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. 2014 Apr 30;9:e29015. doi: 10.4161/psb.29015

Physiological response of rice (Oryza sativa L.) genotypes to elevated nitrogen applied under field conditions

Hukum Singh 1, Amit Verma 2,*, Mohammad Wahid Ansari 3, Alok Shukla 1
PMCID: PMC4091589  PMID: 25763485

Abstract

Field experiment was conducted at G.B.P.U.A.T. Pantnagar, Uttarakhand, India in rainy season of 2008 and 2009 to study the impacts of increased nitrogen doses on growth dynamics, biomass partitioning, chaffy grain and nitrogen use efficiency in 4 rice genotypes viz., Vasumati, Tulsi, Kasturi and Krishna Hamsa. Four doses (N0, N50, N100 and N200 kg N ha−1) of nitrogen in the form of urea were applied in 3 split. Increased trend in growth dynamics during active tillering and flowering stage, and biomass partitioning at the time of active tillering and flowering stage was observed with respect to nitrogen doses. Chaffy grain number and chaffy grain weight per 5 panicles was significantly increased with enhancing nitrogen doses and was highest for Vasumati. Nitrogen use efficiency (NUE) was increased up to N100 kg N ha−1 and it was declined with rising nitrogen doses (N200 kg N ha−1). The highest values for NUE was achieved by rice genotype Krishna Hamsa whereas lowest by Vasumati. In addition to this, a significant correlation between nitrogen doses and growth dynamics, biomass partitioning and chaffy grain was observed. These findings suggest that growth dynamics, biomass partitioning, chaffy grain could be enhanced by the input of high rate of nitrogen fertilizer but not nitrogen use efficiency. Therefore, this study is useful to screen most N efficient genotypes which can be strongly suggested to rice growers to enhance crop yield irrespective of use of high dose of N fertilizers.

Keywords: Growth dynamics, nitrogen application, nitrogen use efficiency, plant productivity, rice genotypes

Introduction

Rice is one of the most important crops of the world and forms the staple diet of about 2.7 billion people and it needs to be produced 50% more than what is produced now by 2050 to cope with the growing demand.1 The doubling of agricultural food production worldwide over the past 4 decades has been associated with a 7-fold increase in the use of nitrogen fertilizers.2 To achieve better yield, farmers use to put elevated dosage of nitrogen fertilizers which generally support crop growth dynamics. However, regular use of heavy chemical fertilizers based on nitrogen supply may impair soil health, which may not sustain crop production even after using heavy dosage of the nitrogen fertilizers. The excessive use of nitrogen fertilizers resulted in decrease of physiological nitrogen use efficiency (NUE) and cause serious environmental pollution.3 One of the critical steps limiting the efficient use of nitrogen is the ability of plants to acquire it from applied fertilizer.4 Improving nitrogen use efficiency in the major cereals is critical for more sustainable nitrogen use in high input agriculture, but our understanding of the potential for nitrogen use efficiency improvement is limited by a scarcity of reliable on measurements.5 Nitrogen fertilizer applied in the form of urea significantly increases growth, yield and yield components of the rice crop and is the main nitrogen carrier worldwide in annual crop production and generally favored by the growers due to lower application cost than other nitrogenous sources.6 Therefore, it is essential to achieve efficient use of nitrogen in chemical fertilizers, through cultivation techniques and fertilizer management with high nitrogen use efficiency and reducing nitrogen inputs from farming to the environment.7 Evaluating the reaction of rice to diverse doses of nitrogen will aid in the development of high nitrogen use efficiency varieties, and the screening of appropriate genotypes for all cultivated condition. Numerous studies have investigated varietal variation in yield and Nitrogen use efficiency. Samonte et al.8 have pointed out that representative varietal variation in yield and nitrogen use efficiency was complex because rice yield was influenced by inherent factors such as the number of productive culms, grains per panicle and 1000 grain weight, in addition to plant management conditions. However, measuring genotypic differences in dry matter production and nitrogen use efficiency at the vegetative growth stage eliminates those additional variables affecting yield.9 Singh and Verma (2013)10 evaluated the genotypic variation among 5 rice genotypes at 4 nitrogen availability (0, 50, 100 and 200 kg N ha−1) in relations to grain yield, biological yield, panicle weight, primary and secondary branch, and recorded significant correlation between nitrogen doses and above discussed traits vice- versa. Nitrogen contributes to sink size by decreasing the number of degenerate spikelets and increasing the hull size and to grain filling by increasing the nitrogen content in leaves. During the grain filling period, a large amount of nitrogen is required but elevated N input decrease grain filling. The remobilized nitrogen from vegetative organs accounts for 70–90% of the total nitrogen.11 Nagegowda and Biradar12opined that site specific nutrient management approach had positive influence on available nutrients in the soil. Understanding the mechanisms regulating the processes of nitrogen uptake, assimilation, utilization efficiency and remobilization are crucial for the improvement of nitrogen use efficiency in crop plants. One important approach is to develop an understanding of the plant response to different nitrogen regimes and studying plants that show better growth under nitrogen limiting conditions.13 Studies on impacts of elevated nitrogen on growth dynamics, biomass partitioning, chaffy grain and nitrogen use efficiency are limited. Hence, the objective of this study was to investigate varietal differences in response to elevated doses of nitrogen fertilizer among 4 rice genotypes to provide essential information for the breeding of varieties that are suitable for cultivation with less application and reduced dose of N fertilizer for eco-friendly sustainable agriculture.

Results

Growth dynamics response to elevated nitrogen doses

The growth dynamics (plant height, number of tillers, number of leaves and leaf area index-LAI) varied significantly (P = 0.05) among elevated nitrogen rates (Table 1). The plant height was measured for growth analysis under different treatments at active tillering and flowering stage and significantly increased with increasing doses of nitrogen fertilizer among all genotypes. The plants treated with 200 kg N ha−1 of showed better growth response in terms of plant height compared with N0, N50 and N100. The highest plant height at active tillering stage was measured for Vasumati even as lowest for Tulsi followed by Kasturi and Krishna Hamsa.

Table 1. Effect of different N levels on plant height (cm) at active tillering and at flowering in rice genotypes.

Genotype Plant height (cm)
Active tillering stage Flowering stage
N0 N50 N100 N200 Mean N0 N50 N100 N200 Mean
Vasumati 53.67 57.33 63.67 72.67 61.84 118.87 132.87 145.73 161.50 139.74
Kasturi 51.00 58.00 60.67 65.67 58.84 118.37 128.30 133.33 145.17 131.29
Tulsi 48.67 60.67 65.67 71.33 61.59 91.40 103.30 108.50 113.60 104.20
Krishna Hamsa 49.33 53.67 57.33 61.67 55.50 92.73 107.57 109.80 117.32 106.86
Mean 50.20 58.07 62.93 68.67 - 106.59 120.98 127.38 138.22 -
Source Treatment (T) Variety (V) T × V Treatment (T) Variety (V) T × V
S.Em. ± 0.11 0.16 0.33 0.20 0.16 0.32
C.D.(P = 0.05) 0.39 0.48 0.97 0.70 0.46 0.92
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Same improved pattern of plant height was recorded during flowering stage in all genotypes. The T x V interaction during both stages was found to be statistically significant for all varieties at N0, N50, N100 and N200 levels. A significant effect of nitrogen was observed on number of tillers at 2 stages. The Table 2 shows the effect of different N levels on the tiller number at active tillering and flowering storage. The maximum tillers number per hill during active tillering stage was reported for Krishna Hamsa while at flowering stage Vasumati had the maximum. The number of leaves increased with application of N fertilizer. The maximum number of leaves during active tillering was found in rice genotype Krishna Hamsa and the minimum in rice genotype Kasturi. Leaf number gradually increased from active tillering to reproductive stage (Table 3). As the N levels increases the leaf area index was also increased gradually from N0 to N200 level and it was highest at N200 level for all the 5 genotypes. Maximum leaf area index was found to be for rice genotype Krishna Hamsa followed by Vasumati, Kasturi and Tulsi (Table 4).

Table 2. Effect of different N levels on number of tillers at active tillering and flowering stage of 5 rice genotypes.

Genotype Number of tillers
Active tillering stage Flowering stage
N0 N50 N100 N200 Mean N0 N50 N100 N200 Mean
Vasumati 5.00 6.33 6.33 7.33 6.25 6.00 7.33 8.33 11.67 8.33
Kasturi 3.33 5.00 5.33 6.33 5.00 5.00 6.67 7.00 8.33 6.75
Tulsi 4.33 5.33 6.33 7.67 5.92 5.33 7.00 7.67 9.00 7.25
Krishna Hamsa 4.67 6.00 7.00 9.00 6.67 6.00 7.33 8.33 9.67 7.83
Mean 4.27 5.73 6.33 7.67 - 5.53 7.07 8.13 10.20 -
Source Treatment (T) Variety (V) T × V Treatment (T) Variety (V) T × V
S.Em. ± 0.076 0.127 0.256 0.086 0.123 0.427
C.D.(P = 0.05) 0.266 0.368 0.736 0.297 0.356 0.712
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Table 3. Effect of different N levels on number of leaves at active tillering and flowering stage of 5 rice genotypes.

Genotype Number of leaves
Active tillering stage Flowering stage
N0 N50 N100 N200 Mean N0 N50 N100 N200 Mean
Vasumati 27.33 27.67 40.33 47.33 35.67 17.67 25.33 29.33 36.33 27.17
Kasturi 24.00 24.33 35.33 38.33 30.50 14.67 21.33 24.33 37.33 24.42
Tulsi 32.67 32.67 39.33 42.33 36.75 21.67 28.33 32.67 37.33 30.00
Krishna Hamsa 33.00 32.67 43.67 47.33 39.17 18.33 24.67 29.33 33.33 26.42
Mean 29.87 29.93 40.60 44.53 - 18.33 26.20 30.60 39.40 -
Source Treatment (T) Variety (V) T × V Treatment (T) Variety (V) T × V
S.Em. ± 0.14 0.16 0.33 0.18 0.13 0.26
C.D. (P = 0.05) 0.48 0.48 0.96 0.64 0.39 0.78
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Table 4. Effect of different N levels on leaf area index (LAI) at flowering stage of 5 rice genotypes.

Genotype Leaf Area Index (LAI) at flowering stage
N0 N50 N100 N200 Mean
Vasumati 4.20 4.79 5.52 6.55 5.27
Kasturi 4.24 4.61 5.12 6.25 5.06
Tulsi 4.01 4.52 5.19 6.21 4.98
Krishna Hamsa 4.38 5.41 5.58 6.90 5.57
Mean 4.19 4.77 5.41 6.64 -
Source Treatment (T) Variety (V) T × V
S.Em. ± 0.074 0.083 0.163
C.D. (P = 0.05) 0.257 0.241 0.482
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Impacts of elevated nitrogen on biomass partitioning

The impacts of elevated nitrogen rates on biomass partitioning in the form of culm weight, leaf weight, shoots weight and total dry matter was investigated. Culm weight of 4 rice genotypes at active tillering, panicle initiation and flowering stage is presented in Table 5. The culms weight (gm−2) improved with enhancing doses of nitrogen fertilizer throughout plant life and it was more calculated during flowering stage followed by panicle initiation and active tillering stage. During active tillering, the mean value of culms weight was highest for rice genotypes Tulsi while lowest for Kasturi. The maximum culms weight during panicle initiation was recorded for Vasumati followed by Tulsi, Kasturi and Krishna Hamsa. Krishna Hamsa got utmost mean value of culms weight during flowering time whereas Vasumati lowest at same moment. The increased trends in culms weight among 4 rice genotype throughout all stage recorded as Tulsi followed by Vasumati and Krishna Hamsa.

Table 5. Effect of different N levels on culm weight at active tillering, panicle initiation and flowering stage.

Genotype Culm weight (g m−2)
Active tillering stage Panicle initiation stage Flowering stage
N0 N50 N100 N200 Mean N0 N50 N100 N200 Mean N0 N50 N100 N200 Mean
Vasumati 233.33 281.17 441.67 535.33 372.88 688.33 446.00 625.67 830.00 647.50 520.00 543.33 627.33 580.00 567.67
Kasturi 245.00 323.33 313.33 366.67 312.08 623.37 548.33 496.33 649.00 579.26 365.67 593.33 596.67 538.33 523.50
Tulsi 284.17 365.83 481.67 482.50 403.54 576.33 582.33 548.00 762.33 617.25 262.33 370.00 412.00 495.67 385.00
Krishna Hamsa 340.00 299.17 311.17 415.00 341.34 503.33 562.33 317.67 791.33 543.67 366.67 650.67 547.67 739.67 576.17
Mean 263.83 343.90 408.07 454.23 - 549.41 518.86 556.87 770.00 - 388.00 579.60 618.20 622.93 -
Source Treatment (T) Variety (V) T × V Treatment (T) Variety (V) T × V Treatment (T) Variety (V) T × V
S.Em. ± 14.01 12.29 30.50 25.02 12.07 29.96 19.31 14.92 29.39
C.D. (P = 0.05) 48.43 35.41 70.83 86.48 34.79 69.5 66.74 42.98 85.97
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The leaves weight increased with increase in doses of N fertilizers at active tillering to panicle initiation but the leaves weight decreased from panicle initiation to flowering stage. Increased pattern in terms of leaf weight (g m−2) with increasing fertigation was observed during all 3 stages among 4 rice geotypes. The leaves weight followed similar pattern of culms weight. The genotype Tulsi had highest leaves weight during active tittering while lowest for Kasturi and Krishna Hamsa and Vasumati got more or less similar value for the leaves weight. The utmost leaves weight for Vasumati considered during panicle initiation although lowest in Krishna Hamsa. During flowering stage, Krishna Hamsa recorded highest culms weight followed by Vasumati, Kasturi and Tulsi. The leaves weight of 4 rice genotypes at the time of active tillering, panicle initiation and flowering stage is given in Table 6. It is interesting to note that the total dry matter accumulation during active tillering and flowering stages was also increased due to increased doses of nitrogen fertilizer among all genotypes. All 4 rice genotypes indicated varietal difference in accumulation of total dry matter at all nitrogen levels and highest total dry matter was determined for genotype Tulsi whereas lowest for Kasturi during active tillering stage. The rice genotype Vasumati had extreme mean value of total dry matter even as Tulsi showed least. A significant variation in terms of dry matter accumulation was observed for all genotypes and all doses of applied nitrogen fertilizer (Table 7). In addition to this, shoot weight was decided (after separation of grains from the panicles) in kg m−2 after harvesting the crops. The maximum shoot weight was observed for Krishna Hamsa followed by Vasumati, Kasturi and Tulsi. The rice genotypes Kasturi and Tulsi accumulated highest shoot weight at N50 compared with N200 nitrogen doses. For Vasumati and Krishna Hamsa, the shoot weight was enhanced with rising doses of nitrogen fertilizer (Table 8).

Table 6. Effect of different N levels on leaf weight at active tillering, Panicle initiation and flowering stage.

Genotype Leaf weight (g m−2)
Active tillering stage Panicle initiation stage Flowering stage
N0 N50 N100 N200 Mean N0 N50 N100 N200 Mean N0 N50 N100 N200 Mean
Vasumati 134.17 172.67 229.17 346.17 220.55 352.33 220.00 299.00 486.67 339.50 196.67 256.67 316.00 319.00 272.09
Kasturi 108.33 210.00 225.00 256.67 200.00 433.33 237.33 239.33 383.00 323.25 165.33 299.67 292.67 278.67 259.09
Tulsi 163.33 271.67 315.00 381.67 282.92 278.33 285.00 237.33 408.67 302.33 121.00 216.00 199.33 244.00 195.08
Krishna Hamsa 211.67 186.67 225.00 260.00 220.84 277.00 319.00 162.67 434.33 298.25 129.00 361.67 304.00 317.00 277.92
Mean 145.17 225.20 266.83 316.24 - 305.13 264.80 276.13 438.87 - 148.47 283.54 323.40 309.20 -
Source Treatment (T) Variety (V) T × V Treatment (T) Variety (V) T × V Treatment (T) Variety (V) T × V
S.Em. ± 11.45 11.08 22.23 15.48 10.25 20.57 7.31 10.81 21.63
C.D. (P = 0.05) 39.57 31.92 63.85 53.51 29.54 59.08 25.27 31.14 62.28
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Table 7. Effect of different N levels on total dry matter in rice genotypes (Mean of 2 y).

Genotype Total dry matter (g m−2)
Active tillering stage At flowering
N0 N50 N100 N200 Mean N0 N50 N100 N200 Mean
Vasumati 367.00 453.70 516.83 881.32 554.71 805.73 878.30 1020.83 987.00 922.97
Kasturi 353.77 553.76 387.39 623.60 479.63 591.30 965.83 951.47 908.00 854.15
Tulsi 448.08 637.50 637.50 864.33 646.85 453.80 667.00 675.67 824.67 655.29
Krishna Hamsa 551.83 486.23 485.50 676.00 549.89 575.93 1111.47 646.83 1139.00 868.31
Mean 409.20 575.40 552.54 770.64 - 611.29 949.87 971.16 1014.71 -
Source Treatment (T) Variety (V) T × V Treatment (T) Variety (V) T × V
S.Em. ± 15.02 19.38 38.88 27.14 29.92 60.03
CD(P = 0.05) 51.90 55.83 111.67 93.81 86.20 172.41
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Table 8. Effect of different N levels on shoot weight after harvesting (Mean of 2 y).

Genotype Shoot weight (kg m−2) after harvesting
N0 N50 N100 N200 Mean
Vasumati 0.633 1.050 1.100 1.300 1.021
Kasturi 0.642 1.185 1.098 1.142 1.017
Tulsi 0.483 0.900 0.758 0.887 0.757
Krishna Hamsa 0.692 1.267 1.167 1.333 1.115
Mean 0.621 1.147 1.153 1.291 -
Source Treatment (T) Variety (V) T × V
S.Em. ± 0.037 0.043 0.088
C.D. (P = 0.05) 0.128 0.126 0.252
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Elevated nitrogen relation to chaffy grain and chaffy grain weight

Number of chaffy grains or number of unfilled or sterile spikelets per 5 panicles was randomly chosen in each plant and counted and presented in Table 9. The maximum weight of unfilled grain was weighted to be for rice genotype Vasumati at all nitrogen levels compared with other genotypes and nitrogen doses. The Kasturi got lower limit of chaffy grains weight per 5 panicles. In adding, the chaffy grains per 5 panicles were highest counted for Vasumati whereas lowest for Kasturi. The N50 and N200 nitrogen rates showed maximum number of chaffy grains for most of the genotypes.

Table 9. Effect of different N levels on chaffy weight and chaffy number per 5 panicles after harvesting.

Genotype Chaffy weight/5 panicles after harvesting (g) Chaffy number/5 panicles after
harvesting
N0 N50 N100 N200 Mean N0 N50 N100 N200 Mean
Vasumati 2.25 2.92 1.88 3.18 2.56 207.33 268.33 171.67 286.67 233.50
Kasturi 2.18 1.55 1.75 1.65 1.78 191.67 131.67 156.67 133.33 153.34
Tulsi 1.71 2.03 1.85 1.80 1.85 140.67 182.00 158.33 160.00 160.25
Krishna Hamsa 1.65 2.50 1.63 2.83 2.15 153.33 233.33 140.00 259.00 196.42
Mean 1.95 2.27 1.91 2.36 - 172.60 207.07 170.33 209.13 -
Source Treatment (T) Variety (V) T × V Treatment (T) Variety (V) T × V
S.Em. ± 0.060 0.056 0.113 8.12 10.15 20.37
C.D. (P = 0.05) 0.209 0.163 0.326 28.08 29.25 58.51
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Nitrogen use efficiency (NUE)

The results showed that the nitrogen use efficiency increased with increasing N levels up to N100 level. Further, increase in N levels decreased the nitrogen use efficiency. It is due to that, at higher concentration of N the absorption exceeds the utilization. The most nitrogen efficient genotype was found Krishna Hamsa and the least efficient was Kasturi. But, in case of Vasumati and Kasturi, no significant difference was observed (Table 10).

Table 10. Effect of different N levels on nitrogen use efficiency (NUE) of different rice genotypes (Mean of 2 y).

Genotype Nitrogen use efficiency
N0 N50 N100 N200 Mean
Vasumati 21.13 22.15 19.91 19.43 20.66
Kasturi 16.94 23.63 20.04 19.64 20.06
Tulsi 25.31 30.55 24.93 25.18 26.49
Krishna Hamsa 25.27 44.26 34.03 33.65 34.30
Mean 23.40 38.17 31.08 27.45 -
Source Treatment (T) Variety (V) T × V
S.Em. ± 0.49 0.39 0.79
C.D. (P = 0.05) 1.70 1.14 2.29
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Discussion

The increased plant height with increasing rate of N fertilizers was due to enhanced rate of translocation of nitrogen from culms to leaves and leads to the production of photosynthates, which enhance the translocation of nutrients for developing panicle. Similar results were obtained by Somasundaram et al.14 when levels of nitrogen were ranged from 0–150 kg N/ha, with maximum plant height at N150 for variety SSRC 91216 and minimum at N0. Rahaman15 also observed maximum plant height for rice variety Taroari Basmati at N100 and the minimum at N200 level. Similar results were also reported earlier by Chaturvedi.16 More number of tillers in experiment might be due to the more availability of nitrogen, which played a vital role in cell division. Similarly it was reported that the maximum number of tillers were at N200 level and the minimum at N0 level.17 Number of leaves per hill enhanced simultaneously nitrogen doses and this might be due to adequate N nutrition in vegetative stage, which results in better root development and increased absorption of nitrogen. Similar results were reported earlier with increase in number of green leaves with reported to different doses of N fertilizer.18 The more leaf area index at higher level of N is due to increased translocation of N to the leaves. Main effect of N fertilizers is to increase the rate of leaf expansion, leading to increased interception of daily solar radiation by the canopy and so increased dry matter production. Similarly, the increase in LAI with increased rate of N fertilizers was also reported by Somasundaram et al.14 They found that leaf area index at N0 treatment was 1.0 and at N150 it was increased up to 4.50. At higher N level the large N uptake resulted in high leaf area, which causes loss of carbohydrates through dark respiration. Some medium duration varieties have limited vegetative growth and prevented the excessive production of vegetative biomass.19

The culm weight was significantly increased with elevating doses of nitrogen fertilizer. The rice genotypes viz., Tulsi, Vasumati and Krishna Hamsa revealed maximum culm weight, which reduced to minimum in Kasturi, Krishna Hamsa and Tulsi genotypes under condition of active tillering, panicle initiation and flowering stage.20 The enhancing culm weight in all genotypes through applying increased doses of nitrogen fertilizers might be due to greater total N uptake by high yielding rice genotypes shoots than conventional genotypes, especially from transplanting to tillering and from panicle emergence to grain filling stages. High yielder rice takes up about 15–20% of the total amount of N accumulated in the plant after heading and responds well to late application of N at flowering. In the same studies, N uptake after heading of conventional varieties was only 6–7% of total N uptake.20 Nitrogen fertilizer application significantly increased leaf weight.15 Similar findings on accumulation of leaf weight were observed by Yang.19 In addition, nitrogen fertilizer application significantly increased green leaves per m2 and leaf weight (g/m2).17 Nitrogen deficiency leads to reduced growth and a decrease in biomass. Stem growth rates and other developmental processes like leaf addition and leaf expansion rates decrease due to N scarcity.21,22

The total dry matter production increased from active tillering to flowering among 4 rice genotypes. The nitrogen absorbed during flowering stage is converted to photosynthates and the rate of nutrient translocation from source to sink and dry matter accumulation is highest during this phase. The N absorbed during this stage contributes to spikelets production and grain filling. The dry matter production increased with increasing N levels and for the same N application range, the N response of the late duration varieties for dry matter production was greater than that of medium duration varieties.19 Nitrogen is the indispensable nutrient to rice production and its uptake is affected by variety of characteristics as soil condition, split application of nitrogen fertilizer, doses of nitrogen, timing of application and environmental factor. Grain yield, number of grains per panicle, number of tillers, plant height, length of flag leaf total dry matter and shoot dry matter, 1000 grain weight and harvest index have been increased by nitrogen applications in field conditions as well as pot conditions.23-25 Nitrogen leads to dry matter accumulation in leaf sheaths and culm during the pre-heading stage and in grain during grain filling stage as a component of photosynthesis.

Nitrogen contributes to sink size by decreasing the number of degenerate spikelets and increasing the hull size and to grain filling by increasing the nitrogen content in leaves. During the grain filling period, a large amount of nitrogen is required.11 During grain filling the ability of a plant to remobilize leaf- stored N is an important factor for NUE in crops, and has been strongly implicated in quantitative trait loci (QTLs) studies with cereals.26 Number of chaffy grains or unfilled or sterile spikelets increased with excess application of nitrogen and show relatively higher response to N fertilization as compared with optimum N level.26 N application that increase plant N before heading is highly effective in maximizing spikelet production among genotypes and filled grains.27 It was reported, that nitrogen use efficiency was increased from N45 (20.00), up to N90 (31.00) but further increase in N levels decreased nitrogen use efficiency as N135 (29.00) and N180 (19.00). Nitrogen use efficiency is a genotypic parameter. The NUE values ranged from 35.6–51.6 (kg grain/kg N absorbed) for different genotypes.8 According to Yaduvanshi28 an increase in doses of N fertilizer rates from 60 to 120 and 180 kg N/ha decreased NUE by 7 and 27% but the difference between 60 kg N 120 kg N was not significant. It was also observed that the excessive use of nitrogen fertilizers resulted in decrease of physiological nitrogen-use efficiency and cause serious environmental pollution.3The current average nitrogen use efficiency in the field was approximately 33% and substantial proportion of the remaining 67% was lost into the environment, especially in the intensively cropped areas.29 Additionally, physiological marker study for resourceful rice genotypes on the basis of correlation exists between guttation fluid leaked by leaf tip and nitrogen use efficiency and productivity among tested KRH-2- hybrid, Kasturi- aromatic, Krishna Hamsa, Tulsi and Vasumati- high yielding genotypes genotypes under 0, 50, 100 and 200 kg ha−1 nitrogen revealed the positive correlation.30

Conclusions

Overall, present study found that there are wide variations in physiological as well as growth dynamics, biomass partitioning, chaffy grain number and weight as well as nitrogen use efficiency among genotypes under different nitrogen treatment conditions. The Krishna Hamsa recorded as high nitrogen efficient rice genotype among genotypes. The important point is to conclude here that increased dose of nitrogen fertilizer could be able to enhance growth dynamics and biomass partitioning of rice plant but not nitrogen use efficiency. In addition, such studies could be used for selection of more nitrogen efficient rice genotypes for minimizing environmental problems caused by excessive use of nitrogenous fertilizers on the basis of discussed traits. The recommendation for application of nitrogen fertilizer to rice grower could be made for cultivating rice will be useful and favor to minimizing negative impacts of nitrogen on biotic component of the crop ecosystem.

Materials and methods

Study area

The field experiment was performed at Dr. NE Borlaug’s Crop Research Center, Department of Plant Physiology, GB Pant University of Agriculture and Technology, Pantnagar, Uttarakhand, India during kharif seasons of 2008 and 2009. Geographically, the site lies in Tarai plains about 30 km southwards on foothills of Shivalik range of the Himalayas at 29° N latitude, 79°29′ E longitude and at an altitude of 243.8 msl. In Tarai region, the climate is humid and sub-tropical with hot summers to cool winters. Monsoon showers here in the mid of June up to the end of September.

Experimental details

The seeds of 4 rice cultivars, viz. Kasturi, Krishna Hamsa, Tulsi and Vasumati were supplied by the Directorate of Rice Research (DRR), Hyderabad. The field experiment was laid out in a split plot design with 3 replicates. Some basic properties of soil from experimental site are shown in Table 11. The plot size for each treatment was 4 x 4 min. Twenty-five-day-old seedlings were transplanted in the puddled soil with 15 cm standing water with 20 x 10 cm plant spacing. Nitrogen (100 kg ha−1), phosphorus (45 kg ha−1) and potassium (60 kg ha−1) were applied in field as basal dose in the form of urea, single super phosphate and muriate of potash respectively. The N was applied @ 0, 50, 100 and 200 kg ha−1 in the form of urea. Nitrogen was applied in 3 splits, viz. 50% of the total N at 15 d after transplanting, 25% at panicle initiation and the remaining 25% at flowering.

Table 11. Some basic properties of soil from experimental site.

Soil properties Values
Soil color Dark grayish brown to dark gray
Texture Loam to silty clay loam
Soil water (dry mass percentage of water) 13.99 to 19.78 (June to September)
Temperature of soil 26 to 32 °C (June to September)
Bulk Densities 1.10 to 1.46 mg m–3 (June to September)
Hydraulic conductivity 317 to 407 mm h−1
Infiltration rate 269 to 624 mm h−1
pH 6.74 to 8.05
EC 0.33 to 0.60 dSm−1
CaCO3 0.42 to 0.87%
CEC 8.1 to 18.22 meq 100 g−1 soil
Organic carbon 0.39 to 1.61%
Zn 0.17 to 2.11 mg kg−1
Cu 0.64 to 2.49 mg kg−1
Mn 1.31 to 45.69 mg kg−1
Fe 3.09 to 21.41 mg kg−1
Total N 0.14%
Available P 44.28 ppm
Available K 280.59 kg ha−1
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Growth dynamics

Observations on growth dynamics was made at the time of active tillering and flowering stage. The parameters to assess growth dynamics such as plant height (cm), number of tillers per hill, number of leaves per hill and leaf area index (LAI) (cm) of 3 randomly selected hills was recorded from each plot at active tillering and flowering stages. The leaf area index (LAI) was calculated by dividing the leaf area per 4 hills by the field area occupied by the 4 hills.29

Biomass partitioning

Biomass portioning in the form of culm weight, leaf weight, total dry and shoots weight matter was calculated at each nitrogen level for all genotypes. The culm and leaf weight (g m−2) was then calculated during active tillering, panicle initiation and flowering stage. The total dry matter (g m−2) was considered at the time of active tillering and flowering stage by uprooting the complete plant and then placing the plant samples in the oven at 65 °C for 3 days whereas shoot weight (kg m−1) after harvesting of the crop. For estimating shoot weight, weight of dried plant with removed roots and panicles was taken.

Chaffy grain number, chaffy grain weight and nitrogen use efficiency

Chaffy grain number and weight per 5 panicles was counted as per Islam et al.31 Five panicles were collected from each of the treatment and grains were separated from primary and secondary branches. The separated grains were poured in NaCl solution by dissolving 315 g of NaCl in one liter distilled water (1.20 specific gravity), which stirred and counted the grains that are sunk. These are high density grains having more than 1.20 specific gravity. The floating grains of the above were transferred to the 1.06 specific gravity NaCl solution (by dissolving 90 g NaCl in one liter distilled water) and the repeated the process of counting. Remaining floating spikelets were chaffy grains that sunk were low density grains of 1.06 (specific gravity). The nitrogen use efficiency was calculated as the ratio of the grain yield (kg) to the N applied (kg).8

Statistical analysis

The data presented in the tables are the mean values for 2 years (2008 and 2009) and the statistical verifications were performed for the analysis of variance (ANOVA), standard error of means (SEm) and critical difference (CD) on the pooled data.32

Disclosure of Potential Conflicts of Interest

No potential conflicts of interest were disclosed.

Acknowledgments

The author is grateful to Joint Director of Dr. NE Borlaug Crop Research Centre, GB Pant University of Agriculture and Technology, Pantnagar, Uttarakhand, India for the permission accorded to conduct the field experiments.

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