SarhadJ . Agric. Vol.27, No.3, 2011
EFFECT OF DIFFERENT LEVELS OF NPK
FERTILIZERS ON THE PROXIMATE COMPOSITION
OF POTATO CROP AT ABBOTTABAD
FALAK NAZ*, ASAD ALI*, ZAFAR IQBAL**, NAVEED AKHTAR*,
SYED ASGHAR*** and BASHIR AHMAD****
Hazara Agricultural ResearchStation, Abbottabad– Pakistan.
Departmentof Agricultural Chemistry, Agricultural University, Peshawar – Pakistan.
AgricultureResearchInstitute, TarnabPeshawar – Pakistan
Departmentof Plant Protection, Agricultural University Peshawar – Pakistan
The experiment was conducted at Hazara Agricultural Research Station, Abbottabad, Pakistan during the
year 2004-05. Themost popular variety of potato “Desiree” was analyzedto find out theeffect of different doses of
NPK on its proximate composition. The results showed that NPK fertilizers had significant effect on nutrient
composition of potato. Moisturecontent was in therangeof 68.8 percent in T6 (140:140:210 NPK) to 81.4 percent
in T2 (60:60:90 NPK). Crudeprotein contents werevery low in potato, which werefrom0.9percent in T1 (control)
to1.4 percent inT6 (140:140:210 NPK). Percent fatsof potatodroppedoff byincreasing thedosesof NPK. Fat was
lowest as 0.4 percent in T7 (160:160:240) and highest as 1.2 percent in T1 (control). The crude fiber in potato is
enhanced by rising amount of NPK. The crude fiber and ash content were ranging from 1.99 (T5) to 3.59 (T7)
percent and 3.68 (T7) to 5.18 (T5) percent respectively. Fromabove results it is commended that right amount of
NPK fertilizers shouldbeappliedtogainhighyieldandnutritious product.
Key Words: Potato, NPK , proximatecomposition.
fertilizers on the proximate composition of potato crop at Abbottabad. Sarhad J. Agric. 27(3): 353-356
Naz, F., A. Ali, Z. Iqbal, N. Akhtar, S. Asghar and B. Ahmad. 2011. Effect of different levels of NPK
Potato is the fourth most important food crop in the world on the basis of production, with annual
production approaching 300 million tons. Both large and small-scale farmers grow potatoes. In Pakistan it is
cultivated twice a year as spring and autumn crop in plains and as summer crop in northern hilly areas. The total
production of potato in Pakistan for the year 2004-05 was 2024,900 tons on total area of 112,000 hectares with 18.1
tones/ hectare yield (Agric. Statistics of Pakistan, 2004-05).
Due to its vegetative origin, the potato tuber is extremely sensitive to environmental impacts. Depending on
variety, climate, soil type, and farming practices, the color and composition of potato tuber may vary widely. Water
content of potato is about 74 to 75 % and gives 97 kcal per 100 grams of weight (Ismail, 2002). Potatoes are good
source of carbohydrates and contain a little proportion of protein and fat. Although the protein content of potato is
low, yet on per acre production basis its protein is two times more than that of wheat and maize and three times
more than that of rice (Ismail, 2002). Due to high carbohydrate contents, weight conscious and diabetic people
should avoid or limit the intake of potatoes.
Fertilizer application is one of the best means of increasing yield per unit area. It is believed that NPK
fertilizers improve both yield and quality of potato tubers. Potato require high amounts of potassium fertilizer for
optimum growth, production and tuber quality (Al-Moshileh and Errebi, 2004), but its recovery of K is often quite
low. The efficiency of NPK fertilizers can be further enhanced by the use of micronutrients (Khalil, et al., 1980).
However response of these fertilizers varies depending upon the variety and location.
The aim of present study is to determine the effect of different doses of fertilizers on nutritional
composition of prominent local variety of potato i.e. Desiree. Results of this study would be worthwhile to improve
the nutritional quality of potato by the use of suitable combination of NPK fertilizers.
MATERIALS AND METHODS
The red variety Desiree is very popular among the farmers of Khyber Pakhtunkhwa, Pakistan. The present
investigations were taken to study the effect of different doses of NPK fertilizers on the nutritional quality and
organoleptic characteristics of this variety under irrigated conditions of Hazara Agricultural Research Station,
Falak Naz etal. Effectof differentlevels of NPK fertilizerson theproximatecomposition …
Abbottabad, Pakistan during 2004-05. One controlled i.e. without fertilizer, and six different doses of fertilizer as
kg/ hectare were applied to the same variety of potato in the form of Urea, Diammonium Phosphate (DAP), and
Potassium Sulphate (SOP) given below:
T1= Controlled (Without fertilizer application).
N : P: K
T2=60 : 60: 90
T3= 80 : 80: 120
T4=100 : 100 : 150
T5= 120 : 120 : 180
T6= 140 : 140 : 210
T7= 160 : 160 : 240
There were three replications for each treatment to obtain valid and reliable results. Urea was applied in
split doses such i.e., half at the time of land preparation with whole doses of DAP and SOP and the second dose of
urea was applied at the earthen up. After fertilizer application one kg of potatoes from each sample were taken for
nutritional analysis. These samples were analyzed for their proximate composition, and to recommend an
appropriate combination of NPK fertilizers.
Proximate composition of samples i.e. determination of moisture, crude protein, crude fat, crude fiber, ash
and energy, was performed in accordance with the standard method of AOAC, 1990.
Moisture was determined by oven drying method. 1 g of each sample was accurately weighed in Petri dish
(W1). The partially covered dish was placed in oven at 105 °C for 6-12 hours. Then the Petri dish was placed in
desiccator for 30 minutes to cool. The sample was reweighed after cooling (W2). The percent Moisture was
%Moisture =(W1-W2) 100
Wt. of sample
Crude fat was determined by ether extract method using Soxhlet apparatus. 1 g of each moisture free
sample was wrapped in filter paper, placed in thimble and then introduced in the extraction tube. Weighed, cleaned
and dried receiving beakers were filled (1/3rd) with petroleum ether and fitted into the apparatus. Extraction was
done until complete drying of solvent.
The percent of Crude Fat was determined by using the formula as given below:
%Crude Fat = Wt. of Ether Extract 100
Wt. of Sample
The weighed sample was first digested with acid and then with alkali.
Acid Digestion: 1 g of each fat free sample was first boiled with 200 ml 2.5% HCl solution on steam bath at 90-95
°C for about 2 hours. It was filtered through the linen cloth and the filtrate was washed with hot distilled water until
it becomes acid free. Residue was transferred to another beaker for alkali digestion.
Alkali Digestion: To the filtrate 200 ml of 2.5% NaOH solution was added and digested again on steam bath for 2
hours. It was filtered through linen and then washed thoroughly with hot water (50ml), alcohol and ether (25 ml) to
alkali free. Crucible was then dried in an oven at 110-120 °C, made it cool in desiccator and weighed (W1). The
residue was then ignited in furnace at 600 °C till gray white ash was appeared. After cooling in desiccator, its weight
was taken again (W2). Percent Crude Fiber was calculated as:
%Crude Fiber =(loss in weight on ignition) 100 – F
Wt. of Sample
F= Crude Fat weight
SarhadJ . Agric. Vol.27, No.3, 2011
1 g of each sample was taken in digestion flasks. 8 g of digestion mixture i.e. K2SO4: CuSO4(8:1) and 12
ml of conc. H2SO4were added. Some pieces of fumic stones were also added to avoid bumping of solution. The
flasks were swirled in order to mix the contents thoroughly. Digestion was carried out by heating the mixture till the
mixture becomes clear. After cooling the digest was then transferred to 100 ml vol. flask and volume was made up
to the mark by the addition of distilled water. Distillation of the digest was performed in Markam Still Distillation
Apparatus. 10ml of digest was introduced in the distillation tube through funnel. Then 10 ml of 0.5 N NaOH was
gradually added through the same way. Distillation was continued for at least 10 minutes and NH3produced was
collected as NH4OH in a conical flask containing 20 ml of 4% Boric acid solution with few drops of modified
methyl red indicator. The tip of condenser was washed in the flask with distilled water. During distillation yellowish
color appears due to Ammonium hydroxide. The distillate was then titrated against the standard 0.1 N HCl solution
till the appearance of pink color. A blank was also run through all the steps as above. Percent Crude Protein was
calculated using the formula given below:
% Crude Protein = 6.25 % N
Conversion factor = 6.25
% N = (S-B) N 0.014 D 100
Wt. Of Sample V
S = Sample titration reading
B = Blank titration reading
N = Normality of HCl
D = Dilution of sample after digestion
V = Volume taken for titration
0.014 = Milli equivalent Wt of Nitrogen
Determination of Ash
Cleaned empty crucibles were placed in a muffle furnace at 660 °C for an hour, cooled in desiccator and
then weight of empty crucible was noted (W1). 1 g of each sample was placed in crucibles (W2). The samples were
charred over the burner with the help of blowpipe. The crucibles were then placed in a muffle furnace at 550 °C for
6- 8 hours. After the complete ignition the furnace was turned off. The crucibles were cooled and weighed (W3).
Percent Ash was calculated as follows:
% Ash =(W3-W1) 100
Wt. of Sample
The percent calories in selected samples were calculated by multiplying the percentage of crude protein and
carbohydrate by 4.1 and crude fat by 9.3. The values are then added to Calories per 100 gram of sample.
RESULTS AND DISCUSSION
It can be observed from the (Table I) that lowest moisture contents 68.75 % were observed in NPK
application of 140:140:210 (T6) as compared to 81.44% when NPK ratio of 60:60:90 (T2) was applied. This value is
closely similar to the result reported by Harris and Loeseck (1960). This shows that higher dose of NPK fertilizer
increases the moisture content of potato. Moisture is very important in fresh potato as well as in the period of storage
of any food material. Availability of high moisture is suitable condition for the growth of microorganism and thus
decreases the shelf life of potatoes. It is also important to have enough moisture in fresh potato so the optimum value
of moisture i.e. 75.81% was taken by applying 120:120:180 ratio of NPK.
Concentration of crude protein was low in potato. It was estimated from 0.95 to 1.39% in all selected
samples. Lowest amount was found in T1 when ratio of 60:60:90 was applied and highest value was found in T6
when dose of 140:140:210 was applied to crop. Optimum protein was reported in T5, i.e. 1.35%. This result shows
strong agreement with the results recorded by Srikumar (1990). Increase fertilization also increases the content of
protein. Same results were also reported by Leszczy (1980). Fats are very important for the body and are the biggest
source of energy providing 9.1 k.cal 100g-1. Fats are important for the proper functioning of nervous system and
maintain fertility in man. Fats act as lubricant in the alimentary canal of man. But higher intake of fats is harmful for
Falak Naz etal. Effectof differentlevels of NPK fertilizerson theproximatecomposition … Download full-text
the health. Potato is very low in fat content. Analysis demonstrated that enhancing the amount of fertilizer reduced
crude fat. The lowest value of crude fat was 0.41 in T7, when applied dosage was 160:160:240 and the highest value
was 1.197% in sample T1. Jacobs (1979) also calculated 0.1 to 0.3% Crude fats in potato, which shows an
agreement with our results.
T1= Controlled (Without fertilizer application), T2= 60:60:90, T3= 80:80:120,
T4= 100:100:150, T5= 120:120:180, T6= 140:140:210, T7= 160:160:240. (N:P:K)
Proximatecomposition of Potato(% DryWeight Basis)
%Moisture%Ash %Protein%Fat%Fiber %Dry MatterEnergy
Reduced proportion of fertilizers amplified the fiber portion of potato. The calculated crude fiber was as
low as 2.05% in T2 and as high as 3.59% in T7. Fiber provides bulk to the food, which enhances the digestibility of
food inside the body. Results regarding fat and fiber are some how different with the results given by Srikumar
(1990). This difference may be due to the variation in environmental conditions and soil type or different chemicals,
used during analysis. Minimum ash was estimated in T7 as 3.67% and maximum was present in T5 as 5.18%. Dry
matter contents are associated with the amounts of starch, proteins and mineral constituents present. In general, high
dry matter is associated with high starch content and high cooking quality in potatoes. Data presented in table
revealed that maximum dry matter contents 28.52% were observed in T6 whereas lowest contents 18.51% were
observed in T2 treatment. The energy calculations show a range in values, and demonstrate effect of fertilizers.
Values were ranging from 93.22 to 108.50 k.cal.100g-1. Sample T5 was providing highest energy, when applied
dosage was 120:120:140. Variation was observed among all samples, which shows the significant effect of
fertilizers on nutrient composition of potato.
CONCLUSION AND RECOMMENDATIONS
Application of different doses of NPK fertilizers on potato variety Desiree indicate that reduced proportion
of NPK fertilizers amplified the fats and ash contents whereas protein, fibre and dry matter contents increased with
increase in NPK ratios.
AOAC. 1990. Official methods of analysis of the Association of Official Analytical Chemists. 15th ed. Washington, DC, Assoc.
of Official Analyt. Chemists.
Agric. Statistics of Pakistan. 2003-2004. Govt. of Pakistan, Ministry of Food, Agric. & Livest. Food, Agric. & Livest. Div.
(Econ. Wing), Islamabad, Pakistan.
Al-Moshileh, A.M. and M.A. Errebi. 2004. Effect of various potassium sulfate rates on growth, yield and quality of potato grown
under sandy soil and arid conditions. IPI regional workshop on Potassium and Fertigation Dev. in West Asia and North
Africa, Rabat, Morocco. Nov. 24-28.
Harries, R.S. and H.V. Loesecke. 1960. Nutritional evaluation of food processing. John Wiley & Sons, Inc. New York. 69p.
Ismail, M.K. 2002. How good is potato for us: Different uses of potato. www.bawarchi.com/health/potato.html
Jacobs, M.B. 1979. The chemical analysis of foods and food products. 3rded. D. Van Nostrand Co. Canada. Ltd.
Khalil, I. A., N. Habib and A. Ghafoor. 1980. Yield –and quality of potato as influenced by nitrogen and potash fertilizer.
Pakistan J. Agric. Res. (1): 26-29.
Leszczy, W. and G. Lisi. 1980. Influence of nitrogen fertilization on chemical composition of potato tuber. Food Chem. 28(1):
Srikumar, T.S. and P.A. Ackerman. 1990. The effect of fertilization and manuring on the content of some nutrient in potato. Food
Chem. 37(1): 47-60.