Genotypic variation in nitrogen use efficiency in medium- and long-duration rice

A field experiment was conducted in the dry season at Los Baños, Philippines, to assess the differences in grain yield and N utilization of 10 medium-duration (119±4 days after seeding [DAS]) genotypes and 10 long-duration (130±4 DAS) ones with varying acquisition and usage of soil and fertilizer N. Significant differences among genotypes were observed in grain yield and N uptake, efficiency and partitioning parameters (physiological N use efficiency [PNUE], agronomic N use efficiency [ANUE], apparent recovery [AR], partial factor productivity of applied N [PFP_N], N productivity index [NPI], and N harvest index [NHI]). The N-efficient genotypes that produced high grain yield at both low and high levels of N were IR54790-B-B-38, BG380-2, BG90-2 (medium-duration), and IR3932-182-2-3-3-2, IR54853-B-B-318, and IR29723-88-2-3-3 (long-duration). Inefficient genotypes that produced low yields at low N levels but responded well to N application were IR58125-B-B-42, IR49457-33-1-2-2-2, and BG34-8 (medium-duration), and IR8192-200-3-3-1-1, IR21848-65-3-2-2, and PR106 (long-duration). IR20 (medium) and Palawan (long-duration) were N-inferior genotypes giving low yields at both low and high N levels. Increase in grain yield was highly correlated with N uptake (r²=0.75**). The grain yield-N uptake relationship for individual genotypes indicated significant differences in slope and in the yield obtained with soil N (GY₀). Differences in GY₀ were due to genotypic variation in N uptake and efficiency of use. NHI was related to both N uptake and use efficiency. NPI, which integrated both GY₀ and PNUE, provided a better ranking of genotypes. The performance of efficient and inefficient genotypes over a range of soil and fertilizer N supply was consistent over three seasons of trials.     

Development of control release urea fertilizer model for water and nitrogen movement in flooded rice

Paddy and Water Environment - Application of control release fertilizer in rice cultivation is a smart way to reduce the environmental nitrogen contamination and enhance the nitrogen use...     

Yield, water use efficiency and nitrogen uptake in potato: influence of drought stress

Summary A lysimeter experiment was performed to study the optimal allocation of limited water supply in potatoes. Irrigation regimes equal to 40, 60 and 80% of maximum evapotranspiration (ET) were evenly applied over the crop cycle. Other treatments involved withholding 80 mm of irrigation, based on ET, beginning at each of three designated growth stages (tuber initiation, early and late tuber growth). An irrigated control treatment, restoring the entire ET, was included for comparison. Continuous drought stress reduced photosynthesis as irrigation volumes were reduced. Plant biomass and tuber yield decreased almost proportionally to water consumption, so that WUE was roughly constant. N uptake was highest in the control and in 80% ET treatment. Withholding water during tuberisation severely hindered plant physiological processes and penalized tuber yield. Reductions in photosynthesis, total biomass and yield were the greatest when drought was imposed during tuber initiation. The earliest stress resulted in the lowest WUE and N uptake. A new crop water stress index (SI) was proposed, which combines atmospheric demand for water and canopy temperature.     

Genetic dissection of grain nitrogen use efficiency and grain yield and their relationship in rice

Breeding for improved grain yield (GY) and grain nitrogen use efficiency (NUE) is an important objective of many rice breeding programs. A better understanding of the genetics of these two complex traits and their genetic relationship is required for more efficient breeding. This study reports the results of a linkage mapping study conducted for these two traits using 127 rice recombinant inbred lines (RILs) derived from the cross of Zhanshan 97/Minghui 63. Phenotypic data were collected under two nitrogen conditions in 2006 and 2007. For NUE, four and six QTLs were identified in 2006 and 2007, respectively. These QTLs were on chromosomes 1, 2, 6, 7 and 11. For GY, nine and five QTLs were detected on chromosomes 1, 2, 7 and 11 in 2006 and 2007, respectively. The phenotypic and genetic correlations between NUE and GY are positive and highly significant. Four genomic regions, including C86-C2340 on chromosome 1, RZ599-R1738 on chromosome 2, RZ471-C1023 on chromosome 7 and R3203-RM20a on chromosome 11, were found to contain QTLs for both NUE and GY. The effects of the co-located QTLs were in the same direction for NUE and GY, providing a genetic basis for the observed positive genetic correlation between the two traits. These genomic regions might be explored for the simultaneous improvement of NUE and GY in breeding.     

Strategies for overcoming low agronomic nitrogen use efficiency in irrigated rice systems in China

Irrigated rice in China accounts for nearly 30% of global rice production and about 7% of global nitrogen (N) consumption. The low agronomic N use efficiency (AE_N, kg grain yield increase per kg N applied) of this system has become a threat to the environment. The objective of this study was to determine the possibility to improve the AE_N of irrigated rice in China by comparing the farmers’ N-fertilizer practices with other N management strategies such as real-time N management (RTNM) and fixed-time adjustable-dose N management (FTNM). Field experiments were conducted in farmers’ fields in four major rice-growing provinces in China in 2001 and 2002. The same experiment was repeated at the International Rice Research Institute (IRRI) farm in the dry seasons of 2002 and 2003. Agronomic N use efficiency was determined by the “difference method” using an N-omission plot. Maximum yield was achieved mostly at 60–120 kg N ha⁻¹, which was significantly lower than the 180–240 kg N ha⁻¹ applied in farmers’ practices at the Chinese sites. With the modified farmers’ fertilizer practice, a 30% reduction in total N rate during the early vegetative stage did not reduce yield but slightly increased yield and doubled AE_N compared with the farmers’ practice at the Chinese sites. The total N rate in RTNM and FTNM ranged from 30 to 120 kg ha⁻¹ at the Chinese sites, but their yields were similar to or higher than that of the farmers’ practice. Compared with the modified farmers’ practice, RTNM and FTNM further increased AE_N at the Chinese sites. Overall, FTNM performed better than RTNM at the Chinese sites because the total N rate of FTNM was closer to the optimal level than RTNM. A quantum leap in AE_N is possible in the intensive rice-growing areas in China by simply reducing the current N rate and by allocating less N at the early vegetative stage.     

Nitrogen use efficiency in selected rice (Oryza sativa L.) genotypes under different water regimes and nitrogen levels

Water and nutrient availability are two major constraints in most rice-based rainfed shallow lowland systems of Asia. Both stresses interact and contribute to the low productivity and widespread poverty in this environment. The objective of this study was to improve the understanding of interaction between the two factors and to identify varietal characteristics beneficial for productivity in a water- and nutrient-limited rice environment. For this purpose, we screened 19 rice genotypes adapted to different rice environments under two water and two nutrient treatments during the wet season of 2004 and 2005 in southern Luzon, Philippines. Across all genotypes tested and in comparison with the irrigated control, rainfed conditions reduced grain yield of the treatment without N application by 69% in 2004 and by 59% in 2005. The mean nitrogen fertilizer response was highest in the dryer season of 2004 and the rainfed treatment, indicating that water stress had no effect on fertilizer response. Nitrogen application reduced the relative yield loss to 49% of the irrigated treatment in 2004 and to 52% of the irrigated treatment in 2005. Internal efficiency of N (IEN) and recovery efficiency of applied N (REN) were significantly different between genotypes, but were not affected by water availability (REN) or by water and nutrient availability (IEN). In contrast, grain yield and total N uptake were affected by cultivar, N and water availability. Therefore, germplasm for rainfed environments should be screened under conditions of limited and good nitrogen and water supplies. The four best cultivars, CT6510-24-1-2, IR55423-01, IR72, and IR57514-PMI5-B-1-2, performed well across all treatments and both years. Except for IR72, they were all characterized by medium height, medium duration, high early vigor, and a moderate level of drought tolerance. This combination of characteristics seems to enable the optimal use of limited water and nutrient resources occurring in many shallow rainfed lowlands. We also concluded that moderate drought stress does not necessarily affect the response to moderate N rates, provided that drought does not induce high spikelet sterility and that fertilizer N is properly managed.     

Modelling the nitrogen-driven trade-off between nitrogen utilisation efficiency and water use efficiency of wheat in eastern Australia

The nitrogen-driven trade-off between nitrogen utilisation efficiency (yield per unit nitrogen uptake) and water use efficiency (yield per unit evapotranspiration) is widespread and results from well established, multiple effects of nitrogen availability on the water, carbon and nitrogen economy of crops. Here we used a crop model (APSIM) to simulate the yield, evapotranspiration, soil evaporation and nitrogen uptake of wheat, and analysed yield responses to water, nitrogen and climate using a framework analogous to the rate-duration model of determinate growth. The relationship between modelled grain yield (Y) and evapotranspiration (ET) was fitted to a linear-plateau function to derive three parameters: maximum yield (Y_max), the ET break-point when yield reaches its maximum (ET^#), and the rate of yield response in the linear phase (ΔY/ΔET). Against this framework, we tested the hypothesis that nitrogen deficit reduces maximum yield by reducing both the rate (ΔY/ΔET) and the range of yield response to evapotranspiration, i.e. ET^# − E_s, where E_s is modelled median soil evaporation.     

Reduced nitrogen application rate with dense planting improves rice grain yield and nitrogen use efficiency:A case study in east China

Dense planting could be a feasible method for reducing nitrogen (N) application rates without compro-mising rice grain yield in northeast and central China. It ...     

Yield, grain quality and water use efficiency of rice under non-flooded mulching cultivation

Plastic film or straw mulching cultivation under non-flooded condition has been considered as a new water-saving technique in rice production. This study aimed to investigate the yield performance in terms of quality and quantity and water use efficiency (WUE) under such practices. A field experiment across 3 years was conducted with two high-yielding rice cultivars, Zhendao 88 (a japonica cultivar) and Shanyou 63 (an indica hybrid cultivar) and four cultivation treatments imposed from transplanting to maturity: traditional flooding as control (TF), non-flooded plastic film mulching (PM), non-flooded wheat straw mulching (SM), and non-flooded no mulching (NM). Compared with those under the TF, root oxidation activity, photosynthetic rate, and activities of key enzymes in sucrose-to-starch conversion in grains during the grain filling period were significantly increased under the SM, whereas they were significantly reduced under the PM and NM treatments. Grain yield showed some reduction under all the non-flooded cultivations but differed largely among the treatments. The reduction in yield was 7.3–17.5% under the PM, 2.8–6.3% under the SM, and 39–49% under the NM. The difference in grain yield was not significant between TF and SM treatments. WUE for irrigation was increased by 314–367% under the PM, 307–321% under the SM, and 98–138% under the NM. Under the same treatment especially under non-flooded conditions, the indica hybrid cultivar showed a higher grain yield and higher WUE than the japonica cultivar. The SM significantly improved milling, appearance, and cooking qualities, whereas the PM or the NM decreased these qualities. We conclude that both PM and SM could significantly increase WUE, while the SM could also maintain a high grain yield and improve quality of rice. The SM would be a better practice than the PM in areas where water is scarce while temperature is favorable to rice growth, such as in Southeast China.     

The effect of straw mulch on nitrogen,phosphorus and potassium uptake and use in hybrid rice

Paddy and Water Environment - To optimize straw application and understand the effects of straw mulch and straw nutrient release on rice nutrient uptake, we investigated the effects of two types of...     

Nitrogen-use efficiency in tropical lowland rice systems: contributions from indigenous and applied nitrogen

Partial factor productivity (P_fp) from N fertilizer is the ratio of grain yield to the applied N rate. It is a parameter that includes contributions to N-use efficiency from both indigenous N of the soil-floodwater system and applied N. Experiments were conducted to quantify P_fp and the contributions of indigenous and applied N to the N efficiency of lowland rice systems. Enormous variation was found in the indigenous N supply among farmers' fields in two rice-growing domains of Central Luzon, Philippines. Fertilizer-N rates farmers applied to these fields also varied greatly, but there was no relationship between applied N rate and indigenous N supply estimated by rice N uptake. Likewise, in the same treatment plots of a long-term experiment, season-to-season variation in the contributions of indigenous and applied N were large and reflected differences in yield and N uptake in plots without applied N. These results indicate that the ability to adjust the quantity of applied N in relation to variation in the indigenous N supply is as important to increased P_fp as are the timing, placement and source of applied N. We conclude that the indigenous N supply of lowland rice systems is highly variable among fields with similar soil types and in the same field over time, that field-specific N management is required to respond to this variability, and that P_fp is a useful parameter for identifying constraints to improved fertilizer-N-use efficiency in farmers' fields.     

Modeling of water and nitrogen balance in the ponded water of rice fields

A water and nitrogen balance model for the surface ponded water compartment of rice fields was developed. The model estimates the daily ponded water depth and the daily losses and the uses of NH₄–N and NO₃–N in their transformation processes. The model was applied with data obtained from two rice fields during 2005 at Thessaloniki plain in northern Greece. Significant amounts of applied irrigation water were lost with the surface runoff and deep percolation to groundwater. The gaseous losses of nitrogen (volatilization and denitrification) and nitrogen uptake by algae were the main processes of nitrogen reduction in the ponded water of rice fields. The study showed that the system of a rice field is a natural system where an important amount of influent nitrogen applied by irrigation water can be reduced. These processes decrease the possibilities of water resources contamination.     

密度和氮肥用量对油菜产量及氮肥利用率的影响?

 为机械化种植油菜,研究不同施氮水平下密度对直播油菜生长发育和氮肥利用效率的影响。以甘蓝型油菜品种中双11号为材料,在低密（15万株/hm2）和高密（45万株/hm2）两种密度下,设施氮0、90、180和270kg/hm2处理,分析施氮量与密度对油菜农学性状、产量、氮肥利用效率的影响,并对比分析了密度与油菜需氮量之间的关系。结果表明,增密后油菜的株高、分枝数、单株角果数和每角粒数显著降低,分枝高度和千粒重显著增加。高密油菜群体株型结构整齐均一,更能满足机械化收获需要。高密处理油菜籽粒产量高于低密处理。施氮0～180kg/hm2时,两个密度下的籽粒产量均随施氮量增加而显著提高,但在270kg/hm2时两密度下油菜产量均有所下降。油菜氮肥表观利用率随着施氮量的增加而下降,但是又随种植密度的增加而增加。说明增加密度能促进氮素向油菜籽粒转移,降低每生产100kg籽粒油菜需氮量,提高氮肥表观利用率。在相同的目标产量（低密下的经济产量、湖北省油菜平均单产和全国油菜平均单产）下,油菜增密后可以节约氮肥用量22.9%~30.6%,增密减氮效果明显。       

Effect of water management on dry seeded and puddled transplanted rice. Part 1: Crop performance

An alarming rate of ground water depletion and increasing labour scarcity are major threats to future rice production in north west India. Management strategies that reduce the irrigation amount and labour requirement while maintaining or increasing yield are urgently needed. Dry seeded rice (DSR) has been proposed as one means of achieving these objectives, but little is known about optimal water management for DSR. Therefore a field study was conducted on a clay loam soil in Punjab, India, during 2008 and 2009, to investigate the effects of irrigation management on the performance of puddled transplanted rice (PTR) and dry seeded rice. Irrigation scheduling treatments were based on soil water tension (SWT) ranging from ponding/saturation (daily irrigation) to alternate wetting and drying (AWD) with irrigation thresholds of 20, 40 and 70 kPa at 18–20 cm soil depth. Rainfall was above average and well distributed in 2008 (822 mm), and average and less well distributed in 2009 (663 mm).     

Comparison of water use efficiency,profitability and consumer preferences of different rice varieties in Punjab,Pakistan

Paddy and Water Environment - Due to rapid population growth, water scarcity and food insecurity have become the major problems for Pakistan. Therefore, the efficient utilization of limited...     

Nutrient uptake and water use efficiency as affected by modified rice cultivation methods with reduced irrigation

A field experiment was conducted in 2005 to investigate the effects of modified rice cultivation methods on: water use efficiency, the uptake of nutrients (N, P and K) by plants, and their distribution within plants and their internal use efficiency. The treatments were modified methods of irrigation, transplanting, weeding, and nutrient management, comparing the System of Rice Intensification (SRI) with standard rice-growing methods including traditional flooding (TF). Results showed that the uptake of N, P, and K by rice plants during their growth stages was greater with SRI management compared to TF, except during the tillering stage. At maturity stage, SRI plants had taken up more nutrients in their different major organs (leaves, stems, and sheaths; panicle axis; and seeds), and they translocated greater amount of nutrients to the grain. Under SRI, the ratio of N, P, and K in seed grain to total plant N, P, and K was 4.97, 2.00, and 3.01% higher, respectively, than with TF. Moreover, under SRI management, internal use efficiency of the three macronutrients (N, P, and K) was increased by 21.89, 19.34, and 16.96%, respectively, compared to rice plants under TF management. These measurements calibrate the crop’s physiological response to differences in cultural practices, including the maintenance of aerobic versus anaerobic environment in the root zones. With SRI, irrigation water applications were reduced by 25.6% compared to TF. Also, total water use efficiency and irrigation water use efficiency was increased with SRI by 54.2 and 90.0%, respectively. Thus, SRI offered significantly greater water saving while at the same time producing more grain yield, in these trials 11.5% more compared to TF.     

Yield potential and water use efficiency of aerobic rice (Oryza sativa L.) in Japan

Intensive rice farming in aerobic soil, referred to herein as aerobic rice, can greatly reduce the water input compared to that of flooded rice cultivation. The objective of this study was to compare the potential productivity of aerobic rice and flooded rice using high-yielding varieties at two locations in Japan in two successive years. In aerobic fields, the total amount of water supplied (irrigation plus rainfall) was 800–1300 mm. The soil water potential at 20-cm depth averaged between −15 and −30 kPa each growing season, but frequently reached −60 kPa. The average yield under aerobic conditions was similar to or even higher than that achieved with flooded conditions (7.9 t ha⁻¹ in 2007 and 9.4 t ha⁻¹ in 2008 for aerobic versus 8.2 t ha⁻¹ for flooded). The average water productivity under aerobic conditions was 0.8–1.0 kg grain m⁻³ water, slightly higher than common values in the literature. The super-high-yielding cultivar Takanari achieved yields greater than 10 t ha⁻¹ with no yield penalty under aerobic conditions in 3 out of 4 experiments. The favorable agronomic characteristic of Takanari was its ample sink capacity (grain number × grain weight). In conclusion, high-productivity rice cultivation in aerobic soil is a promising technology for water conservation. With continued breeding, future aerobic rice varieties will possess large numbers of spikelets and sufficient adaptation to aerobic conditions such that they will consistently achieve yields comparable to the potential yield of flooded rice.     

Effects of different plant density and nitrogen application rate on nitrogen use efficiency of potato tuber

In order to investigate the plant density and nitrogen level on nitrogen use efficiency components (agronomical, physiological, apparent recovery and nitrogen use efficiency), the amount of nitrogen uptake by plant, yield and yield components of potato (Solanum tuberosum L.) Agria cultivars' tuber, a factorial experiment based on randomized complete block design was conducted in Ardabil, Iran, in 2006 with three replications. Factors were adjusted for the nitrogen level (0, 80, 160 and 200 kg ha(-1) net nitrogen) and plant density (5.5, 7.5 and 11 plant m(-2)). Results showed that with increasing the nitrogen levels and plant densities agronomical nitrogen use efficiency, physiological nitrogen efficiency and nitrogen use efficiency were decreased and apparent recovery nitrogen efficiency was increased. The most nitrogen uptake in plant was observed at the 200 kg ha(-1) net nitrogen. The most yield and number of tuber per unit area were gained at the 80 and 160 kg ha(-1) net nitrogen. Increasing the plant density resulted in increasing in the tuber yield per unit area and the rate of nitrogen up to the 160 kg ha(-1) net nitrogen. So, application of the 80 kg ha(-1) net nitrogen and plant density of 11 plant m(-2) is recommended to get highest yield with the most nitrogen use efficiency.