Excessive nitrogen may lead to decreased fruit set, increased
foliage and a decline in yield and bioactive compounds of pumpkin
(Integrated Pest Management, 1995; Oloyede et al., 2012b).
The addition of fertilizer reduced both antioxidant activities and
antioxidant phenolic compounds. These reductions were due to the
increasing N concentration in plants through fertilizer. The result
is similar to the reduction in total phenolics and antioxidant activities
observed in tomatoes. Plants with limited N were shown to
accumulate more flavonoids than those that are well supplied with
inorganic fertilizers. It was concluded that synthetic fertilizers in
which N is easily accessible to the plant may reduce the health
benefits of tomatoes (Mitchell and Chassy, 2007). This agreed with
the observation in this study that over fertilization with N reduces
nutrient quality and the health benefits of pumpkin fruits. Oloyede
and Adebooye (2005) found out that there was reduction in fruit
proximate composition of snake tomato (Trichosanthes cucumerina
L.) belonging to the same family of pumpkin- Cucurbitaceae, as the
concentration of phosphorous application increased.
In conclusion, as observed in this study, early sowing, when
there is less rainfall, moderately higher temperature and more
sunshine favored accumulation of antioxidants in pumpkin fruit.
As sowing date was delayed, climatic conditions changed, there
was more rainfall, lower average temperature and lower total sunlight,
these negatively affected the concentrations of antioxidants.
Early sowing is recommended for cultivation of C. pepo to avert the
influence of climate on production of pumpkin. 135–180 kg ha−1
NPK rates could provide optimal antioxidant contents of pumpkin
fruit.
Acknowledgement
The African-German Network of Excellence in Science (AGNES)
under the Nevile Alexander Memorial Fund, BMBF of Germany is
acknowledged for a grant provision to take care of the preparation
of this article.