Effects of Precise K Fertilizer Application on the Yield and Quality of Rice under the Mode of Light, Simple, and High-Efficiency N Fertilizer Application during the Panicle Stage

Abstract

Light, simple, and high-efficiency fertilization is currently an effective method used to improve quality and increase yield. Most research has only focused on the yield or quality of rice, and no effective or in-depth studies exist on the key stage of panicle, which is essential for these two aspects. This study aimed to determine the effect of applying Nitrogen (N) and Potassium (K) fertilizers on the yield and quality at different leaf ages. The rice cultivar, Shennong 265, was grown in the field-tube condition at the 5-leaf age with K fertilizer at different panicle stages. Five K fertilizer and four N fertilizer levels were applied simultaneously during two growing seasons in 2020–2021. The application of K fertilizer at different panicle stages significantly affected the yield and quality. The application of K and N fertilizers at the 12th-leaf-age increased the number of panicles and grains per panicle, thereby increasing the yield with an average increase of 23.20% over local farmer’s fertilization model (CK) in two years. Application at the 10th-leaf age reduced the starch and protein content of the rice and improved the nutritional quality and taste, with an average increase of 11.08 points compared to CK in two years. The processing quality was the best at the panicle K fertilizer application rate of 47.81–64.69 kg ha⁻¹, and the starch and protein contents were the lowest at the panicle K fertilizer application rate of 56.25 kg ha⁻¹. Under different panicle K fertilizer application rates, N fertilizers had great differences in processing quality but had slight differences in nutritional quality; that is, the starch and protein content (total protein and four protein components) significantly increased. The application of panicle N fertilizer mainly affected starch pasting viscosity (RVA profile characteristics). When panicle K fertilizer was applied after panicle N fertilizer, the yield and quality showed a trend of synergistic improvement. Although this improvement was a low-level synergy, it can still be a direction used to explore the synergistic improvement of output and quality.

1. Introduction

Rice is one of the three most important cereal crops in the world. Asian countries account for 90% of the global rice production [1]. China, located in East Asia, is the world’s largest producer and consumer of rice. Within China, Northeast China is an important commercial grain base and the largest high-quality japonica rice-producer [2]. Therefore, it is very important to ensure the yield and quality of rice in Northeast China [3].

It is well known that nitrogen (N) plays a crucial role in improving rice yield. Potassium (K) is one of the essential macronutrients used for plant growth and development. It is involved in plant photosynthesis, cell osmotic regulation, enzyme activation, protein synthesis, grain quality, and yield in rice. The application of N and K at a reasonable ratio can effectively increase plant height, effective panicle number, and leaf area index; promote photosynthetic product synthesis and accumulation; increase rice yield; and improve rice quality [4,5,6,7]. Over the past 70 years, global rice production has gradually increased owing to increased N inputs [8]. However, with the rapid development of agriculture, N fertilizers are increasingly used in rice production to increase efficiency at a low cost. To ensure a high yield of rice, most rice farmers apply more N fertilizers than necessary. This coupled with runoff, denitrification, and leaching has caused a large amount of N loss, resulting in low N recovery efficiency and serious environmental pollution [9]. Moreover, because of the problem of resource distribution in China, K resources are relatively in short supply and are imported in large quantities. Thus, to save cost, K fertilizer application is neglected in agricultural production, resulting in an unbalanced and unscientific application of N and K fertilizers [10]. In recent years, with the development of China’s economy and the improvement of the living standards of the people, demand for rice has gradually changed from “eat enough” to “eat well”. Therefore, it is necessary to improve the quality of rice while stabilizing the output [11].

The number of various fertilizers required for rice is as follows: 2.0–2.4 kg of N, 0.9–1.4 kg of P₂O₅, and 2.5–2.9 kg of K₂O per 100 kg of rice. The N uptake by rice is relatively average in the early, middle, and late stages, but it is the most significant in the booting and grain filling stages [12,13]. However, the absorption of K in rice is low in the early stages, 35% from the tillering to booting stages and 65% from the booting stage to maturity [14]. Therefore, to establish a balance between the output and quality of rice, more attention should be paid to the key stage affecting the yield and quality of rice—the fertilization management during the panicle stage. A large number of studies have focused on the effects of the total amount of N fertilization, the ratio of N fertilization in each period, the frequency and time of N fertilization on rice population indicators, the N use efficiency (NUE), and yield [15,16,17,18,19]. The results showed that increasing the proportion of nitrogen fertilizer application at a late growth stage could significantly optimize the population quality, N utilization, and yield of rice. However, these studies only focused on a single fertilizer and not on a more detailed and accurate ratio of N and K fertilizers during the panicle stage and the precise application time for the certain key period of rice growth and development and ignored the related effects on rice quality. Ample research has been conducted on the simplified application of N fertilizer in the early stage [20,21]. The results showed that a ratio of 6:4 for base + tiller N fertilizer to panicle N fertilizer has the best results. When the ratio of panicle N fertilizer is increased, the tiller N application period is postponed (the leaf age index is 60%), and the panicle N fertilizer application period is preponed (the leaf age index is 80%), which can significantly improve N recovery efficiency (NRE) and N physiological efficiency (NPE) and lead to high yield and efficiency [22,23]. In previous studies, increasing rice yield inevitably reduced rice quality; yield and quality have never been balanced. In this study, the tube planting method, which better simulates the environmental conditions of the field than the pot planting method, was used for two consecutive years of traditional cultivation methods to precisely control the time and amount of nitrogen and potassium fertilizer application. We focused on how to improve the quality traits of rice as much as possible without reducing the yield and to improve the efficient utilization of fertilizers without increasing the input (fertilizer or other economical inputs), to balance yield and quality. The study will provide ideas for establishing a yield and quality evaluation system in high-quality japonica rice-producing areas in Northeast China.

2. Materials and Methods

2.1. Plant Materials and Site Description

Field experiments were conducted on a farm at Shenyang Agricultural University (41°49′ N, 123°34′ E; 41.6 m above sea level) during the rice-growing season (May to October) in 2020 and 2021. The site was located within the main high-yielding rice region of the Liaohe River basin and has a temperate, semi-humid, continental climate. The daily mean temperatures, precipitation, relative humidity, and total sunshine hours during the growing seasons in 2020 and 2021 are provided (Figure 1). The soil type of the field was brown loam. The total N, available P, available K, organic matter, and pH in 0–20 cm of the soil were 1.07 g kg⁻¹, 35.3 mg kg⁻¹, 143.2 mg kg⁻¹, 25.1 g kg⁻¹, and 7.05, respectively; soil fertility is moderate. The test variety was Shennong 265 (15 leaves on the main stem). The typical plant height is 100–105 cm, the plant type is compact, the leaves are wide and firm, the stems and leaves are dark green, the tillering ability is medium, and the growth period is 155 days. It was a typical erect panicle japonica rice cultivar. It has the characteristics of high yield, high NUE, and a reasonable canopy structure [24]. It is one of the most widely planted japonica rice varieties in the rice-growing region in central Liaoning Province, China [25,26].

2.2. Experimental Design

The experiment was designed in a completely randomized manner with three replications. K fertilizer was applied in five leaf-growth stages in the panicle stage: 10th-leaf, 11th-leaf, 12th-leaf, 13th-leaf, and 14th-leaf. Five K fertilizer levels and four N fertilizer levels were set. The specific fertilization amount and fertilization period are shown in

Table 1. The amount and timing of fertilization.

K Treatment	N Treatment	Basal Fertilizer (kg ha−1)			Tillering Fertilizer (kg ha−1)	Panicle Fertilizer (kg ha−1)		Application Time
		N	P	K	N	N	K
K1	N0	81.00	112.50	56.25	54.00	0	39.38	Basel fertilizer was applied one day before transplanting. Tillering fertilizer was applied on 9th-leaf. Panicle N fertilizer was applied on 12th-leaf. Panicle K fertilizer was applied on 10th-leaf, 11th-leaf, 12th-leaf, 13th-leaf, or 14th-leaf, respectively, and only once.
	N1	81.00	112.50	56.25	54.00	72.00	39.38
	N2	81.00	112.50	56.25	54.00	90.00	39.38
	N3	81.00	112.50	56.25	54.00	108.00	39.38
K2	N0	81.00	112.50	56.25	54.00	0	47.81
	N1	81.00	112.50	56.25	54.00	72.00	47.81
	N2	81.00	112.50	56.25	54.00	90.00	47.81
	N3	81.00	112.50	56.25	54.00	108.00	47.81
K3	N0	81.00	112.50	56.25	54.00	0	56.25
	N1	81.00	112.50	56.25	54.00	72.00	56.25
	N2	81.00	112.50	56.25	54.00	90.00	56.25
	N3	81.00	112.50	56.25	54.00	108.00	56.25
K4	N0	81.00	112.50	56.25	54.00	0	64.69
	N1	81.00	112.50	56.25	54.00	72.00	64.69
	N2	81.00	112.50	56.25	54.00	90.00	64.69
	N3	81.00	112.50	56.25	54.00	108.00	64.69
K5	N0	81.00	112.50	56.25	54.00	0	73.13
	N1	81.00	112.50	56.25	54.00	72.00	73.13
	N2	81.00	112.50	56.25	54.00	90.00	73.13
	N3	81.00	112.50	56.25	54.00	108.00	73.13
CK		81.00	112.50	56.25	54.00	90.00	56.25	Basal fertilizer was applied one day before transplanting. Tiller fertilizer was applied 7 days after transplanting. Panicle fertilizer was applied 60 days after transplanting.

. Urea with an N content of 46.4% was used as N fertilizer, superphosphate with 12.0% P₂O₅ as P fertilizer, and potassium chloride with 60.0% K₂O as K fertilizer. There were 101 treatments in the experiment (5 different periods of K fertilization × 5 K fertilizer levels × 4 spikes of nitrogen fertilizer application amount, a total of 100 treatments, plus 1 CK), and each treatment was performed with one barrel, which was repeated three times, for a total of 303 barrels. Planting in the field was carried out using the tube planting method. After raking the ground evenly, a bottomless PVC cylinder with an inner diameter of 30 cm, a wall thickness of 0.5 cm, and a cylinder height of 50 cm was buried. The cylinder nails were pressed to the bottom of the plow (35 cm). The seeds were sown on 24 April 2020 and 21 April 2021. In the four-leaf heart stage, seedlings with similar growth were selected and transplanted on 23 May 2020 and 27 May 2021, and they were harvested on 8 October 2020 and 7 October 2021. There were two seedlings per barrel at a hill spacing of 15.5 cm × 31.5 cm. Except for the fertilization period, conventional management methods were adopted. Basal fertilizer was applied on 22 May 2020 and 26 May 2021; tillering fertilizer was applied on 23 June 2020 and 1 July 2021; panicle N fertilizer was applied on 22 July 2020 and 26 July 2021. The first K application in the panicle stage was on 12 July and then every 6 days or so (the application time was based on the specific leaf age), and the last application in the panicle stage was on 1 August 2020 and 4 August 2021.

As there were many factors in this experiment, the analysis was divided into two parts. In the first part, we only analyzed the difference between the application ratio of N and K fertilizers at different leaf stages during the panicle stage and CK (the same amount of fertilizer). The different stages were (10,12), (11,12), (12,12), (13,12), and (14,12), which indicate the application times of the panicle K and N fertilizers. That is, the panicle K fertilizer was applied on the 10th-leaf, 11th-leaf, 12th-leaf, 13th-leaf, or 14th-leaf, respectively, and only once, and the panicle N fertilizer was applied on the 12th-leaf. In the second part, we only analyzed the difference in the amount of N and K fertilizers during different panicle stages, regardless of the time of application of panicle fertilizer. Among them, there were three levels of N (N1, N2, and N3) and five levels of K (K1, K2, K3, K4, and K5). N0 was used only for the calculation of the regression equation and does not appear in the analysis as an N application level.

2.3. Sampling and Measurements

2.3.1. Determination of Basic Physical and Chemical Properties of Soil

Before the spring test in 2020, soil samples of 0–20 cm in the experimental field were collected using the “S”-shaped sampling method and transferred to the lab. After air drying the soil samples, they were ground and passed through 20- and 100-mesh sieves. The total N content was determined using the elemental analyzer (EA 3000). The content of available P was determined using the molybdenum antimony scandium colorimetric method [27]. The content of available K was determined using flame photometry [27]. Oxidation of the soil organic matter was assessed using the potassium dichromate-external heating method [27]. The soil pH was measured using an electronic pH meter (PHSJ-3F), and the soil-liquid ratio was 1:2.5 [27].

2.3.2. Grain Yield

All ears of rice were collected and planted in tubes, and each hole was individually marked and packaged. After air-drying, an indoor seed test was conducted, and the number of panicles, number of grains per panicle, seed setting rate, and 1000-grain weight were measured.

2.3.3. Determination of Milling Quality of Rice Grain

The seeds were threshed and naturally dried and then stored for 3 months for grain quality measurement. Milling quality, including brown rice rate, milled rice rate, and head milled rice rate were measured according to the GB/T 17891-1999 (1999) standard.

2.3.4. Determination of Amylose and Protein Contents of Rice Grain

The amylose and protein content of brown rice was measured using the Foss 1241 near-infrared grain analyzer (Infratec TM 1241, FOSS, Hillerød, Denmark). The protein component was determined according to Luthe and Liu [28,29], based on Bradford’s BCA protein quantification method.

2.3.5. Determination of Starch Pasting Viscosity of Rice Grain

Pasting properties of rice flour were measured using a Rapid Viscosity Analyzer (RVA-TecMaster, Perten, Sweden), according to the American Society for Cereal Chemistry Operating Procedures [30]. The RVA spectrum characteristic value was mainly represented by peak viscosity (PKV), hot paste viscosity (HPV), cool paste viscosity (CPV), breakdown viscosity (BDV = PKV − HPV), and setback viscosity (SBV = CPV − PKV) [31].

2.3.6. Determination of Taste Quality of Rice Grain

The taste quality of the rice grain was measured using the STA1A rice taste meter produced by SATAKE in Japan. An amount of 30 g of milled rice was weighed, rinsed until the water became clear, and then soaked in a stainless-steel tank for 30 min. Water was added in a ratio of 1:1.2 (rice:water); the rice was put in a steamer to cook for 40 min and cooled for 1 h 50 min, and a taste meter was used to measure the indicators of appearance, hardness, viscosity, balance degree, and taste value. The process was repeated thrice for each sample.

2.4. Statistical Analysis

For experimental variables, two-factor and three-way analysis of variance (ANOVA) was used to assess differences among treatments using the IBM SPSS Statistics 22.0 software (Softonic International, Barcelona, Spain). Significant differences (p < 0.05) between treatments were indicated by different letters according to Fisher’s LSD. Graphs were drawn with the Origin 2021 software (OriginLab, Northampton, MA, USA).

3. Results

3.1. Grain Yield and Yield Components

The grain yield first increased and then decreased with the increase of leaf age of K application at the panicle stage. Compared with those of CK, the K fertilizer applied to 12th-leaf and 13th-leaf at the panicle stage substantially increased the yield to 1302.76 g∙m⁻² and 1135.91 g∙m⁻² in 2020 and 1174.86 g∙m⁻² and 1070.92 g∙m⁻² in 2021, respectively, with increases of 8.08–23.92% in 2020 and 11.58–22.40% in 2021, respectively. The yield was increased by substantially increasing the number of panicles per plant. The seed-setting rate and 1000-grain weight increased with the increase of the leaf age of the K fertilizer application at the panicle stage and reached the maximum value at the 14th-leaf stage, which was the trend for both years (Figure 2). With the increase of the amount of N fertilizer applied at the panicle stage, the yield increased and then decreased, and it reached the highest yield at the application rate of K2 and K3, which was substantially higher than that of K1, K4, and K5, mainly because the spike number and grain number per spike were substantially increased. With the increase of the N fertilizer application rate at the panicle stage, the panicle number, grain number per panicle, and yield gradually increased under low K (K1 and K2) conditions as N3 > N2 > N1, and there was no substantial difference between the seed setting rate and 1000-grain weight. However, under the condition of medium and high K (K3, K4 and K5), a gradually decreasing trend was observed as N3 < N2 < N1. The interaction of year and N and K application at the panicle stage was not substantial (

Table 2. Effects of different N, K, and Y combined application during the panicle stage on rice yield and yield components in 2020 and 2021, with the results of the three-way ANOVA.

Year	Treatment	NO. of Panicle per Plant	NO. of Grains per Panicle	Seed-Setting Rate (%)	1000-Grain Weight (g)	Grain Yield (g∙m−2)
2020	K1N1	12.53 b	155.83 a	93.84 a	23.12 a	840.71 b
	K1N2	13.47 ab	152.55 a	94.34 a	23.60 a	929.47 b
	K1N3	14.60 a	157.34 a	93.49 a	23.65 a	1087.32 a
	K2N1	12.87 b	149.71 b	94.47 a	24.23 a	958.99 b
	K2N2	13.9 ab	156.67 ab	93.07 a	24.22 a	1097.98 a
	K2N3	14.47 a	165.59 a	93.36 a	24.30 a	1151.49 a
	K3N1	15.73 a	178.96 a	91.91 a	23.70 a	1080.56 a
	K3N2	14.13 b	173.01 a	93.54 a	24.06 a	1080.56 a
	K3N3	13.93 b	168.88 a	95.53 a	23.69 a	1009.22 a
	K4N1	16.07 a	156.71 a	93.58 b	24.38 a	1089.37 a
	K4N2	14.60 b	155.49 ab	94.30 ab	24.38 a	973.14 b
	K4N3	14.07 b	152.74 b	95.45 a	24.09 a	924.55 b
	K5N1	13.13 a	136.44 a	95.47 a	25.41 a	1038.74 a
	K5N2	13.00 a	134.43 ab	96.94 a	25.98 a	982.36 ab
	K5N3	11.87 a	125.47 b	96.16 a	25.58 a	894.21 b
2021	K1N1	11.73 b	152.13 a	94.12 a	24.07 a	914.51 a
	K1N2	12.52 ab	153.12 a	94.03 a	24.32 a	939.31 a
	K1N3	13.46 a	155.27 a	93.78 a	24.62 a	945.05 a
	K2N1	11.92 b	150.27 b	94.75 a	24.72 a	965.76 b
	K2N2	12.91 ab	153.41 ab	94.42 a	24.75 a	1009.01 ab
	K2N3	13.88 a	159.57 a	94.07 a	24.73 a	1064.98 a
	K3N1	15.01 ab	160.23 a	93.21 b	24.31 a	1040.17 a
	K3N2	13.92 b	160.52 a	94.33 a	24.26 a	1022.54 a
	K3N3	12.73 b	163.22 a	94.36 a	24.25 a	998.56 a
	K4N1	15.32 a	150.23 a	94.37 c	24.00 a	925.99 a
	K4N2	14.09 b	154.16 a	94.89 b	24.78 a	877.40 b
	K4N3	13.93 b	150.36 a	95.41 a	24.89 a	867.77 b
	K5N1	12.42 a	140.17 a	96.31 b	25.78 a	954.07 a
	K5N2	12.27 a	137.24 ab	96.48 ab	25.72 a	911.23 a
	K5N3	12.00 a	124.25 b	97.00 a	25.99 a	925.78 a
F-value	K	**	**	**	**	**
	N	**	ns	ns	ns	ns
	Y	*	*	ns	ns	*
	K × N	ns	**	**	ns	*
	N × Y	ns	ns	ns	ns	ns
	K × Y	ns	*	ns	ns	ns
	K × N × Y	ns	ns	ns	ns	ns

Note: Different letters indicate differences between different N levels at the same K level. * p < 0.05; ** p < 0.01; ns, not substantial. K, potassium rate; N, nitrogen rate; Y, year.

).

3.2. Processing Quality

With the increase in leaf age of the K fertilizer application rate at the panicle stage, the processing quality first decreased, then increased, and then decreased. The brown rice rate and milled rice rate reached the maximum at the 12th-leaf stage, while the head rice rate reached the maximum at the 13th-leaf stage. The trend of both years was consistent, and the interaction was not substantial (Figure 3). With the increase of the K fertilizer application rate at the panicle stage, the difference in the brown rice rate and milled rice rate of K1–K4 and K5 reached a substantial level, but the difference between K1 and K4 was not substantial. The head rice rates of K2, K3, and K4 were substantially higher than those of K1 and K5, indicating that too much or too little K fertilizer application would reduce the processing quality. With the increase of the N fertilizer application rate, at the K1 and K2 levels, the brown rice rate, the milled rice rate, and the head rice rate showed a gradually increasing trend, and at the K3, K4, and K5 levels, it showed a gradually decreasing trend. The interaction of N and K both reached a substantial level, and the interaction between N and K and year was not substantial. The interaction between the two factors of N and K reached a substantial level. The interaction of year and N and K application at the panicle stage was not substantial (

Table 3. Effects of different N and K combined application rates during the panicle stage on rice processing quality in 2020 and 2021, with the results of the three-way ANOVA.

Year	Treatment	Brown Rice Rate (%)	Milled Rice Rate (%)	Head Rice Rate (%)
2020	K1N1	67.67 b	60.57 b	56.82 b
	K1N2	68.25 b	61.26 ab	57.17 b
	K1N3	69.96 a	62.00 a	59.40 a
	K2N1	68.65 b	61.25 b	57.50 b
	K2N2	70.00 ab	63.01 ab	60.15 a
	K2N3	71.02 a	64.60 a	62.00 a
	K3N1	71.54 a	64.23 a	61.09 a
	K3N2	71.32 a	64.11 a	60.32 a
	K3N3	70.02 b	63.92 a	59.62 b
	K4N1	70.23 a	64.15 a	61.01 a
	K4N2	68.39 b	63.08 a	59.25 ab
	K4N3	66.57 b	62.52 a	57.56 b
	K5N1	68.32 a	63.10 a	59.95 a
	K5N2	66.40 a	61.00 ab	54.52 b
	K5N3	64.63 b	60.03 b	53.97 b
2021	K1N1	68.66 b	62.63 b	57.37 b
	K1N2	70.14 b	64.56 ab	59.17 b
	K1N3	72.30 a	65.94 a	61.40 a
	K2N1	69.31 b	63.27 b	58.45 b
	K2N2	70.40 ab	64.01 ab	61.15 a
	K2N3	71.92 a	66.60 a	62.40 a
	K3N1	72.64 a	66.19 a	62.13 a
	K3N2	72.31 a	65.92 a	61.09 ab
	K3N3	69.41 b	65.73 a	59.43 b
	K4N1	72.41 a	65.45 a	62.06 a
	K4N2	70.39 b	64.18 a	60.35 ab
	K4N3	69.33 b	63.74 a	59.56 b
	K5N1	70.54 a	64.10 a	60.95 a
	K5N2	70.18 a	61.87 ab	56.60 b
	K5N3	67.53 b	60.21 b	54.77 b
F-value	K	*	**	**
	N	ns	ns	ns
	Y	**	**	**
	K × N	**	*	**
	N × Y	ns	ns	ns
	K × Y	*	*	ns
	K × N × Y	ns	ns	ns

Note: Different letters indicate differences between different N levels at the same K level. * p < 0.05; ** p < 0.01; ns, not substantial. K, potassium rate; N, nitrogen rate; Y, year.

).

3.3. Nutritional Quality

With the increase of the leaf age of the K fertilizer application at the panicle stage, the amylose content first decreased and then increased, and all the content, except the 10th-leaf stage, was substantially lower than that of CK; the protein content showed a gradual upward trend, and only 10th-leaf stage had a substantially lower protein content than that of CK. In terms of protein components, the effect of the K fertilizer application on different leaf ages on albumin and prolamin was not obvious, whereas the effect of globulin and glutenin increased first and then decreased, and they both reached the highest at the 13th-leaf stage. Compared with that of CK, albumin in the 11th–14th-leaf, globulin in the 13th-leaf, and glutenin in the 13th- and 14th-leaf were substantially higher than those in CK; albumin in the 10th- and 11th-leaf, prolamin in the 10th–14th-leaf, and the gluten of the 10th-leaf was substantially lower than that of CK. The two-year trend remained the same; the differences among treatments reached an extremely substantial level, and the inter-annual differences were not substantial, indicating that the application of spike K fertilizers at different leaf ages could change the amylose and protein content and could affect the differences between protein components (Figure 4). With the increase of the K fertilizer application rate at the panicle stage, amylose and protein contents first decreased and then increased, and they reached the lowest value at K3. The change in the K fertilizer application rate can cause a change in protein composition. With the increase in the K application rate, the contents of albumin, prolamin, and glutenin first decreased and then increased, while globulin first increased and then decreased. The four proteins reached the lowest under the K3 treatment and reached the highest under the K5 treatment. Amylose and protein content showed gradual upward trends with the increase of the N fertilizer application. The analysis of the protein components showed that, under the low K condition (K1), the effect of the N fertilizer on gluten did not reach a substantial level, but the effect on the other three proteins reached a substantial level. Under the condition of medium K (K3), except for albumin, the three proteins had substantial differences only under the condition of low N (N1) but not under the condition of medium and high N (N2, N3). Under medium-high K (K4) conditions, the N application rate had the least effect on protein components. Under high K (K5) conditions, high N (N3) substantially increased the contents of the four proteins and severely reduced nutritional quality. The differences of N and K levels reached extremely substantial levels, and the differences in protein components of N and K interactions reached substantial or extremely substantial levels. The two-year trend was consistent. The interaction of year and N and K application at the panicle stage was not substantial (

Table 4. Effects of different N and K combined application rates during the panicle stage on rice amylose and protein components in 2020 and 2021, with the results of the three-way ANOVA.

Year	Treatment	Amylose Contents (%)	Protein Contents (%)	Albumin (mg/grain)	Globulin (mg/grain)	Prolamin (mg/grain)	Glutelin (mg/grain)
2020	K1N1	18.20 a	7.10 b	2.17 c	1.50 b	0.40 c	6.60a
	K1N2	18.35 a	7.16 ab	2.65 b	1.72 b	0.72 b	7.11a
	K1N3	18.48 a	7.31 a	2.95 a	2.23 a	1.05 a	7.11a
	K2N1	17.90 b	7.23 a	2.25 b	1.94 c	0.25 c	5.95c
	K2N2	18.13 a	7.29 a	2.30 b	2.36 b	0.31 b	6.50b
	K2N3	18.23 a	7.32 a	2.61 a	2.71 a	0.90 a	7.00 a
	K3N1	17.33 b	6.75 b	1.85 c	2.12 b	0.15 b	5.58 b
	K3N2	17.60 a	6.85 ab	2.17 b	2.56 a	0.32 a	6.29 a
	K3N3	17.70 a	7.01 a	2.50 a	2.73 a	0.52 a	6.76 a
	K4N1	18.10 b	7.15 a	2.06 c	2.46 b	0.28 b	6.75 a
	K4N2	18.52 a	7.19 a	2.42 b	2.87 b	0.47 a	6.89 a
	K4N3	18.78 a	7.25 a	3.10 a	3.12 a	0.60 a	6.99 a
	K5N1	18.57 b	7.10 b	2.30 c	2.59 c	0.43 c	6.68 b
	K5N2	18.78 a	7.25 b	2.71 b	3.41 b	0.79 b	6.89 b
	K5N3	18.90 a	7.57 a	3.25 a	4.00 a	1.12 a	7.61 a
2021	K1N1	17.73 a	6.97 b	2.11 c	1.56 b	0.42 c	6.63 a
	K1N2	17.90 a	7.03 ab	2.72 b	1.75 b	0.65 b	7.08 a
	K1N3	18.00 a	7.20 a	3.01 a	2.36 a	1.11 a	7.10 a
	K2N1	17.47 b	7.03 a	2.20 b	1.98 c	0.20 c	5.93 c
	K2N2	18.00 a	7.13 a	2.31 b	2.35 b	0.37 b	6.52 b
	K2N3	18.07 a	7.17 a	2.66 a	2.75 a	0.89 a	7.13 a
	K3N1	17.13 b	6.70 b	1.88 c	2.08 b	0.14 b	5.62 b
	K3N2	17.80 a	6.83 b	2.16 b	2.57 a	0.35 a	6.29 a
	K3N3	17.90 a	7.03 a	2.52 a	2.69 a	0.51 a	6.78 a
	K4N1	17.80 b	7.07 a	2.02 c	2.44 b	0.26 b	6.75 a
	K4N2	18.23 a	7.13 a	2.50 b	2.66 b	0.46 a	6.45 a
	K4N3	18.40 a	7.17 a	3.60 a	3.04 a	0.59 a	6.86 a
	K5N1	18.07 b	7.13 b	2.40 c	2.57 c	0.41 c	6.71 b
	K5N2	18.37 a	7.27 b	2.81 b	3.37 b	0.72 b	6.89 b
	K5N3	18.40 a	7.60 a	3.34 a	3.96 a	1.09 a	7.62 a
F-value	K	**	**	**	**	**	**
	N	**	**	**	**	**	**
	Y	**	**	ns	ns	ns	ns
	K × N	ns	*	**	*	**	**
	N × Y	ns	ns	ns	*	ns	ns
	K × Y	ns	*	ns	ns	ns	ns
	K × N × Y	ns	*	ns	ns	ns	ns

Note: Different letters indicate differences between different N levels at the same K level. * p < 0.05; ** p < 0.01; ns, not substantial. K, potassium rate; N, nitrogen rate; Y, year.

).

3.4. RVA Profile Characteristics

With the increase of the leaf age of the K fertilizer application at the panicle stage, PKV, CPV, and SBV showed gradual upward trends; HPV and BDV showed a trend of increasing first, then decreasing, and then increasing. Compared with that of CK, the 10th-leaf application substantially reduced PKV, HPV, and CPV, the 11th-leaf and 12th-leaf applications substantially increased SBV, the 13th-leaf application substantially decreased SBV, and the 14th-leaf application substantially increased CPV and SBV. In 2020, all the differences except PKV reached a substantial level, and in 2021, except for PKV and BDV, the differences reached a substantial level, and the inter-annual differences were not substantial (Figure 5). The two-year trends of the RVA profile differed slightly. The effect of the N application and K application on the RVA profile was quite different, and the effect of the K application on the RVA profile was small. Only the difference between BDV and SBV in 2020 reached a substantial level, and the others were not substantial. The effect of the N application on the RVA profile value was greater, all reaching the substantial or extremely substantial level. With the increase of the N application rate at the panicle stage, PKV, HPV, CPV, and BDV gradually decreased, while SBV increased gradually. The three-factor interaction difference between N and K and annual BDV and SBV reached a substantial level (

Table 5. Effects of different N and K combined application rates during the panicle stage on RVA profile characteristics in 2020 and 2021, with the results of the three-way ANOVA.

Year	Treatment	Peak Viscosity (cP)	Hot Paste Viscosity (cP)	Cool Paste Viscosity (cP)	Breakdown Viscosity (cP)	Setback Viscosity (cP)
2020	K1N1	2741.70 a	2232.70 a	3351.10 a	509.00 a	599.40 b
	K1N2	2704.50 ab	2145.20 a	3307.70 a	502.30 a	603.20 ab
	K1N3	2600.90 b	2106.60 a	3249.30 b	500.30 a	648.40 a
	K2N1	2842.50 a	2213.20 a	3502.80 a	629.30 a	660.30 a
	K2N2	2800.50 ab	2183.00 a	3442.20 ab	617.50 ab	671.70 a
	K2N3	2701.50 b	2127.40 a	3304.80 a	574.10 b	703.30 a
	K3N1	2800.80 a	2202.70 a	3402.10 a	648.10 a	601.30 a
	K3N2	2782.10 a	2152.20 a	3357.50 a	639.90 a	605.40 a
	K3N3	2724.20 a	2124.90 a	3332.60 a	599.30 b	638.40 a
	K4N1	2824.40 a	2222.10 a	3498.40 a	602.30 a	674.00 b
	K4N2	2801.20 ab	2200.70 a	3461.30 a	600.50 a	680.10 b
	K4N3	2713.30 b	2109.30 a	3439.70 a	613.00 a	726.40 a
	K5N1	2871.40 a	2249.70 a	3509.60 a	621.70 a	638.20 b
	K5N2	2853.30 a	2212.50 a	3462.20 ab	621.80 a	638.90 b
	K5N3	2702.30 b	2106.30 a	3430.50 b	596.00 b	728.20 a
2021	K1N1	2836.10 a	2251.80 a	3499.60 a	594.80 a	645.50 a
	K1N2	2761.30 ab	2166.50 ab	3470.70 ab	584.30 a	663.50 a
	K1N3	2622.90 b	2057.80 b	3323.10 b	565.10 a	709.40 a
	K2N1	2902.50 a	2137.00 a	3586.80 a	642.80 a	660.70 a
	K2N2	2828.50 ab	2183.00 a	3489.20 ab	581.50 b	684.30 a
	K2N3	2718.50 b	2256.30 a	3364.00 b	572.20 b	700.20 a
	K3N1	2834.80 a	2244.90 a	3481.40 a	636.50 a	646.60 a
	K3N2	2805.40 a	2168.90 a	3479.40 a	589.90 ab	661.10 a
	K3N3	2734.30 a	2156.90 a	3395.40 a	577.40 b	674.00 a
	K4N1	2866.80 a	2236.30 a	3512.90 a	613.60 a	650.80 b
	K4N2	2816.10 ab	2211.70 a	3541.80 a	604.40 a	712.20 ab
	K4N3	2690.30 b	2123.30 a	3402.50 a	567.00 a	725.70 a
	K5N1	2893.00 a	2270.70 a	3537.70 a	622.30 a	644.70 b
	K5N2	2871.20 a	2262.50 a	3554.20 a	608.70 a	683.00 ab
	K5N3	2752.00 a	2166.30 a	3470.50 a	585.70 a	718.50 a
F-value	K	ns	ns	ns	ns	ns
	N	**	*	**	**	*
	Y	*	*	*	ns	*
	K × N	ns	*	ns	ns	ns
	N × Y	ns	ns	ns	ns	*
	K × Y	ns	ns	ns	*	*
	K × N × Y	ns	ns	ns	*	*

Note: Different letters indicate differences between different N levels at the same K level. * p < 0.05; ** p < 0.01; ns, not substantial. K, potassium rate; N, nitrogen rate; Y, year.

).

3.5. Cooking Quality

With the increase of the leaf age of K fertilizer application at the panicle stage, the taste value gradually decreased. Compared with that of CK, 10th-leaf substantially improved the taste value by increasing the appearance, viscosity, and balance degree and by decreasing hardness. The 14th-leaf substantially reduced the taste value by reducing viscosity and balance degree and increasing hardness. Other leaf ages were not substantially different. The differences between treatments of each index reached extremely substantial levels; the inter-annual differences were not substantial; the differences between treatments and inter-annual interactions were not substantial (Figure 6). With the increase of the K fertilizer application at the panicle stage, the measure of the appearance, viscosity, and balance degree first increased and then decreased, whereas the hardness first decreased and then increased, thus affecting the taste value. The trend of taste value first increased and then decreased, reaching the maximum value of 49.21 points in 2020 and 50.30 points in 2021 at K2. It affected the taste value by substantially increasing appearance, viscosity, and balance degree. The trend was consistent for two years, but the difference in the effect on hardness was inconsistent for the two years, which needs to be further explored. With the increase of the N fertilizer application at the panicle stage, the taste value showed a downward trend. Under medium and high K conditions (K3, K4, K5), appearance, viscosity, and balance degree were substantially reduced and hardness increased substantially, which in turn affected the taste value. Under the condition of low K (K1), the effect of N fertilizer was lower, the difference in taste value was not substantial, and the two-year rule was generally consistent. The interaction of N and K factors reached an extremely substantial level, and the interaction of year and N and K application at the panicle stage and year was not substantial (

Table 6. Effects of different N and K combined application rates during the panicle stage on cooking quality in 2020 and 2021, with the results of the three-way ANOVA.

Year	Treatment	Appearance	Hardness	Viscosity	Balance Degree	Taste Value
2020	K1N1	3.50 a	7.82 a	3.92 a	3.32 a	49.13 a
	K1N2	3.21 a	7.93 a	3.52 b	3.22 ab	47.62 ab
	K1N3	3.21 a	8.01 a	3.32 b	3.18 b	46.22 b
	K2N1	3.72 a	7.72 b	4.11 a	3.69 a	50.25 a
	K2N2	3.41 ab	7.91 a	3.96 ab	3.53 ab	49.13 ab
	K2N3	3.20 b	8.03 a	3.72 b	3.24 b	48.25 b
	K3N1	3.42 a	7.81 b	4.02 a	3.41 a	49.23 a
	K3N2	3.44 a	8.02 ab	3.72 b	3.22 ab	47.14 b
	K3N3	2.96 b	8.17 a	3.53 b	3.01 b	47.25 b
	K4N1	3.62 a	7.61 c	4.12 a	3.32 a	51.12 a
	K4N2	3.07 b	8.03 b	3.45 b	3.17 a	49.31 b
	K4N3	2.71 c	8.32 a	3.02 c	2.71 b	47.11 c
	K5N1	3.52 a	7.71 b	3.86 a	3.41 a	50.92 a
	K5N2	2.72 b	8.03 a	3.21 b	2.82 b	47.22 b
	K5N3	2.42 b	8.25 a	2.66 c	2.51 c	44.22 c
2021	K1N1	3.61 a	8.01 a	4.03 a	3.52 a	50.90 a
	K1N2	3.30 a	8.15 a	3.62 b	3.15 b	50.65 a
	K1N3	3.32 a	8.19 a	3.59 b	3.18 ab	48.70 a
	K2N1	3.77 a	8.00 b	4.29 a	3.73 a	52.15 a
	K2N2	3.55 ab	8.02 b	3.88 b	3.23 b	48.75 b
	K2N3	3.24 b	8.23 a	3.79 b	3.43 ab	50.00 ab
	K3N1	3.51 a	8.08 b	4.06 a	3.51 a	50.65 a
	K3N2	3.50 a	8.17 b	3.50 b	2.89 b	46.95 b
	K3N3	2.92 b	8.38 a	3.77 ab	3.26 a	49.25 a
	K4N1	3.81 a	7.90 c	4.23 a	3.77 a	52.40 a
	K4N2	3.31 b	8.15 b	3.54 b	3.16 b	48.65 b
	K4N3	2.59 c	8.55 a	3.09 c	2.54 c	44.30 c
	K5N1	3.65 a	7.97 b	3.96 a	3.57 a	51.20 a
	K5N2	2.92 b	8.33 a	3.13 b	2.75 b	46.40 b
	K5N3	2.58 b	8.51 a	2.79 c	2.41 b	43.85 c
F-value	K	**	**	**	**	**
	N	**	**	**	**	**
	Y	ns	ns	*	ns	ns
	K × N	**	**	**	**	**
	N × Y	ns	ns	ns	ns	ns
	K × Y	ns	ns	ns	ns	ns
	K × N × Y	ns	ns	*	ns	ns

Note: Different letters indicate differences between different N levels at the same K level. * p < 0.05; ** p < 0.01; ns, not substantial. K, potassium rate; N, nitrogen rate; Y, year.

).

3.6. Correlations between the Traits

Figure 7 shows the correlation between grain yield and K application at different leaf ages at the panicle stage. The two-year average value is related to the output in a univariate nonlinear manner, and the regression equation is y = −0.26 x² + 29.26 x + 211.60 (R² = 0.62, p < 0.05). This shows that the yield increased first and then decreased with the increase of the K application at the panicle stage. When the K application at the panicle stage amount reached 56.27 kg ha⁻¹, the yield reached the maximum, which was 1034.82 g∙m⁻². The trend was different among leaf ages.

Figure 8 shows the correlation between grain yield and N application at different leaf ages at the panicle stage. The two-year average value is related to the output in a univariate nonlinear manner, and the regression equation is y = −0.0012 x² + 0.22 x + 38.86 (R² = 0.95, p < 0.05). This shows that the yield increased first and then decreased with the increase of N application at the panicle stage. When the N application at the panicle stage amount reached 93.96 kg ha⁻¹, the yield reached the maximum, which was 1008.55 g∙m⁻². The trend was the same among leaf ages.

Figure 9 shows the correlation between taste value and K application at different leaf ages at the panicle stage. The two-year average value is related to the output in a univariate nonlinear manner, and the regression equation is y = −0.0023 x² + 0.18 x + 46.83 (R² = 0.93, p < 0.05). This shows that the yield increased first and then decreased with the increase of K application at the panicle stage. When the K application at the panicle stage amount reached 39.13 kg ha⁻¹, the yield reached the maximum, which was 52.97. The trend was the same among leaf ages.

The correlation between taste value and the N application rate at different leaf ages at the panicle stage is shown in Figure 10. The two-year average is linearly correlated with taste value, and the regression equation is y= −0.088 x + 56.84, (R² = 0.96, p < 0.05). This indicated that there was a substantial negative correlation between the N application at the panicle stage and taste value. The trend was the same among leaf ages.

The correlation analysis of the yield and quality indicators of different leaf ages applying K fertilizer during the panicle stage (Figure 11) reveals that the premature application of K fertilizer during the panicle stage (10th, 11th-leaf) had a very substantial positive correlation between the number of panicles per plant and the number of grains per panicle and yield; the PKV, HPV, BDV, appearance, viscosity, and balance degree were positively correlated with taste value; 1000-grain weight, albumin content, globulin content, SBV, and hardness were substantially negatively correlated with taste value (a). When K fertilizer was applied at the 12th-leaf age, its yield-related effects were the same as those at the 10th- and 11th-leaf ages. However, its effect on the taste value was different from that of the 10th- and 11th-leaf. The influence of amylose, viscosity, and balance degree on the taste value was extremely substantially positive; the protein content, globulin content, and SBV were extremely substantially negatively correlated with taste value (b). The correlation between the indicators changed during the panicle stage (13th and 14th leaves) when the K fertilizer was applied too late. The number of panicles per plant, the number of grains per panicle, brown rice rate, milled rice rate, globulin content, and viscosity were substantially positively correlated with yield; total protein content and prolamin content were extremely substantially negatively correlated with yield; brown rice rate, milled rice rate, head rice rate, albumin content, globulin content, appearance, viscosity, and balance degree were substantially positively correlated with taste value; protein content and hardness were substantially negatively correlated with taste value (c).

4. Discussion

4.1. Effects of the Quantitative Application of N and K Fertilizers at Different Leaf Ages on Yield

A large number of studies have shown that adjusting the amount of N fertilizer, optimizing the proportion of N fertilizer in the fertilizer, and appropriately reducing the total amount of N fertilizer application can be more effective than conventional fertilization and improve rice yield [6,20]. It might increase yield by improving the N use efficiency and photosynthesis [32,33,34]. Previous studies have found that Chinese rice farmers used 56–85% of the total N in the season 10 days before transplanting, and most of the N was applied at the seedling and tillering stages, resulting in a waste of N [35]. Delaying fertilization time and reducing fertilization amount in the tillering stage can improve grain yield and NUE [36]. Appropriately delaying the application of tiller fertilizer and advancing the application of panicle fertilizer can increase the tillering panicle rate and the number of spikelets, thereby promoting the increase of tiller and maintaining the number of spikelets [21]. Since K cannot be covalently bound to organic molecules, it cannot be absorbed by plants such as N can [37]. However, K⁺ is the most abundant cellular cation and can regulate stomatal movement, osmotic regulation, and homeostatic enzyme activation and can participate in membrane protein transport [38]. Studies have shown that the response of K fertilizer to agronomic yield is the greatest when the application rate of K fertilizer reaches 130 mg kg⁻¹ [39]. Atapattu A [40] reported that corn and soybeans showed positive returns at low K levels, whereas in moderate K-level soils, K returns were mostly negative. Singh B [41] pointed out that in only 12.5% of the paddy fields in the sample survey, the K application had a significant impact on rice yield. Another study showed that applying K fertilizer 50% (18.75 kg ha⁻¹) more than the recommended amount at the heading stage and five days later than the recommended time could increase the yield of direct-seeded rice [42]. Compared with that on N, the research on the application rate and application period of K is slightly limited. Most of the studies are regarding the improvement of the disease resistance and stress resistance of rice to increase the yield, and the research on its direct effect on yield, especially the research on N and K combined application in the panicle fertilizer stage, is not in-depth or systematic. This study showed that K fertilizer application at the 12th-leaf (80% leaf age) during the panicle stage can significantly increase the number of effective tillers and increase the yield of rice by 23.20%. Application at the 13th- and 14th-leaf (90–95% leaf age) can significantly increase the seed setting rate and 1000-grain weight. With the increase of the N fertilizer and K fertilizer application amounts at the panicle stage, their effects on yield showed a trend of increasing first and then decreasing. According to the results of the equation simulation, the highest yield can be obtained when the application rates of N and K during the panicle stage reach 91.67 kg ha⁻¹ and 55.00 kg ha⁻¹, respectively.

4.2. Effects of the Quantitative Application of N and K Fertilizers at Different Leaf Ages on Various Quality Indicators

Previous studies show that the cooking and processing quality of rice can be improved by changing the main agronomic practices (fertilizing at the right time, rationally improving the amount of fertilizer, etc.) [42]. In addition, the application of comprehensive nutrients (N, P, K, organic fertilizers, etc.) to paddy soil has a significant impact on rice quality. K uptake by field crops is generally faster than N uptake, and K also plays an important role in ensuring efficient N use. K is not as easily absorbed into the organic matter as N and P, but K facilitates the transport of photosynthetic products and other plant metabolites, thereby contributing to improved grain quality, including increased rice aroma, smoothness, and whiter appearance [43]. In this study, it was found that the application of the appropriate panicle K fertilizer at the right time improved the processing quality of rice, that is, the application of K fertilizer at a dose of 47.81–64.69 kg ha⁻¹ at the 12th- and 13th-leaf (80–90% leaf age) was when the processing quality was the best. When the application rate of the K fertilizer per panicle was lower than 47.81 kg ha⁻¹ or higher than 64.69 kg ha⁻¹, the processing quality of the rice was reduced; with the increase of panicle N fertilizer, the processing quality gradually improved, but at high K levels (higher than 56.25 kg ha⁻), the processing quality gradually decreased with the increase of panicle N fertilizer.

Rice grains are made up of about 80–85% starch, 4–10% protein, etc. [44]. The content of amylose, the structure of amylopectin, and the interaction of starch with proteins and lipids are important factors that determine the quality of rice [45]. Among them, amylose content may be the most important factor in determining the cooking taste [46]. Rice with low amylose is usually soft and waxy, whereas white rice with high amylose is hard [47]. Although the protein content of rice is low, in terms of taste quality, some studies have shown that the total protein content is related to the texture of cooked rice [48], and some studies have shown that the difference in the RVA profile between varieties with similar amylose is because of the total protein content. This in turn affects the eating quality, and protein components may also affect eating quality [49]. At present, there are some studies on protein components, but the results are not uniform. Some studies show that globulin has no relationship with RVA eigenvalues, but its variation at very low levels plays a very important function; some studies show that the difference between the content of gluten and prolamin is the largest, and the ratio of these two proteins affects the taste quality [50]. In addition to the above two viewpoints, some believe that the interaction between different types of proteins is the root cause of their influence on the taste value of cooking [51]. A large number of studies have shown that the N application can significantly increase the protein content and starch content of rice [52] and significantly reduce the quality of rice [53], but the effect of K on rice quality is less. The 10th-leaf (70% leaf age) was applied with ear fertilizer, which significantly reduced the starch and protein content and improved the nutritional quality of rice. For the protein component, the early application of ear fertilizer (70% leaf age) decreased gluten content and the too-late application (90% leaf age) increased gluten content. With the increase of K application, the content of albumin and gluten was consistent; that is, it first decreased and then increased, reaching the minimum value at K3. While the content of globulin increased gradually, the content of gliadin changed irregularly. With the increase in the N application rate, albumin, globulin, prolamin, and glutenin all showed an increasing trend. However, there were some differences in the change of each protein component under the action of different K application rates, indicating that different N and K ratios had an impact on the protein components. From the RVA profile characteristics, PKV, CPV, and SBV gradually increased with the increase of leaf age, and the regularity of HPV and BDV was poor. When 10th-leaf (70% leaf age) was applied with ear fertilizer, appearance, viscosity, and balance degree significantly increased and hardness decreased, which in turn significantly improved the cooking and eating taste score, which was 11.08 points higher than that of CK. However, 14th-leaf application (90% leaf age) significantly reduced the cooking and eating taste score, which was 9.11 points lower than that of CK, and the difference between the 11th- and 13th-leaf application and CK was not significant. When the amount of K fertilizer applied at the panicle stage was lower than 56.25 kg ha⁻¹, the content of starch and protein gradually decreased with the increase of application amount and increased gradually when it was higher than 56.25 kg ha⁻¹. The higher the amount of N fertilizer applied at the panicle stage, the higher the starch content and the protein content and the lower the nutritional quality. In the two-year test results, the effect of K application at the panicle stage on the RVA profile characteristics was small and insignificant. However, with the increase of the N application at the panicle stage, it decreased PKV, HPV, CPV, and BDV; increased SBV; and decreased the cooking and eating taste score. When the amount of K applied at the panicle stage was less than 47.81 kg ha⁻¹, the taste score also increased with the increase of the K application. When the K application at the panicle stage was higher than 47.81 kg ha⁻¹, the taste value decreased with the increase of the K application, which affected the taste value by significantly changing appearance, viscosity, and balance degree. With the increase of the N application, the taste value showed a decreasing trend, which was consistent with previous studies, but under low K conditions, with the increase of the N application, the change of the taste value was small and insignificant.

4.3. Study on the Synergistic Improvement of Yield and Quality by the Quantitative Application of N and K Fertilizers at Different Leaf Ages during the Panicle Stage

At present, a large number of studies at this stage have separated rice yield and rice quality and have proposed many methods to increase yield or quality. Using advanced molecular techniques, it is indeed possible to find some genes that regulate yield and quality [54,55,56]. However, there are few studies at present regarding cultivation, especially whether it can have a synergistic effect on yield and quality through the use of fertilizers and precise fertilization. This study integrated the previous research on N management in this subject and drew some preliminary conclusions for the two-year-early N and K fertilizer management: N fertilizer was applied on the 12th-leaf, and K fertilizer was applied on 10th-, 11th-, and 12th-leaf. There was no synergistic correlation between yield and quality, and the indicators affecting the two were different. When the K fertilizer was applied on the 13th- and 14th-leaf, the relationship between yield and quality changed a little, and some indicators had the same effect on both and reached a significant level. This shows that the relationship between yield and quality can be coordinated under different fertilization methods at the early stage, so that the two can be improved synergistically. However, this improvement is still incomplete and low, and further research is needed. Although some preliminary conclusions were drawn in this study, it cannot be further explored due to too much processing. In the future, through reducing the treatment, more precise and in-depth research can be conducted on how to improve the yield and quality together from the perspective of cultivation and reveal its physiological mechanism.