Effect of Potassium Fertilization on Yield and Quality of Some Potato Cultivars

INTRODUCTION

The potato (Solanum tuberosum L.) is a herbaceous annual plant that grows up to 100 cm tall and produces tubers. Potato is one of the more often grown crops. Also, ranks as the world’s fourth most important food crop, after maize, wheat and rice (Spooner and Bamberg, 1994). Their tubers are a good source of carbohydrates, proteins, vitamins, and minerals in human nutrition (Blagoeva et al., 2004). It is a major source of inexpensive energy. It contains high levels of carbohydrate and significant amounts of vitamins B and C and minerals. Moreover, potato is used in many industries, such as French fries, chips and starch (Abdel-Aal et al., 1977).  In Egypt, potato has an important position among all vegetable crops, where about 20% of the total area of vegetables production is devoted for potato (FAO, 2015). Egypt imports annually from 50000 to 55000 ton of potato seeds from the North West European countries, particularly from Netherland and England to be planted in the summer season in January up to middle of February.

Nevertheless, potato plants require nutrients supply through fertilization due to their shallow root system and high demand of nutrients for tuber’s development. For instance, the use of potassium fertilizer is almost negligible in our country which has resulted not only in stagnation of crop yield, but also the quality of the crop. The Ministry of Agriculture of Egypt recorded more than two hundred potato cultivars that are handled in markets. These cultivars are usually subjected for several testes to determine their suitability for farming condition in Egypt. However, the productivity and economic characteristics of some recently introduced cultivars are much unknown. Therefore, developing a good management practices for potato growers in Egypt was selected and the present research was undertaken to:

    i.   Evaluate the three potato cultivars for tuber productivity and quality;

  ii.    Find out the optimal dose of potassium fertilizer in order to improve yields and economical returns to potato growers; and

 iii.   Examine the interaction effect between cultivars and potassium doses.

MATERIALS AND METHODS

Two field experiments were conducted in a private farm during the two successive summer years of 2015 and 2016, in clay loam soil at Maghnine village located at Kom Hamada, El-Behera Governorate to study the effect of potassium fertilizer levels and some potato cultivars on vegetative growth, yield and quality. The physical and chemical analysis of the soil prior to the initiation of the experiments is shown in Table (1). Certified imported Potato seeds of cultivars Spunta, Provento and Galactica were used after splitting. Cut seedy were planted at the 5^th February, in both seasons in dry soil then irrigated. Seeds were planted in two ridges; 0.70 m wide, 6.25 m long and 0.25 m apart between hills on one side of the ridge, making an area of 8.75 m² for experimental plot.

Four potassium levels; 0, 50, 75 and 100 kg K₂O fed^-1 were used. Potassium dosages were applied equally in the form of potassium sulfate (50% K₂O), at 45, 60 and75 days after seed sowing.

The experiments were laid out in split-plot system in randomized complete blocks design (RCBD), with three replications for both seasons. The cultivars were distributed in the main plots, while the potassium levels were distributed in the sub-plots. Data were, statistically, analyzed according to Snedecor and Cochran (1990). The least significant difference (LSD at 0.05) was used to compare the treatment means using CoStat (2005) program. All other agricultural practices for potato production were followed as recommended in the area.  Harvesting was accomplished after 110 days of planting during both years.

Recorded data

Vegetative growth measurements

1. Plant stand: after complete plant emergence, 45 days after planting, the number of plants plot^-1 was counted and plant stand percentage was calculated.
2. Number of main stems plant^-1: it was determined after 45 days of planting, using the average number of main brunches of 10 plants.
3. Plant height (cm): it was measured after 75 days of planting, using the average height of 10 plants.

Yield and its components measurements

1. Average of tuber weight (g): it was determined immediately after harvest, by dividing the weight of tubers yield by tuber^'s number of 10 plants.
2. The number of tubers plant^-1: it was determined just after harvest using the average number of tubers of 10 plants.
3. Total tubers yield fed^-1: The yield of the plot was weighed and then converted into tons fed^-1.
4. Average of tuber yield plant^-1 (g): It was determined using the average weight of tubers of 10 plants.

Chemicals analysis

1. Tuber specific gravity: It was calculated as average of three grades for each treatment according to the methods of (Dinesh et al., 2005) by the following formula: Specific gravity =
2. Tuber starch content (%): It was determined using the method described in (A.O.A.C,1980) on dry matter basis.
3. Tuber reducing sugars content (%): It was determined using 5 g. fresh tuber root, using sulphuric acid and phenol (5%) then colorimetrically determined, according to the method of Dubois et al. (1956).
4. Tuber total sugars content (%): It was determined using Dubois et al. (1956) method on fresh weight basis.

Table (1). The physical and chemical soil properties of experimental site in 2015.

RESULTS AND DISCUSSION

1. Vegetative growth measurements
2. Plant stand (%)

Table (2) shows that there were no significant differences among cultivars on potato plants stand in both seasons. This finding could be taken place due to the physiological status of the seed tubers and cultivars. It can be noticed from Table (2) that the cultivar “Galactica” tended to increase plant stand (%) than.

 Table (2). Effect of potato cultivars, potassium fertilization and their interactions on vegetative measurements of potato plants grown during 2015 and 2016 summer seasons.

Mean values in the same column marked with the same letter(s) is (are) not significantly different at 0.05 level of probability.               

 ns= not significant.

The other cultivars, nevertheless this increase did not reach the significant level, during both seasons of the study. In the same context, that there was no such significant difference regarding potato plants emergence among the K₂O application treatments, during both seasons. This finding is in accordance with those of Singh and Lal (2012)andBerisha et al. (2014) who stated that plant emergence was not influenced by potassium applied levels. No such significant interaction effects between potato cultivars and Potassium fertilization were noticed to change plant stand % during both season of the presented study.

1. Number of main stems plants^-1

Data presented in Table (2) exhibited that number of main stems plants^-1 was not, significantly, affected among the tested cultivars either in the first or second season. It is worth to be mentioned that all the plants in this study produced less than two stems, which reflected that the used mother tubers were not in a good physiological state. This observation may be arised due to the apical dominance phenomenon (Zaky, 2011). As for the potassium fertilization, there was no such a significant difference among the applied K₂O treatments, during both seasons of the study. This phenomenon can be noticed because number of main stems plants is a trait related to physiological status of the used tubers and cultivars. Also, number of stems plant^-1 is a factor dependent variety, seed size and its physiological status; hence, stems per hill were not influenced by potassium levels(Singh and Lal, 2012). El Gamal (1985) who reported that none of N or K levels, significantly affected stem number/ plant of potato cultivars. No such significant interaction effects between potato cultivars and potassium fertilization were noticed to change the number of main stems plant^-1 during both seasons of the presented study.

1. Plant height (cm)

Table (2) illustrated that the “Galactica” cultivar, significantly, surpassed both “Spunta” and “Provento” cultivars regarding plant height, during both seasons of the study. This result may be attributed to varietal differences. Similar conclusion was reported by Tafi et al. (2010).As for potassium fertilization treatments, although it resulted in a gradual increase in plant height, nevertheless, there were no any significant differences among the various tested level of K₂O, including control treatment, during both seasons. On the contrary, Singh and Lal (2012) showed that potassium had significant effect on plant height which, significantly, increased up to 100 kg K₂O/ ha. Meanwhile, the interaction effects between potato cultivars and potassium fertilization concerning plant height was insignificant.

1. Yield and its components

1. Average of tuber weight (g)

Respecting the main effect of cultivars, data of Table (3) exhibited that average tubers weight of potato was, significantly, influenced (P ≤ 0.05) by the three used cultivars during the both seasons of the study. The cultivar “Galactica” was superior on the other two tested cultivars. Despite there was no significant difference in average tuber weight between cultivar “Provento” and “Spunta”. These varietal differences may be due to the differences among the maturity, tuber initiation time, light intersection, the physiological activity, and the ability to accumulate photosynthetically substances (Zaky, 2011). On the other hand, concerning the effect of K₂O fertilization, data claimed that potato average tuber weight, significantly and progressively, increased with increasing K levels. In the first season, maximum and minimum mean values of 154.82 and 110.61 gm per plant were arise from application of 100 kg K₂O fed^-1 and control, respectively.

Table (3). Effect of potato cultivars, Potassium fertilization and their interactions on yield and its components of potato plants grown during 2015 and 2016 summer seasons.

^ϕ Mean values in the same column marked with the same letter (s) is (are) not significantly different at 0.05 level of probability.        *= significant      ns = not significant.                                                        

Similar results were noticed in the second season, Adhikary and Karki (2006) found a sharp response of potato to K₂O application, especially for tuber weight. Many researchers reported that K has desirable effects on potato crop and quality. As for the interaction between the tested cultivars and potassium fertilizer levels, data disclosed that there were significant differences concerning the mean values only during the first season (2015). It was clear that the highest mean value became from cultivar “Galactica” with the level of 100 Kg K₂O fed^-1.

2. Number of tubers plant^-1

Table (3) revealed that number of tubers plant^-1 of “Provento” cultivar was, significantly the most pronounced among the tested cultivars as recorded 8.23 in the first season, and 9.23 in the second one. The differences detected between “Spunta” and “Galactica” cultivars, regarding the average of number of tubers plant^-1 in 2015 season; appeared to be insignificant. Meanwhile, during 2016 season, there was a significant difference between both previous cultivars, where “Provento” cultivar was the first (9.23), “Galactica” cv. recorded the second rank (8.40) and “Spunta” came the third rank (7.61). This result agrees with those of Saluzzo et al. (1999); Tekaling and Hammes (2005) who concluded that some cultivars produced the highest total tuber yield when compared with other cultivars. On the other way, none of the tested K₂O levels, during the first season of the study has expressed such significant difference. Meanwhile, in the second season, the control treatment had the highest mean value for number of tubers per plant (8.88). Whereas, the treatment of 50 kg K₂O fed^-1; gave the lowest mean value (7.86) trait with significant differences among the other K₂O treatments. On the contrary, El-Gamal et al. (1993) reported that insufficient K; results in reduced potato yield and smaller sized tubers. There were no significant differences regarding the interaction between used cultivars and potassium doses to change number of tubers plant^-1 during both seasons.

3. Average of tubers yield plant^-1 (g)

Data in Table (3) disclosed that potato plant tubers yield was significantly (P ≤0.05) affected by used cultivars during both seasons of the study. In the first season, “Galactica” cultivar surpassed the other two cultivars, significantly. It possessed the highest mean value of average tubers yield plant^-1 (1197.45 g), followed by “Provento” cultivar (1039.73 g) which was also, significantly, surpassed the third cultivar “Spunta”. Nevertheless, in the second season, there were also significant differences among the three tested cultivars with the continued of superiority to cultivar “Galactica” (1303.98 g) over the other two cultivars. This result is consistent with that of Abdel-Aal and Imam (1984) who found a wide variation in yield and quality of tubers due to high genetic variability among different cultivars of potato under Assiut conditions. Concerning to the effect of potassium fertilization, the presented data clarified that the potassium levels, significantly, affected tubers yield plant^-1 during both seasons. Potassium level at 100 kg K₂O fed^-1 was superior and led to the highest plant yield mean value of tubers yield plant^-1 (1234.14 g) and (1304.91 g), in 2015 and 2016, respectively. In the same context, Berisha et al. (2014)pointed out that potassium fertilizer rate, significantly, affected potato tuber yield. While, the interaction effects between potato cultivars and potassium fertilization respecting tubers yield plant^-1 was insignificant in both seasons.

1. Total tubers yield ton fed^-1

The investigated cultivars declared significant (P ≤0.05) differences in total tubers yield fed^-1 as shown in Table (3). The cultivar “Galactica” had the highest mean value of total tubers yield ton fed^-1 during the both seasons of study. The difference in total tubers yield fed^-1 between the cultivars “Spunta” and “Provento” was not significant in 2015 season, whereas cultivar “Provento” significantly, exceeded cultivar “Spunta” in 2016 season. As for the effect of potassium fertilization, data in Table (3) announced that Potassium application significantly (P ≤0.05) affected total tubers yield fed^-1 compared with the control. Increasing level of K application up to 100 kg K₂O fed^-1, significantly and progressively, increased the total tubers yield fed^-1, in both seasons. Razaq et al. (2015) revealed that the potash levels had significant effect on potato tubers yield plant^-1. It, also, had a significant effect on total tubers yield ha^-1. There were no significant differences regarding the interaction effect between used cultivars and potassium doses in both seasons.

C. Chemicals analysis

1. Tuber specific gravity

Based on the main varietal effect on tuber specific gravity, it was found to have significant (P ≤0.05) differences among the varieties evaluated (Table, 4). The highest tuber specific gravity (1.092) and (1.086) was derived from cultivar “Provento”, where “Spunta” cv.; produced the lowest ones (1.064) and (1.064) in 2015 and 2016 seasons, respectively. In a similar study, Abong et al. (2010) found that specific gravity and dry matter contents had significant difference among potato varieties. The effect of potassium fertilization on tuber specific gravity was significant and the trend was approximately similar; in both seasons. Application of potassium fertilizer at 100 kg fed^-1, significantly, produced the highest tuber specific gravity, in both seasons.

Table (4). Effect of potato cultivars, Potassium fertilization and their interactions on chemicals analysis of potato plants grown during 2015 and 2016 summer seasons.

Mean values in the same column marked with the same letter(s) is (are) not significantly different at 0.05 level of probability.     ns = not significant.               *= significant.

The sole exception was in 2016 season where the difference in tuber specific gravity between 100 and 50 kg K₂O fed^-1 was not significant. These findings are matching with those reported by Zelelew and Ghebreslassie (2015) who declared thatPotassium application had positive significant effect on specific gravity of potato tubers. Concerning the interaction effect between used cultivars and potassium fertilization was not significant, in both seasons (Table 5).

Table (5). Effect of interactions of potato cultivars and potassium fertilization on tubers specific gravity ant total sugars content (%) of potato plants grown during 2015 and 2016 growing seasons.

Mean values in the same column marked with the same letter(s) is (are) not significantly different at 0.05 level of probability.

1. Tubers^, starch content (%)

Regarding the main effect of cultivars, data presented in Table (4) exhibited that tuber starch content was not, significantly, affected (P≤ 0.05) by tested cultivars during both seasons.  Saluzzo et al. (1999) and Tekalign and Hammes (2005) reported that potato cultivars differ in their starch contents. The impact of potassium fertilizer levels on tuber starch content was significant, in both seasons. Application of potassium fertilizer at 100 kg K₂O fed^-1, significantly, produced the lowest mean value of tuber starch content, whereas, the control treatment, significantly, resulted in the highest mean value of this character, in both seasons. There were significant downs starch content because of increases of potato tubers yield, especially the tubers bigger than 60 mm (Barascu et al., 2015).  Concerning the interaction effect between used cultivars and potassium fertilization was not significant, in both seasons.

1. Tuber’s total sugars content (%)

The influence of the three tested cultivars on tuber total sugars content, significantly varied between the two seasons (Table 4). In 2015 season, no significant differences in tuber total sugars content among the three tested cultivars. In 2016 season, tuber total sugars content was significantly, remarkable in cultivar of “Galactica” followed by “Provento” and “Spunta”, orderly. These results are in accordance with Olsen et al. (2005) who revealed that there are four major factors that influence sugar accumulation in potatoes: cultivar, maturity, stress and storage conditions. Respecting the potassium fertilizer effect, data in the same table expressed that there were no significant differences in tubers total sugars content among the various applied potassium fertilizer levels, including control treatments during both seasons. As about, the interaction effect between the two studied factors on tubers total sugars content of was not significant, in 2015 season, but the reverse was true, in 2016 season. The growing plants of cultivars “Galactica” and “Spunta” fertilized with potassium at 50 kg fed^-1, significantly, attained maximum and minimum tuber total sugars content, respectively. 

1. Tuber reducing sugars content (%)

Data presented in Table (4) expressed that varietal influence on tuber reducing sugars content was insignificant in 2015, but significant in 2016. Tuber reducing sugars content of cultivars “Provento” and “Galactica” was, significantly, higher than “Spunta” cultivar. Difference between cultivar “Provento” and “Galactica” in tuber reducing sugars content was at par. This result was in parallel with that stated byTrehan et al. (2007) who mentioned that “Accent” and “Turbo” cvs.; gave a higher value of total amino acids content and the highest values in reducing, un-reducing and total sugars content of potato tubers. With respective to the main effect of K₂O fertilizer, during the first season (2015), providing the tested potato plants with 50 kg/fed, resulted in the highest mean value of tuber reducing sugars content (0.54 %) despite existence some other insignificant value among the tested treatments, except for those plants fertilized with 100 Kg/fed (0.43 %). But during the second growing season (2016), the control treatment; gave the highest mean value of tubers reducing sugars content (0.53 %) with a significant value with 75 kg/fed (0.48 %) and100 kg/fed (0.43 %), respectively. These results are in harmony with Anon (2000 and 2005) whoindicated that K application through potassium sulphate improved specific gravity, chip color score and decreasing the reducing sugars content of 4 processing grade potato varieties. No interaction effects between potato cultivars and potassium fertilization were noticed to change tubers reducing sugars content during both seasons of the study.

Conclusions

In the light of all the above-mentioned data, it’s possible to conclude that: The cultivar “Galactica” treated with the level of 100 kg K₂O /fed; gave the highest mean values of plant height (cm), plant yield (g), tubers average weight (g) and total yield (ton/ fed). The cultivar “Provento” applied with 100 kg K₂O /fed was the best rang of specific gravity. Generally, we could recommend the following:

• Using the potato cultivar “Galactica” especially, for more yield and quality potato production.
• Using the potassium fertilizers as 100 kg K₂O/fed where it recorded the highest mean values of yield and quality.