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Effect of plant density and nitrogen fertilizer rates on grain yield and nitrogen uptake of hybrid rice (Oryza sativa L.) Article · January 2009 CITATIONS
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Journal of Agricultural Biotechnology and Sustainable Development Vol. 1(2) pp. 044-053, November, 2009 Available online http://www.academicjournals.org/JABSD ©2009 Academic Journals
Full Length Research Paper
Effect of plant density and nitrogen fertilizer rates on grain yield and nitrogen uptake of hybrid rice (Oryza sativa L.) X. Q. Lin1*, D. F. Zhu1, H. Z. Chen1, S. H. Cheng1 and N. Uphoff2 1
Key Laboratory for Rice Biology, Ministry of Agriculture, China, and China National Rice Research Institute, Hangzhou 310006, China. 2 Cornell International Institute for Food, Agriculture and Development, 31 Warren Hall, Cornell University, Ithaca, NY 14853, USA. Accepted 5 October, 2009
Yield of both superior hybrid and inbred lines developed by the Chinese plant breeders has been stagnant even with the standard rice-growing practices; thus raising the need for suitable modifications in these practices. Nitrogen uptake, yield attributes and yield response of two rice cultivars under the varying plant densities and nitrogen application rates has been investigated in these studied. Two management systems including conventional practices or standard rice management (SRM), and new rice management or the system of rice intensification (SRI) have been investigated in a two year trial. -1 Significantly higher grain yields (15%) and higher N uptake rates (24.8 kg ha ) were recorded for SRI compared with SRM during both years of experimentation. In this study, yield optimization under SRI was achieved with substantially lower plant densities than typically planted with super-rice under SRM. According to these experimental results, applications of N fertilizer can also be effectively reduced with concomitant increases in yield. Increasing plant densities associated with SRM were found to decrease the crop performance as increase in yield per unit of input (seeds, water, N fertilizer) were negative at the margin. Although in the SRM experiments, N uptake was enhanced by higher N application and by -1 greater plant density, the uptake of N ha with SRI was greater with lower plant density, and it was not affected in a linear manner by N applications. Compared to SRM, N productivity was higher at all levels of application with SRI. It appears that not only agronomic benefits but also economic and environmental benefits may be accrued from these two methods of rice management, especially with the super-rice varieties developed in China. Trial results indicate that modification in the management practices can positively influence the rice crop outputs. Key words: Standard rice management (SRM), the system of rice intensification (SRI), super-rice, hybrid rice (Oryza sativa L.), grain yield, nitrogen uptake. INTRODUCTION China is the word’s largest rice producer and is the pioneer of hybrid rice, with approximately 31 million ha paddy rice cultivation in the country. The total rice yield reaches 200.5 million tons, which accounts for 39% of the total grain production of the country. It has been found difficult to increase the grain yield of rice under standard rice management (SRM). This has limited the realization
*Corresponding author. E-mail:
[email protected]. Tel: +860571-63370373. Fax: +86-0571-63376702.
of potential yields from the most advanced cultivars, referred to in China as ‘super-rice’ (Yuan, 2000; Lin et al., 2003; Lu and Zou, 2003; Katsura et al., 2007). Cultivation of super-rice varieties with standard irrigation practices and conventional row spacing of 20 cm or less has been seen to decrease rice production, especially in Southern China (Liang et al., 2006).This may be because low plant density and continuous flooding with SRM constrains plant performance. SRM practices also increase the need for fertilizer, raising fertilizer inputs without adequate returns. Such unsuitable management has led to indiscriminate use of chemicals that have further
Lin et al.
worsened the nutrient balance, besides increasing the pest incidence, cost of production and environmental problems. There is a need for diversification from this standard rice management (SRM). One of the viable options is the adoption of making better improved applications of irrigation water, e.g., through alternate wetting and drying (AWD) (Bouman and Tuong, 2001). Maintaining shallow water depth (SWD) through AWD or other water management can improve growth conditions and produce higher grain yields (Lin et al., 2004). Secondly, wider row spacing can improve plants’ total seasonal light exposure and increase yield (Lin et al., 2005, 2006). Another alternative to SRM is the System of Rice Intensification (SRI) developed a decade earlier for the tropical and temperate zones of Madagascar (Laulanié, 1993). SRI was intended to enable resource-limited farmers to obtain higher yields on currently low-fertility soils, with reduced rates of water application and without primarily relying on external inputs for yield improvement. It sought to achieve this by altering the ways that rice plants, soil, water and nutrients are managed (Stoop et al., 2002). Evaluations of SRI methods started at the China National Hybrid Rice Research and Development Centre in 2000-2001 and at the China National Rice Research Institute (CNRRI) in 2001. These found SRI methods suitable for hybrids and high-yielding varieties as well as for less technically-advanced production systems (Yuan, 2001, 2002). With multiple validations and demonstrations, the extent where local adaptations of SRI concepts and practices are being used in two provinces (Sichuan and Zhejiang) reached > 433,000 ha by the 2007 summer cropping season, according to their provincial departments of agriculture. The national Ministry of Agriculture has designated SRI methods as a technical advance to be extended together with the use of hybrid rice varieties. However, many scientific questions remain to be investigated and answered. The research for this article was undertaken to address some of these concerns. This research did not compare the full set of practices recommended for SRI, but rather assessed a less demanding departure from current standard rice cultivation. This research assessed how suitable more incremental changes in farmers’ cultivation methods would be for capitalizing on and extending super-rice varieties, which are becoming widely-used in China. MATERIALS AND METHODS Site and soil The field experiments were conducted on loam soil at the research farm of the China National Rice Research Institute, Hangzhou, China (30° 05’ N, 119° 56’ E, altitude 6 m) in 2006 and 2007. The average annual temperature is 16oC and the annual precipitation is 1388 mm. The soil contains 24.2 g kg-1 organic C, 9.6 mg kg-1 available P, 66 mg kg-1 exchangeable K, and 2.27 g kg-1 total N, with pH 6.8 (1:1 w/v water).
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Experimental materials The rice (Oryza sativa L.) varieties used were Guodao 6 and Zhongzheyou 1. Zhongyou 6 and Zhongzheyou 1 are new three lines hybrid rice. Zhongyou 6 is a single season indica variety with an average plant height of 115 cm. This long duration variety takes about 138 days to mature with an average yield of 9.75 Mg/ha. Zhongzheyou 1 is also a single season indica variety with an average plant height of 120 cm. This long duration variety takes about 140 days to mature with an average yield of 8.03 Mg/ha. The seeds of these varieties were obtained from the China National Rice Research Institute and Zhejiang Seed Company. Seedlings were transplanted in both 2006 and 2007. Layout and experimental design The experimental design was a factorial design with three replications with water management as the main factor for layout of plots. This was necessary to implement the two water management regimes– continuous flooding and AWD – because two respective two main blocks were required to avoid the effects of lateral seepage from plots continuously flooded into AWD plots. These two main blocks were adjacent, and soil analyses showed no significant differences in their nutrient status or physical characteristics. Within the main blocks, random block design was used for the sub-factors evaluated: i) Plant density – three densities (150,000, 180,000 and 210,000 plants ha–1,one plant per hill). ii) Nitrogen application – four rates (120, 150, 180 and 210 kg ha–1). Experimental plots were each 6 × 6 m, split with both varieties grown on 3 x 6 m areas. SRI plots were planted with 30 cm row spacing, and the SRM plots with 20 cm row spacing, while SRI and SRM hills had, respectively, one vs. two plants. Different plant densities were achieved by varying hill-to-hill distances within rows, rather than between rows or within hills. All treatments were replicated three times. Crop husbandry SRM plots received their nutrient amendments in the form of chemical fertilizer, while SRI plots received half that their fertilization chemically and an equal amount through organic soil amendments (in the form of rapeseed cake, as analyzed below). P and K fertilizers were applied on SRM plots in the form of single superphosphate (SSP) and muriate of potash (KCl) at the respective rates of 35 and 125 kg ha-1 as P2O5 and K2O. Half this amount was applied to the SRI plots, with nutrients matched by applications of rapeseed cake. Atomic absorption spectrophotometer and element analysis results showed that the rapeseed cake contained 1.45% potassium (K2O), 1.95% phosphorus (P2O5), and 4.87% nitrogen. The total amount of N applied to each plot was varied according to the experimental design. Full doses of the P and half of the K fertilizer were applied prior to transplanting, with the remaining half of K fertilizer top-dressed 5 days after transplanting. For all plots weeds were controlled by the application of propanil (3',4'- dichloropropananilide) at 4 kg ha-1 along with 0.04 kg ha-1 of bensulfuron methyl {methyl 2-[(4,6-dimethoxypyrimidin-2-yl) carbamoylsulfamoyl-methyl]benzoate} at 5 days after transplanting. Pests were managed by using pesticides only where and when needed with the amount necessary for the control of a specific pest. Fungicides have not been required. The SRI plots were observed to have lower disease and pest incidence as compared with SRM plots in both study years. While this could have had
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Table 1. Comparison of management practices used in SRI (system of rice intensification) and SRM (standard rice management) experiments
Treatment -1 Transplanting density (plants ha )
150,000 180,000 210,000
120
SRI 30 × 22.2 cm 30 ×18.5 cm 30 × 15.9 cm -1 60 kg ha N was provided as compost -1 at transplanting; 36 kg ha N as urea top-dressed 5 days after transplanting -1 (TP); and 24 kg ha N as urea topdressed 40 days after TP. -1
150 -1
Nitrogen application (kg ha ) 180
210
75 kg ha N was provided as compost -1 at transplanting; 45 kg ha N as urea top-dressed 5 days after transplanting -1 (TP); and 30 kg ha N as urea topdressed 40 days after TP. -1 90 kg ha N was provided as compost -1 at transplanting; 54kg ha N as urea top-dressed 5 days after transplanting -1 (TP); and 36 kg ha N as urea topdressed 40 days after TP. -1 105 kg ha N was provided as compost -1 at transplanting; 63 kg ha N as urea top-dressed 5 days after transplanting -1 (TP); and 42 kg ha N as urea topdressed 40 days after TP.
some impact on resulting yield differences, the analysis of yieldcomponent differences showed these to be large and significant enough to account for yield effects without considering pest and disease impacts as well. A separate article is being written to evaluate these factors based on controlled trials. Implementation of treatments The experimental design compared super-rice production in SRI plots with 30 cm row spacing, and in SRM plots having 20 cm row spacing. The treatments have different transplanting densities (Table 1).In the experiments, the nurseries were planted on May 21, transplanted on June 5 in SRI plots and June 20 in SRM plots. The use of 15-day seedlings in the SRI treatments. In the experimental, SRI has nitrogen application with four rates : 120, 150, 180, and 210 kg ha–1 (Table 1).Chemical fertilizer was applied but with a 50% reduction in quantity of inorganic N; organic fertilizer (rapeseed cake) was applied to match the N reduction from chemical fertilization. Half of the N was provided as compost at transplanting; 30% as urea top-dressed 5 days after transplanting (TP); and 20% as urea top- dressed 40 days after TP. The appropriate amount of fertilizer for each plot was weighed and hand broadcast. SRM has nitrogen application with four rates: 120, 150, 180, and 210 kg ha– 1 .Chemical fertilizer was applied without organic fertilizer. Fertilizer N was all applied as urea: half at transplanting; 30% top-dressed at 5 days after TP and 20% top-dressed at 40 days after TP. Appropriate amount of fertilizer for each plot was weighed and hand broadcast. Data recording The stages of plant development were monitored frequently, with
SRM 20 × 33.3 cm 20 × 27.8 cm 20 × 23.8 cm Fertilizer N was all applied as urea: -1 60 kg ha at transplanting; 36 kg ha 1 top-dressed at 5 days after TP; and -1 24 kg ha top-dressed at 40 days after TP. Fertilizer N was all applied as urea: -1 -1 75 kg ha at transplanting; 45kg ha top-dressed at 5 days after TP; and -1 30 kg ha top-dressed at 40 days after TP. Fertilizer N was all applied as urea: -1 90 kg ha at transplanting; 54 kg ha 1 top-dressed at 5 days after TP; and -1 36 kg ha top-dressed at 40 days after TP. Fertilizer N was all applied as urea: -1 105 kg ha at transplanting; 63 kg -1 ha top-dressed at 5 days after TP; -1 and 42 kg ha top-dressed at 40 days after TP.
whole-plant samples of both cultivars taken at maturity. For plant characteristics, at each of the individual sampling stages, 0.5 m2 sub-plots (1 × 0.5 m) consisting of typical average-size plants were selected from each treatment plot. Within this 0.5 m2 area, all plants were dug up with a spade to a 15 cm depth, and a subset of plants was separated into leaves, stems (culm + sheath), and grain. The separated plant material was dried for at least 48 h in a forced-air oven. Leaf area was measured with an area meter (LI-3100A, LiCor, Lincoln, NE). Dry weights of the separate plant parts as well as the total dry weight of the 0.5 m2 harvested area were recorded. The dry weight of plant tissues was calculated on the basis of the dry weight of the total harvested area and the percentage of dry matter in the plant parts (with dry weight of plant part divided by total weight of the plants). The separated and dried tissue samples were ground with a Wiley mill (1 mm mesh screen) from which a 1.000 g sample was removed, and N concentration was determined with a N analyzer (model DDY-5). The N concentration of the individual tissue was multiplied by the calculated weight of the tissue to determine total N content of the tissue. Nitrogen uptake was calculated from the yield measurements and total N in the plant parts. Leaf chlorophyll content was estimated with a chlorophyll meter (SPAD 502; Minolta Corp., Tokyo) at the middle portion of a leaf and it was expressed as leaf N content. SPAD 502 was used for chlorophyll measurement on ten top fully expanded leaves (that is, index leaves) per plot at flowering stage (FL). Twenty leaf SPAD readings were averaged to represent the mean SPAD readings of each plot. Yield measurements were made from whole-plot recovery of grains, from both the sampled plants described above and the remaining plants in each experimental plot. Because the grain moisture standard used for Indica rice varieties in China is 13.5%, the grain was dried to this standard before being weighed. All
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Table 2. Grain yield of hybrid-rice in experiments grown on loam soil with different inter-row spacing, plant population densities, and fertilizer N rates, averaged for 2 yrs -1
Plant density -1 (ha ) 150,000 180,000 210,000 Means
120 9042.2 cd 8287.3 ef 8086.9 ef 8472.2
New rice management 150 180 9403.0 bc 9951.0 a 8387.5 e 9474.5 abc 7754.5 fg 9142.4 c 8515.0 9522.6
210 9771.2 ab 8537.9 de 7482.3 g 8597.1
N (kg ha ) Means 120 9541.8 6127.8 e 8671.8 7091.2 cde 8116.5 6650.2 de 8776.7 6623.1
Standard rice management 150 180 7299.9 bcd 7266.2 bcd 6799.4 de 7827.4 abc 7814.0 abc 8151.9 ab 7304.4 7748.5
210 7993.1 abc 8040.3 abc 8620.4 a 8217.9
Means 7171.7 7439.6 7809.1 7473.5
Means followed by different letters are significantly different at the p = 0.05 level according to Duncan’s multiple range test.
measurements and techniques used were the same for both SRM and SRI plots. Statistical analysis Analyses were conducted on individual year data and then on the two years combined. In the combined-year analysis, year was treated as the main unit, and variety was the subunit, N rates were the sub-subunits, and plant population densities were the sub-subunits. Year and replication were considered random effects, and all other effects were considered fixed effects. Combined year data are presented unless significant year × treatment interactions occurred, in which case the data are presented for each year. When significant treatment effects were found, data were compared utilizing the correct error terms for the specific split-plot comparison.
RESULTS Grain yield Rice producers have the impression that superrice requires higher N rates than inbred rice. In the present study, however, N rate responses for two super-rice varieties were consistent across years as their grain yields did not vary significantly between years and there were no significant year × N rate interaction effects. Accordingly, yield results for both SRI and SRM
are presented in Table 2 as averages for 2006 and 2007. With SRI, the application of N fertilizer at rates –1 greater than 180 kg ha did not increase superrice grain yield, whereas with SRM, there was a consistent increase in yield as more N fertilizer was applied (Table 2). However, even the –1 highest SRM yield (8217.9 kg ha at 210 kg N –1 ha ) does not match the lowest SRI yield –1 –1 (9522.6 kg ha at 180 kg N ha ). The experiments did not evaluate a wider range of possible N application rates, e.g., down to the lower rates recommended for SRI. However, these data indicate rather clearly that super-rice does not need the high rates of fertilizer N that are normally applied under standard management to get higher yield. Grain yields were significantly affected by plant population density with both sets of management practices, but in a reverse way. With SRM, greater plant density contributed to higher yield as SRM yields rose from 7171.7 kg –1 –1 yield ha with 150,000 plants ha to 7809.1 kg –1 –1 yield ha with 210,000 plants ha . With SRI practices, an opposite pattern was seen, as average SRI yields rose when plant population was reduced, going from a yield of 8116.5 kg –1 –1 ha at 210,000 plants ha to 9541.8 kg yield –1 –1 -1 ha with 150,000 plants ha , almost 2.3 t ha
with 30.6% fewer plants. The divergence in yield response to N application and plant density as seen in Table 2 when alternative management practices are used suggests that SRI practices contribute to phenotypically-different rice plants elicited from super-rice genomes compared with those produced by SRM. Super-rice grain yield with –1 SRM practices averaged 7473.5 kg ha , that is, 15% lower than the average from SRI experiments. Across the two years of experiments increasing N fertilization rates increased SRM grain yields significantly from 6623.1 to –1 8217.9 kg ha when going from 120 kg to 210 -1 kg ha . But even with SRM plants having a higher rate of response to N than did SRI plants, the latter produced consistently higher yield than SRM plants of same variety. A comparison between Tables 2 shows different patterns of response to higher or lower rates of N application. With SRM, the lowest yield result -1 (6127.8 kg ha ) was seen with the lowest plant -1 population (150,000 ha ) and lowest N -1 application rate (120 kg ha ), while the highest -1 SRM yield (8620.4 kg ha ) came with highest -1 plant population (210,000 plants ha ) and -1 highest N application (210 kg ha ). This is what is usually expected and seen with SRM. Conversely, with SRI, considering the effects
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SRI
To ta l d ry w e ig h t ( k g h a -1 )
25000.0
SRM
20000.0 15000.0 10000.0 5000.0 0.0 150,000
180,000
210,000 -1
Transplanting density (plant ha ) Figure 1. Average total dry weight with the System of Rice Intensification vs. Standard Rice Management at different plant densities averaged across different N application rates.
-1
of spacing, the highest yield (9951.0 kg ha ) was -1 achieved with just 150,000 plants ha , while the highest -1 plant density, 210,000 plants ha , gave the lowest yield -1 (7482.3 kg ha ). Regarding N application, application -1 rates of 120, 150 and 210 kg ha with SRI did not give significantly different yield. This ranged between 8472.2 -1 and 8597.1 kg ha . Of both agronomic and economic interest is the observation that SRI yield with 120 kg N -1 ha and low plant density essentially equaled the SRM yield with 75% more N fertilizer application and much higher seed costs 0(data not shown). With SRI, the highest fertilizer application rate (210 kg -1 N ha ) produced only 1.5% more rice than while using -1 75% more N than at the lowest rate (120 kg ha ), hardly a cost-effective management practice. The highest grain yield was achieved under SRI had an application rate of -1 180 kg N ha and the lowest plant density evaluated -1 (150,000 plants ha ). This combination of practices -1 produced 9951.0 kg ha under SRI. While this was significantly more than produced from the other N application levels evaluated, it was not much more yield than achieved with the lowest N application tested. With SRI at a low plant density, comparing a low N rate (120 -1) -1 kg N ha with a fertilization rate of 180 kg N ha , only 12.4% more rice was produced by adding 50% more N. This also suggests the need to consider what N is being supplied from soil biological processes. With SRM, there was a better response to N fertilization, as increasing N application from 120 to 180 kg ha 1 (by 50%) raised yield by 17.0%. Raising the application -1 rate to 210 kg N ha (by 75%) boosted yield by 24.1%. But neither of these is a high marginal rate of return, and all of the SRM yields were lower than those achieved with SRI – and high applications involve both economic and
environmental costs. The accumulation of nitrate in groundwater in some parts of China is already reaching levels well in excess of those considered acceptable by the U.S. Environmental Protection Agency (Peng et al., 2004). Total biomass and leaf area index With SRM, greater plant density contributed to higher – biomass as SRM biomass rose from 13367.6 kg yield ha 1 –1 –1 with 150,000 plants ha to 15989.1 kg yield ha with –1 210,000 plants ha . With SRI practices, an average total dry weight rose when plant population was reduced, –1 going from a yield of 17735.8 kg ha at 210,000 plants –1 –1 –1 ha to 19943.2 kg yield ha with 150,000 plants ha (Figure 1). The divergence in biomass yield response to N application and plant density seen in Figure 2. With SRM –1 practices averaged 15989.1 kg ha , that is, 10.9% lower than the average from SRI experiments. Across the twoyears of experiments, increasing N fertilization rates increased SRM biomass significantly from 12606.6 to –1 17431.4 kg ha when increasing N fertilizer input from -1 120 to 210 kg ha . But SRI biomass with N application of -1 180 kg ha has the highest dry weight in the experiments. In SRI trials, there was higher leave area index (LAI) at flowering stage under the same density (Figure 3) and N application (Figure 4).With less dense plant populations LAI at flowering stage increases from 7.07 to 7.15 with SRI and decreases from 6.84 to 6.56 with SRM. With less N application rate LAI increases from 6.83 to 6.98 with SRI and decreases from 6.89 to 6.13 with SRM. The
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SRI
Total dry weight (kg h a -1 )
25003.0
049
SRM
20003.0 15003.0 10003.0 5003.0 3.0 120
150
180
210
-1
N rate (kg ha )
Figure 2. Average total dry weight with the System of Rice Intensification vs. Standard Rice Management at different N application rates averaged across different plant densities.
9.0
SRI
8.0
SRM
7.0
LAI
6.0 5.0 4.0 3.0 2.0 1.0 0.0 150,000
180,000
210,000 -1
Transplanting density (plant ha ) Figure 3. Average Leaf Area Index (LAI) of super-rice with the System of Rice Intensification vs. Standard Rice Management at different plant densities averaged across different N application rates.
results of this analysis indicate that the increased LAI needed to establish higher plant density under SRM -- as well as the higher N fertilizer inputs that SRM requires. In addition, SRM requires more application of water for continuous flooding (data not shown). This may or may not represent a monetary cost to farmers, but it certainly has environmental costs, subjecting rice plants to anaerobic stress in an era of growing water scarcity. Nitrogen uptake With SRI, increasing the N application rate from 120 to -1 180 kg ha significantly increased nitrogen uptake -- from
-1
140.2 to 156.7kg ha – as it also enhanced yield. But then further increase in N application – from 180 to 210kg -1 ha - decreased nitrogen uptake, although the effect was not great (Table 3). Actually, N uptake at the highest rate -1 of application (180 kg N ha ) was only 11.8% more than -1 N uptake at the lowest rate (120 kg N ha ). With SRM, on the other hand, there were consistent and significant increases in N uptake as the rate of N application was boosted (Table 3). Increasing the N application rate from -1 120 to 210 kg N ha boosted N uptake by 32.1% -- from -1 105.5 to 139.4 kg ha . This follows expectations with conventional rice production methods. Increasing super-rice plant density caused significant decreases in nitrogen uptake under SRI (Table 3). N
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9.0
SRI
8.0
SRM
7.0 6.0
LA I
5.0 4.0 3.0 2.0 1.0 0.0 120
150
180
210
-1
N rate (kg ha ) Figure 4. Average Leaf Area Index (LAI) of super-rice with the System of Rice Intensification vs. Standard Rice Management at different N application rates averaged across different plant densities Table 3. N uptake in super-rice in experiments grown on loam soil with different inter-row spacing, plant population densities, and fertilizer N rates, averaged for 2 years. -1
Plant density -1 (ha ) 150,000 180,000 210,000 Means
120 141.9 d 136.7 d 142.0 d 140.2
New rice management 150 180 152.2 bc 170.6 a 136.6 d 154.6 b 140.1 d 144.9 cd 143.0 156.7
210 165.9 a 139.9 d 137.3 d 147.7
N (kg ha ) Means Standard rice management 120 150 180 210 157.6 96.2 f 104.1 e 117.2 d 126.6 c 142.0 103.8 e 111.7 d 123.5 c 133.0 b 141.1 116.6 d 138.1 b 136.0 b 158.7 a 146.9 105.5 118.0 125.6 139.4
Means 111.0 118.0 137.4 122.1
Means followed by different letters are significantly different at the p = 0.05 level according to Duncan’s multiple range test.
-1
uptake fell from 157.6 kg N ha at the lowest plant –1 -1 density (150000 plants ha ) to 141.1 kg N ha at the –1 highest plant density (210000 plants ha ). However, a reverse relationship was seen in the SRM experiments, -1 where going from 150,000 to 210,000 plants ha raised N -1 -1 uptake ha by 23.7%, from 111 to 137.4 kg with a significant increase. However, SRM plant uptake of N was consistently lower compared to that from SRI (Table 3). In this study, the highest nitrogen uptake of super-rice -1 was with SRI at 150,000 hills ha plant density and an -1 application rate of 180 kg N ha . Increasing N rates for super-rice further was thus not advantageous for nitrogen uptake of super-rice under SRI. With SRI, N uptake at its -1 lowest (for 210,000 plants ha ) was higher than SRM N uptake at its highest (with the same plant density).It is seen that N uptake with SRI dominated that for SRM practices at all plant densities.
flowering stage (Figures 5-6). The results show that hybrid rice with SRI can give better SPAD value with lower plant density and the same varieties grown with SRM methods, at least under the soil, climatic and other conditions of the CNRRI experimental farm at Hangzhou. With SRI and SRM, increasing the N application rate from 120 to 210kg -1 ha significantly increased SPAD value of flag leaf at flowering stage. There were significant effects of different rice management systems on SPAD value of flag leaf as well. With the same inherent soil N fertility, SPAD value of hybrid rice in SRI experiments averaged 12.3% greater than in SRM experiments. This was partly because organic matter was applied to the SRI plots and not to the SRM plots, and also because SRI irrigation management reduced water applications and made soil condition more aerobic.
SPAD values comparison of SRI with SRM
DISCUSSION
SPAD value of flag leaf with SRI was more than SRM at
The yield potential of rice is conditioned by a large
Lin et al.
50.0
SRI
051
SRM
40.0
SPAD
30.0 20.0 10.0 0.0 150,000
180,000
210,000 -1
Transplanting density (plant ha )
Figure 5. SPAD value of super-rice with the System of Rice Intensification vs. Standard Rice Management at different plant densities averaged across different N application rates.
50.0
SRI
SRM
40.0
SPAD
30.0 20.0 10.0 0.0 120
150
180
210
-1
N rate (kg ha )
Figure 6. SPAD value of super-rice with the System of Rice Intensification vs. Standard Rice Management at different N application rates averaged across different plant densities.
number of genes, whose expression is decisively influenced by the environment. SRI improve the environment of growing rice, reveals some very different potentials and growth relationships in super-rice, and probably other rice cultivars. In particular, a compensatory relationship between plant density and tillering has been observed which maintains panicle density within a certain range of variation in plant density. This is not a new observation (Counce et al., 1989; Counce and Wells, 1990; Gravios and Helms, 1992; Wu et al., 1998). But this effect is not something independent of other cultural practices employed. In China, the average N application rate for rice −1 cultivation is about 200 kg N ha during 2000-2005,and −1 varies within a range of 130-330 kg N ha in different provinces; in most provinces the application rate ranges −1 between 170 - 250 kg N ha (Yan, 2008; Xie et al.,
2009).In the present evaluations of SRI practices, increasing plant density from 150,000 to 210,000 plants –1 ha decreased grain yield, an increase in the fertilizer –1 application rate from 120 to 210 kg N ha had no effect on grain and biomass yield (Table 2 and Figures 1-2). -1 With SRI practices, a rate of 120 kg N ha supports basically the same yield as N amendments 75% higher -1 (that is, 210 kg ha ). This could reflect a greater mobilization of biological N when soil conditions are more aerobic and soil organic matter levels are higher; however, these trials were not constructed to evaluate such a relationship if it exists. Indeed, low plant density and higher N uptake of super-rice had a compensatory effect at the population level under SRI. This compensatory relationship between plant density and tillering is produced by cultivar characteristics and management practices for rice. Thus under SRI, compensation among
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plants resulted in the same number of panicles being produced per unit area when plant density changed (Lin et al., 2009). With SRM, on the other hand, increasing plant density increased the grain yield of super-rice. Production costs for super-rice varieties can be minimized by planting at lower plant population densities and by using a fertilizer N rate that is optimum rather than maximum. Note that SRI super-rice consistently yielded more than SRM super-rice under both high and low fertilizer rates. The yield advantage of super-rice in SRI experiments in the present study can be partly explained by the improved soil environment under SRI. This improves the conditions for growth and functioning of rice root systems as well as more diverse and active populations of soil biota (Lin et al., 2009). Partitioning of assimilates to the grain is influenced by the source and sink. The biomass and LAI at flowering stage express the size of source. In the present experiment, SRI has more biomass and LAI than SRM (Figures 1-4), with beneficial effect to grow super-rice. Furthermore, rice grown in paddy fields that have increased applications of fertilizer can produce higher yields, but this incurs considerable economic cost. Also, consumers are now questioning whether these kinds of intensive production methods produce safe food, and citizens are raising queries about damage being done to the environment. With SRI, organic fertilizers can become a larger source of N in paddy production and could replace some or most if not all inorganic N fertilizer (Cho and Choe, 1999a, b). In the present experiment, organic fertilizers replaced half of the inorganic N fertilizer, with beneficial effect. It is accepted that only 30–40% of the total fertilizer N applied to flooded rice gets utilized by the crop (Patrick and Mahapatra, 1968), and also that 60–70% of the N assimilated by lowland rice originates from the soil or irrigation water (Broadbent, 1979; Murayama, 1979). It has been suggested that there are significant advantages to using high-yielding rice cultivars at reduced N fertilizer rates, giving such cultivars potential benefits in alternative cropping systems for temperate regions (Hasegawa, 2003). The N response and absolute yield level of rice cultivar is affected by inherent soil N fertility, which is evaluated as the nitrogen taken up without N fertilizer. The nitrogen -1 uptake of tropical rice plants ranges from 35 to 95 kg ha 1 season- (IRRI, 1994), while in temperate regions it -1 -1 ranges from 32 to 91 kg ha (average of 68 kg ha ) (Toriyama, 2002). In the experiments, the average nitrogen uptake of super rice plants with SRI is 20.3% more than SRM, the average SPAD value of flag leaf at flowering with SRI is 12.3% more than SRM. Esfahani et al. (2008) demonstrated that there was a statistically significant (p < 0.01) relationship between leaf N concentration and chlorophyll meter (SPAD-502) readings. Therefore, the results suggest that nitrate and agrochemicals discharge from agriculture cause surface
water pollution, due at least in part to high rates of N fertilizers. Nitrates and agrochemicals can also be accumulated in groundwater stores. Conclusion It has already been shown that the N distribution in a crop is affected by plant density (Shiratsuchi et al., 2006; Schieving et al., 1992), and this affects crop performance. The constrained yields of super-rice in the SRM experiments reported here are probably related to decrease the source size in biomass and LAI at flowering stage, induced abiotic and biotic stresses, which are more likely to occur with continuous flooding than with intermittent irrigation. Also a factor in the SRM experiments was that there was no organic fertilizer input into their soils, which limited the N-holding capacity in SRM plots. The nitrogen uptake of super-rice in the SRM experiments was seen to be greatly affected by N rate and/or plant density. With SRI, one sees density having an inverse impact on crop performance, and all levels of N application have a greater impact on yield than under standard rice management (SRM). The SPAD value of flag leafs at flowering stage response to the above results. Similar evaluations to this research undertaking should be undertaken in a variety of agro-environments before drawing firm conclusions. But these data indicate consistently that for super-rice varieties, SRI gives superior results to SRM. Similar research should be conducted with other varieties and across a range of soil and other conditions. From this and other evaluations done at the China National Rice Research Institute, it appears SRI practices could have fairly wide application because they have positive effects on rice plant root development and on soil biological conditions, which will be reported and analyzed separately. ACKNOWLEDGMENTS This study had financial support from the Ministry of Agriculture and the Ministry of Science and Technology of the People’s Republic of China. The first author is grateful to Mr. Xingjun Lin, Dr. Liyong Cao and Ms. Yupin Zhang for their help in the experiments. The authors are thankful to anonymous reviewers for their valuable suggestions that have substantially improved the quality of the manuscript. REFERENCES Broadbent FE (1979). Mineralization of organic nitrogen in paddy soils. In: Nitrogen and Rice, International Rice Research Institute, Los Baños, Philippines 10(5): 118. Bouman BAM, Tuong TP (2001). Field water management to save water and increase its productivity in irrigated rice. Agric. Water
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Manage. 4(9): 11-30. Cho YS, Choe ZR (1999). Effect of Chinese milk vetch (Astragalus sinicus L.) cultivation during winter on rice yield and soil properties Korean J. Crop Sci. 4(4): 49–54. Cho YS. Choe ZR (1999). Effects of straw mulching and nitrogen fertilization on the growth of direct seeded rice in no-tillage rice/vetch cropping system. Korean J. Crop Sci. 4(4): 97–101. Counce PA, Moldenhauer KAK, Marx DB (1989). Rice yield and plant yield variability responses to equidistant spacing. Crop Sci. 2(9): 175179. Counce PA, Wells BR (1990). Rice plant population density effect on early-season nitrogen requirement. J. Prod. Agric. 3(3): 90-393. Esfahani M, Ali Abbasi HR, Rabiei B, Kavousi M (2008). Improvement of nitrogen management in rice paddy fields using chlorophyll meter (SPAD).Paddy Water Environ. 6(1): 81–188. Gravios KA, Helms RS (1992). Path analysis of rice yield and yield components as affected by seeding rate. Agron. J. 8(4): 1-4. Hasegawa H (2003). High-yielding rice cultivars perform best even at reduced nitrogen fertilizer rate. Crop Sci. 4(3): 921-926. IRRI (1994). Program Report. International Rice Research Institute, Los Baños, Philippines. Katsura K, Maed S, Horie T, Shiraiw T (2007). Analysis of yield attributes and crop physiological traits of Liangyoupeijiu, hybrid rice recently bred in China. Field Crops Res. 10(3): 170-177. Laulanié H (1993). Le système du riziculture intensive malgache. Tropicultura (Brussels) 11: 10-114. Liang YM, Lin XQ, Sun YF (2006). Effects of different crop management on dry matter accumulation and plant type characteristics of rice (Oryza sativa L). Acta Agriculture Zhejiangensis 1(8): 82-85. Lin XQ, Zhu DF, Zhou WJ (2003). Relationship between specific leaf weight and photosynthetic rate at panicle initiation stage in super hybrid rice. Chinese J. Rice Sci. 1(7): 281-283. Lin XQ, Zhou WJ, Zhu DF (2005). The photosynthetic rate and water use efficiency of leaves at different position at panicle initiation stage under the System of Rice Intensification (SRI). Chinese J. Rice Sci. 1(9): 200-206. Lin XQ, Zhou WJ, Zhu DF, Chen HZ, Zhang YP (2006). Nitrogen accumulation, remobilization and partitioning in rice (Oryza sativa L.) under an improved irrigation practice. Field Crops Res. 9(6): 448– 454. Lin XQ, Zhu DF, Lin XJ (2009). Studies of different managements of water and N fertilizer on the growth and root environment of hybrid rice (Zhongyou 218). J. Irrigation and Drainage 4(2):-31-236. Lu CG, Zou JS (2003). Comparative analysis on rice plant type of two super hybrids and Shanyou 63. Agricultural Sciences in China 2(5): 513-520. Murayama N (1979). The importance of nitrogen for rice production. In: Nitrogen and Rice. International Rice Research Institute, Los, Baños Philippines p. 5-23.
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Patrick JR WH, Mahapatra LC (1968). Transformation and availability to rice of nitrogen and phosphorus in waterlogged soils. Adv. Agron. 2(0): 323–359. Peng S, Buresh R, Huang JL, Yang JC, Zhong XH, Zou YB, Wang GH, Hu R, Shen JB (2004). Improving fertilizer-nitrogen use efficiency of irrigated rice: Progress of IRRI's RTOP Project in China. Paper for International Conference on Sustainable Rice Production, China National Rice Research Institute, Hangzhou, Oct. 1(5): 17. Shiratsuchi H, Yamagishi T, Ishii R (2006). Leaf nitrogen distribution to maximize the canopy photosynthesis in rice. Field Crops Res. 9(5): 291–304. Stoop WA, Uphoff N, Kassam A (2002). A review of agricultural research issues raised by the system of rice intensification (SRI) from Madagascar: Opportunities for improving farming systems for resource-poor farmers. Agric. Syst. 7(1): 249-274. Toriyama K (2002). Estimation of fertilizer nitrogen requirement for average rice yield in Japanese paddy fields. Soil Sci. Plant Nutr. 4(8): 293–300. Wu G, Wilson LT, McClung AM (1998).Contribution of rice tillers to dry matter accumulation and yield. Agron. J. 9(0): 317-323. Xie BH, Zheng XH, Zhou ZX, Gu JX, Zhu B, Chen X, Shi Y, Wang YY, Zhao Z, Liu C, Yao Z, Zhu J (2009). Effects of nitrogen fertilizer on CH4 emission from rice fields: multi-site field observations. Plant Soil,DOI 10.1007/s. 1110(4): 009-0020-3. Yan X (2008). PhD dissertation: Study on present status of chemical fertilizer application and high efficient utilization of nutrition in China (in Chinese), Chinese Academy of Agricultural Sciences, Beijing p. 64-78. Yuan LP (2000). Super hybrid rice. Chinese Rice Research Newsletter 8(1): 13-15. Yuan LP (2001). The system of rice intensification. Hybrid Rice in Chinese 16: 1-3, Yuan LP, Uphoff N, Fernandes E, Peng JM, Rafaralahy S, Rabenandrasana J (2002). A scientist’s perspective on experience with SRI in China for raising the yields of super hybrid rice. In:. (Eds.), Assessments of the System of Rice Intensification. Cornell International Institute for Food, Agriculture and Development, Ithaca, NY, http://ciifad.cornell.edu/sri/proc1/sri_06.pdf. pp. 23-25.
