The effects of dosages of potassium fertilizer on growth and harvest index of two types of sweet potato (Ipomoea batatas L.)

This research aims to determine the effect of potassium fertilizer dosages and the type of sweet potato plant as well as the interaction between these two factors on the growth and harvest index of sweet potato plants. This research was carried out at Saree, Aceh Besar Regency and the Plant Physiology Laboratory, Faculty of Agriculture, Universitas Syiah Kuala Darussalam, Banda Aceh. This research was carried out for 4.5 months from April to September 2023. The research design used was a Randomized Block Design with a 4 x 2 factorial pattern with 3 replications, so that there were 8 treatment combinations consisting of two factors, namely the dosages of potassium fertilizer consisting of 4 levels, namely: control, 100, 200, and 300 kg ha−1 and sweet potato types consisting of 2 levels, namely: Saree local clone and Cilembu. The results of the research showed that the plant growth and harvest index were better when treated with a potassium fertilizer dosage of 300 kg ha−1. Better plant growth and harvest index were found in the Cilembu variety. There was no significant interaction between dosages of potassium fertilizer and types of sweet potato plants on all the parameters observed.


Introduction
Sweet potato (Ipomoea batatas L.) is within the group of tuber plants that have important potential as a source of food substitution.This is because sweet potato tuber contains a number of important minerals and nutrients such as the nutritional content of rice, corn and other groups of tubers [1].
Indonesia's sweet potato production in 2018 was 1.8 million tons of tubers.Sweet potato production decreased by 5.63% compared to production in 2017 which reached 1.9 million tons.As sweet potato yields decrease, harvest area also decreases.Indonesia's sweet potato harvest area in 2018 was 90.7 thousand ha, a decrease of 14.61% compared to the harvest area in 2017, which reached 106.2 thousand ha [2].
The decrease in harvested area could be the cause of the decline in sweet potato production.Therefore, land intensification activities are needed to increase sweet potato production.One of the land intensification activities that can be taken includes the use of good cultivation techniques such as mulching, plant spacing adjustment, fertilization and using superior varieties.
Sweet potato plant is highly responds to fertilization, especially potassium.This is very important because potassium plays a role in stimulating the process of opening and closing of stomata, by 2 increasing cell turgor activity.The potassium element also functions in stimulating the translocation of assimilate from source to sink, and maintaining the stems upright which allows the flow of nutrients and water from the soil into the plant body [3].Potassium is classified as a macro nutrient that is essential for plant growth and production.The response of sweet potato plants to potassium fertilization is related to their ability to absorb large amounts of potassium nutrients, so that the availability of potassium can encourage optimal growth and tuber formation [4].
The size of the impact of potassium fertilizer application on the plant growth and development processes is greatly influenced by the amount of nutrients available, both in the soil and provided through fertilization, as well as differences in different sweet potato varieties.Research by [5] found that sweet potato plants absorb potassium in different amounts for each component.The highest tuber yield was achieved by the Sukuh variety at a planting distance of 100 cm x 100 cm, namely 16.83 ton ha -1 with an optimum dose of potassium fertilizer of 108.43 kg ha -1 .
The opportunity to increase sweet potato production and productivity is still widely open.The availability of superior clones can provide hope that they have the potential to be released as new superior varieties.The opportunity to add new superior varieties is quite large with efforts to introduce varieties from outside [6].The low production of sweet potatoes is caused by poor cultivation techniques, the use of local clones with low production, environmental factors, and also the clones' poor adaptability to the environment [7] old clones whose production is relatively low [8].
The type of sweet potato plant used in this research is the local Saree clone.This type of sweet potato plant is popular among the Saree community.The sweet potato variety that is popularly consumed by the public is Cilembu.This sweet potato is the result of cultivation by the people of Cilembu Village, Tanjung Sari, Sumedang [9].The Cilembu variety of sweet potato has a high content of carotene and lycopene and has a characteristic yellow-orange tuber color [10].
Therefore, there is a necessity to conduct research on the effect of dosages of potassium fertilizer and types of sweet potato plants as well as the interaction between them on the growth and harvest index of two types of sweet potato plants.

Materials and methods
This research was conducted at Saree, Aceh Besar Regency and Plant Physiology Laboratory, Faculty of Agriculture, Universitas Syiah Kuala, Darussalam, Banda Aceh.This research was carried out for 4.5 months from April to September 2023.The tools used in this research were a hoe, measuring tape, digital scale, oven, camera, and Soil Plant Analysis Development (SPAD) chlorophyll meter.The materials used in this study were sweet potato cuttings from the local Saree clone and the Cilembu variety, 480 cuttings, 240 each.The sweet potato cuttings used are shoot cuttings, 25 cm long with about 4 buds.Cuttings are taken from mother plants that are more than two months old.Other materials used are plastic bags, paper bags, sacks, plastic ropes, manure (10 tons ha -1 ), KCl fertilizer (according to treatment), Urea (200 kg ha -1 ) and SP 36 (210 kg ha -1 ).

Research design
Units of treatments were arranged according to a factorial Randomized Block Design, consisting of two factors.The first factor is the dosages of potassium fertilizer (KCl) consisting of 4 levels, namely: K0 = Control, K1 = 100 kg ha -1 , K2 = 200 kg ha -1 , K3 = 300 kg ha -1 .The second factor is the type of sweet potato plant (J) consisting of two levels, namely: J1 = Saree local clone, J2 = Cilembu variety.Each of which was repeated with 3 times.This research consisted of 8 treatments so that it consisted of 24 beds (20 plants per bed).The data were analyzed with analysis of Variance and continued with the Tukey Test at a 5% level.

Research procedure
Preparation of sweet potato seeds means the seeds are left for two days before planting, placed in a 3 shady place in a sack to get root growth and the seeds are planted in a bed with a spacing of 50 cm x 35 cm, and one cutting hole is planted.Manure is applied one week before planting at a dosage of 10 tons ha -1 (4 kg bed -1 ).Potassium inorganic fertilizer (KCl) is given at planting in a series of dosages given at 100 kg ha -1 (40 g bed -1 ), 200 kg ha -1 (80 g bed -1 ) and 300 kg ha -1 (120 g bed -1 ).Basic fertilizers are Urea (source of N) and SP36 (source of P).Urea basic fertilizer is applied at a dosage of 200 kg ha -1 , fertilized twice when planting, 1/3 of the dosages (26 g bed -1 ).The remaining 2/3 of the Urea fertilizer is given when the plants are 2 weeks after planting (WAP) at a dosage of (54 g bed -1 ).Meanwhile, SP36 was given at a dosage of 210 kg ha -1 (84 g bed -1 ) at planting time.

Observed parameters
The variables observed in this research were: the number of branches and branch length at 2, 4, 6 and 8 WAP, biomass fresh weight at 16 WAP, biomass dry weight per plant carried out by weighing each plant.The wet biomass was placed in an oven at 60°C for 72 hours.The chlorophyll content in three places on the leaves was measured at 6 WAP (end of vegetative period) using a SPAD (Soil Plant Analysis Development) chlorophyll meter.All observations used a sample of 5 plants bed -1 , except for the amount of chlorophyll in three leaves per plant, and the harvest index with the formula [11]: Where, TW = Total sweet potato yield, TWB: total biomass weight (biomass weight and sweet potato tuber weight)

Results and discussion
A recapitulation of the results of the variance analysis of the influence of potassium fertilizer dosages and types of sweet potato as well as the interaction between them on the growth and harvest index of sweet potato plants is presented in Table 1.
Table 1 shows that the dosages of potassium fertilizer have a very significant effect on the number of branches at 4 WAP and harvest index, has a significant effect on branch length at 2 WAP and biomass fresh weight, but has no significant effect on other parameters.The type of sweet potato plant had a very significant effect on branch length at 4 WAP, has a significant effect on the number of branches at 8 WAP, branch length at 2 WAP, fresh fruit weight, and chlorophyll content, but has no significant effect on other parameters.There is no significant interaction between treatments on all variables observed.

Number of branches
Table 2 shows that the number of branches at the age of 4 WAP was greater at a dosage of 100 kg ha -1 which was significantly different from a fertilizer dosage of 300 kg ha -1 but not significantly different from treatments with fertilizer dosage of 0 and 200 kg ha -1 .The number of branches of sweet potato plants at the age of 2 WAP tended to be more often found in the treatment with a potassium fertilizer dosages of 0 kg ha -1 and at the age of 6 WAP tended to be more common at the potassium fertilizer dosages of 0 kg ha -1 and 300 kg ha -1 whereas at the age of 8 MST tended to be more common at a potassium fertilizer dosage of 100 kg ha -1 , although statistically it was not significantly different from other treatments.This is because the dosage of potassium fertilizer has less influence on branch formation because what is needed more in this phase is the element N. Because the element potassium tends to play a greater role in increasing photosynthetic activity and has a greater influence on the tuber formation process than the growth of branches and leaves [12].
The number of branches in the treatment of sweet potato plants type at the age of 2, 4 and 6 WAP tended to be higher in the Cilembu variety treatment although was not significantly different from the Saree local clone treatment (Table 2).The highest number of branches aged 8 WAP was found in the Cilembu variety which was significantly different from the treatment of the local Saree clone.This is thought to be because each variety has a different ability to adapt to the environmental conditions in which it grows so that it can show a good response to plant growth.According to [13] varietal treatment and sweet potato planting location gave rise to significant interactions between genotype and environment on plant length and number of branches.The number of branches will vary, sometimes more or less.

Branch length
Table 3 shows that the branch length of sweet potato plants at the age of 2 WAP was found to be longer in the treatment with a potassium fertilizer dosage of 300 kg ha -1 which was significantly different from the control treatment, but not significantly different from the treatment with a potassium dosage of 100 kg ha -1 and 200 kg ha -1 .Branch length at the age of 4 WAP tends to be longer when found at a potassium fertilizer dosages of 300 kg ha -1 , whereas at the age of 6 WAP it tends to be longer at the potassium dosage of 200 kg ha -1 and at the age of 8 WAP tends to be longer at the treatment dosage potassium 100 kg ha -1 although statistically was not significantly different from other treatments.[14] stated that adequate use of potassium nutrients can increase the growth of meristem tissue in plant stems and regulate stomata movement.The longest branch lengths at ages 4 and 6 WAP were found in the Cilembu variety which was significantly different from the Saree local clone treatment, whereas at ages 6 and 8 WAP it tended to be longer in the Saree local clone treatment although statistically it was not significantly different from the Cilembu variety treatment (Table 3).It is assumed that varieties have different adaptability to the environment.Better growth and yield tend to be had in varieties that are able to quickly adapt to their environment than varieties that are slow to adapt even though their genotypes have similar growth rates [15].

Fresh weight and dry weight of biomass
Table 4 shows that the fresh biomass weight in the sweet potato was heavier in the 300 kg ha -1 potassium fertilizer treatment which was significantly different from the control treatment and 100 kg ha -1 but not significantly different from the 200 kg ha -1 treatment.The dry biomass weight tended to be heavier when treated with a potassium fertilizer dosage of 200 kg ha -1 , although statistically this was not significantly different from other treatments.This is thought to be due to the administration of potassium 200kg ha -1 can increase the fresh and dry biomass weight.High fresh and dry biomass weights indicate more optimal growth, whereas low dry biomass weights indicate disturbed plant vegetative growth.
The heaviest fresh biomass weight in the sweet potato plant type treatment was found in the Cilembu variety which was significantly different from the local Saree clone.Dry biomass weight tended to be heavier in the local Saree clone although statistically it was not significantly different from the Cilembu variety (Table 4).The Cilembu variety has more fresh and dry biomass, this shows that more leaves will increase the total dry biomass weight of the plant and increase plant harvests.
The greater the number of leaves, the more effective photosynthesis can occur and more photosynthate is produced, thus having an influence on the dry weight of the plant.This is in line with [16] which states that potassium can increase tuber yield and can also increase the total dry matter yield of plants.

Chlorophyll content and harvest index
The chlorophyll content of sweet potato plants tended to be higher when treated with a potassium fertilizer dosage of 300 kg ha -1 , although statistically was not significantly different from other treatments.This is thought to be because the potassium element greatly influences the formation of chlorophyll and the photosynthesis process in plants (Table 5).Chlorophyll is an important key in photosynthesis, so increasing chlorophyll will increase photosynthetic activity which affects the yield and growth and development of plants [17].
The highest chlorophyll content in the sweet potato plant was found in the Cilembu variety which was significantly different from the local Saree clone.This is due to the influence of genetic characteristics in the variety.This is in accordance with [18] statement that differences in genetic characteristics tend to cause differences in the response of each variety to various environmental conditions so that the resulting growth tends to be different too.
Table 5 shows that the sweet potato harvest index was higher in the treatment with a potassium fertilizer dosage of 300 kg ha -1 with a value of 1.1 which was significantly different from the treatment with a fertilizer dosage of 0 kg ha -1 but not significantly different from the potassium fertilizer treatment of 100 kg ha -1 and 200 kg ha -1 with a harvest index value of more than one.A harvest index of more than 1 indicates high, meaning that the distribution of assimilation results is greater in growing sweet potato tubers, whereas if the harvest index is low (<1), it indicates that assimilation to sweet potato tubers is smaller.The higher the harvest index value, the higher the weight of sweet potato per plant and the potential yield [19]. Providing potassium fertilizer can increase the harvest index of sweet potato.
The availability of potassium is very important to increase sweet potato yields.Potassium is functions in forming and stimulating the synthesis of proteins and carbohydrates, stimulating root growth and development, increasing root turgor pressure and increasing nutrients absorption.The weight of the tubers planted will be optimal if the development of the tubers and roots is optimal [20].The research results of [21] show that plant dry weight production is the result of 3 processes, namely: accumulation of assimilate through photosynthesis, decrease in assimilate due to respiration and accumulation in the sink.The increase in plant dry weight is due to an increase in leaf area to optimum and an increase in the rate of photosynthesis, which results in an increase in the harvest index.Table 5 shows that the harvest index in the sweet potato plant type tends to be higher in the Cilembu variety, although statistically is not significantly different from the local Saree clone.This is because each variety has different growth due to genetic differences in each plant and is also influenced by environmental factors.This is in accordance with the statement by [22] who stated that apart from genetic factors, tuber weight is also influenced by environmental factors which influence the growth and yield of a plant.

Conclusions
The better plant growth and harvest index of sweet potato was found in the treatment with a potassium fertilizer dosage of 300 kg ha -1 and Cilembu variety.Interaction between the dosages of potassium fertilizer and the type of sweet potato plant was not significant on the growth and harvest index of sweet potato plants.

Table 1 .
Recapitulation of analysis of variance the effects of potassium fertilizer dosages on growth and harvest index in two types of sweet potato plants.
K: dosages of potassium fertilizer, J: type of sweet potato, K x J: Interaction between potassium fertilizer dosages and sweet potato plant type KK: Variation Coefficient (%) WAP: Week after Planting **: very significant, *: significant, tn: not significant HI = TW TBW

Table 2 .
The average number of branches of sweet potato plants at the ages of 2, 4, 6 and 8 WAP due to treatment with potassium fertilizer dosage and type of sweet potato.
Numbers followed by the same letter in the same column are not significantly different at the 5% level (Tukey0.05Test)

Table 3 .
The average of branch length of sweet potato plants at 2, 4 and 6 WAP due to treatment with potassium fertilizer dosages and type of sweet potato.

Table 4 .
The average weight of fresh and dry biomass due to treatment with potassium fertilizer dosage and type of sweet potato plant.

Table 5 .
The average chlorophyll content and harvest index due to treatment with potassium fertilizer dosages and sweet potato plant types.Numbers followed by the same letter in the same column are not significantly different at the 5% level (Tukey0.05Test)