Drought Tolerance and Nitrogen use Efficiency of Upland Rice (Oryza Sativa L.) Genotypes Grown under Varying Water and Nitrogen Regimes
Abstract
Rice genotypes were grown under different water regimes and nitrogen levels. Sufficient soil moisture content (SMC) and high N level caused optimum growth of the genotypes. Deficient water and N supply both retarded growth of rice. PSB Rc14, P42, and P38 had high number of tillers, number panicles per hill, number of spikelets per panicle, relative growth rate (RGR), water use efficiency (WUE), harvest index (HI), straw yield, grain weight, and grain yield at field capacity (FC). These genotypes also had high values in the aforementioned growth and yield parameters at 120 kg N ha-1 treatment. In terms of the efficiency in the use of N as indicated by agronomic efficiency of nitrogen application (AEN), recovery efficiency of nitrogen application (REN), and internal efficiency of nitrogen application, PSB Rc14, P42, and P38 still performed better than the rest of the genotypes tested. Evaluation of the combined effect of water and N application showed that PSB Rc14, P42, and P38 significantly produced high grain yields among the genotypes under SMC at FCwith 120 kg N ha-1 which suggests that water plays a fundamental role in rice growth in combination with N. P42 showed the less affected by water deficit and low N nitrogen levels, hence, produced the high grain yield.
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Introduction
Rice (Oryza sativa L.)is one of the most important staple food of over half of the world’spopulation. Globally, it ranks third after wheat and maize in terms of production (Bandyopadhay and Roy, 1992). According to International Rice Research Institute (IRRI) 2012, there is about 50,000 ha of upland rice in Cambodia (2-4% of total rice area) with an average grain yield of 2.97 t ha-1, much less compared to potential yield of the newly-developed varieties (MAFF, 2011). At present, upland rice production contributes about 5-6% of Cambodia’snational rice production (CRD, 2008), which is one of the potential areas considered in maintaining the country’srice production level.
The major factor for the low productivity in rainfed uplands is the lack of water. Rice is usually subjected to prolonged drought due to less rain as well as erratic rainfall pattern in the certain years (NARC, 1996). This inadequacy and untimely availability of rainwater is a major limitation of rice production resulting to low yield in the rainfed ecosystems (Kamoshita et al., 2000). The effect of drought differs with varieties, growth stage, level and duration of drought stress occurrence (Kato, 2004), hence, results to varying yields (Lafitte et al., 2007). The reduction ingrowth and photosynthetic rate in such fragile environment are the major causes of yield reduction (Zlatev and Lidon, 2012). In addition to its direct effect on yield, drought can also reduce the potential beneficial effects of improve crop management practices, such as fertilizer application, pest and disease management.
The use of varieties that are adapted under limited water is one of the strategies to enhance production in rainfed uplands. Different varieties may have varying degrees of drought tolerance (Zeigler et al., 1994). Water deficit during the vegetative stage may have lesser effect on grain yield, but have tremendous effect during reproductive and grain filling stages (Fukai and Cooper, 1995). Growing appropriate varieties in rainfed areas that are drought-prone could be a practical strategy to enhance production. Selections of early maturing rice varieties that are adaptable to drought stress could be one of the pragmatic strategies (Juliano et al., 2007). Selection of drought tolerant rice varieties with good N efficiency could improve rice production in rainfed upland areas that are gradually becoming water limited.
Okonje et al. (2012) reported that application of low N levels results to low yields, considering that N deficiency is a major abiotic stress that limits rice productivity in rainfed upland soils, such as ultisol and alfisol that are acidic in general (Kirk et al., 1998). The low yield of upland rice is a consequence of infertile soils and drought conditions, that are adapted to low harvest index (HI) traditional cultivars (George et al., 2001). Among essential plant nutrients, N is one of the most yield-limiting nutrients for upland rice production. Farmers relate theN deficiency in upland rice to low soil organic matter, low soil pH, soil erosion, and low application of N fertilizers. Nitrogen use efficiency in rice production is subjected toN loss by leaching, volatilization, denitrification and erosion (Fageria and Baligar, 2005). Thus, the use of N-efficient varieties in combination with proper fertilizer application is an important complementary strategy in improving rice yield.
Conclusion
The first experiment determined the effect of different water regimes in selected upland rice genotypes in terms of agronomic parameters, yield and its components, and water use efficiency. The six upland rice genotypes used in the study were: 1). Salumpikit (susceptible drought check), 2). P31, 3). P38, 4). P42, 5). P44, and 6). PSB Rc14 (drought tolerant check). Water regime treatments were: 1) SMC at FC; 2) SMC at 75% FC, and 3) SMC at 50% FC. Genotypes grown under adequate SMC (at FC) were taller than those grown underwater deficit condition. Salumpikit was the tallest plant among the genotypes but it also had high percentage reduction from 100% FC to 75% FCand 50% FCamong the genotypes. PSB Rc14, P42 and P38 were among the genotypes that had low percentage reduction when SMC was decreased to 75 % FCand 50 FC %. Indicating that these genotypes were less affected by water deficit. The RGR was significantly affected by the interaction of water regime and rice genotypes. P42 had the highest RGR among the genotypes and result was consistent when exposed to decreasing water regime treatments at 75 % FCand 50 % FC. PSB Rc14, which is a drought-tolerant genotype, had similar performance with P42 in terms of RGR and WUE parameters, which lead to have better grown.
Flowering occurred earlier in genotype the PSB Rc14 while other genotypes had later day to flowering. At reproductive stage, the allocation of photosynthates started to become directed to the production of grains (10.92 g). Shoot weight lower (14.26 g) compared to the previous crop stage as senescence of old shoots started. High values of HI in PSB Rc14, P42, and P38 (0.32 and 0.28, respectively) imply that these genotypes efficiently allocated the photosynthates in the production of grains under different water regimes. Subsequently, the numbers of panicles per hill (10 panicles), number of filled grains per panicle (77.69), number of spikelets per panicle (101.49) and grain weight per hill (10.92 g) were high in these genotypes. Water limitation (50 FC %) is one of the main factors that determinations of rice growth and grain yield, significantly affect grain filling. Among the genotypes evaluated, PSB Rc14, P42, and P38 had good performance under drought condition based on growth and yield parameters, hence can be considered as drought-tolerant genotypes while P44, P31 and Salumpikat were least tolerant to water deficit.
The second experiment revealed the importance of N in upland rice production. N rates applied in the experiment were 60 kg ha-1 and 120 kg ha-1. Indicator genotypes were PSB Rc14 as the N-responsive and Salumpikit as the non N-responsive. Application of N significantly increased all the growth and yield parameters measured and significant differences were also observed in all parameters among the genotypes. Moreover, maximum N rate of 120 kg ha-1 application resulted to optimum growth of the genotypes. PSB Rc14, P42, and P38 performed well under varying N treatments as indicated by their high RGR values. P42 also had the highest straw yield than other genotypes, although was not significantly different from P38 and PSB Rc14. This means that these genotypes allocated most of their photosynthates in the maintenance of vegetative parts, while the other genotypes concentrated most of their photosynthates for the production of reproductive parts. Thousand-grain weight (23.22 g), number of spikelets per panicle (95.16), number of filled grains (71.33), and grain yield (7.41 g) were also high in PSB Rc14, P42, and P38 suggesting the good grain filling qualities of rice genotypes. The efficiency of N use as calculated in AEN, REN, and IEN showed that with doubled N rate (120 kg N ha-1), P38 and P44, and N-responsive check, PSB Rc14, had high values for the aforementioned parameters. Nitrogen application increased the dry matter partitioning, grain yield and its components. Without N application, reduction ingrowth parameters, dry matter and grain yield were observed. Further increased N level up to 120 kg N ha-1 increased growth parameters and grain yield by 35%. The effect of combined N levels and water regimes three selected upland genotypes were evaluated in the last experiment. Nitrogen rates applied were 0 kg N ha-1 and 120 kg N ha-1 under SMC at 100% FCand 50% FC. The genotypes that performed well in experiments 1 and 2 were used: PSB Rc14, P42 and P38. Significant differences were observed in all growth and yield parameters measured among the genotypes. Optimum growth of the genotypes was observed under 100% FCapplied with 120 kg N ha-1 wherein P42 obtained the highest RGR, WUE, IEN, TNU, straw yield, and grain yield. Therefore, varying water regimes at FC, together with proper N level application up to 120 kg ha-1, can be used as an effective and practical agronomic strategy to get good or high economic yield under water-limited conditions. Apparently, efficiency in rice cultivation can be addressed by providing the necessary and precise inputs of water and nitrogen regimes since the experiment was done in screen house and pot experiments. P42 showed the number of filled grain was not much affected by water deficit, hence showed drought tolerance and produced high yield.
