Keywords

1 Introduction

Dryland farming is often defined as crop production in areas subjected to annual rainfall of less than 500 mm and specially practised in arid and semiarid regions in which annual precipitation is about 20–35% of potential evapotranspiration. Drylands account for 44% of the world’s cultivated area and endowed with one-third of its population. It possesses only 8% of the global renewable water supply, whereas in India dryland agriculture occupies 68% of India’s cultivated area and supports 40% of the human and 60% of the livestock population. It contributes 44% of food requirements, which highlights it plays a critical role in India’s food security. The substantial development in drylands has been impeded due to immense pressure from the burgeoning populations, land degradation, and climate change impacts. Along with this nowadays water scarcity is the most prominent challenge that drylands face which implies the need of begin to see the lights in efficacious management of water resources. As the competition for water resource swells due to certain anthropogenic concerns and the insufficient attention paid for its management, the access of agriculture to this crucial source is no longer guaranteed for dryland condition. The chronic water scarcity scenario, worsened by the above explained reasons, leads to an imbalance between supply and demand for water (Seckler et al. 1998; Kushwaha et al. 2016). Therefore, in a stage of water scarcity, water management needs to be rationalized in a scientific manner to ensure efficient water saving and maximized productivity.

Apart from this in water-scarce areas releasing of water to other sectors with maintaining the productivity to meet the demands raised is a complicated picture. However, Food and Agricultural Organization (2012) estimated that to meet the demand of future 80% of the additional production is required which can be fulfilled by intensification and enhancement of yield. Hence there has been a paradigmatic shift of increasing productivity per unit land towards increasing productivity per unit water consumed which heightened by limited possibilities for extension of more irrigated areas (Shanan 1992a, b; Kushwaha and Kanojia 2018). The strategy of supply irrigation with abundant water up to the maximum ET requirements to enhance the yield becomes challenging in water-scarce region. Therefore, a plausible and robust strategy is mostly needed to limit the available water supply with insignificant reduction in yield. In this situation rather than covering the whole land, small area should be concentrated, or irrigate the total area below full ET requirements.

Taking these above said concerns in account deficit irrigation is an assuring solution to lessen the supply-demand gap of water in dryland regions. Below ET-based application of water is termed as deficit irrigation (English et al. 1996). This strategy differs from the traditional one by actively managing the crop water stress during the growing season (Klocke et al. 2007). Though producers can obtain maximum profit by propitiating entire crop water requirements, practicing deficit irrigation as a consequence of limited water supply can increase the irrigated area by saving considerable amount of water. Application of water on the right time can galvanize the enhancement of water use efficiency for most of the crops. During growing season a rationalized irrigation management should be allowed to double the area covered by crops with minimum decrease in yield loss and substantial fetching of economic return considering the economic standpoint, whereas according to Zhang et al. (2018), the optimization of irrigation water application revolves around the estimation of crop water use, determination of irrigation scheduling, and proper management of agronomical measures.

Nevertheless, on the basis of these background information, the focus of this chapter is on providing a clear-cut understanding about deficit irrigation, intervention of new techniques to enhance water use efficiency with limited water supply, management of soil and water in deficit irrigation, and its economic analysis which will definitely provide new avenue for the betterment of DI practice in water-scarce situation.

2 Definition and Feature of DI

Deficit irrigation (DI) is a reasonable and manageable depletion of water to enhance water use efficiency (WUE) for higher yields per unit of consumed water. As stated by English, DI can be defined as “methodical and systematic under-irrigation of crops” (English 1990; English et al. 1996) integrated with development of methodical framework to maximize the profit with restriction of water availability. Behind this approach a certain level of water stress is allowed during a particular period or for the whole growing season. Apart from this Chai et al. (2016) defined water deficit for different level of field capacity:

  • Severe water deficit—soil water < 50% of the field capacity.

  • Moderate water deficit—soil water = 50 to 60% of the field capacity.

  • Mild water deficit—soil water = 60 to 70% of the field capacity.

  • No deficit or full irrigation—soil water > 70% of the field capacity.

  • Over-irrigation—amount of water application > optimum crop water requirement.

This irrigation strategy is considered with an expectation that benefits gained from the conserved water should be greater than insignificant reduction in yield (Fan et al. 2014; Pereira et al. 2012). Despite of reduction in yield, this strategy has opportunities of maintaining considerable quality of crop compared to full irrigation condition. However, the response of crop yield to water stress at critical growth stages or throughout the growing season and maximum allowable with minimum reduction in crop yield is necessary to be known before adopting deficit (Kirda and Kanber 1999). Along with this pertinent knowledge of crop ET, identification of critical crop growth periods, and the economic impacts of yield, reduction strategies are needed for the adaptation of DI. However, the soil salinity consequence of limited water used by DI raised due to lack of leaching and its impacts on sustainable water management have been considered as greater risk (Schoups et al. 2005). In spite of certain limitation, DI can contribute to (i) reducing overall water demand, (ii) reducing declination of productivity of land, (iii) decreasing operation and maintenance cost, (iv) fixed amount of water increase in areas under irrigation, and (v) upliftment of economic return and food security (Geerts and Raes 2009).

There are certain factors that need to be considered before adopting deficit irrigation. Sensitivity of crop growth to water deficit is an essential factor in this strategy. Hence it is preferred to select crop having high water resistance. In deficit irrigation, short-growing and drought-tolerant crop varieties are more suitable (Stewart and Musick 1982). Generally, high-yielding varieties (HYVs) are more water-sensitive than low-yielding varieties. For example, new maize varieties show poor result in deficit irrigation compared to the traditional verities (Food and Agriculture 1979). Apart from this to achieve blooming and robust deficit irrigation strategy, soil parameter also plays an important role. To ensure this concept, soil water retention capacity should be considered. In sandy soil crops may be exposed to water stress very quickly compared to those in fine-textured soil. Low soil matric pressure can be easily maintained in fine-textured soil without affecting the soil water content. Therefore, successful deficit irrigation is more relevant to fine-textured soil.

3 Types of Deficit Irrigation

PRD and RDI strategies are the most important types of DI which involve enhancement of crop water use efficiency by manipulating in irrigation water application and deficit of moisture within the root zone. On the basis of maximum crop ET-based water supply level, each DI situation can be defined. In this chapter two major types of deficit irrigation have been discussed.

3.1 Regulated Deficit Irrigation

According to English et al. (1990), regulated deficit irrigation modified as controlled deficit irrigation is a conscious restriction of irrigation water which may be a justifiable management during certain crop-growing phases to manipulate crop water use (Chalmers et al. 1981). At different crop development stages, RDI (RDIC) is a standardized approach where critical growth stages (most sensitive growth stages) are supplied by full irrigation and noncritical growth stages are restricted by limited water application. This practice imposes water stress during insignificant yield reducing crop-growing phases with considerable maintenance plant water status below the permissible limits of deficit to control vegetative and reproductive growth (Chalmers et al. 1981; Li et al. 1989; Girona et al. 1993; Kriedemann and Goodwin 2003). RDI has been often demonstrated to be an optimized tool for water use efficiency (WUE) for different crops such as citrus, grapes, pears, (Romero et al. 2013; Cui et al. 2008; Panigrahi et al. 2014; Chalmers et al. 1981; Matthews et al. 1987; Mitchell et al. 1989; Girona et al. 2006). sugar beet (Miller and Hang 1980; Fabeiro Cortes et al. 2003), cotton (Snyder 1992), and tomatoes (Hsiao 1993). Precision irrigation strategies are the paramount for a successful application of RDI by taking into account the timing control and soil water level monitoring. According to Kriedemann and Goodwin (2003) in regulated deficit irrigation, size and quality of fruit and vegetative growth can be controlled fruit size and quality, vegetative growth can be achieved.

3.2 Partial Root Zone Drying

Partial root zone drying (PRD) is where half of the root system is irrigated, while the remaining half is exposed to drying soil. The principle behind this approach is considering a frequency at which previously well-watered side of the root zone should be dried down while the previously dried side is fully irrigated and the alternate partial wetting and drying of the root zone is done. In this strategy alternate plant sides are imposed by a percentage of crop evapotranspiration which is ensured by allowing partial wetting of root system. However partial root zone drying is based on two assumptions: (1) dried partial root zone tends to send root-shoot signal (induced by Abssisic ABA) to limit the stomatal aperture for limited transpiration (Dry and Loveys 1999), and (2) with limited availability of water, a partial closing of stomatal aperture may be effective in reducing loss of water substantially with insignificant impact on photosynthesis (Dry and Loveys 2000). The concept of PRD depicted in Fig. 11.1 is hypothesized for water use efficiency enhancement and reduced vegetative growth, stomatal conductance by root to shoot signalling induced by abscisic acid (ABA) during alternative drying and wetting of root zone (Wang et al. 2012). In this strategy the crop growth and development are not affected as the decrease in leaf water potential has no effect on decrease in irrigation to the part of the root zone, and instead the protective process of plant may be stimulated by PRD. PRD has been represented as a potential technique in saving water and enhancing water use efficiency (Wang et al. 2012; Kang et al. 2001; Guang-Cheng et al. 2008; Wakrim et al. 2005; Savic et al. 2008; Stikic et al. 2003. The nature of the confined soil moisture and crop water status conditions (Ruiz-Sanchez et al. 2010) makes PRD to be differed from RDI.

Fig. 11.1
A schematic diagram of root zone drying method at different centimeter by water deficiency, Abcisic acid production in roots, A B A transporting to the leaves, and reducing aperture to the stomata.

Schematic diagram of partial root zone drying method

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4 Water Productivity and Deficit Irrigation

At present, the consequence of global expansion of irrigated areas and the restricted availability of irrigation water compel to adopt appropriate water management to achieve efficient use of water. Increase net economic return per unit consumed water should be concentrated instead of per unit land when limited water supply is concerned. Recently, water productivity concept has been emphasized which is defined as the yield per unit of water used in evapotranspiration (Kijne et al. 2003a, b). This leads to reduce ultimately maximum investment returns and production costs and simultaneously supports the sustainability under frequently occurring situations of deficit irrigation. Oweis et al. (1998) and Zhang et al. (1998) stated that the concept of water productivity revolves around optimal irrigation schedules when multifactorial field trials derive different strategies for deficit irrigation. When specific crop development period is exposed to water deficit, there is a variation in yield response based on sensitivity of crop at different growth stage. Therefore, in order to minimize the yield loss, controlled time of irrigation is appropriate tool for scheduling irrigation. According to Kirda (2002), careful evaluation is needed in irrigation scheduling to ensure enhanced efficiency in limited water supply condition.

Moutonnet (2002) further stated that when there is a maximum reach of evapotranspiration, then the yield approaches to the maximum value. Generally, a significant reduction in soil water storage affects the crop water availability which ultimately affects the actual yield and evapotranspiration. A standard formulation represents a relative yield decrease to relative evapotranspiration deficit including the yield response factor (Ky), (Food and Agriculture Organization 2002) earlier used by Stewart et al. (1977) which is given below:

$$ \frac{Y}{Y\mathrm{m}}=1-k\mathrm{y}\left[1-\left(\frac{\mathrm{ETa}}{\mathrm{ETm}}\right)\right] $$
(11.1)

  • Here Y is actual yield (kg/ha).

  • Ym is maximum yield (kg/ha).

  • ETa is actual evapotranspiration (mm).

  • ETm is maximum evapotranspiration (mm).

  • Ky is yield response factor.

A crop yield response factor is known as water production function (ky) which depends upon several factors such as species, variety, irrigation method, management, and growth stage when deficit evapotranspiration is imposed. It indicates the unit change in yield as there is a unit change in evapotranspiration. When its value exceeds 1, it indicates that the relative decrease in evapotranspiration is proportionality lower than expected relative yield decrease for a given evapotranspiration deficit (Kirda et al. 1999a, b), and it is vice versa for when its value less than unity. Nevertheless it has been experimented that relative to under full irrigation, WP increases under DI for many crop (Zwart and Bastiaansen 2004; Fan et al. 2005; Ozbahce and Tari 2010; Kumar et al. 2018) and the regression analysis for WP increment and yield reduction versus saved water represented higher values, which indicates that DI could be an option for enhancement of WP and increasing overall yield by expanding irrigated area and applying the saved water in water-scarce region.

In Table 11.1 yield response factors for different crops where there is a less yield reduction compared to relative evapotranspiration deficit have been presented (Kirda et al. 1999a, b).

Table 11.1 Crop response factors for different crops
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Elias and Soriano (2007) has stated that limited irrigation amounts increase crop ET; the relationship between ET and yield is found to be linear up to a certain point where it turns curvilinear because some fraction of water applied is not contributed in crop evapotranspiration and is neglected. After hitting the peak point where yield approaches its maximum value, then further addition of water does not have any effect on yield increase. However, the uniformity in irrigation is needed to approach the maximum yield for given amount of water. According to Elias and Soriano (2007), it is also important to highlight the need of irrigation systems of high application uniformity under DI so that the over-irrigated area should be restricted by limited supply and under-irrigated area should be irrigated to deficit level to enhance the water productivity.

According to Kirda et al. (1999a, b), water use efficiency at deficit ET is 1.09 times higher than at full irrigation. This indicates that there is a compensating effect between the increased irrigated area by saved water and the yield loss. Throughout the season if the planned ET is imposed, then the total irrigation water saved can be calculated on the basis of crop water requirement. However, it is crucial to know the water requirement of crop if the stress is presumed during a specific growth stage, to quantify the water saved. This concept is very much important to select crops which have lower crop yield response factor (ky < 1.0) to achieve significant irrigation water savings with an considerable increase in water productivity. Where as it has been studied that at high yield level water productivity decreases i.e., enhancing water production tends to lower yields. Example in Northern Syria, Oweis et al. (1998) reported that 10–15% yield will be reduced when 50% of full supplemental irrigation requirement is satisfied.

However, there is a lack of precession in knowing the yield function and the water use cost. Due to this fact, there is an uncertainty associated with this type of irrigation system. There is a difficulty in estimation of water losses which is contributed by different components when there is a variability related to weather, soil, and topography; the yield function tends to be uncertain. It is also difficult to predict, for a given amount of root zone stored soil water, what yield would be produced which ultimately contributes to economic risk (English et al. 1990).

5 Deficit Irrigation Scheduling

Deficit irrigation can be successfully applied when there is a better understanding about when and how to irrigate. According to Goodwin and Boland (1998), scheduling has been relied on pan evaporation (Epan), soil moisture measurement, and plant response before taking management decision. Pereira (2001) reported that through validation and calibration of simulation models, the irrigation scheduling strategies for deficit irrigation have been generated. This modelling approach includes the yield-water function by which the yield impact of water deficit can be evaluated. El Amami et al. (2001) concluded from this study that when there is ten times reduction in available water, it decreases the yield per unit surface cropped land, but the yield per cubic metre of water applied is increased. Therefore, for each irrigation strategy, land should be allocated to crop based on balance between economic return and cropped area; for a low deficit irrigation, the water productivity increases and decreases afterwards when there is a severe deficit. Therefore, according to Kirda et al. (1999a, b), cropping only a fraction of land rather than the full land is the best option for deficit irrigation. It implies scheduling of deficit irrigation requires not only knowledge of crop but also the yield response to water. However, controlling time of irrigation and crop water stress identification are the best approach to for scheduling the deficit irrigation. According to Goodwin and Boland (1998), in the case of drip irrigation, for scheduling RDI the time of run can be calculated by a standard formula based on Epan which is

$$ \raisebox{1ex}{$\mathrm{Run}\ \mathrm{time}=\left(\Big(\mathrm{Epan}-\mathrm{Rain}\right)\ast \%\mathrm{Replacement}\ast \mathrm{Row}\ \mathrm{spacing}\ast \mathrm{Plant}\ \mathrm{spacing}\Big)$}\!\left/ \!\raisebox{-1ex}{$\mathrm{Emitter}\ \mathrm{rate}\ \mathrm{per}\ \mathrm{plant}$}\right. $$
(11.2)

Where, run time is in hour, rainfall is in mm, plant spacing and row spacing are in m, and emitter rate is in litres/h.

Apart from estimation of run time, determination of irrigation interval is also important for scheduling deficit irrigation for system other than trickle. According to Mitchell and Goodwin (1996), the formula for calculation of irrigation interval based on average daily pan evaporation is the following:

$$ \mathrm{Interval}\ \left(\mathrm{days}\right)=\frac{\mathrm{Volume}\ \mathrm{of}\ \mathrm{water}\ \mathrm{in}\ \mathrm{root}\ \mathrm{zone}\left(\mathrm{litres}\right)}{\mathrm{Average}\kern0.5em \mathrm{daily}\ \mathrm{ater}\ \mathrm{use}\ \left(\frac{\mathrm{litres}}{\mathrm{day}}\right)} $$
(11.3)

Precise determination of crop water stress based on different strategy enhances the proportion of water saving. According to Carmen et al. (2018), in water stress condition, water stress threshold can be determined by different water stress detection technologies such as physiological sensor, dendrometry, thermography, and soil water content measurement depicted in (Fig. 11.2) which is related to yield and fruit quality, nutritional status, and water saving. By water production function, the amount of water saved can be estimated and water use efficiency which decrease in case of over irrigation. Based on these two factors, plausible strategy can be determined for deficit irrigation.

Fig. 11.2
A flowchart starting with deficit irrigation techniques leading to water stress and ultimately leading to strategies for adaption in the contex of water scarcity. Two line graphs at both sides indicate yield at irrigation strategy, and yield at E T or applied irrigation water.

Schematic diagram on irrigation strategy based on water scarcity scenarios

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6 Techniques for Enhancing Water Use Efficiency

Dryland farming, which is common in semiarid and arid regions, is basically crop cultivation process where water supply is a key limitation. According to ACIAR (2002), dry land farming can be defined as agricultural areas in which the average water supply of the crop limits potential production to less than 40% of full production (without water). Various factors like soil erosion by wind and water, depletion of organic matter content (OMC), salinity and chemical deterioration, etc. contributed to soil degradation in dry environments. Apart from it, the water availability for crop use, as well as its spatiotemporal distribution, is a major challenge in dryland agriculture. Desertification also occurs in the worst circumstances. Despite of it, degradation mechanisms are often considerably more prevalent than soil conservation techniques in dryland environments, allowing the soil resource base to swiftly erode. As soil quality deteriorates, infiltration rates and water-holding capacity decline, making an already scarce water resource increasingly less efficient, resulting in a negative twist in soil-water quality and crop productivity in dryland agriculture. Processes of soil degradation and conservation practices have a complex relationship with soil quality (Fig. 11.3).

Fig. 11.3
A block illustration depicts the interconnection between soil degradation processes and soil conservation practices and the positive and negative impact on soil quality.

Relationship of process of soil degradation and conservation practices with their quality

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To enhance agricultural production and improve water use efficiency, suitable tillage and residue management strategies, well-adapted varieties of crops, and fertility management are required. Water harvesting, which concentrates/collects runoff water from non-cropped regions and applies it to neighbouring agriculture, is another method for improving productivity in specific circumstances. Generally, the options to improve water use efficiency in dryland regions are categorized into two major sections: agronomic and engineering practices. Detailed description of agricultural practices including both agronomic and engineering has been given below.

6.1 Agronomical Measures

Agronomic measures basically include different types of bench terraces, contour bunding, contour strips, strip cropping, cover crops, crop rotation, off-season and deep tillage, summer fallow, mulching, sowing in furrows, etc.

6.2 Mulching

In dryland agriculture, the primary limiting component is soil moisture. It evaporates from soil by evaporation and is lost by transpiration from canopy surfaces. Evaporation loses between 60% and 75% of the rainfall, and mulches check these losses. Mulch is any material that is placed to the surface of the soil to reduce evaporation. Apart from it, it is a water-saving practice for soil moisture conservation, controlling temperature, preventing erosion, and lowering evaporation from soil in dryland regions also (Vishwakarma et al. 2022; Kader et al. 2017; Qin et al. 2016; Yang et al. 2015). Surface mulching is an overarching water conservation tactic for rainfed systems (Chakraborty et al. 2008; Zribi et al. 2015). Plastic mulching conserves soil water better than straw mulch of wheat (Li et al. 2013). Different types of mulching like stubble mulch, straw mulch, dust mulch, plastic mulch, etc. have been used to check soil evaporation and conserve soil moisture (Fig. 11.4).

Fig. 11.4
A schematic diagram of mulching depicts the different types including dust mulch, stubble mulch, and plastic mulch with their respective qualities.

Types of mulching

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6.3 Tillage

Tillage is often beneficial to crop productivity in dryland farming. It has several advantages, including seedbed preparation, weed control, and incorporation of excess crop residues on soil surface, fertilizers and pesticides, etc., but it can also be harmful to maintaining soil sustainability for longer durations. Tillage has a minimal impact on long-term dynamics and survival of weed seed in soil when crops rotate with diverse life cycles, i.e. crop rotations and diversifications (Anderson et al. 2006). Off-season tillage increases moisture conservation and minimizes weed development especially in alfisols, whereas in soils with hard pan, deep tillage aids in boosting water intake (Sivanappan 1995). Due to its positive consequence on soil moisture storage, conservation tillage systems like reduced tillage or no tillage have been identified as one of the most promising strategies for increasing SOC stocks in dryland areas (Aguilera et al. 2013). When adopting no tillage, significant C sequestration rates have been documented in various dryland systems (Palm et al. 2013; Farina et al. 2011; Govaerts et al. 2009; Vågen et al. 2005). Reduced tillage has a positive impact on many characteristics of the soil, but unsustainable and unneeded tillage operations have the reverse effect, causing soil damage. As a result, there is a lot of attention and focus right now on the transition from high tillage to minimal/no tillage.

6.4 Intercropping/Mixed Cropping and Crop Rotation

Agronomic practices that boost crop yield, such as intercropping and crop rotation, must be popularized in dryland regions. Crop rotation provides a number of advantages like lowering the prevalence of insect pests, weeds, and crop diseases, as well as improving the physical like better water-holding capacity and aggregate stability, chemical, and biological qualities like improvement in organic matters of the soil, etc. Crop rotation combined with a no-till system can also help with soil aggregation and water saving in intensified agriculture cropping systems, particularly in dry and semiarid climate regions (Lal 2015). Similarly, in intercropping/ mixed cropping, crop water requirements for different crops can be influenced by the variation in root structures and their length in the soil profile, especially in rainfed or dryland agriculture (Nielsen et al. 2011). These systems also help in minimization of crop failure risk and enhancing water productivity of cropping systems. Intercropping has also huge potential for improvement of crop yield and water productivity (Borghi et al. 2013; Qin et al. 2013), as well as the crop yield in next year in rotational mode (Sharma et al. 2017). A combination of intercropping and deficit irrigation (Chai et al. 2014) or crop straw mulching (Yin et al. 2017) can significantly improve WUE in semiarid/arid areas (Yang et al. 2011; Fan et al. 2013). Both (intercropping and mixed) cropping systems in a broad range of situations are expected to enhance resource usage efficiency (Willey 1979; Francis 1989).

6.5 Nutrient Management

Fertilizers not only promote crop development, but it also encourages root growth, which allows water to be absorbed from deeper soil layers, which is very important during droughts. Apart from it, quick expansion of the plant canopy as a result of fertilizer application provides more shade on soil, which reduces the amount of evaporated water. Various scholars have demonstrated the positive influence of nutrient management on water use efficiency (IAEA 2005; Rao and Ryan 2004; Van Duivenbooden et al. 1999; Monteith and Webb 1981). INM (integrated nutrient management) needs to be promoted with special prominence on biofertilizers used to maintain the soil fertility in dryland areas. Biofertilizers like blue green algae, Rhizobium, Azospirillum, Azotobacter, vesicular arbuscular mycorrhiza, and phosphate-solubilizing organisms could be used as part of dryland agriculture’s INM. Fertilizer efficiency can be increased by using biological nitrification inhibitors as well as slow and controlled release fertilizers and also led to reduction of nitrogen losses in dryland soils (Nawaz and Farooq 2016).Correct fertilizer application in the soil at sowing time can boost the production and quality of dryland crops by reducing leaching and the aerial environment (Janzen et al. 1999).Trials of balanced nutrient management have proved that agronomic efficiency of used nitrogen can be enhanced by adding P and K nutrients, 6.7 kilograms of sorghum grain per kilogram of nitrogen, 10.3 kilograms of pearl millet per kilogram of nitrogen, and 19.5 kilograms of maize grain per kilogram of nitrogen, etc. Nitrogen usage efficiency went from a pitiful 6% to 20% in rainfed pearl millet, sorghum, and maize (Prasad 2009). The 50 percent N through organics or FYM and the remaining N through inorganic fertilizer as integrated nutrient management method can be widely advocated (Vittal et al. 2002).

6.6 Use of Antitranspirants

Antitranspirants inhibit photosynthesis, and their application is restricted to preventing crop death due to extreme moisture stress. The main benefits of antitranspirants are to reduce transplantation shock especially in nurseries and horticultural crops. There are generally four types: stomatal closure (phenylmercuric acetate), reflectant (5% Kaolin spray), film forming (Mobileaf, hexadeconol, etc.), and growth retardant (Cycocel).

6.7 Crop Choice and Improved Varieties

Many conventional dryland crops do not meet with water availability due to longer crop duration. Therefore, numerous trials have been done to meet crop water requirement with rainfall and duration of water availability. A vast variety of enhanced pulses, millets, and oil seeds were examined for yield variation trend in comparison to local farmers’ used varieties (All India Coordinated Research Project for Dry land Agriculture 2000). Yield improvements of 15–50% were noted by high-yielding varieties and 15–25% by more suitable crops. Adoption of short duration crops and varieties are more recommended in dryland regions to enhance crop productivity. For example, rice cultivars ZHU-11–26 in Phulbani and brown gora in Ranchi, linseed cultivar HUL-62 in Varanasi, black gram cultivar KB-51, green gram cultivar CO-5 in Kovilpatti, and soybean cultivar JS-87–59 in Rewa are also extremely sustainable in context of Indian dryland scenario (Vittal et al. 2002). Sowing at the right time helps to maximize seasonal rainfall use, lowers the incidence of pests and diseases, and provides a buffer against drought. The ideotype should have a short growth cycle, extensive root growth, fundamental dryland adaptations, and drought resistance. Apart from this can be written in place of apart from it, diversification by high-value crops like aromatic, spices, dye-yielding, medicinal plants, sericulture, and alternative land uses included to maximize returns, such as agri-horticulture, silvipasture, agroforestry, hortipasture, and other viable strategies, should come under agronomic practices for minimizing risk and maximizing return on investment in dryland environment.

6.8 Engineering Measures

Engineering measures varied spatially with respect to slope, soil type, and rainfall variation in terms of intensity, quantity, and other factors. Contour trenches, staggered trenches, contour stone walls and bunding, compartmental bunding, creating temporary and permanent check dams, gully plugging, land levelling, and other techniques are used as engineering approaches depending on these parameters.

6.9 Water Harvesting

Water harvesting is one of the viable options for excess runoff collection in a tank and utilizing it to improve agricultural output in the collected or other locations in dryland agriculture. Farm ponds (lined/unlined), percolation ponds, and silt detention tanks are the three types of collector tanks which are mainly recommended in these regions. Protective irrigation is carried out with water collection in the farm pond. Whereas, roof water harvesting also recharges the groundwater and is used for protective or supplementary irrigation by dig wells. The rainwater harvesting system basically classified into in situ moisture conservation like micro-catchment system (within field) and runoff-based system (catchment/storage) like small and macro-catchment systems (Ngigi 2003; Kushwaha and Bhardwaj 2017). They reduce runoff, promote water infiltration into soils, recharge aquifers, and help to improve local water supplies.

6.10 In Situ Water Conservation

Several technology treatments like terraces and conservation bench to improve in situ rainwater conservation have been demonstrated to be efficient in dryland regions. Technical interventions’ success is determined by local biophysical and socioeconomic factors and therefore necessitates local neighbourhood action. Planting pits or zai, demilunes (half-moon-shaped moons that have been raised), earthen dividers, stone lines go along the contours, ridge tillage following the contours, etc. are also the examples of in situ rainwater harvesting techniques (Winterbottom et al. 2013).

6.11 Terraces

Terraces are built by bringing soil from the upper to lower side of a strip to form a level bench/step which has been used to control soil erosion and runoff. Because of the diversity of the landscape, they are guided by neighbourhood and local conditions when they are designing and building. Among terraces, CBTs (conservation bench terraces) also known as Zingg terraces are one of the recommended practices, where rainfall varied from 300 to 600 mm for appropriate crop production, also control erosion in addition to reduce overall runoff, and reliably boost yields (Koohafkan and Stewart 2008; Kushwaha and Yousuf 2017). But, their design should be location-specific for the most effective operation. Conservation terraces are unlikely to be effective in places with minimal rainfall (less than 300 mm) due to high installation costs.

6.12 Contour Furrow

They are similar to CBTs in concept but need less soil movement and more popularized among small/marginal farmers and/or in locations with minimal rainfall. Contour furrows at a 1- to 2-metre interval are made, and cropping is frequently done in strips or in rows. Apart from it, the excavated trench is sometimes used for runoff water collection which overflows without being damaged in severe storms.

6.13 Contour Bunds

Contour bunds are constructed with ties in the basin on a level gradient. On the bottom side of the earth bund, a stone wall is built to prevent harm if the basin is overtopped. They are also one of the more efficient SWC (soil and water conservation) measures in dryland areas.

6.14 Tied Ridges

Mechanized farming systems that use tie-ridges or furrow-diking for SWC (soil and water conservation) are proven methods. Crops are grown on contour ridges, with crossties/dykes blocking the furrows to catch rainwater for irrigation. Apart from it, they can be cultivated on the contours with any tillage strategy, including RT(reduced tillage) and no tillage. TR (Tied ridging), on the other hand, has not been widely embraced by small farmers, owing to variable yields.

6.15 Land Levelling with Lasers and Mini Benches

Laser-assisted land levelling is also very effective to overcome runoff losses. For example, this approach resulted in 20% water savings, a 30% increase in crop yields, and a 50% labour savings with 90% irrigation uniformity in the Tadla region of Morocco (Koohafkan and Stewart 2008). Minimum soil cutting and soil fertility issues connected with large volume of surface soil transfer are greatly reduced by the use of thin mini benches. They are generally built on gentle slopes of up to 2%, which is an alternative to land levelling (Jones et al. 1985). Kahlown et al. (2006) reported that technologies focus on efficient use of resource conservation like zero tillage, laser levelling, and bed and furrow planting leads to water saving of 23–45% at the same time as increasing yield in Indus basin of Pakistan.

6.16 Windbreaks and Shelterbelts

Wind breakers are any constructions that hinder wind flow and slow it down, whereas shelterbelts are rows of trees placed to protect crops from the wind. They do not totally block the wind flow. Amount of wind travels through the shelterbelts, while the rest deflect and cross over them, depending on their porosity. As a result, the wind speed is reduced without disturbance. The amount of protection provided by shelterbelts is determined by the height of the middle tree row. Shelterbelts provide protection against desiccating winds up to 30 times and 5 to 10 times their height, respectively, on the leeward and windward side. Evaporation losses are reduced as a result of the reduced wind speed, resulting in more water available for plants. During dry years, the protective impact of shelterbelts is more visible. They also help to prevent erosion from wind.

7 Irrigation Methods

India is the agricultural power house at global level in which 63% is rainfed and 37% is irrigated out of approximately 195 million-hectare (M ha) area under cultivation. India has the second largest net irrigated area, after China, but the share of water allotted for irrigation has been decreased by 10–15% in the next two decades, and average yield in irrigated and canal command area is still pathetically low. Climate change has also aggravated these problems. Presently, most of the farmers are marginal and irrigate their lands manually through conventional irrigation. In spite of its wide use, the method is characterized by poor irrigation efficiency (35–40%) which might be due to more conveyance, distribution, and application losses as well as lack of availability of reliable gadgets for water accounting and auditing at on-farm. Apart from it, most of the canal command farmers don’t get timely and adequate amount of water, and tail-end farmers suffer from water shortage especially during peak season. Promoting micro-irrigation (irrigation efficiency 75–95%) and adopting advanced technologies to fulfill the dream of “more crop per drop” mantra is today’s need. Enhancing land and water productivity (WP) in dryland agriculture is important not only for enhancing agricultural production on existing land with limited water availability but also for saving water for future use. It has been the subject of long-term researches, and they are well documented (Elbeltagi et al. 2021; Rockstrom and Barron 2007; Molden 2007; Bouman 2007; Kijne et al. 2003a, b). Enhancing water productivity options depends upon various factors like reducing water losses, judicious use of water resources, adopting modern agronomic practices, etc. Regarding engineering aspects, several examples described the irrigation water management effect on water productivity (Kushwaha et al. 2021; Oktem et al. 2003; Yazar et al. 2002; Kang et al. 2000; Zhang et al. 1998). Some important irrigation methods suitable to dryland regions (Fig. 11.5) are described below:

Fig. 11.5
A block diagram of dryland water management options includes alternate furrow irrigation, surge irrigation, drip, sprinkler, soil moisture sensors, decision support system, and I O T based irrigation system.

Options of irrigation water management in drylands

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7.1 Alternate Furrow Irrigation (AFI) Method

In it, water applies in alternate furrows and reported as more efficient (25–50% water saving) as compared to the regularly utilized every furrow irrigation approach (Eba 2018; Golzardi et al. 2017; Kang et al. 2000). Many researchers also reported that such type of strategy has enormous potential to improve crop water productivity by reducing soil water loss through evaporation (Einsenhaver and Youth 1992; Davies and Zhang 1991; Stone et al. 1982).

7.2 Surge Irrigation

Surge irrigation refers to irrigation water applied intermittently at steady or variable rates in “on” and “off” series of pulses (Bahu et al. 2005). This method works well for Vertisols because they expand and contract when wet and dried (Stringham 1988). This approach is more suitable for uniform infiltration in Vertisols led to irrigation water saving, improving irrigation efficiency (20–30%), and higher crop water productivity in addition to achieving water application efficiency up to 85% (Valipour 2013; Horst et al. 2007; Mintesinot et al. 2007).

7.3 Pressurized Irrigation System

Pressurized systems like centre pivot system, drip, sprinkler, low-energy precision application (LEPA) system, etc. are one of the most popular for effective utilization of resources like water, soil nutrients, and energy. This system has capacity to reduce the irrigation cost (20%–50%), electricity consumption (about 31%), and fertilizer saving in the range of 7–42% (PMKYS). Among them, subsurface drip irrigation is one of the effective techniques to reduce soil evaporation in context of dryland agriculture. Similarly, bucket kits of gravity-run drip irrigation are one of the low-cost viable options in vegetable garden of dryland regions. They produce vegetable as par with commercial drip systems by efficient water utilization. Sensor-based irrigation system also helps in scheduling of irrigation and enhances water use efficiency in these regions. Aside from it, it is high time to increase the use of solar energy in agriculture. Solar micro-irrigation system can play a significant role in reducing energy consumption and carbon emissions. The variable rate irrigation system enhances water efficiency by managing nutrient and water uses at the site, but in Indian dryland condition due to lack of land consolidation, such types of technologies are not feasible.

7.4 Sensor-Based Irrigation System

Sensors basically help in irrigation scheduling and automation of irrigation system. Keeping these facts, various soil moisture sensors, i.e. neutron probe, tensiometers, watermarks, granular matrix, TDR (time domain reflectometry), and FDR (frequency domain reflectometry), and canopy sensors like dendrometer, infrared thermometer, infrared gas analyser, sap flow metre, etc., have been widely used in irrigation scheduling (Fig. 11.6). They help the irrigators to take the decision regarding irrigation scheduling, but site-specific calibration is required before taking moisture content in field (Kumari et al. 2019). Wireless sensor array also helps in real-time irrigation scheduling and saves a lot of water (Vellidis et al. 2008).

Fig. 11.6
A set of 4 photographs of irrigation scheduling sensor includes F D R, watermark, tensiometer, and infrared sensor.

Sensors for irrigation scheduling

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7.5 Decision Support System (DSS)

Policymakers/decision-makers use DSS to solve complex problems in an improved and fast system by providing many alternatives. It also acquires real-time weather data from weather station and monitoring of soil moisture by sensor network distributed across the field via wireless communication. Various applications such as water management in various crops, yield forecasting, irrigation scheduling, computer-aided mapping, etc. have been implemented by DSS. In this context, soil-water balance softwares like CROPWAT (Smith and Martin 1991), IrriSatSMS (John et al. 2009), IrriSat (Urso et al. 2013), PILOTE (Khaledian et al. 2009), etc. help in various crop irrigation scheduling, and the DRIPD developed by Rajput and Patel (2003) was used to determine the design criteria for a drip irrigation system. Thus, the irrigation scheme derived from DSS helps the precise application of water and supports “more crops per drop” paradigm.

7.6 IOT-Based Smart Irrigation System

This helps in automatic regulation of the irrigation system at predefined moisture content in fields from remote areas by using mobile phone which saves irrigation time and water along with farmers’ drudgery reduction (Abhilash et al. 2020). They have applied uniform moisture distribution in the farm which ultimately enhances crop water productivity even in dryland agriculture also. It also provides web-based services for collection of field sensor data, weather information, soil water status, as well as precise irrigation. It has huge potential to site-specific irrigation control even in dryland regions.

8 Economics of Deficit Irrigation Strategies

The main advantage of deficit irrigation is that the water saved from optimal irrigation may be used to irrigate more area, enhancing net income (English et al. 2002). But the accurate quantification of this economic gain is critical for future cropping and irrigation strategies. Reduced planting area, reduced water use, adoption of drought-resistant cultivars, or change in crop planning may be optimal options for increasing economic return. However, by using a good economic optimization model for irrigation and other inputs, potential income from the same land and crop type can be improved. This model primarily establishes the relationship between crop growth, water, and other inputs.

8.1 Bio-Economic Model for Deficit Irrigation

English et al. (1990) provided a simplified economic model that provides insight into the field level application of deficit irrigation and the economic gain associated with it in the context of limited inputs. Because it incorporates both land and water limitation constraints, this economic model may be applied to all places with minimal variation based on regional agricultural and climactic characteristics. Figure 11.7 depicts the analytical framework used in the basic English model.

Fig. 11.7
Analytical framework of English model for economics of deficit irrigation works on the assumption of fixed water supply and land area leading to optimum level of deficit irrigation. It also involves 2 graphs of yield versus applied water, and cost and gross revenue versus applied water.

Analytical framework of English model for economics of deficit irrigation

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To obtain an optimum deficit irrigation strategy, the English model and all other economic optimization models use both crop water production functions and revenue functions. Crop production functions describe the correlation between plant yield and water applied, which is not always a deliberate under-irrigation strategy (Doorenbos and Kassam 1979). It is an analytical framework for determining an optimal profit-maximizing water application level that is less than full irrigation under specified conditions. Because gross income is closely linked to crop yield, the revenue function will exhibit the same trend as the crop production function. This revenue function covers both fixed and variable costs incurred in farm level processes, and it is mostly influenced by regional farm input variables.

8.2 Land Limiting Condition and Opportunity Cost of Water

A bio-economic model for deficit irrigation must account for regional land and water resource limitations. Because these elements influence the plant’s marginal production, the model should anticipate the optimal level of irrigation while taking into account the limiting conditions of land and water. The term “land limiting condition” refers to a non-water scarcity situation with fixed land usage. The most effective deficit irrigation approach maximizes income per unit of land. However, the opportunity cost of water is the water saved in deficit irrigation practice in the field that can be used to irrigate more farmlands, increasing overall gross income. This essentially illustrates water-limiting conditions in which we have a scarcity of water resources yet need to irrigate as much area as possible for cultivation.

8.3 Empirical Models Used in Deficit Irrigation Economics

To be sustainable, a system must strike a balance between profit and the environment in which it operates. On the one hand, it should provide the maximum benefit while without endangering natural resources such as crops, land, and water. An economic analysis gives a clear overview of any irrigation practices used in a certain set of conditions. Many researchers investigated the economic benefit of deficit irrigation by using various approaches and bio-economic models to assess its long-term viability in crop yield and farmer profitability. Table 11.2 shows the various approaches used for deficit irrigation economics.

Table 11.2 Various types of methods used for economics of deficit irrigation
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9 Conclusion and Outlook

Being able to provide food and fibre for the world’s population has become a conundrum amidst freshwater scarcity especially in arid and semiarid region. The dryland areas (i.e. 41% of the global terrestrial) are dominated for grazing and rainfed cropping because of water scarcity, and the crop water productivity generally remains low due to on-farm water losses through seepage and evaporation. In water-short areas, irrigation water supplies remain abundant, and efforts are to maximize crop productivity and may be done through on-demand irrigation service. This will help to meet the full crop demand with negligible deep percolation losses. Stressing crops enhances water usage efficiency, without hampering the yields. Under such conditions in the dryland farming system, sustainable crop production may be achieved by employing deficit irrigation (DI) techniques. Deficit irrigation with scheduling reduces irrigation water consumption and conserves available water resources.

This chapter presents detailed discussion on improving water productivity through deficit irrigation in conjunction with irrigation scheduling and management practices such as mulching, tillage, mixed cropping or crop ration, and nutrient management. Major water saving from the irrigation system is the future need, and that could be achieved by precise management and innovative design for water delivery and field irrigation. Previous study showed that deficit irrigation has potential for sustainable reducing in agricultural water use. Present chapter could provide information that contributes in improving crop water productivity in high water-competitive environment. In conclusion, the adoption of DI may be promising in areas where available soil moisture for crop is limited and adequate land is available.