Effects of nitrogen fertilization strategies on nitrogen use efficiency in physiology, recovery, and agronomy and redistribution of dry matter accumulation and nitrogen accumulation in two typical rice cultivars in Zhejiang, China

Effects of nitrogen fertilization strategies on nitrogen use efficiency in physiology, recovery, and agronomy and redistribution of dry matter accumulation and nitrogen accumulation in two typical rice cultivars in Zhejiang, China first-author corresp ‡Corresponding Author ‡Corresponding Author †E-mail:wanggh@zju.edu.cn †E-mail:wanggh@zju.edu.cn wanggh@zju.edu.cn Institute for Soil and Water Resources and Environment, Zhejiang University, Hangzhou 310029, China Institute for Soil and Water Resources and Environment, Zhejiang University, Hangzhou 310029, China Field experiments were conducted in farmers’ rice fields in 2001 and 2002 to study the effects of nitrogen (N) management strategies on N use efficiency in recovery (RE), agronomy (AE) and physiology (PE) and redistribution of dry matter accumulation (DMA) and nitrogen accumulation (NA) in two typical rice cultivars in Jinhua, Zhejiang Province. This study aimed mainly at identifying the possible causes of poor fertilizer N use efficiency (NUE) of rice in Zhejiang by comparing farmers’ fertilizer practice (FFP) with advanced site-specific nutrient management (SSNM) and real-time N management (RTNM). The results showed that compared to FFP, SSNM and RTNM reduced DMA and NA before panicle initiation and increased DMA and NA at post-flowering. There is no significant difference between SSNM and FFP in post-flowering dry matter redistribution (post-DMR) and post-flowering nitrogen redistribution (post-NR). These results suggest that high input rate of fertilizer N and improper fertilizer N timing are the main factors causing low NUE of irrigated rice in the farmer’s routine practice of Zhejiang. With SSNM, about 15% of the current total N input in direct-seeding early rice and 45% in single rice could be reduced without yield loss in Zhejiang, China. Recovery N use efficiency (RE) Agronomic N use efficiency (AE) Physiological N use efficiency (PE) Nitrogen management Rice Accumulation and redistribution INTRODUCTION 1 Researches have revealed the poor fertilizer N use efficiency (NUE) of rice in China (Wang et al., 2001a 2001a ; Peng et al., 2002 2002 ). This could be partially due to high N input (Peng et al., 2002 2002 ; 2006 2006 ). New technologies in nutrient management in rice have been developed to increase nutrient use efficiency in recent years, such as site-specific nutrient management (SSNM) and real-time N management (RTNM). These advanced N management strategies could significantly increase NUE for rice in China (Wang et al., 2001b 2001b ; Dobermann et al., 2002 2002 ; Peng et al., 2006 2006 ). Since the pioneering work in the 1960s, crop growth model had developed rapidly with the in-depth understanding of physiological and ecological mechanisms and improving of computer science (Lin et al., 2003 2003 ; van Ittersum et al., 2003 2003 ). Several models of rice had been set up and have shifted from understanding and explaining towards practical application and operationalization (Bouman et al., 1996 1996 ; ten Berge et al., 1997a 1997a ; 1997b 1997b ; Yan and Quan, 2002 2002 ). However, existing rice models did not comprise overall environmental elements owing to faulty simulating technique and imperfect understanding of rice physiological and ecological mechanisms for different ecosystems or different rice varieties (Yan and Quan, 2002 2002 ). The new findings in N management had not been wholly considered in rice models. The models have limitations on the whole, such as ambiguous or inadequately clear mechanism, imprecise quantitative indexes (Yan and Quan, 2002 2002 ; Lin et al., 2003 2003 ; van Ittersum et al., 2003 2003 ). Moreover, rice cultivars have changed rapidly in recent years (Shan et al., 2001 2001 ; Jiang et al., 2003 2003 ; 2004 2004 ). It is necessary to further understand physiological characteristics of the new varieties under different nutrient fertilization strategies in different areas. The objectives of this study were to (1) identify the possible cause of poor fertilizer NUE of rice through evaluating the effect of nitrogen fertilization strategies on recovery efficiency (RE), agronomy efficiency (AE) and physiology efficiency (PE) in two typical cultivars, and (2) specifically compare the dry matter accumulation (DMA) and N accumulation (NA) and their redistribution of the two cultivars between two advanced N management strategies (SSNM and RTNM) and farmers’ routine N fertilizer practices (FFP). This study might provide information in developing and refining rice models in the area of Zhejiang Province. MATERIALS AND METHODS 1 Field experiments 2 Field experiments were conducted at Shimen State Farm, Jinhua (29°7′ N, 119°39′ E, 64 m altitude) of Zhejiang Province in 2001 to 2002. A widely grown indica hybrid Shanyou63 (single rice from late May to early October) and a conventional indica Jinzao22 (double early rice from early April to middle July) were used. Some basic properties of the soils are shown in Table 1 1 . For Shanyou63 transplanting spacing was 20 cm×20 cm with one seeding per hill. Plot size was 30 m 2 . Phosphorus at 40 kg P/ha, potassium at 100 kg K/ha, and zinc at 5 kg Zn/ha were applied at basal fertilizer. For Jinzao22, direct sawn, plot size was also 30 m 2 . Phosphorus at 15 kg P/ha was applied at basal fertilizer, potassium at 60 kg K/ha was applied at early tillering. The plots were kept flooded throughout the growing season. Pests, diseases, weeds were intensively controlled to avoid yield loss. Seven N treatments were arranged in randomized complete block design with four replicates. Variety pH Org. C (g/kg) Total N (g/kg) Olsen-P (mg/kg) Xch. K (cmol/kg) CEC (cmol/kg) Sand (g/kg) Silt (g/kg) Clay (g/kg) Jinzao22 4.85 25.2 2.47 12.83 0.15 7.04 387 469 144 Shanyou63 4.50 16.1 1.68 28.50 0.13 5.40 280 585 135 The seven N treatments (Table 2 2 ) were different fertilize N management strategies, including control (N 1 ) and three fixed-N split treatments. The three fixed-N split treatments with total N rates of 60 (N 2 ), 100 (N 3 ) and 140 (N 4 ) kg N/ha with 20% applied at three-leaf stage, 35% at early tillering, 45% at panicle initiation in Jinzao22 and total N rates of 60 (N 2 ), 120 (N 3 ) and 180 (N 4 ) kg N/ha with 35% applied at basal fertilizer, 20% at midtillering, 30% at panicle initiation and 15% at heading in Shanyou63. Control plots (N 1 ) received a full dose of phosphorus, potassium but no N. 2 Code 2 N treatments Jinzao22 Shanyou63 N 1 Zero-N control Zero-N control N 2 Fixed-N split with total N rate of 60 kg/ha Fixed-N split with total N rate of 60 kg/ha N 3 Fixed-N split with total N rate of 100 kg/ha Fixed-N split with total N rate of 120 kg/ha N 4 Fixed-N split with total N rate of 140 kg/ha Fixed-N split with total N rate of 180 kg/ha N 5 Farmers’ fertilizer practice (FFP) Farmers’ fertilizer practice (FFP) N 6 Site-specific nutrient management (SSNM) Site-specific nutrient management (SSNM) N 7 Real-time N management using SPAD (RTNM) Real-time N management using SPAD (RTNM) FFP (N 5 ) was based on the common practice of the farmers near the sites. Total N rate was 140 kg N/ha with 40% applied before sowing, 20% at three-leaf stage, 40% at early tillering in Jinzao22 and total N rate was 200 kg/ha with 50% applied before transplanting, 35% at tillering, 15% at flowering (FL) in Shanyou63. Treatment N 6 is SSNM, the timing of N application was fixed but the rate of N application was varied depending on leaf N status. N applications in Jinzao22 and Shanyou63 are described in Table 3 3 , respectively. A chlorophyll meter (SPAD-502) was used to obtain SPAD values on ten uppermost fully expanded leaves in each plot. Variety Growth stage SPAD value N application (kg/ha) Jinzao22 Three-leaf 20 Early tillering >34 25 32~34 35 <32 45 Panicle initiation >34 35 32~34 45 < 32 55 Shanyou63 Basal 50 Midtillering >36 20 34~36 30 <34 40 Panicle initiation >36 30 34~36 40 <34 50 Heading >36 0 <36 20 Treatment N 7 is RTNM, there was no basal N application. Weekly SPAD monitoring started at 10 d after transplanting (or 30 d after sown) and continued until flowering. If the SPAD reading was below 35, 45 kg N/ha was applied around the panicle initiation (PI) stage, 30 kg N/ha was applied for other growth stages in Shanyou63. If SPAD reading was below 34, 45 kg N/ha was applied from PI to booting stage and 35 kg N/ha was applied at other stages in Jinzao22. Sampling and measurements 2 At transplanting (TP), midtillering (MT), panicle initiation (PI), flowering (FL) and maturity (MA) stages, five representative hills of the plants at each plot were separately sampled and divided into leaf blades, stems plus sheaths and grains. The samples were oven-dried at 70 °C till constant weight. Nitrogen concentration in plant tissues was determined by the Kjeldahl method (Lu, 1999 1999 ). At maturity, rice was harvested and grain yield was expressed as 14% water content. Data analysis 2 The term NUE is used in different contexts by different workers (Craswell and Godwin, 1986 1986 ). The following definitions are used here. Post-flowering dry matter redistribution (post-DMR)=DMA at flowering−DMA in stems and leaves at maturity, Post-flowering nitrogen redistribution (post-NR)=NA at flowering−NA in stems and leaves at maturity, RE =100×Δ TN / FN , AE =Δ GY / FN , PE =Δ GY /Δ TN , where Δ TN was total aboveground plant N accumulation in the plot that received N fertilizer minus total aboveground plant N accumulation in the zero-N control, FN was the amount of N fertilizer applied, Δ GY was grain yield in the plot that received N fertilizer minus grain yield in the zero-N control. Analyses were conducted on individual year data and then on 2001 and 2002 combined. Year was treated as the main unit with replication nested within years; the treatments were the subunits. Data were analyzed by the following analysis of variance (SPSS, version 11.5). Differences among treatment means were compared by least significant difference ( LSD ). For mean separations, LSD values were used at P < 0.05. RESULTS 1 Rates of N application and yield response 2 In SSNM and RTNM treatments, total fertilizer N rates which were determined by SPAD readings were 120 and 106 kg/ha in Jinzao22, 110 and 60 kg/ha in Shanyou63 in 2001 and 2002, respectively. The grain yields of Jinzao22 and Shanyou63 in different treatments was in the range of 4.0~5.9 t/ha and 6.3~7.1 t/ha, respectively (Table 4 4 ). The yield difference between N 1 and other N rates was significant; yield response to fertilizer N was obvious. Though fertilizer N rates of SSNM and RTNM were much lower than farmer’s fertilizer practice (FFP), yields in SSNM and RTNM increased yield by about 12%, 8% in Jinzao22 and 8%, 5% in Shanyou63 compared with FFP. The difference in N rate between N 3 level and SSNM was not significant, yet yield in SSNM was higher observably than that in N 3 level in two cultivars (Table 4 4 ). Grain yields followed by the same letter are not significantly different at 5% level 2 Treatment 2 Yield (t/ha) 2 N application (kg/ha) Jinzao22 Shanyou63 Jinzao22 Shanyou63 N 1 4.0c 6.3c 0 0 N 2 5.1b 7.0a 60 60 N 3 5.9a 6.9ab 100 120 N 4 5.7ab 6.9ab 140 180 FFP 5.2ab 6.6bc 140 200 SSNM 5.8ab 7.1a 120 110 RTNM 5.6ab 6.9ab 106 60 Effects of fixed-N split rates on DMA, NA and NUE 2 Increasing fixed-N split rates (N 1 ~N 4 ) enhanced DMA and NA at different stages in two cultivars, while there was no significant difference between N 3 and N 4 level (Figs. 1 1 and 2 2 ). NA at N 3 and N 4 level tended to decrease from flowering to maturity in two cultivars (Fig. 2 2 ). This indicated that high N rates increased N loss at post-flowering in two cultivars. DS: Direct seeding; TP: Transplanting; MT: Midtillering; PI: Panicle initiation; FL: Flowering; MA: Maturity DS: Direct seeding; TP: Transplanting; MT: Midtillering; PI: Panicle initiation; FL: Flowering; MA: Maturity Carbohydrates stored in vegetative organs were partially redistributed to seeds during grain filling. Post-flowering dry matter redistributed from vegetative organs to seeds (post-DMR) of Jinzao22 and Shanyou63 was 809~2169 kg/ha, 2272~4789 kg/ha and accounted for 26%~44%, 25%~38% of the total dry matter at flowering stage, respectively. Post-flowering nitrogen redistributed from vegetative organs to seeds (post-NR) was 22~46 kg/ha in Jinzao22, 70~120 kg/ha in Shanyou63 and accounted for 68%~75%, 38%~72% of the total nitrogen accumulated in vegetative organs at flowering, respectively. Post-DMR and post-NR in Shanyou63 were higher than those in Jinzao22. This showed that DMA and NA from vegetative organs to seeds of Shanyou63 were more than those of Jinzao22. Post-DMR, post-NR, post-DMR/DMA at flowering stage (pre-DMA) and post-NR/NA at flowering stage (pre-NA) increased from N 1 to N 4 for the two cultivars except for post-DMR of Jinzao22 at N 4 level (Figs. 3 3 and 4 4 ). Pre-DMA: DMA at flowering; Pre-NA: NA at flowering There were no significant differences in yield, DMA and NA at different stages, and post-DMR/pre-DMA and post-NR/pre-NA between N 3 and N 4 level in the two cultivars. So the fixed-N treatments with total N application 100 (Jinzao22) and 120 (Shanyou63) kg/ha could supply enough nitrogen and N rates at N 4 level was overfull. RE, AE and PE were from 16%~33%, 8.02~20.14 kg/kg and 52~67 kg/kg in Jinzao22, and 26%~60%, 3.4~18.37 kg/kg and 9~28 kg/kg in Shanyou63 differing with N management, respectively. RE, AE and PE decreased with increasing N rate for the two cultivars from N 2 to N 4 (Fig. 5 5 ). Comparison of DMA, NA, post-DMR, post-NR and NUE in SSNM, RTNM and FFP 2 DMA at panicle initiation stage accounted for 21% and 37% of total DMA in Jinzao22 and Shanyou63 in FFP, which were 8%~9% and 8%~12% higher respectively than SSNM and RTNM. For Jinzao22, NA at PI accounted for 54%, 32% and 36% of total nitrogen accumulation in FFP, SSNM and RTNM, respectively. For Shanyou63, NA at panicle initiation accounted for 75%, 46% and 45% of total nitrogen accumulation and NA at post-flowering in FFP had negative values (Table 5 5 ). DMA and NA at panicle initiation stage in FFP were significantly higher than SSNM and RTNM, while DMA and NA from PI to MA were on the contrary, the cause was high proportion of total N input at early stage of rice growth in FFP, but in SSNM and RTNM N applications in the middle and late growth stages was stressed. Means in row followed by the same letter are not significantly different at 5% level 2 Items 2 Stages 3 Jinzao22 3 Shanyou63 FFP SSNM RTNM FFP SSNM RTNM 3 DMA (t/ha) Pre-PI 1.6a 0.9b 1.0b 5.2a 4.2ab 3.6b PI-FL 3.4a 3.6a 3.6a 7.2b 7.6a 7.1b Post-FL 2.6a 2.9b 3.3b 1.5a 2.3b 3.6b 3 NA (kg/ha) Pre-PI 30a 23b 22b 104a 63b 50b PI-FL 20a 37b 31b 67a 97b 84b Post-FL 6a 13b 8b −33a −23b −23b There was no significant difference in post-NR among FFP, SSNM and RTNM for the two cultivars, except that for post-NR of Shanyou63 at RTNM was lower. It indicated that dry matter redistributed from vegetative organs to seeds at FFP was close to SSNM and RTNM in the same cultivar. In Jinzao22, post-DMR in SSNM and RTNM was lower than that in FFP. In Shanyou63, there was no significant difference between FFP and SSNM, but post-DMR in FFP was higher significantly than that in RTNM (Table 6 6 ). Means in row followed by the same letter are not significantly different at 5% level 2 Items 3 Jinzao22 3 Shanyou63 FFP SSNM RTNM FFP SSNM RTNM Post-DMR (kg/ha) 2187a 1971a 1638b 4389a 4146a 3430b Post-NR (kg/ha) 35a 37a 36a 116a 111ab 96b RE, AE and PE in SSNM and RTNM increased significantly, in contrast to FFP. Increment of RE, AE and PE in SSNM and RTNM were 7%~9%, 5.57~6.29 kg/kg, 7~9 kg/kg in Jinzao22, and 14%~19%, 7.96~14.97 kg/kg, 12~33 kg/kg in Shanyou63, respectively (Table 7 7 ). Means in row followed by the same letter are not significantly different at 5% level 2 Items 3 Jinzao22 3 Shanyou63 FFP SSNM RTNM FFP SSNM RTNM RE (%) 16a 23b 25b 26a 45b 40b AE (kg/kg) 8.02a 13.59b 14.31b 3.40a 11.36b 18.37b PE (kg/kg) 51a 60b 58b 13a 25b 46b In RTNM, nitrogen application of Shanyou63 was 60 kg/ha, which was lower significantly than NA in rice at maturity. And it may produce a bad negative effect on soil fertility, so we consider that SSNM is superior to RTNM. DISCUSSION AND CONCLUSION 1 In this study the fixed-N split treatments (N 1 ~N 4 ) indicated that RE, AE and PE of the two cultivars tended to decrease with increased N application, as reported in previous researches (Peng and Cassman, 1998 1998 ; Timsina et al., 2001 2001 ; Liu et al., 2004 2004 ; Jiang et al., 2004 2004 ; Peng et al., 2006 2006 ; Mae et al., 2006 2006 ). High N rate increased post-DMA and post-NR, which theoretically could result in large grain yield and large PE, RE and AE, however, high N rates did reduced them in the two cultivars, In this study, NA at flowering accounted for 99% and 100% of total nitrogen uptake under high N rates in Jinzao22 and Shanyou63 respectively, which resulted in high nitrogen concentration and accumulation in rice plant at flowering stage. It was reported that the decreased accumulation of nitrogen before flowering could be caused by nitrogen volatilization from plant tissues and death of partial leaf and organ at post-flowering stage, and that nitrogen volatilization was the main cause (Huang et al., 2004 2004 ; Jin and Mian, 2005 2005 ). In this study high N rate decreased NA at post-flowering in Jinzao22 and increased nitrogen volatilization in Shanyou63. High nitrogen concentration and accumulation at flowering stage was the basis of large post-flowering dry matter production and N redistribution. The negative effect caused by volatilization of large nitrogen concentration and accumulation at flowering stage was larger than the positive effect of post-flowering dry matter production and N redistribution at high N rate, so NUE decreased with increasing N rates. In addition, a high indigenous N supply of soil (INS) will result in higher N concentration in rice straw and produce the phenomenon of luxury consumption of N (Liu et al., 2004 2004 ; 2005 2005 ; Feng et al., 2006 2006 ). In this study, the average grain yield in N omission plots of Jinzao22 and Shanyou63 were higher than 4 t/ha and 6 t/ha, respectively, indicating that the INS of the soil was high. de Datta ( 1986 1986 ) reported that RE is usually 30%~50% in the tropics and PE in the tropics is about 50~70 kg rough rice per kg N absorbed. Yoshida ( 1981 1981 ) estimated AE to be 15~25 kg/kg and Cassman and Pingali ( 1996 1996 ) reported AE was 15~20 kg/kg in the dry season in the farmers’ fields in the Philippines. NUE of the farmer’s practice in irrigated rice in Zhejiang Province was reported by Wang et al.( 2001a 2001a ) and Feng et al.( 2006 2006 ). Wang et al.( 2001a 2001a ) measured AE in 21 farmers’ fields for four seasons and found that the average AE of the farmers’ practice was 6.4 kg/kg. Feng et al.( 2006 2006 ) reported that N use efficiency was so low that RE was only 21.55% in average in high-fertility paddy field in Northern Zheiiang Province, which was close to 19.9% in Jiangsu Province (Li, 2000 2000 ). In this study, RE, AE and PE were 16%, 8.02 kg/kg, 51 kg/kg in Jinzao22 and 26%, 3.4 kg/kg, 13 kg/kg in Shanyou63 in FFP. SSNM and RTNM increased RE, AE and PE significantly in contrast to FFP (Table 7 7 ). Previous studies reported there was great potential for NUE improvement by changing accumulation and redistribution of dry matter and nitrogen under optimal nitrogen management in different cultivars (Jiang et al., 2003 2003 ; 2004 2004 ). We speculate the reasons that may explain the phenomena. In this study, DMA and NA at pre-PI in FFP were significantly higher than SSNM and RTNM for the two cultivars, while DMA at post-flowering was lower. Post-DMR and post-NR in FFP were higher or close to SSNM and RTNM. These results showed accumulation of dry matter and nitrogen before PI in the FFP was excessive, and will cause much invalid tillering and deficient nitrogen supplies in the middle and late rice growth stages. Yet SSNM and RTNM could not improve post-DMR and post-NR. So the disadvantage of FFP in Zhejiang was the improper timing of N applied, and N supply cannot be satisfied with N requirement, as reported in previous research (Zhang and Wang, 2002 2002 ; Liu et al., 2004 2004 ; Peng et al., 2006 2006 ; Lin et al., 2006 2006 ). Second, overfull N input in FFP was also the important factor causing low NUE of irrigated rice in Zhejiang. Some reporters believe that 30%~50% reduction in N application in most cases would be feasible and necessary in China (Yang et al., 2003 2003 ; Liu et al., 2004 2004 ; Feng et al., 2006 2006 ). In this study, N input can reduce about 15% in Jinzao22 and 45% in Shanyou63; waste of N in single rice was more severe than direct-seeding early rice. As dominant cultivars in Zhejiang, Shanyou63 and Jinzao22 have shown great differences in plant type, panicle size and grain yield under production practices. There were different NUE in different varieties under the different levels of N fertilizer (Jiang et al., 2003 2003 ; Luan et al., 2005 2005 ). In this study, RE of Shanyou63 was higher than that of Jinzao22 while PE was lower than that of Jinzao22 under the same condition (Table 7 7 ). RE, AE and PE of the two cultivars tended to decrease and post-DMR, post-NR increased with increased N application under fixed-N split treatments for two cultivars. 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Chin J Rice Sci , 2002 . 16 ( 4 ): 346 - 350 . (in Chinese) . Optimal nitrogen application for direct-seeding early rice 10.1631/jzus.2007.B0208 Project supported by the International Rice Research Institute (IRRI), Swiss Agency for Development and Cooperation (SDC), the Potash & Phosphate Institute and the Potash & Phosphate Institute of Canada (PPI-PPIC), the International Fertilizer Industry Association (IFA), the International Potash Institute (IPI), and 948 Project of the Ministry of Agriculture of China (No. 2003-Z53) 2006-03-16 2006-07-31 2022-01-05 Copyright © 2007, Journal of Zhejiang University Science 2007 Journal of Zhejiang University-SCIENCE B (Biomedicine and Biotechnology) 03 08