrigation. This irrigation water is a precious resource and need to be used cautiously. There are three important things need to be understood for optimum utilization of irrigation water with basic purpose to maximize the yield and returns. These three things are:

(i) When to irrigate?

(ii) How much to irrigate? and

(iii) How to irrigate?

In fact these three things form the core concept of irrigation scheduling.

The purpose of irrigation scheduling is to decide upon the amount of water to be applied for irrigation and timing of irrigation in order to avoid wastage of precious water. The irrigation scheduling is also used to determine the number of irrigations required for a crop during its growth cycle and judicious use of water depending upon the weather forecasts issued from time to time. The irrigation scheduling has to be planned for either full irrigation or supplementary irrigation depending upon the availability of water resources and the season during which crops are grown. Crops grown during the dry season requires full irrigation and crops grown during the rainy season require supplementary irrigation. The third category of irrigation is protective irrigation which is practiced in dryland areas. The protective irrigation is given when the crops are experiencing severe moisture stress due to prolonged dry spells wherever the farmers has access to small ponds and tanks developed within his own field as water harvesting structures.
10.1. Full Irrigation
Under full irrigation, the crops are provided with irrigation right from land preparation till the crop is getting ready for harvest maturity. The full irrigation will be usually planned for maximum yields of the crop (Fig.10.1).

The following various types of irrigation methods and their systems are used in crop production in greenhouses and plant nurseries.

1.Hand Watering

2.Perimeter Watering System

3.Tube Watering System

4.Drip Irrigation System

5.Overhead Spray System

6.Ebb and Flow System.

Efficient irrigation water management is essential for achieving high crop productivity while conserving limited water resources and minimizing environmental hazards. This chapter presents the principles and practices required to manage irrigation according to crop demand and soil-water conditions. It begins with how plants obtain water from soil and explains irrigation requirements, crop water requirement terminology, water-use efficiency, field water balance and the effective root zone. Crop response to water at different growth stages is considered for important crops including rice, wheat, maize, sugarcane and mustard. Different irrigation methods are described, including surface, corrugation, sub-irrigation, sprinkler and drip irrigation. The chapter provides several approaches to irrigation scheduling based on water-holding capacity, degree of water depletion, soil-water potential, evaporation pans, leaf-water potential, canopy temperature, crop water stress index and leaf reflectance. Methods for measuring irrigation water and flowing water, including water-measuring devices and current meters, are also discussed. Scheduling based on IW/CPE ratio and depletion of available soil moisture provides practical approaches for improving water-use efficiency.

For better yield irrigation water must be free from soluble salts and from concentration of specific chemical substances that may hazard to soil with respect to salinity, sodicity, alkalinity and toxicity. Water analytical data which helpful to predict the magnitude of the effect of irrigation water on soil and plant growth under specific environmental circumstances so irrigation water must be analyzed for EC, pH, Na+, Ca⁺⁺, Mg⁺⁺, Cl^-, CO₃–, HCO₃-  and SO₄.^– 

Water Quality Parameters
Irrigation water contains impurities in varying concentration. The suitability of irrigation water mainly depends up on the amount and type of salts present in the water. The main soluble constituents are calcium, magnesium, sodium as cations and chloride, sulphate, bicarbonates as anions. The other ions present in minute quantities are boron, selenium, molybdenum and fluorine which are harmful to animals fed on plants grown with excess of these ions.
Quality of irrigation water is judged with three parameters
1. Total salt concentration
2. Sodium absorption
3. Bicarbonate and boron content.
Total Salt Concentration
Salt content of irrigation water is measured as electrical conductivity (EC). Conventionally, water containing total dissolved salts to the extent of more than 1.5m mhos /cm has been classified as saline. Saline waters are those which have sodium chloride as predominant salt. Brackish water is one that is contaminated with acid, bases, salts or organic matter, whereas saline water contains mainly dissolved salts, Based on EC irrigation water is classified as below.

6.1. Quality of irrigation water

Asia per capita water availability has fallen by around 80 per cent during last five decades.

Suitability of waters for a specific purpose depends on the types and amounts of dissolved salts.

Some of the dissolved ions such as NO₃ are useful for crops.

Water required for irrigation of cropped land is being degraded in terms of quantity and quality due to fast increasing demand for its use. Furthermore, the soil quality and crop productivity is linked to the quality of the water available for irrigation. In general, evaluation of irrigation water quality should focus on salt content, sodium concentration, the occurrence of nutrients and trace elements, alkalinity, acidity, and hardness of the water.

Introduction

Irrigated agriculture is dependent on an adequate water supply of usable quality. The water quality used for irrigation is essential for the yield of crops, maintenance of soil productivity, and protection of the environment as well. The quality of irrigation water is defined with respect to its effect on plant growth, soil properties, soil biological equilibrium, and irrigation technology. Conceptually, water quality refers to the characteristics of a water supply that will influence its suitability for a specific use, i.e. how well the quality meets the needs of the user. Specific uses have different quality needs and one water supply is considered more acceptable (of better quality) if it produces better results or causes fewer problems than an alternative water supply. For example, good quality river water which can be used successfully for irrigation may be unacceptable for municipal use without treatment to remove its sediment load. Similarly, snowmelt water of excellent quality for municipal use may be too corrosive for industrial use without treatment to reduce its corrosion potential.

1.1 Introduction

Water scarcity is seen as a major constraint to intensify agriculture in a sustainable manner as an attempt to meet the food requirements of a rapidly growing human population. The ever-increasing human population, climate change due to increased emissions of greenhouse gases (GHGs), and intensification of agriculture, are putting severe pressure on the world’s two major non-renewable resources of soil and water, and thus pose a big challenge to produce sufficient food to meet the current food demand. The present world population of 7.3 billion people is predicted to grow to over 9 billion by 2050, with the majority of this population increase occurring in developing countries, most of which already face food shortages. A 70% increase in current agricultural productivity will be required to produce sufficient food if these human population growth predictions prove to be correct. In this context, concerted efforts are being made globally to improve the effectiveness of water which will be used for enhancing the production of irrigated crops. Additionally, efforts are also being made to improve water harvesting and water conservation in rain-fed agriculture.

The injudicious use of saline/brackish water is all too often associated with the development of soil salinity, sodicity, ion toxicity, and groundwater pollution. Because of these negative effects, it is important to have a better understanding of exactly how the quality of water influences the management of irrigated agriculture, especially in arid and semi-arid regions.

Introduction

Irrigation is the artificial application of water to soil or land to assist in the growth of crops, vegetation, or landscaping. It is a crucial agricultural practice used to supplement natural rainfall and provide controlled and consistent moisture to plants when needed. Irrigation systems can vary in complexity, from simple methods like watering cans and hoses to more advanced systems like drip irrigation, sprinklers, and flood irrigation.

The primary purpose of irrigation is to ensure that plants receive an adequate and consistent supply of water, especially in regions with insufficient or irregular rainfall. This helps promote healthy plant growth, increase crop yields, and prevent drought-related crop damage. Irrigation is not only used in agriculture but also for landscape maintenance, recreational fields, and other applications where controlled watering is essential.

Irrigation

Irrigation is defined as the artificial application of water to the soil for the purpose of crop production in supplement to rainfall and ground water contribution.

Time of Irrigation

The time schedule which indicates when irrigation water is to be applied and the quantity of water to be applied at that time is called irrigation schedule. There are several approaches for scheduling irrigation:

1. Soil moisture depletion approach based on the available soil moisture in the root zone.
2. Climatological approach based on the amount of water lost by evapotranspiration.
3. Combination approach based on soil moisture depletion and climatological approaches.
4. Critical stage approach which indicates the growth stages at which moisture stress leads to yield loss. These stages are known as critical period or moisture sensitive period. In cereals and millets panicle initiation and flowering stages are moisture sensitive stages. In pulses and oilseeds, flowering and pod development stages are critical stages. In sugarcane active tillering or formative stage is critical and in cotton boll development is the critical stage.

Technical Term            Definition

Infiltration                    Infiltration is movement of water from the surface into the soil or ground.

OBSERVATION

The examination of the IRS - 1A imagery under raw and the digitally enhanced modes vividly display heavy concentration of suspended sediments in certain sectors along the east coast of Tamil Nadu. Such pockets of suspended sediments are seen as long and linear bodies trending parallel to the coast to the strike length of 20 - 30 km and width of 5 - 10 km. Such Phenomenon of suspended sediments concentration are strikingly observed in two sectors. One in between Tuticorin harbour and Vaippar river mouth and the other just at the mouth of Ponnaiyar river along Cuddalore-Pondicherry coast. Both of them are observed along conspicuous (Fig.1& 2) concave coasts.