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Influence of nitrogen supply on the area, mass and relative growth rate of maize leaf
Section 5. Agricultural sciences
Oroka Frank Oke, Delta State University, Asaba Campus, Nigeria PhD in Crop Science, Department of Agronomy, E-mail: [email protected]
Influence of nitrogen supply on the area, mass and relative growth rate of maize leaf
Abstract: The study was aimed at assessing the effect of nitrogen application on the area, biomass and relative growth rate of maize leaf using a non-destructive method. Results showed high nitrogen supply, leaf area and leaf biomass.
Keywords: maize, leaf area, leaf biomass, nitrogen supply.
Introduction
Cereals are generally nitrogen demanding crops, thus adequate supply of nitrogen is needed for protein-based metabolic processes necessary for vegetative growth and subsequent reproductive development
and crop yield. The leaf is the main organ of photo-assimilate in crops. Increasing nitrogen supply has been shown to result in increased vegetative growth and photosynthesis in maize. This has been confirmed in related studies (13, 64-73; 2, 171-189]. This is because larger supply of nitrogen enhances apical growth, resulting in increase rate of cell division or on cell size, increased size of the mature leaf to such an extent that maintenance of the N concentration and higher photosynthetic capacity per unit leaf area is achieved [14, 642-650]. Limitation of nitrogen (N) directly reduces the rate of individual leaf area, total leaf area, new leaf area development, and promotes leaf senescence and leaf ageing. Reduced leaf area results in reduced area for light interception and leaf photosynthesis, and decreasing canopy carbon assimilation [4, 1379-1385].
Most studies on leaf growth and leaf biomass use the destructive sampling method. This study was therefore aimed at assessing the effect of nitrogen application on the leaf area, biomass and growth rate of the maize leaf using the non-destructive method.
Materials and Methods
A pot experiment was conducted in 2013 in the Teaching and Research Farm of Delta State University, Abraka (latitude 5° 46’N and longitude 6° 5’E), Nigeria between April and July. Variety used was TZSR-Y. Seeds were sown in 10 litre capacity pots filled with top soil.
Properties of top soil used were: 785g kg-1 sand, 93 gkg-1 silt, 122g kg-1 clay; pH (in water) 5.5; 0.65 g kg-1; total nitrogen and 46.8g kg-1 organic matter. Each pot was initially planted with two seeds and later thinned to one. Crops were regularly watered and placed were there was no shading. Nitrogen fertilizer used was urea (46%).
Treatments consist of five nitrogen rates (0, 0.58, 1.16, 1.74 and 2.32 g per pot), equivalent to 0, 35, 70, 105 and 140 kgN ha-1 on the field. The five treatments were replicated three times in a randomized complete block design. Data collected was only on leaf length and leaf width, which as done at 3, 6, 9 and 12 weeks after planting (WAP).
The leaf area (LA), leaf fresh weight (LFW) and leaf dry weight (LDW) were estimated with a non-destructive method derived from the length (L) and width (W) of the maize leaf using the formula developed by [8, 19-26] while the relative leaf growth rate (RLGR) of maize leaf was estimated using the formula by [6, 1-161].
Measured parameters (leaf length and leaf width) and derived parameters such as leaf area, leaf fresh weight and leaf dry weight and relative leaf growth rate were subjected to analysis of variance appropriate for randomized complete block design. Mean separation was done using the least significant difference (LSD) at 5% probability level.
Results and Discussion Leaf dimensions and Leaf Area High nitrogen supply did not significantly affect leaf width, except at 3WAP but significantly increased leaf length throughout the experimental period (Table 1).This is corroborated by earlier reports of [9, 1-16]
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Section 5. Agricultural sciences
that nitrogen supply increase leaf expansion. Nitrogen application significantly affected leaf area (P<0.05) of maize (Table 2). Within the first 3WAP, leaf area increased with rate of nitrogen supply. However from 6 WAP, plants that received equivalent of 70kgN ha-1 showed highest leaf area. N applications beyond 70kgN ha-1 did not show any increase in leaf area of the maize plants. Other researchers [12, 199-206; 10, 81-89] have demonstrated that leaf growth is
highly responsive to nitrogen supply largely due to cell production and cell expansion. Shortage of nitrogen in the earlier stages of leaf development when cell division is still taking place will result in greater reduction in final leaf area as shown in plants without nitrogen application. At early growth stage, a decrease in the quantity of cells produced could result in drastic reduction in the final leaf size have been reported [10, 81-89].
Table 1. - Length and width of maize leaf
N rate (g pot1) 3WAP 6WAP 9WAP 12WAP
L W L W L W L W
0 35.0c 4.2b 85.6b 9.2a 95.2b 10.3a 96.2b 10.3a
0.58 40.0b 4.5ab 98.6a 9.5a 103.1ab 10.0a 105.2ab 10.3a
1.16 50.7ab 5.2ab 100.7a 10.0a 110.4a 10.7a 112.1a 11.0a
1.74 60.1a 6.1a 92.1ab 10.8a 96.6ab 10.5a 98.3b 10.5a
2.32 60.8a 6.3a 95.3ab 10.8a 95.8b 10.8a 96.7b 10.9a
LSD (5%) 10.8 1.9 11.4 1.6 14.3 1.0 13.9 1.2
Means followed by the same letter on the same row are not significantly different at LSD (5%)
Table 2. - Leaf area (cm2) of maize as influenced by nitrogen supply
N rate (g pot1) Weeks after planting
3 6 9 12
0 100.67d 591.82c 742.56d 752.20d
0.58 125.90c 723.57b 798.63b 839.35b
1.16 190.64b 775.88a 920.48a 960.45a
1.74 269.29a 742.26b 768.55c 786.55cd
2.32 280.84a 774.18a 779.15bc 794.50c
LSD (5%) 12.81 28.17 25.89 37.61
Means followed by the same letter on the same row are not significantly different at LSD (5%)
Leaf growth rate
Table 3 shows relative growth rate of maize leaf. The relative growth rate of maize leaf was significantly affected by nitrogen supply at 6WAP to 9WAP. The results did not show any consistent trend of relative leaf growth rate of maize with rate of nitrogen application. The rate of leaf growth from 3WAP to 6WAP was more pronounced, was less from 6WAP to 9WAP and more
decline was observed from 9WAP to 12WAP. This trend of leaf growth rate follows the sigmoid curve, indicating exponential leaf growth rate during early development and decline in crop growth rate during the final development phase associated with decline in green leaf area, due to leaf senescence and leaf ageing. Similar results has been reported in earlier studies [1, 171-189; 4, 1379-1385; 4, 656-665].
Table 3. - Relative leaf growth rate (cm2 cm2 day1) of maize as influenced by nitrogen supply
N rate (g pot1) Weeks after planting
3-6 6-9 9-12
0 0.0395a 0.00960a 0.00061a
0.58 0.0393a 0.00448a 0.00233a
1.16 0.0359a 0.00748a 0.00207a
1.74 0.0303a 0.00163b 0.00101a
2.32 0.0303a 0.00030c 0.00092a
LSD (5%) 0.0110 0.0072 0.0019
Means followed by the same letter on the same row are not significantly different at LSD (5%)
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Influence of nitrogen supply on the area, mass and relative growth rate of maize leaf
Leaf biomass
Nitrogen application significantly (P<0.05)
influenced fresh and dry weights of maize leaf in this study (Tables 4 and 5). Low nitrogen supply reduced leaf biomass accumulation in this study. This result is confirmed by earlier studies [4, 1379-1385]. At 3 WAP nitrogen supply increased leaf fresh weight by 28.5, 102.3, 193.9 and 206.5% at 35, 70, 105 and 140 kgN ha-1 respectively while leaf dry weight was increased by 33.3, 166.7, 309.5, 338.1% respectively at same application rate relative to the control. When compared with the control, at 12 WAP, application ofnitrogen increased leaf fresh weight
by 13.5, 31.1, 4.8 and 5.6% at 35, 70, 105 and 140 kgN ha-1 respectively while same nitrogen supply increased leaf dry weight by 11.0, 37.0, 6.7 and 13.0% respectively. The observed reduction in rate of biomass accumulation at the later growth stage is in consonance with the findings of other researchers [8, 19-26; 3, 519-526; 4, 13791385] who noted that the photosynthetic capacity of a leaf increases to a maximum at or before full leafexpansion, followed by a linear decrease with time. Lower rates of photosynthesis under conditions of nitrogen limitation have been attributed to decrease in chlorophyll content and Rubisco activity [11, 627-634].
Table 4. - Leaf fresh weight (g leaf-1) of maize as influenced by nitrogen supply
N rate (g pot1) Weeks after planting
3 6 9 12
0 2.14b 14.59b 18.63b 18.91b
0.58 2.75b 18.31a 20.56ab 21.46ab
1.16 4.33ab 19.68a 23.72a 24.80a
1.74 6.29a 18.46a 19.33b 19.81b
2.32 6.56a 19.40a 19.55b 19.96b
LSD (5%) 3.01 2.88 3.17 3.53
Means followed by the same letter on the same row are not significantly different at LSD (5%)
Table 5. - Leaf dry weight (g leaf-1) of maize as influenced by nitrogen supply
N rate (g pot1) Weeks after planting
3 6 9 12
0 0.21b 3.07c 4.39b 4.45b
0.58 0.28b 3.87b 4.53b 4.94b
1.16 0.56ab 4.41a 5.65a 6.10a
1.74 0.86a 4.66a 4.65b 4.75b
2.32 0.92a 4.88a 4.88ab 5.03b
LSD (5%) 0.38 0.78 0.85 0.77
Means followed by the same letter on the same row are not significantly different at LSD (5%)
Conclusion
The results of this study have shown increased leaf dimensions, resulting in increased leaf area with improved nitrogen supply. Shortage of nitrogen significantly reduced leafarea and leafbiomass, although
leaf growth rate showed no consistent trend with N supply. The study concludes that sufficient nitrogen supply is needed for the leaf (the photosynthetic organ) to effectively increase in size at a good rate and accumulate biomass.
References:
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Section 5. Agricultural sciences
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