• Nitrogen is the first limiting nutrient for plant growth.
• Its application is indispensable for successful potato production.
• An adequate amount of nitrogen increases root and shoot number and size of tubes.
• So it should be applied in right amount at right time through right method.
• The comprehensive studies results, quoted and compiled in the bulletin No. 32 reveal the following information with regard to nitrogen application.
• Nitrogen response varies with the soil type, varieties, length of growing season, organic manures, kind of fertilizers, time and method of application, moisture supply and nutrient interaction affect nitrogen needs of the crop.
• Long duration potato varieties like Kufri Badshah, Kufri lalina and Kufri Sindhuri producing large-sized tubers are more responsive to nitrogen than short duration ones producing small and medium sized tubers.
• The use of organic manure's, FYM, green manuring, composts and oil cakes have been found to improve the yield.
• On N basis, the organic manures are less efficient than the fertilizers.
• However, the combined use of organic manures and fertilizers has been found better than the use of fertilizer alone.
• Ammonium Sulphate and Ammonium Sulphate Nitrate are usually the best fertilizers followed by CAN, Ammonium Chloride and Urea.
• Application of urea by furrow method affects sprout growth and in turn crop emergence.
• Its application at planting by furrow method should not exceed 40-50 Kg N/ha otherwise emergence would be affected.
• Its application by broadcast or in bands 5 cm away from the tubers is advocated.
• In case of CAN, Ammonium Sulphate furrow method is better than broadcast.
• The application of urea at top dressing is as effective as Ammonium Sulphate or CAN. Therefore, the application of urea at top dressing is advocated.
• The split application of urea, ½ at planting and ½ at earthing-up has been found better than three splits where the duration of the crop is short.
• Urea can also be applied through foliar sprays where it should be preferably combined with fungicidal or pesticidal sprays.
• Nitrogen depresses potassium composition in the plant. So an adequate amount of potassium in soil is necessary for getting full benefit from nitrogen.
• Nitrogen applied to Potato leaves sufficient residues in the soil so as to affect the nitrogen needs of succeeding crop like wheat, sunflower, onion etc.
• The residual effect reduces the N requirement of succeeding wheat by about 50 per cent.
• Application of nitrogen has been found to increase the crude and true protein content of tubers.
• Lower doses have little effect on dry matter and ascorbic acid content but higher doses could depress them.
• N-application has been found to adversely affect keeping quality of Potato tubers.
• Its application increases the size of tubers and respiration rate of tubers.
• Big tubers exhibit higher rate of respiration than small ones and are prone to more rotting.
• Nitrogen was also effective in decreasing the incident of leaf spot diseases but increased the incident of early blight, late blight and charcoal rot.
• Nitrogen also increased the incidence of cut worms and aphids.
• Nitrogen needs are found to vary with the potato growing zone.
• However, the application of 180 to 240 kg N/ha is advocated for the Indo
• Gangetic plains, alluvial soil zone.
• For the seed crop, the N-needs are about 30-40% lower than the main crop.

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• Phosphorus improves yield by its positive effect on tuber number as well as the size of potato tubers.
• In the event of P deficiency, leaves lose lustre and show curling with purple pigmentation and sometimes marginal scorching.
• P hastens maturity and thus it contracts the delayed maturity induced by excessive N fertilization.
• P deficiency is there in the alluvial soils of Punjab, Uttar Pradesh and Bihar.
• Potato needs varied from 50 to 150 kg P2O5 /ha.
• Attempts have been made to recommend application on the basis of soil test.
• The information on the critical level of soil P and organic carbon could help in deciding whether a particular soil requires P incorporation or not.
• If soil P is below the critical level it requires P fertilization, otherwise not.
• Critical level of soil nutrients for getting economic response of Potato to P application.

Soil	Variety	Critical P level	Source
Alluvial (Punjab)	Kufri Chandramukhi (Autumn)	10 ppm (Olsen)	Grewal and Singh (1976)
Alluvial (Punjab)	Kufri Chandramukhi (Spring)	13 ppm (Olsen)	-do-
Hill Soil (HP)	Kufri Jyoti (Summer)	35 ppm (Bray P1)	Grewal and Sharma (1979)

• P-needs also vary with the objective of Potato cultivation.
• If the crop is raised for seed propose, higher dose may not be required as raising the dose from 40 to 80 Kg P2O5/ha resulted in a decrease in seed sized tuber yield.
• But for main crop production, higher dose is required.
• The water soluble P-carrier namely superphosphate, mono, diammonium phosphate and pyrophosphates are a better source of P than rockphosphate and bonemeal (Negi et al., 1982).
• The recovery of P even from single superphosphate by Potato is about 10-15%.
• This shows that most of P remains unutilized in the soil.
• Lot of efforts have been made to improve P-use efficiency as listed below.
• Soaking of mother seed tubers in a solution containing 1.5% single superphosphate and 0.5% urea for 4 hr before planting has been found to economize on P input by about 50 Kg P2O5/ha.
• The soaking in NH4 PHO4 solution was also effective in supplying P to Potato crop (Sharmal et al, 1977).
• Care should be taken that the seed tubers after soaking treatment should be dried in shade before planting.
• Entire dose of P should be applied at planting as split application has not proved advantageous (Sahote and Govinda Krishnan, 1984).

• Potassium chloride (MOP) and Potassium sulphate (SOP) are the two major fertilizers used for supplying the potash needs of crop. MOP usually contains 60 percent K2O while SOP contains 50 per cent K2O plus 18 percent sulphur.
• The Potato crop is highly influenced by the potassium on account of the following reasons.
• The quality of Potatoes grown on soils low in Potash becomes easily impaired by 'black spot' or bruise blue.
• The potato flesh under the skin turns bluish-black if the tubers are mechanically injured in the course of harvesting or of storing and parking.
• The tuber content of starch, ascorbic acid, cystine, methionine and protein increased with increasing rates of S-containing fertilizers and decreased by increasing the rates of Cl-containing fertilizer (Duba L.V., 1973).
• Sulphate of Potash is a better source of K than Muriate of Potash for yield as well as quality of Potato tubers because of the adverse effect of Chloride (present in MOP) on dry matter and starch. (Bhandari et al., 1987) Farmer and Parliament 22(2):11-12.
• Sulphur source in SOP (sulphate of Potash) improves the quality of Potatoes (Dande et al., 1986).
• Two possible influences of Chloride on the carbohydrate metabolism were studied by Halder, H.E., 1976 (Lordwirstchaftliche Forschung, Sonderhelf 32/I, 122-131). P. Takeduch.

  i)Reduction of photosynthesis in the leves

  ii)Retardation of assimilate transport into the tubers.

• During the whole growing season Potato plants were supplied with 3 different amounts of chloride and sulphate:

  i)High amount of chloride (12 me/lt) and traces of sulphate

  ii)Chloride and sulphate in equal amounts

  iii)high amounts of sulphate (12 me/lt) and traces of Chloride

• When the growth rate of tubers was high (six weeks after flowering), the distribution of labeled photosynthesis in the plants was studied after they had been supplied with 14CO2 for 24 hours.
• Most of the 14CO2 was assimilated by the plants given equal amounts of chloride and sulphate.
• The percentage preparation of labeling in the leaves did not differ significantly between the three treatments.
• Therefore, chloride could not have inhibited the photosynthesis in the leaves.
• But there was a negative correlation between the proportions in tubers and in stems.
• In the so-called "sulphate plants" the proportion in the tubers was much higher than in the stems. In the 'chloride plants' it was reverse.
• This indicates that chloride has retarded the translocation of photosynthates from the stem into the tubers.
• The 'sulphate plants' yielded the highest tuber weight in connection with a slightly higher starch content.
• Application of low rates of K reduced the tendency of tubers (var. Bintje) to sloughing.
• After cooking the discolouration was not affected by the amount of K. (Hojmarh J.V., 1977).
• Salinity demands specific care in the choice of mineral fertilizer.
• Suitable for saline conditions are fertilizers that are osmotically less effective and low in their content of salts which are already present in the soil.
• Chloride is one of the constituents in saline soils.
• If taken up in excessive amounts, it may cause physiological disorders and consequently diminish quality as described with vegetables potato, fruit, tobacco and sugarcane.
• Apart from being virtually free of chloride, SOP contributes less to osmotic stress than other K sources and provides two essential nutrients - potassium and sulphur.
• The latter becomes increasingly important in intensively cropped areas with light-textured soils, high yields and predominant use of high-grade fertilizers.
• A 'K' content of 7-8 per cent in petioles at the time of tuber initiation was adequate for the production of maximum yields.
• MOP generally resulted in higher petiole K levels (9-12 per cent) than did SOP (8-9 percent).
• Specific gravity of tubers was reduced with increasing rates of K.
• It was lower at MOP than at SOP treatment (Mcdole et al., 1978).
• Increased K application raised K contents in leaves and tubers of Potatoes remarkably independent of the K source.
• Raised K contents in leaves and tubers in any case lowered contents of reducing sugars, total sugar contents and blackspot of potatoes as well. By this way the quality of colour of baked chips was improved.
• Raising the K rate from 170 to 306 Kg K2O/ha increased tuber yields but lowered starch contents.
• Starch contents were lower in the Cl treated plots and higher in the SOP treated plots (Patletschny and Kick, 1979).
• Industrial food potatoes (chips, crisps) should be manured somewhat more lightly than general table potatoes but more heavily than starch potatoes so as to combine the highest possible dry matter content with the least possible tendency to undesirable browning (Prummel, J. 1983).
• K - application enhanced the yield of large sized tubers. (Sadaphal et al. 1973).
• Potassium sulphate as a source of K was comparatively more effective than MOP in acidic and alluvial soils with respect to yield and K-uptake.
• Tuber drymatter, starch, total sugars, and ascorbic acid content were comparatiely higher with SOP than with MOP.
• The beneficial effect of sulphate ion in SOP in acidic or light textured alluvial soil may be due to sulphur deficiency in soils (Sharma et al, 1980).
• Although potato is sensitive to excess Cl during early growth, MOP and SOP give the same yield if the chloride ion has the time to move.
• For starch production and for chipping / dehydration, there seems to be an advantage for SOP as shown in Germany, Japan, Switzerland and USA (Sprott and Storer, 1984).
• No doubt, SOP is more expensive but the extra cost may will be repaid by the higher quality of the resulting produce and consequently higher market price while SOP may also offer the cheapest and most convenient means of supplying the crop's need for sulphur.