Effects of organic fertilizers on growth, yield, quality and sensory evaluation of red lettuce (Lactuca sativa L.) Veneza Roxa

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1 AGRICULTURE AND BIOLOGY JOURNAL OF NORTH AMERICA ISSN Print: , ISSN Online: , doi: /abjna , ScienceHuβ, Effects of organic fertilizers on growth, yield, quality and sensory evaluation of red lettuce (Lactuca sativa L.) Veneza Roxa Michael T. Masarirambi 1 *, Mduduzi M. Hlawe 1, Olusegun T. Oseni 1 and Thokozile E. Sibiya 2 1 *Horticulture Department, Faculty of Agriculture, University of Swaziland, PO Luyengo M205-SWAZILAND 2 Consumer Sciences Department, Faculty of Agriculture, University of Swaziland, PO Luyengo M205-Swaziland *Author for correspondence: mike@ agric.uniswa.sz, Tel./Fax ABSTRACT Lettuce (Lactuca sativa L.) is one of the widely used salad vegetable in Swaziland. However, there is a dearth of information pertaining to organic lettuce production. An experiment was conducted in a lath house at the Horticulture farm, Luyengo Campus of the University of Swaziland to assess the effects of organic fertilizers on yield and quality of lettuce grown in river sand. The organic fertilizers used were (a) bounce back compost, (b) cattle manure and(c) chicken manure. The rates of application were 40 tones per hectare (t/ha) for chicken and cattle manures, 1.5 t/ha basal dressing and 1.0 t/ha side dressing for bounce back compost. Inorganic fertilizers 2:3:2 (22) % zinc (Zn) and limestone ammonium nitrate (LAN 28%) were included at specific application rates of 955 kg/ha basal dressing and 100 kg/ha side dressing as control. The results showed that type of fertilizer applied significantly (P< 0.05) affected growth, yield and nutritional quality of lettuce. A trend in superiority of the different types of organic fertilizers was observed as the chicken manure exhibited relatively higher values on number of leaves, plant height, marketable yield and mean leaf dry mass. Cattle manure was second, and then bounce back compost and lastly the inorganic fertilizers. However, plants produced by bounce back compost were higher in calcium, iron and Zn contents on fresh mass basis while plants produced by cattle manure followed, and then inorganic fertilizers and lastly chicken manure. Organoleptic tests showed that there were no significant (P> 0.05) differences in appearance and taste among treatments. Results of this experiment showed that inorganic fertilizers were less suitable in lettuce production in river sand when compared to organic fertilizers. It is recommended that lettuce can be grown successfully using organic fertilizers. Keywords: Organic fertilizers, Yield, Quality and sensory evaluation, Red lettuce (Lactuca sativa) INTRODUCTION Commercial and subsistence farming has been and is still relying on the use of inorganic fertilizers for growing crops, (Lampkin, 1990). This is because they are easy to use, quickly absorbed and utilized by crops. However, these fertilizers are believed to contribute substantially to human, animal food intoxication and environmental instability/degradation. The continued dependence of Swaziland and other developing countries on inorganic fertilizers has made prices of many agricultural commodities to skyrocket. The chemical fertilizers used in conventional agriculture contain just a few minerals, which dissolve quickly in damp soil and give the plants large doses of minerals (Vernon, 1999). Organic fertilizers can therefore be used to reduce the amount of toxic compounds (such as nitrates) produced by conventional fertilizers in vegetables like lettuce, hence, improving the quality of leafy vegetables produced as well as human health. Increased consumer awareness of food safety issues and environmental concerns has contributed to the development of organic farming over the last few years (Worthington, 1998; Worthington, 2001; Relf et al., 2002). Thus, it may be possible to lessen the escalating effects of diseases such as cancer and boost immunity of humans. Farm income will also

2 improve when farmers use less money on fertilizers and pesticides for growing crops, (Vernon, 1999). There is increased demand of organically produced vegetables in view of its health and nutritional benefits. There is paucity of information on the use of organic fertilizers for vegetable production and therefore the objective of this study was to asses the effects of different sources of organic fertilizers on growth, yield, quality and organoleptic properties of red lettuce (Lactuca sativa) in Swaziland. MATERIALS AND METHODS Site and environment: The experiment was conducted in a lath house at the University of Swaziland, Horticulture Farm, Luyengo Campus. This farm is located between latitude 26 o 58 S and longitude of 31 o 18 E at an altitude of 734 m above sea level. This area receives an average rainfall of 800 mm per annum and most of the rains fall during summer and there is little or no rain in winter. The experimental lath house was made of black polyethylene net and light transmission into the lath house was 412 lumens. The experiment was carried out from January to March Medium and fertilizer analysis: The growing medium (river sand) and locally available organic fertilizers (cattle and chicken) analysis was done at Malkerns Research Station to determine its physical and chemical properties. Experimental design: The experiment comprised of four treatments laid in a randomised complete block design (RCBD), replicated four times. The gross experimental area was 4m x 17m (68m 2 ) and the net experimental area was 3m x 12m (36m 2 ). Each plot dimensions were 1.5m x 1.5m (2.25m 2 ) and there were 16 plots. Each plot had 25 pots. Plant spacing was 30 cm between rows and plants, because 30cm diameter plastic pots were used. The media was filled to ¾ of the volume of the plastic pot. Variety used: The lettuce variety used was Veneza Roxa (red lettuce)[ Mayford, SA] which is becoming prominent among vegetable growers and consumers in Swaziland. Seedlings were obtained from Vickery Seedlings Nursery. They were transplanted at the age of four weeks after sowing Fertilizers : There were four types of fertilizers used. They were organic and inorganic fertilizers. The organic fertilizers included; bounce back compost (composted chicken manure), cattle manure and chicken manure. The inorganic fertilizers used were 2:3:2 (22) % Zn for basal dressing and Limestone Ammonium Nitrate 28% (L.A.N) for side dressing. The inorganic fertilizer was applied at 955 kg per hectare basal dressing and 100 kg per hectare side dressing. The application rate of the chicken manure and cattle manure was 40 tonnes per hectare which was applied a week before transplanting. However, the application rate for the bounce back compost was 1.5 t/ ha basal dressing and 1 tonne per hectare side dressing. Side dressing was done every two weeks after transplanting until harvest. Data collection: Data were collected 2 weeks after transplanting (WAT) and at weekly intervals there after. The data collected during the experiment included the following parameters: plant height, leaf area, marketable yield, root-shoot ratio, and the nutrient composition of fresh lettuce (leaf tissue analysis). The graph paper method was used for determining the leaf area of lettuce plants from second week after transplanting to the sixth week after transplanting (Edje and Osiru, 1988). Data were collected from five sample plants from inside rows per plot. Organoleptic tests for appearance and taste were done for all treatments. Procedure for leaf tissue analysis: A microwave was used for digestion. A sample of 0.5 grams of each treatment plant material was weighed and put in microwave bombs (Microsoft Encarta, 2003). For calcium (Ca) and Zinc (Zn) analysis, 10 ml 6M HCl and 10ml 6M HNO 3 were used for digestion. For iron (Fe) analysis, 10ml 6MH 2 SO 4 and 10ml 6M HNO 3 were used for digestion (Microsoft Encarta, 2003). These acids were added into the bombs containing the samples and digested in the microwave for two minutes. The samples were cooled to room temperature in a water bath and filtered into 50ml volumetric flasks (Microsoft Encarta, 2003). Dilutions to the mark were done using deionized water. Preparation of standards: Standard solutions of 0.5ppm, 1.0ppm, 1.5ppm, and 2.0ppm were prepared from a 1000ppm stock solutions of Ca, Fe and Zn using the formula: C 1 V 1 = C 2 V 2 With a known concentration (C 2 ) and volume (V 2 ) required, the volume of the 1000ppm stock solution was calculated and necessary dilutions done to make V 2. Standards were run in the atomic absorption spectrophotometer (AAS) to determine their absorbance from which calibration curves were plotted. The operating parameters of the AAS are shown in Table

3 Procedure for organoleptic tests: Fresh lettuce from all treatments was washed and prepared (chopped). The prepared lettuce was placed in identical dishes tagged with codes signifying the treatments [Food and Agriculture Organization (FAO, 2000)]. This helped in avoiding bias preferences of panellists. The salad was not dressed in order to prevent bias preferences or dislikes of panellists due to flavour and/or taste of dressing (FAO, 2000). The panellist number was 60. There were 30 females and 30 males that did the organoleptic tastes. The panellists were aged between 18 and 25 years. Data analysis: The data collected were analysed using MSTAT-C (Nissen, 1989) statistical package. Analysis of variance (ANOVA) was undertaken on data collected so as to determine if there were any significant differences amongst treatments. Mean separation where significant differences were detected was done by Duncan s New Multiple Range Test (DNMRT) (Gomez and Gomez, 1984). Organoleptic test data were analysed using Microsoft Office Excel and single factor ANOVA was done to determine if significant differences existed among treatments (FAO, 2000). Table 1. Operating parameters for AAS Parameter Fe Ca Zn Wavelength Slit width (nm) Lamp current (ma) RESULTS Results indicated significant differences in growth parameters amongst treatments. Plant height exhibited a significant (P<0.05) difference in all treatments (Figure 1). The chicken manure fertilized plants were the tallest followed in decreasing order by cattle manure; bounce back manure and lastly inorganic fertilizers exhibited the least plant height. Similarly, the results showed significant (P<0.05) differences in average number of leaves per plant. The lettuce plants fertilized with chicken manure had relatively higher average number of leaves per plant, followed by cattle manure and bounce back compost which exhibited a non-significant difference in the average number of leaves per plant (Figure 2). The lettuce plants fertilized with inorganic fertilizers exhibited the least number of leaves amongst treatments. However, all treatments showed a nonsignificant difference in the average number of leaves from the second week after transplanting (2 WAT) to the fourth week after transplanting. The results indicated significant (P<0.05) differences in leaf area index (LAI) amongst treatments (Figure 3). The lettuce fertilized with chicken manure eventually exhibited relatively higher LAI, followed by lettuce grown using cattle manure, then bounce back and the one fertilized with inorganic fertilizers had the least LAI. Different treatments behaved differently to the harvest characteristics as was depicted by the significant (P<0.05) differences in marketable yield, root-shoot ratio, zinc (Zn), calcium (Ca), and iron (Fe) contents of fresh lettuce (Table 4). Chicken manure treatment gave a relatively higher marketable yield of red lettuce; cattle manure was second, then bounce back and inorganic fertilized plants had the least. However, there was a no significant difference in root-shoot ratio amongst treatments. There was a significant difference (P<0.05) in Zn content of red lettuce amongst treatments. Lettuce plants fertilized with bounce back manure exhibited relatively higher Zn content followed by cattle manure, inorganic fertilizers and chicken manure treatments in decreasing order of Zn content. Treatments significantly (P<0.05) affected Ca content. The highest Ca content was recorded for bounce back compost. However, all the other treatments (chicken manure, cattle manure and inorganic fertilizers) showed a non-significant difference in Ca content on fresh mass basis of lettuce. Similarly, the lettuce fertilized with bounce back compost had a relatively higher content of Fe than its counterparts. Lettuce grown using cattle manure was second in Fe content to the one produced by bounce back compost. A nonsignificant difference in Fe content was found between chicken manure and inorganic fertilizers treatments. There was a significant (P<0.05) difference on dry matter among treatments. Dry matter content was higher in plants from the organic fertilizers and followed in decreasing order: chicken, cattle and bounce back manures and lastly inorganic fertilized plants (Table 4). There were no significant (P>0.05) differences amongst treatments on organoleptic test for preference taste and appearance of red lettuce Veneza Roxa, 1321

4 Table 2. Physical and chemical characteristics of the medium (sand), cattle and chicken manure Material ph Exchangeable acidity (meq/100g) Phosporus (P) (mg/kg) Potassium (K) (mg/kg) Chicken manure Cattle manure Medium (sand) Table 3. Bounce back compost components Moisture Nitrogen N Phosphorus : P P 2 O 5 Potassium : K Calcium : Ca Sulphur : S K 2 O Magnesium : Mg Zinc : Zn Product Density Organic Matter Component Dry weight basis %W/W 120g/kg 30g/kg 11g/kg 25g/kg 10g/kg 12g/kg 25g/kg 6g/kg 8g/kg 443mg/kg 655kg/m3 655 kg/m3 Based on composted poultry manure. Source: Neutrog fertilizers (South Africa) Table 4. Harvest characteristics of red lettuce Veneza Roxa grown with different fertilizers treatments Treatment Marketable yield (g) Mean leaf dry mass (g) Root-shoot ratio Zinc (mg/100g) Calcium (mg/100g) Iron (mg/100g) Bounce back c 6.97c 6.55a 3.18a 7.70a 4.91a Cattle manure b 8.07b 8.20a 1.91b 4.12b 3.32b Chicken manure Inorganic fertilizers a 9.21a 6.91a 0.62d 2.30b 0.00c 48.13d 3.77d 8.00a 0.91c 2.82b 0.00c CV (%) Means with different letters are significantly different at P<

5 H e i gth (c m ) Plant heigth of red lettuce 'Veneza Roxa' 2 WAT 3 WAT 4 WAT 5 WAT 6 WAT Time [Weeks after transplanting (WAT)] Bounce back Cattle manure Chicken manure Inorganic fertilizers Fig 1. Plant height (cm) of red lettuce Veneza Roxa recorded from two weeks after transplanting (2WAT) to harvest (6WAT) Num ber of leaves Number of leaves of red lettuce 'Venaza Roxa' 2 WAT 3 WAT 4 WAT 5 WAT 6 WAT Time [Weeks after transplanting (WAT)] Bounce back Cattle manure Chicken manure Inorganic fertilizers Fig 2. Number of leaves of red lettuce Veneza Roxa recorded from two weeks after transplanting (2WAT) to harvest (6WAT) Leaf area index (LAI) Leaf area index (LAI) of red lettuce 'Veneza Roxa' 2 WAT 3 WAT 4 WAT 5 WAT 6 WAT Time [Weeks after transplanting (WAT)] Bounce back Cattle manure Chicken manure Inorganic fertilizers Fig 3. Leaf area index of red lettuce Veneza Roxa recorded from two weeks after transplanting (2WAT) to harvest (6WAT) DISCUSSION There were differences in the growth parameters, of red lettuce at 2, 3, 4, 5 and 6 weeks after transplanting. This depended on the type of fertilizer used. Plants which had been fertilized with chicken manure had the highest growth parameters and marketable yield Similar results have been reported (Uddin et al., 2009). This could be attributed to the nutrient content of the fertilizer used. Cantaloupe (Cucumis melo) plants receiving chicken litter exhibit relatively higher marketable yield than those receiving no chicken litter (Ghanbarian, et al., 2008). Similar results were obtained with broccoli (Ouda and Mahadeen, 2008) and cattle manure was found to increase pod yield of okra (Ogunlela et al., 2005). This could also be attributed to the large quantities of available phosphorus and available potassium contained in the chicken manure. Studies by Rao (1991) indicated that the soil could be enriched with the application of organic material which tends to decompose and release relatively large amounts of nitrogen into the soil before planting each fresh crop to boost yield. The method of application and the quantity of organic fertilizers have effects on crop yield and nutrient uptake. Xu et al. (2005) in a study on yield and quality of leafy vegetables grown with organic fertilizers showed that vegetables grown with organic fertilizers grew better and resulted in a higher total yield than those grown with chemical fertilizers. Therefore, the research suggested that vegetables grown with organic fertilizers showed higher growth and yield than those grown with inorganic fertilizers. This research showed that inorganic fertilizers resulted in lower yields compared to organic manures in the production of red lettuce Veneza Roxa in river sand medium. Owen (2003) reported that industrial fertilizers do not possess good characteristics of aggregating the soil particles. As a result, the plants produced by inorganic fertilizers showed relatively lower yield compared to organic materials. There were considerable variations in mean leaf dry matter of red lettuce. A study by Magkos et al. (2003) evaluated the dry matter content of several vegetables and found that organically cultivated crops had higher dry matter content than those grown conventionally. These findings, however, are evident only for the plants that grow above the ground (leaf vegetables) such as spinach, lettuce, chard, savoy cabbage and white cabbage (Magkos et al., 2003). 1323

6 Therefore, our results concurred with results obtained by Magkos et al. (2003). In all treatments, fertilization type resulted in significant effects in mineral composition of red lettuce on fresh mass basis. There was relatively higher zinc (Zn), iron (Fe) and calcium (Ca) contents in plants produced by bounce back compost. This can be attributed to the balanced quantity of nutrients in the bounce back compost. Magkos et al. (2003) reported that although a small number of studies have been published, slightly higher contents of minerals such as Fe, Ca, phosphorus (P), manganese (Mn), magnesium (Mg), zinc (Zn), copper (Cu), and potassium (K) have been obtained in organic vegetables; the majority of evidence, however, has revealed no significant differences between organic and conventional vegetables. There was no significant difference in the sensory and organoleptic evaluation of lettuce grown with both organic and inorganic fertilizers. Similar result was reported by FAO (2005). CONCLUSIONS: Red lettuce Veneza Roxa can be grown better in sand amended with organic fertilizers than when fertilized with inorganic fertilizers. Inorganic fertilizers were less suitable for use in the growth of red lettuce in a sand medium. Red lettuce plants grown in sand medium amended with organic fertilizer (chicken, cattle and bounce back) exhibited a more vigorous growth (higher values of leaf number, fresh marketable weight, plant height and leaf area index) than those grown with inorganic fertilizers. Lettuce grown with organic fertilizers showed a relatively higher mineral content than those grown with conventional fertilizers and thus improve lettuce production using hydroponics system. REFERENCES Edje, T.O. and Osiru, D.S.O. (1988). Methods for determining leaf area in some crop plants, In: Contributions from the first annual meeting of the collaborative group in cassava-based cropping systems research. International Institute of Tropical Agriculture (IITA). Ibadan. Nigeria.pp Food and Agriculture Organization (FAO), (2000). Food and quality as affected by organic farming. Twenty second FAO Regional Conference for Europe, Porto, Portugal. Ghanbarian, D., Youneji, S., Fallah, S. and Farhadi, A., (2008). Effect of broiler litter on physical properties, growth and yield of two cultivars of cantaloupe (Cucumis melo L.). Int. J. Agric. Biol., 10: Gomez, K.A. and Gomez, A.A. (1984). Statistical Procedures for Agricultural Research. Second edition. John Wiley and sons. Singapore. Lampkin, N. (1990). Organic farming. Farming press books. Ipswich. United Kingdom. Magkos, F., Arvaniti, F. and Zampelas, A. (2003). Organic food: Nutritious food or food for thought? A review of evidence. Int. J. of Food Sci. Nutri., 54: Microsoft Encarta Encyclopedia, (2003) Microsoft Cooperation. Nissen, O. (1989). MSTAT-C. A micro-computer program for the design, management and analysis of agronomic research experiments. Michigan State University. East Lansing. Michigan. USA. Ogunlela, V.B., Masarirambi, M.T. and Makuza, S.M. (2005). Effect of cattle manure application on pod yield and yield indices of okra (Abelmoschus esculentus L. Moench) in a semi-arid sub-tropical environment. J. Food Agric. Environ. 3 (1): Ouda, B.A. and Mahadeen, A.Y. (2008). Effect of fertilizers on growth, yield comoponents, quality and certain nutrient contents in broccoli (Brassica oleracea). Int. J. Agric. Biol., 10: Owen, P. (2003).Origin and distribution of lettuce. (16/08/2008) Rao, M.K. (1991). Textbook of Horticulture. University of Madras. Chennai (Madras) India. Relf, D.,McDoniel,A., and Tech, V., (2002): Fertilising the vegetable garden. tilizers/contents/inorganic_fertilizers.htm (21/08/2008) Uddin, J. Solaiman, A.H.M. and Hasanuzzaman, M. (2009). Plant characteristics and yield of Kohlabi (Brassica oleracea var. gongylodes) as affected by different organic manures. J. Hort. Sci. Ornament. Plants 1 (1): 1-4 Vernon, G. (1999). Sustainable Vegetable Production from Start-Up to Market. Cornell Univesity. Ithaca, New York. Worthington, V. (1998). Effect of agricultural methods on nutritional quality: a comparison of organic with conventional crops. Alternative Therapies Health Med., 4 (1): Worthington, V. (2001). Nutritional quality of organic versus conventional fruits, vegetables and grains. J. Alternative Complent. Med., 7: Xu, H.L., Wang, R., Xu, R.Y., Mridha, M.A.U. and Goyal, S., (2005). Yield and quality of leafy vegetables grown with organic fertilizations. Acta Hort., 627: