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Research Article
 

Effects of NPK (15:15:15) Fertilizer on Some Growth Indices of Pumpkin



K. Okonwu and S.I. Mensah
 
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ABSTRACT

Effects of NPK (15:15:15) fertilizer on some growth indices of pumpkin, Cucurbita moschata (Duch. ex Lam.) Duch. ex Poir. were studied. Eight treatments viz; 0, 200, 250, 300, 350, 400, 450 and 500 kg of NPK fertilizer per hectare (kg ha-1) were used in a Randomized Complete Block Design (RCBD) with four replicates. These treatments were applied once to two week-old seedlings of C. moschata using ring method. The effects of these treatments on Leaf Area (LA), stem diameter (STD) and number of leaves (NL) were monitored weekly while fresh weight and dry weight were determined after 6 weeks. Soil Organic Matter (OM), Organic Carbon (OC), ash content, pH and nutrient (N, P, K, Ca, Na and Mg) levels were also monitored at 0, 2 and 6 weeks. The study showed that NPK fertilizer increased the LA, STD, NL and nutrient (N, P, K, Ca, Na and Mg) contents of the soil. The highest leaf area, stem diameter, fresh weight and dry weight were obtained from NPK treatment at 300 kg ha-1 while 350 kg ha-1 rate gave the highest number of leaves. Two weeks after treatment, the concentrations of N, Ca, Mg, OM and OC content in the soil were highly increased by the 400 kg ha-1 treatment but the 500 kg ha-1 rate gave the highest concentrations of K and Na. The study after six weeks showed that 450 kg ha-1 rate gave the highest concentrations of Ca, Mg and K in the soil whereas 500 kg ha-1 rate gave the highest concentrations of P, Na and ash content. The 350 kg ha-1 gave the highest N, OM and OC content. At p<0.05, there were significant difference among treatments. The use of NPK fertilizer at an application range between 400 and 450 kg NPK ha-1 is therefore recommended for growing of C. moschata and improvement of the soil nutrients level.

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  How to cite this article:

K. Okonwu and S.I. Mensah, 2012. Effects of NPK (15:15:15) Fertilizer on Some Growth Indices of Pumpkin. Asian Journal of Agricultural Research, 6: 137-143.

DOI: 10.3923/ajar.2012.137.143

URL: https://scialert.net/abstract/?doi=ajar.2012.137.143
 
Received: March 15, 2012; Accepted: May 23, 2012; Published: July 04, 2012



INTRODUCTION

C. moschata commonly known as musk pumpkin belongs to the family Cucurbitaceae and is native to Nigeria. Its flowers, young stems and ripe fruits are eaten as a vegetable (Grubben et al., 2004). The leaves are also commonly used to prepare sweets as well as been used as fodder. The seeds are eaten whole, roasted or toasted and are ground into different stews. Achu et al. (2005) reported that the seeds of pumpkin have high oil and protein contents and their consumption in urban areas is also fairly common. It is cultivated for both the leaves and fruits while the leaves are important vegetables, the pulp of the fruit is eaten when cooked (Okoli, 1984; Ndukwu and Okoli, 1992). In Nigeria, cultural practices are still extensive and yield levels are low.

Fertilizers are sources of plant nutrients that can be added to the soil to supply its natural fertility (Abd El-Aziz, 2007). Profitable responses to NPK fertilization are mentioned by Conover and Poole (1990). Organic matter also has been reported to acts as a reservoir of plant nutrients especially N, P, K and micronutrients and also prevents leaching of nutrients. Karim et al. (1994) reported that due to poor management and intensive manipulation of soil, organic matter content is getting reduced day by day. Available data according to Karim et al. (1994) and Ali et al. (1997) showed that the fertility of most soils has deteriorated over the years. The reduction in the soil fertility level is responsible for stagnating and, in some cases, even declining crop yields (BARC, 1997; Cassman et al., 1995). This was also supported by BARC (1999) that about 45% of net cultivable area of Bangladesh has less than 1% organic matter content. However, John et al. (2004) reported that inorganic fertilizers are the most important sources of Nitrogen (N) and adequate supply of N is associated with high photosynthetic activity, vigorous vegetative growth and a dark green colour of the leaves. Although, it has been mentioned by several researchers that the availability of nutrients influences plant growth and can determine community structure. However, there are species and community specific responses and adaptations that enable plants to cope with specific nutrient limitations. The use of chemical fertilizers as a supplemental source of nutrients has been on the increase but they are not applied in balanced proportions by most farmers. The study, therefore, seeks to determine the effects of rates of NPK fertilizer application on soil nutrient level and growth of pumpkin, C. moschata.

MATERIALS AND METHODS

The mature fruits of pumpkin, C. moschata used for this study were harvested from a subsistent farm in Abiriba, Abia State. The seeds were removed from the fruits, air dried and stored at room temperature. Soil samples were obtained from the upper soil surface layer (0-15 cm) using a 5 cm diameter soil auger. The soil samples were air dried for analysis to establish the initial soil chemical properties used for the experiment. About 5 g of the air-dry soil was taken in a glass beaker and 10 mL of distilled water was added. The contents were mixed thoroughly with a glass rod and allowed to stand for 30 min. The soil pH was measured using EQUIP-TRONICS Digital pH meter model EQ-610. The soil samples and poultry manure were digested on a labcon digester at 300°C in a mixture of hydrogen peroxide, sulphuric acid, selenium and salicylic acid (Okalebo et al., 2002). The digests were analysed for total N, P, K, Na, Ca and Mg. The total N content in the digests were determined by Kjeldahl method, 10 mL of the digest solution was taken in the distillation flask, 20 mL of 40% NaOH was added and the NH3 evolved was collected in a flask containing 4% H3BO3. Finally, the distillate was titrated against 0.1 N H2SO4. Total phosphorous was determined using the ascorbic acid blue colour procedure and the absorbance measured at 880 nm wavelength UV-spectrophotometer. The Ca, K and Mg contents in 1/20 dilution (sample/distilled water) soil digests were measured by reading their absorbance on a UNICAM 969 Atomic Absorption Spectrophotometer at 766.5, 422.7 and 285.2 nm, respectively. The sodium content in 1/20 diluted sample were determined by reading their absorbance at 248.3 nm (Okalebo et al., 2002). For total organic carbon, two gram of soil was taken in a 500 mL Erlenmeyer flask, 10 mL of 1 N K2Cr2O7 was added and the flask was swirled to mix the contents. Twenty milliliter of conc. H2SO4 was added to the soil suspension; flask was swirled again for 1 min and allowed to stand for 30 min. After this, 200 mL of water, 10 mL of H3PO4 and 1 mL of diphenylamine indicator were added and the contents were titrated against 0.5 N FeSO4.7H2O until the colour changed from blue to red. The organic matter was obtained by multiplying total organic carbon values by a conversion factor of 1.27 (AOAC, 1990). NPK (15:15:15) fertilizer was used as treatment. The treatments were 0, 200, 250, 300, 350, 400, 450 and 500 kg NPK ha-1. The experiment was laid out in a Randomized Complete Block Design (RCBD). The treatments were applied once to two week-old seedlings of C. moschata using ring method. Each treatment was replicated four times. The plants were staked to avoid creeping on the ground. The soil chemical properties (N, P, K, Ca, Na and Mg) were assessed 2 and 6 weeks after planting following the method described above.

Measurement of plant material: The leaf area, stem diameter and number of leaves were measured weekly, while fresh weight and dry weight of C. moschata were measured 6 weeks after planting. The leaf area was determined by rapid leaf area estimation as described by Salau and Olasantan (2004) for pumpkin leaf. The stem diameter was determined by measuring the stem close to the ground with vernier caliper while the number of leaves was obtained by direct counting of the leaves. The fresh weights of C. moschata were obtained using Metler balance (Model PN 163) which were measured immediately after harvest to avoid water loss while the dry weight were obtained by drying the samples in a plant dryer (Baird and Tatlock, Greenfield England) at 80°C for 48 h to obtain a constant weight.

Statistical analysis: Statistical analyses of data obtained for plant parameters and soil samples were by Analysis of Variance (ANOVA) using the statistical package, SPSS 17.3. Means were compared using the 5% level of significance.

RESULTS AND DISCUSSION

Effect of NPK on some growth indices of C. moschata: The addition of NPK treatments to the soil increased the leaf area, stem diameter, number of leaves, fresh weight and dry weight of C. moschata and all NPK treatments had significantly broader leaf area, stem diameter, number of leaves (Table 1), fresh weight and dry weight (Table 2) than the control respectively. However, among treatments, 300 kg ha-1 showed the highest leaf area. The 300 kg ha-1 treatment consistently increased the stem diameter, fresh weight and dry weight of C. moschata while the 350 kg ha-1 treatment gave the highest number of leaves (Table 1).

Table 1: Effect of NPK treatments on number of leaves, leaf area and stem diameter of C. moschata
Image for - Effects of NPK (15:15:15) Fertilizer on Some Growth Indices of Pumpkin
DAT: Days after treatment, NL: Number of leaves, LA: Leaf area, STD: Stem diameter, SE: Standard error, SD: Standard deviation, LSD: Least significant different (p<0.05)

Table 2: Effect of NPK treatments on dry weight and fresh weight of C. moschata
Image for - Effects of NPK (15:15:15) Fertilizer on Some Growth Indices of Pumpkin
SE: Standard error, SD: Standard deviation, LSD: Least significant different (p<0.05)

The leaf area and stem diameter obtained from 300 kg ha-1 treatment after 10 DAT (152.50 cm2, 0.843 cm), 17 DAT (265.75 cm2, 1.063 cm), 24 DAT (271.50 cm2, 1.245 cm) and 31 DAT (277.75 cm2, 1.273 cm), respectively. Abd El-Aziz (2007) reported that lower level (4 g pot-1) significantly increased plant height, number of leaves, number of branches, root length, diameter of stem and leaf area by about (29.4, 62.1, 58.3, 39.7, 46.2 and 44.3%, respectively) compared with the control croton plant. 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, they reported increase in leaf area and fruit yield. Oad et al. (2001) reported that application of NPK fertilizer doses equally showed efficiency of producing taller plants, more branches, increased number of siliqua, lengthy siliqua, bold seeds in siliqua and heavier seed index, which in-turn increased seed yield and oil content of the crop. Omotoso and Shittu (2007) reported that the fertilizer NPK significantly increase growth parameters (plant height, leaf area, root length, number of leaves), yield and yield components with fresh leaf, root and stem weight been higher in treatments that received 300 NPK kg ha-1 than those that received 0 and 150 NPK kg ha-1 while application of 250 kg ha-1 of NPK gave the highest number of leaves and stem girth (Awodun et al., 2007).

Effect of NPK on the soil nutrient content: The initial chemical compositions of the soil used in this study are presented in Table 3. The organic matter, total nitrogen, exchangeable Ca, Mg and K were quite high except pH and available phosphorus contents of the soil when compared with the work of Ayeni (2010). The soil pH is slightly acidic with the value of 5.94. Similarly, the organic matter and organic carbon were quite high when compared with the work of Ibeawuchi et al. (2007).

Table 4 presents results on soil nutrient composition 2 Weeks after Planting (WAP). The NPK treatments increased the OM, OC and nutrient content of the soil while the control showed reduction in OM, OC and all nutrients assessed except available P and K. Among treatments, 400 kg ha-1 had the highest value for N. The value was not significant at p<0.05 among NPK treatments but significant when compared with the control. The 400 kg ha-1 consistently increased the available P, Ca, Mg, OM and OC while 500 kg ha-1 gave the highest value for K and Na content of the soil. The pH values varied from control (5.78) to 500 kg ha-1 (7.32) while, the percentage ash content ranges from 90.9-93.6% for 500 and 300 kg ha-1, respectively. The ash content was not significant among treatments.

However, the results obtained 6 WAP was not consistent with the results obtained 2 WAP. The trend changed and different treatments showed varied improvement to macro and micro-nutrients of the soil. The OM and OC were quite high with 350 kg ha-1 and P and Na at 500 kg ha-1 while 450 kg ha-1 gave the highest value for K, Ca and pH. Though not significant, 250 kg ha-1 gave the highest value for N. However, the control showed highest Mg content of the soil 6 weeks after planting (Table 5).

Table 3: Initial chemical properties of soil
Image for - Effects of NPK (15:15:15) Fertilizer on Some Growth Indices of Pumpkin

Table 4: Effect of NPK on soil nutrient composition, 2 weeks after planting (WAP)
Image for - Effects of NPK (15:15:15) Fertilizer on Some Growth Indices of Pumpkin
SE: Standard error, SD: Standard deviation, LSD: Least significant different (p<0.05)

Table 5: Effect of NPK on soil nutrient composition, 6 weeks after planting (WAP)
Image for - Effects of NPK (15:15:15) Fertilizer on Some Growth Indices of Pumpkin
SE: Standard error, SD: Standard deviation, LSD: Least significant different (p<0.05)

CONCLUSION

The NPK fertilizer increased the leaf area, stem diameter, number of leaves and nutrient contents (N, P, K, Ca, Na and Mg) of the soil. The use of NPK fertilizer at an application range between 400 and 450 kg NPK ha-1 is therefore recommended for growing of C. moschata and improvement of the soil nutrients level.

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