Journal of Food Quality
Volume 2021 (2021), Article ID 6611124, 11 pages
https://doi.org/10.1155/2021/6611124

Research Article

Gradual Application of Potassium Fertilizer Elevated the Sugar Conversion Mechanism and Yield of Waxy and Sweet Fresh-Eaten Maize in the Semiarid Cold Region

Li Yang,1,2 Yu Xin Chi,² Yu Feng Wang,² Muhammad Zeeshan,¹ and Xun Bo Zhou¹

¹College of Agriculture, Guangxi University, Nanning,530004, China
²The Key Laboratory of Germplasm Improvement and Cultivation in Cold Regions, College of Agronomy, Heilongjiang Bayi Agricultural University, Daqing 163319, China

Correspondence should be addressed to Yu Feng Wang; wangyf0918@163.com and Xun Bo Zhou; xunbozhou@gmail.com

Received 24 December 2020; Revised 25 January 2021; Accepted 1 February 2021; Published 13 February 2021

Academic Editor: Fabio Napolitano

Copyright © 2021 Li Yang et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

Fresh-eaten maize (Zea mays L.) is favored by consumers for its unique flavor, good health, and medical effects. Heilongjiang province is a semiarid cold region with the annual output of 3.35 billion ears, and the demand for fresh eaten maize is increasing in the region. Therefore, improving its yield and quality is urgently needed in this area. In this study, two of thirty varieties (waxy maize Jin-262 and sweet maize Jingke-183) were used and five proportions of potassium (K₂O, 120 kg/ha) were applied at sowing, jointing, and large trumpet stages to identify the high yield and quality of fresh-eaten maize under a semiarid cold ecological condition in Daqing, Heilongjiang province, China, during 2017-2018. The results from the screening of eighteen maize varieties showed that waxy maize Jin-262 and sweet maize Jingke-183 had higher starch content and soluble sucrose contents than those of other varieties. While the potassium proportions application during the sowing (20%), jointing (40%), and large trumpet stages (40%) had further significantly increased the starch content, soluble sugar content, sucrose content, and sucrose metabolic enzymes activities of Jin-262 and Jingke-183, however, the yields of Jin-262 and Jingke-183 had increased by applying potassium fertilizer during the sowing stages (50%) and jointing stages (50%). Considering the overall higher maize quality, we recommended the waxy maize Jin-262 and sweet maize Jingke-183 varieties along with application of 20% (sowing), 40% (jointing), and 40% (large trumpet stages) of 120 kg/ha potassium fertilizer for the improvement of grain quality of maize planting in the semiarid cold region. Otherwise, reasonable gradual potassium fertilization might be a wiser option.

1. Introduction

Potassium fertilizer (K) helps the formation and convertion of energy and sugar that the crops need for their development through photosynthesis process [1], which plays a crucial role in improving the quality and yield of crops [2]. Many countries have been actively promoting and applying balanced fertilizer application with the appropriate amounts and proportions of K [3]; balanced crop nutrient management is a key factor for improving crop productivity [4]. Heilongjiang province is a cold and semiarid region in China; imbalanced use of chemical fertilizers is one of the major reasons of low maize productivity under semiarid condition [5]; K application under semiarid climates condition not only improves crop tolerance to drought stress [6] but also improves crop growth and dry matter partitioning and increases yields significantly [7]. Potassium application is beneficial for promoting carbohydrate and nitrogen (N) metabolism; K ions significantly promote the absorption and utilization of N and P by crops in the form of compensation charges, thus improving the quality of crop products [8, 9]. Potassium is required for efficient transformation of solar energy into chemical energy [10]. Accurate application of K fertilizers can stimulate biomass and carbohydrate of crops [11, 12] which is considered as an important factor in food and industrial usage. Although effect of K fertilizers on other plants is reported [11] but there are few reports regarding the effect of K fertilizers on gradual application of fresh-eaten maize.

Fresh-eaten maize is favored by consumers for its unique flavor effect [10], which increased the consumption. To generate more revenue from agricultural products and make it more attractive for the buyer at marketplace mainly depends on the amount and quality of the product delivered to the market. The amount and quality of the products contributes largely in the income return for the producers. In fact, for some crops, quality plays an increasing role and, in some cases, the dominant role in generating revenue [13]. The fresh-eaten maize kernels quality is determined by its composition and content of carbohydrates; soluble sugar and sucrose influence the taste and sweetness of fresh-eaten maize, respectively [14]; starch is hydrolyzed and converted into monosaccharide, affecting the taste of fresh-eaten maize [15]. The relationship between sugar accumulation and sucrose metabolic enzymes has been previously reported by many researchers and demonstrated that they have important effects on sugar metabolism and accumulation on tomato [16], wheat [17], and common maize [18, 19].

Many studies have highlighted in an aggressive way by mentioning K as a plant nutrient of the role in crop yield and produce quality [20]; the grain weight, single ear weight, and yield of fresh-eaten maize of potassium fertilizer treatments were significantly higher than those of nonpotassium treatments [21]. The rate of soil applied K up to 90 kg/ha can improve growth and maize productivity under semiarid climates [4]. Keeping in mind the importance of the product quality and the crucial role of potassium in quality improvement, this study was accordingly designed to investigate the quality of two different types of fresh-eaten maize including sweet maize (Jingke-183) and waxy maize (Jin-262) under the different potassium fertilizer treatments in a cold semiarid area. The specific aim of this field experiment was to determine the effects of potassium on (i) fruit quality, (ii) enzyme activity, and (iii) grain yield of fresh-eaten maize.

2. Materials and Methods

2.1. Environmental Conditions

The field experiment was conducted at the Experimental Base (46°37′N, 125°11′E), Daqing, Heilongjiang Bayi Agricultural University, in 2017-2018, which is a continental monsoon climate city of the North Temperate Zone in China. The experimental site was meadow soil, and baseline levels in the soil before fertilization were average soil organic matter of 28.9 mg/kg, alkaline hydrolysis nitrogen (N) of 118.3 mg/kg, available P of 16.6 mg/kg, available K of 106.2 mg/kg, and pH 8.3.

Meteorological data during the growing season (April to September in 2017 and 2018) were provided by local weather stations (Figure 1).

Figure 1: Monthly temperature, rainfall, and photosynthetically active radiation (PAR) average in 2017 and 2018.

2.2. Plant Materials and Experimental Design

A total of 30 fresh-eaten maize varieties (15 waxy maize varieties and 15 sweet maize varieties) were planted manually on 25 May 2017; each plot was 5.2 m × 10.0 m in size having the plant density of 52300 plants/ha. The experiment was conducted in a randomized complete block design (RCBD) with three replications and had 0.650 m row spacing and 0.293 m plant spacing. The irrigation amount was 50 mm before sowing and the N : P : K in the form of N 135 kg/ha (urea), P₂O₅ 120 kg/ha (calcium superphosphate), and K₂O 90 kg/ha (potassium sulfate) was applied as base fertilizer, respectively. Additionally, 90 kg/ha of N was applied at jointing stage.

2.3. Growth- and Yield-Related Parameters

Data collection was carried out for the seedling emergence rate, plant heights, kernels per ear, fresh ear weight, and bald length in all the thirty varieties of sweet maize. Based on these parameters, 12 varieties were eliminated from analysis because of their poor performance. The remaining 18 varieties were selected for further study.

2.4. Measurement of Starch Content, Total Soluble Sugar, and Residue Ratio

Five middle ears of maize in each plot were harvested at 18, 21, 24, 27, 30, and 33 days after flowering (DAF) with a filigree length of 2-3 cm. Grains were collected, oven-dried at 75°C for 7 days up to constant weight, and ground and sieved through 100 mesh. The total soluble sugar contents and starch contents of these samples were analyzed by the anthrone-colorimetry method, while the sucrose contents were measured by the resorcinol method [22], and the residue ratio was determined by following the previous protocol [23].

2.5. Field Adaptability Test Based on the Quality Parameters

Eighteen fresh-eaten maize varieties with high adaptability in the field were harvested at 24 DAF and cooked in boiled water for 30 individuals of different ages and genders for the tasting experiment to determine the cooking taste qualities of flavor, color and luster, sweetness, tenderness, pericarp thickness, sensory quality, and taste quality [23].

Based on the results of screening experiment in 2017, two varieties, Jin-262 (waxy maize; Jinniu Seed Industry Ltd.) and Jingke-183 (sweet maize; Beijing Academy of Agriculture and Forestry Sciences) were selected for further experiment in 2018. The field experimental procedure was consistent with that in 2017. However, K₂O 120 kg/ha was supplied as five potassium fertilizer treatments: K1, K2, K3, K4, and K5 (Table 1).

Table 1: Schedule, proportion, and amount of potassium fertilizer applied.

Stages
K treatments (kg/ha)

K1
K2
K3
K4
K5

Basal
0% (0)
100% (120)
50% (60)
50% (60)
20% (24)

Jointing
0% (0)
0% (0)
50% (60)
0% (0)
40% (48)

Big trumpet
0% (0)
0% (0)
0% (0)
50% (60)
40% (48)

2.6. Measurement of Sucrose Metabolism Enzyme Activities

Samples from the middle of the ear were collected at 18, 21, 24, 27, 30, and 33 DAF and stored at −80°C in a refrigerator for further analysis. Each sample of maize grains was weighted (0.5 g) and grinded in mortar with liquid nitrogen to analyze the sucrose metabolic enzyme activity. The sucrose metabolism enzymes activities (sucrose synthase and sucrose phosphate synthase) were determined by detection kits (Solarbio Life Sciences Ltd., Beijing, China).

2.7. Yield and Yield Components

A total of 10 representative ears (error less than 0.05 kg) were sampled from the middle of each plot to measure the grain yield (kg) and yield components according to the grain moisture content of fresh-eaten maize and converted to yield (14% moisture content).

2.8. Statistical Analysis

All data were subjected to one-way ANOVA analysis using SPSS 21.0 software [24]. Means of all treatments and genotypes were compared by performing Duncan’s multiple comparison tests at . Graphs were generated using SigmaPlot 10.0 (SPSS Inc., Chicago, IL).

3. Results and Discussion

3.1. Growth and Yield Component of Waxy and Sweet Maize

The growth and yield component related parameters for both waxy and sweet maize varieties are presented in Tables 2 and 3, respectively.

Table 2: Growth and yield of waxy maize during 2017.

Varieties
Seedling emergence rate (%)
Tumor black powder (%)
Plant height 160 cm (%)
Grain yield (ears/ha)
Kernels per ear
Spike length (cm)
Fresh ear weight (kg/ear)
Bald length (cm)

Bai-998
98.04ab
0.00b
2.97b
40020de
575bcd
20.09b
0.34ab
0.61cde

Hua-3
97.06ab
0.00b
0.00c
39443e
739a
22.32a
0.39a
1.20bcd

Jin-262
100.00a
0.00b
0.00c
45215ab
602bc
19.30b
0.36ab
0.36de

Jing-318
95.10ab
0.00b
0.00c
42329cd
614bc
16.97c
0.34ab
1.70b

Kennian-7
99.02ab
0.00b
3.95b
26744f
614bc
21.91a
0.39a
1.52bc

Jingke-623
95.10ab
0.00b
0.00c
44253b
556cd
18.52bc
0.33ab
0.03e

Jingke-2010
100.00a
0.00b
0.00c
40982de
640bc
18.26bc
0.33ab
0.81bcde

Jingke-2016
99.02ab
0.00b
0.00c
41367d
630bc
18.20bc
0.36ab
0.02e

Jingke-569
95.10ab
1.96a
0.00c
43868bc
544cd
19.17b
0.33ab
1.18bcd

Jingke-928
96.08ab
0.00b
0.00c
43483bc
606bc
18.28bc
0.33ab
0.00e

Yinsenianhua
94.12b
0.00b
0.00c
40597cd
667ab
19.64b
0.37a
0.90bcde

Lvyuhuang
49.02c
0.00b
100.00a

Lv-5
49.02c
0.00b
100.00a

Lv-2
46.08c
0.00b
100.00a

Kennian-1
98.04ab
0.00b
0.00c
45984a
500d
19.53b
0.28c
2.88a

The different lowercase letters in the same column are significantly different at the 5% level. Inadequate for field growth.

Table 3: Growth and yield of sweet maize during 2017.

Varieties
Seedling emergence rate (%)
Tumor black powder (%)
Plant height 160 cm (%)
Grain yield (ears/ha)
Kernels per ear
Spike length (cm)
Fresh ear weight (kg/ear)
Bald length (cm)

Jingke-183
99.02a
1.96de
0.00c
54258a
586b
19.56bc
0.28c
0.05c

Zheng-66
95.10ab
5.15bcde
0.00c
40405c
566b
21.01ab
0.23d
0.23b

WSC-1701
47.06c
6.00bcde
8.23a

WSC-1702
46.08cd
8.47bc
6.39ab

WSC-1703
49.02c
9.95bc
9.72a

Syngenta-wangchao
42.16de
4.60cde
2.38bc

Syngenta-kupula
39.22ef
42.49a
2.38bc

Syngenta-overland
96.08ab
5.11bcde
0.00c
39635c
659ab
22.52a
0.31bc
0.23b

Hetian-1
94.12b
8.34bc
0.00c
37326c
579b
21.07ab
0.31bc
0.33ab

Hetiannuo-1
98.04ab
0.00e
0.00c
40790c
641ab
20.82ab
0.37a
0.39a

Syngenta-mige
98.04ab
3.98cde
0.00c
45792b
695a
22.73a
0.35ab
0.27b

Syngenta-cuiwang
49.02c
45.95a
0.00c

Syngenta-double color honey
45.10cd
43.47a
0.00c

T1
36.27f
8.12bcd
2.56bc

W625
35.29f
11.11b
0.00c

The different lowercase letters in the same column are significantly different at the 5% level. Inadequate for field growth.

Among waxy maize varieties, the seedling emergence rates of Lvyuhuang (49.02%), Lv-5 (49.02%), and Lv-2 (46.08%) were the lowest and plant height of these three maize varieties was less than 160 cm (Table 2). Jin-262 had significantly higher () seedling emerging rates (100%), kernels per ear (602 kernels/ear), and fresh ear weight (0.36 kg/ear) as compared with other varieties. The bald length of Jin-262 was 0.36 cm, which was significantly lower than that of Kennian-1 (). However, there were no significant differences between the grain yield and spike length of Jin-262 and Kennian-1 (), however higher than other varieties of the same group.

In sweet maize varieties, the seedling emergence rates of WSC-1701, WSC-1702, WSC-1703, Syngenta-wangchao, Syngenta-kupula, Syngenta-cuiwang, Syngenta-double color honey, T1, and W625 were less than 50%. For instance, the emergence rates of tumor black powder of Syngenta-kupula, Syngenta-cuiwang, and Syngenta-double color honey seedling were 42.49%, 45.95%, and 43.47%, respectively (Table 3). The grain yield of Jingke-183 was 54258 ears/ha, which was significantly higher than those of other varieties (). Surprisingly, the bald length (0.05 cm) of Jingke-183 was significantly lower than those of other varieties ().

3.2. Quality of Fresh-Eaten Maize Grains

In the waxy maize varieties, the increased amount of grain starch content was in order Jin-262 > Bai-998 > other varieties. In detail, grain starch content was 54.91% in Jin-262 and 53.68% in Bai-998 variety (Table 4). The total soluble sugar content of Jin-262 was significantly higher than that of Bai-998 (). There was no significant variation between the residue ratios of Bai-998 and Jin-262 (). The scores of order flavor, color and lustre, waxy, sweetness, tenderness, skin thick and thin, sensory quality, and taste quality in averages of Jin-262, Jingke-623, Jingke-2010, Jingke-569, Jingk-928, and Kennian-1 were 77.38, 75.63, 76.38, 71.25, 77.25, and 77.38, respectively, which were significantly higher than those of other varieties (). The color and luster of Jingke-623, Jingke-569, and Jingke-928 were significantly lower than those of other varieties (). The tenderness of Jingke-2010, Jingke-569, and Kennian-1 was significantly lower than that of other varieties (). The pericarp thickness of Jingke-569 was significantly lower than that of other varieties (). There was no significant difference in the flavor and sweetness among varieties ().

Table 4: Grain and taste quality of fresh-eaten maize during 2017.

Varieties
Grain quality
Fresh ear cooking taste quality

Soluble sugar (%)
Sucrose (%)
Starch (%)
Residue ratio (%)
Flavor
Color and lustre
Sweetness
Tenderness
Pericarp thickness
Sensory
Taste
Quality average

Waxy

    Bai-998
16.03f
1.36e
53.68a
30.41d
73abc
69de
61bc
71de
68cde
70bc
70bc
69.38bcd

    Hua-3
12.31h
1.14ef
48.90b
32.22c
62d
64e
50c
72cde
73abcd
64c
60de
62.88e

    Jin-262
18.53cd
0.43g
54.91a
29.82d
74ab
86a
63abc
77abcd
76abc
79a
77ab
77.38a

    Jing-318
19.49b
2.28bcd
47.71bc
29.92d
64cd
67e
65ab
80abcd
78abc
69bc
68bcd
69.88bcd

    Kennian-7
13.93g
2.89a
43.92d
34.67b
66bcd
66e
59bc
66e
68cde
65c
62cde
64.25de

    Jingke-623
19.06bc
2.41abc
42.54d
32.32c
73abc
70cde
72ab
81abc
79abc
75ab
81a
75.63ab

    Jingke-2010
20.65a
1.86d
46.77c
28.11e
79a
79abc
78a
72cde
69bcde
75ab
81a
76.38a

    Jingke-2016
17.88e
2.04cd
43.78d
28.01e
65bcd
70cde
73ab
81abc
64de
72abc
69bc
69.75bcd

    Jingke-569
18.20de
2.58ab
44.17d
30.54d
74ab
71cde
70ab
74bcde
61e
75ab
74ab
71.25abc

    Jingke-928
19.33b
1.22e
38.58e
28.13e
77a
77bcd
73ab
82ab
80ab
76ab
82a
77.25a

    Yinsenianhua
18.15de
1.33e
39.37e
27.95e
65bcd
65e
63abc
86a
81a
64c
59e
67cde

    Kennian-1
13.59g
0.66fg
48.65b
36.56a
80a
82ab
67ab
75bcde
74abcd
80a
83a
77.38a

Sweet

    Jingke-183
29.71b
6.49a
15.20a
25.55c
71ab
78a
98a
76ab
75a
76a
79a
79.00a

    Zheng-66
28.61c
3.26c
12.09c
26.70b
70ab
69b
78b
69c
65ab
75ab
80a
72.29a

    Syngenta-overland
37.10a
5.66b
9.17f
22.64e
76a
84a
76b
82a
57b
79a
85a
77.00a

    Hetian-1
28.17c
5.22b
10.19e
24.76d
76a
83a
83b
76ab
76a
82a
78a
79.14a

    Hetiannuo-1
29.98b
1.64d
13.58b
31.76a
64b
64b
54c
70bc
60b
68b
65b
63.57b

    Syngenta-mige
30.36b
3.89c
11.07d
20.56f
76a
86a
76b
81a
74a
81a
74a
78.29a

The different lowercase letters in the same column are significantly different at the 5% level.

In sweet maize as shown in Table 4, higher amount of sucrose (6.49%), starch content (15.2%), and sweetness was found in Jingke-183 when compared with remaining varieties of sweet maize; however, the soluble sugar content of Jingke-183 was only higher than Zheng-66 and Hetian-1. Furthermore, lower grain quality related parameters were observed in Hetiannuo-1; for example, the flavor, sweetness, sensory quality, taste quality, and quality average of Hetiannuo-1 were significantly lower as compared to other varieties (). There was no significant difference in the flavor, color and luster, tenderness, sensory quality, and taste quality among Jingke-183, Syngenta-overland, Hetian-1, and Syngenta-mige ().

3.3. Grain Soluble Sugar Content

Subsequently, the soluble sugar content was measured again during 2018 in the grain of Jin-262 and Jingke-183. The result of time course analysis showed that the soluble sugar content of Jin-262 was first increased and then decreased during the flowering stage, and the maximum value was detected at 21 DAF (Figure 2). For example, the soluble sugar contents of K1, K2, K3, K4, and K5 at 21 DAF were 22.91%, 22.09%, 20.34%, 21.93%, and 24.48% which were higher than those of 18, 24, 27, 30, and 33 DAF. There were nonsignificant differences between K1 and K5 () in soluble sugar content at 18 DAF. Furthermore, the higher and lower soluble sugar content were found in treatment K5 and K3, respectively, at 21, 24, and 30 DAF; however, there were nonsignificant differences among all treatments at 27 DAF (). At 33 DAF, the significantly higher () sugar content was observed in treatment K4 followed by K5; for instance, the soluble sugar contents of K1, K2, K3, K4, and K5 were 9.38%, 10.4%, 10.36%, 12.56%, and 10.48%, respectively. Taking together, during 18-33 DAF, the mean soluble sugar content of K5 was significantly higher than the remainder treatments ().

Figure 2: Effects of potassium on the grain soluble sugar content of fresh-eaten maize grains. The different lowercase letters are significant differences at the 5% level; AVG, average; the bars are standard deviation (n = 5).

Similarly, the soluble sugar content of Jingke-183 showed a decreasing trend (Figure 2). The soluble sugar content of K5 was 33.03% at 18 DAF and 17.67% at 33 DAF. Regarding assessment during 18–33 DAF, the average soluble sugar content of K5 was significantly higher than other treatments of the group (); however, considering the mean upper values, there was nonsignificant increase between treatment K5 and K3 in the soluble sugar content.

3.4. Grain Sucrose Content

Figure 3 shows the sucrose content in the grain of Jin-262 and Jingke-183. In accordance with the soluble sugar content, the sucrose content of Jin-262 was also first increased and then declined during the flowering stages, and the maximum peak was observed at 21 DAF. In detail, the sucrose contents of K1, K2, K3, K4, and K5 at 21 DAF were 3.69%, 3.06%, 3.33%, 3.42%, and 3.79%, respectively. At 24 DAF, the sucrose content was not significantly different between treatments (). Moreover, the sucrose content of only treatment K5 rose again at 27 DAF and then dropped during 30–33 DAF. Regarding average during 18–33 DAF, the average sucrose contents of treatments K1, K4, and K5 were 2.0%, 2.0%, and 2.1%, respectively, and there was no significant difference among them ().

Figure 3: Effects of potassium on the grain sucrose content of fresh-eaten maize kernels. The different lowercase letters are significant differences at the 5% level; AVG, average; the bars are standard deviation (n = 5).

The sucrose content of Jingke-183 showed a decreasing trend from the first to the last day of assessment (Figure 3). During 18–33 DAF, the sucrose contents of treatments K1, K2, K3, K4, and K5 declined by 0.53%, 0.45%, 0.50%, 0.49%, and 0.47% per day, respectively. The sucrose content of K5 was 33.03% at 18 DAF and then sharply declined to 17.67% at 33 DAF. Considering the mean upper values, there were nonsignificant differences () between K3 (14.0%) and K5 (14.1%).

3.5. Sucrose Synthase Activity

The time course analysis showed that the sucrose synthase activity of Jin-262 first increased and then decreased during the flowering stages as shown in Figure 4. In general, the sucrose synthase activity started to rise during 21–27 DAF and then declined during the remaining assessment time regardless of treatment. However, among the treatments during 18–21 DAF, the enzyme activity of treatment K5 was significantly higher than those of the other treatments (). Time course and treatments data showed that the activity of this enzyme was significantly higher () under treatments K3 at 24 DAF, K5 at 27 DAF, and K2 at 30 DAF in waxy variety Jin-262. Taking the average of all assessment days from 18 to 33 DAF, the average sucrose synthase activity of K5 was significantly higher when compared with remaining treatments ().

Figure 4: Effects of potassium on grain sucrose synthase activity of fresh-eaten maize kernel fresh weight. The different lowercase letters are significant differences at the 5% level; AVG, average; the bars are standard deviation (n = 5).

Similarly, regardless of treatment, the sucrose synthase activity of Jingke-183 was increased during the assessment periods during 21–24 DAF; the highest peak was detected at 24 DAF and then a sharp decline was observed in the activity values (Figure 4). At 18 DAF, the significantly higher and lower sucrose synthase activities were reported for treatments K1 and K4, respectively, compared to those of the other treatments (). Under treatments K3 and K5, the enzyme activity was significantly enhanced () during 21–24 DAF relative to other treatments; in addition, there were no differences between K3 and K5; although the decline was observed during the remaining days of flowering under the treatment, it remained significantly higher under treatment K5 than other treatments. The results showed that treatment K5 significantly increased the average sucrose synthase activity during 18–33 DAF compared to other treatments ().

3.6. Sucrose Phosphate Synthase Activity

The effect of potassium on the sucrose phosphate synthase activity in the grain of fresh-eaten maize varieties (Jin-262 and Jingke-183) is presented in Figure 5. The results show that the enzyme activity value was first increased till 24 DAF and then decreased during the remaining flowering stages. Upon the time course analysis, the sucrose phosphate synthesis activity was highly induced under treatment K5 in both Jin-262 and Jingke-183 relative to remaining treatments, except at 24 DAF; the activity value of treatment K3 was higher than treatment K5 in variety Jin-262. Furthermore, there were no differences of K5 with K2 and K3 at 18 DAF, with K4 at 27 and 33 DAF in Jin-262. Similarly, no differences were reported between K5 and K3 at 21, 30, and 33 DAF in the upper value of Jingke-183.

Figure 5: Effects of potassium on grain sucrose phosphate synthase (SPS) activity of fresh-eaten maize kernel fresh weight. The different lowercase letters are significant differences at the 5% level; AVG, average; the bars are standard deviation (n = 5).

3.7. Grain Starch Content

The current study showed that all five treatments induced the starch content in an increasing manner under the 6 sampling periods in both varieties Jin-262 and Jingke183; however, the extent of increase is smaller in Jingke-183 than that observed in Jin-262 (Figure 6). In detail, considering the upper value, there were no differences in starch content between treatments K1 and K5 at 18 and 24 DAF in waxy maize Jin-262 (); however, at 21 DAF differences were found upon imposition of treatment K5. Surprisingly, this study did not report any differences in starch content among the treatments in the 27- and 30-day samplings. On the other hand, in variety Jingke-183, the least starch content was noted under treatment K4 throughout the sampling days, relative to other treatments. Overall, taking the average of all sampling days, from 18 to 33 DAF, the highest starch content was 32.2 and 32 under treatments K1 and K5 in the Jin-262 and 10.6 and 10.2 under treatments K2 and K1 in the variety Jingke-183 which are nonsignificant () from each other, respectively.

Figure 6: Effects of potassium on the starch content of fresh-eaten maize kernels. The different lowercase letters are significant differences at the 5% level; AVG, average; the bars are standard deviation (n = 5).

3.8. Yield and Yield Components

The effect of potassium on yield and yield component in fresh-eaten maize is presented in Table 5. Grain yield, kernels per ear, and spike length were increased under treatment K3 in both varieties Jin-262 and Jingke-183. In detail, the grain yield (44107.69; 65128.2 ears/ha), kernels per ear (658; 545), and spike length (19.1; 18.8 cm) were noted in Jin-262 and Jingke-183, respectively, which were higher than other treatments. However, there were no significant differences () in the ears per hectare and spike length between treatments K3 and K4, in the kernels per ear between treatments K3 and K5, and in fresh ear weight among treatments K2, K3, and K4 in variety Jin-262. Under the imposed treatments K2 and K3 in variety Jingke-183 and treatment K2 in variety Jin-262, the fresh ear weight was enhanced as compared with the other treatments.

Table 5: Effect of potassium fertilizer on the yield of fresh-eaten maize during 2018.

Varieties
Treatment
Grain yield (kg/ear)
Kernels per ear
Spike length (cm)
Fresh ear weight (ears/ha)

Jin-262
K1
34354bc
615cd
17.8b
0.24c

K2
28723c
609d
18.1b
0.29a

K3
44108a
658a
19.1a
0.26abc

K4
40508ab
632bc
18.6ab
0.28ab

K5
36415b
646ab
18.2b
0.25bc

Jingke-183
K1
45641c
511ab
17.7ab
0.14b

K2
42564c
494b
17.1b
0.16a

K3
65128a
545a
18.8a
0.16a

K4
54872b
532a
18.4a
0.15bc

K5
47692c
522ab
18.1ab
0.15bc

The different lowercase letters in the same column are significantly different at the 5% level.

There were no significant differences () in the kernels per ear and spike length among K1, K3, K4, and K5 in variety Jingke-183.

3.9. Discussion

Potassium is an essential nutrient for plant growth and activating several enzymes used as a catalyst in promoting the metabolic processes of the crops, which plays an important role in increasing crop yields and plant growth [25, 26]. This is significantly influenced by various K fertilizer levels in different crops [27]; recent research indicates that K fertilization has increased the yield and carbohydrates content in maize [2, 4], sorghum [12], soybean [2], wheat [28], and mung bean [29]. In the northeast black soil with medium available potassium content of (113.36 mg/kg), the optimal potassium application amount of sweet maize was 107–140 kg/ha K₂O. When the application of K₂O is greater than 200 kg/ha, it is harmful to the growth, yield, and quality of sweet maize [30]. Balance K fertilization applied at the right time of plant development increases maize yield [31]. According to Amanullah et al. [4], early potassium application (vegetative stage) resulted in better growth and higher yield than late potassium application (reproductive stage); from tasseling to maturity, the potassium absorption rate decreases due to nutrient transport and distribution. In this study, we found that the application of 120 kg/ha K₂O had positive effects on the yield and quality of maize varieties at different flowering stages. Notably, the half-half dose application of K on basal and jointing stage (60 kg/ha basal + 60 kg/ha jointing stage; treatment K3) increased the grain yield, kernels per ear, spike length, and fresh ear weight. For instance, the grain yield of Jingke-183 was 65128 ears/ha, which was higher than plant density of 52300 plants/ha; this may be the increase of double ears number per plant under K3 (60 kg/ha basal + 60 kg/ha jointing stage). Similar positive increase in the yield and relative component has also been observed in others crops such as soybean [2] and wheat [28], where they mentioned that the increase was due to either the increase in the number of pods per plant or the weight of individual kernel.

Sugars function as signals and metabolic intermediates used for growth, energy production, storage, and long-distance transport in plants [32, 33]. The total soluble sugar is used as a proxy for sugar and its higher values are positively correlated with the consumers acceptance [34], which determines the quality of fresh-eaten maize [35, 36]. Sucrose is the main component of soluble sugar, which is also helpful in accumulation and storage of carbohydrates and plays a leading role in sweetness of maize [37] and rice [38]. The K cation directly affects the structure of many enzymes [39], which can improve the sugar content due to the interaction by enzymes [40]. Altered sugar metabolism, together with corresponding changes in the sugar transport system, contributes to growth of plants [41, 42]. The main enzymes that participate in sucrose metabolism are sucrose phosphate synthase and sucrose synthase [37]. The sucrose phosphate synthase activity plays an important role in sucrose synthesis [43]; sucrose synthase is another enzyme initially involved in sucrose breakdown [44]. Sucrose synthase in sucrose metabolism can effectively regulate quality by sucrose synthesis and degradation as mentioned by [30, 45]. Furthermore, sucrose phosphate synthase and sucrose synthase are the key enzymes affecting starch synthesis [46]. Hashida et al. [47] studied that starch synthesis and sucrose phosphate synthase may play an important regulatory role in maintaining the balance between sucrose accumulation and consumption. The amount of sucrose converted to starch in seeds may change through the coordination of sucrose synthase and sucrose phosphate synthase to regulate the supply level of adenosine diphosphate glucose, the substrate required for starch synthesis [48]. Bioinformatic analysis indicates that sucrose phosphate synthase interacts with sucrose phosphate phosphatase, impacting soluble carbohydrate pools and affecting carbon partitioning to starch [49].

Data from this study showed that potassium application induced the soluble sugar content sucrose content, sucrose metabolic enzyme activity, and starch of fresh-eaten maize. Importantly, the split application of K (24 kg/ha basal + 24 kg/ha jointing + 48 kg/ha big trumpet stage; treatment K5) was beneficial for increasing the soluble sugar content, the sucrose content, sucrose synthase activity, and sucrose phosphate synthase activity in Jin-262 and Jingke-183. The soluble sugar and sucrose content of Jin-262 and Jingke-183 were decreasing during 21-33 DAF, but significantly increased under split potassium fertilizer application (treatment K5; basal fertilizer 20%, jointing stage 40%, and big trumpet stage 40%); so, the increase of soluble sugar and sucrose content might be a reason of fresh-eaten maize’s improved quality under the potassium treatment. Furthermore, sucrose content decreased while sucrose phosphate synthase and sucrose synthase activity both increased during 18–24 DAF; this might be because sucrose resolves to fructose and glucose, and the resolve rate is greater than the synthesis rate; the application of potassium effectively improved the decomposition ability of sucrose, rather than increase of synthetic quantity leading to the decrease in sucrose. In this study, the starch content increased, and the sucrose content decreased, indicating that the sucrose content in fresh-eaten maize was continuously transformed into starch by synthesis and degradation.

4. Conclusions

This study revealed the effect of potassium on the grain quality related parameter in two fresh-eaten maize varieties, Jin-262 (waxy maize) and Jingke-183 (sweet maize). The results showed that the gradual potassium fertilizer application (treatment K5; basal fertilizer 20%, jointing stage 40%, and big trumpet stage 40%) increased the quality related parameters such as soluble sugar, sucrose, and sucrose metabolic enzymes activities in the grain of Jin-262 and Jingke-183. However, the yield and related parameters of both varieties were enhanced under treatment K3 (basal 50% and jointing stage 50%). The results of this study showed that treatment K3 (basal 50% and jointing stage 50%) was beneficial for improving the yield and quality of fresh eaten maize; the early application is beneficial for nutrient absorption by crops. Therefore, we suggested that a reasonable application of potassium fertilizer is crucial to improve the quality and yield of fresh-eaten maize in semiarid cold regions.

Data Availability

The original data used to support the findings of this study are available from the corresponding author upon request.

Conflicts of Interest

The authors declare that they have no conflicts of interest.

Acknowledgments

This study was supported by the Chinese National Key Research and Development Program (2017YFD0300502 and 2018YFD0300101), the National Natural Science Foundation of China (31760354), and Natural Science Foundation of Guangxi (2019GXNSFAA185028).

References

K. Mengel, E. A. Kirkby, H. Kosegarten et al., Principles of Plant Nutrition, Kluwer Academic Publisher, Amsterdam, Netherlands, 5th edition, 2001.

W. T. Pettigrew, “Potassium influences on yield and quality production for maize, wheat, soybean and cotton,” Physiologia Plantarum, vol. 133, no. 4, pp. 670–681, 2008.

A. T. Köseoglu, N. Eryüce, and H. Çolakoglu, “The effects of N, P, K fertilizers on fruit yield and quality of satsuma mandarines (citrus unshiu marc.),” Acta Horticulturae, vol. 379, no. 379, pp. 89–96, 1995.

Amanullah, A. Iqbal, Irfanullah, Z. Hidayat et al., “Potassium management for improving growth and grain yield of maize (Zea mays L.) under moisture stress condition,” Scientific Reports, vol. 6, Article ID 34627, 2016.

AmanullahK. M. Kakar, A. Khan, I. Khan, Z. Shah, and Z. Hussain, ““Growth and yield response of maize (Zea mays L.) to foliar NPK-fertilizers under moisture stress condition,” Soil and Environment, vol. 33, no. 2, pp. 116–123, 2014.

I. Cakmak, “The role of potassium in alleviating detrimental effects of abiotic stresses in plants,” Journal of Plant Nutrition and Soil Science, vol. 168, no. 4, pp. 521–530, 2005.

A. Iqbal, Amanullah, and M. Iqbal, “Impact of potassium rates and their application time on dry matter partitioning, biomass and harvest index of maize (Zea mays L.) with and without cattle dung application,” Emirates Journal of Food and Agriculture, vol. 27, no. 5, pp. 447–453, 2015.

R. Gaj, D. Gorski, and J. Przybył, “Effect of differentiated phosphorus and potassium fertilization on winter wheat yield and quality,” Journal of Elementology, vol. 18, no. 1, pp. 55–67, 2013.

J. B. Reid, S. N. Trolove, Y. Tan, and P. R. Johnstone, “Nitrogen or potassium preconditioning affects uptake of both nitrate and potassium in young wheat (Triticum aestivum),” Annals of Applied Biology, vol. 168, no. 1, pp. 66–80, 2016.

M. M. Williams and M. Martin, “Relationships among phenotypic traits of sweet corn and tolerance to crowding stress,” Field Crops Research, vol. 185, pp. 45–50, 2016.

A. Adeli and J. J. Varco, “Potassium management effects on cotton yield, nutrition, and soil potassium level∗,” Journal of Plant Nutrition, vol. 25, no. 10, pp. 2229–2242, 2002.

A. Almodares, R. Taheri, I. M. Chung, and M Fathi, “The effect of nitrogen and potassium fertilizers on growth parameters and carbohydrate contents of sweet sorghum cultivars,” Journal of Environmental Biology, vol. 29, no. 6, pp. 849–852, 2008.

Y. Zhao, X. Mao, Y. Yong, and X. Zhou, “Effects of irrigation and planting patterns on photosynthetic capacity and grain quality of winter wheat,” International Agrophysics, vol. 33, no. 3, pp. 313–321, 2019.

X. Hu, C. Fang, L. Lu, Z. Hu, Y. Shao, and Z. Zhu, “Determination of soluble sugar profile in rice,” Journal of Chromatography B, vol. 1058, pp. 19–23, 2017.

A. S. Jennifer and A. J. John, “Current models for starch synthesis and the sugary enhancer1 (se1) mutation in Zea mays,” Plant Physiology and Biochemistry, vol. 42, no. 6, pp. 457–464, 2004.

B. Nguyen-Quoc and C. H. Fover, “A role for ‘futile cycles’ involving invertase and sucrose synthase in sucrose metabolism of tomato fruit,” Journal of Experimental Botany, vol. 52, no. 358, pp. 881–889, 2001.

W. Li, S. Yan, and Z. Wang, “Effect of spikelet position on starch proportion, granule distribution and related enzymes activity in wheat grain,” Plant Soil and Environment, vol. 59, no. 12, pp. 568–574, 2013.

X. Ren and J. Zhang, “Research progresses on the key enzymes involved in sucrose metabolism in maize,” Carbohydrate Research, vol. 368, pp. 29–34, 2013.

H. Rolletschek, M.-R. Hajirezaei, U. Wobus, and H. Weber, “Antisense-inhibition of ADP-glucose pyrophosphorylase in Vicia narbonensis seeds increases soluble sugars and leads to higher water and nitrogen uptake,” Planta, vol. 214, no. 6, pp. 954–964, 2002.

Z. Rengel and P. M. Damon, “Crops and genotypes differ in efficiency of potassium uptake and use,” Physiologia Plantarum, vol. 133, no. 4, pp. 624–636, 2008.

Z. G. Li, R. H. Zhang, S. J. Xia et al., “Interactions between N, P and K fertilizers affect the environment and the yield and quality of satsumas,” Global Ecology and Conservation, vol. 19, p. 19408, 2019.

J. F. Gao, Experimental Guidance of Plant Physiology, Higher Education Press, Beijing, China, 2006, in Chinese.

P. Liu, W. P. Lu, and D. L. Lu, “Study on quality differences and index for the optimum harvest stage in fresh waxy corn,” Maize Science, vol. 17, no. 6, pp. 5–8, 2009, in Chinese.

B. S. Everitt and T. Hothorn, A Handbook of Statistical Analyses Using R, Chapman and Hall/CRC, Boca Raton, FL, USA, 3rd edition, 2014.

H. Marschner, Mineral Nutrition of Higher Plants, Academic Press, Cambridge, MA, USA, 2nd edition, 1995.

X.-G. Wang, X.-H. Zhao, C.-J. Jiang et al., “Effects of potassium deficiency on photosynthesis and photoprotection mechanisms in soybean (Glycine max (L.) Merr.),” Journal of Integrative Agriculture, vol. 14, no. 5, pp. 856–863, 2015.

H. Çelik, B. B. Aşik, S. Gürel, and A. Vahap, “Effect of potassium and iron on macro element uptake of maize,” Zemdirbyste-Ariculture, vol. 97, no. 1, pp. 11–22, 2010.

Y. Wang, Z. Zhang, Y. Liang, Y. Han, Y. Han, and J. Tan, “High potassium application rate increased grain yield of shading-stressed winter wheat by improving photosynthesis and photosynthate translocation,” Frontiers of Plant Science, vol. 11, p. 134, 2020.

Z. Yin, W. Guo, H. Xiao et al., “Nitrogen, phosphorus, and potassium fertilization to achieve expected yield and improve yield components of mung bean,” PloS One, vol. 13, no. 10, Article ID e0206285, 2018.

Y. J. Cao, H. W. Zhao, X. H. Wang et al., “Effects of potassium application on yield quality and sucrose metabolism of sweet maize,” Journal of Plant Nutrition Fertilizer, vol. 17, no. 4, pp. 881–887, 2011, in Chinese.

A. P. Mallarino, J. M. Bordoli, and R. Borges, “Phosphorus and potassium placement effects on early growth and nutrient uptake of no-till corn and relationships with grain yield,” Agronomy Journal, vol. 91, no. 1, pp. 37–45, 1999.

D. M. Braun, L. Wang, and Y.-L. Ruan, “Understanding and manipulating sucrose phloem loading, unloading, metabolism, and signalling to enhance crop yield and food security,” Journal of Experimental Botany, vol. 65, no. 7, pp. 1713–1735, 2014.

Y.-L. Ruan, “Sucrose metabolism: gateway to diverse carbon use and sugar signaling,” Annual Review of Plant Biology, vol. 65, no. 1, pp. 33–67, 2014.

D. M. Beckles, N. Hong, L. Stamova, and K. Luengwilai, “Biochemical factors contributing to tomato fruit sugar content: a review,” Fruits, vol. 67, no. 1, pp. 49–64, 2012.

Z. Dai, H. Wu, V. Baldazzi et al., “Inter-species comparative analysis of components of soluble sugar concentration in fleshy fruits,” Frontiers of Plant Science, vol. 7, p. 649, 2016.

D. Lu, X. Cai, J. Zhao, X. Shen, and W. Lu, “Effects of drought after pollination on grain yield and quality of fresh waxy maize,” Journal of the Science of Food and Agriculture, vol. 95, no. 1, pp. 210–215, 2015.

W. F. Tracy, S. R. Whitt, and E. S. Buckler, “Recurrent mutation and genome evolution example of sugary and the origin of sweet maize,” Crop Science, vol. 46, pp. 49–54, 2006.

T. T. Chen, G. Y. Li, M. R. Islam et al., “Abscisic acid synergizes with sucrose to enhance grain yield and quality of rice by improving the source-sink relationship,” BMC Plant Biology, vol. 19, no. 1, p. 525, 2019.

E. D. Cera, “A structural perspective on enzymes activated by monovalent cations,” Journal of Biological Chemistry, vol. 281, no. 3, pp. 1305–1308, 2006.

W. Zhang, X. Zhang, Y. Wang et al., “Potassium fertilization arrests malate accumulation and alters soluble sugar metabolism in apple fruit,” Biology Open, vol. 7, no. 12, p. bio024745, 2018.

J. Yang, J. Zhang, C. Li, Z. Zhang, F. Ma, and M. Li, “Response of sugar metabolism in apple leaves subjected to short-term drought stress,” Plant Physiology and Biochemistry, vol. 141, pp. 164–171, 2019.

R. Zahoor, W. Zhao, M. Abid, H. Dong, and Z. Zhou, “Title: potassium application regulates nitrogen metabolism and osmotic adjustment in cotton (Gossypium hirsutum L.) functional leaf under drought stress,” Journal of Plant Physiology, vol. 215, pp. 30–38, 2017.

R.-C. Fan, C.-C. Peng, Y.-H. Xu et al., “Apple sucrose transporter SUT1 and sorbitol transporter SOT6 interact with cytochrome b5 to regulate their affinity for substrate sugars,” Plant Physiology, vol. 150, no. 4, pp. 1880–1901, 2009.

L. Shangguan, C. Song, X. Leng, E. Kayesh, X. Sun, and J. Fang, “Mining and comparison of the genes encoding the key enzymes involved in sugar biosynthesis in apple, grape, and sweet orange,” Scientia Horticulturae, vol. 165, no. 1, pp. 311–318, 2014.

A. C. Worrell, J.-M. Bruneau, K. Summerfelt, M. Boersig, and T. A. Voelker, “Expression of a maize sucrose phosphate synthase in tomato alters leaf carbohydrate partitioning,” The Plant Cell, vol. 3, no. 10, pp. 1121–1130, 1991.

H. Yang, X. Gu, M. Ding et al., “Activities of starch synthetic enzymes and contents of endogenous hormones in waxy maize grains subjected to post-silking water deficit,” Scientific Reports, vol. 9, p. 7059, 2019.

Y. Hashida, T. Hirose, M. Okamura, K.-i. Hibara, R. Ohsugi, and N. Aoki, “A reduction of sucrose phosphate synthase (SPS) activity affects sucrose/starch ratio in leaves but does not inhibit normal plant growth in rice,” Plant Science, vol. 253, pp. 40–49, 2016.

J. M. Hibberd and A. P. M. Weber, “Plant metabolism and physiology,” Current Opinion in Plant Biology, vol. 15, no. 3, pp. 225–227, 2012.

V. J. Maloney, J.-Y. Park, F. Unda, and S. D. Mansfield, “Sucrose phosphate synthase and sucrose phosphate phosphatase interactin plantaand promote plant growth and biomass accumulation,” Journal of Experimental Botany, vol. 66, no. 14, pp. 4383–4394, 2015.