Effects of Mixed Organic and Inorganic Fertilizers Application on Soil Properties and the Growth of Kenaf (Hibiscus cannabinus L.) Cultivated on Bris Soils

The demand for kenaf in the world increases rapidly by the years. Cultivation of the crop in Malaysia is a challenging task, especially when kenaf is grown on sandy soils with low fertility, such as the BRIS Soils (Beach Ridges Interspersed with Swales). A pot study was conducted in a glasshouse at Universiti Putra Malaysia to evaluate the potential of inorganic and organic fertilizers or their combination for growing kenaf on very sandy BRIS Soils, using variety V36. There were altogether sixteen treatments: (T1)-control (100% BRIS soil), (T2)-NPK (chemical fertilizer), (T3)-CM (chicken manure), (T4)-B (biochar), (T5)-Z (zeolite), (T6)-NPK+CM, (T7)-NPK+B, (T8)-NPK+Z, (T9)-CM+B, (T10)-CM+Z, (T11)-B+Z, (T12)-NPK+CM+B, (T13)-NPK+CM+Z, (T14)-CM+B+Z, (T15)-NPK+B+Z and (T16)NPK+CM+B+Z. Results showed that application of inorganic material or organic fertilizer in combination with chemical fertilizer (T2 and T16) improved soil fertility, which are reflected by the increase inexchangeable K, Ca and Mg, CEC, total N, total C and available P. The highest kenaf growth was observed in T15 treatment.Application of biochar, zeolite or chicken manure alone on the soils did not result in better kenaf growth compared to the control. Zeolite and biochar should be applied with other fertilizers or organic substrate to obtain a positive yield of crop and increase the soil properties. In addition, more studies on the application of chicken manure at different ratios should be conducted to obtain the best yield. Combination treatment, T15 (NPK + biochar + zeolite) can be suggested to the farmers especially cultivation of kenaf on sandy BRIS soil in order to obtain the best kenaf growth performance and indirectly reduce excessive use of chemical fertilizers.


INTRODUCTION
Kenaf (Hibiscus cannabinus L.) is a warm-season annual crop that is similar tocotton, okra and Hibiscus. It can reach the height of 2 to 6 m and is harvested for their stalks from which the fiber is extracted (Preston, 2003). Kenaf is native to East-Central Africa and all over South America-Asia. It is utilized in the cordage and sacking manufacture as a substitute of jute and more recently as a raw material for the production of paper pulp (Abdul-Hamid et al., 2009).

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In Malaysia, Kenaf is normally planted on sandy BRIS Soils due to its ability to adapt to adverse environmental conditions, such as low soil fertility. BRIS Soils are located along the coastal plains of Peninsular Malaysia and Sabah with an approximate area of 200,000 ha (Abdul-Hamid et al., 2009). They contain up to 82-99% sand particles with cation exchange capacity of 9.53 cmol c kg -1 soil and the soil reaction is usually acidic (Chen, 1985;Roslan et al., 2010). Because of high surface soil temperature, low water holding capacity, low organic content, high infiltration rate and low nutrients availability, most of the crops planted on BRIS Soils do not perform well (Hanafi et al., 2010). Lack of moisture and low nutrient retention are the main limitations for crop production on BRIS Soils.
There are some fertilizers and soil amendments that are able to improve the fertility of BRIS Soils. Biochar or charcoal is one of the potential soil amendments that can be used to improve the productivity of these problematic soils. Biochar is produced from combustion of plant residues and it contains stable carbon that is able to remain for a long period of time in soil (Major et al., 2010). Addition of biochar into the soils would increase plant nutrients, resulting in improved soil fertility (Lehmann et al., 2003;Rondon et al., 2007). Steiner et al. (2008) found that application of biochar amended with fertilizer increased crop yield.
Utilization of chicken manure as an organic fertilizer nowadays has been increasing dramatically especially in improving soil productivity and crop production. Chicken manure is believed to be able to supply many plant nutrients to soils. Study carried by Dikinya and Mufwanzala (2010) showed that soil fertility can be enhanced by chicken dung application by way of increasing exchangeable bases in the soils. Furthermore, other nutrients such as nitrogen and phosphorus can be increased. Chicken manure is one of the preferred organic fertilizers because of the high content of macronutrients in it (Warman, 1986;Duncan, 2005).
Zeolite is derived from volcanic ash and is sometimes used as a soil conditioner to improve soil fertility. It has high cation exchange capacity and therefore can reduce nutrient loss via leaching during rainy season (Mumpton, 1999;Glisig et al., 2008;Hecl and Toth, 2009). Its high CEC is also able to reduce ammonia volatilization and increase the affinity of ammonium ions binding (Ming and Dixon, 1986). Nutrient uptake efficiency of crops can be enhanced by applying urea in combination with zeolite (Ahmed et al., 2008). In addition, available nutrients in the soils can be retained at much longer time. This study was undertaken to determine the effects of mixed organicinorganic fertilizer application on the properties of BRIS Soils and the growth of Hibiscus cannabinus L.

Study Site and the Soil Used
A study was conducted at the Controlled Environment Structure, No. 2(CES 2), Agrotech Agriculture Complex, University Putra Malaysia, Serdang, (2° 58'54" N, 101° 42'51" E) for a period of four months (January to April 2012). The minimum and maximum temperatures recorded during the study period inside the glasshouse were 23°C and 38°C, respectively. The soil used in this experiment was Baging Series, taxonomically classified as sandy, siliceous family of Typic Quartzipsamments, containing 88.68 % sand, 4.68 % silt and 6.64 % clay. This soil type is normally located nearest to the coastline and can be found in east coast of Peninsular Malaysia, especially along Kelantan-Terengganu and Borneo Island, Sabah. These coastal plains comprised of many soil series whereas the common can be found are Baging, Rhu Tapai, Rudua and Jambu series (Roslan et al., 2011).

Treatments and Experimental Design
Twenty kilograms of the sandy BRIS Soils was filled in pots of 35 cm height and 35 cm diameter. The soils were treated with fertilizers (inorganic and organic), biochar and/or zeolite. The biochar used in this study was derived from oil palm Empty Fruit Bunch (EFB). Processed chicken manure used was in pellet form. Zeolite was added seven days before planting.  (CEC,171.74 cmol c kg -1 soil). Rate of NPK used was as recommended by National Kenaf and Tobacco Board for BRIS Soils management, which was applied twice (before and after planting). There were altogether sixteen treatments: (T 1 )-control (100% BRIS soil), (T 2 ) -NPK (chemical fertilizer), (T 3 ) -CM (chicken manure), (T 4 ) -B (biochar), (T 5 )-Z (zeolite), (T 6 )-NPK+CM, (T 7 )-NPK+B, (T 8 )-NPK+Z, (T 9 )-CM+B, (T 10 )-CD+Z, (T 11 )-B+Z, (T 12 )-NPK+CM+B, (T 13 )-NPK+CM+Z, (T 14 )-CM+B+Z, (T 15 )-NPK+B+Z and (T 16 )-NPK+CM+B+Z were established in this experiment, with six replications for each treatment ( Table 1). Biochar and chicken manure were applied at the rate of 1000kg/ha, respectively and scaled down to per pot basis equivalent to 100g. Zeolite was applied at 80g per pot. NPK fertilizer was applied at the rate of 100 kg/ha for N, 100 kg/ha for P 2 O 5 and 100kg/ha for K 2 O. The NPK fertilizer was scaled down to per pot basis equivalent to 1 g urea, 2 g TSP and 1 g of MOP. For NPK application, it was applied two times: 3 days before planting and 30 days after planting. The experimental design was Completely Randomized Design (CRD).

Kenaf Seedlings
Kenaf seedlings, variety V36, were used in the study. This is the variety recommended by the National Kenaf and Tobacco Board for growing on infertile soils. Seven kenaf seeds were planted at 0.5 cm depth and the seedlings were thinned down to three plants per pot during the germination stage.

Soil Sampling and Analyses
Soil samples were collected randomly from three points in each pot (0-15 cm depth), before planting and after harvesting. The soils were mixed uniformly to form a composite sample and air-dried for 24 fours, followed by sieving through a ≤2.0 mm sieve and kept in polyethylene bags for further analysis in the laboratory. The selected soil physico-chemical properties determined were texture, pH, exchangeable cations (K, Na, Mg, Ca), exchangeable Al, exchangeable ammonium (NH 4 + ), Nitrate (NO 3 -), available P, cation exchange capacity, total N and total C. Soil texture was determined by the pipette method of Day (1965). Total N and C and were analyzed by dry combustion method using LECO CHNanalyzer (model VICNS Tru Mac Analyzer). pHKCl and pH water of the soils were measured with a glass electrode at soil:KCl/water ratio of 1:5 (Jones, 2001). Exchangeable bases (K, Ca, Mg and Na) and Cation Exchange Capacity (CEC) were determined by the leaching method with ammonium acetatesolution (NH 4 OA c ) buffered at pH 7 (Lavkulich, 1981). The concentration of exchangeable bases was then analyzed using Atomic Absorption Spectrophotometer (AAS), model Shimadzu AA-6800. Available P was determined by Bray and Kurtz procedure no. 2 (Bray and Kurtz, 1945) and the concentrations were analyzed using Auto analyzer. Exchangeable acidity and exchangeable aluminum were extracted by 1 MKCl. The exchangeable acidity was determined by the titration method using 0.01 M NaOH and the concentration of Al using 0.01 M HCl (Sumner and Stewart, 1992). Exchangeable ammonium and nitrate were extracted from the soil samples using 2M KCl, followed by steam distillation method (Keeney and Nelson, 1982).

Measurement on Growth Performance of Kenaf
Height, diameter and the number of kenaf leaves were taken and recorded every month for a period of 16 weeks. Plant height was measured using a stainless steel ruler and height pole was used when the height reached 1 m and above. The height was measured from cotyledon level up to the base at the terminal bud. The diameter of the plant was measured at 10 cm above the ground using a digital caliper (Model Mitutoyo 200 mm). Two readings were recorded at the stem for diameter and marked using a permanent marker pen. Total number of leaves for each plant was calculated manually and the data were recorded.

Statistical Analysis
Growth parameter of different kenaf parts and soil parameters were analyzed using Analyses of Variance (ANOVA), followed by Duncan's Multiple Range Test Test (DMRT) to detect the significant difference among the treatments (SAS, 2001).

Initial Properties of the Soil
The physico-chemical properties of the soil before amending with fertilizersare presented in Table 2. The soil texture was mainly loamy sand (84.14% sand, 6.37% silt and 9.33% clay) and the pH KCl and pH water was 4.20 and 3.14, respectively. The exchangeable bases (K, Ca, Mg, Na) were low, with a range between 0.174 and 0.311 cmol c kg -1 . The low exchangeable bases were related to the sandy nature of the soils. Previous studies conducted by Toriman et al. (2009) reported that due to the sandy structure of the soil, the contents of bases in

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BRIS soil such as phosphorus, potassium, magnesium and calcium were relatively low. The CEC recorded in this study was very low with a value of 3.94 cmol c kg -1 soil which was due to low clay content and similar to other study found by (Malisa et al., 2011;Roslan et al., 2011) reported that the CEC values on a BRIS soil less than 5 cmol c kg -1 .This means that the bases are easily lost via leaching during rainy season. This is similar to Akbar et al. (2010) who reported that different in CEC values due to soil erosion or leaching. Parfitt et al. (1995) also reported that lower contents of clay and loam in the soil lead to a low CEC values. Other researchers also found that the CEC of soils in tropics were affected by different negative charges derived from clay minerals and due to the amount of clay in soil (Ohta and Effendi, 1992;Hamzah et al., 2009;Saga et al., 2010;Zaidey et al., 2010;Sakurai et al., 1998;Arifin et al., 2008;Roslan et al., 2011). Total N and total C were also low and hence these soils are considered as very poor. Previous studies also found that essential nutrient such as total N and total C in BRIS soil are relatively low (Malisa et al., 2011). Study conducted by Dharejo et al. (2012) who reported that the total N content in the BRIS soil was in range of 0.01-0.03% and similar reported to the present study.

Soil Properties at Harvest
There were significant differences detected between the control (T 1 ) and other treatments at p≤0.05 which prove that addition of organic and inorganic fertilizers improved the soil fertility ( Table 2). The soil pH in water and KCl was nearly neutral. The highest value of pH was observed for T 10 treatment with the respective value of 6.82 and 6.45. Chicken manure has an ability to increase acidic soils. The high pH value in this treatment was due the effect of chicken manure which contained calcium carbonate (Camberato and Mitchell, 2011). The lowest pH was recorded in T 5 treatment with the value of 4.21 in water and 3.82 in KCl. Present study showed that application of zeolite alone without combining with other soil amendment or any fertilizer cannot be expected to increase the BRIS soil chemical properties. In fact, the soil properties are more acidic and almost similar with control treatment. Zeolite should be applied with other fertilizer or soil amendment. Zeolite mixed with nitrogen, phosphorus and and potassium compounds enhances the actions of nutrient compounds as slow-release fertilizers, both in horticultural and extensive crops (Dwairi, 1998). Similar studies reported by Leggo (2000) who suggested that zeolite should be applied with organic substrate. Total N varied from 0.03 to 0.14 having the highest value of 0.14% in T 7 , followed by T 15 (0.137%), while the lowest value was recorded in T 1 (0.03%). Nitrogen, in the form of ammonium, is easily lost via volatilization. Results from this study showed that the loss can be minimized by combining N-fertilizer with biochar (T 7 ). This result is similar reported by Zheng et al. (2013), who stated that addition of biochar reduced N fertilizer demand in crop production due to reduction in N leaching, hence increase N use efficiency for agricultural purposes. Taghizadeh-Toshi et al. (2012) also reported that addition of biochar may influence N bioavailability and alter bioavailability of other nutrients for plant uptake. This agreed with the concept that N is an essential nutrient in supporting plant growth, physiology and carbohydrate content (Terbe, 2004;Almodeares et al., 2008).
Total C was the highest in T 4 treatment (1.6%) which was due to the application of biochar only, followed by T 14 (1.41%). The lowest content of total carbon was observed in T 8 (0.66). The available P in the soil of the current study varied from 182 to 3.55 ppm, with the highest value found in T 12 (182 ppm), followed by T 16 (103 ppm). The lowest available P was found in T 1 (control). Mixing fertilizers with amendments enhanced soil available P in the soil. Use of amendments such as plant residue in combination with fertilizers acts as a source of nutrients and hence increases the availability of soil P to plants (Sabrina et al., 2013). In addition, organic matter from several amendments contains organic P and can be mineralized into inorganic forms (Guppy et al., 2005).
The control treatment reported the lowest CEC and exchangeable bases (K, Ca, Mg, Na). Treatment T 14 treatment produced the highest CEC, followed by T 16 . It showed that application of organic fertilizer in combination with amendments increased the CEC of the BRIS soils. Application of zeolite in combination with organic and inorganic fertilizers had also shown positive impact in terms of CEC. This result is comparable to that reported by Ahmed et al. (2010).

Growth Performance of Kenaf
The diameter of kenaf stem varied significantly (p≤0.05) due to different application rate or combination of organic and inorganic fertilizers (Fig. 1). Islam et al. (2011) stated that differences in combination of application of organic and chemical fertilizers significantly affected the growth and yield of plants, which supports the findings of this study. The diameter of kenaf stem in this study varied from 6.07 mm to 15.47 mm, with the highest value observed in T 2 (15.47mm). Diameter increment, in descending order, are: T 2 (15.47 mm) > T 16 (15.18 mm) >T 15 (14.83 mm) >T 13 (14.742 mm) >T 12 (14.54 mm) >T 7 (14.35 mm) >T 8 (14.11 mm) >T 6 (13.65 mm) >T 9 (12.37 mm) >T 10 (10.83 mm) >T 14 (10.048 mm) >T 3 (9.017 mm) >T 1 (7.86 mm) >T 4 (7.487 mm) >T 11 (7.44 mm) >T 5 (6.07 mm). Treatments with chemical fertilizer (NPK) showed the highest increment of diameter stem. These may be due to the plants receiving more readily available applied nutrients (NPK) in comparison with other treatments. Parraga et al. (1995) mentioned that application of organic matter with NPK fertilizer increased the diameter of root per plant.
Mixed fertilizer treatments resulted in higher stem diameter than the other treatments, which are consistent with the study of Srivastava et al. (2012). They reported that the combination of chemical fertilizer with organic materials significantly increased the number of leaves, diameter, fresh weight and leaf length.
It was observed that treatment T 5 showed lower basal diameter compared to that of treatment T 16 . This shows that application of zeolite alone (T 5 ) does not help in kenaf growth. Treating BRIS Soils with zeolite in combination with organic and/or inorganic fertilizers produced contrasting results. Results from T 16 , T 15 , T 14 , T 13 , T 11 , T 10 and T 8 treatments were significantly different from that of T 5 . These findingsare similar with those reported by Ahmed et al. (2010). Combining chemical fertilizer (T 7 ) or chicken dung with biochar (T 9 ) produced better result compared to single fertilizer application (T 3 and T 4 ). If this finding is adopted by farmers in the BRIS Soils areas, the use of chemical fertilizers can be somewhat minimized, maintaining environmental conditions. Combining chicken manure with chemical fertilizer may inhibit the growth of kenaf Science Publications AJAS compared than chemical fertilizer alone because of the presence of excessive soluble salts (or salinity) supplied by chicken manure. This is consistent with the study conducted by Stephenson et al. (1990) who stated that high electrical conductivity caused by excessive application of chicken manure increased salinity in soils which consequently affected plant growth. Although some studies revealed that the temperature of the greenhouse also affected the salt concentration in the soils (Sun and Chen, 1992). From this study, its means that the mixture of chicken manure and NPK fertilizers should not be applied on BRIS soils. However, with a suitable and appropriate ratio of chicken manure and lower chemical fertilizer applied, the yield will be similar to application of chemical fertilizer alone. Hence, the use of chemical fertilizer may be minimized. Boateng et al. (2006) found in their study stated that low rate of chemical fertilizer and suitable amount of poultry manure increase the grain yield. This is because of the complementary and synergistic effects of the organic and inorganic fertilizers. Other study conducted by Magid et al. (1995) also suggested that application of chicken manure beyond a certain amount resulted in decreasing of grain yield. Hence, it is recommended more studies should be carried out in order to obtain the best method and application rate for mixing the chicken manure with chemical fertilizer on BRIS soil in Malaysia.
The height of kenaf recorded in this study was in the range of 126.89 to 292.22 cm (Fig. 2). The highest height increment was recorded in treatments T 15 and the lowest height was in T 5 . This result indicates that application of biochar in combination with chicken dung gave lower height increment as compared with the fertilizer plus organic material treatment. Zhou et al. (2002) reported that plants grown on soil streated with chemical fertilizer together with organic manure grew quite well by adjusting nutrients released into the soil. Xu et al. (2008) also supported that combining the chemical fertilizer with organic manure gave a better yield of crops due to the increasing of soil organic matter, improved soil function, decreased the nitrate in soil and increased the soil buffering capacity.
The height of kenaf due to treatment is ranked in the following orders: . This study showed that the highest value was observed in treatment T 15 , reaching almost 3m in height. The total height recorded was lower than 3 probably because of high temperature in the glasshouse with in a range of 23°C and 38°C. This is similar reported by Roslan et al. (2011), high average temperatures up to 28°C seriously affected kenaf height. Figure 2 shows that the Kenaf height in treatment T 7 was significantly higher than the treatment in T 6 . The highest height value recorded in T 15 may be due to the properties of the mixture.T 15 consists of chemical fertilizer, organic material (biochar) and secondary minerals (zeolite). Biochar having the ability to retain nutrients, reduce nutrient leaching, improving soil quality and carbon sequestration, hence even supplying nutrients to plants (Lehmann and Joseph, 2009;Glaser et al., 2002). Hence, amending soil with biochar may increase plant growth and crop yields (Rondon et al., 2007;Graber et al., 2010). Furthermore, zeolites enable both organic and inorganic fertilizers slowly release their nutrients (Perez-Caballero et al., 2008). Hence, application of zeolite functions as an excellent carrier and as a good source to supply plant nutrients such as K, Ca and Mg (Bagdasarov et al., 2004). With the combination of zeolite and chemical fertilizer, may increase the properties and indirectly improve the poor soil. Research conducted by Supapron et al. (2002) found that combination of chemical fertilizer with zeolite improved soil chemical properties, sugarcane growth and yield. Mixing Zeolite with chemical fertilizer also plays an important role to control ammonia loss and enhance the nutrient efficiency (Leggo, 2000;Latifah et al., 2011). However, from this study revealed that application of zeolite alone, T 5 gave the lowest yield as compared than mixed treatment due to the acidic condition and not suitable for plant growth. This result was similar reported by (Burriesci et al., 1984;Dwairi, 1998) in their studies who stated that zeolite cannot be fully substituted with fertilizer and should be mixed with other fertilizer in order to obtained a positive crop yield.
The maximum number of leaves was recorded in T 15 (102.33), followed by T 8 (92.00), T 7 (86.00), T 16 (80.33), T 2 (78.33), T 12 (72.00), T 13 (70.33), T 6 (65.00), T 9 (57.00), T 10 (36.00), T 14 (33.00), T 3 (29.00), T 1 (23.67), T 4 (22.00) and T 11 (19.00) (Fig. 3). The combined NPK and organic fertilizer treatment resulted in higher number of leaves as compared to organic fertilizer treatment. Xu et al. (2008) also reported that application of single fertilizer gave a poorer result as compared to mixed fertilizer. In the case of mixed fertilizer treatment, T 15 obtained higher number of leaves, which may be due to the properties applied in the mixture. A combination between NPK, biochar and zeolite not just give a best yield in term of height, but relatively affected the number of leaves produced by kenaf. From

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this study, T 15 shows the highest ranking for both height and number of leaves respectively. This was similar to a research reported by Hossain et al. (2012) who found a positive a relationship between plant height and the number of leaves of kenaf grown on sandy soil. The number of leaves influence the total leaf area, which was important in determine the photosynthesis rate (Li et al., 2009). Studies by Ogbonnaya et al. (1998) also describe how well the functions of leaf photosynthesis in order to get a necessary carbohydrate that were importance for plant growth.

CONCLUSION
Application of organic fertilizer in combination with chemical fertilizer (NPK) had significant effects on the growth of kenaf. The highest height increment and number of leaves for kenaf in this study was recorded in T15, followed by treatment T 2 and T 16 . The highest diameter was obtained in T 2 , followed by T 15 and T 16 . The fertility of the BRIS Soils was significantly improved due to treatment of fertilizers in combination with amendment. The highest total N (0.14%) was found in T 7 , while the untreated soil contained only 0.04% total N. Treatments 15 (NPK + Biochar + Zeolite) showed better result in terms of growth performance although total N content in the soil was lower than other treatments. It seemed that the improvement of the fertility of BRIS soils in Malaysia can be achieved by applying a suitable combination of fertilizers mixed with biochar or zeolite.

ACKNOWLEDGEMENT
The researchers are grateful to the staff Department of Forest Management, Faculty of Forestry, Institute of Tropical Forestry and Forest Products, University Putra Malaysia for assisting during site preparation and laboratory analysis. This study was financially supported by the Ministry of Higher Education (MOHE) under Fundamental Research Grant Scheme (FRGS) and Research University Grant Scheme (RUGS) through Universiti Putra Malaysia (UPM).