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Global food and nutrition security is largely dependent on rice (Oryza sativa L.). More than 3 billion people (mostly Asian) use rice as the staple food. Based on UN 2010 the population projection, population of Asia will reach to about 5 billion by 2035 and 5.15 billion by 2050. In such scenarios, overall consumption will grow either with the same pattern as population growth or even more than that if present trend of per capita consumption continues. An alternative solution for the Asian people is to diversify their food habit relying less on rice or increasing rice production to meet the growing rice demand. To fulfill the rising global needs of rice, an increase of 1.2{u2013}1.5% in production is required to be maintained by 2020, and 1.0{u2013}1.2% per year beyond 2020. Asia, which is the major rice producer, is predicted to face serious water shortage by 2025 where 2 mha of its irrigated dry season and 13 million ha of irrigated wet season rice will face physical water scarcity. In such situations food production needs to be increased but with multiple challenges of environmental degradation, decline in soil fertility, excessive use of agrochemicals, water scarcity and climate change. In Asia, water use efficiency (WUE) of rice is very low, especially for small farmers who can contribute 75% of the production in the coming years. The yield gap in this region is very high, which could be narrowed down through efficient use of resources and increasing WUE of rice. For this purpose, several rice production management strategies have been designed, some of which are closely related. Among these techniques, the most common are alternate wetting and drying (AWD), integrated crop management, aerobic rice culture, use of controlled-release fertilizer, system of rice intensification (SRI) and direct seeding (DS). To evaluate the performance of different water and nutrient management strategies (AWD, DS, integrated nutrient management [INM] and potassium (K)-as a drought stress relieving agent), a series of polyhouse and field trials were conducted in the dry season of 2016{u2013}2017 (December 2016{u2013}April 2017) and 2017{u2013}2018. The main objectives were to find alternatives of growing more rice with less water in the changing climate scenarios. The performance of popular irrigated lowland Thai rice varieties (Pathumthani 1, RD57, RD41) was evaluated under these water and nutrient management techniques in terms of root system development, grain yield and its components as well as water productivity (WP). A pot study was conducted to evaluate root system response of three Thai rice varieties (Pathumthani 1, RD57, RD41) under three cultivation methods (dry direct seeding [DDS], wet direct seeding [WDS], transplanting [TP]) and three levels of AWD irrigation ({u2013}5, {u2013}15, {u2013}30 kPa). A second pot study examined the effect of K rates (0, 80, 120, 160 kg ha{u2013}1 ) on root system response of the same varieties under DDS and TP subjected to AWD at {u2013}5 kPa. Pathumthani 1 was more tolerant to moisture stress; RD57 and RD41 showed an inconsistent response to moisture-deficit conditions. Rice plant under TP was more sensitive to moisture stress and performed better under DDS even at the highest soil moisture stress of {u2013}30 kPa. K application at the rate of 120 kg ha{u2013}1 as basal under DDS was optimum for root system development of Pathumthani 1, while RD57 and RD41 had higher actual root length at the same K rate regardless of cultivation methods. A pot experiment was conducted to evaluate the performance of selected lowland Thai rice varieties grown under different cultivation methods subjected to AWD irrigation. Treatments included were three varieties (Pathumthani 1, RD57, RD41), three cultivation methods (DDS, WDS, TP) and four AWD irrigation levels (re-watered when soil water potential reached at 0, {u2212}5, {u2212}15, {u2212}30 kPa). DDS resulted in higher grain yield at {u2013}5 and {u2013}15 kPa (74 and 68 g pot{u2013}1 , respectively) with a respective reduction of 15% and 34% under WDS and TP at {u2013}5 kPa, and 15% and 28% at {u2013}15 kPa. The highest WP was recorded at {u2212}30 kPa under DDS, which was reduced by 17{u2013}61% for other soil water potentials irrespective of varieties. The effects of INM, cultivation method and variety on root and shoot growth, grain yield and its components of rice under AWD irrigation were evaluated in another pot study. Treatments included were three varieties (Pathumthani 1, RD57, RD41), three cultivation methods [DDS, WDS, TP] and three nutrient combinations [100% NPK (160 kg ha{u2013}1 ), 50% NPK (80 kg ha{u2013}1 ) + 50% FYM (5 t ha{u2013}1 ), 100% FYM (10 t ha{u2013}1 )] under AWD. Root dry matter of RD41 and RD57 was reduced by 12{u2013}25% at the 100% NPK and 100% FYM compared with the 50% NPK + 50% FYM. Panicle number, panicle length and 1000-grain weight were higher at the 50% NPK + 50% FYM. An experiment consisting of three lowland Thai rice varieties (Pathumthani 1, RD57, RD41), two cultivation methods [DDS, TP] and four K doses (0, 80, 120,160 kg K ha{u2212}1 ) under AWD water regime was conducted to investigate the impact of K and cultivation method on lowland rice varieties subjected to AWD. Pathumthani 1 had 58% higher grain yield at the 120 kg K ha{u2212}1 while RD57 and RD41 had similar responses at all K doses but were significantly higher than the control. The performance of DDS and TP was better at the 80 and 120 kg K ha{u2212}1 , respectively. A two-year field experiment was conducted during the dry rice growing season of 2016 and 2017 to investigate the effects of establishment method and irrigation level on growth, yield, and water productivity of irrigated lowland rice. The treatments consisted of two Thai rice cultivars (Pathumthani 1 and RD57), two establishment methods (DDS and transplanting [TP]), and three irrigation levels (continuous flooding [CF], 15 cm threshold water level below the soil surface for irrigation [AWD15], and 30 cm threshold water level below the soil surface for irrigation [AWD30]). Overall, the performance of RD57 was better than Pathumthani 1 under DDS with 50% higher grain yield and 90% higher water productivity at AWD15. RD57 also had higher shoot dry matter, number of tiller m{u2013}2 , and number of panicle m{u2013}2 across establishment methods and irrigation levels. Grain yield and water productivity of RD57 were similar under two establishment methods across irrigation levels, whereas the performance of TP was better than DDS for Pathumthani 1 irrespective of irrigation levels. The highest grain yield and water productivity of Pathumthani 1 was observed at AWD15 under TP and that of RD57 under both establishment methods at the same irrigation level. AWD15 saved 26% and 32% irrigation water under TP and DDS, respectively, compared with TP-CF treatment combination. AWD15 could be safely recommended for the tested varieties without compromising yield with either of the cultivation methods. Application of the 50% NPK + 50% FYM could be a feasible option under AWD irrigation; however, benefits may vary with varieties and cultivation methods. Application of K at the optimum dose with proper selection of variety and cultivation method could help in sustainable rice production under water-saving cultivation techniques. |
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