Abstract
To compare N uptake and use efficiency of rice among different environments and quantify the contributions of indigenous soil and applied N to N uptake and use efficiency, field experiments were conducted in five sites in five provinces of China in 2012 and 2013. Four cultivars were grown under three N treatments in each site. Average total N uptake was 10–12 g m−2 in Huaiji, Binyang, and Haikou, 20 g m−2 in Changsha, and 23 g m−2 in Xingyi. Rice crops took up 54.6–61.7% of total plant N from soil in Huaiji, Binyang, and Haikou, 64.3% in Changsha, and 63.5% in Xingyi. Partial factor productivity of applied N and recovery efficiency of applied N in Changsha were higher than in Huaiji, Binyang, and Haikou, but were lower than in Xingyi. Physiological efficiency of soil N and fertilizer N were lower in Changsha than in Huaiji, Binyang, and Haikou, while the difference in them between Changsha and Xingyi were small or inconsistent. Average grain yields were 6.5–7.5 t ha−1 (medium yield) in Huaiji, Binyang, and Haikou, 9.0 t ha−1 (high yield) in Changsha, and 12.0 t ha−1 (super high yield) in Xingyi. Our results suggest that both indigenous soil and applied N were key factors for improving rice yield from medium to high level, while a further improvement to super high yield indigenous soil N was more important than fertilizer N, and a simultaneous increasing grain yield and N use efficiency can be achieved using SPAD-based practice in rice production.
Introduction
Nitrogen (N) is usually the nutrient limiting rice production and current high yields of irrigated rice were associated with large applications of fertilizer N (Cassman et al., Citation1998). It is projected that a rice yield increase of more than 1.2% per year will be required in the next decade (Normile, Citation2008). To maximize grain yield, farmers often apply a higher amount of N fertilizer than the minimum required for maximum crop growth (Lemaire & Gastal, Citation1997). On-farm experiments in four major rice-growing provinces revealed that farmers applied 180–240 kg N ha−1 to their rice (Peng et al., Citation2006). Recently, Li et al. (Citation2014) stated that as high as 270–330 kg N ha−1 is applied to achieve the high rice yield of japonica rice in the Jiangsu province. Because of the high rate of N application, only 20–30% of N is taken up by rice and a large proportion of N is lost to the environment (Peng et al., Citation2009). As a result, physiological efficiency (PE) of applied N decreased from 45.0 to 22.7 kg kg−1 (Zhang et al., Citation1988). Therefore, it is important to improve N use efficiency (NUE) in rice production systems through cultivar improvement and better crop management.
NUE can be defined as the ratio of grain yield to N supplied, which is affected by both N uptake efficiency and physiological N use efficiency (PE). PE is a key parameter for evaluating NUE in rice (De Datta, Citation1986; Peng et al., Citation2002). PE is separated into two component indices based on N uptake of rice plants from indigenous soil N and fertilizer N. Yield increase from applied N divided by rice plant N accumulation from applied N was defined as PE of applied N (PEN, kg grain yield increase per kg N uptake from applied N). Grain yield of the zero-N control divided by total rice plant N accumulation in the zero-N control was defined as PE of soil N (PES, kg grain yield per kg N accumulation in the zero–N control). PE varies greatly depending on genotype, environment, and agronomic practices (Dobermann, Citation2007). With proper N management, up to 53 kg of grain per kg of N uptake of PE can be achieved (Peng et al., Citation1996). A higher panicle nitrogen fraction is beneficial to increasing nitrogen recovery efficiency, while resulting in a decrease of nitrogen PE (Jiang et al., Citation2004).
The amount of N uptake of crops depends on the yield level and environmental conditions (Cassman et al., Citation1996; Yoshida, Citation1983). Schnier et al. (Citation1990) and Peng et al. (Citation1996) stated that irrigated rice produced a grain yield of 9 to 10 t ha−1 in tropical environment required the accumulation of 180–200 kg ha−1. Recently, a number of field studies showed that the yield potential of rice could be over 13 t ha−1 in some sites, for example, Taoyuan, Yunnan Province, China (Katsura, Citation2008; Li, Citation2009; Ying, Citation1998a) and Yanco, Australia (Horie, Citation1997). The high grain yields of rice in Taoyuan and Yanco were associated with high N uptake, the accumulation of N more than 250 kg ha−1 is required to achieve these yield levels (Horie, Citation1997; Ying, Citation1998b). However, these previous studies on the N uptake requirements at these yield levels were usually conducted by comparing a high-yielding site with a check site, or using only one cultivar. It is difficult to obtain information about the characterizing N uptake and use efficiency of rice under different environments. In our present study, ten field experiments were conducted with four rice cultivars in five sites in China in two years. The objectives of this study were to (1) compare the characteristics of N uptake and NUE of rice among different environments and (2) quantify the contribution of soil indigenous and applied N uptake and use efficiency over a wide range of environments.
Materials and methods
Field experiments were conducted in farmers’ fields in major rice-growing areas of China in 2012 and 2013. The experimental fields were located in Huaiji county (24°03′52″N, 112°03′27″E), Binyang county (23°09′33″N, 108°52′43″E), Haikou city (19°45′12″N, 110°11′52″E), Changsha city (28°11′11″N, 113°04′15″E), Xingyi city (25°07′16″N, 104°55′56″E), of Guangdong, Guangxi, Hainan, Hunan, and Guizhou provinces, respectively. The properties of experimental soil are described in Table . In five locations, soil samples were collected in cores from the 0- to 20-cm layer before rice transplanting in the first year.
Table 1. Soil properties of the experimental fields.
Two hybrid rice varieties Liangyoupeijiu and Yliangyou 1, and two inbred cultivars Yuxiangyouzhan and Huanghuazhan were used in each location. Liangyoupeijiu is an indica–japonica hybrid (Peiai64S × 9,311) developed by the Jiangsu Academy of Agricultural Science and released in 1999. Yliangyou 1 is an indica hybrid (Y58S × 9,311) developed by the Hunan Academy of Agricultural Science and released in 2006. Yuxiangyouzhan and Huanghuazhan are inidca inbred cultivars developed by the Guangdong Academy of Agricultural Science and released in 2005. These varieties have been widely grown by rice farmers in China because of their good yield.
Field experiments were arranged in a split plot design with three N rates as main plots and four rice varieties as subplots. Each treatment was replicated three times and subplot size was 20 m2. In each location, the two-year experiments were conducted in the same field with the same treatment layout. Nitrogen rates applied were 225 kg ha−1 in N1, 161–191 kg ha−1 in N2 and 0 kg ha−1 in N3. N1 was deemed as the upmost N level, N2 was adjusted to the optimum N level by using chlorophyll meter readings, and N3 indicated the relative N-supplying capacity of paddy soils in all locations and years. Main plots were separated by making levees, and subplots were separated by one empty row. N in the form of urea was applied as basal and top dressing and the details of application rates and timings are shown in Table . Phosphorus (112.5 kg P2O5 ha−1) in the form of superphosphate was applied and incorporated in all main plots 1 day before transplanting. Potassium (157.5 kg K2O ha−1) was split equally at basal and panicle initiation.
Table 2. Nitrogen application at each experimental site in China in 2012 and 2013.
Pre-germinated seeds were sown at a rate of 25 g m−2 on 10 March in Huaiji, 20 March in Binyang, 15 January in Haikou, 13 May in Changsha, and 8 April in Xingyi. Seedlings were transplanted at a spacing of 20 cm × 27 cm, with two seedlings per hill. Seedling age at transplanting was 27–33 d in Huaiji, 21–22 d in Biangyang, 33–36 d in Haikou, 27 d in Changsha, and 35 d in Xingyi. Fields were irrigated with a water depth of 2–3 cm from transplanting to the end of productive tiller growth and then made the soils in sun-drying to control unproductive tillers. Ten to 15 days later, the fields were imposed by shallow irrigation from panicle formation to physiological maturity. Intensive management for pest, diseases, and weeds was applied using a combination of pesticides, fungicides, herbicides, and manual weed removal.
Ten hills were diagonally sampled in each subplot (exclude outside 3 lines) at maturity stage and separated into straws (including rachis) and grains. All grains were submerged in clean water to distinguish into filled and unfilled spikelets. Dry weights of straw, filled and unfilled spikelets were determined by oven-drying at 70 °C at constant weight. N concentrations in straw, and filled and unfilled spikelets were determined in an autoanalyzer (Integral Futura, Alliance Instruments, Frépillon, France) to calculate aboveground total N uptake. Grain yield was determined from a 5-m2 area in the middle of subplot at maturity stage and adjusted to a moisture content of 0.14 g H2O g−1 fresh weight. The agronomic indices of nitrogen (N) fertilizer use efficiency are calculated as follows:
Partial factor productivity of applied N (PFPN, kg kg−1)=GY/FN
Agronomic efficiency of applied N (AEN, kg kg−1) = (GY–GY0)/FN
Crop recovery efficiency of applied N (REN, %) = (TN–TN0)/FN
PE of applied N (PEN, kg kg−1) = (GY–GY0)/ (TN–TN0)
PE of soil N (PES, kg kg−1) = GY0/ TN0
Where GY is the grain yield of the treatment receiving applied N fertilizer; GY0 is the grain yield in a control treatment with no N fertilizer; FN is the amount of fertilizer N applied; TN is the total N uptake in aboveground biomass at maturity in a plot that received fertilizer N; TN0 is the total N uptake in aboveground biomass at maturity in a plot that received no fertilizer N.
Statistix 8 software package (Analytical software, Tallahassee, FL, USA) was used for analysis of variance. Means of varieties were compared based on the least significant difference test (LSD) at the 0.05 probability level for each location and year.
Result
Grain yield varied greatly among sites (Table ). The grain yield ranged from 4.13 to 7.67, 4.43 to 9.08, 5.16 to 9.68, 6.61 to 10.82, and 9.07 to 14.09 t ha−1 in Huaiji, Binyang, Haikou, Changsha, and Xingyi, respectively. When averaged across four cultivars, three N treatments, and two years, grain yield was 6.29–7.47 t ha−1 in Huaji, Binyang, and Haikou, 9.20 t ha−1 in Changsha, and 11.80 t ha−1 in Xingyi. The difference in grain yield among cultivars was significant in all 10 experiments. Hybrid cultivars produced approximately 10% higher average grain yield for the treatments receiving applied N than inbred cultivars.
Table 3. Grain yield (t ha−1) of 4 rice cultivars grown under 3 N treatments in 5 locations in 2012 and 2013.
N application had significant effect on grain yield in all experiments. Average grain yields under N1 and N2 were 9.03 and 9.11 t ha−1, respectively, which were about 30% higher than that under N3. The grain yield under N3 varied greatly among sites (Table ). Averaged across four cultivars and two years, grain yield without N treatment (N3) was 4.72–6.23 t ha−1 in Huaji, Binyang, and Haikou, 7.97 t ha−1 in Changsha, and 10.52 t ha−1 in Xingyi. The mean grain yield across two years increase from applied N was 1.85–2.38 t ha−1 in Huaiji, Binyang and Haikou, 1.85 t ha−1 in Changsha, and 1.92 t ha−1 in Xingyi. The difference in these yields among five sites was relatively small. In no application N treatment (N3), hybrid rice produced about 13% higher average grain yield than inbred cultivars.
N uptake was significantly affected by site (Table ). Averaged across four cultivars and two years, total N uptake, N uptake from soil, and N uptake from fertilizer N were siginificantly lower in Huaiji, Binyang, and Haikou than those in Changsha by 53.6–90.8%, 77.9–120.0%, 15.7–77.2%, respectively. The total N uptake and N uptake from soil were significantly higher in Xingyi than those in Changsha by 14.8–16.2 and 14.4%, respectively; while there was not significant difference in N uptake from fertilizer N between Xingyi and Changsha (execpt in N2 in 2012). The proportion of N uptake from soil differed among five sites. When averaged across four cultivars, two N treatments, and two years, rice crops took up 54.6–61.7% of total plant N from soil in Huaiji, Binyang, and Haikou, 64.3% of total plant N from soil in Changsha, 63.5% of total plant N from soil in Xingyi. The difference in total N uptake, N uptake from soil, and N uptake from fertilizer N between hybrid rice and inbred cultivar was relatively small or not consistent. The magnitude of difference in total N uptake and N uptake from fertilizer between N1 and N2 varied with sites. In general, total N uptake and N uptake from fertilizer N under N1 were higher than those under N2, except in Binyang in 2012.
Table 4 N uptake (g m−2) at maturity of four cultivars grown under 3 N treatments in 5 locations in 2012 and 2013
Table shows PE of soil (PES) and physiological efficiency of fertilizer N (PEN) of four cultivars in 2012 and 2013. PES varied greatly among sites, which ranged from 58.5 to 85.8 kg kg−1 in 2012, and from 52.0 to 72.3 kg kg−1 in 2013. Averaged across four cultivars and two years, PES was 73.0–76.5 kg kg−1 in Huaiji, Binyang, and Haikou, 55.3 kg kg−1 in Changsha, 64.1 kg kg−1 in Xingyi. The difference in PES between hybrid rice and inbred cultivars was relatively small or not consistent. Similarly, physiological efficiency of fertilizer N (PEN) also varied markedly among different sites from 8.3 to 54.5 kg kg−1 and 18.3 to 42.9 kg kg−1 for N1 in 2012 and 2013, respectively; and from 20.7 to 68.4 kg kg−1 and 24.2 to 51.4 kg kg−1 for N2 in 2012 and 2013, respectively. When averaged across four cultivars and two years, PEN was 32.6–43.8 kg kg−1 for N1 and 40.1–52.4 kg kg−1 for N2 in Huaiji, Binyang, and Haikou, 18.8 kg kg−1 for N1 and 28.8 kg kg−1 for N2 in Changsha, 18.9 kg kg−1 for N1 and 25.3 kg kg−1 for N2 in Xingyi. The difference in PEN between hybrid rice and inbred cultivars was relatively small or not consistent.
Table 5. PE of soil N (PES, kg kg−1) and physiological efficiency of fertilizer N (PEN, kg kg−1) of 4 cultivars grown under 3 N treatments in 5 locations in 2012 and 2013
There were no consistent differences in agronomic efficiency of applied N (AEN) among sites (Tables and ). The difference in AEN between hybrid rice and inbred cultivars was relatively small or not consistent. Partial factor productivity of applied N (PFPN) considerably varied among sites. When averaged across four cultivars, two N treatments, and two years, PFPN was 36.0–42.0 kg kg−1 in Huaiji, Binyang, and Haikou, 58.2 kg kg−1 in Changsha, and 66.4 kg kg−1 in Xingyi. There were significant differences in PFPN among cultivars. Hybrid rice had about 9.0% higher average PFPN than inbred cultivars. Recovery efficiency of applied N (REN) was significantly affected by site. When averaged across four cultivars, two N treatments, and two years, REN was 26.0–32.4% in Huaiji, Binyang, and Haikou, 42.6% in Changsha, and 50.1% in Xingyi. The difference in REN was relatively small or not consistent between hybrid rice and inbred cultivars. Additionally, N1 generally had lower AEN, PFPN, and REN than N2 for the four cultivars.
Table 6. Agronomic efficiency of applied N (AEN, kg kg−1), partial factor productivity of applied N (PFPN, kg kg−1), and recovery efficiency of applied N (REN, %) of 4 cultivars grown under 3 N rates and in 5 locations in 2012
Table 7. Agronomic efficiency of applied N (AEN, kg kg−1), partial factor productivity of applied N (PFPN, kg kg−1), and recovery efficiency of applied N (REN, %) of 4 cultivars grown under 3 N rates and in 5 locations in 2013
Disscusion
In our present study, rice yield varied greatly with site. Averaged across cultivars, N treatments, and years, grain yields were approximately 6.0–7.5 t ha−1 in Huaiji, Binyang, and Haikou, 9.0 t ha−1 in Changsha, and 12.0 t ha−1 in Xingyi. The changing pattern of total N uptake among different sites was similar to grain yield. Averaged across four cultivars, three N treatments, and two years, total N uptake was approximately 10–12 g m−2 in Huaiji, Binyang, and Haikou, 20 g m−2 in Changsha, and 23 g m−2 in Xingyi. This finding indicated that total N uptake increased with yield level, but the amplitude of increase in total N uptake was different. Improving rice yield from medium (6.0–7.5 t ha−1) to high level (9.0 t ha−1) more 8–10 g m−2 of total N uptake was required, while a further improvement to super high level (12.0 t ha−1) just more 3 g m−2 of total N uptake was required.
The total N uptake in rice plants is derived from fertilizer N and soil indigenous N (Cassman et al., Citation1996; Guo et al., Citation2007). A number of field studies indicated that the indigenous N supply varies greatly among soils within a rice-growing domain and in the same soil in different seasons or years (Cassman et al., Citation1996; Dolmat et al., Citation1980; Toriyama & Sekiya, Citation1991), and soil indigenous N was of great importance as a nitrogen source for rice growing (Shoji et al., Citation1974). Averaged across four cultivars and two years, N uptake from soil indigenous N was 6.6–8.1 g m−2 in Huaiji, Binyang, and Hiakou, 14.5 g m−2 in Changsha, and 16.5 g m−2 in Xingyi. This result was in agreement with Shoji et al. (Citation1974), who reported that indigenous N supply varied with experimental sites. The total biomass production of N3 treatment was higher in Changsha than in Huaiji, Binyang, and Haikou by 44–118% in 2012 and 68–76% in 2013 (data not shown), which was partially responsible for higher total N uptake of N3 treatment. On the other hand, the higher total N uptake of N3 treatment in Changsha was probably associated with the higher climatic yield potential caused by lower air temperature during grain filling period compared with Huaiji, Binyang, and Haikou. This was also supported by the results that grain yield without applied N (N3) was significantly higher in Changsha than in Huaiji, Binyang, and Haikou. However, the higher total N uptake of N3 treatment in Xingyi than in Changsha was mainly due to higher climatic yield potential and soil fertility (Table ). Soil organic matter and total N concentrations were 89.9 and 62.5% higher in Xingyi than in Changsha, respectively. The N uptake from fertilizer N was significantly higher in Changsha than in Huaiji, Binyang, and Haikou by 27.1–57.2%, while there was no significant difference in N uptake from fertilizer N between Xingyi and Changsha, execpt N uptake of treatment N2 in Xingyi in 2012. These findings indicate that both N uptake from fertilizer N and soil indigenous N are important for improving rice yield from medium to high level, while a further improvement to super high level N uptake from soil indigenous N should be emphasized more than the N uptake from fertilizer N.
PE was defined as the ability of a plant to transform N acquired from fertilizer N or soil indigenous N into economic yield (grain), and which depends on genotype, environment, and cultivation practices (Dobermann, Citation2007). The present study indicated that the PE decreased with grain yield from medium (6.0–7.5 t ha−1) to high level (9.0 t ha−1). Average PEN across four cultivars, two N treatments, and two years was 38.5–48.1 kg kg−1 in Huaiji, Binyang, and Haikou, and 23.8 kg kg−1 in Changsha. Those values in Huaiji, Binyang, and Haikou approach the PEN of 35 kg kg−1 reported for wet season rice by Cassman et al. (Citation1996). PEN of irrigated rice could reach 50 kg kg−1 in well-managed systems, at low levels of N use, or at low soil N supply (Dobermann, Citation2007). Higher PEN in Huaiji, Binyang, and Haikou was associated with lower N accumulation at maturity, since grain yield was significantly lower in Huaiji, Binyang, and Haikou than in Changsha (Table ). The difference in PEN between Changsha and Xingyi was relatively small or not consistent. That means further improvement to super high level (12.0 t ha−1) PE does not significantly decrease. On the other hand, the PES was also significantly higher in Huaiji, Binyang, and Haikou than in Changsha, while the difference in PES between Changsha and Xingyi was small or not consistent. The higher PES in Huaiji, Binyang, and Haikou was associated with low soil indigenous N supply capacity which resulted in low N accumulation.
PFPN is an aggregate efficiency index that includes contributions to grain yield derived from uptake of indigenous soil N, N fertilizer uptake efficiency, and the efficiency with which N acquired by the rice plant is converted to grain yield (Cassman, Citation2003). PFPN of irrigated rice could reach 60 kg kg−1 in well-managed systems or at low levels of N use (Dobermann, Citation2007). In our present study, PFPN varied greatly with site. Average PFPN was 39.4 kg kg−1 in Huaiji, Binyang, and Haikou, 52.5 kg kg−1 in Changsha, and 66.4 kg kg−1 in Xingyi. High yield and high PFPN in those sites (Changsha and Xingyi) result from a combination of fertile soil and favorable climate. This was also supported by the fact that grain yield without applied N (N3) was consistently higher in Changsha and Xingyi than in Huaiji, Binyang, and Haikou (Table ).
REN was another subject for the agronomist’s concern (Penget al., Citation2002; Wang et al., Citation2001), which is affected by the application method (amount, timing, placement, N form) and the factors that determine the size of the crop nutrient sink (genotype, climate, plant density, abiotic/biotic stress). The data in the present study (Tables , and ) show that the REN increased with yield levels. The result indicated that a closely coordinated relationship existed between higher yield and the higher REN.
Hybrid rice cultivars had higher total N uptake than inbred cultivars by 2.0–4.7% in Huaiji, Binyang, and Haikou, and by 2.7% in Changsha, and by 7.1% in Xingyi. Higher N uptake from soil indigenous N was partially responsible for the difference in total N uptake between hybrid rice and inbred cultivars in Huaiji, Binyang, and Changsha; meanwhile, which resulted in hybrid rice having lower REN than inbred cultivars. Higher total N uptake of hybrid rice in Haikou was associated with higher N uptake from fertilizer N. In Xingyi, higher total N uptake of hybrid rice was mainly attributed to higher N uptake from fertilizer N and soil indigenous N. Hybrid rice had higher REN in Haikou and Xingyi than inbred cultivars which result from the fact that hybrid rice had higher N uptake from fertilizer N than inbred cultivars. The difference in AEN between hybrid rice and inbred cultivars was not consistent. About a 9% difference in PFPN existed between hybrid rice and inbred cultivars. However, the magnitude of difference in PFPN between hybrid rice and inbred cultivars varied with sites. Hybrid rice had higher PFPN than inbred cultivars by 3.6, 7.8, 5.3, 5.5, and 19.0% in Huaiji, Binyang, Haikou, Changsha, and Xingyi, respectively.
The present study showed that N2 had equally or higher grain yield than N1 in all sites. Moreover, all NUE indices were increased under N2 than under N1 due to a decreased N application rate. These results indicated that adopting a chlorophyll meter to monitor leaf N status and guide N application rate is helpful to a simultaneous increase in grain yield and NUE for rice over a wide range of environments.
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
This work was financially supported by the earmarked fund for Modern Agro-Industry Technology of China [grant number CARS-01-34].
References
- Cassman, K. G. (2003). Meeting cereal demand while protecting natural resources and improving environmental quality. Annual Review of Environment & Resources, 28, 315–358.
- Cassman, K. G., Peng, S., Olk, D. C., Ladha, J. K., Reichardt, W., Dobermann, A., & Singh, U. (1998). Opportunities for increased nitrogen–use efficiency from improved resource management in irrigated rice systems. Field Crops Research, 56, 7–39.10.1016/S0378-4290(97)00140-8
- Cassman, K. G., Gines, G. C., Dizon, M. A., Samson, M. I., & Alcantara, J. M. (1996). Nitrogen-use efficiency in tropical lowland rice systems: Contributions from indigenous and applied nitrogen. Field Crops Research, 47, 1–12.10.1016/0378-4290(95)00101-8
- De Datta, S. K. (1986). Improving nitrogen fertilizer efficiency in lowland rice in tropical Asia. Fertility Research, 9, 143–169.
- Dobermann, A. (2007). Nutrient use efficiency–measurement and management. In Fertilizer best management practices IFA international workshop on fertilizer best management practices (pp: 1–28). Brussels, Belgium.
- Dolmat, M. T., Patrick, W. H., & Peterson, F. J. (1980). Relation of available soil nitrogen to rice yield. Soil Science, 129, 229–237.10.1097/00010694-198004000-00006
- Guo, S., Wu, L., Shen, Q., & Zhang, F. (2007). Practices and theoretics of non–flooded rice mulching cultivation in China: China Agricultural University Press Beijing. China., 3–6. (in Chinese).
- Horie, T. (1997). Physiological characteristics of high–yielding rice inferred from cross–location experiments. Field Crops Research, 52, 56–67.
- Lemaire, G., & Gastal, F. (1997). Nitrogen uptake and distribution in plant canopies. In G. Lemaire (Ed.), Diagnosis of the nitrogen status in crops (pp. 3–43). Berlin: Springer-Verlag.10.1007/978-3-642-60684-7
- Li, G. H. (2009). Comparison of yield components and plant type characteristics of high–yield rice between Taoyuan, a ‘special eco–site’ and Nanjing, China. Field Crops Research, 112, 214–221.
- Li, M., Zhang, C., Yang, X., Ge, M., Ma, Q., Wei, H., … Luo, D. (2014). Accumulation and utilization of nitrogen, phosphorus and potassium of irrigated rice cultivars with high productivities and high N use efficiencies. Field Crops Research, 161, 55–63.10.1016/j.fcr.2014.02.007
- Jiang, L., Dai, T., Jiang, D., Cao, W., Gan, X., & Wei, S. (2004). Characterizing physiological N–use efficiency as influenced by nitrogen management in three rice cultivars. Field Crops Research, 88, 239–250.10.1016/j.fcr.2004.01.023
- Katsura, K. (2008). The high yield of irrigated rice in Yunnan, China ‘A cross location analysis’. Field Crops Research, 107, 1–11.
- Normile, D. (2008). Agricultural research: reinventing rice to feed the world. Science, 321, 330–333.10.1126/science.321.5887.330
- Peng, S., Huang, J., Zhong, X., Yang, J., Wang, G., Zou, Y., Zhang, F., Zhu, Q., Buresh, R. J., & Witt, C. (2002). Challenge and opportunity in improving fertilizer–nitrogen use efficiency of irrigated rice in China. Agric. Sci. China., 1, 776–785.
- Peng, S., Buresh, R. J., Huang, J., Yang, J., Zou, Y., Zhong, X., Wang, G., & Zhang, F. (2006). Strategies for overcoming low agronomic nitrogen use efficiency in irrigated rice systems in China. Field Crops Research, 96, 37–47.10.1016/j.fcr.2005.05.004
- Peng, S., Tang, Q., & Zou, Y. (2009). Current Status and Challenges of Rice Production in China. Plant Production Science, 12, 3–8.10.1626/pps.12.3
- Peng, S., Garcia, F. V., Laza, R. C., Sanico, A. L., Visperas, R. M., & Cassman, K. G. (1996). Increased N-use efficiency using a chlorophyll meter on high-yielding irrigated rice. Field Crops Research, 47, 243–252.10.1016/0378-4290(96)00018-4
- Schnier, H. F., Dingkuhn, M., De Datta, S. K., Mengel, K., & Faronilo, J. E. (1990). Nitrogen fertilization of direct-seeded flooded vs. transplanted rice: I. Nitrogen uptake, photosynthesis, growth, and yield. Crop Science, 30, 1276–1284.10.2135/cropsci1990.0011183X003000060024x
- Shoji, S., Nogi, T., & Suzuki, K. (1974). Absorption of fertilizer and soil nitrogen by rice plants under the various cultural conditions of different paddy fields. I. Relationships between the rate of basal nitrogen and nitrogen absorption by rice plants. Tohoku Joural of Agricultural Research., 25, 113–124.
- Toriyama, K., &Sekiya, S. I. (1991). Method of forcasting the nitrogen release pattern of paddy soil for the fertilizer management of rice plants. In: Siol management for sustainable rice production in the tropical. IBSRAM monograph no. 2 (pp. 287–302). Bangkok, Thailand: International Board for Soil Research and Mangement.
- Wang, G., Dobermann, C., Witt, Q., Sun, Q., & Fu, R. (2001). Performance of site-specific nutrient management for irrigated rice in southeast China. Agronomy Journal, 93, 869–878.10.2134/agronj2001.934869x
- Ying, J. F. (1998a). Comparison of high–yield rice in tropical and subtropical environments: I. Determinants of grain and dry matter yields. Field Crops Research, 57, 71–84.
- Ying, J. F. (1998b). Comparison of high–yield rice in tropical and subtropical environments: Ⅱ. Nitrogen accumulation and utilization efficiency. Field Crops Research, 57, 85–93.
- Yoshida, S. (1983). Rice. In W. H. Smith & S. J. Banta (Eds.), Potential productivity of field crops under different environments (pp.103–127). Los Baños: International Rice Research Institute.
- Zhang, S., Zhu, Z., Xu, Y., Chen, R., & Li, A. (1988). On the optimal rate of application of nitrogen fertilizer for rice and wheat in Tai–lake region. Soils, 20, 5–9. (in Chinese).