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(The Gist of Kurukshetra) Water Management: Towards Sustainable Agriculture INDIA [JUNE-2020]

(The Gist of Kurukshetra) Water Management: Towards Sustainable Agriculture

INDIA [JUNE-2020]

Water Management: Towards Sustainable Agriculture

Water is one of the most critical resources for sustainable agricultural development worldwide.

Background:

Sustainable water management in agriculture aims to match water availability and water needs in quantity and quality, in space and time, at reasonable cost and with acceptable environmental impact.
Irrigated areas will increase in the forthcoming years, while fresh water supplies will be diverted from agriculture to meet the increasing demand of domestic use and industry. Furthermore, the efficiency of irrigation is very low, since less than 40 percent of the applied water is actually used by the crops.

Significance:

The sustainable use of irrigation water is a priority for agriculture in arid and semi-arid areas. So, under scarcity of water and changing climate scenario, India has a very formidable and challenging task of feeding 17.5 percent of the world’s human population from a meagre 2.3 percent of land area which is further constrained by the fact that the country has only 4 percent of the global water resources at its disposal.
In addition to the second largest human population, the country also has to provide feed and fodder to 11 percent of the world’s livestock population.
Combination of high yielding varieties, enhanced availability of water and fertilisers—the three key inputs in agriculture—transformed India from a country of begging bowl to one with overflowing granaries. It has imparted stability and resilience to the agricultural production system in the country.
With the foodgrain production touching an all-time record level of 284 plus million tonnes (MT) in 2018–19, Indian agriculture has made stupendous progress in ensuring food security to its vast population.
The new emerging demands of the relatively more-affluent Indian population, particularly its middle class, coupled with a net cultivated area unlikely to exceed 143 million hectare (MH) in 2050 as well as an estimated rainfed agriculture to cover around 45 percent of the net sown area, are further compounded with the harsh reality that highly productive agricultural land is being continuously lost out to the industry and urban sectors.

Steps needed to meet the target:

How will the country meet the target of 355 MT for foodgrains, 180 MT for vegetables, 182 MT for milk, 15 MT for meat, and 16 MT for fish by 2030, warranting an improvement of 50–100 percent over the current production, in a situation where the natural resources base is continuously degrading and climate change with its attendant impacts is adversely affecting the agricultural production system.
The strategies to attain this are water-intensive. Further, increased production is to be achieved through reduced emission of Greenhouse Gases (GHGs) and using cleaner energy.
Therefore, development strategies in agriculture need to be centred on regional water availability, water budgeting and its efficient use.
Sustainable agriculture is a way of farming according to the location-specific ecosystem and study of relationships between organisms and their environment.
The sustainable agriculture is a form of agriculture aimed at meeting the needs of the present generation without endangering the resource base of the future generations. Thus, a holistic and systematic approach is essential for achieving sustainability.
Such systems must be resource-conserving, socially supportive, commercially competitive and environmentally sound. Such systems aim to produce qualitative and nutritious food without harming human health and ecosystem.
Thus, such systems generally avoid the use of synthetically compounded fertilisers, pesticides, growth regulators and livestock feed additives, instead they rely upon crop rotations, crop residues, animal manures, legumes, green manures, off-farm organic wastes, appropriate mechanical cultivation, and mineral bearing rocks to maintain soil fertility and productivity.

Ways to sustain agricultural productivity:

Soil management through conservation agriculture, organic farming, integrated nutrient management system and on-farm residue management;
Efficient water resource management techniques like right method of irrigation, micro-irrigation, life-saving irrigation, use of mulches etc.;
Crop management includes right time of sowing, cultivation of suitable crops and varieties in rotation, inter cropping, mixed-cropping, integrated pests management, etc.
The sustainability in agriculture i.e. for crops/cropping systems primarily depends upon the availability of water in its optimum quantity and acceptable quality.
Agriculture might not sustain its productivity if irrigation is not sustainable and water supplies are not reliable. Especially in areas of water scarcity the major need for development of irrigation is to minimise water use. Efforts are needed to find economic crops using minimal water, to use application methods that minimise loss of water by evaporation from the soil or percolation of water beyond the depth of the root zone and to minimise losses of water from storage or delivery systems.
Nowadays, during a period of dramatic changes and uncertain water resources, there is a need to provide support and encouragement to farmers to move from their traditional high-water demand cropping viz. rice–wheat to maize–wheat/pigeonpea–wheat and irrigation practices to modern, reduced demand systems and technologies.
Under scarcity conditions considerable effort has been devoted over time to introduce policies aiming to increase water efficiency based on the assertion that more can be achieved with less water through better management.
Better management usually refers to improvement of allocative and/or irrigation water efficiency. The former is closely related to adequate pricing, while the latter depends on the type of irrigation technology, environmental conditions and on scheduling of water application. Thus, water management has been a key issue in realising commendable progress in agricultural production.
All India Coordinated Research Project on Water Management, Water Technology Centre, Water and Land Management Institute and various central and state agricultural universities in the country have made remarkable progress in evolving different strategies and technologies for improving sustainable use of available water resources for enhancing water and crop productivity.

Water Resources of India:

Rainwater is the primary source to meet the demand of water in Indian agriculture. India annually receives a rainfall of 1,085 mm. Nearly three-fourths of the total rainfall received in India is through south-western monsoon activity. The remaining amount of rainfall comes via pre or post and north-eastern monsoon activity.
Total utilisable water resource in the country has been estimated to be about 1,123 billion cubic metres (BCM) (690 BCM from surface and 433 BCM from ground water), which is just 28 percent of the total precipitation. About 80 percent of the water (688 BCM) is being diverted for irrigation, which may increase to 1,072 BCM by 2050.
On the basis of the available water resources, the total irrigation potential from surface and ground water resources is estimated to be 139.9 MH. The major source for irrigation is groundwater. Annual groundwater recharge is about 433 BCM of which 212.5 BCM is used for irrigation and 18.1 BCM for domestic and industrial use.
By 2025, demand for domestic and industrial water usage may increase to 29.2 BCM. Today at 68.1 MH (2013–14), India has one of the largest net irrigated areas in the world but if one examines the productivity of irrigated areas at the national level, it is only around 3 tonnes per hectare.3 The efficiency of surface irrigation systems is around 30–40 percent which implies that at least 60 percent of the water being supplied is being lost at various stages in the system.

Efficient Water Management Practices:

Efficient and sustainable water management practices in agriculture aims to match water availability and water needs in quantity and quality, in space and time, at reasonable cost and with acceptable environmental impact. Under water demand management most attention has been given to irrigation scheduling (when to irrigate and how much water to apply) giving minor role to irrigation methods (how to apply the water in the field). Many parameters like crop growth stage and its sensitivity to water stress, climatic conditions and water availability in the soil determine when to irrigate or the so-called irrigation frequency.
However, this frequency depends upon the irrigation method and therefore, both irrigation scheduling and the irrigation method are interrelated. The National Agricultural Research System (NARS) through its vast network of State Agricultural Universities (SAUs), Indian Council of Agricultural Research (ICAR) institutions and All India Coordinated Research Projects (AICRPs) have developed a plethora of technologies and practices focusing on enhancing water use efficiency at all levels, which are described below:

1. Laser Land Levelling:

Proper land levelling is one of the management options which is generally ignored by most farmers.
It increases the water application efficiency which leads to higher yields as well as rise in water use efficiency. It also has a direct impact on the nutrient use efficiency.

2. Irrigation Scheduling:

Irrigation scheduling is the decision-making process for determining when to irrigate the crops and how much water to apply.
The goal of an effective irrigation scheduling programme is to supply the plants with sufficient water while minimising loss to deep percolation or runoff. It forms the sole means for optimising agricultural production and for conserving water and it is the key to improving performance and sustainability of the irrigation systems.
It requires good knowledge of the crops’ water requirements and of the soil water characteristics that determine when to irrigate, while the adequacy of the irrigation method determines the accuracy of how much water to apply. In most cases, the skill of the farmer determines the effectiveness of the irrigation scheduling at field level.
With appropriate irrigation scheduling deep percolation and transportation of fertilisers and agro-chemicals out of the root-zone is controlled, water-logging is avoided, less water is used (saving water and energy), optimum soil water conditions are created for plant growth, higher yields and better quality are obtained and rising of saline water table is avoided.
In water-scarce regions, irrigation scheduling is more important than in conditions of abundant water, since any excess in water use is a potential cause for deficit for other users or uses.
Irrigation scheduling techniques and tools vary greatly and have different characteristics related to their applicability and effectiveness. Timing and depth criteria for irrigation scheduling can be established by using several approaches based on soil water measurements, soil water balance estimates and plant stress indicators, climatic parameters, in combination with simple rules or very sophisticated models.

3. Methods of Irrigation:

Once the water requirement of crops is quantitatively and temporally determined then methods of irrigation make water available to crop plants. Water use efficiency mainly depends on the way water is applied in the field. Efficient irrigation method is always aimed at reducing the various losses of water during application. It is very important to employ the correct method of water application to minimise the adverse effects of irrigation.
The selection of the right method of irrigation is influenced by soil type, land topography, crops to be grown, quality and quantity of water available for irrigation and other site-specific variations. Various irrigation methods are described below which are commonly used in different crops and cropping systems under specific situations:

3.1 Check Basin and Border Strip Irrigation:

Surface irrigation involves the application of water by gravity flow to the surface of the field. Over the years many surface methods of irrigation have been developed. Among them, the check basin method of irrigation is the most popular.
Check basin is the easiest and least costly method, but is usually highly inefficient only less than 20 percent of the water is taken up by the plant. Unfortunately, this is also the most widely used method among Indian farmers in different crops and cropping systems.
Farmers also go for surface flooding which is also an inefficient manner of using this precious natural resource.

3.2 Furrow Irrigation:

The furrow method of irrigation is generally used to irrigate row crops and vegetables, and is suited to soils in which the infiltration rates are between 0.5 and 2.5 cm/hr. It is ideal for slopes varying from 0.2 to 0.5 percent and a stream size of 1–2 litre/second.
Many of the field crops in which water is applied through flooding, check basin or border strip methods, can easily be adapted for furrow irrigation or its modified version i.e. raised bed system and 20–30 percent savings in irrigation water can be achieved by switching over to raised bed furrow irrigation systems.

3.3 Surge Flow Irrigation:

Excessive water intake and deep percolation losses are major limitations for irrigation through furrows and border strips.
Surge flow irrigation, the intermittent application of water in a series of on and off modes of constant or variable time spans has the potential of reducing intake and percolation losses, increasing the irrigation efficiencies and conserving irrigation water.

3.4. Micro-irrigation:

Micro-irrigation is one of the most efficient methods of irrigation which not only enhanced water use efficiency but also increased crop productivity. Promotion of micro-irrigation is critical to enhance water use efficiency in the context of rampant extraction of groundwater for irrigation and high variability in rainfall due to climate change. Micro-irrigation in India is popularised with a subsidy component, by both the central and state governments.
In 2006, the Government of India (GOI) started a Centrally Sponsored Scheme (CSS) for micro irrigation. In 2010, CSS was enhanced in scope and renamed as National Mission on Micro Irrigation (NMMI), which was subsequently brought under the ambit of the National Mission on Sustainable Agriculture.
In 2015, NMMI was brought as a scheme under the Prime Minister’s Krishi Sinchayee Yojana (PMKSY). The scheme envisages providing end-to-end solution to irrigation supply chain. Micro-irrigation helps in attaining greater water-use efficiency, thereby reducing the pressure on groundwater sources with reduced GHG emissions.
Micro-irrigation has the potential to function both as demand- and supply-side management tool. However, only about 15 percent of potential areas could be brought under micro-irrigation, warranting a course correction.
Micro-irrigation should be popularised in more water scarce and unsustainable water extraction regions to sustain the productivity and water use efficiency. Micro-irrigation mainly includes drip irrigation and sprinkler system water application.

3.4.1. Sprinkler Irrigation:

Sprinkler irrigation systems imitate natural rainfall. Water is pumped through pipes and then sprayed onto the crops through rotating sprinkler heads. These systems are more efficient than surface irrigation, however, they are more costly to install and operate because of the need for pressurised water. Conventional sprinkler systems spray the water into the air, losing considerable amounts to evaporation.
Low Energy Precision Application (LEPA) offers a more efficient alternative. In this system the water is delivered to the crops from drop tubes that extend from the sprinkler’s arm. When applied together with appropriate water-saving farming techniques, LEPA can achieve efficiencies as high as 95 percent.
Since this method operates at low pressure, it also saves as much as 20 to 50 percent in energy costs compared with conventional systems.

3.4.2. Drip Irrigation:

Drip method of irrigation gives many advantages over the gravity surface irrigation methods in terms of water savings and yields. Drip and micro-sprinkler irrigation systems, which apply water slowly on or below the soil surface as discrete or continuous drips, tiny streams, or miniature spray through emitters or applicators placed along a water delivery line adjacent to the plant row, is often preferred over other irrigation methods because of its high (90 percent) water application efficiency and have been proved as one of the best ways to increase water productivity.
Evidences show that the water use efficiency increases up to 100 percent in a properly designed and managed drip irrigation system. Drip method of irrigation helps to reduce the over-exploitation of groundwater that partly occurs because of inefficient use of water under surface method of irrigation. Water logging and salinity are also completely absent under drip method of irrigation.
It also helps in attaining early maturity of crops, higher quality produce, increased crop yields and higher fertiliser-use efficiency, reduction in weed growth, less labour requirement and less electric power consumption, cost of cultivation especially in inputs like fertilisers, labour, tilling and weeding.

3.4.3. Fertigation:

The application of fertilisers through the irrigation system (fertigation) became a common practice in modern irrigated agriculture. Localised irrigation systems, which could be highly efficient for water application, are also suitable for fertigation.
Thus, the soluble fertilisers at concentrations required by crops are applied through the irrigation system to the wetted volume of the soil. Possible disadvantages include the nonuniform chemical distribution when irrigation design or operation are inadequate, the over-fertilisation in case that irrigation is not based on actual crop requirements and the excessive use of soluble fertilisers.

3.4.4. Subsurface Drip Irrigation:

Subsurface Drip Irrigation (SDI) is a low-pressure, low volume irrigation system that uses buried tubes to apply water. The applied water moves out of the tubes by soil matric suction. Wetting occurs around the tube and water moves out in the soil all directions.

The potential advantages of SDI are:

water conservation,
enhanced fertiliser efficiency,
uniform and highly efficient water application,
elimination of surface infiltration problems and evaporation losses,
flexibility in providing frequent and light irrigations,
Reduced problems of disease and weeds,
lower pressure required for operation.

Subsurface irrigation is suitable for almost all crops, especially for high value fruit and vegetables, turfs and landscapes. The tube is installed below the soil surface either by digging the ditches or by special device pulled by a tractor.
The depth of installation depends upon soil characteristics and crop species ranging from 15–20 cms for vegetables and field crops and 30–50 cms for tree crops. The main disadvantages are the high cost of initial installation and the increased possibility for clogging, especially when poor quality water is used.

3.5. Deficit Irrigation Practices:

In arid and semiarid regions, water availability is usually limited, and certainly not enough to achieve total crop water requirement and the maximum yields. Then, irrigation strategies should not be based on full crop water requirements but should be adopted for more effective and rational use of water based on the critical or sensitive growth stages to water deficit. Thus, at non-sensitive growth stages irrigation is withheld which is called deficit irrigation.

3.5.1. Regulated Deficit Irrigation:

Regulated Deficit Irrigation (RDI) is an optimising strategy under which crops are allowed to sustain some degree of water deficit and yield reduction. During RDI the crop is exposed to certain levels of water stress either during a particular period or throughout the growing season.
The main objective of RDI is to increase Water Use Efficiency (WUE) of the crop by eliminating irrigations that have little impact on yield and to improve control of vegetative growth (improve fruit size and quality). RDI is a sustainable way to cope with water scarcity since the allowed water deficits favour water saving, control of percolation and runoff return flows and the reduction of losses of fertilisers and agrochemicals. It provides for leaching requirements to cope with salinity and the optimization approach leads to economic viability. The adoption of deficit irrigation implies appropriate knowledge of crop evapotranspiration, of crop response to water deficits including the identification of critical crop growth stages, and of the economic impact of yield reduction strategies.

3.5.2. Partial Root Drying:

Partial Root Drying (PRD) is a new irrigation technique, first applied to grapevines that subject one half of the root system to dry or drying conditions while the other half is irrigated. Wetted and dried sides of the root system alternate on a 7–14 day cycle. PRD uses biochemical responses of plants to water stress to achieve balance between vegetative and reproductive growth.
The PRD has been successfully applied with drip irrigation in grapevines, with subsurface irrigation in grapevines and even furrow irrigation in pear, citrus and grapevines. Improvement of WUE results from partial stomatal closure and reducing evapotranspiration during drying period.

4. Agronomic Practices:

Agronomic practices, such as soil management, fertiliser application, and disease and pest control are related to sustainable water management in agriculture and the protection of the environment.
These practices are very important for increasing crop productivity as well as WUE. There are large number of traditional and modern soil and crop management practices for water conservation (runoff control, improvement of soil infiltration rate, increase soil water capacity, control of soil water evaporation) and erosion control in agriculture which increase WUE. Some of the important agronomic practices, which increase the water use efficiency, are discussed below:
- Contour Tillage: Soil cultivation is made along the land slope and the soil is left with small furrows and ridges that prevent runoff. This technique is also effective to control erosion and may be applied to row crops and small grains provided that field slopes are low. This is one of the techniques to increase better use of the rain water, especially in rainfed areas.
- Broad Bed Planting: Cultivation of crop on broad beds and irrigation is applied in furrows. This method helps to save 30–40 percent water and is typically suitable for close planted field crops and horticultural row crops.
- Conservation Tillage (CT): CT includes zero tillage and retention of crop residuals on the soil surface at planting. Crop residues acts as mulches and reduce evaporation losses and protect the soil from direct impact of raindrops, thus controlling crusting and sealing processes. CT helps to maintain high levels of organic matter in the soil thus it is highly effective in improving soil infiltration and controlling erosion which results in an increase of WUE.
- Mulch: Mulching with crop residues on soil surface shades the soil, slows water overland flow, improves infiltration conditions, reduces evaporation losses and also contributes to control of weeds and therefore of non-beneficial water use.
- Addition of Organic Manures: Increasing or maintaining the amount of organic matter in the upper soil layers provides for better soil aggregation, reduced crusting or sealing on soil surface and increased water retention capacity of the soil.
- Addition of Clay or Hydrophilic Compound: This technique increases the water retention capacity of the soil and controls deep percolation. Thus, water availability in soils with low water holding capacity is increased.
- Control of Acidity: Lime application to soils with high pH favours more intensive and deep
- rooting, better crop development and contributes to improved soil aggregation, thus producing some increase in soil water availability.
- Weed Control Measure: Adoption of appropriate weed control techniques to alleviate competition for water and transpiration losses by weeds is very important agronomic practice to increase water use efficiency in different crops and cropping systems.
- Integrated Pests Management (IPM): IPM techniques aim to increase crop productivity with the same amount of other inputs like water, fertilisers etc. Pests cause severe losses to the different crops and cropping systems. However, timely control of the severe pests and diseases of different crops will not only increase the productivity and profitability to the farmers but also improve water use efficiency and water productivity.

Conclusion:

Share of water to agriculture is going to decline in the future due to the stiff competition from the industrial and domestic sectors and compounded further by global warming and associated adverse impact of climate change.
Since, water is a critical input for agriculture, therefore, adoption and upscaling of new technologies of efficient water management especially micro-irrigation as quickly as possible is the only viable solution to sustain agricultural productivity.