RELATIVE EFFECT OF ORGANIC AND INORGANIC FERTILIZERS ON THE GROWTH OF OKRA [ ABELMOSCHUS ESCULENTUS ( L . ) MOENCH ]

A greenhouse experiment was conducted to study the relative effect of organic and inorganic fertilizers on the growth of okra (Abelmoschus esculentus). The experiment consisted of four treatments. Cow dung and poultry droppings were applied at the rates of 2.5 kg per 10 kg of soil one week before sowing, while NPK fertilizer (15:15:15) was applied at the rate of 6 g per 10 kg of soil three weeks after sowing. The treatments were laid in a completely randomized design with three replications. Plant growth was assessed using plant height, fresh weight, leaf area and dry weight. The application of cow dung, poultry droppings and NPK fertilizer had significant effects on all the parameters assessed. The application of poultry droppings gave plants with the greatest plant height, leaf area and fresh weight, while cow dung application gave the greatest dry weight. The data obtained from these treatments were significantly higher than the data obtained from the control. It was, therefore, concluded that the use of organic manure in the production of vegetables like okra should be encouraged.


Introduction
Okra, Abelmoschus esculentus (L.) Moench, is a vegetable crop grown both in tropical and subtropical regions of the world (Ahmed et al., 2006).In the Middle East it is known as bamia, bamya or bamieh and gumbo in the Southern USA, and lady's finger in England.It is an erect herbaceous annual crop species that belongs to the family Malvaceae and is principally used in the preparation of soup in Nigeria (Tindall, 1986).According to Awodoyin and Olubode (2009), the immature fruits and leaves of Abelmoschus esculentus are used in soup as a thickener because it is a rich source of vitamins and minerals.Okra is recommended for consumption by World Health Organization due to its ability to fight diseases.Okra has been found to be a rich source of vitamins A and C, calcium, thiamine and riboflavin.It is also rich in iron and is used as a medicine in the treatment of the peptic ulcer.
The application of inorganic fertilizers results in yield increase of this crop.Unfortunately, inorganic fertilizers reduce the quality of arable lands.The Economic Commission for Africa (2001) reported that tropical soils are adversely affected by suboptimal soil fertility and erosion, causing a deterioration of the nutrient status and changes in soil organism populations.Akanbi et al. (2010) asserted that inorganic fertilizers can improve crop yields and soil pH, total nutrient content, and nutrient availability, but their use is limited due to scarcity, high cost, nutrient imbalance and soil acidity.Hence the need to look for alternative ways of improving this crop plant.This study will enrich the literature on fertilizers concerning the production of okra.Therefore, the objective of this study is to examine the effect of inorganic and organic fertilizers on the growth of okra.

Material and Methods
The experiment was carried out at the greenhouse of Abia State University, Uturu located at latitude 7°6'N and longitude 6°E.Okra seeds used in the experiment were obtained from the National Seed Centre, South East field, Umudike-Nigeria.The study was carried out between 30 May 2012 and 30 August 2012 in the screen house in experimental pots.
The experiment was conducted using 15-litre plastic pots containing 10 kg of soil.The pots were perforated at the base to allow excess water to drain out.It was arranged in a completely randomized design with three replications.Cow dung and poultry droppings were applied at the rates of 2.5 kg per 10 kg of soil one week before sowing, while NPK fertilizer (15:15:15) was applied at the rate of 6 g per 10 kg of soil three weeks after sowing.The samples that were left without treatment served as the control.Ten viable seeds of okra were planted at an average depth of 2-3 cm in each of the plastic buckets.The plants were later thinned to one stand per bucket, two weeks after germination.
A week after planting, data on plant height, fresh weight, leaf area and dry weight were taken to assess plant growth.Thereafter, harvesting was done fortnightly until the 12 th week of plant age.Data were subjected to analysis of variance using SPSS version 16 (SPSS Inc., Chicago, IL, USA).Means were separated using Fisher's least significance difference (P≤0.05).

Results and Discussion
The application of cow dung, poultry droppings, and NPK fertilizer had a significant effect on the performance of Abelmoschus esculentus (P<0.05).At week 10 after sowing, the application of poultry droppings produced the greatest plant height (67.8 cm) followed by cow dung (61.9 cm), and NPK fertilizer (55.87 cm), while the lowest plant height was obtained from the control (47 cm) (Figure 1).Within the weeks, as regards the treatments significant differences in plant height were observed between week 2 and week 6.The largest leaf area (252.3 cm 2 ) was produced by the application of poultry droppings.This is followed by cow dung application (235.8 cm 2 ), and NPK application (193.9 cm 2 ), while the least leaf area (118.5 cm 2 ) was produced in the control (Figure 2).Within the weeks, there was no significant difference between the treatments.Similarly, there was no significant difference in the treatments in weeks 2 and 5.In week 3, there was no significant difference between cow dung and poultry droppings.There was no significant difference in week 6 between NPK fertilizer and cow dung.Furthermore, there was no significant difference between poultry dropping treated soil and cow dung treated soil in week 5. Fresh plant weight was significantly affected by the application of the treatments (Figure 3).It ranged from 67.13 g in poultry dropping treated soil to 28.77 g in the control.Within the weeks, there was no significant difference among the treatments in weeks 1 and 2. Also within weeks 3 and 4, there was no significant difference between NPK treated soil and the control.Likewise, significant differences did not exist within week 3 and week 6 between poultry dropping treated soil and the control and within week 3 and 4 between poultry dropping treated soil and NPK treated soil.Differences in the fresh weight of okra were also not significant between NPK and cow dung treated soils in week 4. Similarly, in weeks 5 and 6, significant differences between treatments with NPK fertilizer and cow dung were not found.Dry plant weight ranged among the treatments as follows: 0.39-9.16g in cow dung, 0.39-8.43g in poultry droppings, 0.62-7.55g in the control, and 0.57-6.13g in NPK treatment (Figure 4).However, these differences were significant (P<0.05).In weeks 1 and 3, there was no significant difference among the treatments (P>0.05).Similarly, in week 2, there was no significant difference between poultry droppings and NPK fertilizer.There was also no significant difference between the control and NPK fertilizer in weeks 3 and 4. Likewise, in week 4, there was no significant difference between poultry dropping treated soil and the control.Significant differences did not exist between cow dung treated soil and NPK treated soil in weeks 3 and 6.In week 5, there was no significant difference between poultry dropping treated soil and the control.Dry plant weight of okra was not significantly different between cow dung and poultry dropping treated soil in weeks 4 and 6.
The Abelmoschus esculentus plant grown on NPK fertilizer, cow dung and poultry dropping treated soils responded differently regarding plant height.Poultry dropping treated soil gave the greatest mean plant height, while the control had the lowest plant height.This result is in agreement with previous reports (Agboola and Obigbesan, 1975;Agboola and Omueti, 1982;Agboola and Fagbenro, 1985;Okwuagwu et al., 2003).Tiamiyi et al. (2012) reported that plant height of okra was greater in poultry dropping treated soil.They attributed it to the ready availability of nutrients for the easy absorption by plant root, thus resulting in an increase in plant growth.Ajari et al. (2003) asserted that poultry dropping treated soil could increase plant height when compared with other sources of manure.Comparatively high nitrogen content of poultry manure buttresses the vegetative growth of crops.Seyedbagheri (1999) reported a positive effect of organic fertilizer on vegetative growth.The plants treated with NPK fertilizer grew fastest in the first three weeks.The plants treated with organic fertilizer grew higher from the sixth week up to the end of the experiment in week 10.This is consistent with the report of Adewole and Ilesanmi (2012) in which it was demonstrated that inorganic fertilizers like NPK worsen soil degradation resulting from loss of inorganic matter which leads to higher acidity, nutrient imbalance and low crop yield.On the other hand, organic manures promote microbial degradation and the gradual release of nutrients over time.Leaf area was the greatest in the treatments with fertilizers and the lowest in the control.Increased leaf area implies higher light interception and dry matter product which invariably promotes plant growth (Ofosu-Anim and Leitech, 2009).An enhanced production of dry matter resulting from high nutrient level increased the development of plant parameters (Katung et al., 1996).Nutrient availability in the correct proportion leads to increased photosynthetic activity, thus an increase in light interception, dry matter production, accumulation and partitioning (Robert and Walker, 1989;Smith et al., 1992;Hartz et al., 1996).

Conclusion
The study revealed that both mineral (NPK) and the organic manure (cow dung and poultry droppings) improved the growth performance of Abelmoschus esulentus seedlings, but to varying degrees.Organic fertilizers were better than the NPK mineral fertilizer.The treatment with poultry droppings was found to be the best, and the treatment with cow dung was better than the NPK treatment.Hence, the use of organic manure in the production of vegetables like okra should be encouraged.

Figure 1 .
Figure 1.Effects of NPK fertilizer, cow dung and poultry droppings on the height of Abelmoschus esculentus.Bars indicate standard errors.

Figure 2 .
Figure 2. Effects of NPK fertilizer, cow dung and poultry droppings on the leaf area of Abelmoschus esculentus.Bars indicate standard errors.

Figure 3 .
Figure 3. Effects of NPK fertilizer, cow dung and poultry droppings on the fresh weight of Abelmoschus esculentus.Bars indicate standard errors.

Figure 4 .
Figure 4. Effects of NPK fertilizer, cow dung and poultry droppings on the dry weight of Abelmoschus esculentus.Bars indicate standard errors.