Feeding a growing population and meeting their water demands will become increasingly challenging in the future. Sustainability in agricultural water resource utilization is crucial for achieving global food security [9
]. To address food scarcity caused by water scarcity, there are three approaches: (i) increasing water availability through wastewater recycling, (ii) enhancing water productivity through higher yields or better water use, or both, and (iii) addressing regional water scarcity through importing water in the form of food through virtual water trade [10
]. The main objective of all three approaches is to maximize the use of available rainfall, make efficient use of limited irrigation water, and enhance crop water use efficiency through integrated techniques. Improving water efficiency in agriculture is a crucial approach for India to meet the growing demand for food. This can be achieved through various practices and technologies, including (i) upgrading and optimizing irrigation and drainage systems, (ii) building and lining field channels and waterways, (iii) land leveling and shaping, (iv) constructing field drains, (v) conjunctive use of surface and groundwater together, (vi) implementing and regulating appropriate cropping patterns, (vii) introducing and enforcing rotational water distribution systems (warabandi’s), (viii) developing plans for providing inputs such as credit, seeds, fertilizers, and pesticides, and (ix) strengthening current extension, training, and demonstration programs in farmers’ fields to conserve freshwater and increase irrigation efficiency.
2.2. Alternate Wetting and Drying
AWD irrigation was developed by the International Rice Research Institute (IRRI) and is a technically promising, realistically water-saving, and economically viable environmentally benign technique [14
]. AWD has been extensively tested and is now being implemented in many Asian countries, including India, the Philippines, Vietnam, and Bangladesh. AWD irrigation subjects the field to alternating cycles of saturation (flooding) and drying (unsaturation), thereby saving irrigation water, improving water-use efficiency, reducing greenhouse gas emissions, and saving fertilizer, pesticide, and labor inputs. Once the soil reaches a specific lower moisture level, irrigation is provided. During the crop growing season, the fields are switched from a continually wet rice field to a field with occasional dry spells. After transplanting (or three to four weeks after sowing), the field is allowed to dry out for about two to three weeks until the water table reaches about 10–15 cm below the surface of the soil [13
]. If no precipitation occurs, this could take anywhere from 1 to 7 days, depending on the soil. Once the threshold is met, irrigation water should be applied until the field receives 3–5 cm of standing water [15
]. A sunk perforated plastic field tube (PVC pipe) allows examination of the below-ground water table and assists in making a decision to irrigate at the appropriate time (Figure 1
). A safe level of 15 cm has been identified so that plants do not experience stress due to drought and yields do not suffer. The effect of AWD on rice yield and WUE is presented in Table 1
The AWD irrigation method can reduce water usage by up to 37% without affecting production. AWD has shown 23% less water use compared to continually flooded rice systems [16
]. In addition to saving water, the AWD system has the potential to improve grain quality by lowering total arsenic (As) and mercury (Hg) content in rice grains by 50%, reducing greenhouse gas (GHG) emissions by 45–90%, boosting water efficiency, and keeping or even increasing grain output [17
]. In rice cultivation, intermittent watering with AWD was found to decrease insect pests by 92% and diseases by 100% [11
]. Additionally, the study by Duttarganvi et al. (2016) showed that the use of AWD in conjunction with cono-weeding resulted in significantly higher yields compared to other irrigation and weed management methods. This is due to the promotion of abundant root growth and an aerated growing environment [18
Furthermore, the AWD method has also resulted in a 22% reduction in the frequency of watering compared to conventional rice production systems [19
]. The significant decrease in irrigation water input in AWD is mainly due to a reduction in deep drainage, seepage, runoff, and evapotranspiration [20
]. The absence of flooding in the AWD method minimizes water loss through seepage and percolation, although the rate of these processes is largely dependent on soil hydrological properties. The use of AWD under dry direct-seeded rice (DDSR) reduced the total water input by 27–29% and water productivity by 44–50% [11
]. Another study by Sujono et al. (2011) reported that the practice of AWD in rice reduced the irrigation water input by 13.1%, increased the grain yield by 22.9%, and improved water productivity by 41.6% compared to shallow intermittent irrigation [21
]. Likewise, Ceesay et al. (2006) also reported 60% water savings under AWD compared with continuous submergence [22
]. The absence of standing water in the field under AWD is a key factor contributing to the reduced water input in this technique [23
Based on the meta-analysis of 56 studies, Carrijo et al. (2017) established that severe AWD in rice saved 33.4% of water input with a 22.6% yield reduction, whereas mild AWD saved 25.7% of water input with increased rice productivity [24
]. AWD promotes root growth, enabling better uptake of water and nutrients from deeper soil layers, which leads to increased grain productivity [25
]. AWD plots received 57% less irrigation water than CF with a non-significant difference in grain yield, indicating that AWD could considerably enhance crop water use efficiency in Nepal [26
]. In addition to reducing water usage and increasing yields, the use of AWD has also been found to modify plant hormone signaling, which in turn enhances grain filling rate, decreases the percentage of unfilled grain, and improves water use efficiency [27
Research has found that the use of intermittent irrigation with three-day and seven-day intervals can save 55% and 74% of water, respectively, compared to CF irrigation. The seven-day intervals were found to have an irrigation water productivity of 0.48 kg grain/m3
and a total water productivity of 0.35 kg grain/m3
]. Maintaining a six-centimeter standing water depth at seven-day intervals has been shown to support plant growth while also boosting yields. Keeping soil moisture at optimum levels without inducing stress is crucial for the growth and development of the rice crop. While the adoption of AWD has proven to be effective in enhancing water use efficiency, saving water inputs, and increasing or maintaining yields, it is important to note that in some cases, particularly with light-textured sandy soils, the implementation of severe AWD may result in a sacrifice of yield for the sake of water savings and improved WUE. Additionally, the impact of soil characteristics on the effectiveness of AWD was found to be more pronounced in cases of severe AWD [24
To prevent yield reductions in AWD, it is important to continuously irrigate crops during and after the start of the reproductive phase. Compared to CF, the AWD has been shown to significantly reduce water usage while maintaining or even improving yields [32
]. The 34% reduction in water input in AWD, in turn, increased the water productivity of rice compared to continuous submergence [33
]. Tan et al. (2013) found no significant decrease in yields under the AWD method, and the use of AWD resulted in a 17% increase in water productivity compared to CF irrigation. According to Islam et al. (2022), the AWD irrigation system mitigated GHG emissions by 27% compared to CF irrigation. The methane (CH4
) emission for AWD was lower (1.67 kg ha−1
) than that of CF (2.33 kg ha−1
]. The study conducted by Djaman et al. (2018) found that the implementation of AWD irrigation management with a pressure head of 30 kPa resulted in a substantial increase in rice yield and nitrogen use efficiency while reducing the need for irrigation applications by 27.3% compared to CF. The performance of AWD was found to be most effective in soils with a pH of less than 7 and a soil carbon content of at least 1% [35
Although AWD reduced water input and gives a reasonable yield in many parts of the world, it has not been widely adopted due to its potential for reduced yields [24
]. Adoption of AWD resulted in reduced rice productivity in certain conditions [24
]. The significant disparities in grain yield across soils, climates, seasons, years, cultivars, and management practices pose a significant challenge to the widespread adoption of AWD [16
]. Humphreys et al. (2012) found only a slight reduction in yield under AWD [40
]. Similarly, Carrijo et al. (2017) reported a yield reduction of 5.4% under AWD. However, research has shown that under mild AWD, such as maintaining a soil water potential (SWP) of −20 kPa or higher or ensuring that the field water level does not drop below 15 cm from the soil surface, grain yields are not significantly impacted [24
]. Despite the ability of the AWD method to conserve irrigation water, it is unlikely that this method will be widely adopted in Nepal, as the current water administration system is not providing any direct incentives to reduce irrigation water usage [26
]. It should be noted that AWD may not be the most suitable approach for rice cultivation in sandy soils, as the water drains quickly and results in minimal water savings. Similarly, in soils with thick clay and shallow water tables, AWD may not be necessary, as the water table never drops below the lowest roots in these soils [41
Paddy yield and water use efficiency (WUE) of rice under alternate wetting and drying (AWD) and continuously flooded (CF) methods.
Paddy yield and water use efficiency (WUE) of rice under alternate wetting and drying (AWD) and continuously flooded (CF) methods.
|S.No.||Season/Location||Paddy Yield (t/ha)||Increase in WUE than CF||Reference|
|AWD||CF||Percentage Increase over CF|
|1||Northwestern Bangladesh (Boro, dry season)||6.28||5.92||6.1||33.26|||
|2||Philippines (dry season)||7.6||7.2||5.6||11.66|||
|5||Punjab, Pakistan (summer)||4.03||4.18||−3.6||21.0|||
2.3. The Effect of AWD on Grain Quality of Rice
The rice grain quality may change while transitioning from the conventional flooding system to water-saving rice production technologies [45
]. The effect of AWD on rice grain quality is presented in Table 2
. CF has been shown to have negative impacts on grain quality, as it accumulates harmful heavy metals such as arsenic and mercury [46
]. On the other hand, the implementation of AWD irrigation has been found to improve grain quality by increasing protein content, milling recovery, and grain yield. However, excessive AWD can result in reduced protein content [48
]. Song et al. (2021) reported that AWD improved the nutritional quality of milled rice by increasing amino acids and phenolic acids and decreasing lipids and alkaloids [49
]. Rice plants grown under AWD showed higher levels of leaf abscisic acid and increased concentrations of foliar isopentenyladenine (37%), while leaf trans-zeatin concentrations decreased by 36% compared to CF [50
]. In comparison to aerobic irrigation management, AWD irrigation reduced the number of opaque kernels (62%), abortive kernels (51%), and chalkiness (42%). Additionally, AWD irrigation decreased the kernel amylose levels by 15%, amylopectin by 6%, and mercury uptake by 21% compared to CF [51
]. The nutritional quality of brown rice was improved under AWD water management, as there was an increase in grain antioxidants, flavonoids, γ-oryzanol, total tocopherols, grain iron, and zinc, as well as a significant decrease in grain arsenic compared to CF [52
AWD is a simple and low-cost method that can be easily adopted by smallholder farmers. AWD requires careful management to prevent damage to the rice crop and ensure optimal water and nutrient uptake by the plants. Additionally, the effectiveness of AWD may vary depending on local soil and climatic conditions, and it may not be suitable for all regions and climatic conditions. To further improve the adoption and effectiveness of AWD, some future research areas include Optimization of AWD practices: AWD is a complex agricultural technique that involves the manipulation of soil water dynamics. There is a need for further research to optimize AWD practices such as irrigation scheduling, drainage management, and water-saving technologies to maximize yields while minimizing water use. Soil health and nutrient management: AWD can have significant impacts on soil health and nutrient cycling. Future research should focus on understanding the long-term impacts of AWD on soil properties, nutrient availability, and GHG emissions, as well as developing strategies for managing soil health and fertility in AWD systems. Scaling up and dissemination: Despite the many benefits of AWD, adoption rates remain low in many regions. Future research should focus on identifying the barriers to adoption and developing strategies for scaling up and disseminating AWD practices to farmers, including training programs, farmer field schools, and extension services.
2.4. Aerobic Rice System
Aerobic rice cultivation is an innovative approach to growing rice in well-drained, non-flooded, and unsaturated soils without ponded water [56
]. This method incorporates the use of specialized aerobic rice cultivars that are responsive to inputs and optimized water management techniques, resulting in an impressive yield of 4 to 6 tonnes per hectare with a water consumption rate of only 50 to 70% compared to traditional irrigated rice cultivation. This method is highly recommended for regions facing water scarcity or high water costs, as well as areas where there is a pressing need for labor and rising wages. The WUE and water productivity of rice under an aerobic system are presented in Table 3
. The most serious barrier to the widespread adoption of aerobic rice is weed infestation. Various low-dose high-efficacy herbicides are available on the market to control weeds in the aerobic rice system. These herbicides also have a wider window of application. Shahane et al. (2019) reported that the aerobic rice system saved 37.4% and 50.8% of irrigation water during the first and second years of the experiment, respectively, over conventional transplanted rice [57
]. More water is saved in the aerobic system than in puddled transplanted rice and the SRI due to the absence of nursery raising, puddling of fields, and maintenance of arable soil.
However, the aerobic rice system caused a significant yield penalty over puddled transplanted rice. In addition to water-saving, aerobic rice is known to reduce greenhouse gas emissions and lower global warming potential [58
]. Changing rice cultivation from conventional flooded rice to an aerobic rice system emitted an average of 79.8% less CH4
, whereas it emitted 14.4% more nitrous oxide (N2
O) than transplanted paddy [59
]. Aerobic rice cultivation resulted in lower yields, averaging 3 tonnes per hectare with 27% lower water use compared to traditional flooded conditions, which produced 5.8 tonnes per hectare [60
]. Additionally, Kato et al. (2009) found that water productivity was 1.4 to 3.7 times higher in aerobic rice systems compared to transplanted rice (Table 3
]. The implementation of aerobic irrigation with DDSR increased water productivity by 22–30% and water savings by 49–55%, despite a decrease in paddy yield of 36–39% due to higher panicle sterility [11
]. In a study conducted by Shahane et al. (2019), which compared the water productivity of aerobic rice, the system of rice intensification (SRI), and transplanted rice, it was found that aerobic rice saved 50.8% of the water used in transplanted rice [57
]. Similar results were reported by Ramulu et al. (2020), who found that aerobic rice in sandy loam soil saved 50% of the irrigation water compared to transplanted rice [62
Water use efficiency and water productivity of aerobic rice systems.
Water use efficiency and water productivity of aerobic rice systems.
|S.No||Season/Location||WUE or WP or % Water Saving||Reference|
|1||IRRI, Philippines||In aerobic rice, water productivity ranged from 0.88 to 1.13 compared to 0.54 to 0.66 kg grain m−3 under the alternate flooding method. The total water used in aerobic plots was 27% lower than the alternate flooding method of irrigation. |||
|2||The University of Tokyo, Japan and Kyoto University, Osaka, Japan||Water productivity in the aerobic system ranged from 0.75 to 0.96 kg grain m−3 and 1.4 to 3.7 times higher than transplanted rice. The grain yield of aerobic and transplanted rice did not differ significantly in the clay loam soils of Japan.|||
|3||IARI, New Delhi||The highest water productivity was recorded with the aerobic rice system (3.52 kg ha−1 mm−1) followed by the SRI method (3.07 kg ha−1 mm−1), and the lowest water productivity was noted with transplanted rice (2.28 kg ha−1 mm−1). The aerobic rice system saved 50.8% of water over transplanted rice. |||
|4||Hyderabad, India||The aerobic rice system (0.70 kg grain m−3) has higher water productivity than transplanted rice (0.55 kg grain m−3). Aerobic management saved nearly 50% more water than conventional rice cultivation in sandy loam soils. |||
|5||UAS, Banglore||Aerobic farms have a greater (3.84 q acre−1 inch) water use efficiency than traditional farmers (1.64 q acre−1 inch). Additionally, compared to conventional farms (₹ 269.41 acre inch−1), aerobic farms’ economic WUE was greater (₹ 1643.54 acre inch−1).|||
Aerobic rice has several challenges, including, Nutrient deficiencies: The non-flooded aerobic soil conditions favor the development of nutrient deficiencies, such as iron and phosphorus which are typically more available under flooded conditions. Farmers must carefully manage nutrient inputs and may need to use fertilizer formulations that are specifically designed for non-flooded conditions. Weed control: Farmers may need to use more intensive weed control measures, such as herbicides or manual weeding, to maintain yields. Pest and disease management: Non-flooded conditions can also create favorable conditions for certain pests and diseases. For example, root-knot nematode infestation is more common under aerobic rice systems compared to flooded rice production systems.
2.5. The System of Rice Intensification
For more than a decade, the system of rice intensification (SRI) has been pushed as a set of agronomic management approaches for rice farming that increases output while lowering water usage. Henri de Laulanié invented the SRI in Madagascar in 1983 while working with peasant farmers [64
]. The system has spread rapidly to dozens of rice-growing countries. It consists of several distinctive practices including transplanting young (13–15 days old) and single seedlings, wider and square planting, intermittent water management (irrigation after hair-like crack development), weed control with a cono-weeder/mechanical weeder for better weed control and soil aeration, and encouraging the use of organic nutrients and inorganic fertilizers.
It has been demonstrated that paddy farming using the SRI approach significantly increases land productivity while consuming less water. The SRI method of paddy cultivation saved up to 50% of irrigation water in comparison to the traditional method by avoiding evaporation and deep percolation losses. The SRI is the preferred method for rice cultivation on flat and irrigated land compared to uneven rainfed land [66
]. This method is highly suitable for water-scarce regions, although this method slightly increases the need for human manpower initially.
The primary difference between the SRI and non-SRI irrigation techniques in terms of water use is that the former uses a dry-wetting irrigation system while the latter uses the more traditional inundation technique. Second, the SRI approach saves a significant quantity of water because it does not require deep or repetitive puddling. Third, irrigation is applied sparingly at the time of transplanting, contrasting with the typical procedure. Fourth, a simple wetting of the ground is sufficient to operate a hand-drawn cono-weeder or mechanical weeder efficiently in a paddy field. Extended root growth takes place due to the wide spacing followed during transplanting. This robust root system in the SRI facilitates the uptake of water and nutrients from a large volume of soil and results in higher yield. The SRI method can enhance rice grain yield with substantially less water input than the conventional method of rice cultivation [66
]. Shahane et al. (2019) reported that the SRI method saved 21.9% and 27.4% of irrigation water without any reduction in yield during the first and second year of the experiment, respectively, over conventional transplanted rice [57
]. When compared to normal transplanting, the SRI method saved 31 and 37 percent of irrigation water during the Kharif
seasons, respectively [67
]. The saving of water with the SRI was due to the lower depth of irrigation water application in the SRI than in conventional transplanted rice during the early growth period. The SRI method of stand establishment saved irrigation water and has a greater WUE (70.8 kg rice equivalent yield/ha/cm) than the conventional transplanted rice (67.0 kg rice equivalent yield/ha/cm) and the alternate wetting and drying method of irrigation [68
]. Farmers who use the SRI method instead of the usual inundation approach can save around 40% of irrigation water, enhance land yield by about 46%, and reduce cultivation costs by 23% [69
According to Toungos (2018), the SRI method of rice production reduced 40% of irrigation water usage in Indonesia, 67% in the Philippines, and 25% in Sri Lanka when compared to traditional farming practices [70
]. During the Kharif
seasons, the SRI method recorded 31% and 37% less water usage for irrigation compared to normal transplanting [71
]. The SRI method had a higher irrigation water productivity (IWP) and economic water productivity (EWP) of 6.62 kg and ₹ 108, respectively, while the non-SRI method had a lower IWP and EWP of 2.70 kg and ₹ 45, respectively. The IWP was found to be 145% higher in the SRI method compared to the non-SRI method [69
]. The higher IWP and EWP in the SRI method are due to the fact that farmers who adopt this approach generally save more water and produce more rice. SRI proponents suggest the use of cono-weeders for weeding and soil aeration, but poor farmers find the equipment to be too expensive and struggle to use it in field conditions [72
The amount of water saved using the SRI approach was found to be higher in groundwater-irrigated areas (roughly 45 percent) than in canal-irrigated areas (about 33 percent) [69
]. The reason for this variance is that farmers were able to closely adhere to a dry-wetting irrigation method since water availability was guaranteed in the groundwater-irrigated region. This allowed the farmers growing an SRI paddy to save a sizable amount of water. However, it was not feasible in the canal-irrigated area since farmers are not in charge of water management and are, therefore, prone to over-irrigate crops whenever water is available in plenty [69
]. The SRI method improves the water and nutrient-holding capacity of soil as it adds more organic manure through the incorporation of weeds and promotes the use of organic nutrient sources (green manure, green leaf manure, farmyard manure, compost). Greenhouse gas emissions are also lower in the SRI method of cultivation, as it emitted an average of 26.8% less CH4
and 3.8% more N2
O than the conventional flooded paddy [59
]. The majority of farmers that adopted the SRI approach did not adhere to all of the suggested practices due to inadequate literacy and limited knowledge of the recommended irrigation practices. As a result, farmers have not used the SRI technique to its full potential [69
]. Depending on local agronomic or institutional opportunities and constraints, partial implementations of SRI principles, i.e., adopting individual SRI practices, could provide some benefits to farmers but could not derive synergies between all of the principles [66
The SRI may not be suitable for all farmers or all rice-growing conditions. Farmers must carefully weigh the advantages and disadvantages of the SRI and determine whether it is a suitable option for their specific situation. There are some challenges associated with the SRI system include Labor-intensive: The SRI requires more labor than traditional rice cultivation methods, particularly during the transplanting stage when seedlings are planted individually. This can be a challenge for smallholder farmers who may have limited labor resources. Water management: The SRI requires careful water management, and an area that has high rainfall may not be ideal as it does not allow better soil aeration for root growth and tiller development. Knowledge and skills: The SRI requires farmers to have a certain level of knowledge and skills, particularly in terms of transplanting, water management, and nutrient management. This can be a barrier to adoption for some farmers, particularly those with limited access to training and extension services. Time-consuming: The SRI requires more time and attention from farmers, particularly during the transplanting stage and in terms of soil management.
2.6. Saturated Soil Culture
Saturated soil culture (SSC) entails providing shallow irrigation to achieve around 1 cm of ponded water depth for a day or two after the ponded water has vanished. In SSC, the soil is kept as close to saturation as feasible, lowering the ponded water’s hydraulic head, seepage, and percolation flow. In SSC (no standing water), the deep percolation losses are zero, while in continuously flooded conditions percolation of water is high (Figure 2
). The percolation rate increases along with increasing irrigation water depth in the field [73
]. The water depth above the soil is kept below 3 cm in SSC compared to other methods, where 5 cm is followed. The lower water depth reduces the percolation loss of water in SSC. The effect of SSC on rice yield and WUE is presented in Table 4
. Tuong and Bhuiyan (1999) reported that SSC can reduce water losses, diminish water use, and maintain or increase productivity in rice-based systems. However, plants reduced evapotranspiration under severe water stress, which led to a decrease in photosynthesis, which in turn caused a decrease in chlorophyll, height, and tiller number [74
]. Water stress during the tillering stage reduced the number of panicles per hill significantly [75
]. Keeping the soil moisture in saturation avoids the problem of moisture stress and did not affect root growth, tiller production, and biomass accumulation. On average, SSC can decrease water input by 40% from the continuously flooded condition with a non-significant yield reduction of 6% [76
Among different irrigation water depths, viz., 5, 4, 3, and 2 cm, the application of 3 cm of irrigation at weekly intervals appeared suitable and beneficial to rice crops in loamy textured soil, as it recorded significantly higher total water productivity (0.35 kg/m3
) and irrigation water productivity (0.79 kg/m3
) with non-significant yield reduction [77
]. Another study reported 32% less water usage under SSC compared to intermittent irrigation at a weekly interval [78
]. According to Matsue et al. (2021), SSC irrigation significantly increased grain yield by increasing the percentage of filled grains compared to CF [79
]. The quality of rice grains was also improved, with a higher percentage of head rice recovery and improved cooking quality due to a lower protein content and hardness/adhesion ratio. In the Philippines, SSC irrigation has been shown to save 30–60% of water compared to the CF system, with only a slight reduction in grain yield (4–9%) and an increase in WUE by 30–115% [27
]. On the other hand, AWD saved 16–24% of irrigation water and 20–25% of production costs while maintaining the same yield as farmers’ practices [80
]. Growing rice (cv. IR20) in the dry season under AWD saved 56% of irrigation water, whereas the yield was reduced from 7.9 t ha−1
to 3.4 t ha−1
In Australia, SSC used about 32% less water compared to traditional flooded rice production in both seasons (wet and dry), with no effect on grain yield and quality. Another study in Australia reported that SSC reduced water use by 16–28 percent and improved water use efficiency by up to 20 percent [82
]. For growers in semi-arid tropical areas, SSC provides a practical substitute for flooded rice production [83
]. Weekly irrigation at 120% soil saturation exhibited greater irrigation water productivity (0.69 kg/m3
), rainwater productivity (1.02 kg/m3
), and water-saving (90.53%), with less production penalty (5 × 10−3
) compared to irrigation at 200% soil saturation (farmer practice) [84
]. SSC facilitates maximum utilization of rainfall, thereby increasing the effective rainfall percentage during the crop season. Moreover, high effective rainfall is recorded from panicle initiation to physiological maturity, as the increased moisture content in this stage helps with faster crop recovery from moisture stress, better initiation of panicle, and higher panicle fertility. Thus, it will be more suitable for rainfed rice-growing areas. SSC has the ability to significantly reduce unnecessary water outflows while increasing water productivity. Compared to other water-saving irrigation methods, SSC is a low-cost technology that has greater potential to save available irrigation water. SSC reduces the number of irrigations required to raise the crop, thereby reducing the irrigation cost, energy required for irrigation, and irrigation water.
The effect of the saturated soil culture irrigation method on rice yield, water use efficiency, and irrigation water saving.
The effect of the saturated soil culture irrigation method on rice yield, water use efficiency, and irrigation water saving.
|1||Irrigated field, Australia||Among four levels of soil saturation, viz., 120% (2 cm), 180% (3 cm), 240% (4 cm), and 300% (5 cm), the application of 180% (3 cm) was found effective, as it saved 40% irrigation with low yield sacrifice (6% of reduction).|||
|2.||Philippines||SSC saved 30–60% of water compared with the conventional flooded system with little reduction in grain yield (4–9%) and increased WUE by 30–115%.|||
|3.||National Pingtung University of Science and Technology in Southern Taiwan||Among different irrigation water depths, viz., 5, 4, 3, and 2 cm, the application of 3 cm of irrigation at weekly intervals appeared suitable and beneficial to rice crops, as it recorded significantly higher total water productivity (0.35 kg/m3) and irrigation water productivity (0.79 kg/m3) with non-significant yield reduction.|||
|4.||IRRI, Philippines||AWD saved 16–24% of irrigation water and 20–25% of production cost with the same yield as farmers’ practice.|||
|5.||Philippines/dry season||Growing rice (cv. IR20) under AWD saved 56% of irrigation water, whereas the yield was reduced from 7.9 t ha−1 to 3.4 t ha−1.|||
|6.||Eastern Burkina Faso. Semi-arid region. Irrigated field. ||Weekly irrigation at 120% soil saturation exhibited greater irrigation water productivity (0.69 kg/m3), rainwater productivity (1.02 kg/m3), and water-saving (90.53%) with less production penalty (5 × 10−3 kg/m3) compared to irrigation at 200% soil saturation (farmers’ practice).|||
|7.||Millaroo Research Station, BRIA, Australia||SSC used about 32% less water compared to traditional flooded rice production in both seasons (wet and dry) with no effect on grain yield and quality. SSC is a viable alternative to flooded rice production for growers in semi-arid tropical environments. |||
2.7. Direct-Seeded Rice
DSR is also an efficient resource conservation technology that holds great promise in rice-based cropping systems. DSR can be established by broadcasting or line-sowing at 20 cm row-to-row spacing, a 3–4 cm seeding depth, and using a mechanical seed-cum-fertilizer drill in unpuddled and well-prepared dry soil followed by light irrigation (2 cm) for germination. Thereafter, irrigation is somewhat delayed and given 20 days after the sowing to encourage a sturdy root system. Later irrigations are given by adopting the AWD cycle at the interval of 7–10 days depending on rainy events, soil type, crop growth stage, and ET demand. Alternatively, wet DSR involves the sowing of pre-germinated seeds (radicle 1–3 mm) on puddled wet soil.
The labor-intensive practice, viz., raising the nursery and transplanting the rice, is eliminated in DSR [85
]. In the event of a monsoon delay or a water constraint, DSR allows the farmer to direct sow a paddy with an appropriate short-duration variety to fit within the cropping system. This also enables the timely seeding of succeeding wheat crop rice-wheat systems where delayed wheat sowing causes significant yield loss in the IGP region [86
]. When compared to transplanted flooded rice, DSR uses less water and provides several other advantages such as reduced crop duration, cost of cultivation, etc. DSR is proven to yield more than conventional transplanted rice production if weeds are controlled properly at the right time. DSR is more prone to weed infestations than traditional transplanted rice, as the rice plants are initially smaller and weeds can more easily compete for resources. Herbicides are mostly used for weed control in DSR. The herbicides recommended for different rice production methods along with their rate and time of application are summarized by Saravanane et al. (2021) [87
]. Poor seed germination and sub-optimal plant population are major causes of low yields in DSR. To ensure an optimum plant population, it is essential to use high-quality seeds with a high germination percentage. By doing so, farmers can increase the chances of successful germination and establish a healthy and uniform plant stand, ultimately resulting in higher yields.
The effect of DSR on WUE and water productivity is presented in Table 5
. Dry direct-seeded rice produced higher yields (13–18%) and reduced the total water inputs (8–12%) in comparison to transplanted rice [11
]. Gill et al. (2006) indicated that water productivity was improved to 0.46 from 0.36 by following the DSR compared to transplanted rice due to less irrigation water consumption (18%) and a similar yield [88
]. Despite having more irrigation events, the average water input of DDSR was lower than that of transplanted rice for both rice seasons, as DSR omits the large amounts of early-season water input used to puddle the field. The extent of water savings in DDSR was relatively low (only 8–12%) in the sandy loam composition of the soil in comparison to transplanted rice, which might be attributed to the absence of a plow pan or a hard pan [11
]. DSR with sesbania co-culture saved irrigation water (34%), increased water productivity (0.43 kg m), reduced labor requirements (24%), and saved electricity (29%) [89
]. Similarly, when compared to transplanted rice, the global warming potential (GWP) of dry DSR rice was 76.2 percent lower than that of wet direct-seeded rice, which was 60.4 percent lower [90
]. The new technology would not be widely used if it just served to save water without increasing the yield. Farmers would not use the technology if it was not profitable for them.
2.8. Drip-Irrigated Rice
Drip irrigation is a modern water-saving technology used in direct-seeded rice production (Figure 3
). The water productivity in drip-irrigated rice under a direct-seeded system was significantly higher compared to transplanted rice under flood irrigation due to higher evaporation, deep percolation, runoff, and seepage in the later system. In drip irrigation, precise water application and ensuring consistent wetting of the rice field to meet crop evapotranspiration would be possible. Drip irrigation also promotes healthy crop development by reducing soil evaporation and deep percolation [91
]. Furthermore, drip fertigation increases rice yield potential by administering divided fertilizer doses precisely at the proper moment according to crop developmental phases at the right place, i.e., the zone of maximum root activity. Additionally, the physiology of the rice crop was positively influenced by drip irrigation with enhanced water, nutrient, and resource use efficiency.
Rice cultivation with drip irrigation resulted in longer and denser roots, which boosted canopy photosynthesis and tiller numbers [91
]. Planting on either side of the dripline or one dripline feeding 2 to 3 rows on the bed was a preferred option by the farmers. The narrow dripline spacing gives farmers more flexibility and options for including a range of rotational crops. However, narrow spacing of 0.5 to 0.6 m also means more dripline, more connections, and higher costs. Emitter spacing used by researchers was mostly narrow and varied from 0.3 to 0.5 m, depending on soil characteristics. Seasonal irrigation requirements for drip-irrigated rice in the semi-arid region of Hyderabad, Telangana, India, were estimated to be 801 mm, which was 51.6% less than flooded irrigated rice. The quantity of irrigation water for drip-irrigated rice varied from 547 to 844 mm in the semiarid region of South India, 882 mm in Ludhiana, Punjab, 639 mm in Pantnagar, Uttarkhand, and 789 mm in Nashik, Maharashtra [93
]. The continuous flood-irrigated rice across different agroecological conditions needed 150 to 853 mm more water (27.4 to 106.4%) than drip-irrigated rice. The water-saving in drip irrigation is mainly due to reduced evaporation, deep percolation, and conveyance losses. The WUE of surface drip-irrigated rice was 0.0576 t/ha-cm compared to 0.0181 t/ha-cm under conventional transplanted flooded rice [94
]. In addition to saving 50–61 percent more water than the flood system, the drip system with fertigation also boosted yield and water productivity [95
]. The effect of drip irrigation on WUE and water productivity is presented in Table 6
However, the advantage of drip irrigation in terms of yield can vary based on environmental conditions. According to He et al. (2013), the decrease in yield with drip irrigation in rice is largely due to a reduction in the number of productive tillers [96
]. Additionally, root length is also found to be reduced, with more roots distributed in deeper soil layers under drip irrigation compared to CF irrigation. On the other hand, Sharda et al. (2017) found that the higher grain yield in drip-irrigated DSR was mainly attributed to higher root density at deeper soil layers (15–30 cm), which in turn increased the irrigation WUE and the number of filled grains per panicle [97
]. He et al. (2013) also found that drip irrigation with plastic mulch was more efficient in terms of water savings compared to furrow irrigation in rice cultivation [96
]. This was attributed to two factors: (i) plastic mulching, which can effectively reduce evapotranspiration compared to bare land, and (ii) seepage, which was significantly lower in the drip irrigation treatment than in the furrow irrigation treatment in loamy soil. The adoption of water-saving practices in irrigated rice increased paddy productivity, promoted soil carbon sequestration, assisted in resource conservation (water, labor, energy, and time), and lowered greenhouse emissions [11
Drip irrigation helped with the production of more roots in the topsoil layer than furrow-irrigated rice [96
]. Spacing between the lateral should be kept optimum for higher yield along with water-saving. Ramesh et al. (2020) reported an 80 cm interval between the lateral optimum for hybrid rice [98
]. In the changing climate scenario, a continuous flooding system contributes more methane gas to global warming; adopting drip irrigation for growing rice reduced methane and nitrous oxide emissions. According to Ramesh and Rathika (2020), an average of 68.6 and 34.4% less CH4
O emissions were noticed under drip irrigation over a conventional flooded paddy [59
]. Considering the seriousness of fast-depleting groundwater reserves and international commitments to address climate change issues, drip-irrigated rice would be of immense value to various stakeholders for saving water in agriculture. The evidence suggests that farmers do not embrace the drip fertigation technique in rice solely to conserve water, electricity, or other resources. In India, electricity is heavily subsidized, and water is not metered. The farming community will readily adopt the new technology only if it increases profits and is supported by farmer-friendly government policies that offer subsidies and other incentives. Installation and maintenance of the system. Drip irrigation systems require specialized installation and maintenance, including checking for leaks or clogs in the emitters, adjusting the water flow rate, and monitoring soil moisture levels. This can require additional labor input.
Water use efficiency and water productivity of drip-irrigated rice.
Water use efficiency and water productivity of drip-irrigated rice.
|S.No||Season/Location||WUE or WP or % Water Saving||Reference|
|1||G. B. Pant University of Agriculture and Technology||The WUE of drip-irrigated rice is 0.095 t/ha-cm compared to 0.021 t/ha-cm under transplanted rice with continuous submergence.|||
|2||Multi-location with different varieties ||Under drip fertigation, rice yields (13–28%) and water productivity (0.46 to 0.67 kg/m3) were higher across locations, irrespective of the cultivar compared to the conventional method.|||
|3||Agricultural Drought Research Institute, China||The grain yield is reduced by 31.76–52.19% under drip irrigation with plastic mulch, although the WUE (0.38 kg grain m−3) is 1.52–2.12 times higher than the CF. Drip-irrigated rice has greater water-saving capacity (57.4–67.9%) and lower yield and economic benefit compared to CF. So, drip-irrigated rice is a better option for water-scarce areas.|||
|4||PAU, Ludhiana||Drip-irrigated rice recorded higher WUE (0.81–0.88 kg m−3) and saved 42% of irrigation water compared to flood irrigation, which had a WUE of 0.42–0.52 kg m−3. |||
|5||Research farm of Jain Irrigation, in Tamil Nadu||Drip irrigation in rice increased grain yield by 17–22% and saved irrigation water by 50–61%. Similarly, higher water productivity (0.365 to 0.714 kg/m3) was recorded in drip-irrigated rice compared to the flooded method of irrigation (0.097 to 0.224 kg/m3).|||
2.9. Smart Irrigation
Sensor technology, the Internet of Things, wireless communications, public automatic weather station networks, improved crop evapotranspiration measurements, satellite and aerial imaging, and cloud computing technology are all promising areas for developing robust irrigation advisory tools to assist farmers in accurately determining and meeting crop water needs. Wireless networks can be used to collect data from soil moisture sensors, which can then be accessible via a web browser or smartphone app. Many of the computations involved in crop evapotranspiration-based irrigation scheduling have been automated using web and smartphone applications [100
]. Smart irrigation apps are mobile-based irrigation scheduling tools that use weather data to determine irrigation scheduling protocols (when to apply and how much to apply) based on water losses from cropped fields. The weather data is obtained from the nearest automated weather monitoring network stations. A user’s new field is automatically associated with the nearest weather station when they register it in the smart irrigation apps; however, the user has the option of selecting any of the other available weather stations [101
Around the world, agriculture automation is becoming more and more important. Irrigation systems can be automated to suit different crops, soil, climate, and other factors with the help of sensors (moisture, temperature, and humidity), IoT devices, and machine learning algorithms. The automation of irrigation systems increases crop output, quality, and water use efficiency while reducing irrigation water, time, cost, and electricity [102
]. By measuring the level of water, soil temperature, nutrient content, and weather forecasting, smart irrigation technology increases production without requiring manpower. However, for an automated irrigation system to be implemented successfully, sensor installation is crucial [102
]. Sensors need to be put in the area where plants’ roots extract water (ensuring that there are no air gaps around the sensor). This will guarantee that the crops obtain enough water. Solar-powered raindrops and soil moisture sensors were buried in the root zones of the crops, and all these sensors are managed by a wireless internet network. The GSM module is used in the soil moisture sensor and raindrop sensor to transmit SMS notifications on soil moisture to the farmer’s cell phone. As a result, the farmer may control the water supply using SMS (Figure 4
The intelligent water-saving irrigation system based on the agricultural IoT enables the real-time remote monitoring of moisture content and the accurate management of irrigation in paddy fields. These intelligent automatic irrigation systems are simple to adopt, function perfectly, and have high reliability and low power consumption. Currently, the cost of sensors used for intelligent automatic irrigation is prohibitively high, making it unfeasible for small and marginal farmers to adopt this type of system in their farms [103
]. Manufacturers are actively working to develop low-cost sensors that can be linked to nodes, thus facilitating the implementation of budget-friendly irrigation management systems and agriculture monitoring solutions. An IoT-based modern irrigation system has been found to reduce the water footprint by 40.29% and 29.22% compared to AWD and basin irrigation, respectively [104
]. The water footprint of the IoT-based modern irrigation system, AWD, and basin irrigation was 2343, 3924, and 3310 m3
/tonnes of paddy, respectively. The effect of smart irrigation on rice is presented in Table 7
Future research that could further improve the effectiveness of these systems includes Sensor accuracy and reliability: which is the idea that the accuracy and reliability of the sensors used in automated IoT sensor-based irrigation systems can affect the precision and efficiency of the irrigation process. Future research could focus on improving the accuracy and reliability of sensors to ensure that they provide accurate and timely data to the system. Crop modeling and prediction: Developing accurate crop models and prediction tools can help farmers optimize irrigation schedules and avoid over- or under-watering of their crops. Future research could focus on developing more accurate and sophisticated models for rice crops that take into account factors such as soil moisture, weather conditions, and plant growth stage. Optimization of water use efficiency: Automated IoT sensor-based irrigation systems can help farmers optimize their water use efficiency by providing real-time data on soil moisture levels and crop water requirements. Future research could focus on developing more efficient irrigation scheduling algorithms and control strategies to further improve water use efficiency. Integration with other technologies: Automated IoT sensor-based irrigation systems can be integrated with other technologies, such as weather forecasting or drone-based imaging, to further optimize the irrigation process. Future research could focus on developing more sophisticated and integrated technologies that provide farmers with a comprehensive and data-driven approach to crop management. Adoption and dissemination: Despite the potential benefits of automated IoT sensor-based irrigation systems, their adoption and dissemination in rice farming communities can be slow due to factors such as a lack of awareness, technical expertise, or financial resources. Future research could focus on developing effective dissemination strategies and outreach programs to promote the adoption and scaling up of these technologies.
2.10. Comparision of Different Water Saving Technologies with Conventional Flooding
Comparing water-saving rice production methods based on climate, soil type, labor, energy, and GHG is important for several reasons (Figure 5
). Firstly, it helps farmers to select the most appropriate method based on the specific conditions of their farm, which can lead to higher yields, reduced costs, and improved WUE. Secondly, it allows policymakers to identify the most sustainable methods for a particular region, taking into account the local climate, soil type, and labor availability. This can help to reduce the environmental impact of rice cultivation while ensuring food security for local communities. Thirdly, comparing water-saving rice production methods based on energy and GHG emissions can contribute to the reduction in carbon footprints associated with rice production. Therefore, comparing water-saving rice production methods based on various factors is essential for sustainable rice production and achieving global food security and climate goals.
Production cost: The adoption of DSR may result in lower cultivation costs when compared to traditional rice farming, as it eliminates the need for transplanting and reduces labor requirements for water management. Conversely, aerobic rice cultivation may incur higher production costs compared to traditional rice farming due to the additional inputs and equipment required. Similarly, the SRI may also lead to higher production costs due to its labor-intensive nature, including the need for manual labor in activities such as transplanting, weed control, and irrigation. Drip-irrigated rice may also have a higher cost of cultivation compared to traditional methods, as it requires the use of drip irrigation equipment and maintenance. Finally, the implementation of IoT-based automated irrigation may also incur higher cultivation costs than traditional rice farming due to the requirement for sensors, monitoring equipment, and maintenance.
Soil type: Aerobic rice is most suitable for well-drained soils, while heavy clay soils are not recommended. DSR, on the other hand, is not recommended for soils with high water tables, high soil pH, or salinity, as all of these factors can lead to poor seed germination. The SRI is not suitable for poorly drained or waterlogged soils as it can result in poor tiller and root development and higher seedling mortality. Similarly, drip irrigation may not be ideal for soils with high clay content as it can lead to clogging of the emitters. However, IoT-based automated irrigation can be implemented in any soil type as long as the sensors and monitoring equipment can be installed and function properly. GHG emissions: The implementation of practices that reduce water and fertilizer inputs while promoting soil aeration can significantly reduce methane emissions associated with rice cultivation. However, these practices increase nitrous oxide emissions, as alternate wetting and drying irrigation cycles promote the conversion of ammonia to nitrate. Similarly, the adoption of energy-intensive drip irrigation equipment may lead to an increase in GHG emissions during production and operation. This is also true for IoT-based automated irrigation systems.
Weed pressure: Weeds are a serious problem in aerobic rice, especially during early growth stages. Similarly, DSR faces weed competition due to limited water availability. The SRI requires more manual weeding because of a reduced number of plants per unit area. IoT-based automated irrigation and SSC also have weed control issues, but SSC uses stale seedbed preparation to reduce weed germination, and drip-irrigated rice reduces weed growth by minimizing soil moisture levels. Improved water-saving rice production systems have higher weed pressure than conventional flooded rice systems. However, the availability of broad-spectrum herbicides with a wider window of application helps the farmers to control weeds in these systems. Labor requirement: The labor requirement varies across different rice production methods. The SRI demands more manual labor due to transplanting single seedlings, maintaining wider spacing, weeding, and irrigation. Similarly, aerobic rice also requires more labor during the early growth stages for manual weed control. In contrast, drip-irrigated rice requires less labor for weeding but requires more labor for installation and maintenance of the drip irrigation system. DSR, on the other hand, requires less labor for land preparation and transplanting but more for weeding. Therefore, labor-intensive rice production systems are better suited for regions with ample and affordable labor resources. Climate: The SRI, aerobic rice, and DSR are not suitable for regions with high rainfall, as these methods require well-drained soil and do not perform well under flooded conditions. Drip-irrigated rice and SSC may not be suitable for arid regions where the availability of water for irrigation is limited.