Effect of Filter Cake and Mineral Fertilizers on Yield of Plantcane in the Sugarcane Plantations of Ethiopia

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1 Proc. Ethiop. Sugar. Ind. Bienn. Conf., 1: (2009) RESEARCH PAPER Effect of Filter Cake and Mineral Fertilizers on Yield of Plantcane in the Sugarcane Plantations of Ethiopia Girma Abejehu Ethiopian Sugar Development Agency, Research Directorate P.O. Box 15, Wonji, Ethiopia Abstract A study was conducted in the sugarcane plantations of Ethiopia to determine the optimum rates of filter cake and mineral fertilizers for sugarcane production. The experiment was laid out in randomized complete block design with three replications. Five levels of filter cake (0, 30, 60, 90, 120 t ha -1 ) in factorial combination with four levels of N (0, 52, 78, 104 kg ha -1 as ASN at Metahara and 0, 46, 92, 138 kg ha -1 as Urea at Wonji-Shoa) and with four levels of NP (0+0, , , kg ha -1 as Urea and DAP at Finchaa) were studied as treatment combinations. The results indicated that filter cake by mineral fertilizers interaction had a highly significant (P 0.01) effect both on cane and sugar yields in the plantations. Moreover, application of filter cake resulted in improved fertility status of soils (especially P) in all plantations. In addition, filter cake application showed promising response at 30 t ha -1 and 60 t ha -1 each applied with 78 kg N ha -1 (300 kg ha -1 ASN) at Metahara, 46 kg N ha -1 (100 kg ha -1 Urea) at Wonji- Shoa, and kg NPha -1 (150 kg ha -1 Urea and 250 kg ha -1 DAP) at Finchaa. Cost-benefit analysis of adjusted sugar yield also revealed that the above-mentioned rates of filter cake and mineral fertilizer combinations were economically viable at each plantation. Thus, 30 t ha -1 or 60 t ha -1 filter cake is recommended to be applied with 78 kg N ha -1 (300 kg ha -1 ASN) at Metahara; with 46 kg N ha -1 (100 kg ha -1 Urea) at Wonji-Shoa and with kg ha -1 NP (75 kg ha -1 Urea kg ha -1 DAP) at Finchaa, regardless of soil types. Introduction Sugarcane (Saccharum officinarum L) is an important industrial crop cultivated in different parts of the world for cane sugar manufacturing. In Ethiopia, the crop is cultivated at a commercial scale at Metahara, Wonji-Shoa, and Finchaa sugarcane plantations with a potential of expansion to new sites. Reports indicated that sugarcane is a heavy feeder of nutrients (Blackburn, 1984; Kakde, 1985; Faucconnier, 1993; Sundara, 2000). Hence to meet the nutrient requirements of the crop and achieve higher yields, fertilizers are commonly applied in sugarcane production. Use of mineral fertilizers alone as a source of nutrients, however, can not ensure sustainable productivity of soils and higher ISSN print version,

2 Girma A. 127 yields; especially in soils which are low in organic matter contents, fertilizers can not express their full beneficial effects on crop yields (Incle, et al., 1999; FAO, 2000). Thus, combined use of organic materials and mineral fertilizers can be an important option if productivity of soils is to be maintained at desirable level. Organic additions are known to improve both physical and chemical properties of soils (Ahenkorah, et al., 1993; Miller and Donahue, 1997; Scholl, 1998; Shakweer et al., 1998; Sundara, 2000; Kaur, et al., 2004). Studies carried out in Ethiopia (Holeta, Bako and Awassa) also indicated that combined use of organic materials and mineral fertilizers resulted in increased grain yield of cereals (Taye, 1996). Likewise, Korndorfer and Anderson (1997), and Morris et al (2007) indicated that use of filter cake with mineral fertilizers in sugarcane cultivation had positive effect on sugar yield. In the sugarcane plantations of Ethiopia, filter cake is produced each year at large quantities during sugar processing. Such by-product is known to have diverse agricultural benefits in view of sustaining productivity of soils besides being rich in some plant nutrients mainly nitrogen, phosphorous, and micronutrients (Chang Yen et al., 1983; Blackburn, 1984; Kakde, 1985; Fauconnier, 1993; Korndorfer and Anderson, 1997). Because of its high organic matter content it has also beneficial effects on soil physical properties such as aeration and drainage, moisture retention and nutrient retention capacities (Sundrara, 2000). From environmental point of view, filter cake is known to have no side effects when applied to farmlands especially after 1to 2 months of curing (Korndorfer and Anderson, 1997, Sundara, 2000). However, according to the same authors, when filter cake is applied at higher doses it could affect permeability and infiltration rate of the soil. In Ethiopian sugarcane plantations, filter cake has been used for agricultural purpose since long time. However, limited information is available on the optimum amount to be applied to cane fields. Today since cost of mineral fertilizers is increasing at an alarming rate on one hand and there is a high need to increase productivity per unit area on the other, effective use of such byproducts for agricultural purpose becomes an important approach to ensure sustainable and profitable of sugarcane production in the country. Therefore, this study was conducted with the major objective of determining optimum rates of filter cake and mineral fertilizers for sugarcane production. Materials and Methods Description of the Study Area The study was conducted in the sugarcane plantations fields of Wonji-Shoa (8 o 30' to 8 o 35' N; 39 o 20' E; 1540 m.a.s.l.), Metahara ( 8 o N; 39 o 52' E; 950 m.a.s.l.) and Finchaa (9 o 31' to 10 o N; 37 o 15' to 37 o 30' E; 1350 to 1650 m.a.s.l.). They receive an average of 831, 554 and 1280 mm rainfall, respectively.

3 Effect of filter cake and mineral fertilizers 128 Methodology The experiment was conducted on light and heavy soil types at Wonji-Shoa and Metahara, and on Luvisols and Vertisols at Finchaa. Filter cake rates were 0, 30, 60, 90, and 120 t ha -1 in all plantations while mineral nutrients rates include 0, 52 78, and 104 kg Nha -1 at Metahara; 0, 46, 92, and 138 kg N ha -1 at Wonji-Shoa; and 0+0, , , kg N+P ha -1 at Finchaa. The sources of nitrogen were ASN at Metahara, Urea at Wonji-Shoa, and Urea and DAP at Finchaa. While the source of phosphorous was DAP. The experiment was laid out in randomized block design with three replications in factorial arrangement. Treatment combinations are presented in Table 1. Filter cake (air dried) was manually applied and incorporated in the furrows and at ridge sides after furrowing. To prevent mixing of treatments between plots each plot was irrigated separately by closing furrow ends during pre-planting and early irrigations after planting (particularly in case of Metahara and Wonji- Shoa). Planting was executed using healthy setts of test variety (NCo 334). After planting, the setts were covered with soil immediately and each plot was irrigated lightly. After 3 to 4 irrigations, furrow ends of each plot (particularly in case of Metahara and Wonji-Shoa) were opened and the usual irrigation activity was made to continue as per the practice of the plantations. The respective doses of phosphorous (as DAP) and nitrogen (as Urea and ASN) were applied at planting and at 2.5 months of crop age, respectively. Composite soil samples were taken before treatment application and at harvest. The samples were analyzed for major chemical properties (EC1:2.5, ph1:2.5, organic carbon (OC), available phosphorous, total nitrogen and texture following standard analytical procedures (Sahlemedhin and Taye, 2000). Air dried filter cake samples were analyzed for ph, EC, P, N and organic carbon following standard procedures (Girma, 2001). Its moisture content was also determined before application. During the course of the experiment, sprout count was done a month after planting. Tiller and stalk population counts were done at 3 and 9 months of crop age, respectively. At harvest, 21 millable stalks were taken for stalk length, diameter, weight and juice quality parameters (pol, brix, purity, and rendement) determinations. In addition, for each plot cane weight of the middle four furrows was measured using grab loader mounted crane scale at harvest. Data Analysis The cane and sugar yields data were subjected to analysis of variance using the MSTAT computer software (MSTATC, 1988). Mean yields of the interaction effects and the main effects were compared using Duncan s Multiple Range Test (DMRT) and Least Significant Difference (LSD), respectively. Moreover, costbenefit analysis was done by considering the following conditions: sugar price at the factory gate (Birr t -1 ): 4000 for Metahara and Wonji-Shoa sugarcane

4 Girma A. 129 plantations (fixed value), and 3680 for Finchaa sugarcane plantation (actual value or the official selling price); estimated cost of mineral fertilizers (Birr t -1 ): for ammonium sulphate nitrate (ASN), for Urea, and for DAP; cost of production (Birr t -1 of sugar): , and Birr in case of Metahara, Wonji-Shoa, and Finchaa, respectively; cost of filter cake application to cane fields within the average distance of about 8.5km from the Factory site (which also includes loading and transportation costs) (Birr ha - 1 ): , , , and for application of filter cake rates 30, 60, 90, and 120 t ha -1, respectively. The costs of other cultural practices like weeding, irrigation, and harvesting were similar with the plantations. For the purpose of cost-benefit analysis, the experimental sugar yield was adjusted down by 15% to reflect commercial sugar yield under the actual plantations management practices. Table 1. Treatment combinations for filter cake and mineral fertilizers experiment Filter cake (t ha -1 ) + Filter cake (t ha -1 ) + (N+ Treat. Filter cake (t ha -1 ) + N (kg ha -1 ) Filter cake (t ha -1 ) + (N+ Treat. N (kg ha -1 ) P2 O5) (kg ha -1 ) code P2 O5) (kg ha -1 ) Code Metahara Wonji- Finchaa Metahara Wonji- Finchaa Shoa Shoa A K ( ) B ( ) L ( ) C ( ) M D ( ) N ( ) E O ( ) F ( ) P ( ) G ( ) Q H ( ) R ( ) I S ( ) J ( ) T ( ) Results and Discussion Effects of Filter Cake on Major Soil Chemical Properties Analytical results of soil samples taken from experimental sites immediately after harvesting of plantcane showed that application of filter cake had no remarkable effect on ph and EC (salt content) of soils in the plantations. However, it highly improved available phosphorous and organic carbon contents of the soils (Table 2). Moreover, the high values of organic carbon in soils recorded at harvest indicated that filter cake could be an important source of organic matter to the soil which plays a key role in maintaining nutrient supply and retention properties of soils and in improvement of soil structure.

5 Effect of filter cake and mineral fertilizers 130 Application of filter cake to heavy soil at Metahara and Wonji-Shoa and to Vertisols at Finchaa had also similar effect on soil properties. Similarly, different authors reported the importance of filter cake in improving quality of (Fauconnier, 1993; Sundara, 2000; Moris et al., 2007). Table 2. Residual effect of filter cake on major soil properties Filter cake (tha -1 ) ph (H2O) (1:2.5) Major soil properties at harvest (0-60cm) EC (1:2.5) (dsm -1 ) Organic C (%) Total N (%) Available P (ppm) Metahara (8.2) 0.21 (0.29) 1.10 (1.47) 0.10 (0.12) 9.6 (7.81) (8.1) 0.20 (0.33) 2.97 (3.66) 0.14 (0.14) (41.65) (8.2) 0.21 (0.34) 3.08 (4.06) 0.16 (0.16) (69.79) (8.3) 0.20 (0.29) 3.13 (4.24) 0.14 (0.18) (75.90) (8.2) 0.19 (0.38) 3.17 (4.51) 0.16 (0.16) (87.35) Wonji-Shoa (7.1) 0.25 (0.28) 1.22 (1.47) 0.09 (0.13) 8.59 (7.42) (7.5) 0.36 (0.24) 3.79 (3.77) 0.12 (0.15) (42.35) (7.6) 0.37 (0.45) 4.81 (4.86) 0.14 (0.15) (58.70) (7.7) 0.37 (0.45) 4.11 (4.94) 0.16 (0.21) (79.13) (7.6) 0.39 (0.58) 4.93 (4.96) 0.15 (0.25) (89.38) Finchaa (6.1) 0.11 (0.10) 1.51 (1.45) 0.10 (0.12) 5.30 (4.81) (6.7) 0.13 (0.11) 3.73 (3.79) 0.13 (0.15) (42.35) (6.9) 0.12 (0.15) 4.22 (4.86) 0.17 (0.16) (56.70) (7.1) 0.13 (0.21) 4.11 (4.97) 0.14 (0.21) (89.13) (7.1) 0.15 (0.24) 4.16(4.98) 0.16 (0.26) (98.35) Numbers within and outside parenthesis are values of light and heavy soil, respectively at Metahara and Wonji-Shoa, and of Luvisols and Vertisols at Finchaa Effect of Filter Cake on Cane and Sugar Yields At Metahara, analysis of variance (ANOVA) of cane and sugar yields indicated that regardless of soil types the main effect of filter cake was highly significant (P 0.01) but that of nitrogen was non significant. The interaction effect between filter cake and nitrogen was highly significant (P 0.01) for cane yield and significant (P 0.05) for sugar yield on light soil; and it was highly significant (P 0.01) both for cane and sugar yields on heavy soil (Table 3). This showed that the two materials have complementary effects in improving production and productivity. On both soil types, cane and sugar yields due to either nitrogen (as ASN) or filter cake applied alone were inferior compared to that obtained due to combined applications of both materials. Moreover, application of filter cake highly increased sugar yield compared to mineral fertilization.

6 Girma A. 131 Table 3. Cane and sugar yields as affected by filter cake and nitrogen application on light and heavy soils of Metahara Filter cake (t ha -1 ) N (kg ha -1 ) Light soil e (26.0f) 225.7de (27.2ef) 243.7b-d (30.8b-f) 243.7b-d (30.9b-f) cd (27.5ef) 253.9b-d (30.4b-f) 268.5ab (34.8a-c) 268.5ab (34.0a-c) b-d (28.8d-f) 262.7a-d (31.9a-e) 298.3a (36.5a) 298.3a(35.5ab a-d (30.8b-f) 265.3a-d (33.4a-d) 296.0a (36.2a) 296.0a (34.0a-c) a-d (30.0c-f) 270.0a-c (32.8a-d) 297.0a (36.4a) 297.0a (34.1a-c) Heavy soil f (33.8f) 281.7ef (36.0ef) 293.0d-f (37.0de) 297.3c-e (38.2b-e) d-f (36.3ef) 302.9b-e (38.0b-e) 325.4ab (41.5a) 322.4a-c (40.0a-d) de (37.5c-e) 310.6a-d (39.6a-d) 338.5a (41.8a) 328.0ab (40.2a-c) b-e (37.4c-e) 315.4a-d (39.7a-d) 327.9ab (40.9ab) 325.8ab (39.8a-d) b-e (38.4b-e) 313.0a-d (39.4a-d) 328.0a (40.8ab) 327.3ab (40.9ab) Means followed by the same letter for each parameter at each soil type were not significantly different at P<0.05 according to DMRT; numbers within and outside parenthesis are cane and sugar yield, respectively Similarly, on light soil, about 12.6 % (3.9 t ha -1 ) and 18.1 % ((5.6 t ha -1 ) sugar yield advantage was obtained over the conventional ASN rate due to combined application of 30 t ha -1 filter cake with 78 kg N ha -1 (300 kg ha -1 ASN), and 60tha -1 filter cake with 78 kg N ha -1 (300 kg ha -1 ASN), respectively. Whilst, on heavy soil, 8.6 % (3.3 t ha -1 ) and 9.4 % (3.6 t ha -1 ) increase in sugar yield was obtained over the conventional ASN rate at 30 t ha -1 and 60 t ha -1 filter cake rates, respectively, each applied with 78 kg N ha -1. In general, both soil types responded to filter cake application in a similar pattern in terms of yield improvements. This is in agreement with findings from similar studies (Tangkoonbornibun et al, 2007); where application of 50 t ha -1 filter cake increased yield from 60 t ha -1 up to 100 t ha -1. At Wonji-Shoa, ANOVA of cane and sugar yields indicated that the main effect of filter cake and the interaction effect of filter cake with N were highly significant (P 0.01) on light soil and significant (P 0.05) on heavy soil. The main effect of nitrogen was, however, non significant (P 0.05) both for cane and sugar yields on both soil types. Moreover, combined application of filter cake with nitrogen showed improved sugar yield compared to conventional nitrogen rate (Table, 4). Thus, on light soil, about % (4.1t ha -1 ) and 26.9

7 Effect of filter cake and mineral fertilizers 132 % (8.0 t ha -1 ) sugar yield advantage was obtained over the conventional nitrogen rate at combined application of 30 t ha -1 filter cake with 46 kg N ha -1, and 60 t ha - 1 filter cake with 46 kg N ha -1, respectively. On heavy soil, the relative sugar yield advantage of about 14.0 % (5.0 t ha -1 ) and 17.3 % (6.2 t ha -1 ) was obtained over the conventional nitrogen rate at 30 t ha -1 filter cake applied with 46 kg N ha -1, and at 60 t ha -1 filter cake applied with 92 kg N ha -1 rate, respectively. In line with this, studies carried out using filter cake and mineral fertilizers indicated that application of filter cake increased both cane and sugar yields by 26 % compared to mineral fertilizer treatment (Mories et al., 2007). Kaur et al (2004) also stressed the importance of nutrient recycling by using mineral fertilizers with organic materials together. Table 4. Cane and sugar yields as affected by filter cake and nitrogen application on light and heavy soils of Wonji-Shoa Fiter cake (t/ha) N (kg ha -1 ) Light soil d (25.9e) 203.6b-d (29.7c-e) 203.0cd (29.8c-e) 207.0cd (30.1b-e) cd (29.3c-e) 245.5ab (33.9a-d) 238.7ab (32.6a-d) 245.4ab (33.9a-d) bc (29.6c-e) 261.4a (37.8a) 267.9a (37.9a) 260.7a (35.4a-c) ab (31.4b-e) 245.7ab (32.7a-d) 262.2a (35.1a-d) 263.5a (35.3a-d) ab (29.0de) 259.2a (35.3a-d) 263.7a (36.0ab) 262.8a (33.1a-d) Heavy soil c (32.0c) 252.1bc (35.3bc) 253.2bc (35.8bc) 253.6bc (35.6bc) bc (35.2bc) 285.6ab (40.8ab) 273.2ab (38.5ab) 267.5a-c (38.6ab) a-c (36.0bc) 285.4ab (40.1ab) 299.8a (42.0a) 272.3ab (40.1ab) ab (38.3ab) 282.7ab (40.1ab) 267.3a-c (37.5a-c) 275.8ab (38.8ab) ab (38.0ab) 296.0a (40.7ab) 265.1a-c (37.2a-c) 259.9a-c (36.3b-c) Means followed by the same letter for each parameter at each soil type were not significantly different at P<0.05 according to DMRT; numbers within and outside parenthesis are cane and sugar yield, respectively However, as indicated in table (4), application of nitrogen without filter cake on both soil types resulted in low sugar tonnage at all levels compared to combined applications of both materials. However, considering nitrogen application, there was no statistically significant difference in cane and sugar yields among all nitrogen rates unlike the case at Metahara. This implies that at present condition application of nitrogen above 46 kg ha -1 (as Urea) is not economical.

8 Girma A. 133 At Finchaa, as shown in table (5), ANOVA of cane and sugar yields on two soil types (Luvisols and Vertisols) showed that the main effect of filter cake was highly significant (P 0.01), while that of mineral fertilizers was non significant (P 0.05). The interaction effect between filter cake and mineral fertilizers was highly significant (P 0.01) for cane yield and significant (P 0.05) for sugar yield on Luvisols, and it was highly significant (P 0.01) both for cane and sugar yields on Vertisols. Similar to Wonji-Shoa and Metahara, combined application of filter cake and mineral fertilizers resulted in increased sugar yield compared to conventional mineral fertilizers rates. Accordingly, sugar yield advantage of 15.2 % (4.6 t ha -1 ) was obtained on Luvisols over the conventional mineral fertilizers rates at combined application of 30 t ha -1 filter cake and the conventional rates of mineral fertilizers (150 kg ha -1 Urea and 250 kg ha -1 DAP) (Table 5). Likewise, on Vertisols application of 30tha-1 filter cake with conventional rates of mineral fertilizers increased sugar yield by 18.2 % (4.8 t ha -1 ) over that at conventional mineral fertilizers rates. Table 5. Cane and sugar yields as affected by filter cake and NP fertilizers (Urea and DAP) application on Luvisols and Vertisols of Finchaa Filter cake (t ha -1 ) N+P2O5 (kg ha -1 ) Luvisols h (24.3g) 222.9gh (26.9fg) 241.4f (30.2b-f 248.5ef (30.3b-f) fg (27.3e-f) 259.4c-e (30.3b-f) 275.4a-c (34.8a 263.3b-e (31.4a-f) d-f (29.0d-f) 269.4a-d (30.8a-f) 284.4a (33.4ab 267.3a-d (31.7a-d) c-e (28.8d-f) 269.9a-d (30.7a-f) 278.7ab (32.0a-d 278.2ab (33.3a-c) d-f (29.6c-f) 271.3a-c (31.4a-e) 285.0a (34.3ab 274.2a-c (31.8a-d) Vertisols h (20.4h) 168.6h (22.7gh) 202.3ef (26.4d-f) 202.7ef (26.0ef) fg (23.1gh) 190.3fg (27.4b-f) 239.0a-c (31.2a) 231.7a-d (28.7a-e) d-f (24.9fg) 210.2d-f (29.3a-e) 248.0a (31.2a) 236.4a-c (29.4a-d) c-e (27.1b-f) 223.2c-e (29.9a-c) 247.8ab (30.3ab) 247.8a-c (28.0a-e) a-d (26.7c-f) 228.9a-d (29.0a-e) 243.3a-c (29.6a-d) 243.5a-c (28.8a-e) Means followed by the same letter for each parameter at each soil type were not significantly different at P<0.05 according to DMRT; numbers within and outside parenthesis are cane and sugar yield, respectively Application of mineral fertilizers without filter cake, however, resulted in low cane and sugar tonnages compared to combined applications of both materials on both soil types. Among the mineral fertilizer rates, however, no significant difference in yield was observed between the highest rates and the middle rates

9 Effect of filter cake and mineral fertilizers 134 (currently recommended NP rates). The lowest NP rates resulted in poor cane and sugar yields. Thus the present finding is in agreement with the already recommended NP rates as far as crop response is concerned. Economic Analysis Cost-benefit analysis result of this study revealed that highest net return at the selling price of 4000 Birr t -1 of sugar was obtained at 60 t ha -1 filter cake rate applied with 78 kg N ha -1 (as ASN) at Metahara, at the same filter cake rate applied with 46kg N ha -1 (as Urea) at Wonji-Shoa, and at 30 t ha -1 filter cake applied with conventional rates of mineral fertilizers (75 kg ha -1 Urea and 125 kg ha -1 DAP) at Finchaa (Table 6). On the other hand, economically viable filter cake-mineral fertilizer treatment combinations were found to be 30 t ha -1 filter cake and 78 kg N ha -1, 60 t ha -1 fitter cake and 78 kg N ha -1 at Metahara; 30 t ha -1 filter cake and 46 kg N ha -1, and 60 t ha -1 filter cake rate applied with each of 46 kg N ha -1 and 92 kg N ha -1 at Wonji-Shoa, and the two filter cake rates (30 t ha -1 and 60 t ha -1 ) each applied with lowest and conventional mineral fertilizers rates at Finchaa. All filter cake rates applied without mineral fertilizers were also found to be economically viable in all the plantations although the extra sugar yield (or net return) obtained at such rates was low. On the other hand, except at Wonji-Shoa, all mineral fertilizer rates applied without filter cake were not economically viable. In Wonji-Shoa, however, 46 kg N ha -1 was found economically viable compared to other mineral fertilizer treatments. In general, the present findings revealed that combined use of filter cake and mineral fertilizers was advantageous compared to use of mineral fertilizers alone to ensure productivity of sugar per unit area and attain better economic return. The available literature also indicate that use of filter cake with mineral fertilizers has beneficial effect in increasing sugar yield compared to mineral fertilization alone (Korndorffer and Anderson, 1997; Sundara, 2000; Moris et al. 2007; Tangkoonboribun et al., 2007). Moreover, economic viability of filter cake rates applied without mineral fertilizers (especially at 60 t ha -1 filter cake rate) indicates the possibility of producing organic sugar which has high demand and high price in the world market today.

10 Girma A. 135 Table 6. Net return (Birr ha -1 ) and cost benefit ratio analysis for filter cake and mineral fertilizers in the sugarcane plantations of Ethiopia Treat. code Metahara Wonji-Shoa Finchaa Light soil Heavy soil Light soil Heavy soil Luvisols Vertisols NR CBR NR CBR NR CBR NR CBR NR CBR NR CBR A B : : : : : :1.18 C : : : : : :1.24 D : : : : : :1.12 E : : : : : :1.33 F : : : : : :1.32 G : : : : : :1.31 H : : : : : :1.17 I : : : : : :1.37 J : : : : : :1.35 K : : : : : :1.30 L : : : : : :1.19 M : : : : : :1.40 N : : : : : :1.34 O : : : : : :1.27 P : : : : : :1.13 Q : : : : : :1.37 R : : : : : :1.31 S : : : : : :1.24 T : : : : : :1.15 Note: NR = Net return, CBR = Cost benefit ratio

11 Effect of filter cake and mineral fertilizers 136 Conclusion and Recommendations Findings of this study indicated that application of air dried filter cake with mineral fertilizers resulted in higher cane and sugar tonnages in the sugarcane plantations of Ethiopia. In addition, filter cake application improved nutrient reserve potential of soils, i.e, after harvesting plant cane, the amount of available phosphorous was exceptionally high in soils receiving filter cake. It also improved organic carbon or organic matter content of soils at harvest, which is important for improving both physical and chemical properties of soils. Hence use of filter cake could be one of important options for sustaining productivity of soils under intensive farming systems like sugarcane production. On the other hand, the cost-benefit analysis result revealed that different treatment combinations including filter cake rates applied without mineral fertilizers were found economically viable at each sugar estate regardless of soil types. Therefore, based on the present findings 30tha -1 or 60tha -1 filter cake is recommended to be applied with 78 kg N ha -1 (300 kg ha -1 ASN) at Metahara; with 46 kg N ha -1 (100 kg ha -1 Urea) at Wonji-Shoa and with kg ha -1 N+P 2 O 5 (75 kg ha -1 Urea kg ha -1 DAP) at Finchaa, regardless of soil types. References Ahenkorah Y, E Owusu-Bennoah and GNN Dowuoana (eds.) Sustaining soil productivity in intensive African agriculture. Seminar proceedings, Acra, Gahana, November Blackburn F Sugarcane. Tropical Agricultural Series, Longman Group, UK Ltd. Chang-Yen I, PI Bodoe and R Mohammed Chemical analysis of seven nutrient elements in some sugarcane by-products. Tropical Agriculture, 60 (1): Facounnier R Sugarcane. The Tropical Agriculturalist. The MacMillan Press Ltd. FAO (Food and Agriculture Organization) Fertilizers and their use. A pocket guide for extension officers. 4 th edition, FAO, Rome, Girma Abejehu Laboratory procedures for determination of important constituents in organic wastes/materials: Literature Review. Ethiopian Sugar Industry Support Center Sh. Co., Research and Training services, Wonji, Ethiopia Gustafson AF Soils and soil management. Agrobios, India. Inckel M, T Smet De, T Tersmette and TVeldkamp Preparation and use of compost. Agrodok-series, No. 8, CTA, The Netherlands. Kakde JR Sugarcane production. Metropolitan Book Co., Pvt. Ltd., India. Kaur K, KK Kapoor and AP Gupta Impact of organic manures with and without mineral fertilizers on soil chemical and biological properties under tropical conditions. Journal of Plant Nutrition and Soil Science, 168(1): Korndorfer GH and DL Anderson Use and impact of sugar-alcoohol residues vinase and filter cake on sugarcane production in Brazil. SUGAR y AZUCAR, 26-35, March 1997.

12 Girma A. 137 Miller RW and RL Donahue Soils in our environment. 7 th ed., Prentice House of India, New Delhi, Moris DR, RA Gilbert, CR Rainbol, RE Perdomo, G Powell, B Eiland and G Montes Sugarcane yields and soil chemical properties due to mill mud application to sandy soil. Proceedings of International Society of Sugar Cane Technologists. 26: MSTATC MSTAT Version2.10. Crop and soil science department, Michigan State University. Sahlemedhin Sertsu and Taye Bekele (eds.) Procedures for soil and plant analysis. Technical paper 74. National Soil Research Center, Ethiopian Agricultural Research Organization, Addis Ababa, Ethiopia. Sandara B Sugarcane cultivation.vikas Publishing House, Pvt. Ltd., India Scholl LV Soil fertility management. Agrodok-series No.2, CTA, The Netherlands. Shakweer MHA, EA Sayed and SA Ewees Soil and plant analysis as a guide for interpretation of the improvement efficiency of organic conditioners added to different soils in Egypt. Communication in Soil Science and Plant Analysis. 29 (1-4): Tangkoonboribun R, S Ruaysoongnern, P Vityakon, B Toomsan and MS Rao Effect of organic ameliorants to improve soils using sugarcane as a model. Proceedings of International Society of Sugar Cane Technologists. 26: Taye Bekele Utilization of organic residues in Ethiopia. A Review. In: Teshome Yizengaw, Eyasu Mekonnen and Minesnot Behailu (eds). Proceedings of the Third Conference of Ethiopian Society Soil Science (ESSS), , February 28-29, 1996, Addis Ababa, Ethiopia.