Application of Nitrogen and Silicon Rates on Morphological and Chemical Lodging Related Characteristics in Rice ( Oryza sativa L . ) at North of Iran

Rice-based irrigated lowlands are the major cropping system in north of Iran. This experiment was carried out in split plot in basis of randomized complete block design with three replications at north of Iran in 2010. Main plot was nitrogen rates including (0, 50, 100 and 150 kg N ha) applied as urea and sub plot was silicon rates (0, 300 and 600 kg ha) applied as calcium silicate. Results showed that minimum of the plant height, flag leaf length, fourth inter-node bending moment and grain yield (4350 kg ha) were obtained at N0, as well as the maximum of the plant height, panicle length, flag leaf length, third inter-node length were observed at N100 and N150, respectively. But the highest of bending moment obtained for fourth inter-node and maximum grain yield (6063 kg ha) was observed in N150. Treatment Si600 had increased significantly over control in plant height, stem length, panicle length, third inter-node length, third inter-node bending moment, cellulose, hemi-cellulose and lignin in relation to 7.76, 9.91, 30.18, 31.03, 18.71, 7.60, 34.50 and 26.26 %, respectively. Therefore treatment with N150 and Si600 had shown best results for agronomical indices and grain yield.


Introduction
Rice is one the most important crops in developing countries and a main food stuff for about 35% of the whole world population (Becker and Asch, 2005).Rice plants require large amounts of mineral nutrients including N for their growth, development and grain production (Ma, 2004).Rice continuous cultivation in the north of Iran has recently decreased rice production and farmers for increasing yield used nitrogen application resulting in coast increasing and production decreasing duo to highland sensitive to disease especially blast and lodging, where disease and lodging have caused major yield losses.Rice production in much of the world increasingly focuses on optimizing grain yield, reducing production costs, and minimizing pollution risks to the environment (Koutroubas and Ntanos, 2003).Nitrogen nutrition is critical in yield realization of irrigated rice ecosystems.Nitrogen is clearly the most limiting element; we proposed a set of basic guidelines for improved nutrient management, which after further efforts of all stakeholders involved, could contribute to increased system productivity (Haefel et al., 2006).Nitrogen fertilization increased the number of stems and panicles per square meter and the total number of spikelets, reflecting on grain productivity.Excessive tillering caused by inadequate nitrogen fertilization reduced the percentage of fertile tiller, filled spikelet percentage and grain mass (Mauad et al., 2003).N application significantly increased grain yield largely through an increased biomass and grain number (Belder et al., 2005).Nitrogen rates of 138 and 0 kg ha -1 produced maximum and minimum grain yield, biological yield and straw yield, respectively.Si at 500 and 0 kg ha -1 produced maximum and minimum biological yield with 11874 and 10538 kg ha -1 , and straw yield, respectively (Ghanbari-Malidarreh et al., 2008).
Silicon is one of the most abundant elements in Earth's crust and plants ash (Jones and Handereck, 1976).It is necessary element for rice because of positive effaces on rice planting (Mengel and Kirkby, 1987).Silicon uptake is activated in rice and wheat, so it's not be affected by the rate of transpiration and this element is located in leaf, sclerenchyma, vascular tissues and vascular sheaths, old leaves have more silicon than the young leaves (Tanaka and Park, 1996).Silicon caused to be vertical in leaves (Elwad and Green, 1979), increase to resistance in fungal diseases (Datnoff et al., 1997) and caused to increase filled spikelets percentage and grain yield (Datnoff et al., 2001).Silicon caused to increase total number of spikelets per panicle, filled spikelets percentage, 1000-seed weight, grain yield and to decrease lodging (Chaoming et al., 1999).Silicon increase vegetative growth, dry matter and decrease transpiration and affects on qualitative and grain yield (Agarie et al., 1993).Silicon is necessary for grain yield stability in rice (Mauod et al., 2003).Silicon application showed direct growth in leaves, stems and plants sheaths specially in rice consequently silicon application improved light contributing inside of canopy (Savant et al., 1997).Silicon uptake is different in varieties and parts of plants (Windslow et al., 1997).Optimal silicon application increase tolerance of plants to salinity and drought (Bocharnikova and Matichenkov, 2008).Silicon improved plant height, inter-node length, fresh weight, bending moment, breaking resistance, lodging index, and increase tolerance of lodging in rice (Fallah, 2008).So according to silicon and potassium importance on growth and yield an experiment was carried out intitled: "Application of Nitrogen and Silicon Rates on Morphological and Chemical Lodging Related Characteristics in rice (Oryza sativa L.)."

Materials and Methods
The field experiment was conducted at Neka region in the north of Iran (Latitude 36° 46 N, Longitude 53° 13 E and altitude 4 m above sea level) in 2010.The minimum and maximum daily temperatures were obtained from the Dashte-Naz airport at Sari near to farm (Table 1).The soil was a loamy, with a sand, silt, and clay composition of 39, 39, and 22%, respectively.The soil chemical analysis indicates (Table 2).The experiment was carried out as split-plot in randomized complete block design with four replications.The rice cultivar was Tarom Hashemi that is one of medium grain yield, early-maturing, tall and sensitive cultivar to blast.Main plots were nitrogen rates in four levels including (0, 50, 100 and 150 kg ha -1 N) applied as urea and sub plots were three silicon rates (0, 300 and 600 kg ha -1 ) applied as calcium silicate (total silicon oxide (SiO 2 )=62%), pH in water = 7.1 to 7.4, solubility in water negligible, 91% calcium silicate.Seeds were soaked for 12 to 24 h and emergence date was considered to be five days after sowing, when 90% of the seedlings showed coleoptile.Seeds spread with hands into an area of 10 m 2 (2 × 5).Sowing arrangement was 20 × 20 cm 2 .The water depth was controlled at 3 to 5 cm.Nitrogen, phosphorous and potassium fertilizers were used at the rates of N 150 kg ha -1 urea, P 2 O 5 100 kg ha -1 triple superphosphate and K 2 O 100 kg ha -1 potassium sulphate.Basal fertilizers were applied in all plots 1 day before transplanting.Nitrogen was applied by designing map arrangement.Nitrogen was applied three times (first at planting time, second at tillering time and third panicle imitation, using 33.3%, 33.3% and 33.3% in each stage in plot.Calcium silicate was used in the field 10 days before sowing.Phosphate and potassium fertilizers weren't used during of growth stages.Weeding was made 22 days after sowing by hand.characteristics.12 samples were used for measuring of plant height, stem length and panicle length.Grain dry weight from panicle in each plot was measured as final grain yield (g m -2 ).Lodging characteristic was observed when the flowering of the plant just started.Stem characters related to lodging were determined at 10 days after flowering.12 samples were measured in each plot for lodging characteristics.Stem length (length between plant base and panicle neck node), and the lengths of the third inter-node (N 3 ), and fourth inter-node (N 4 ) from the top were measured.Bending moment (BM) at N 3 or N 4 inter-node was calculated using the following formula (Islam et al., 2007).

Results and Discussion
Stem length had significant effect under nitrogen treatment in 5 % probability level and under silicon treatment 1 % probability level (Table 3).Maximum stem length (137.1 cm) was observed for 100 kg h -1 nitrogen and minimum of that (122.7 cm) was for control (no nitrogen application).Stem length decreased 9.1 % by silicon application.Maximum stem length (135.3 cm) was obtained for control (no silicon application) and minimum of that (123.1 cm) was for 600 kg h -1 silicon application (Table 4).Saadati and Fallah (1995) stated stem length had significant effect in tillering time by nitrogen contributing treatments in 1 % probability level.
Panicle length had significant effect under nitrogen treatment in 5 % probability level and under silicon treatment 1 % probability level (Table 3).Maximum panicle length (34.9 cm) was observed for 100 kg h -1 nitrogen and minimum of that (28.2 cm) was for control (no nitrogen application).Panicle length decreased 30.18 % by silicon application.Maximum panicle length (35.8 cm) was obtained for control (no silicon application) and minimum of that (27.5 cm) was for 600 kg h -1 silicon application (Table 4).Panicle length affects in grain yield by more transport of photosynthesis material (Dobermann et al., 2002).Saadati and Fallah (1995) stated panicle length had significant effect in tillering time by nitrogen contributing treatments in 1 % probability level.Mobasser (2004) found that panicle length had significant effect by interaction year × nitrogen amounts × nitrogen contributing in 5 % probability level.
Plant height had significant effect under nitrogen treatment in 5 % probability level and under silicon treatment 1 % probability level (Table 3).Minimum plant height (154.6 cm) was noted for control (no nitrogen application) and maximum of that (168.7 cm) was for 100 kg h -1 nitrogen.Plant height decreased 7.2 % by silicon application.Maximum plant height (168 cm) was obtained for control (no silicon application) and minimum of that (155.9 cm) was for 600 kg h -1 silicon application (Table 4).Absorbed silicon is located on leaf area in rice and by this, decreased cuticle transpiration and it decreases plant elongation (Datnoff et al., 2001).Silicon improved plant height, inter-node length and fresh weight in rice (Fallah, 2008).Yoshida et al. (1962) stated that plant height increased by increase of sodium silicate levels because of silicon effect on straight stature of leaves.Agarie et al. (1993) showed silicate fertilizers increased vegetative growth, dry matter and grain yield.Saadati and Fallah (1995) stated plant height had significant effect in tillering time by nitrogen contributing treatments in 1 % probability level.
Flag leaf length had significant effect under nitrogen treatment in 5 % probability level (Table 3).Maximum flag leaf length (37.00 cm) was observed for 150 kg h -1 nitrogen and minimum of that (29.9 cm) was for control (no nitrogen application) (Table 4).Sedghi et al. (2007) reported that silicon had no significant effect on flag leaf length and this result supported our experiment.Pantuwan et al. (2002) stated that grain yield had a positive correlation and significant with flag leaf length.
3 rd inter-node length had significant effect under nitrogen and silicon treatments in 1 % probability level (Table 3).Maximum 3 rd inter-node length (36.7 cm) was observed for 150 kg h -1 nitrogen and minimum of that (27.1 cm) was for control (no nitrogen application).3 rd inter-node length decreased 23.7 % by silicon application.Maximum 3 rd inter-node length (38 cm) was obtained for control (no silicon application) and minimum of that (29 cm) was for 600 kg h -1 silicon application (Table 4).Silicon improved inter-node length in rice (Fallah, 2008).4 th inter-node length had significant effect under silicon treatment in 1 % probability level and under interaction nitrogen × silicon in 5 % probability level (Table 3). 4 th inter-node length decreased 10.1 % by silicon application.Maximum 4 th inter-node length (27.7 cm) was obtained for control (no silicon application) and minimum of that (24.9 cm) was for 600 kg h -1 silicon application (Table 4).Minimum 4 th inter-node length (23.3 cm) was obtained under interaction control (0 kg h -1 nitrogen) × silicon (600 kg h -1 ) and maximum of that (29 cm) was for interaction 100 kg h -1 nitrogen × control (0 kg h -1 silicon) (Figure 1).Yoshida (1981) stated that inter-node length decreased by less than 40 kg h -1 nitrogen application.3 rd and 4 th inter-nodes length are important for morphological characteristics related to lodging, because the most lodging were happened in this two areas, on the other hand 3 rd and 4 th inter-nodes length have positive correlation with lodging index (Islam et al., 2007).
Bending moment of 3 rd inter-node had significant effect under silicon treatment in 5 % probability level (Table 3).Silicon application had decreasing trend in bending moment of 3 rd inter-node because of decrease in stem length, panicle length, plant height, 3 rd and 4 th inter-nodes length.Maximum bending moment of 3 rd inter-node (2588 g cm) was obtained for control (no silicon application) and minimum of that (2180 g cm) was for 600 kg h -1 silicon application (Table 4).
Bending moment of 4 th inter-node had significant effect under nitrogen treatment in 5 % probability level (Table 3).Maximum bending moment of 4 th inter-node (4585 g cm) was obtained for control (no nitrogen application) and minimum of that (3652 g cm) was for 100 kg h -1 nitrogen application.Maximum and minimum of plant height and stem length were observed by 100 kg h -1 nitrogen and control (no nitrogen application) respectively, so most bending moment was also for these treatments (Table 4).Silicon contents in rice stem had a direct relation with lodging resistance (Ma and Yamaji, 2006).Mobasser et al. (2008) found that bending moment of 4 th inter-node decreased by 500 kg h -1 silicon, but it didn't support our results.
Cellulose had significant effect under silicon treatment in 1 % probability level (Table 5).Cellulose increased 7.6 % by silicon application.Maximum cellulose (46.7 %) was noted for 600 kg h -1 silicon application and minimum of that (43.4 %) was for control (0 kg h -1 silicon application) (Table 6 ).
Grain yield had significant effect under nitrogen treatment in 5 % probability level (Table 5).Maximum grain yield (6063 kg h -1 ) was observed for 150 kg h -1 nitrogen application and minimum of that (4350 kg h -1 ) was for control (0 kg h -1 nitrogen application) (Table 6 ).Pantuwan et al. (2002) reported that grain yield had positive correlation with flag leaf length.Chaoming et al. (1999) stated that silicon application increased grain yield by increase of spikelet number, filled spikelet percentage and 1000-seed weight.Mauod et al. (2003); Ma and Takashi, (1990); Mobasser et al. (2008) reported that grain yield increased by silicon application.Maximum grain yield was obtained by 69 kg h -1 nitrogen and nitrogen contributing in three times (transplanting time, panicle initiation and heading time) (Mobasser et al., 2005).Grain yield increased by 120 kg h -1 nitrogen contributing in three times (transplanting time, tillering time and panicle initiation) (Singh et al., 2002).
Straw yield had significant effect under silicon treatment in 5 % probability level (Table 5).Maximum straw yield (9846 kg h -1 ) was observed for 300 kg h -1 silicon application and minimum of that (8558 kg h -1 ) was for control (0 kg h -1 silicon application) (Table 6 ).Agarie et al. (1993) showed that silicate fertilizers increased dry matters by effect on vegetation growth consequently increase grain yield.Matsuo et al. (1995) stated that silicon increased vegetation growth and dry matter.Sedghi et al. (2007) reported that grain yield increased by silicon application.

Conclusions
According to results of this study, plant height, stem length, panicle length and third inter-node length were increased by increasing the nitrogen fertilizer.With increase of nitrogen, the fourth inter-node length had increased and it caused more lodging.Application of silicon increased lodging-related traits such as plant height, panicle length, third inter-node length and stem length, but the fourth inter-node length was reduced which is so important to breaking resistant.So there was no significant difference in the bending moment of fourth inter-node, although the bending moment of the third inter-node was significant and the use of silicon was increased the bending moment and it seems that use of silicon can be distributed between the third and fourth inter-node and had increased resistance to lodging.

BMN 3 =
Length from the lowest node of N 3 to the top of panicle × weight of this portion BMN 4 = Length from the lowest node of N 4 to the top of panicle × weight of this portion The data were analyzed with SAS software.Mean comparison calculated by method of Duncan's multiple range tests at the 0.05 significance level.

Table 6 .
Mean comparison of nitrogen and silicon rates on chemical traits and grain yield and straw yield in rice Treatments column followed by same letter are not significantly different at Duncan (P ≤ 0.05).

Figure 1 .
Figure 1.Interaction effects of nitrogen silicon rates on fourth interned length

Table 1 .
Weather condition in experiment site in rice growth stages at Neka in 2010

Table 3 .
Mean square of nitrogen and silicon rates on lodging related characteristics in rice ** and * respectively significant in 1% and 5% level.

Table 4 .
Mean comparison of nitrogen and silicon rates on lodging related characteristics in riceValues within each column followed by same letter are not significantly different at Duncan (P ≤ 0.05).

Table 5 .
Mean square of nitrogen and silicon rates on chemical traits and grain yield and straw yield in rice ** and * respectively significant in 1% and 5% level.