Response of sugarcane ratoon to nitrogen in form of ammonium nitrate and urea

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1 Response of sugarcane ratoon to nitrogen in form of ammonium nitrate and urea Awad Elhag, Mohammed A. Abouna, Salah A. Mukhtar Naiem A. Ali and Abbas E. M. Elamin Abstract Researcher managed and on farm experiments were conducted at Guneid during the cropping seasons 2005/2006 and 2006/2007. The objective was to study the influence of the fertilizer ammonium nitrate (AN) at different nitrogen rates on cane and sugar yields of the sugarcane ratoon crop. Three rates of AN equivalent to 46, 69 and 92 kg N/Fed were compared with the standard fertilization practice (92 kg N/Fed applied as urea (46 % N)). Zero treatment was added as a control. All data was statistically analyzed and economically evaluated. Percent leaf N markedly increased in the fertilized treatments compared with zero treatment, but there was no trend among the fertilized treatments. There was significant cane and sugar yield increase in all levels of the applied fertilizers when compared with no fertilizer application, but the differences among the treated plots were generally non - significant. However, results in all 4 experiments (small + large in 2 seasons) showed cane and sugar yields in treatment 69 kg N/F as AN were either higher or similar to yields of the standard practice (92 kg N/F as urea). These results favour the recommendation of this level of AN fertilizer to be applied for sugarcane ratoon production. Introduction Nitrogen is the most essential element for plant growth and development. It is an integral part of the plant cell and it is essential for the synthesis of proteins, protoplasm and nucleic acids. Sugarcane plant contains about 1.5 % nitrogen in the dry matter and is known to be a heavy feeder on the soil nutrients. It is reported that 100 tons of cane removes about 100 kg N, 50 kg P and 75 kg K from the soil (Bakker 1999). The bulk of the cane plants are usually transported outside the field. Moreover, the vertisolic characteristics of the soils of the present sugarcane estates impose some physical and chemical limitations. To cope with these limitations these soils must be well managed and properly fertilized, especially with nitrogenous fertilizers, for suitable and sustainable crop production. The ratoon crop is more responsive to the applied nutrient fertilizers (Humbert 1968, EL Hag et al. 2007, Osman 2007). 1

2 Urea is the most common nitrogenous fertilizer for its high nitrogen content (46 %) and relatively easiness to handle. However, urea N is subjected to high losses through hydrolysis and during transformation to nitrate. In the soil urea is readily converted by enzyme urease to ammonium carbonate, which is unstable and releases free ammonia. Part of this ammonia is lost by volatilization under the high temperature and alkaline conditions of our soils (Musa 1968). These conditions aggravated by the high soil bulk density that impedes transformation of urea N to the plant available forms of NH4 and NO3-. Therefore, other sources of fertilizes with less loss of N are being considered. Ammonium nitrate is a widely used fertilizer for crop production and contents 35 % N in the readily plant available forms of NH 4 and NO 3 -. Thus it is less prone to losses of nitrogen (Ali 2000). In the current trial the response of sugarcane to AN, which contains 35 % plant available N, as compared to urea N is studied. Materials and Methods The experiments were carried out within Guneid Sugar Scheme on the East bank of the Blue Nile, 117 km south of Khartoum, Latitude 150 N, Longitude 330 E. The climate is tropical aridic. There are two main seasons; the summer from April to October including the rainy season, and the winter from November to March which includes the cane crushing period. The average rainfall is 112 ml, 90 % of which is in July and August. The average temperature in summer is in the range 29 39oC and in winter oC. (Sugarcane Res. Center Met. Station Guneid). The relative humidity is low and the potential evapotranspiration exceeds precipitation in the most part of the year. The soil is described as clayey (52 55 %), smectitic alluvium with suitability subclass S2v, bulk density 1.7 gm cm-3, % N 0.03, % O.C 0.4, available P (mg/ kg soil) 0.9 3, Exchangeable K (cmol/kg soil) 0.6 and CEC (Idris 1990). In small scale (researcher managed) and large scale (field) experiments different rates of ammonium nitrate were compared against the standard rate of urea. The experiment was established in the second ratoon of the sugarcane cultivar Co 6806 in two successive seasons (2005/2006 and 2006/2007). After the removal of the first ratoon crop, the remaining trash was raked out and the stubble was given a first irrigation before treatments. The design of the small experiment was randomized complete block with 4 replications. The subplot size was 6 x 10 meters for the small scale and 1 feddan for each treatment in the large scale experiment without replication. The fertilizers were surface applied 2

3 as one dose at the establishment of the ratoon prior to the second irrigation. Followed immediately by ripping, reshaping of furrows and irrigation. Doses of ammonium nitrate and the standard dose of urea for both experiments were the same. The levels of the fertilizer products were equivalent to 46, 69 and 92 kg N/fed. Zero treatment was included as control. Hence the doses were as follows: 0N N0 fertilizer (control). 130 kg AN/fed (46 kg N/F). 195 kg AN/fed (69 kg N/F). 260 kg AN/fed (92 kg N/F). 200 kg urea/fed (92 kg N/F). At 5 month age of cane leaf samples were collected from the index tissue (leaf No. 3, 4, 5 and 6 counting from the top) of 4 plants from each subplot of the small scale experiment. P and K were determined in the leaf sheath while N was determined in the blade after removing the midrib. Cane yield (TC/fed) and yield components viz plant population (x 1000), plant height (cm), stalk thickness (cm) and number of nodes were recorded. Samples of 10 millable stalks were collected from each plot for juice analysis. The juice quality parameters including Brix % cane, Pol % cane, purity and estimated recoverable sugar (ERS) were obtained from juice analyzed according to ICUMSA (International Commission for Uniform Methods of Sugar Analysis) methods of analysis. Results and Discussion (Table 1) shows concentration of NPK nutrients in the index tissues of the cane plant. Nitrogen is the main nutrient element in cane vegetative growth and yield. Cane yield is reduced under low supply of readily available form of nitrogen, while excess supply negatively affects sugar accumulation by prolonging the vegetative stage (Humbert 1968, Bakker 1999). The nitrogen concentration in the index tissue increased markedly in the fertilized treatments compared with zero treatment (Table 1). The differences among the treated rates were negligible. Nitrogen concentration in these treatments is close to the sufficiency level (appendix 1). Phosphorus in the leaf sheath did not show any trend. Potassium concentration increased in the fertilized treatments. The difference was significant in the kg as AN compared with either the control or the urea treatment. However, K concentration was above the sufficiency level even in the zero treatment Table 1 (appendix 1). 3

4 Our soils are known to be high in K (Ibrahim 1978, Idris 1990). NH 4 + ion present in ammonium nitrate can exchange with K + in the soil colloid. Sugarcane is known to absorb luxury amounts of K. Cane population ranged from 36 to 44 thousands Millable stalks/fed. The highest plant population was found in 69 kg N/fed AN treatment, but there was no specific trend. Stalk length was significantly higher in all fertilizer treatments compared with zero. Plant height steadily increased with increasing applied N as AN, but the difference among treatments was not significant. Variation in stalk thickness was minimal and inconsistent. Number of internodes was highest at zero treatment; while plants were shorter which means high number of the fibrous and low sugar nodal parts. Cane yield data in Table 3 show clear response of the sugarcane ratoon to applied N fertilizers. This is in contrast with the findings of the authors and other workers who reported lack of consistent response of sugarcane to applied N in the plant cane stage. Fertilizer application significantly (P = 0.05) increased cane tonnage over the control (no fertilizer) even in the lowest treatment (46 kg N/fed as AN). Cane yield was highest in the 69 kg N AN treatment in both seasons of the experiment (Figure 2). The yield difference in this treatment was significant over the control and the lowest fertilizer treatment while it gave 3 4 tons/fed of millable cane more than the standard treatment (92 kg N/fed urea). In the on farm trial treatment 69 N AN gave yield difference of 4 7 tons/fed more than the standard urea treatment. Nitrogen use efficiency (N.U.E), which indicates the state of utilization of applied N fertilizers as reflected in the yield, was consistently higher in the 69 kg N AN treatment in all trials (Tables 5 and 6). Table 4 shows the juice quality parameters as affected by the treatment for 2 seasons. Juice quality, which includes the percent sugar (pol % cane), % purity and estimated recoverable sugar (ERS %), is a main attribute of sugar production. Increasing applied readily available above 69 kg N/fed as AN significantly decreased pol % and purity. Excess N is known to have negative effect on juice quality (Table 4, Figure 1). Sugar yield followed a similar trend as the cane yield. The highest sugar yield was obtained in treatment 69 kg N (AN) compared with all other treatments 6.88 and 4.07 (TS/fed) in season 2005/2006 and 2006/2007 respectively (Table 5). Sugar yield in all treated plots was significantly higher than the control. As shown above, the statistical analysis revealed significant differences in sugar production with respect to the application of different levels of nitrogenous fertilizers in Guneid scheme. For this 4

5 reason, an economic evaluation has been conducted to rank the most cost effective level of nitrogen in form of ammonium nitrate and urea fertilizers and to arrive at the most economic optimum level of these fertilizers through assessing their profitability. Partial budget, dominance and marginal analysis were used to achieve the stated objectives of the study. The value of sugar that has resulted from different levels of fertilizers was compared with the cost of fertilizer in question. Only costs of fertilizers were considered in the partial budget for being the only variable cost of production that affects the productivity of sugar cane crop. The marginal rate of return (MRR), which reflects the relationship between the variable cost of fertilizer levels and the net benefits between these fertilizers is equal the marginal net benefit divided by the related marginal cost of each treatment. The economic analysis shows that increasing the nitrogen level from 46 to 69 kg N/fed (130 to 195 kg/fed) has resulted in increasing the production of sugar for the ratoon crop. The maximum yield and the maximum net return has been reached at a level of 195 kg/fed, after which the production and the net revenue start to decline. In this respect, the dominance and marginal analysis showed that 195 kg/fed of ammonium nitrate is the best fertilizer level followed by 130 kg/fed of ammonium nitrate. These levels are better than the higher level (92 kg N/ fed) of both urea and ammonium nitrate. Return to investment in this fertilizer level was estimated in the form of marginal rate of return (MRR), which came out to be about 3,171 for the best treatment (130 kg), indicates that every monetary unit (SDG 1) invested in the mentioned level of ammonium nitrate fertilizer would be returned back, plus additional amount of SDG 31. This indicates that an increase in the fertilizer cost will be compensated for by an increase in sugar yield as a result of the fertilizer application. The results of the study conclude that 195 and 130 kg/fed ammonium nitrate are the most economically viable fertilizer levels for the ratoon crop, respectively. High yield advantage and higher rate of return were realized by these fertilizers at varying degree and therefore, represent the economically viable level of fertilizer in the ratoon crop of sugar cane. Conclusion and Recommendations The response of sugarcane (ratoon) to applied nitrogen was studied at the Guneid scheme, for two seasons 2005/ /07. The tested rates of nitrogen were 46, 69, 92 kg N/fed in form of ammonium nitrate and 92 kg N/fed in form of urea for the ratoon of sugar cane in addition to the control. 5

6 Based on the statistical and economic analysis of this experiment which show the superiority of low application rate of ammonium nitrate fertilizer to sugar cane ratoon, the study recommended to apply 195 kg AN (equivalent to 69 kg N/fed) as alternative to the current rate of 200 kg/fed urea which is equivalent to (92 kg N/fed). References Ali, Naiem, A. (2000). Ammonium nitrate and urea as sources of nitrogen for crop growth under Sudan Gezira conditions. X th International Colloquium for Optimization of Plant Nutrition. Cairo, Egypt. Bakker, H. (1999). Cane nutrition. In: Sugarcane Cultivation and Management pp Kluwer Academic/ plenum Publishers, U.S.A. EL Hag, A, M. A. Abouna and S. A. Mukhtar (2007). Response of sugarcane in different levels of nitrogen in four estates of the Sudanese Sugar Company. Sudan J. agric res. (2007), 8, Humbert, R. P. (1968). Sugarcane nutrition. In: The Growing of Sugarcane pp Pub. Elsevier Publishing Company, Amesterdam London New York. Ibrahim, H. S. (1978). The potassium status of the sugarcane areas of the Sudan. The International Sugar Journal, 1978, 80, Idris, M. A. (1990). Re evaluation of Guneid scheme land potential for sugarcane production. Report 139, SSA. Medani. Musa, M. M. (1968). Nitrogenous fertilizer transformation in the Sudan Gezira soil, 1. Ammonia volatilization losses following surface application of urea and ammonium Sulphate. Plant and Soil 28, 413. Osman, A. A. (2007). Sugarcane response to applied nitrogen for different cane Ratoons at Kenana Sugar Company. Sudan J. agric. Res. (2007), 8. Rozett, N. (1990). A survey of South Texas of nutrient studies and current recommendations derived from this survey. J. Amer. Soc. Sugarcane Technol. 10: Schneider, F. (1979). ICUMSA Methods of Analysis In: Cane Sugar Handbook. Pub. British Sugar Corporation. London. 6

7 Table 1. Effect of AN and urea treatments on NPK Concentration in sugarcane plant tissue season 2005/2006 Treatments Kg N/fed N % P % K % O N 46 (as NH 4 NO 3 ) 69 (NH 4 NO 3 ) 92 (NH 4 NO 3 ) 92 (Urea) Mean CV % SE ± Table 2. Cane and sugar yield and their components Treatments Kg N/fed O N 46 (as AN) 69(as AN) 92 (AN) 92 (Urea) Mean CV % SE ± Sig. Plant population x Season 2005/2006 Height (cm) Thick. (cm) Nodes No Plant population x Season 2006/2007 Height (cm) Thick. (cm) Nodes No

8 Table 3. Sugar yield components Season 2005/2006 Treatments Kg N/fed Pol % Purity % ERS % Fiber % Moist. % O N 46 (as AN) 69(as AN) 92 (AN) 92 (Urea) Mean CV % SE ± Sig non non non non Table 4. Sugar yield components Season 2006/2007 Treatments Kg N/fed O N 46 (as AN) 69(as AN) 92 (AN) 92 (Urea) Mean CV % SE ± Sig. Pol % Purity % ERS % Fiber % non Moist. % non 8

9 Table 5. Sugarcane yield (TC/F) N.U.E. (kg cane/kg N) and sugar yield (TS/F) second ratoon Treatments Kg N/fed O N 46 (as AN) 69(as AN) 92 (AN) 92 (Urea) Mean CV % SE ± Sig. Researcher managed 2005/006 TC/F c b a ab ab NUE TS/F 4.18 c 6.21 a 6.88 a 5.46 bc 6.27 a Researcher managed 2006/2007 TC/F b a a a a NUE TS/F 1.55 c 2.99 b 4.07 a 2.80 b 3.69 ab Table 6. Sugarcane yield (TC/F) N.U.E. (kg cane/kg N) and sugar yield (TS/F) second ratoon. Treatments Kg N/fed O N 46 (as AN) 69(as AN) 92 (AN) 92 (Urea) Mean On Farm experiments 2005/2006 TC/F NUE TS/F NUE: nitrogen use efficiency On Farm experiments 2006/2007 TC/F NUE TS/F

10 Table 7. Dominance analysis on the effect of fertilizer on sugar cane production in Guneid Scheme. Fertilizer Average Fertilizer Gross Variable dose yield Price return cost Net return Treatments (kg/fed) (t/fed) (SDG/kg) (SDG/fed) (SDG/fed) (SDG/fed) Dominance ON ,740-5, Kg N/fed as AN , , Kg N/fed as AN , , Kg N/fed as Urea , ,776 D 92 Kg N/fed as AN , ,042 D Price of urea equals 46 SDG/50 kg Price of Ammonium nitrate equals 42 SDG/50 kg Table 8. Marginal analysis on the effect of fertilizer on sugarcane production in Guneid Scheme Average Variable cost Net return Marginal Treatment yield (t/fed) (SDG/fed) (SDG/fed) cost Marginal return MRR ON , Kg N/fed as AN , ,351 3, Kg N/fed as AN , ,060 3,

11 8 7 6 Sugar yield TS/F AN 92Urea Fertilizer rate kg N/F Fig. 1: Average sugar yield TS/F 2005/2006 Vs fertilizer rates Yield TC/F Yield TC/F 2005/2006 Yield TC/F 2006/ AN 92Urea Fertilizer rate kg N/F Fig.2: Average Yield TC/F 2005/2006 and 2006/2007 Vs fertilizer rates Appendix 1. Tissue Analysis guide to deficient and non deficient sugarcane Nutrient Plant part Critical Range showing deficiency 11 Range without deficiency Nitrogen Blades 3,4,5,6 1.0 % % % Phosphorus Sheath 3,4,5, % %

12 Internodes % - - Potassium Sheath 3,4,5, % % % Calcium Sheath 3,4,5, % % 1 2 % Magnesium Sheath 3,4,5,6 0.1 % < 0.1 % % Sulfur Blades 3,4,5, ppm ppm Zinc Sheath 3,4,5,6 10 ppm < 10 ppm ppm Copper Blades 3,4,5,6 5 ppm < 3.5 ppm ppm Iron Blades 3,4,5, ppm ppm Manganese Blades 3,4,5, ppm ppm Molybdenum Blades 3,4,5, < ppm Boron Blades 3,4,5,6 1 ppm < 1 ppm 2 30 ppm Humbert (1968) ppm 12