Organomineral Fertilizer in Planting of Potato Cultivars Ágata and Atlantic

Abstract

Given the importance of potatoes in Brazilian agribusiness and the need to establish sustainable production systems, interest has increased in the implementation of more efficient fertilization methods for the cultivation. Thus, the objective of this study was to evaluate the response of the cultivars Ágata and Atlantic to fertilization with a pelleted organomineral source in comparison to conventional fertilization performed with a mineral source. A causal block design was used with five treatments [100% of the recommendation for fertilization with mineral sources 03-35-06; and 100%, 80%, 60%, and 40% of the recommended dose with organomineral fertilizer (02-20-05)] in four replications, totaling 20 plots. The application of the organomineral in plant fertilization can be an interesting source of fertilizer for the cultivation of Ágata and Atlantic potatoes and can be applied with dose adjustments. For the cultivar Ágata, the doses of 100% and 80% organomineral fertilizer together with mineral fertilization resulted in the highest total yields. The lower doses (60% and 40%) made it possible to obtain a higher percentage of special potatoes, considered to be of the highest commercial value, than 80% of the organomineral fertilizers and 100% mineral standard. For the Atlantic cultivar, the total yield responses to organomineral were like those obtained with exclusively mineral fertilization. These findings indicate that organomineral fertilizers can be used efficiently with adjusted doses, maintaining productivity and tuber quality while potentially reducing fertilizer input costs and environmental impacts, contributing to more sustainable potato cropping systems.

1. Introduction

The potato (Solanum tuberosum L.) is an annual nightshade that represents one of the main vegetables produced in Brazil [1]. A large part of potato production is intended for fresh consumption, and the main potato to cultivate for this purpose is cv. Ágata. On the other hand, cultivars that are intended for the industrial sector and are processed in the form of chips, such as the Atlantic cultivar, stand out. The differences between the cultivars reflect specific nutritional and physiological demands, which makes it relevant to evaluate the performance of both under different sources and doses of fertilization. Regardless of cultivar, potatoes are intensive crops that are characterized by a short cycle, delicate and superficial root system, high yields per area, and consequently high nutrient requirements.

Thus, fertilization represents one of the main stages of crop management because, in addition to directly impacting the productivity and final quality of tubers, it also affects the maintenance of soil health. Owing to these particularities, it is common to use high doses of chemical fertilizers to supply nitrogen, phosphorus, and potassium. However, the application of large quantities of these fertilizers does not result in significant increases. On the contrary, negative effects have been observed, both in terms of the cost of production and the sustainability of the soil and water [2,3].

In this context, organomineral fertilizers have emerged as a promising alternative, as they combine the immediate nutrient availability of mineral fertilizers with the gradual release and soil-conditioning benefits of organic matter. These formulations can reduce nutrient losses through leaching, particularly for nitrogen and phosphorus, while improving the soil’s cation exchange capacity and water retention. Additionally, the organic fraction supports microbial activity, enhancing nutrient cycling and soil health. Such improvements are particularly relevant in potato cropping systems, which are nutrient-intensive and susceptible to environmental degradation from excessive mineral fertilizer use. Therefore, evaluating the performance of organomineral fertilizers compared to mineral sources is essential for developing more sustainable and efficient fertilization strategies [4,5].

Potatoes are among the commercial crops with the highest consumption of fertilizers per hectare, reaching a much higher relative demand (approximately 6 times greater) than that required by other crops normally used for rotation, such as soybeans, corn, and beans [2]. To optimize potato fertilization practices, increasingly sustainable management is required which includes the application of more technological fertilization sources that contain organic matter [3].

Brazil is one of the largest producers of sugarcane (Saccharum officinarum L.) in the world [6]. Given the importance, scope, and volume of production of the crop, significant amounts of waste are also produced by the sugar and alcohol sector, highlighting the need to efficiently reuse all this material generated in industrial processes [7].

Filter cake comes from the treatment and clarification of sugarcane juice and is composed of a mixture of ground bagasse and settling sludge. This is a waste produced in abundance, with each ton of ground sugarcane generating around 40 kg of filter cake [7]. Approximately 30% of the phosphorus present in the filter cake is in organic form and the N is in protein form, which makes the release of these elements highly utilized by plants. In addition to the increase in cation exchange capacity, there is an increase in water retention capacity and improvements in the microbiological conditions of the soil and, consequently, in the development of plants [8].

Given all these positive characteristics of the filter cake, this type of waste has gained a lot of space and means of reuse, which include fertilizer management techniques within the sugarcane plantations themselves and also in other forms, such as in the composition of organomineral fertilizers [9]. According to Borges et al. [10], the use of waste for the production of fertilizers can immediately eliminate 50% of the environmental liabilities generated by them.

In this sense, organomineral fertilizers bring together interesting qualities that meet the nutritional needs of the crop while conditioning the soil through the benefits in physical, chemical, and microbiological properties offered by the organic fraction of the fertilizer [11]. Although the use of organomineral fertilizers in potatoes has already been addressed in previous studies, such as that of [12], these studies have generally focused on a single cultivar and on organic sources of animal origin, such as chicken manure. In view of the needs of the crop in relation to the adoption of more efficient and sustainable fertilization techniques and the possibilities that the fertilizer industry has offered through organominerals, the objective of this work was to evaluate the productivity and quality of the tubers and the nutritional aspects as a function of doses of organomineral fertilizer compared to with those of mineral fertilizer, in the potato cultivars Ágata and Atlantic.

2. Materials and Methods

2.1. Site and Soil Characterization

The experiment consisted of two trials conducted simultaneously from June to October 2017 (118-day cycle) at Cristalina-GO (latitude of 16°5′56″ S, longitude of 47°30′55″ W and altitude of approximately 1000 m). In one of the experiments, the cultivar Ágata was used and in the other, the cultivar Atlantic.

The climate of the region is classified as high-altitude tropical (Cwa type according to Köppen and Geiger) with a dry winter and a hot, rainy summer. The soil at the experimental site is of the Ferralsol dystic clayic (WRB). Before planting, sampling was carried out in the 0–20 cm layer and chemical characterization was carried out according to the method described by Embrapa [13] (

Table 1. Chemical characterization of the soil, before planting, at the depth of 0–20 cm.

Water pH (1:2.5)	pH CaCl2	P meh−1	K	S	Ca2+	Mg2+	Al3+	H + Al	CEC
		mg dm−3			cmolc dm−3
5.80	5.27	9.76	116.71	10.63	3.24	1.16	<0.13	5.52	10.23
O.M	BS	Al(sat)	B	Zn	Fe	Mn	Cu	SB
g kg−1		mg dm−3					cmolc dm−3
30.29	45.75	0	0.67	11.41	41.12	19.77	0.92	4.70
CaMg−1	CaK−1	MgK−1	CaCEC−1	MgCEC−1	KCEC−1	H + AlT−1	Sand %	Silt%	Clay%
2.90	11.28	4.03	31.50	11.25	3.00	54.25	4.95	30.05	65

P, K = (HCl 0.05 mol L⁻¹ + H₂SO₄ 0.0125 mol L⁻¹); P meh⁻¹ (Mehlich⁻¹ extractor); S (sulfur), Ca, Mg, Al (KCl 1 mol L⁻¹); H + Al = (buffer solution—SMP (Shoemaker, McLean, and Pratt method) at a pH of 7.5); CEC = cation exchange capacity; O.M = organic matter; BS = base saturation (%); Al(sat) = aluminum saturation (%) [13]; SB = sum of bases; B (boron) = (BaCl₂·2H₂O 0.0125% warm); Cu, Fe, Mn, Zn = (DTPA—diethylenetriaminepentaacetic acid 0.005 mol L⁻¹ + TEA—triethanolamine 0.1 mol L⁻¹ + CaCl₂ 0.01 mol L⁻¹ at a pH of 7.3).

).

2.2. Experimental Design

The experimental design of the two experiments was in randomized blocks with 5 treatments: a “Standard” with application of the formulation NPK 03-35-06 (equivalent to 100% of the recommendation for potato crops) and organomineral 02-20-05 applied at 100%, 80%, 60%, and 40% of the planting recommendation, with 4 replications (

Table 2. Characterization of the treatments.

NPK Treatments	Planting Fertilization					Top-Dress Fertilization 350 kg ha−1 20-00-20		Total Quantity Applied in Cycle
	Dose		N	P2O5	K2O	N	K2O	N	P2O5	K2O
	kg ha−1 % *		kg ha−1
SMF 03-35-06	2300	100	69	805	138	70	70	139	805	208
OM 02-20-05	3680	100	74	736	184	70	70	144	736	254
OM 02-20-05	2944	80	59	589	147	70	70	129	589	217
OM 02-20-05	2208	60	44	442	110	70	70	114	442	180
OM 02-20-05	1472	40	30	294	74	70	70	100	294	144

* Equivalent percentage of the dose applied by the producer. SMF: standard mineral fertilization (03-35-06 N:P:K ratio) OM: organomineral.

). The plots of the experiments consisted of 4 rows of 6 m in length, spaced 0.8 m apart and 0.35 m between plants, totaling 19.2 m² of plot area. The organomineral fertilizer doses (100%, 80%, 60%, and 40%) were calculated based on the total recommended rate for potato crop fertilization using the mineral formulation (2300 kg ha⁻¹ of 03-35-06). The corresponding organomineral doses (02-20-05) were proportionally adjusted to reflect the same percentage of total nutrient supply at planting. The choice of the 100%, 80%, 60%, and 40% organomineral fertilization levels was based on the need to identify the minimum effective dose capable of maintaining tuber productivity and quality. These levels allow the assessment of a potential substitution of conventional mineral fertilization by organomineral inputs, supporting recommendations for more sustainable and cost-effective fertilization strategies. Similar dose ranges have been adopted in other studies on organomineral fertilization efficiency in potato crops, such as Cardoso et al. [12].

The soil preparation used was the one used by the producer and recommended in the region, which includes plowing followed by harrowing, unraveling/leveling, and subsequent opening of planting furrows mechanically.

The fertilizer for each treatment was manually added to the planting furrow on the day of planting (0 DAP) and after fertilization, the plants were cultivated mechanically. Type II potatoes seed (tubers between 40 and 50 mm) treated with insecticides, fungicides, and nematicides were used to better guarantee the health of the plant population.

Sprouting occurred 12 days after planting (DAP) and at 15 DAP, mounding and topdressing fertilization were performed only once for all the treatments with 350 kg ha⁻¹ of the mineral formulation from 20-00-20.

All the culture treatments and phytosanitary controls were carried out through pest and disease monitoring. Upon reaching the control level, the products registered for the crop were applied according to the manufacturers’ standards and instructions. The irrigation system was the central pivot system in which plants received approximately 500 mm of water during the crop cycle, with applications approximately twice per week, depending on crop water demand and soil moisture status.

The fertilizer for each treatment was added manually to the planting furrow for later mechanized planting.

The desiccation was performed at 95 DAP and for the evaluations throughout the cycle, the two central lines of each plot were considered. At harvest, the central 4 m of these same lines that composed the useful area of the plot were considered.

2.3. Characterization of Fertilizer Sources

As a source of fertilization for the standard treatment, the exclusively mineral formulation NPK 03-35-06, composed of urea as the nitrogen source, triple superphosphate as the phosphorus source, and potassium chloride as the potassium source, was applied as recommended according to the results of the technical analysis on the basis of the soil report. For the top dressing, the mineral formulation 20-00-20 was applied to supply nitrogen and potassium in all the treatments. The mineral fertilizer 20-00-20 used for topdressing consisted of urea as the nitrogen source and potassium chloride as the potassium source.

The organomineral fertilizer 02-20-05 was produced by the company Vigor Fertilizantes^® (Uberlandia, Brazil) from an organic source of vegetable origin derived from sugarcane (filter cake), through an aerobic process of controlled decomposition until a stabilized compost was obtained. After this process, mineral sources (urea, triple superphosphate, monoammonium phosphate (MAP), and KCl) were added to achieve nutrient balance and later, the material was homogenized and pelletized.

The chemical composition of the 02-20-05 organomineral consisted of N in total: 2.2%, P₂O₅ soluble in neutral ammonium citrate (CNA) + H₂O 19.3%, total P₂O₅ 20.1%, K₂O soluble in H₂O 5.4%, Ca: 1.4%, Mg: 0.6%, S: 1.6%, B: 0.4%, Cu: 0.01%, Fe: 1.7%, Mn: 0.02%, organic carbon: 14.5%.

2.4. Variables Evaluated

2.4.1. SPAD Index at 48, 62, 76 and 91 Days After Planting

In both experiments, the critical level of the Soil Plant Analysis Development (SPAD) index was determined via SPAD-502 Plus portable chlorophyll meter (Soil-Plant Analysis Development-502 of Minolta Co., Osaka, Japan, 1989) [14], with the objective of indirectly identifying the nutritional condition of the plants in relation to nitrogen. The SPAD index is a dimensionless value derived from measurements obtained by the SPAD meter, which uses dual-wavelength optical absorbance to estimate the relative chlorophyll content in plant leaves. The meter measures the transmittance of light through the leaf at two wavelengths: 650 nm (red light, strongly absorbed by chlorophyll) and 940 nm (infrared light, minimally absorbed). The SPAD value is then calculated internally by the device based on the ratio of absorbance at these two wavelengths, providing a quick, nondestructive estimation of chlorophyll concentration, which is often correlated with plant nitrogen status [14].

In the experiments, 10 plants chosen at random in the useful area of each plot were evaluated, with two readings per plant totaling 20 readings per plot, from which the average was calculated. The determination of the relative chlorophyll index (CRI) was carried out in the morning (08:00 AM 10:00 AM), the device was shaded with the body to avoid interference from sunlight, and the results are expressed in SPAD units. Each reading was measured at the terminal leaflet of the fourth leaf fully expanded from the apex of the plant. Four evaluations were carried out throughout the crop’s development, corresponding to 48, 62, 76, and 91 days after planting (DAP).

2.4.2. Tuber Classification and Productivity

After harvest (118 DAP), the tubers were classified according to diameter according to the following standard: “Special” (42–70 mm) which is considered the tuber with the highest commercial value; “First” (33–42 mm); “Second” (28–33 mm); “Diverse” (up to 28 mm); “Jumbo” (greater than 70 mm); and “Discard” (noncommercial tubers due to damage) (Figure 1).

The tubers were subsequently weighed to account for the productivity of the useful area of the plots, which was converted into kg ha⁻¹. The total tuber productivity was determined from sum of all classes (except “Discard”) and the percentage of Special type potatoes within the total productivity was also determined.

2.4.3. Dry Matter, pH, and Carbohydrates in Tubers

After harvesting, the following characteristics were evaluated: (a) dry matter: determined by drying the pulp of the tubers in an oven (Solidsteel, SSDicrd, 40L, Piracicaba, Brazil) at 105 °C with air circulation to a constant weight and, by difference, moisture was determined [15]; (b) pH determination: performed with 10 g of crushed pulp in 100 mL of distilled water, where the pH was directly read with a digital pH meter (Oakton, Z527807-1EA, Wilmington, NC, USA) [15]; (c) carbohydrates: analyzed via the phenol–sulfuric method by spectrophotometer (Shimadzu, UV-1280, Kyoto, Japan), which is based on the determination of available carbohydrates (sugars, oligosaccharides, and polysaccharides) after their dehydration with sulfuric acid and subsequent complexation of the products formed with phenol [15,16,17].

2.5. Statistical Analysis

First, through the statistical program SPSS version 22.0 (Statistical Package for the Social Sciences) [18], the verification of the assumption was carried out by analyzing the homogeneity of variance (Levene test), normality (Shapiro–Wilk or Kolmogorov–Smirnov), and additivity (Tukey’s additivity test) at α = 0.01. For the “First (1st)” classification of the Ágata cultivar; and the “Special” and “Second (2nd)” classifications of the Atlantic cultivar, √x transformation was carried out.

The data were subjected to analysis of variance and the means were compared in two different ways: by the Tukey test (p < 0.05) and Dunnett (p < 0.05), whose objective was to compare the performance of the fertilization sources with each other and individually with standard fertilization, with the aid of the SISVAR version 5.6 (Analysis of Variance System) [19] and SPSS [18]. To evaluate the dosages of the organomineral fertilizer, both linear and quadratic models of regression analysis was performed considering the significant statistical models that best fit the data.

3. Results

3.1. SPAD Index as a Function of Organomineral Fertilizer Dose

For the cultivar Ágata, all sources (mineral and organomineral) provided similar results in terms of the SPAD index, except for 48 DAP. At 48 DAP, the dose of 100% of the organomineral recommendation resulted in a higher SPAD index than did the doses of 80% and 40%. For the Atlantic cultivar, the SPAD index did not differ regardless of the source or dose of fertilizer used at 48, 62, and 76 DAP. However, at 91 DAP, the doses of 100% and 80% of the organomineral source resulted in a 10% increase in the SPAD index when compared with standard fertilization (

Table 3. Estimates of the SPAD index in cultivar potato Ágata and Atlantic as a function of the application of organomineral fertilizer.

Treatments	SPAD Ágata				SPAD Atlantic
Recommended Dose Equivalent (%)	Days After Planting				Days After Planting
	48 *	62 ns	76 ns	91 ns	48 ns	62 ns	76 ns	91 *
Standard-100	1 52.7 ab	49.5 a	50.0 a	47.8 a	61.5 a	49.8 a	47.3 a	42.6 b
100	58.1 a +	51.2 a	51.6 a	51.7 a	56.0 a	52.2 a	49.0 a	46.9 a +
80	51.9 b	50.1 a	50.9 a	47.8 a	55.4 a	51.6 a	49.0 a	46.3 ab +
60	55.2 ab	50.3 a	49.8 a	48.4 a	54.8 a	51.7 a	48.6 a	43.1 ab
40	52.2 b	49.8 a	49.6 a	46.9 a	54.1 a	51.2 a	47.6 a	43.4 ab

¹ Means followed by the same letter do not differ from each other in the columns by Tukey’s test (p < 0.05). * Significant and ^ns not significant by the F test at 0.05 of significance. ⁽⁺⁾ Values that differ from the control (Standard) by Dunnett’s test at 0.05 significance.

).

The SPAD index did not obtain a satisfactory fit in the linear regression model for the cultivar Ágata (R² = 0.4049) at 48 DAP; however, there was an adjustment for the Atlantic cultivar (R² = 0.8134) at 91 DAP. The R² = 0.4049 indicated considerable variability and a weak linear relationship with the applied doses of organomineral fertilizer. Although a numerical trend can be observed, the results suggest that other factors may also influence the chlorophyll content at this stage. In this evaluation for the Atlantic cultivar, for each percentage of the recommended dose applied with organomineral, a linear increase of 0.067 was obtained in the SPAD index (Figure 2).

3.2. Tuber Classification and Productivity According to the Application of Organomineral Fertilizer

For the cultivar Ágata, there was no difference in classification for potatoes in the “Special” category when fertilizers with 100 and 80% of the recommended dose with organomineral fertilizer versus the company’s standard fertilizer (performed with exclusively mineral fertilizer) were used (

Table 4. Classification of Ágata potato tubers according to the application of organomineral fertilizer.

Treatments	Ágata Classification kg ha−1							Atlantic Classification kg ha−1
Recommended Dose Equivalent (%)	Special *	1st *	2nd ns	Different *	Jumbo	Discard *	Specials	1st *	2nd ns	Different *	Jumbo *	Discard *
Standard-100	1 30,600 a	1040 ab	320 a	4840 a	2730 a	820 a	42,450 a	1410 a	200 a	1660 b	1610 b	410 ab
100	29,980 a	1130 ab	340 a	3790 a	2620 a	1730 b+	42,330 a	1150 ab	220 a	3450 a +	3580 a +	1250 c +
80	29,240 ab	1200 ab	230 a	4500 a	2850 a	1300 ab	41,140 a	1100 ab	430 a	1620 b	2630 ab	980 bc +
60	26,620 b +	980 b	270 a	1630 b +	1343 b +	890 a	39,160 a	880 b +	250 a	800 b	2580 ab	460 ab
40	25,910 b +	1340 a+	290 a	1040 b +	1753 ab	700 a	39,210 a	1440 a	230 a	1660 b	1740 b	190 a

¹ Means followed by the same letter did not differ from each other in the columns by Tukey’s test (p < 0.05). * Significant and ^ns not significant by the F test at 0.05 of significance. ⁺ Values that differ from the control (Standard) by Dunnett’s test at 0.05 of significance.

). In general, the doses of 60% and 40% of the recommended dose provided a smaller number of potatoes classified as “Diverse” (1630 and 1040 kg ha⁻¹, respectively). For the “Jumbo” classification, the dose of 60% of the recommendation provided the lowest amount of potatoes in this category (1340 kg ha⁻¹).

For classification of the tubers of the Atlantic cultivar, the use of various sources and doses of fertilizers did not result in differences in the ability to produce potatoes in the “Special” category. Similarly, for the classification of the “First” category, there were also no differences from standard fertilization, except for the dose of 60% of the recommended dose.

Standard fertilization and reduced doses of the organomineral (80, 60, 40%) led to a lower number of tubers of the “Diverse” type. For “Discard”, the best results were observed for the lowest dosages (60 and 40%) of the organomineral, together with the Standard, highlighting the 40% dose that, numerically, obtained the lowest value for the category of discarded potatoes (187.50 kg ha⁻¹).

When the linear regression models for the potato classifications of the cultivar Ágata, are analyzed, increases in the categories “First”, “Diverse”, “Jumbo”, and “Discard” are observed when organomineral fertilization is used; these values are 74.20, 55.47, 20.53, and 17.62 kg ha⁻¹, respectively (Figure 3A–D) for each 1% of organomineral fertilizer applied. Therefore, the total productivity increased by 148.61 kg ha⁻¹ of tubers for every 1% increase in the applied dose of organomineral fertilizer (Figure 3E).

When the linear regression models for the potato classifications of the Atlantic cultivar were analyzed, an increase in potatoes in the “First” category was observed from the dose of 74.31% organomineral fertilizer (Figure 4A); meanwhile, the number of potatoes classified as “Diverse” increased from the dose of 60.77% (Figure 4B). The classifications “Jumbo” and “Discard” showed linear growth, and for each 1% of the recommendation for fertilization with organomineral, there were increases of 27.87 and 18.59 kg ha⁻¹, respectively (Figure 4C,D). From the dose of 49.49% of the recommended dose of organomineral fertilizer, the total tuber yield was (43,862 kg ha⁻¹) (Figure 4E).

With respect to the total yield of the potatoes, all dosages of the organomineral fertilizer provided productivity similar to that obtained via standard fertilization. Similarly, the percentage of potatoes in the special category was also similar to that in the organomineral and standard sources, except at the 100% dose. The 100% fertilization with organomineral resulted in a lower percentage of potatoes in the special category than in the other categories (

Table 5. Total yield and percentage of special Ágata potatoes as a function of organomineral fertilizer application.

Treatments Recommended Dose Equivalent (%)	Ágata		Atlantic
	Total Productivity *	%Special *	Total Productivity ns	% Special *
	kg ha−1		kg ha−1
Standard-100	1 39,520 a	77,410 c	47,330 a	89,600 a
100	37,840 a	79,220 bc	50,730 a	83,370 b
80	38,000 a	76,920 c	46,910 a	87,740 a
60	30,840 b	86,630 a	43,670 a	89,710 a
40	30,320 b	85,390 ab	44,270 a	88,570 a

¹ Means followed by the same letter did not differ from each other in the columns by Tukey’s test (p < 0.05). * Significant and ^ns not significant by the F test at 0.05 of significance.

).

3.3. Dry Matter, pH, Carbohydrate, and Solid Content in Tubers Resulting from Organomineral Fertilization

The dry matter from the cultivar Ágata resulting from organic fertilization was greater than or similar to that resulting from mineral fertilization. A difference of up to 16% was observed between the sources for the dry matter of the cultivar Ágata (

Table 6. Dry matter, pH, and carbohydrate contents of tubers of the cultivars Ágata and Atlantic as a function of the application of organomineral fertilizer.

Treatments %	Ágata			Atlantic
	Dry Matter	pH	Carbohydrate	Dry Matter	pH	Carbohydrate
	g/kg
Standard-100	1 114.1 b	6.50 d	130.4 a	223.9 a	7.12 a	132.5 ab
100	151.4 ab	6.40 e *	114.7 ab *	203.1 ab *	7.08 a	136.2 a
80	148.0 ab	6.58 c *	108.0 b *	194.8 b *	6.86 c *	125.3 b
60	161.7 a *	6.77 b *	119.1 ab	191.0 b *	7.03 ab	126.3 ab
40	155.0 ab *	6.91 a *	120.0 ab	219.8 a	6.94 bc *	129.9 ab
CV (%)	3.49	0.41	5.86	4.10	0.58	2.90

¹ Means followed by the same letter did not differ from each other in the columns by Tukey’s test (p < 0.05). * Values that differ from the control (Standard) by Dunnett’s test at 0.05 of significance. CV: coefficient of variation (%).

).

For the Atlantic cultivar, the highest values of dry matter were obtained with the application of 40% organomineral, similar to potatoes fertilized with a mineral source.

With respect to the pH, fertilization with 100% organomineral, together with standard fertilization, resulted in the lowest acidity for the cultivar Ágata. A linear decrease in pH was observed as the tested dose of the organomineral for the cultivar Ágata increased (Figure 5). For the Atlantic cultivar, lower acidity values were found with the dose of 80% organomineral.

With respect to the carbohydrate (starch) content of Ágata and Atlantic, the different doses of the organomineral presented results similar to those of standard fertilization, except for the doses of 100 and 80% in Ágata. In this cultivar, the standard fertilization, and doses of 60% and 40% stood out numerically, with an average of 12.32%; meanwhile, for the Atlantic cultivar, the best results reached an average of carbohydrate content of 13.12%.

4. Discussion

4.1. SPAD Index

The SPAD chlorophyll meter is a portable device that allows a relative chlorophyll index (CRI), or SPAD index, which is based on the intensity of the green color of the leaves, which can correlate with the chlorophyll content and, consequently, with the nitrogen (N) content in the leaf. Thus, N deficiency is quickly reflected in relatively low chlorophyll concentrations, as this element is a key component of this molecule. This type of evaluation represents a practical tool that helps in the decision concerning nitrogen fertilization. It is a nondestructive method, that is efficient in terms of time and response, allowing in situ evaluations to be carried out and detecting N deficiencies in crops in advance [20].

The values found for the SPAD index in this study were close to or above the indices considered adequate for the potato crop, which is 49–56 SPAD units [21]. This interval indicates that the nitrogen contents of the crop were satisfactory for its full development. Notably, spike readings should occur in later periods of development and are useful tools to define the amount of N required by the potatoes. This explains why the SPAD readings were carried out after the initial stages of crop development, because in earlier periods, the readings tended to be remarkably high, demonstrating that the plants contained sufficient levels of N in this phase. According to Fernandes et al. [20], there is a greater correlation between chlorophyll readings in the terminal leaflet and the N content in the leaf from 24 days after emergence (DAE), which coincides with the onset of tuberization.

The SPAD indices of the cultivars Ágata and Atlantic, even at an advanced stage of development, revealed that regardless of the different doses of organomineral fertilizer applied, there was good N absorption and assimilation by the plants. In numerical terms, at the end of the cycle of the two cultivars, the SPAD index values were lower than those of the first evaluations. This is justified by the advanced stage of crop development in which the plants had a greater number of old and yellow leaves and because of these conditions, the chlorophyll concentrations were likely low, resulting lower SPAD values.

The results observed in the cultivars Ágata and Atlantic demonstrate that the benefits of the application of organomineral fertilizer are noticeable throughout crop development. It can be inferred that such results reflect the positive effects on root growth, which include exploring a greater volume of soil from the beginning of the cycle and promoting adequate absorption of nutrients, formation, and maintenance of leaves in the plant. The components of humic substances present in the organic fraction of the organomineral generally stimulate the microbial flora in the rhizosphere, facilitating the retention and release of nutrients, retaining water, and forming natural chelates, which favor the better use of nutrients by the roots [4].

4.2. Tuber Classification and Productivity

The classification of potato tubers into categories such as Special, First, Second, Diverse, Final, and Discard is more common in the commercial context, where the quality and appearance of the tubers are evaluated. The Special potato is characterized by large, uniform tubers, without defects, stains, or damage, with clean and smooth skin, which is intended for export and consumers seeking high quality. The First classification includes medium to large tubers with few imperfections, while the Second covers medium to small tubers with more visible imperfections. Both are common in supermarkets for home consumption and culinary preparations. The Diverse potato classification represents a mixture of various sizes and shapes with various imperfections and are used for industrial processing in the preparation of potato chips, straw, or starch. The Jumbo classification refers to potatoes that are uniform in size and large, usually larger than Special potatoes, whereas the Discard category includes potatoes with no commercial value.

In this context, the classification of potatoes is especially important as it determines the commercial value of production. In this work, it was observed that organomineral fertilizer at doses of 60 and 40% of the recommended concentration resulted in a relatively percentage of Special potatoes. These results indicate that the application of the organomineral formulation in plant fertilization represents an interesting source of fertilization for the crop.

In addition, for the Ágata cultivar, the organomineral fertilizer provided productivity and quality results of the final product as good as the mineral sources, even at low doses, indicating the possibility of using it with dose reduction or adjustment without damage to the crop. One of the reasons for these results is related to the characteristics of this fertilizer which is composed of an organic matrix that allows gradual release of the nutrients and greater efficiency in the use of minerals. This is possible because the protection that organic matter exerts on the mineral fraction ensures that nutrients are less exposed to the processes of losses by leaching, volatilization, and fixation [22,23]. Thus, the application of organomineral fertilizer allows the dose to be reduced in a feasible and efficient way, as long as the growing conditions and crop requirements are also considered.

For the Atlantic cultivar, the use of organomineral doses also influenced the production of tubers of higher commercial value (Special), where at a dose of 58% of the recommendation it provided 89.79% of Special-type potatoes. Notably the efficiency of the organomineral, both with 100% of the recommendation and with the adequacy of the dose, was also observed in the potato crop under other management conditions.

Cardoso et al. [12] evaluated the effects of the application of an organomineral fertilizer produced from chicken manure on the yield and quality of Atlantic potato tubers in different planting seasons (winter and rainy) and reported that in the rainy season, the application of organominerals provided results similar to those obtained with mineral application, even in situations of lower dosages. In the winter harvest, the response was even more expressive, where all the doses studied (from 40% to 120% of the mineral recommendation dose) were higher than the mineral formulation. In the study conducted by Cardoso et al. [12], the dose equivalent to 100% of the recommendation provided higher productivity and better tuber quality in both seasons. In addition to the positive results for total productivity, tubers with higher commercial value and a lower percentage of Discard were obtained.

The results obtained in this study, especially regarding the yield and commercial classification of the tubers, were similar to those reported by Cardoso et al. [12], who also observed a favorable response of the Atlantic cultivar to the application of organomineral fertilizer. However, there are important differences between the studies. While Cardoso et al. [12] used poultry manure as the organic source, this study employed filter cake of plant origin. This distinction is relevant, as the chemical composition, nutrient release dynamics, and microbial effects on the soil can vary significantly between animal- and plant-based materials. Furthermore, our experiment was conducted on a dystrophic Ferralsol with naturally high acidity under a high-altitude tropical climate, which may have positively influenced nutrient uptake efficiency from the organomineral fertilizer. Another important difference is the simultaneous evaluation of two cultivars with distinct market purposes, whereas many studies focus on a single cultivar. Therefore, while the similar agronomic efficiency reinforces the potential of organomineral fertilizers, the methodological and environmental differences highlight the need for validation under diverse conditions.

The effects observed in this study may be attributed to the synergistic properties of organomineral fertilizers, which act through multiple mechanisms. The gradual release of nutrients from the organic matrix improves nutrient use efficiency by synchronizing supply with crop demand, thus reducing leaching losses—especially of nitrogen and phosphorus. Moreover, the presence of organic matter enhances the soil’s physical structure and water-holding capacity, which are particularly relevant in potato cultivation due to its shallow root system. Additionally, humic substances and microbial stimulants present in the organic fraction can modulate root architecture, increase root surface area, and promote rhizosphere microbial activity, all of which contribute to improved nutrient uptake and plant development. Similar mechanisms have been reported in [22,23,24], where enhanced nutrient retention and plant growth under organomineral treatments was observed. The improved tuber quality, especially in terms of dry matter and carbohydrate content, may also be linked to more stable and efficient nutrient supply throughout the crop cycle.

4.3. Dry Matter, pH, Carbohydrate, and Solid Contents in Tubers

Post-harvest characteristics relating to the chemical composition of tubers such as dry matter, pH, and carbohydrates are important for determining the quality of the potato, directly impacting the acceptability of the product on the market. These characteristics can be affected by several factors, such as the factors of the cultivar itself and the availability of nutrients [25]. Unbalanced nutrition can lead to disproportionate growth of the shoot at the expense of the tubers, delay maturation, and reduce dry matter, resulting in greater fat absorption and browning after frying. This variable is particularly important for the quality of tubers since it affects oil absorption during frying, texture, flavor, and factory yield [25,26].

The dry matter content varies according to each cultivar, and for cultivars intended for processing in the form of chips, such as Atlantic, the dry matter content is recommended to be between 20% and 24% to obtain a high-quality product. On the other hand, values above 24% are not desirable, as they lead to the production of brittle slices and cause excessive wear of the slicing machines [27]. In this experiment, for the Atlantic cultivar, the best results obtained presented dry matter values within the range considered ideal.

The pH of the pulp is one of the most important post-harvest evaluation characteristics for evaluating the chemical and biological conditions of tubers and is essential for recognizing and controlling processes in food. The pH determines enzymatic activity, degree of deterioration, texture variation, degree of ripeness, and even the choice of packaging or preservation medium. Thus, a pH above 6.0 indicates a good state of ripeness and conservation, since values below this value (between 5.5 and 4.7) favor the action of enzymes that degrade starch [25,27]. For the two cultivars tested in this study, all the treatments provided pH values above this critical range.

According to Braun et al. [28], starch represents 60 to 80% of the dry matter of the tuber, and glucose, fructose, and sucrose are the main carbohydrates. Upon reaching physiological maturity, the potato starts to have starch granules and variable amounts of sugars that are interconvertible substances, that is, they can be converted to each other. This relationship is dependent on enzymes involved in the synthesis and breakdown of starch. The accumulation of reducing sugars, such as glucose and fructose, especially in tubers intended for processing and storage under refrigeration, is crucial for obtaining high-quality products since these sugars lead to browning of the potato, a result of the Maillard reaction. Thus, according to the cultivar and degree of maturation of the tubers, the starch and sugar contents change, reducing the amount of starch and increasing the presence of reducing sugars [28]. The optimal amount of starch and reducing sugars after harvest is related to the quality of the tubers. These substances are determined by genotype and environmental factors, which include an adequate fertilization program [28]. According to the data obtained in this study, regardless of the dose or source of fertilization, carbohydrate production was satisfactory.

The application of the pelleted organomineral 02-20-05 in planting fertilization proved to be an interesting source of fertilization for the cultivation of Ágata and Atlantic potatoes and can be applied with dose adjustments without affecting the productivity or quality of the tubers.

The results obtained in this study expand knowledge on the use of organomineral fertilizers in potatoes by demonstrating that even with reduced doses, it is possible to maintain or even improve the commercial quality of tubers, depending on the cultivar. This finding complements previous studies, such as that of Cardoso et al. [12], by using a different organomineral source (vegetable filter cake) and by applying the study simultaneously to two cultivars with different market purposes. The inclusion of post-harvest and physiological variables contributes to a more comprehensive view of the effects of the input, reinforcing its potential as a viable alternative to conventional fertilization.

It is important to highlight that the experiment was conducted in the municipality of Cristalina-GO, a region characterized by a dystrophic Ferralsol with high clay content and high natural acidity, but good physical structure and drainage. These soil characteristics, combined with the use of irrigation and adequate soil preparation, may have contributed to the efficient uptake of nutrients from both mineral and organomineral sources. Furthermore, the region’s high-altitude tropical climate (Cwa type) with defined dry and wet seasons may have influenced tuber development, especially under controlled water availability. These specific edaphoclimatic conditions could affect the generalization of the results to other regions with different soil types or climates. Therefore, further studies under varying environmental conditions are necessary to validate the consistency of the benefits observed with organomineral fertilization.

In addition, although this study demonstrated the agronomic potential of organomineral fertilizer, further research is needed to investigate the nutrient dynamics through post-harvest soil analysis and plant tissue nutrient content. Such data would also provide insights into nutrient use efficiency, potential residual effects, and environmental sustainability of organomineral fertilization strategies.

5. Conclusions

The almost exclusive application (80% and 100%) of organomineral fertilization can provide productivity equivalent to that of mineral fertilization. In the doses containing organomineral fertilizer in 60% and 40% of the planting recommendation, there is a higher production of higher quality potatoes, classified as “Special”. For the Ágata cultivar, the application of organomineral fertilizer at reduced doses can increase the dry matter in the tubers, reduce the acidity of the pulp, and maintain a satisfactory amount of carbohydrates. On the other hand, the Atlantic cultivar had higher doses of organomineral fertilization, resulting in greater dry matter and lower pulp acidity. Organomineral fertilizers can be applied with dose adjustments without affecting the productivity or quality of potato tubers.

This has direct practical implications for farmers, as it enables a reduction in the use of mineral fertilizers, with potential reductions in costs and environmental impacts. Furthermore, the results reinforce the role of organomineral fertilizers as a viable alternative in more sustainable production systems, aligned with the demands of the current market.

Future research suggestions include evaluating the performance of organomineral fertilizers in different soil types and climate conditions, as well as their interaction with other management practices, such as the use of plant cover and growth-promoting microorganisms. It would also be relevant to study the long-term effects on soil fertility and microbiota, in addition to comparative economic analysis between fertilization systems.