Abstract: Effect of nitrogen (N) rate and its split application (AP) on qualitative and quantitative characteristics of sugarcane (Saccharum officinarum L.) cultivar CP48-103 was investigated on a loamy soil texture from 2006 to 2008 in the Sugarcane Research Center of the Khuzestan Province, Iran. The experiment was arranged in split plot randomized complete block design with three replications consisted of three different rates of N (N1 = 92, N2 = 138, N3 = 184 kg N ha-1) as main plots and three different AP (AP1 = 20-40-40%, AP2 = 30-35-35%, AP3 = 30-30-40%) as subplots. Twenty canes were randomly harvested from each plot and their quantitative and qualitative characteristics were determined. The results showed that both rate and split application of N fertilizer had no significant effect on sugarcane characteristics. The interactive effects of N application rate and AP on juice purity depicted applying 92 kg N ha-1 and AP of 30-30-40% gave the purest juice with 90%. The Nitrogen Use Efficiency (NUE) was significantly greater for N1 with values of 1.39 and 0.13 t kg-1 N in Cane Yield (CY) and Sugar Yield (SY), respectively. The results showed that the highest cane and sugar yield was obtained with 92 kg N ha-1 and AP of 30-35-35%.
INTRODUCTION
Nitrogen is vital for most plant metabolic processes and plays an important role in tillering and stalk elongation. In addition, N deficiency results in reduction of leaf area and thus, causes photosynthesis reduction which in turn leads to suppress in yield and quality (Sreewarome et al., 2007).
Fertilizers application is more common in intensive sugarcane cultivation which requires a high amount of nitrogen due to production of a great deal of biomass (Thorburn et al., 2005). However, N application may lead to soil acidification, ground or surface water contamination and emission of greenhouse gases such as nitrous oxide (Keating et al., 1997). The high water and N requirements of sugarcane, has the maximum potential for polluting ground or surface water (Peralta and Stockle, 2001). N uptake depends on the quantity and quality of the N fertilizer, time and frequency of application, the crop grown and its duration, crop N-utilization efficiency, rooting depth, rainfall, soil hydraulic characteristics and management practices (Rasiah and Armour, 2001).
In Australia, fertilizer N rates between 97 and 160 kg ha-1 generated returns above 95% of the optimum (Keating et al., 1997). Thorburn et al. (2001) depicted that cane yield increases from 102 to 117 t ha-1 after raising N rate from 100 to 150 kg ha-1. However, it was reported that cane yield was not affected with increasing N. The NUE of sugarcane is related to dry matter yield. Dilz (1988) reported that typical ranges of N recovery for some crops under good conditions in Western Europe are 50-60% for wheat; 77% for sugar beet; 50-60% for potato and 50-70% for grassland. Also, the results of Isa et al. (2006) showed high recoveries (>90%) in the sugarcane plant growing on a non-saline soil.
Proper land management programs should include the establishment of fertilization regimes that optimize growth with minimum nutrient leaching (Van Miegroet et al., 1994). These involve adjusting fertilizer application rates and frequencies to maximize N utilization while minimizing N leaching from the rooting zone (Lee and Jose, 2005). Sugarcane has been cultivated in the Khuzestan province (SW of Iran) since 1956. The area under sugarcane is estimated to be 100000 ha. Fertilizer application for plant crop was 400 kg ha-1 urea and the same amount diammonium phosphate annually (Barzegar and Koochekzadeh, 2001). But, this amount has declined to 300 kg ha-1 in recent years. Urea is applied for crop in 2 or 3 split applications through May to July. However, it is necessary to find out the appropriate doses and application methods.
The objectives of this study were to assess the effects of rates and split applications of nitrogen on (1) qualitative and quantitative characteristics of plant cane and (2) nitrogen use efficiency in sugarcane cultivation.
MATERIALS AND METHODS
The study was conducted in South West of Iran at Sugarcane Research Center, (31°02’N, 48°14’E). The study area has a semiarid climate (average annual temperature of 24.9°C and average annual rainfall of 170 mm). Soil is fine loamy carbonatic hyperthermic, typic torrifluvents. Before planting on August 2006, 300 kg ha-1 diammonium phosphate was added to the soil and then, sugarcane cultivar CP48-103 was planted through placing stalks in the furrows.
On May 2007, mixed samples were taken from soil at depth of 0-30, 30-60 and 60-100 cm before adding N to soil. Soils were air dried and sieved 2 mm in diameter. Electrical conductivity of saturated extract (Rhoades, 1996) and pH of saturated paste (Thomas, 1996) of soil samples were determined. Organic carbon content was measured by the oxidation procedure (Nelson and Sommers, 1996). Particle size distribution was measured by the pipette method (Gee and Bauder, 1986). Soil samples were analyzed for total nitrogen after digestion with concentrated sulfuric acid (Bremner, 1996). Available P was measured by ascorbic acid method (Kuo, 1996). Available K was determined by the ammonium acetate method (Helmke and Sparks, 1996) and nitrate and ammonium by the KCl method (Mulvaney, 1996).
The experiment was arranged in a split plot design including three N application rates 92, 138 and 184 kg N ha-1 (hereafter refereed as N1, N2 and N3, respectively) as main plots and three split applications of N (AP1: 20-40-40%, AP2: 30-35-35%, AP3: 30-30-40%) as subplots with three replications. The applied fertilizer was dissolved in water and then added to the soil at grand growth period on 5 May, 5 June and 6 July (263, 294, 325 days after planting, respectively). Each plot was 6 rows 10 m length with 1.83 m apart. A 2 m distance between adjacent plots and 3.66 m between blocks was established to prevent N leach of any plot to each others.
Sugarcane was harvested on 28 February 2008 (562 days after planting). The middle two rows of each plot were harvested, then all leaves and sheaths of all canes were removed. Fresh weight of canes and leaves plus sheaths were measured separately. These values were attributed as cane yield and trash, respectively. A random 20-canes sample from each plot crushed using a Hydraulic Roller Mill and juice were analyzed for total dissolved solids (brix) and sucrose concentration (pol) using refractometer and Saccharimeter, respectively. Cane sucrose content was calculated using the Winter-Carp formula (Chen and Chou, 1993). Electrical conductivity, sodium and potassium contents and residual N of juice were also determined. Ten canes were taken separately from each subplot and fiber content was measured by wet disintegrator method (ICOUMSA, 1994). Also, nitrogen use efficiency was calculated as the ratio of yield over applied N (Lakshmikantham, 1983).
Data were statistically analyzed using the SAS 9.1 package and mean comparisons were made using Duncan’s multiple range test.
RESULTS AND DISCUSSION
Soil Characteristics
Soil texture of different soil layers varied from loam to silty clay loam
with highest clay content at 60-100 cm depth. The organic carbon of soil is
4 g kg-1. Total N and NO3−
concentration of soils are relatively low (Table 1).
Cane and Juice Characteristics
Variance analysis of data (Table 2) revealed that except
N effect on NUE for cane and sugar and interactions between N and AP on juice
purity, there is no other significant effect.
Interaction between N rates and split applications in different treatments
is shown in Table 4. Present results indicated that cane yield
was varied from 114.5 t ha-1 in N3AP1 to 133.5
t ha-1 in N1AP2 (Table 4).
Cane yield reached the value of 128.2 t ha-1 averagely with application
of 92 kg N ha-1. This value is slightly greater with respect to cane
yield values obtained in other N treatments, 138 and 184 kg N ha-1,
but the difference is not significant (Table 3). The high
level of N concentration resulted in unbalance uptakes of other crop nutrients
such as P and microelements, which in turn may reduced cane yield from 128.2
to 120.4 t ha-1. Gawander et al. (2004)
found that cane yield and sucrose content are significantly interrelated with
applied fertilizers. Wiedenfeld (2000) reported that
N application is not required for plant cane in a sandy clay loam soil, in Texas.
| Table 1: | Mean soil characteristics before N application |
| aEC: Electrical Conductivity, bOC: Organic Carbon, cL: Loam, dCL: Clay Loam, eSiCL, Silty Clay Loam, fAva: Available | |
| Table 2: | Analysis of variance of sugarcane quality parameters (mean squared) |
| Without any superscription indicate not significant, * and ** are significant at 0.05 and 0.01, respectively. aCY: Cane Yield, bRS: Recovery Sugar, cSY: Sugar Yield, dEC: Electrical Conductivity, eRes.N, Residual Nitrogen, fNUE: Nitrogen Use Efficiency | |
| Table 3: | Mean comparison by Duncan’s method |
| Without and with letter(s) in superscription within the column indicate non-significant and significant difference (p<0.05), respectively. aCY: Cane Yield, bRS: Recovery Sugar, cSY: Sugar Yield; dEC: Electrical Conductivity, eRes.N: Residual Nitrogen, fNUE: Nitrogen Use Efficiency | |
| Table 4: | Interaction between N rates and split applications on quantitative and qualitative characteristics of plant cane |
| Without and with letter(s) in superscription within the column indicate non-significant and significant difference (p<0.05), respectively. aCY: Cane Yield, bRS: Recovery Sugar, cSY: Sugar Yield, dEC: Electrical Conductivity, eRes.N: Residual Nitrogen, fNUE: Nitrogen Use Efficiency | |
However, Van Antwerpen et al. (2001) revealed that sugar cane production in the absence of N inputs reduces amounts of soil organic matter and hence soil health. Gana (2008) found that application of more than 120 kg N ha-1, there was no significant difference between tillers number, stalk length and cane yield. Keating et al. (1997) showed that low application rates of N could be applicable in fertile soils and plant crops. Present study also indicated that a substantial amount of cane yield can be achieved with applying 92 kg N ha-1.
The values of brix, pol, purity and recovery sugar varied from 16.6, 14.4, 86.7 and 8.9% to 18.0, 16.2, 90 and 10.2%, respectively against different treatments. However, comparison of their means in different treatments and split applications was not significant. Since sugar yield is gained by product of recovery sugar and cane yield, this parameter is highest in N1AP2 and reached 12.9 t ha-1 and is the lowest for N3AP1 and N3AP2, equivalent to 11.0 t ha-1 (Table 4). Rattey and Hogarth (2001) and Muchow et al. (1995) reported that sugar yields reduced with increasing levels of N. This study also shows that with application of 92 kg N ha-1, the average sugar yield reached its highest value of 12.5 t ha-1 (Table 3).
Electrical conductivity, Na, K and residual N contents of juice are varied from 8.8 to 10.0 dS m-1, 33.3 to 36.5 mg kg-1, 3987.1 to 4232.8 mg kg-1 and 0.025 to 0.036%, respectively (Table 4).
Potassium and sodium in juice lead to increasing of ash in juice which prevents sugar to be extracted in factory. Malavolta (1994) reported that lack of K decreased the translocation of the assimilates from leaves into stalks. Table 1 shows that the K content of soil ranged from 121.8 to 87.0 mg kg-1. Thus, the high concentration of K may result in higher K accumulation in juice. The current study also showed that potassium content was more than sodium in juice. Whitbread et al. (2005) observed that potassium ion in juice is one of the main components of ash. Present results illustrated that the values of K in N1 treatment was less than other treatments. Na content in both N1 and N2 are identical and the highest in N3 treatment (Table 3). Electrical conductivity was not significantly influenced by different treatments. Residual N in juice which prevents sugar to be extracted in factory was negligible in different treatments.
The fiber value was varied from 10.8% in N3AP1 to 13.0% for N1AP2 (Table 4). Fiber value was decreasing from 12.5% for N1 treatment to 11.1% for N3 treatment (Table 3). Malavolta (1994) indicated that with increasing N application, the fiber value decreases. Also the amount of trash ranged from 3.4 to 3.8 t ha-1 with mean values of 3.5 t ha-1 in N3 and 3.7 t ha-1 in N2 (Table 3). The comparison among means of data in Duncan’s method revealed that different rates of fertilizer and its split application had no significant effect on different measured parameters (Table 3).
Nitrogen Use Efficiency
The highest NUE in sugar was obtained for N1AP2 treatment
with the value of 0.14 t kg-1N and the least value in
sugar is belonged to N3 treatment which is equivalent to 0.06 t kg-1
N. In addition, these extreme values for NUE in cane are 1.45 for N1AP1
and N1AP2 and 0.62 t kg-1 N for
N3AP1. Comparison of means indicated that NUE value in
sugar and cane for N1 treatment (92 kg N ha-1) are the
highest and are 0.13 and 1.39 t kg-1 N, respectively which
are significantly different to other treatments. These results depicted that
split application of N had no effect on NUE (Table 3). According
to Table 2, different rates of nitrogen can cause significant
changes in NUE due to higher N uptake, thus less amounts of this nutrient is
absorbed by the plant. Results of variance analysis and mean comparison of NUE
data in cane and sugar yield are shown in Tables 2 and 3, respectively. The
reason of NUE being significant after application of N1 treatment
may be explained in such a way that high rates of fertilizer may make the vegetation
growth period longer and shorten the period of sugar accumulation and as consequence,
sugar yield did not increase while a better balance was made after applying
92 kg N ha-1. The highest NUE is achieved when the least rate of
N is applied. Present results indicated that the NUE values in sugar and in
cane are highest and reached the values of 0.13 and 1.39 t kg-1 N,
respectively when applying the least rate for N application (92 kg N ha-1)
which are significantly different in comparison with other treatments (Table
3).
The interactive effects of N and AP on juice purity depicted that application of 92 kg N ha-1 and AP of 30-30-40% gave the purest juice with percentage of 90 and increasing N rate with this AP treatment results in declining the juice purity noticeably (Fig. 1). Although, AP treatment of 20-40-40% resulted in more pure juice with increasing N rate, the juice purity in the best condition can reach 89.4% which is still a bit lower than the situation when 92 kg N ha-1 was applied in AP treatment of 30-30-40%. Therefore, it is not economically and environmentally justified to apply N3 (184 kg ha-1) due to high cost of fertilizers and adverse environment impacts. Excessive use of N fertilizers has resulted in increasing leaching of NO3− and caused groundwater pollution (Ersahin, 2001). Lee and Jose (2005) revealed that increasing N application raises nitrogen leaching without making any difference in woody plants growth.
Although, none of the influences related to N rates and split applications
and their interactive effects was significantly effective on sugar yield, studying
the effect of application method showed that the highest sugar yield can be
obtained by application of the lowest N rate (92 kg ha-1) and AP
treatment of 30-35-35% and it reached to 12.9 t ha-1 (Fig.
2a). Neither increasing N application nor the kind of split application
can compensate the adverse effect of N application on sugar yield. Rattey
and Hogarth (2001) reported that sugar yields reduced with increasing N.
| Fig. 1: | Effect of N rate on juice purity for different split applications (The bars on the plot are SD) |
| Fig. 2: | Effect of N rate and split application on (a) sugar yield and (b) cane yield (The bars on the plot are SD) |
The similar trend is obtained for cane yield (Fig. 2b). In the other words, the highest cane yield obtained after the lowest N application rate and it reached the maximum value of 133.5 t ha-1. Even, increasing N rate led to decreasing of cane yield. But Thorburn et al. (2001) reported that cane yield was not affected with increasing N. Wiedenfeld (2000) depicted that rate of N application did not affect cane and sugar yields in the plant crop.
CONCLUSION
Among all applied nitrogen rates (92, 138 and 184 kg N ha-1) and different split applications (20-40-40, 30-35-35 and 30-30-40%), the treatment of 92 kg N ha-1 and AP of 30-30-40% gave the purest juice. But, the greatest amount of sugar yield achieved using treatment of 92 kg N ha-1 and AP of 30-35-35% because cane yield was the highest in this treatment. Also, the highest NUE value gained after applying the least amount of N. The amount of potassium content in juice was higher than sodium content. In general, the least amounts of potassium and sodium of juice of sugarcane obtained when applying 92 kg N ha-1. The N application rate had no influence on enhancing the fiber and trash amounts of sugarcane.
ACKNOWLEDGMENT
We thank Sugarcane Research Center of Khuzestan for their valuable assistanc