Abstract: This study was conducted to determine the effect of NPK fertilizer application rates and method of application on growth and yield of okra (Abelmoschus esculentus (L.) Moench) at the Teaching and Research Farm, University of Ado-Ekiti. Okra seed variety LD88 were treated to three levels of NPK fertilizer rates (0, 150 and 300 kg NPK ha-1) and two methods of fertilizer application (ring and band method). Treatments were arranged in a split-plot design with fertilizer application method as main plot factor and NPK rates as sub-plot factor. The treatments were replicated three times to give a total of eighteen experimental field plots. The result indicated that the fertilizer NPK significantly increase growth parameters (plant height, leaf area, root length, number of leaves), yield and yield components with optimum yield of okra obtained at 150 NPK kg ha-1 and ring method of application seems appropriate for okra production.
INTRODUCTION
Abelmoschus esculentus (L.) okra is a widely cultivated vegetable and can be found in almost every market all over Africa (Schippers, 2000). The nutritional constituents of okra include calcium, protein, oil and carbohydrates; others are iron, magnesium and phosphorus. Most okra is eaten in cooked or processed form. Young fruits may be eaten raw. The oil in the seed could be as high as in poultry eggs and soybean (Akinfasoye and Nwanguma, 2005).
Nitrogen as well as Phosphorus plays an important role in fruit, seed and quality development of okra (Nihort, 1985). NPK fertilizer has been reported to give a yield increase in okra (Babatola, 2006). Different methods of fertilizer application have been known to influence plant yields. Sweeney et al. (1996) reported that greater yields of early-grazing samples and higher P and K concentration was obtained by broadcasting fertilizer than was obtained for knifing (subsurface banding).
Crop response to N fertilization varies with rate, timing and methods of N application in relation to plant development. Cochran et al. (1978) reported increased biomass build-ups of soft white winter wheat due to accumulation of fall-applied fertilizer in the lower layers of the root profile, which can be available to the crop late in the growing season. Mahler et al. (1994) reported better use of banded fertilizer by spring wheat and attributed this to the fact that the banded fertilizer is positionally more available to the crop than germinating weeds.
In broadcasting, the fertilizer is uniformly applied over the soil surface and may be incorporated in the soil or left on the soil surface and may reach the root zone by percolating rainfall or irrigation water. Application of NPK fertilizer by broadcasting method encourages vigorous and wider root network for absorption of available plant nutrients from the soil solution (Toews and Soper, 1998). N fertilizer placement by broadcasting method does not optimize the use of limited fertilizer resources, which may just be as available to the weeds as it is to the crop (Tisdale et al., 1985).
The effect of NPK fertilizer application rates on growth and yield of okra has been studied by many researchers in Nigeria, but there seem to be a dearth of information on the effect of NPK fertilizer application rates and methods of application. This study was therefore carried out with the objective of examining the effect of NPK fertilizer rates and the appropriate method of application on growth and yield of okra.
MATERIALS AND METHODS
Trial Sites
The study was conducted at the Teaching and Research Farm, University of
Ado-Ekiti between May and July 2006. Ado Ekiti is located on latitude 7°30
N and longitude 7°48’ E. The area has a bimodal rainfall with mean
annual rainfall of 1367 mm and a daily temperature of 27°C. The area falls
within the high forest zone where the rich tropical forests once thrived. The
region has a tropical humid climate with distinct wet and dry seasons. The wet
season is from late March to October with little dry season in July and August.
Soil Preparation and Analysis
Prior to planting, soil samples were collected air-dried in the Laboratory,
ground and sieved through a 2 mm sieve. Particle-size distribution was determined
by the hydrometer method (Bouyoucos, 1951). Soil pH was measured using the pH
meter at 1:1 soil to water ratio. The percentage organic carbon was determined
by the Walkey Black wet oxidation method (Walkley and Black, 1934) while percent
total Nitrogen (N) was determined by the micro-kjeldahl technique (Jackson,
1962). The present organic matter was estimated by multiplying the percent organic
carbon with a factor of 1.724. Available P was extracted by the Bray/method
and determined colorimetrically (Bray and Kurtz, 1945). Exchangeable bases were
displaced by NH4 + from neutral/NH4OAC solution as described
by Jackson (1958). Calcium (Ca) and magnesium (Mg) were determined by the Atomic
Absorption Spectrophotometer (AAS) and potassium (K) and sodium (Na) were determined
by flame emission photometry. Cation Exchange Capacity (CEC) was determined
by the neutral/NH4OAC saturation method. Base saturation was calculated
with reference to the NH4OAC-CEC. Exchangeable acidity was extracted
with IM KCL and determined by titration with NaOH solution.
Field Trials
Field trial was conducted between July and October, 2005 and May to August
2006 at the Teaching and Research Farm, University of Ado-Ekiti. The size of
the plot used was 12x8 m. This was divided into three blocks (replicates) each
measuring 4x2.5 m. The trial was a 2x3 factorial experiment in randomized complete
block design.
Three seeds of okra variety LD 88 (Nihort) were planted on the field at spacing of 50x30 cm which were latter thin to one per stand. Before sowing, the seeds were soaked in water to determine its viability through floating method. NPK 15:15:15 fertilizer was applied at 0, 150 and 300 NPK kg ha-1 and two method of fertilizer application (ring and band methods) were adopted.
Treatments were arranged in split-plot design with application method as main plot factor and NPK 15:15:15 fertilizer rates as sub-plot factor. The six treatments were randomized completely within each block separately using the random digit of number and were replicated three times to give a total of eighteen experimental field plots.
Weeding commenced at two weeks after sowing of okra seed and subsequent weeding was carried out as at when due. Thinning was done two weeks after sowing of okra seed. Chemical spraying with hypermetricin was carried out to control some insect pests that affect the leaves of okra plant. Eight plants were selected per plot for determination of growth and yield parameters. Successive harvesting was done thrice as fruits reached marketable size. Number of fruits was counted on each occasion and fresh weight obtained to determine yield. The vegetative parameters assessed included plant height, number of branches, root length, leaves area. At final harvest, the okra plants were uprooted partitioned into leaves, stem and roots and were measured Each of these part were oven-dried in brown envelope for 48 h at 60°C. Measurements of dry weight were taken of stem, leaves and roots.
RESULTS AND DISCUSSION
Characteristics of the Soil Used
The result of the analysis of soil used for the experiment were presented
in Table 1, which gave particle size as sand 720 g kg-1,
silt as 229 g kg-1 and clay as 51 g kg-1. The pH of the
soil was 6.3 which is slightly acidic, organic carbon content was 6.15% which
is high for this soil, Nye (1950) who worked on the relationship between Nitrogen
responses on previous soil treatment and C/N ratio in soil of Gold coast savanna
area reported that derived savanna soils have lower N status and wider C/N ratio
than forest soils which greatly affect N availability. ECEC was 1.03 cmol kg-1
while total N and available P were 0.07% and 6.20 mg kg-1, respectively.
The soil was sandy loam, Total N and available P content were very low compared
with critical levels of 0.1% for N (Adeoye, 1986) and a range of 10-12 mg kg-1
for available P (Adeoye and Agboola, 1985) obtained for soils in southwestern
Nigeria (FMANR, 1990). Using the critical levels of 0.16-0.20 cmol kg-1,
exchangeable K was low (Agboola and Obigbesan, 1974).
Effect of NPK Fertilizer Rates on Growth Characters of Okra
The height of plant is an important growth character directly linked with
the productive potential of plant in terms of fodder, grains and fruit yield.
An optimum plant height is claimed to be positively correlated with productivity
of plant (Saeed et al., 2001). The results showed significant (p<0.05)
response to different rates of NPK fertilizer application (Table
2). Okra plants were taller in those plants that received 300 NPK kg ha-1
than those that received lower rates of application due to higher nitrogen content
which induced higher plant height, number of leaves, leaf area, root length
and number of branches. This is in agreement with the findings of Babatola et
al. (2002) who reported that increasing level of NPK 20:10:10 was observed
to increase growth and yield of okra in an okra/sweetcorn intercrop. There was
however no significant difference in plant height, number of leaves and number
of branches irrespective of the method of fertilizer application although, those
plants that received ring method of application gave the highest value in plant
height, number of leaves, number of branches while there was significant (p<0.05)
increase in leaf area and root length.
| Table 1: | Physico-chemical properties of surface soil used |
| Table 2: | Effect of NPK fertilizer rates and application method on growth characters of okra |
| Mean with the same letter in each column for each factor are not significantly different (p<0.05) by DMRT | |
| Table 3: | Effect of NPK fertilizer rates and application method on fresh weight and dry matter accumulation of okra |
| Mean with the same letter in each column for each factor are not significantly different (p<0.05) by DMRT | |
Effect of NPK Fertilizer Rates on Fresh Weight and Dry Matter Yield of Okra
Fresh leaf, root and stem weight was higher in treatments that received
300 NPK kg ha-1 than those that received 0 and 150 NPK kg ha-1
(Table 3). At higher fertilizer rate. Also, dry weight shows
that only root and stem weight were significantly higher (4.43 and 10.75 g plant-1).
There was no significant difference in dry fruit weight. These findings are
in accordance with previous reports of Obi et al. (2005) who reported
no significant increase in both fresh and dry weight of okra plant with increasing
NPK fertilizer treatment rates. Treatments having ring method of application
gave significant difference (p<0.05) at leaf fresh and dry weight. There
was also significant increase in fruit dry weight in treatment that received
ring method of fertilizer application. This trend has been reported by Olufolaji
et al. (2002) in a comparative evaluation study on soil and foliar applied
fertilizer on growth and yield of celosia argentea reported increase in leaf
area and fruit yield.
Effect of NPK Fertilizer Rates on Yield and Yield Components of Okra
The number of fruit per plant, fruit length, fruit girth and fresh fruit
weight per plant (Table 4) were significantly (p<0.05)
increased when 150 NPK kg ha-1 was applied. Trends in the data of
yield and yield components was such that 150 NPK kg ha-1>300 NPK
kg ha-1>0 NPK kg ha-1. The ring method of fertilizer
application gave a significant (p<0.05) increase in fruit length and fresh
fruit weight per plant while there was no significant difference in fruit girth
and number of fruit per plant. Okra yield and yield components were least without
application of N, P and K nutrients. This confirms findings from earlier studies
in Nigeria which showed that application of these nutrients are important for
enhanced yield of okra (Adediran and Banjoko, 2003; Adepoju, 1995; Akintunde
et al., 2000). Uyovbisere et al. (2000) noted that there was substantial
depletion of nutrients when no NPK fertilizer was applied and that nitrates
and available phosphorus were substantially reduced with cropping in humid zone
of southwestern Nigeria.
Effect of NPK Fertilizer on Marketable Yield
Seed sown in 150 kg NPK ha-1 rate produced plants with the highest
number of fruits. The lowest was produced at zero and 300 kg NPK ha-1.
Okra plant that received fertilizer by ring method of application produced the
highest number of fruits.
| Table 4: | Effect of NPK fertilizer rates and application method on yield and yield components of okra |
| Mean with the same letter in each column for each factor are not significantly different (p<0.05) by DMRT, All the tables present results of two growing season, late season of 2005 and early season of 2006 | |
The interaction showed that Band-150 kg NPK ha-1 and Ring 150 kg NPK ha-1 produced the highest number of fruits which were not significantly different from each other. However, ring method gave the highest value. Also, there were significant interactions in fresh fruit weight between the two methods of application. Ring method significantly (p<0.05) gave the highest fruit weight per plant.
CONCLUSIONS
The result showed that NPK fertilizer rates and methods of application have a profound effect on the overall performance of okra. Application of NPK fertilizer at the different levels used in this study had significant effect on the growth characters except number of leaves. Similarly, NPK fertilizer at different levels had significant effect on the yield and yield components of okra. Methods of application had significant effect only on fruit length and fruit fresh weight. Fertilizer application rate of 150 kg NPK ha-1 and ring method of fertilizer application are effective for the growth and yield of okra.