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Article

Effects of Integrated Management Strategies on Pepper Yield and Quality: A Study of Cultivation and Nutrient Management Practices

by
Yiming Tian
1,2,
Junjie Wang
1,2,
Juan Chen
3,
Duan Yu
4,
Zhen Zeng
5,
Jian Fu
5,
Fen Zhang
1,2,
Hailin Cao
1,2,
Fabo Liu
1,2 and
Tao Liang
1,2,4,*
1
College of Resources and Environment, Southwest University, Chongqing 400716, China
2
Interdisciplinary Research Center for Agriculture Green Development in Yangtze River Basin, Southwest University, Chongqing 400716, China
3
Beijing Cultivated Land Construction and Protection Center, Beijing 102600, China
4
Chongqing Academy of Agriculture Sciences, Chongqing 401329, China
5
Tongliang District Agricultural Technology Extension Service Center, Chongqing 402560, China
*
Author to whom correspondence should be addressed.
Agronomy 2024, 14(12), 2754; https://doi.org/10.3390/agronomy14122754
Submission received: 22 October 2024 / Revised: 12 November 2024 / Accepted: 19 November 2024 / Published: 21 November 2024
(This article belongs to the Section Horticultural and Floricultural Crops)
Browse Figures
Figure 1
<p>Precipitation and mean temperature during the pepper growing season in 2020 (<b>A</b>) and 2021 (<b>B</b>).</p> "> Figure 2
<p>Test pepper cultivars.</p> "> Figure 3
<p>Nitrogen use efficiency of different pepper cultivars under different planting densities. Different letters indicate significant differences among different cultivars by Duncan’s multiple comparison test (<span class="html-italic">p</span> &lt; 0.05). Error bars indicate standard errors (<span class="html-italic">n</span> = 3).</p> "> Figure 4
<p>Aboveground dry matter biomass accumulation (aboveground DMB) in different N levels including N0 (<b>A</b>), OPT-N (<b>B</b>), planting density and pepper cultivars. Under the same planting density, different lowercase letters denote significant changes among different cultivars, and different capital letters denote significant changes between treatments at different densities by Duncan’s multiple comparison test (<span class="html-italic">p</span> &lt; 0.05). Error bars indicate standard errors (<span class="html-italic">n</span> = 3).</p> "> Figure 5
<p>Effects of N application rate including N0 (<b>A</b>), OPT-N (<b>B</b>), planting density and above-ground DMB ratio of different pepper cultivars. Values are means (<span class="html-italic">n</span> = 3).</p> "> Figure 6
<p>Fruit nitrogen (<b>A</b>), phosphorus (<b>B</b>) and potassium (<b>C</b>) concentration in different N fertilizer application rates of different pepper cultivars. N fertilizer application rates included N0 and OPT-N. The different lowercase letters indicate significant difference between cultivars by Duncan’s multiple comparison test (<span class="html-italic">p</span> &lt; 0.05). Error bars indicate standard errors (<span class="html-italic">n</span> = 3).</p> "> Figure 7
<p>Fruit nitrogen (<b>A</b>), phosphorus (<b>B</b>), potassium (<b>C</b>) and plant nitrogen (<b>D</b>) accumulation in N fertilizer application rates of different pepper cultivars. N fertilizer application rates included N0 and OPT-N. The different lowercase letters indicate significant difference between cultivars by Duncan’s multiple comparison test (<span class="html-italic">p</span> &lt; 0.05). Error bars indicate standard errors (<span class="html-italic">n</span> = 3).</p> "> Figure 8
<p>Ca (<b>A</b>), Mg (<b>B</b>), Fe (<b>C</b>), Mn (<b>D</b>),Cu (<b>E</b>) and Zn (<b>F</b>) concentration of pepper in different N levels and cultivars. N fertilizer application rates included N0 and OPT-N. The different lowercase letters indicate significant difference between cultivars by Duncan’s multiple comparison test (<span class="html-italic">p</span> &lt; 0.05). Error bars indicate standard errors (<span class="html-italic">n</span> = 3).</p> ">
Versions Notes

Abstract

:
Integrated agronomic management strategies, including nutrient management, planting density, and cultivar selection, are crucial for improving vegetable yield and quality. Here, we conducted a 2-year field experiment to examine the effect of cultivars, planting density and optimal nitrogen application rate on pepper yield, nutrient absorption and quality, and further screened the suitable cultivars and planting density. The experiment included two N application rate treatments (0, 250 kg ha−1), five pepper (Capsicum annuum L.) cultivars (‘Xin xiang #8’, ‘King’, ‘Strip pepper #28’, ‘Er jing tiao’, ‘Red pepper #425’), and three planting density treatments (0.4 m × 0.6 m; 41,667 plants ha−1, 0.5 m × 0.6 m 33,333 plants ha−1; and 0.6 m × 0.6 m; 27,778 plants ha−1). Our results showed that the optimal N application rate can significantly increase the yield, nutrient absorption (e.g., N accumulation) and quality (e.g., Vitamin C content) by 23.7–120.2%, 66.1–125.5%, and 1.0–20.0%, respectively. Different cultivars had different responses to N-fertilizer. Under the optimal nitrogen fertilizer rate, ‘King’ and ‘Strip pepper #28’ had the strongest response to N, and their yield, nutrient uptake and quality (e.g., VC content) were significantly higher than those of other cultivars by 3.4–56.7%, 22.7–227% and 21.3–42.0%, respectively. The highest index of Nutritional Quality (INQ) values for Fe, Mn, and Cu were found in ‘Er jing tiao’, and the highest INQ values for Zn and VC were found in ‘King’, indicating that ‘Er jing tiao’ and ‘King’ have greater nutritional value. In addition, the yield and aboveground dry matter biomass accumulation increased with increasing planting density. Therefore, integrated agronomic management measures, which included high-yield cultivars (‘King’, ‘Strip Pepper #28’), suitable planting density (0.4 m × 0.6 m) and reasonable nutrient management, could be a potential strategy to achieve a high yield and quality of pepper production in southwest China. This study serves as a practical example for the highly efficient development of vegetable production in southwest China.

1. Introduction

Pepper (Capsicum annuum L.) is one of the most important vegetables. China has been the largest producer of pepper in the world, accounting for half of the total global vegetable production [1]. However, pepper production suffers from high inputs of nitrogen fertilizer [2,3]. The average nitrogen fertilizer application rate in open-field vegetable production in southwest China was 352 kg N ha−1, which was 60–68% greater than the cereal crop in China and 2.1-fold higher than the vegetable crop in the United States [4,5,6]. Excessive N fertilizer application causes low N use efficiency (NUE), yield and quality, and high reactive N loss [7]. Therefore, exploring effective management measures is needed to achieve vegetable sustainable production.
Optimizing N fertilizer management, especially for the N application rate, is crucial to improve fertilization efficiency and obtain high yields and quality [8]. How to maximize the benefits of nitrogen fertilizer and reduce losses has received widespread attention [9,10]. Previous studies in vegetable and tomato yield have shown that optimizing the N application rate reduces N fertilizer input and improves N recovery without affecting crop yield [11,12]. Many previous studies have indicated that an optimized N application rate could reduce fertilizer dosage and significantly improve fertilizer use efficiency, whereas it could only maintain or slightly increase vegetable yield [10,13,14]. To obtain high yields and quality, integrated agronomic management measures with a combination of nutrients and cultivation measures, rather than single-nutrient management, are needed [15]. Previous studies indicated that integrated knowledge and products strategy increased vegetable yield by 17% but decreased N rates by 38.0%, and integrated soil–crop system management increased overall yield by 10.8–11.5% and reduced the NUE by 14.7–18.1% [16,17].
Finding suitable cultivars is also essential to achieve high yields. Previous research, focused on the response of different oat varieties to N fertilizer, found that Checota had a significantly higher yield and NUE than Amasya by 30% and 33%, respectively [18]. Different cultivars have different responses to N, and high-response cultivars have significant advantages in yield and quality [19,20]. However, the current research mainly focuses on maize [21], rice [22], wheat [23] and other food crops, while only a few studies have focused on vegetables. Therefore, screening N-efficient genotypes and high-yield cultivars is feasible to enhance the NUE and increase crop yield and quality.
Enhancing planting density is also an effective cultivation measure to improve yields and quality in crop production [24], as it can fully utilize the existing population structure and light and heat resources [25]. However, when plants are crowded under high planting density, it can lead to a reduction in yield per plant due to increased competition for resources [26]. Previous studies concluded that the seed yield of soybean under a high planting density was 22.8% higher than that under a normal planting density [27]. Meanwhile, previous research compared three different planting densities and showed that sweet sorghum obtained the highest yields under an intermediate plant population density [28]. Moreover, several studies have also shown the possibility of obtaining a high yield and protein content in maize under a suitable planting density [26,29,30]. The optimal plant density under optimizing N fertilizer application rate condition for pepper to obtain great yield NUE and quality remains unknown in southwest China. Consequently, determining the suitable planting density will further improve vegetable yield, quality and nutrient uptake.
Southwest China is an important pepper production area in China, accounting for 33.4% of national production [31]. In this study, a 2-year field experiment in Southwest China, was carried out to investigate three objectives: (1) to explore the responses of different cultivars to nitrogen further to select the optimal cultivars; (2) to illustrate the effect of planting densities on yield and NUE, to choose the optimal density; (3) to propose an integrated agronomic management measure combined with planting density, cultivation and nutrient management measures. This study provides practical example for seeking effective integrated management strategies to improve vegetable yields and quality in southwest China.

2. Materials and Methods

2.1. Experimental Site

A two-year field experiment was conducted from 2020 to 2021 at the He Chuan Base of the Southwest University Experimental Farm (30°0′ N, 106°7′ E) in Chongqing, China. This region has a typical subtropical monsoon climate, characterized by high temperatures, and high but uneven precipitation. Based on measurements at a weather station close to the experimental site, the mean air temperature over the pepper cropping season was 26.1 °C in 2020 and 24.9 °C in 2021, and total precipitation over the pepper cropping season was 289 mm in 2020 and 351.7 mm in 2021. The precipitation was mainly concentrated in 30–75 days after transplanting in 2020, and 30–60 days after transplanting in 2021. The average temperature during the planting period is generally 25–35 °C (Figure 1). The soil is classified as purple soil according to the Chinese soil classification system. The primary characteristics before planting pepper in 2020 for the initial top soil layer (0–0.2 m) were pH 5.65 (1:2.5, soil/water), organic matter content 9.19 g kg−1, total N 0.50 g kg−1, soil NO3− (extracted by CaCl2) 4.89 mg kg−1, soil NH4+ (extracted by CaCl2) 2.06 mg kg−1, total P 24.3 g kg−1, available phosphorus 19.5 mg kg−1, ammonium acetate available potassium 99.9 mg kg−1, and bulk density 1.42 Mg m−3.

2.2. Experimental Design and Field Management

The experiment included 2 N levels: 0 N control (N0) and optimal N application rate (OPT-N, 250 kg N ha−1); 3 planting densities: 0.4 m × 0.6 m (41,667 plants ha−1), 0.5 m × 0.6 m (33,333 plants ha−1) and 0.6 m × 0.6 m (27,778 plants ha−1); and 5 local main cultivars: ‘Xin xiang #8’, ‘King’, ‘Strip pepper #28’, ‘Er jing tiao’, ‘Red pepper #425’ (Figure 2), which are the main cultivation types in southwest China. ‘Xin xiang #8’ can produce numerous long, slender fruits that turn bright red upon ripening; ‘King’ is predominantly harvested while green, with long and straight fruits that mature later. ‘Strip pepper #28’ features both red and green fruits, with shorter and thicker peppers that are suitable for multiple harvests; ‘Er jing tiao’ has slender, curved fruits mostly green in color, and with sparse branches, allowing for good air circulation, and is suitable for warmer climates. ‘Red pepper #425’ has shorter, thick upward-growing fruits that turn red upon ripening, and sturdy plants that are early-maturing. The optimal N recommendation rate is based on a root-zone N management experiment from a four-year continuous field experiment in Hechuan Base [32,33]. In each growing season, each treatment received 140 kg P2O5 ha−1 and 300 kg K2O ha−1. For all treatments, N fertilizer was applied at a ratio of 2:1:1:1 through four fertilization events at the seedling, early-fruiting, mid-fruiting and full-fruiting growing stages, respectively, with P fertilizer applied at a 1:1 ratio and K fertilizer applied at a 3:4:4:4 ratio. All fertilizers, except organic fertilizers, were applied by digging 10–15 cm deep holes near the plants. In this experiment, the selected N fertilizers were conventional urea (N ≥ 46.2%), super phosphate (P2O5 ≥ 12%), and potassium sulfate (K2O ≥ 52.0%) produced by Tianhua Chemical (Luzhou, China), Hanzhong Tangfeng Chemical (Hanzhong, China) and SDIC Xinjiang Lop Nur Potash Salt Co., Ltd. (Korla, China), respectively. The commercial organic fertilizer had 30% N substituted (manufactured by Sichuan Goldenway Bio-tech Co., Ltd. (Nanchong, China), with C, N, P2O5 and K2O contents of 46%, 1.69%,0.65% and 0.46%) and 70% was conventional urea-N. The organic fertilizer was surface-applied as basal fertilizer before transplanting and immediately incorporated to 15 cm depth.
The field experiment used a split-plot design with three replicate plots, and each plot was 46.5 m2 (5.6 m × 8.3 m). A 1 m buffer zone between blocks and a 0.5 m buffer zone between plots were maintained to minimize nutrient flow between plots. All other field management practices followed local practices for high-yield systems.

2.3. Sampling and Laboratory Analysis

2.3.1. Yield and Aboveground Dry Matter Biomass

The total yield was determined by the sum of the fresh weight of 24 pepper plants in the middle row of each plot. Three pepper plants with uniform growth were collected from each plot as a sample, washed, divided into four parts (root, stem, leaf and fruit), placed in a constant temperature oven at 75 °C, dried to a constant weight, and then weighed to obtain aboveground dry matter biomass accumulation.

2.3.2. Mineral Nutrient Content

The dry samples of different organs were subsequently ground into a powder for determination of the N concentration (Kjeldahl procedure). For other mineral nutrients (P, K, Ca, Mg, Cu, Fe, Mn and Zn), the samples were digested with HNO3-H2O2 in a microwave-accelerated reaction system (Auto Digib lock S60UP, LabTech, Santa Ana, CA, USA) and then measured for element concentration by inductively coupled plasma optical emission spectroscopy (ICP–OES, 5110 SVDV, Agilent, Santa Clara, CA, USA).
The N accumulation was calculated as follows:
N accumulation = DMB × NC
where DMB represents aboveground dry matter biomass accumulation, and NC represents N concentration during the harvest period. The calculation of P and K accumulation is the same as that of N accumulation.
The N fertilizer use efficiency (NUE) was calculated as follows:
NUE (%) = (N accumulation in N application treatment-N accumulation in N0 treatment)/N rate × 100%

2.3.3. Quality Determination

Four fresh fruits were mixed as samples from each plot for quality measurement. Vitamin C (VC) was measured using the 2,6-dichloroindophenol titrimetric method [34]; nitrate was measured using the salicylic acid-sulfuric acid method [35]; soluble protein was measured using the Bradford assay [36]; amino acids were measured using the ninhydrin colorimetric method [37]; total phenolics were measured using the Folin–Ciocalteu reagent method [38]; and total flavonoids were measured using the NaNO2-Al(NO3)3-NaOH colorimetric method [39].

2.3.4. Nutritional Quality Assessment

The Index of Nutritional Quality (INQ) is an indicator to evaluate the nutritional quality of food [40]. In this paper, INQ was used to evaluate the supply of nutrients in peppers. When INQ > 2, it indicates a good source of this nutrient; when 1 < INQ ≤ 2, it indicates that the nutrient is sufficient; when INQ < 1, it indicates that the nutrient is deficient and may be deficient in long-term consumption.
The INQ was calculated as follows:
INQ = The   content   of   a   nutrient / NRV Calorie / Recommended   intake
where NRV represents nutrient reference values and recommended intake reference [41].

2.4. Statistical Analysis

The primary data were processed using Microsoft Excel Sheets and SPSS software (version 21.0 for Windows, SPSS Inc., Chicago, IL, USA). IBM SPSS Statistics 27 (IBM Co., Ltd., New York, NY, USA) was used to perform a multi-factor analysis of variance on the data obtained from 2 N treatments, 5 pepper cultivars and 3 planting densities, followed by Duncan’s (p < 0.05) significant difference method. Prior to analysis of variance ANOVA, the normality of all data was checked using Shapiro–Wilk’s test, and for non-normally distributed data, we used the Kruskal–Wallis test for the analysis. The above data plots were drawn using GraphPad Prism 9.5.1 (San Diego, CA, USA) and PowerPoint 2019 (Microsoft, Redmond, WA, USA).

3. Results

3.1. Yield

The yield under OPT-N was found to increase by 23.7–120.2% compared to N0 (Table 1). The response of different cultivars to the N fertilizer rate was different. ‘Strip pepper #28’ had the greatest response to N fertilizer, and the yield increased by 68.5%, which was significantly higher than that of the other cultivars by 20.6–56.7%. In addition, pepper yield was found to increase with increasing planting density in all treatments. The yield of ‘Strip pepper #28’ and ‘King’ was highest in all planting densities, 10.2–19.4%, 1.7–8.3% higher than other cultivars, respectively, in 0.6 m × 0.6 m. In a planting density of 0.5 m × 0.6 m, ‘Strip pepper #28’ and ‘King’ were 10.99–47.6% and 5.2–33.0% higher than those of others. The yield was significantly increased by 8.6–71.8% under a planting density of 0.4 m × 0.6 m compared to 0.6 m × 0.6 m. There was no significant difference between planting densities of 0.5 m × 0.6 m and 0.4 m × 0.6 m for all cultivars under the OPT-N treatment.

3.2. Nitrogen Use Efficiency

The NUE increases with the increase in planting density, and the NUE is the highest at a planting density of 0.4 m × 0.6 m. The NUE ranged from 37.8% to 58.6% among the different cultivars under 0.4 m × 0.6 m (Figure 3). The NUE of ‘Strip pepper #28’ was the highest, reaching 58.6%, which was higher than that of ‘King’, ‘Er jing tiao’, ‘Xin xiang #8’ and ‘Red pepper #425’ by 8.0%, 15.3%, 44.4%, 55.0%, respectively. That of ‘King’ was higher than that of the other cultivars (6.7–50.5%). There was no significant difference between King and Er jing tiao. The NUE of Red pepper #425 was the lowest, 21.1%.

3.3. Aboveground Dry Matter Biomass and Allocation Ratio

N application can significantly increase the aboveground dry matter biomass (DMB) of pepper, ranging from 24.4 to 91.3%, compared with N0 (Figure 4). Under OPT-N, the aboveground DMB of ‘Stripe pepper #28’ was highest, which was significantly higher than that of ‘Er jing tiao’, ‘King’, ‘Xin xiang #8’ and ‘Red pepper #425’, by 3.3%, 20.3%, 30.4%, 42.4%, respectively (Figure 4B). Meanwhile, the aboveground DMB of pepper increased with increasing planting density. Under different density treatments, there was no significant difference in DMB between ‘King’ and ‘Stripe pepper #28’ (Figure 4A,B).
Compared with N0, adding N fertilization increased the proportion of DMB allocated to fruits at harvest, which ranged from 34 to 63% under the N0 treatment (Figure 5A) and 37–73% under the OPT-N treatment (Figure 5B). Meanwhile, the proportion of DMB allocated to each treatment increased with increasing planting density. Among the pepper varieties, ‘King’ and ‘Stripe pepper #28’ were allocated 2.7–70.2% and 2.0–66.0% higher in fruits than the other cultivars, respectively.

3.4. Micromineral Nutrient Absorption

Compared to N0, fruit N concentration was increased by 8–25% under OPT-N (Figure 6A), while P and K concentrations had effect (Figure 6B,C). Under OPT-N, the N concentration among cultivars from high to low was as follows: ‘Stripe pepper #28’ > ‘Er jing tiao’ > ‘Xin xiang #8’ > ‘King’ > ‘Red pepper #425’. Under the OPT-N treatment, the N concentration of ‘Stripe pepper #28’ was the highest, which was 27 g kg−1, 2.0–45.0% higher than other cultivars, followed by ‘Er jing tiao’, and the difference between them was not significant. The highest P and K concentrations were found in ‘King’, while P concentration was not significant among all cultivars.
Compared to N0, OPT-N significantly increased the accumulation of N, P and K in pepper fruits by 66.1–125.5%, 39.1–122.9% and 11.7–68.8%, respectively (Figure 7A–C). Compared with other varieties, the N accumulation of King pepper increased by 22.7–145.4%, and there was no significant difference between ‘King’ and ‘Stripe pepper #28’. The highest P accumulation was found in ‘King’, which was 1.4–195.2% higher than that of other varieties. But the differences were not statistically significant among all cultivars. Fruit K accumulation in ‘Stripe pepper #28’ was 108 kg ha−1, which was significantly higher than that of the other cultivars. OPT-N significantly increased plant N accumulation by 73.3–104.7%, compared to N0 (Figure 7D). Compared with other varieties, OPT-N increased plant N accumulation of ‘Stripe pepper #28’ by 104.7%. The highest plant N accumulation was found in ‘Stripe pepper #28’, which was 1.9–103.8% higher than that of other varieties.

3.5. Mineral Nutrient Absorption

Compared with N0, OPT-N significantly increased the contents of Ca (2.86–14.7%), Fe (17.9–26.7%), Cu (11.3–32.8%) and Zn (4.4–36.3%) (Figure 8). There was no significant difference in Ca content among different varieties (p< 0.05). Under OPT-N, different varieties had different responses to various nutrient elements. The Fe and Cu contents of ‘Er jing tiao’ were the highest, which were 14.1–62.6% and 24.2–58.4% higher than those of the other varieties, respectively. King had the highest Mn and Zn contents, which were 20–55.3% and 52.1–70.9% higher than those of other the varieties, respectively. The Mg content of ‘Strip pepper #28’ was the highest, and there was no significant difference among ‘Er jing tiao’, ‘King’ and ‘Strip pepper #28 (p < 0.05). The highest Mn content was found in ‘King’ and ‘Er jing tiao’, which was 45.2 mg/kg and 44.4 mg/kg, respectively, and the difference was not significant (p < 0.05).

3.6. Quality

In the green ripening period, OPT-N significantly increased the Vitamin C (VC) and free amino acid content of peppers by 13.2–206.9% and 84.9–276.6%, respectively (Table 2). There was no significant difference in the nitrate, soluble protein and total flavonoid contents of pepper among all cultivars (p < 0.05). In the red ripening period, OPT-N significantly increased the nitrate content of peppers by 6.5–124%. However, OPT-N significantly decreased the VC content of ‘Red pepper #425’ and ‘Er jing tiao’ by 13.2% and 37.7%, respectively, and had no significant effect on that of the other cultivars. OPT-N increased the total phenolics content in ‘King’, ‘Red pepper #425’ and ‘Er jing tiao’ by 40%, 20% and 22%, respectively, while it led to a decrease in the other cultivars. OPT-N also decreased the total flavonoid content of all pepper cultivars except ‘Xin xiang #8’. OPT-N had no significant effects on the soluble protein and amino acid content for all cultivars.
Different pepper cultivars have different responses to N fertilization. ‘King’ had the highest VC content in both periods, which was higher than that of the other cultivars. There were significant differences in the soluble protein content of peppers among different cultivars, with an average of 31.0 mg/g; the highest free amino acid content of 48.6 µmol/g was found in the green ripening stage of ‘Strip pepper #28’, which was 3.70–52.7% higher than that of the other cultivars. The total phenolics and total flavonoid contents of ‘Red pepper #425’ at the red ripening stage were the highest and were 11.7–66.7% and 24.0–68.0% higher than those of the other cultivars, respectively (p < 0.05).

3.7. Nutrient Quality Index

The INQ indicated that pepper is a good source of Fe, Mn, Cu, Zn mineral nutrients and VC (INQ > 2) (Table 3). OPT-N slightly improved the nutritional value of pepper compared to N0. The highest INQ values for Fe, Mn, and Cu were found for ‘Er jing tiao’, and the highest INQ values for Zn and VC were found for ‘King’ under both N0 and OPT-N, indicating that ‘Er jing tiao’ and ‘King’ have higher nutritional values.

4. Discussion

4.1. N-Efficient Varieties Can Achieve Higher Yield, Quality and Nutrient Absorption

The optimization of nitrogen management plays a critical role in enhancing yield, quality, and nutrient uptake in crops [42,43]. Our results indicate that OPT-N could increase pepper yield by 23.7–120.2% and nutrient uptake (N accumulation) by 66.1–125.5%, consistent with other studies [44,45]. This result could be attributed to a better balance between the N demand of pepper throughout the growth period and further promoting pepper growth in the OPT-N treatment [46]. Additionally, OPT-N positively affects pepper quality, as seen in the increased vitamin C (VC) content (1.0–20.0%) and amino acid content (74–250%) (Table 2). These increases were attributed to the following: (1) N provided the basic material for the synthesis of related nutrients, like free amino acids [47]; (2) N can increase the activity of enzymes that promote nutrient absorption and further increase the nutrient content [48]. OPT-N positively improved vitamin C content because nitrogen promotes photosynthesis and metabolic processes that support the synthesis of antioxidant compounds [49]. Total phenolics have antioxidant properties in plants that help plants cope with environmental stress. Appropriate nitrogen application can generally promote the growth of pepper, enhance its photosynthesis and metabolic activity, and thus increase the total phenol content [50].
The type of cultivar selected significantly affects crop yield, nutrient uptake and quality. The response of different cultivars to the N fertilizer rate was different due to the large difference in genotype. Our results indicated that ‘King’ and ‘Strip pepper #28’ had the greatest response to N fertilizer, as their yield, nutrient absorption (e.g., N accumulation) and quality were 3.4–56.7%, 22.7–227% and 21.3–42.0% significantly higher than those of other cultivars, respectively. These results are attributed to the fact that ‘Xin xiang #8’, ‘King’ and ‘Strip pepper #28’ belong to the line pepper, and ‘Red pepper #425’ belongs to the Chao tian pepper. First, line peppers are usually longer and grow vertically, while Chao tian peppers have upward-growing fruits and are usually compact plants. The higher growth structure of line pepper may make it more efficient to promote root growth and leaf expansion when receiving nitrogen fertilizer so as to better absorb and use nitrogen. Meanwhile, fruit metabolites differ greatly among different pepper cultivars, especially for cultivars with different fruit shapes [47]. The difference in fruit metabolites was significantly related to fruit shape and color, and was affected by different varieties’ genotypes [51]. These factors directly affected nutrient absorption abilities and further affect yield and quality improvement.

4.2. Reasonable Planting Density Significantly Improved Yield, Nutrient Accumulation and Quality

Rational planting density is an important agricultural measure to increase crop yield [52]. Different varieties show different adaptability to planting densities, and the differences between varieties are significant under the same planting density conditions [53,54]. Our study confirmed that with increasing planting density, the yield of peppers continues to increase, which is consistent with most previous research results [55,56]. Tremblay et al. showed that soybean grain yields increased linearly with increasing plant density [57]. Previous research indicated that higher planting density increased the leaf area index and biomass accumulation but decreased the biomass accumulation per plant [58]. These results were probably explained by the increase in planting density improving the efficiency of solar and thermal energy utilization and promoting the formation of photosynthetic products, subsequently increasing biomass accumulation and crop yield [59]. However, several previous studies have suggested that yield may no longer increase, or may even decline, with increasing planting density [60]. This is likely because the planting density used in our experiment did not reach the critical density—the minimum density required to achieve maximum yield.
Integrated agronomic management measures, rather than single-nutrient management or cultivation measures, are the key to achieving high yield, nutrient efficiency and quality [4,16,61]. Our results confirmed that by using integrated measures combined with optimal variety, planting density, and nutrient management, yield can be significantly increased by 10.4–242.3%, nutrient absorption (e.g., N accumulation) by 4.1–226.6% and quality (e.g., VC content) by 2.3–40.8%. Our findings are similar to those of previous studies [62]. Our results clearly show the potential for adopting integrated management strategies for sustainable vegetable production in this region. In the future, more suitable soil–crop integrated management should be developed in more regions and crop systems to achieve highly efficient in vegetable production.

5. Conclusions

OPT-N can significantly increase yield and nutrient absorption (e.g., N accumulation) and quality (e.g., VC content) by 23.7–120.2%, 66.1–125.5%, and 1.0–20.0%, respectively. Different pepper cultivars vary in their response to N due to the large genotypic difference. Line pepper may have a stronger ability to metabolize nitrogen, which can promote growth and yield more effectively when nitrogen supply is sufficient. Under OPT-N, ‘Strip pepper #28’ and ‘King’ had the highest response to N, and their yield, nutrient absorption (e.g., N accumulation) and quality (e.g., VC content) were significantly higher than those of other cultivars by 3.4–56.7%, 22.7–227% and 21.3–42.0%, respectively. The highest index of Nutritional Quality (INQ) values for Fe, Mn, and Cu were found in ‘Er jing tiao’, and the highest INQ values for Zn and VC were found in ‘King’, indicating that ‘Er jing tiao’ and ‘King’ have greater nutritional value. In addition, as the planting density increased, the yield continued to increase. In conclusion, integrated agronomic management measures, which included high-yield cultivars (‘King’, ‘Strip pepper #28’), suitable planting density (0.4 m × 0.6 m) and OPT-N management, could be a potential strategy to achieve a high yield and improve quality for pepper production in Southwest China. Our study serves as a practical example for the highly efficient development of vegetable production in southwest China.

Author Contributions

Conceptualization, methodology, formal analysis, writing, Y.T.; formal analysis, Y.T., J.W., F.Z., H.C. and F.L.; writing—review and editing, J.C., D.Y., Z.Z., J.F. and T.L.; supervision, T.L. All authors have read and agreed to the published version of the manuscript.

Funding

We are very grateful for the support from the Research project of Chongqing Academy of Agricultural Sciences, cqaas2023siczzd003, National Natural Science Foundation of China (U20A2047), Innovation Research 2035 Pilot Plan of Southwest University (SWU-XDZD22001), and General Program of Natural Science Foundation of Chongqing (grant number CSTB2023NSCQ-MSX0661).

Data Availability Statement

The data that support the findings of this study are available from the corresponding author (Dr. Tao Liang) upon reasonable request.

Conflicts of Interest

The authors declare that they have no competing interests.

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Figure 1. Precipitation and mean temperature during the pepper growing season in 2020 (A) and 2021 (B).
Figure 1. Precipitation and mean temperature during the pepper growing season in 2020 (A) and 2021 (B).
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Figure 2. Test pepper cultivars.
Figure 2. Test pepper cultivars.
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Figure 3. Nitrogen use efficiency of different pepper cultivars under different planting densities. Different letters indicate significant differences among different cultivars by Duncan’s multiple comparison test (p < 0.05). Error bars indicate standard errors (n = 3).
Figure 3. Nitrogen use efficiency of different pepper cultivars under different planting densities. Different letters indicate significant differences among different cultivars by Duncan’s multiple comparison test (p < 0.05). Error bars indicate standard errors (n = 3).
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Figure 4. Aboveground dry matter biomass accumulation (aboveground DMB) in different N levels including N0 (A), OPT-N (B), planting density and pepper cultivars. Under the same planting density, different lowercase letters denote significant changes among different cultivars, and different capital letters denote significant changes between treatments at different densities by Duncan’s multiple comparison test (p < 0.05). Error bars indicate standard errors (n = 3).
Figure 4. Aboveground dry matter biomass accumulation (aboveground DMB) in different N levels including N0 (A), OPT-N (B), planting density and pepper cultivars. Under the same planting density, different lowercase letters denote significant changes among different cultivars, and different capital letters denote significant changes between treatments at different densities by Duncan’s multiple comparison test (p < 0.05). Error bars indicate standard errors (n = 3).
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Figure 5. Effects of N application rate including N0 (A), OPT-N (B), planting density and above-ground DMB ratio of different pepper cultivars. Values are means (n = 3).
Figure 5. Effects of N application rate including N0 (A), OPT-N (B), planting density and above-ground DMB ratio of different pepper cultivars. Values are means (n = 3).
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Figure 6. Fruit nitrogen (A), phosphorus (B) and potassium (C) concentration in different N fertilizer application rates of different pepper cultivars. N fertilizer application rates included N0 and OPT-N. The different lowercase letters indicate significant difference between cultivars by Duncan’s multiple comparison test (p < 0.05). Error bars indicate standard errors (n = 3).
Figure 6. Fruit nitrogen (A), phosphorus (B) and potassium (C) concentration in different N fertilizer application rates of different pepper cultivars. N fertilizer application rates included N0 and OPT-N. The different lowercase letters indicate significant difference between cultivars by Duncan’s multiple comparison test (p < 0.05). Error bars indicate standard errors (n = 3).
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Figure 7. Fruit nitrogen (A), phosphorus (B), potassium (C) and plant nitrogen (D) accumulation in N fertilizer application rates of different pepper cultivars. N fertilizer application rates included N0 and OPT-N. The different lowercase letters indicate significant difference between cultivars by Duncan’s multiple comparison test (p < 0.05). Error bars indicate standard errors (n = 3).
Figure 7. Fruit nitrogen (A), phosphorus (B), potassium (C) and plant nitrogen (D) accumulation in N fertilizer application rates of different pepper cultivars. N fertilizer application rates included N0 and OPT-N. The different lowercase letters indicate significant difference between cultivars by Duncan’s multiple comparison test (p < 0.05). Error bars indicate standard errors (n = 3).
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Figure 8. Ca (A), Mg (B), Fe (C), Mn (D),Cu (E) and Zn (F) concentration of pepper in different N levels and cultivars. N fertilizer application rates included N0 and OPT-N. The different lowercase letters indicate significant difference between cultivars by Duncan’s multiple comparison test (p < 0.05). Error bars indicate standard errors (n = 3).
Figure 8. Ca (A), Mg (B), Fe (C), Mn (D),Cu (E) and Zn (F) concentration of pepper in different N levels and cultivars. N fertilizer application rates included N0 and OPT-N. The different lowercase letters indicate significant difference between cultivars by Duncan’s multiple comparison test (p < 0.05). Error bars indicate standard errors (n = 3).
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Table 1. Yield of pepper as affected by different pepper cultivars, N application rates and planting densities on average in 2020 and 2021. N application rates including 0 N control (N0) and optimal N application rate (OPT-N).
Table 1. Yield of pepper as affected by different pepper cultivars, N application rates and planting densities on average in 2020 and 2021. N application rates including 0 N control (N0) and optimal N application rate (OPT-N).
N Application RateCultivarYield (t ha−1)
0.6 m × 0.6 m0.5 m × 0.5 m0.4 m × 0.6 m
N0Xin xiang #816.4 ± 4.2 a B17.8 ± 1.2 ab A18.8 ± 1.6 b A
King19.0 ± 3.0 a B24.3 ± 0.8 a A25.4 ± 2.4 a A
Strip Pepper #2816.0 ± 2.3 ab B18.3 ± 2.4 ab B26.4 ± 1.7 a A
Er jing tiao 14.6 ± 2.0 ab B17.9 ± 0.5 ab AB20.0 ± 2.7 b A
Red Pepper #42513.0 ± 2.4 b B16.1 ± 1.5 b AB18.7 ± 1.7 b A
OPT-NXin xiang #822.2 ± 7.2 a B30.3 ± 0.9 b A30.8 ± 1.0 bc A
King23.5 ± 7.7 a B36.3 ± 4.1 ab A36.9 ± 5.3 ab A
Strip Pepper #2825.9 ± 4.0 a B40.3 ± 3.4 a A44.5 ± 7.8 a A
Er jing tiao 23.1 ± 5.5 a B34.5 ± 2.2 b A35.7 ± 3.4 ab A
Red Pepper #42521.7 ± 2.9 a B27.3 ± 0.8 c A28.4 ± 6.4 c A
Significant level (P)
Cultivar (A) ***
N application rate (B) ***
Planting density(C) ***
A × B ***
A × C ***
B × C **
A × B × C ns
Values are means ± standard deviation (n = 3). Within a column in the same planting density, different lowercase letters denote significant difference among different cultivars at p < 0.05 by Duncan’s multiple comparison test. Within a row in the same cultivar, different capital letters denote significant difference among different planting densities at p < 0.05 by Duncan’s multiple comparison test, **, ***, indicate significant difference at 0.01 and 0.001 levels; ns, not significant.
Table 2. Quality of different pepper cultivars under N fertilizer application rates in different growth periods.
Table 2. Quality of different pepper cultivars under N fertilizer application rates in different growth periods.
N Application RateCultivarMass Concentration
Vitamin C (mg/100 g)Nitrate (mg/kg)Soluble Protein (mg/g)Free Amino Acid (μ mol/g)Total Phenolics (mg/g)Total Flavonoid (mg/g)
Green Ripening PeriodRed Ripening PeriodGreen Ripening PeriodRed Ripening PeriodGreen Ripening PeriodRed Ripening PeriodGreen Ripening PeriodRed Ripening PeriodGreen Ripening PeriodRed Ripening PeriodGreen Ripening PeriodRed Ripening Period
N0Xin xiang #823.1 ± 1.60 a92.6 ± 7.5 a11.2 ± 0.35 b52.5 ± 1.5 b30.4 ± 1.16 a30.8 ± 0.75 a12.1 ± 1.08 a16.6 ± 2.9 ab0.92 ± 0.10 b1.2 ± 0.1 a0.14 ± 0.01 c0.10 ± 0.00 d
King12.9 ± 2.75 b107.8 ± 2.4 a7.3 ± 2.25 c40.4 ± 1.4 d30.8 ± 1.33 a29.8 ± 0.38 a12.8 ± 0.47 a18.3 ± 1.9 ab0.78 ± 0.05 bc0.5 ± 0.1 c0.15 ± 0.03 c0.15 ± 0.02 c
Strip Pepper #28 19.7 ± 2.81 a63.7 ± 2.7 b13.1 ± 0.55 ab46.2 ± 4.1 c31.4 ± 0.32 a31.2 ± 4.86 a13.7 ± 1.06 a16.0 ± 2.5 ab0.86 ± 0.09 bc0.6 ± 0.1 c0.22 ± 0.02 b0.12 ± 0.01 d
Er jing tiao23.6 ± 3.79 a90.1 ± 7.2 b12.4 ± 0.8 ab69.1 ± 2.8 a31.2 ± 0.38 a32.9 ± 1.84 a13.6 ± 0.59 a14.6 ± 2.8 b0.73 ± 0.11 c1.1 ± 0.1 a0.24 ± 0.01 b0.35 ± 0.01 b
Red Pepper #42515.9 ± 1.03 b59.6 ± 2.7 c13.4 ± 0.55 a70.6 ± 0.5 a31.0 ± 0.70 a30.8 ± 0.69 a12.6 ± 1.01 a20.0 ± 0.3 a1.21 ± 0.10 a1.0 ± 0.1 b0.33 ± 0.04 a0.37 ± 0.01 a
OPT-NXin xiang #828.5 ± 0.61 a94.5 ± 2.0 ab14.6 ± 1.09 b64.9 ± 2.8 d29.1 ± 0.58 a30.9 ± 0.98 a46.4 ± 2.49 b18.2 ± 2.0 bc0.71 ± 0.09 b0.5 ± 0.1 c0.14 ± 0.01 c0.17 ± 0.01 b
King39.6 ± 9.8 a106.8 ± 2.4 a13.7 ± 1.80 b90.5 ± 0.2 b29.7 ± 0.32 a32.6 ± 3.32 a47.0 ± 2.12 b18.3 ± 0.6 bc0.61 ± 0.15 b0.7 ± 0.1 b0.15 ± 0.03 c0.13 ± 0.00 c
Strip Pepper #2826.1 ± 4.52 a64.9 ± 1.2 c15.0 ± 1.55 b60.6 ± 3.7 d29.8 ± 0.29 a31.4 ± 0.30 a48.6 ± 0.46 a16.3 ± 1.0 c0.64 ± 0.05 b0.5 ± 0.02 c0.22 ± 0.02 c0.08 ± 0.00 d
Er jing tiao32.5 ± 7.02 a76.4 ± 3.8 b13.7 ± 1.07 b92.0 ± 5.9 a30.4 ± 0.41 a30.8 ± 0.60 a37.1 ± 4.02 c20.1 ± 2.8 bc0.92 ± 0.01 a0.4 ± 0.07 d0.24 ± 0.01 b0.08 ± 0.00 d
Red Pepper #42518.0 ± 2.32 b75.0 ± 3.9 b20.4 ± 5.00 a83.0 ± 2.6 c30.0 ± 0.43 a30.1 ± 0.47 a23.3 ± 0.86 d24.3 ± 1.8 a1.07 ± 0.09 a1.2 ± 0.06 a0.33 ± 0.04 a0.25 ± 0.00 a
Significant level (P)
Cultivar (A)************nsns******************
N application rate (B)**************ns**********ns***
AB*****ns***nsns***ns***********
Values are means ± standard deviation (n = 3). Within a column in the same planting density, different lowercase letters denote significant changes among different cultivars at p < 0.05 by Duncan’s multiple comparison test. Within a row in the same cultivar at p < 0.05 by Duncan’s multiple comparison test. **, ***, indicate significant changes at the 0.01 and 0.001 levels, respectively; ns, not significant.
Table 3. Index of nutrition quality of seven nutrients in different pepper cultivars.
Table 3. Index of nutrition quality of seven nutrients in different pepper cultivars.
N Application RateCultivarIndex of Nutrition Quality
CaMgFe Mn Zn CuVC
N0Xin xiang #80.30.72614166.97.1
King0.30.6312119108.3
Strip Pepper #280.40.7282212124.9
Er jing tiao0.30.7342416137.0
Red Pepper #4250.30.7222012106.9
OPT-NXin xiang #80.30.53215179.17.3
King0.40.6372326128.2
Strip Pepper #280.40.7351915105.0
Er jing tiao0.40.6432317145.9
Red Pepper #4250.30.52615169.55.8
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Tian, Y.; Wang, J.; Chen, J.; Yu, D.; Zeng, Z.; Fu, J.; Zhang, F.; Cao, H.; Liu, F.; Liang, T. Effects of Integrated Management Strategies on Pepper Yield and Quality: A Study of Cultivation and Nutrient Management Practices. Agronomy 2024, 14, 2754. https://doi.org/10.3390/agronomy14122754

AMA Style

Tian Y, Wang J, Chen J, Yu D, Zeng Z, Fu J, Zhang F, Cao H, Liu F, Liang T. Effects of Integrated Management Strategies on Pepper Yield and Quality: A Study of Cultivation and Nutrient Management Practices. Agronomy. 2024; 14(12):2754. https://doi.org/10.3390/agronomy14122754

Chicago/Turabian Style

Tian, Yiming, Junjie Wang, Juan Chen, Duan Yu, Zhen Zeng, Jian Fu, Fen Zhang, Hailin Cao, Fabo Liu, and Tao Liang. 2024. "Effects of Integrated Management Strategies on Pepper Yield and Quality: A Study of Cultivation and Nutrient Management Practices" Agronomy 14, no. 12: 2754. https://doi.org/10.3390/agronomy14122754

APA Style

Tian, Y., Wang, J., Chen, J., Yu, D., Zeng, Z., Fu, J., Zhang, F., Cao, H., Liu, F., & Liang, T. (2024). Effects of Integrated Management Strategies on Pepper Yield and Quality: A Study of Cultivation and Nutrient Management Practices. Agronomy, 14(12), 2754. https://doi.org/10.3390/agronomy14122754

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