Influence of anthocyanins in relation to nutrition, stomata and yield of purple cabbage (Brassica oleracea var. capitata f. rubra) nourished with market waste-based compost

Influência das antocianinas na nutrição, estômatos e produtividade do repolho-roxo (Brassica oleracea var. capitata f. rubra) adubado com composto à base de resíduos comerciais

Abstract

The high price of synthetic fertilizers, the continuous use of pesticides, and other related problems threaten Peru’s food security. The reason for the investigation was to study the influence of anthocyanins on the nutrition, stomata, and yield of purple cabbage fertilized with compost based on market waste (CBRM). The main objective was to determine the influence of anthocyanins in relation to nutrition, stomata, and the yield of purple cabbage fertilized with CBRM. It is based on applied methodology with an experimental approach; therefore, the Completely Randomized Block Design statistical model was employed, consisting of 3 blocks and 5 treatments: T₁ with 0, T₂ with 10, T₃ with 12, T₄ with 14, and T₅ with 16 t ha-1 of CBRM. 15 days after transplanting, we applied the treatments and evaluated physical characteristics such as plant height, purple cabbage head weight, commercial yield, and diameter. In leaves (nitrogen, potassium, phosphorus, calcium, magnesium, sulfur, molybdenum, iron, manganese, copper, zinc, boron, chlorides, and sodium), anthocyanins, and stomatal density. Total nitrogen and phosphorus input and profitability. The results determined that T₅ stood out in plant height with 39.21 cm, weight of a purple cabbage head with 814.3 g, commercial yield with 94.85 t ha⁻¹, and equatorial diameter with 15.51 cm. Total nitrogen input of 365.94 kg ha^-1 of nitrogen. Total phosphorus input of 796.27 kg ha^-1 of P₂O₅. Stomatal density of 691 stomata/mm². Profitability at 252.78%. T₄ stood out in nutrients with total nitrogen, potassium, phosphorus, iron, manganese, zinc, chlorides, sodium, and anthocyanin concentration with 122.65 mg/100 g in leaves. We concluded that T₅ excelled in calcium, magnesium, sulfur, boron, and stomatal density in leaves, which optimized transpiration, photosynthesis, carbohydrate formation and translocation, and other biochemical processes, generating a considerable concentration of anthocyanin that acted as a defense mechanism against nutritional and environmental stress and pests, resulting in higher yield.

Keywords:
compost; market waste; dosage; nutrients; anthocyanin; yield

Resumo

O alto preço dos fertilizantes sintéticos, o uso contínuo de pesticidas e outros problemas relacionados ameaçam a segurança alimentar do Peru. O objetivo da investigação foi estudar a influência das antocianinas na nutrição, estômatos e produtividade do repolho-roxo adubado com composto à base de resíduos comerciais (CBRM). O objetivo principal foi determinar a influência das antocianinas na nutrição, estômatos e produtividade do repolho-roxo fertilizado com CBRM. Baseia-se em metodologia aplicada com abordagem experimental; portanto, foi empregado o modelo estatístico de Delineamento em Blocos Completamente Casualizados, composto por 3 blocos e 5 tratamentos: T1 com 0, T2 com 10, T3 com 12, T4 com 14 e T5 com 16 t ha^-1 de CBRM. Quinze dias após o transplantio, foram aplicados os tratamentos e avaliadas características físicas como altura da planta, peso da cabeça de repolho-roxo, produtividade comercial e diâmetro. Nas folhas (nitrogênio, potássio, fósforo, cálcio, magnésio, enxofre, molibdênio, ferro, manganês, cobre, zinco, boro, cloretos e sódio), antocianinas e densidade estomática. Foram também quantificados o aporte total de nitrogênio e fósforo e rentabilidade. Os resultados determinaram que o T5 se destacou em altura da planta com 39,21 cm, peso de uma cabeça de repolho-roxo com 814,3 g, produtividade comercial com 94,85 t ha⁻¹ e diâmetro equatorial com 15,51 cm. Aporte total de nitrogênio de 365,94 kg ha^-1. Aporte total de fósforo de 796,27 kg ha^-1 de P₂O₅. Densidade estomática de 691 estômatos/mm². Rentabilidade de 252,78%. O T4 destacou-se em nutrientes, com concentração total de nitrogênio, potássio, fósforo, ferro, manganês, zinco, cloretos, sódio e antocianina, com 122,65 mg/100 g nas folhas. Concluímos que o T5 se destacou em cálcio, magnésio, enxofre, boro e densidade estomática nas folhas, o que otimizou a transpiração, a fotossíntese, a formação e translocação de carboidratos e outros processos bioquímicos, gerando uma concentração considerável de antocianina que atuou como mecanismo de defesa contra estresses nutricionais, ambientais e pragas, resultando em maior produtividade.

Palavras-chave:
Composto; resíduos comerciais; dosagem; nutrientes; antocianina; produtividade

1. Introduction

Currently, food security in Peru faces urgent challenges such as the increase in the prices of synthetic fertilizers, inadequate agricultural management, the continued use of chemical inputs in conventional agricultural activities, and other difficulties. All these factors have had a direct impact on the country's agricultural production, resulting in a significant increase in production costs over the last five years, which has led to a food and social crisis. In this regard, Pillaca-Medina (2018) mentions that food is one of the basic needs of every human being and that poverty and hunger are inextricably linked to food insecurity. For their part, Legua Cárdenas et al. (2023) state that Peru has faced adverse effects due to the increase in fertilizer prices, which have risen by more than 25% compared to previous years.

It is worth mentioning that within the country, the dependence on synthetic fertilizers has had negative effects on the economy and the health of communities. The lack of access to affordable chemical inputs has caused food crises and debt, as this shortage has hampered production. This crisis has also related to the nutritional deficiency of available food, which affects the health of the population and worsens food quality in Peru. Nacimento (2024) mentions that Peru is experiencing an agricultural crisis generated by several factors, including the conflict between Russia and Ukraine, which has led to a global shortage of fertilizers, thus affecting food production in Peru and jeopardizing food security. Chávez-Miguel et al. (2024) state that in Peru, the effects of the crisis led to disinvestment and low incomes, decreased production, increased food insecurity, and abandonment of agricultural land.

Due to this situation, it is necessary to innovate in alternatives such as the use of waste generated in the markets of the province of Barranca, which generate an excessive average of 6 tons per month and often do not have adequate final disposal. Ramírez (2018) supports this statement by noting that Barranca generates approximately 6.29 tons of waste each month, which amounts to a total of 188.02 tons per year. Given this situation, CBRM production presents itself as a sustainable and feasible option, since it incorporates beneficial microorganisms that improve the availability mechanisms for greater absorption of nutrients such as nitrogen, phosphorus, potassium, and other elements, which optimizes biochemical reactions, as in the case of purple cabbage. In this regard, Ipanaqué (2023) states that the CBRM has a moisture content of 10.82%, 12.93% organic matter, 1.06% nitrogen, 2.17% P₂O₅, 0.65% K₂O, 1.81% CaO, 1.30% MgO, and a C/N ratio of 7.07. Furthermore, Aguilar-Paredes et al. (2023) mention the importance of the microorganisms present in compost, which maintain and multiply beneficial microbial consortia and their functions in the soil ecosystem, promoting sustainable and resilient agriculture.

It is important to mention that fertilization with CBRM increases nutrient availability, which improves their absorption by purple cabbage and contributes to optimizing biochemical reactions, such as photosynthesis, carbohydrate biosynthesis, and translocation to the vegetable's reserves. These nutrients also influence the increase in anthocyanin concentration, which strengthens resistance to nutritional, environmental, and pest stress, and reduces reactive oxygen species (ROS), thus improving plant physiology. According to Yassen et al. (2018), the application of vermicompost increased the growth and yield of Roselle plant sepals, as well as their chemical composition (nitrogen, phosphorus, potassium, zinc, anthocyanin percentage, and total carbohydrates), compared to the control. For its part. Likewise, Savy et al. (2022) state that plants treated with compost showed a higher content of metabolites involved in modulating the response to saline stress, such as molecules related to energy transfer and precursors of ROS scavenging compounds.

On the other hand, the use of CBRM in purple cabbage not only reduces production costs and pollution. It also improves the development characteristics, yield, and anthocyanin concentration, resulting in an organic vegetable. Furthermore, the application of this fertilizer benefits health and nutrition and strengthens disease prevention for the consumer. In this regard, El-Mogy et al. (2024) point out that the combined application of biochar, vermicompost, and compost constitutes a promising technique for improving the growth, nutrition, yield, and quality of pepper fruits while reducing nitrate concentration. Alam et al. (2021) state that anthocyanins, which are water-soluble natural pigments from the flavonoid family, are found in the red, blue, and purple colors of leaves, flowers, and fruits, and that their health benefits have been demonstrated, such as antioxidant, antidiabetic, anti-inflammatory, anti-obesity, antihypertensive, and anticancer properties.

For this reason, the influence of anthocyanins on the nutrition, stomata, and yield of purple cabbage (Brassica oleracea var. capitata f. rubra) fertilized with CBRM was investigated. The main objective was to determine the influence of anthocyanins on the nutrition, stomata, and yield of purple cabbage grown with CBRM. For this purpose, the statistical model of completely randomized block design employed consisted of three blocks and five treatments, including the standard dose and the control.

2. Methodology

2.1. Type of research

The study employs applied research with an experimental approach. After continuously evaluating the experiment samples and processing the data through statistical analysis, the appropriate dose was determined to optimize both yield and anthocyanin concentration in the red cabbage crop. This result will serve as a technical recommendation for local farmers.

2.2. Population

It refers to purple cabbage plants that are cultivated at an altitude of between 50 and 150 meters above sea level. Therefore, the data obtained in this experiment are valid.

2.3. Sample

The sample consisted of 50% of the plants from each plot. We took these from the central twin furrows. They were marked to avoid the edge effect. Subsequently, the physical characteristics of the plants we evaluated, such as height, the weight of a purple cabbage head, the commercial yield, and the diameter of this vegetable.

2.4. Study factor

The CBRM dose was established based on soil analysis, the amount of fertilizer applied by farmers in the area (12–16 t ha^-1 for purple cabbage cultivation), and recommendations from other research. According to Hirzel and Salazar (2016), cabbage cultivation requires between 10 and 16 t ha^-1 of compost made from plant residues or a mixture of animal and plant by-products. Consequently, we set a standard dose of 14 t ha^-1 and applied it once. Table 1 details the CBRM doses used in each treatment.

Table 1
CBRM dosage per treatment.

Tratamientos	Dosis de CBRM (t ha-1)
T1	0
T2	10
T3	12
T4	14
T5	16

2.5. Determination of the standard CBRM dose

2.5.1. Calculation of arable soil layer Weight

The weight of the arable soil layer of the experimental area was determined by applying the soil weight per hectare Formula 1 presented by Muguruza (2024).

Formula for arable layer weight.

$\left[W.ha\right]=\left[\left(Depth\right)\left(AD\right)\left(Ha\right)\right]$ (1)

Where:

W. ha : Weight of the arable layer per hectare (3500 t ha^-1 of soil)

Depth : Depth of the arable layer (0.25 m)

AD : Apparent density (1.4 g/cm³)

Ha : Hectare (10000 m²)

2.5.2. Calculation of organic carbon.

We calculated the organic carbon by applying the Van Bemmelen formula (Vela et al., 2012).

Organic carbon Formula 2.

$\left[OC\right]=\left[\left(OM\right)\left(0.58\right)\right]$ (2)

Where:

OC: Organic carbon

OM: Organic matter (1.50%) (See Table 3) (INIA, 2025a)

Table 3
Soil analysis of the experimental area.

N° Lab.	EC 1:2:5 dS/m	pH 1:2:5	OM (%)	N (%)	P (ppm)	K (ppm)	CaCO3 (%)	Cation Exchange (mEq/100 g of soil)				CEC
								Ca	Mg	Na	K
080292-24	0.0344	7.83	1.50	0.07	16.70	155.08	0.01	7.17	1.81	0.97	0.39	10.34

• Source: INIA (2025a) "Soil Analysis".
• Note: OM = Organic matter.

2.5.3. Quantification of the Carbon-Nitrogen (C/N) Ratio

To determine the carbon-nitrogen ratio, we applied the following Formula 3.

C/N Ratio Formula.

$\frac{C}{N}=\frac{\left[\left(OM\right)\left(0.58\right)\right]}{N}$ (3)

Where:

OC: Organic carbon

OM: Organic matter (1.50%) (See Table 3) (INIA, 2025a)

N: 0.07% de N (nitrogen) (See Table 3) (INIA, 2025a)

C/N: Carbon/Nitrogen Ratio (12.43)

Based on the C/N ratio of 12.43, the nitrogen content in ppm of the soil was established. To do this, the indicator was set within the C/N ratio range corresponding to a value greater than 12, which is equivalent to 11.2 ppm (See Table 2).

Table 2
Conversion of total nitrogen to available nitrogen in relation (C/N).

C/N Ratio Range	Conversion factor from Total Nitrogen (T.N.) in percentage to Nitrogen in (ppm)
Greater than 12	11.2
10 to 12	140
Less than 10	225

• Source: Kass (1998).

After converting nitrogen to ppm, available nitrogen (ND) was calculated using the formula ND = 11.2 ppm of nitrogen multiplied by 0.07 of soil nitrogen (see Table 3) (INIA, 2025a), resulting in 0.784 ppm of ND. Subsequently, we projected this value using the weight of 3500 t ha^-1 of the arable layer, which resulted in a total of 2,744 kg ha^-1 of nitrogen available in the soil (NDS).

2.5.4. Calculation of the standard dose of CBRM in relation to nitrogen

We carried out this procedure as follows:

We took the recommended nitrogen dose for purple cabbage crop nutrition, equivalent to 240 kg ha⁻¹ (see Table 4) (INIA, 2025b). Then, we subtracted 2.744 kg ha⁻¹ of NDS from this value, which resulted in 237.256 kg ha⁻¹ of applied available nitrogen (NDA).

Table 4
Nutrient recommendations for growing purple cabbage.

Cultivation	Macronutrients
kg ha-1	N	P2O5	K2O
	240	100	140

• Source: INIA (2025b) "Nutritional Recommendation".

Next, we took the nitrogen content of the CBRM, which is 2.27% (see Table 5) (INIA, 2025c). We then continuously projected this amount for CBRM doses of 10, 12, 14, and 16 t ha⁻¹, resulting in 227, 272.4, 317.8, and 363.2 kg ha⁻¹ of nitrogen, respectively.

Table 5
Chemical analysis of the CBRM.

ID Sample	pH	EC dS/m	Humidity (%)	OM (%)	N (%)	P2O5 (%)	K2O (%)	CaO (%)	MgO (%)	C/N
CBRM	8.65	6.05	8.97	49.94	2.27	4.14	3.82	6.56	1.66	11.42

• Source: INIA (2025c) "Chemical analysis of fertilizer".

Finally, we took the 237.256 kg ha⁻¹ of NDA, which we obtained by subtracting the recommended nitrogen amount from the soil nitrogen amount. Then, we compared this value with the projected nitrogen from the CBRM doses, equivalent to 227, 272.4, 317.8, and 363.2 kg ha⁻¹. Consequently, we set 12 t ha⁻¹ of CBRM as the standard dose.

2.6. Determination of the amount of phosphorus in the soil

We carried out the procedures to determine the phosphorus in the soil as follows:

2.6.1. Calculation of arable soil layer Weight

To determine the amount of phosphorus in the soil, we used the arable layer weight formula presented by (Muguruza N, 2024).

Formula 4 for arable layer weight.

$\left[W.ha\right]=\left[\left(Depth\right)\left(AD\right)\left(Ha\right)\right]$ (4)

Where:

W. ha : Weight of the arable layer per hectare (3500 t ha^-1 of soil)

Depth : Depth of the arable layer (0.25 m)

AD : Apparent density (1.4 g/cm³)

Ha : Hectare (10000 m²)

2.6.2. Calculation of soil phosphorus amount

We determined the soil's phosphorus content from the amount indicated in the soil analysis. Using this data, we projected it in relation to the arable layer's weight. This method was presented by Bello and Pino (2000).

Formula 5 for soil phosphorus projection as a function of arable layer weight.

$$\left[WP\left(kgh{a}^{-1}\right)\right]=\frac{\left[W.ha\left(kgh{a}^{-1}\right)\right]\left[WPS\left(mg\right)\right]}{1kg}$$ (5)

Where:

WP: Phosphorus weight (58.45 kg ha⁻¹ of P₂)

W. ha: Weight of the arable layer per hectare (3500 t ha^-1 of soil)

WPS: Phosphorus weight in soil (16.70 mg kg^-1 of P₂) (See Table 3) (INIA, 2025a).

2.6.3. Calculation of Soil P₂O₅ Weight.

Next, we determined the amount of P₂O₅ in kilograms in the soil from the number of moles of P₂O₅ and P₂, and we projected it using the weight of P₂ in kilograms. Carrasco and Aguirre (2023) established this procedure.

Formula 6 for determining the weight (kg) of P₂O₅ in the soil.

$[W{P}_2{O}_5(kgh{a}^{-1})]=\frac{[Nmoles{P}_2{O}_5][WPkgh{a}^{-1}]}{[Nmoles{P}_2]}$ (6)

Where:

Weight of P₂O₅: Weight of P₂O₅ provided by the soil (133.87 kg ha⁻¹)

N moles P₂O₅: Number of moles of P₂0₅ (142 moles)

N moles P₂: Number of moles of P2 (62 moles)

WP : Phosphorus weight (58.45 kg ha⁻¹ of P₂)

2.7. Statistical analysis

2.7.1. Statistical analysis of purple cabbage physical characteristics

2.7.1.1. Analysis of variance

Once we obtained the data for physical characteristics like plant height, purple cabbage head weight, marketable yield, and cabbage diameter, we processed them using analysis of variance. This way, we determined whether there was statistical significance between treatments (F cal. > F tab. at 5% error) or not. In other words, we assessed if the CBRM application had an effect or not. We should note that we obtained the tabulated F values from Fisher's F distribution table, considering a 5% error level.

2.7.1.2. Duncan's test

After obtaining the data on the purple cabbage's physical characteristics, we processed them through Duncan's test with a 5% margin of error. This way, we were able to determine which treatment stood out compared to the others. In addition, the test classified and grouped the treatments by letters, which allowed us to determine if they were statistically homogeneous or if there were significant differences between them.

2.7.2. Statistical procedure to determine the total nitrogen input

We performed the procedure using the nitrogen content from the CBRM chemical analysis, which was 2.27% (see Table 5) (INIA, 2025c). We projected this amount of nitrogen at 0, 10, 12, 14, and 16 t ha^-1 of CBRM, obtaining 0, 227, 272.4, 317.8, and 363.2 kg ha^-1 of nitrogen, respectively. To each of these nitrogen amounts, we add the nitrogen from the soil to obtain the total contribution. Then, we correlated the obtained results with the anthocyanin concentration and the commercial yield. It is important to note that we ordered and arranged these results from highest to lowest in a table according to the treatment doses. Finally, these results allowed us to interpret and analyze how much of the total nitrogen input influenced the concentration of anthocyanins and the yield of purple cabbage (see Table 9).

Table 9
Total nitrogen supply in relation to anthocyanin and yield.

Treatment	CBRM Dosage (t ha-1)	Nitrogen in CBRM (kg ha-1)	Nitrogen in soil (kg ha-1)	Total nitrogen input (kg ha-1)	Anthocyanin concentration (mg/100 g)	Yield (t ha-1)
T5	16	363.2	2.74	365.94	88.19	34.85
T4	14	317.8	2.74	320.54	122.65	32.03
T3	12	272.4	2.74	275.14	85.40	30.00
T2	10	227.0	2.74	229.74	85.68	26.50
T1	0	0.0	2.74	2.74	91.83	18.92

• Note: The nitrogen concentration is 2.27%, which is equivalent to 227 kg of nitrogen per 10,000 kg of CBRM (See Table 5).

2.7.3. Statistical procedure to determine the total P₂O₅ input

For the statistical analysis of the total P₂O₅ input in relation to anthocyanin concentration and commercial yield (see Table 10), we performed the following steps: We took the phosphorus content from the CBRM analysis, which was 4.14% (see Table 5) (INIA, 2025c). We projected this amount for doses of 0, 10, 12, 14, and 16 t ha^-1 of CBRM, obtaining amounts of 414, 496.8, 579.6, and 662.4 kg ha^-1 of P₂O₅. We ordered this data, along with its corresponding anthocyanin concentrations and commercial yields, from highest to lowest with respect to the treatments. In this way, we were able to determine and analyze the influence of different amounts of phosphorus in relation to the anthocyanin concentration and the commercial yield of purple cabbage.

Table 10
Total phosphorus input in relation to anthocyanin and yield.

Treatment	CBRM Dosage (t ha-1)	P2O5 in CBRM (kg ha-1)	P2O5 in soil (kg ha-1)	Total P2O5 Input (kg ha-1)	Anthocyanin concentration (mg/100 g)	Yield (t ha-1)
T5	16	662.4	133.87	796.27	88.19	34.85
T4	14	579.6	133.87	713.47	122.65	32.03
T3	12	496.8	133.87	630.67	85.40	30.00
T2	10	414.0	133.87	547.87	85.68	26.50
T1	0	0.0	133.87	133.87	91.83	18.92

• Note: The concentration of P₂O₅ is 4.14%, which is equivalent to 414 kg of P₂O₅ per 10,000 kg of CBRM (See Table 5).

2.7.4. Statistical processing to determine the number of stomata

In this evaluation, we took a sample of fresh, undamaged leaves from each treatment. We selected the sample randomly, without repetition, and from any block. Then, we placed the leaf sample in the Quanta scanning electron microscope, where we observed it at a scale of 200 µm (micrometers). Next, we printed the image on an A4 sheet and calculated the scale corresponding to an area of 0.3141 mm² (see Table 12). In that area, we counted the stomata and then divided the resulting number by the projected area. We performed this procedure for all treatments, which allowed us to determine the number of stomata that influenced both the anthocyanin concentration and the commercial yield of the purple cabbage. Below, we detail the Formula 7 for stomatal density.

Table 12
Stomatal density in relation to anthocyanin and yield.

Quantification of stomata in leaves.	Treatments
	T1	T2	T3	T4	T5
Number of stomata/ 0.3141 mm2 (lens area).	145	162	170	183	216
Stomatal density (number of stomata/mm2).	461.6	515.8	541.2	582.6	690.9
Anthocyanin concentration (mg/100 g of matter).	91.83	85.68	85.40	122.65	88.19
Commercial yield (t ha-1).	18.917	26.500	30.000	32.034	34.850

• Note: The projected area of the micrograph is 0.3141 mm².

Formula for stomatal density.

$SD=\frac{NS}{LA}$ (7)

Where:

SD: Stomata density

NS: Number of stomata

LA: Lens area (0.3141 mm²)

2.8. Data collection techniques and instruments

2.8.1. Data collection techniques and instruments for cabbage characteristics

In data collection, we used observation and measurement techniques. We also used precision instruments, such as a digital scale, a measuring tape, and a caliper, to measure physical characteristics: plant height, the weight of the purple cabbage heads, commercial yield, and cabbage diameter. For the chemical analysis of the soil and the CBRM, we used materials from the INIA-Huaral laboratory. Regarding the nutrient analysis in red cabbage leaves, we used materials from the accredited laboratory of AGQ Peru SAC. For the analysis of anthocyanin concentration, we used materials from the IIN, while for the observation and quantification of stomata; we used the Quanta scanning electron microscope.

2.8.2. Techniques for determining anthocyanin concentration

To measure the concentration of anthocyanins in purple cabbage. We present the differential pH method. As described by Giusti and Wrolstad (2001), cited by Paredes (2018), it is possible to determine the total concentration of anthocyanins in leaves, detect the presence of pigments and other compounds using a buffer system, a blocking agent, and precision equipment such as UV-visible spectroscopy. Below, we show the Formula 8 proposed by Paredes (2018) to determine the concentration of anthocyanins in vegetables.

Formula for determination of anthocyanin concentration.

$\text{Monomeric anthocyanins}\left(\frac{mg}{100g}\right)=\frac{AxMMxFD}{ϵx1}x100$ (8)

Where:

A = Absorbance

MM = Molar Mass

FD = Dilution factor

ε = Molar absorptivity

2.8.3. Techniques for soil nutrient quantification

To determine the nutrient concentration of the soil in the experimental area, we used the following methods: for pH determination, we used method 9045D, and for waste, also. For organic matter, we applied the AS-07 techniques of Walkley and Black, which allowed us to quantify the nitrogen concentration in the soil. Regarding phosphorus concentration, we used the Olsen method. To determine the potassium concentration, we used calcium carbonate techniques (AS-29 acid neutralization method). Finally, for exchangeable cations (Ca, Mg, Na, and K), we performed the analyses using cation exchange capacity techniques, and for exchangeable bases, using ammonium acetate.

2.9. Experiment procedures

We made the compost from 25 kg of fruit, 25 kg of vegetables, 25 kg of seafood products, and 25 kg of dried grass, all of which were market waste. We put the materials in a plastic bag and covered them. Every two weeks, we turned the compost with a shovel and added water until the fourth month. The compost then presented the right conditions: no odor, a fluffy consistency, and a dark color.

We prepared the land in the conventional way, just as the farmers in the Supe Puerto district, in the province of Barranca, Lima, do. At that time, we used the zigzag method. This consisted of taking a soil sample from a depth of 0.25 meters using a shovel. Then, we piled it onto a blanket, where we mixed it until we obtained a representative 1 kg sample of soil. Finally, we took that sample to the INIA-Huaral laboratory for analysis.

To establish the seedbed, we consider certain aspects necessary, such as soil preparation and seed quality. We ensured that the seeds had a high germination rate, were intact, and were of varietal purity. We sowed the seeds evenly and broadcast. Then, on the fourth day, we performed a light watering. Fifteen days later, we performed the necessary cultural practices, including thinning and weed removal. Additionally, we constantly monitored key pests, which allowed us to control them immediately.

On November 30, 2024, 25 days after sowing in seedbeds, we carried out the transplant, taking into account the height of the purple cabbage plant, which was between 15 and 18 cm. Then, we disinfected using a solution of 4 g of Benomyl per liter of water. Next, we transplanted at a distance of 0.25 m between twin rows and 0.6 m on both sides of the rows. It is worth mentioning that the plot consisted of five treatments and three blocks: each treatment measured 2.5 m long by 1.2 m wide, and the space between rows was 0.5 m.

Afterwards, we water lightly once a week. Fifteen days after the transplant, we applied the CBRM doses indicated in Table 1. It is important to mention that we carried out the evaluations of the plant characteristics until harvest, which was on March 10, 2025, that is, 100 days after transplanting. Subsequently, we processed the collected data using statistical analysis.

Subsequently, we took representative 200 g samples of purple cabbage leaves from the five treatments, without repetition and from any block. We sent these samples to the AGQ Peru SAC and IIN laboratories to determine the concentration of nutrients and anthocyanins, respectively. Additionally, we also took samples of fresh, undamaged leaves to the Quanta scanning electron microscope, where we observed and quantified the stomata. The results of these analyses made it possible to understand the influence on yield.

Finally, we calculated profitability by projecting the costs and yield of each treatment per hectare. In this way, we obtained the production cost and the commercial yield. We multiplied this last quantity by the unit price of the purple cabbage, which resulted in the total revenue. Then, we subtract the total revenue minus the cost of production, and we divide the result by the cost of production; subsequently, we multiply it by 100 (see Table 13). Below, we show the profitability Formula 9.

Table 13
Profitability of purple cabbage according to CBRM doses.

Treatment	CBRM Dosage (t ha-1)	Commercial yield (kg ha-1)	Unit value (kg)	Income Totals ($)	Production cost ($)	Profit ($)	Profitability (%).
T1	0	18917.00	0.45	8525.97	2904.68	5621.30	193.53
T2	10	26500.00	0.45	11943.66	3872.00	8071.66	208.46
T3	12	30000.00	0.45	13521.13	4065.46	9455.66	232.59
T4	14	32034.00	0.45	14437.86	4258.93	10178.93	239.00
T5	16	34850.00	0.45	15707.04	4452.39	11254.65	252.78

• Note: The price of dollar is equivalent to S/. 3.54 Soles.

Profitability formula.

P$=\frac{Pf}{PC}*100$ (9)

Where:

P : Profitability

Pf : Profit

PC : Production cost

3. RESULTS

3.1. Soil analysis of the experimental area

After analyzing the soil sample at INIA-Huaral, Table 3 indicates that the pH is within normal values and that, the electrical conductivity (EC) indicates a low salt content. We observed that organic matter and nitrogen remain at low levels, while phosphorus shows a slight increase and potassium presents adequate levels, according to Prialé (2016). Regarding the cation exchange elements (calcium, magnesium, sodium, and potassium), they are within normal ranges, but the cation exchange capacity (CEC) shows that it is slightly low, according to the ranges of McKean (1993). Therefore, the soil is suitable for growing purple cabbage. However, we must apply organic matter in the form of compost to improve its properties.

Regarding nutritional recommendations, we observe that we require a greater amount of nitrogen relative to the other elements. We also mentioned that we took into account the amount of 240 kg ha^-1 of nitrogen to determine the standard dose of the CBRM (see Table 4).

3.2. Chemical analysis of the CBRM

In the chemical analysis of the CBRM detailed in Table 5, we determined that the concentration of organic matter is low, which we relate to the low concentration of nitrogen. We also observed the low concentration of phosphorus and potassium. Regarding the carbon-nitrogen ratio, it indicates that it is within the appropriate values. We support this result with Román et al. (2013), who mention that the parameters of suitable compost are a pH of 6.5 to 8.5, humidity of 50 to 60%, organic matter of 50 to 70%, nitrogen of 1 to 2%, phosphorus of 0.1 to 1%, potassium of 0.3 to 1%, and a carbon ratio of 10 to 15:1. Therefore, the CBRM is within the appropriate ranges for the nutrition of purple cabbage.

Analyzing the CBRM indicated in Table 6, we determined that the concentration of all microelements is lower, although in the case of manganese the data are close. We compared this data with that of other fertilizers made from market waste. According to Romero (2024), the fertilizer produced from market waste showed concentrations of 456.32 ppm of iron, 511.92 ppm of zinc, 66.79 ppm of copper, and 3.27 ppm of manganese. Consequently, although the CBRM showed lower values of these micronutrients, we found that it is favorable for the development of purple cabbage cultivation.

Table 6
Concentration of microelements in the CBRM.

Elements	Fe	Zn	Cu	Mn
Quantity (mg kg-1)	382.20	215.43	33.25	2.81

• Source: INIA (2025d) "Concentration of microelements in the CBRM".

3.3. Physical characteristics of purple cabbage

By processing the data on the physical characteristics of purple cabbage using analysis of variance and the Duncan test, with a 5% error level, we determined that there was no significant difference between the treatments. In addition, we classified and grouped the data using letters (a, b). We interpret these results as an indication that the application of CBRM did not have a dose effect on the assessments and that there were no statistical differences between treatments; however, T₅ stood out compared to the others (see Table 7) and (Figure 1).

Table 7
Physical characteristics of the red cabbage crop by treatment.

Treatment	CBRM Dosage (t ha-1)	Plant height (cm)	Weight of a head of purple cabbage (g)	Commercial yield (t ha-1)	Equatorial diameter (cm)
T5	16	39.213 a	814.3 a	34.850 a	15.509 a
T4	14	37.854 a	721.6 a	32.034 ab	15.000 a
T3	12	36.124 a	683.2 a	30.000 ab	14.394 a
T2	10	35.564 a	548.8 a	26.500 ab	14.031 a
T1	0	34.624 a	510.2 a	18.917 b	13.842 a
Coefficient of variation (%)		8.57	38.30	24.17	12.07
Significance		N.S.	N.S.	N.S.	N.S.

• Note: Not significant (N.S.) and significant (S.). The letter grades (a) and (ab) obtained through the Duncan test mean that there is a homogeneous relationship between the treatments.

Figure 1
Comparison of the development of red cabbage according to the doses of CBRM.

3.4. Nutrient concentration in leaves

Following the analysis of nutrients in purple cabbage leaves carried out by AGQ Perú SAC, we observed that T₄ excelled in most elements, such as total nitrogen, potassium, phosphorus, iron, manganese, zinc, chlorides, and sodium. However, we determined that these amounts of nutrients did not influence higher yields. In contrast, the T₅ showed that elements such as calcium, magnesium, sulfur, and boron contributed to a considerable concentration of anthocyanin, which we correlated with higher yield (see Table 8). Therefore, we interpret that a higher dose of CBRM favors a considerable concentration of anthocyanins, which we associate with the higher yield of the crop.

Table 8
Concentration of nutrients in the leaves according to the CBRM doses.

Elements	T1	T2	T3	T4	T5	Normal ranges according to AGQ Peru SAC (2025)
Macronutrients (%)
Total Nitrogen	1.70	2.20	2.60	3.10	2.50	3.60 – 5.00
Potassium	1.60	1.78	1.81	2.04	1.46	3.00 – 5.00
Phosphorus	0.126	0.153	0.174	0.230	0.160	0.330 - 0.750
Calcium	3.19	3.70	3.57	3.63	5.17	1.10 – 3.00
Magnesium	0.288	0.325	0.297	0.349	0.430	0.400 – 0.750
Sulfur	1.47	2.13	1.97	1.55	2.51	0.30 – 0.75
Micronutrients (mg kg-1)
Molybdenum	2.57	4.25	4.66	2.88	3.66
Iron	170	220	202	321	248	30.0 - 200
Manganese	31.9	46.7	53.3	53.9	50.4	25.0 - 200
Copper	4.55	4.74	10.70	9.53	3.86	5.00 – 15.00
Zinc	16.4	21.7	26.4	31.7	17.6	20.0 – 200
Boron	60.3	64.4	70.5	58.9	85.4	25.0 – 75.0
Phytotoxic elements (%)
Chlorides	0.226	0.366	0.436	0.557	0.468
Sodium	0.499	0.374	0.274	0.641	0.619

• Source: AGQ Peru SAC (2025) "Nutrient analysis in red cabbage leaves".

3.5. Total nitrogen contribution in relation to anthocyanin

Regarding the total nitrogen contribution related to anthocyanin concentration, T₅ stands out with a contribution of 365.94 kg ha^-1, representing a 99.25% difference compared to the nitrogen contribution of T₁, which is 2.74 kg ha^-1. This amount of nitrogen contributed to a higher yield of 34.85 t ha^-1 of purple cabbage, which, in turn, slightly increased the anthocyanin concentration to 88.19 mg/100 g. Therefore, we interpret that a higher dose of CBRM added a nitrogen contribution of over 99% to the crop, which we associate with a higher yield and a considerable concentration of anthocyanin (see Table 9).

3.6. Total P₂O₅ input in relation to anthocyanin and yield

Regarding the total phosphorus contribution in relation to anthocyanin and yield, we detail it in Table 10. We observed that T₅ stood out with 796.27 kg ha^-1 of P₂O₅ contribution, representing a difference of 83.18% compared to treatment T₁, which contributed 133.87 kg ha^-1 of P₂O₅. This amount of nutrient influenced the higher yield of purple cabbage (34.85 t ha^-1) and the increase in anthocyanin concentration. Therefore, we interpret that a higher dose of CBRM contributed to a greater supply of phosphorus, which we associate with a higher yield and a higher concentration of anthocyanin.

3.7. Anthocyanin concentration in purple cabbage leaves

Analyzing the anthocyanin concentration in purple cabbage leaves shown in Table 11, we determined that T₄, with 122.65 mg of anthocyanin per 100 g of matter, differs by 25.12% from T₁, with 91.83 mg of anthocyanin per 100 g of matter. However, we observed that this concentration did not influence yield, since T₅, with 88.19 mg of anthocyanin per 100 g of matter, obtained a yield of 32.034 t ha^-1. Therefore, we interpret that a higher dose of CBRM leads to a considerable concentration of anthocyanin, which strengthens the plant against stress factors and allows us to obtain a higher yield as a response.

Table 11
Concentration of anthocyanins in leaves in relation to yield.

Treatment	CBRM Dosage (t ha-1)	Anthocyanin concentration (mg/100 g matter)	Commercial yield (t ha-1)
T1	0	91.83	18.917
T2	10	85.68	26.500
T3	12	85.40	30.000
T4	14	122.65	32.034
T5	16	88.19	34.850

• Source: IIN (2025) "Anthocyanin Concentration Test Report".

3.8. Quantification of stomatal density in leaves

Regarding the quantification of stomata in leaves, detailed in Table 12, we observed that T₅, with 691 stomata/mm², shows a 33.18% difference compared to T₁, with 462 stomata/mm². This result shows that increasing the dose of CBRM leads to an increase in the number of stomata, which we relate to a considerable increase in anthocyanin and, consequently, to a higher yield of purple cabbage. Therefore, we interpret the greater number of stomata as an indicator, since we associate it with a considerable concentration of anthocyanin and, consequently, with a higher yield.

3.9. Profitability per treatment

Regarding the economic analysis, T₅, with 252.78%, stood out from the others, showing a difference of 23.49% compared to T₁, which reached 193.53% (see Table 13). We interpret this result as meaning that, with a higher dose of CBRM, the value increased by approximately almost a quarter compared to the control. Likewise, we obtain a profit exceeding 2.5 times the initial investment. This benefits the local farmer.

4. DISCUSSION

4.1. Physical characteristics of purple cabbage

After processing the data on the physical characteristics of the purple cabbage using an analysis of variance, we determined that there were no significant differences between the treatments; that is, the comparison between them showed no statistical differences in development and yield, although we should also note that T₅ stood out compared to the others (see Table 11). We analyzed these results as follows: Increasing the dose of CBRM along with the addition of nutrients and microorganisms such as Bacillus subtilis and Oceanobacillus, among others, improved nutrient availability and absorption by the plant and optimized photosynthesis, carbohydrate formation and translocation, and other biochemical reactions. This strengthened the plant against environmental, nutritional, and pest stress factors, resulting in higher quality and yield. These results coincide with those of Liu et al. (2022), who mention that the use of biocompost enriches the soil with beneficial microorganisms (such as Sphingomonas, Acidibacter, Streptomyces, Oceanobacillus, etc.) and reduces harmful microorganisms (such as Stachybotrys and Aspergillus), thus improving conditions for the plant. Similarly, Supriyono et al. (2021) state that the use of organic fertilizer provided nutrients, improving biochemical reactions such as photosynthesis, which produced more carbohydrates and proteins; these carbohydrates were translocated to the tillers, leaves, and roots of the red ginger, increasing fresh weight. Finally, Imrán and Ortas (2025) state that the use of organic matter in the soil fosters a thriving microbial community, boosting agricultural productivity and soil fertility; this is vital for maintaining a healthy soil ecosystem, promoting nutrient cycling, and suppressing disease.

4.2. Nutrient concentration in leaves

Analysis of the nutrients in the purple cabbage leaves determined that T₄ stood out in most elements, such as total nitrogen, potassium, phosphorus, iron, manganese, zinc, chlorides, and sodium. In contrast, T₅, which excelled in calcium, magnesium, sulfur, and boron, contributed to a considerable concentration of anthocyanin, which we associate with higher yield (see Table 8). We analyze this result as follows: A higher dose of CBRM highlighted the calcium, magnesium, sulfur, and boron elements in the leaves. Calcium strengthens cell walls, magnesium is essential for photosynthesis, sulfur is fundamental in protein synthesis, and boron regulates key enzymes for anthocyanin production. This process optimized biochemical reactions and strengthened the plant's resistance to stress, resulting in a higher yield. According to El-Hadidi et al. (2017), calcium is essential for plants to absorb nutrients; it promotes the proper functioning of plant cells, strengthens the cell wall structure, forming calcium pectate compounds that provide stability, participates in hormonal enzymatic processes, and protects the plant. Furthermore, Cakmak and Yazici (2010) mention that magnesium's participation in metabolic processes depends on its activating function in numerous enzymes, such as ribulose-1,5-bisphosphate (RuBP) carboxylase, which is essential in photosynthesis. In addition, Za et al. (2017) found that anthocyanins in grapes showed a positive correlation only with the boron and potassium content in the petiole, while other nutrients in the soil and petiole did not have a significant relationship with total anthocyanin. Finally, Narayan et al. (2023) mentions that, in plants, sulfur and its compounds participate directly or indirectly in the management of biotic and abiotic stress, in metabolism and signaling, and are important for development.

4.3. Total nitrogen contribution in relation to anthocyanin

Table 9 highlights the total nitrogen contribution of T₅, which registered 365.94 kg ha^-1 and exceeded the control by 99.25%; this greater amount of nitrogen promoted a considerable concentration of anthocyanin, resulting in a higher yield of purple cabbage. We analyzed this result based on a higher dose of CBRM, which added nutrients such as nitrogen and beneficial microorganisms to the soil. This favored nitrogen availability for greater plant absorption and optimized essential biochemical reactions such as transpiration, photosynthesis, carbohydrate formation and translocation, nucleic acid synthesis, and nutrient fixation mechanisms. All these processes are essential for tissue development and other functions, strengthening the plant against nutritional, environmental, and pest stress. These findings coincide with Cruz Nieto et al. (2025), who determined that treatment T₅, with 12 t ha^-1 of bleaching earth compost, contributed 255.1 kg ha^-1 of nitrogen, exceeding the control by 86.55%, which significantly increased the anthocyanin content to 62.86 mg/100 g. Furthermore, Numan et al. (2018) mention that plant growth-promoting bacteria produce regulators such as siderophores, which fix nitrogen and solubilize phosphate, which is important for compensating for salinity stress. Finally, Wang et al. (2025) point out that the addition of compost promotes the biosynthesis of foliar hormones such as indole-3-acetic acid (IAA) and abscisic acid (ABA), known to improve photosynthesis and reduce transpiration.

4.4. Total P₂O₅ input in relation to anthocyanin and yield

Regarding the total contribution of P₂O₅ in relation to anthocyanin and yield, Table 10 indicates that T₅ stood out with 796.27 kg ha^-1 of P₂O₅, which differs by 83.18% from T₁, which contributed 133.87 kg ha^-1; this amount of phosphorus influenced the considerable increase in anthocyanin, which, in turn, we associate with the higher yield of purple cabbage. We analyzed this result based on the higher dose of CBRM, since we added nutrients such as phosphorus and beneficial microorganisms, which contributed to improving the plant's nutritional availability. This element formed phosphate compounds that served as an energy source, optimizing photosynthesis reactions, carbohydrate formation and translocation, and improving nutrient absorption mechanisms. Although the environmental conditions caused a physiological response that considerably increased the concentration of anthocyanin, which acts as a defense mechanism. Therefore, this amount of phosphorus strengthens the plant against nutritional and environmental stress, resulting in a considerable level of anthocyanin associated with higher yield. In this sense, Bohórquez-Sandoval et al. (2024) mention that phosphorus-solubilizing microorganisms (bacteria and arbuscular mycorrhizal fungi) determine the availability of phosphorus in both soil and organic waste, being specifically responsible for solubilizing or mineralizing it. Also, Khan et al. (2023) state that phosphorus is essential as a regulator in the activation of physiological responses to abiotic stress, highlighting its influence on critical processes such as root system architecture, nutrient absorption, photosynthetic activity, and stomatal regulation. On the other hand, Henry et al. (2018) point out that phosphorus restriction can improve anthocyanin concentrations, resulting in darker red foliage; however, these concentrations can increase with reduced or restricted phosphorus, as evidenced in 'Salanova Red' lettuce.

4.5. Anthocyanin concentration in purple cabbage leaves

When analyzing the anthocyanin concentration in purple cabbage leaves, we determined that T₄, with 122.65 mg/100 g, differs by 25.12% from T₁, which registered 91.83 mg/100 g. However, this concentration did not influence yield, since T₅, with 88.19 mg/100 g of anthocyanin, obtained a higher yield of 34.85 t ha^-1 of purple cabbage (see Table 11). We analyzed this result as follows: a higher dose of CBRM improved nutrient availability in the soil, which optimized plant uptake and biochemical reactions, and produced a considerable increase in anthocyanin that influenced the higher yield. However, this considerable concentration of anthocyanin acted as a defense mechanism against stress from temperature variations, nutritional deficiencies, the presence of pests, and oxidative stress, which strengthened the plant for higher yields. In this regard, Papafotiou et al. (2007) mention that anthocyanin production seems to be related to the accumulation of excess carbohydrates, viral or fungal infection, treatment with growth regulators, wounds, temperature, and light. Meanwhile, Cruz Nieto et al. (2025) determined that treatment T5, with 12 t ha^-1 of compost based on bleaching earth, highlighted elements in the leaves of purple lettuce such as phosphorus, sulfur, molybdenum, manganese, copper, zinc, and boron; although these did not influence a higher concentration of anthocyanin (62.86 mg/100 g), they did contribute to a higher crop yield.

4.6. Quantification of stomatal density

Regarding the quantification of stomata in leaves in relation to anthocyanin and the yield of purple cabbage, we highlight T₅, with 691 stomata/mm², differing by 33.18% compared to T₁, which registered 462 stomata/mm² (see Table 12 and Figure 2). We analyzed this result as follows: a higher dose of CBRM added nutrients to the soil, which improved their availability for absorption by the plant. These nutrients increased stomatal density, which optimized transpiration and favored gas exchange, photosynthesis, carbohydrate formation and translocation to the plant's reserves, and other biochemical reactions. Furthermore, these physiological processes generated a considerable increase in anthocyanin, which acted as a defense mechanism under the climatic conditions of the area. Therefore, we took this number of stomata as an indicator, since it contributed to the increase in anthocyanin, which strengthened the plant against stress, and this was associated with a higher yield. In this regard, Zahara et al. (2021) mention that the application of manure resulted in the largest stomatal area on both sides of the leaf surface, which produced a significant response in the net photosynthetic rate and stomatal conductance of some plants. Furthermore, Li et al. (2022) highlight that stomata play a vital role in the gaseous and water exchange of leaves, while Shahinnia et al. (2016) describe them as specialized foliar epidermal cells responsible for regulating the photosynthetic uptake of CO₂ and water loss through transpiration. For their part, Álvarez-Holguín et al. (2018) mention that the characteristics of stomata and their concentration can be determining factors in the differences in biomass production. Finally, Iffah Hazirah et al. (2017) state that, despite having the lowest anthocyanin content among all species, H. camargoana has the highest number of stomata per unit area, while H. rigidofolia has the lowest.

Figure 2
Micrographs of purple cabbage stomata by treatment. Source: UNJFSC (2025) "Micrographs of stomata".

4.7. Economic profitability

Regarding economic profitability per treatment, Table 13 indicates that T₅ stood out with 252.78%, differing by 23.49% from T₁, which obtained 193.53%. We analyzed this result based on the highest dose of CBRM, since its difference from the control reached almost a quarter. It is worth noting that the application of this dose of CBRM generated a return of more than 2.5 times the investment, making the use of this fertilizer profitable. Therefore, we recommend that farmers in the area apply this dose of CBRM for growing purple cabbage.

5. Conclusion

We determined that T₄, with 122.65 mg/100 g, showed the highest concentration of anthocyanin. However, T₅, with 88.19 mg/100 g of anthocyanin, contributed to a higher yield of 34,850 t ha^-1 of red cabbage. Therefore, the higher dose of CBRM added nutrients to the soil, improving their availability for greater nutrient absorption, which optimized photosynthesis, carbohydrate formation, and translocation to the plant's reserves. These biochemical reactions, along with the climatic conditions, favored a considerable increase in the concentration of anthocyanin associated with the higher yield.

We also determined that T₄ excelled in most elements, such as total nitrogen, potassium, phosphorus, iron, manganese, zinc, chlorides, and sodium. On the other hand, T₅, which contains calcium, magnesium, sulfur, and boron, contributed to a considerable concentration of anthocyanin, which we associate with higher yield. Therefore, the aforementioned elements of the highest dose influenced and promoted the reinforcement of the cell wall, photosynthesis, carbohydrate formation, and anthocyanin concentration, which strengthened the plant against nutritional, environmental, and pest stress, resulting in a higher yield.

Finally, we determined that T₅ presented the highest stomatal density, with 691 stomata/mm², which influenced a considerable concentration of anthocyanin associated with the yield of red cabbage. Therefore, we took the highest stomatal density as a key indicator, as it contributed to optimizing transpiration, photosynthesis, carbohydrate formation and translocation to reserves, and other biochemical reactions. These processes generated an increase in anthocyanins and, in the climatic conditions of the area, strengthened the plant against nutritional, environmental, and pest stress, which resulted in a higher yield.

• Data Availability Statement
  The entire data set supporting the results of this study was published in the article itself.

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Edited by

• Editor:
  Takako Matsumura Tundisi

Data availability

The entire data set supporting the results of this study was published in the article itself.

Publication Dates

• Publication in this collection
  06 Mar 2026
• Date of issue
  2026

History

• Received
  03 Aug 2025
• Accepted
  06 Jan 2026