Water use efficiency is a function of yield and evaporation. Any agronomic management practices that increase the grain yield will also increase the WUE. Along with these improved irrigation methods, smart irrigation technologies the adoption of other improved agronomic management practices is highly essential to achieve higher yield potential. Agronomic management practices such as the optimum time of sowing, adequate plant population establishment, timely control of weeds, balance and optimum fertilization, the proper control of insect pests and disease, and harvest are highly important to increase WUE. Additionally, various agronomic practices, including crop rotation, water conservation through minimum- or no-tillage, the use of plastic film or straw mulching, regulated deficit irrigation, fertigation, anti-transpirants, and soil amendments, can be employed to enhance soil water-holding capacity and WUE of rice-based cropping systems ^[1][14]. Engineering approaches such as rational exploitation of surface and groundwater resources, rainwater harvesting and storage for life-saving irrigation and groundwater recharge, the utilization of recycled sewage water or marginal quality saline water, the modernization of canal irrigation systems, low-pressure pipe conveyance, laser-controlled land leveling technology ^[1][14], improved surface irrigation by shortening or narrowing borders or furrows, and sprinkler irrigation implementation are highly recommended to increase water use efficiency ^[2][109].

Vijayakumar et al. (2021) demonstrated that the application of nutrients based on the 4R principle of nutrient stewardship (right dose, right time, right place, and right method) led to increased water use efficiency in aerobic rice systems ^[3][110]. A supply of 100% of the recommended dose of fertilizer through drip fertigation was found optimum for higher yield and WUE ^[4][98]. Several new-age fertilizer carriers such as nano fertilizers, slow-release fertilizers, and organic nitrification inhibitors were found to be effective in reducing nutrient loss and increasing the recovery efficiency of nutrient and crop yield ^[5][111]. Similarly, Jinger et al. (2020) reported that the application of silicon fertilizer increased the yield and water use efficiency of rice ^[6][7][112,113]. Farmers can utilize tools such as decision support systems ^[8][9][67,114], riceNxpert ^[10][115], and other Android-based applications to adopt site-specific nutrient management in rice cultivation ^[11][116]. Nitrogen is a major key nutrient to rice, and response to nitrogen application is reported in all the rice growing ecosystems. The nitrogen use efficiency in rice is very low (~30%) and improving nutrient use efficiency directly increases rice yield and WUE. Subramanian et al. (2020) recommended the application of 175 kg N/ha in four equal splits at 10–12 days after emergence, at active tillering, panicle-initiation, and flowering for sustaining the aerobic rice yield ^[12][117]. Similarly, two to three split applications of the recommended dose of potassium were found to be more economical in the aerobic rice system ^[13][118]. In addition to macronutrient application, the need-based use of secondary micronutrients is also equally important. The application of iron foliar spray is important in DSR and aerobic rice, especially in the early stage of the crop to overcome iron deficiency ^[14][119]. Under surface drip irrigation with zinc fertigation (8 kg/ha), rice crops need 1246 L of water to produce one kg of rice compared to 4263 L under conventional transplanted rice with 25 kg Zn/ha application ^[15][94]. The water productivity is highest (1.13 g kg⁻¹) in nitrogen-fertilized plots in comparison to no nitrogen (0.62 g kg⁻¹) under aerobic rice ^[16][60].

As water scarcity becomes more acute, rice farmers may face limitations on the amount of water available for rice production and may not be able to rely on continuous flooding as a method for weed control in the future ^[17][120]. Though flooding helps in eliminating grass and sedges in rice cultivation, it failed to control broadleaf weeds ^[18][121]. Weed menace is the major problem in the SRI, DSR, aerobic rice, and drip-irrigated rice ^[14][119]. The occurrence of non-aquatic weeds increased in these systems due to the absence of flooding. The time of weed removal is more important in these methods. Early control of weeds helps with better crop establishment and turns crop weed competition in favor of rice plants ^[19][122]. The use of herbicides ensures that weeds are controlled at the time of germination. In direct-seeded rice systems, the use of a sequential approach consisting of a pre-emergence herbicide followed by a post-emergence herbicide was found to be more effective and cost-efficient than traditional hand weeding ^[20][21][22][87,123,124]. Several improved farm tools and implements were available for weed control in the SRI, line-sown DSR, and line-transplanted rice. The use of these tools improves soil aeration, root growth, and yield, in addition to better weed control ^[23][24][18,125].

DSR can reduce GHG emissions, improve soil quality, and save money on labor, water, and energy. However, weeds constitute a significant problem that could result in the total failure of the rice crop. To increase output and optimize resource utilization, effective weed management is vital. Compared to other weed control strategies, herbicides are a more efficient and cost-effective solution in the case of DSR. The sequential use of pendimethalin 1000 g/ha as a pre-emergence herbicide applied 1 day after sowing and penoxsulam + cyhalofop-butyl 130 g/ha as a post-emergence herbicide applied 25 days after sowing significantly increased grain yield, irrigation water productivity, and total water productivity by 378.9%, 378%, and 380%, respectively, compared to the unweeded control ^[25][126]. Effective weed control, which reduces competition for growth resources, such as water and nutrients, is essential for maximizing water use efficiency in direct-seeded aerobic rice systems. In aerobic rice, the herbigation with pretilachlor + bensulfuran methyl as pre-emergence, and bispyribac sodium as post-emergence at 20 days after sowing, resulted in higher water use efficiency (153.45 kg/ha cm) compared to the weedy check (7.07 kg/ha cm) ^[26][127]. This improvement was attributed to increased grain yield due to better weed management in the weed-free and herbigation treatments.

Seed priming is a pre-sowing seed treatment that helps rice seeds overcome various biotic and abiotic stressors, leading to improved seedling growth and an increase in crop productivity. Based on the substance/material used for priming, it is classified into hydro-priming (water), osmo-priming (osmotic agent), halo-priming (use of specific salts for priming), bio-priming (microbial bio-agents), and hormo-priming (plant growth regulators). Priming does not allow radical protrusion through the seed coat but allows the seeds to imbibe water and stay ready for quick germination. Seed priming has been shown to enhance plant germination even in adverse soil and weather conditions. It reduces the average time for seeds to sprout and increases the energy used for germination, resulting in a higher germination index and improved seedling vigor. This helps to ensure more robust plant growth and development, even in challenging environments ^[27][128]. The reduced imbibition lag time ^[28][129], osmotic adjustment ^[29][130], accumulation of germination-enhancing metabolites ^[30][131], enzyme activation ^[31][132], and metabolic repair during imbibition ^[32][133] ensure higher and uniform germination of primed seeds. Rice cultivation is possible with limited irrigation levels, even as low as −15 kPa and −30 kPa. In areas where it is challenging to maintain frequent irrigation and soil water levels drop below −15 kPa, seed priming with Trichoderma is advised, as this technique can result in a significant boost in grain yield, with an increase of 68% at −15 kPa and 77% at −30 kPa, as well as an improvement in water productivity, with a rise of 70% at −15 kPa and 66% at −30 kPa, compared to non-primed seeds ^[33][134].

The use of potassium nitrate as a seed priming agent is another promising option, especially when soil water levels fall below −15 kPa. This substance has the potential to improve seed performance in these challenging conditions. Seed priming with moringa leaf extracts (3.3%) or CaCl₂ (2.2%) improved the direct-seeded rice performance when practiced with AWD irrigation ^[34][135]. According to research by Hussain et al. (2016), chemical priming with selenium and hormonal priming with salicylic acid were found to be more effective at mitigating the effects of chilling stress in rice seedlings ^[35][136]. These priming methods improved seedling performance and tolerance by enhancing starch metabolism, increasing respiration rates, reducing lipid peroxidation, and strengthening the plant’s antioxidant defense system. Seed priming can be a useful approach to improve rice germination and stand establishment in the rabi season, particularly in the eastern part of India where low temperatures can cause poor germination. Additionally, Dhillon et al. (2021) found that halo-priming with 2.0% potassium nitrate and hormo-priming with 50 ppm GA3 had the potential to improve rice crop establishment and yield by 7–11% in both conventional and soil mulch DSR systems ^[36][137]. The higher yields were attributed to faster and more successful germination and crop emergence, improved root growth, and enhanced yield attributes. The priming treatments also activate important enzymes such as superoxide dismutase, peroxidase, and catalase, and increase the accumulation of glutathione and free proline in rice seedlings, which protect the seedlings from chilling-induced oxidative stress.

The water footprint (WF) is a comprehensive indicator of the environmental impact of rice cultivation and can help identify more sustainable and efficient irrigation practices to reduce water use and improve water quality. The WF in rice cultivation refers to the amount of water used for irrigating rice fields throughout its growth cycle, as well as the amount of water required to dilute pollutants, such as nitrogen and phosphorus, that may be released into the environment due to agricultural activities. It includes both the direct water consumption by the crop through evapotranspiration (green water) and the water used for irrigation (blue water), as well as the water required to dilute and transport pollutants in the environment (grey water). The worldwide WF of rice production is estimated to be 1308 Mm³ per year, with 707 Mm³ per year attributed to evaporation, of which 332 Mm³ per year is attributed to green water use and 374 Mm³ per year to blue water use. Furthermore, 64 Mm³ per year is related to pollution, while 538 Mm³ per year is lost through percolation and residual soil moisture after harvest ^[37][138]. In Thailand and Malaysia, the WF of rice cultivation was estimated to be 1665 m³ per ton and 2500 L/kg based on life cycle assessment, respectively ^[38][39][139,140]. Wu et al. compared the WF of paddy rice production under common flood irrigation (CFI) and water-saving irrigation (SWI) in Nanjing, East China, and found that the WF was 1000 m³/t for CFI and 910 m³/t for SWI, with a 9% reduction in WF for SWI compared to CFI. SWI reduced irrigation during non-critical periods, shifting the ratio of blue to green water fluxes in field water and using green water preferentially ^[40][141]. Another study evaluated the WF of rice production in the Walawe irrigation scheme of Sri Lanka over three years. Results showed that the average annual WFblue was found to be 2.27 m³/kg, which is higher than global and national WFtot, indicating that irrigation water usage in the area may be significantly higher due to relatively higher evapotranspiration in the area, suggesting the need to reduce excess water usage by shifting irrigation practices from flooded irrigation to the SRI ^[41][142]. In India, the WF of rice in 2014 was found to vary with region. Among the five rice-growing regions (south, north, east, west, and northeast), the western region showed the highest WF of 3.52 m³ per kilogram of rice due to the region’s high irrigation water usage ^[42][143]. This study also recommended large-scale promotion and adoption of water-saving irrigation techniques such as SRI, aerobic rice, AWD, DSR, etc., to reduce blue WF. Another interesting study in Indonesia compared the WF of conventional rice with organic rice cultivation, and the result showed that organic rice cultivation saves up to 52.8% of the WF compared to conventional flooded rice, demonstrating the potential of organic farming practices to promote sustainable water use in agriculture in Indonesia ^[43][144].