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CROP PRODUCTION • Cienc. Rural 55 (2) • 2025 • https://doi.org/10.1590/0103-8478cr20240046 linkcopy

Open-access Yield and nutritional composition of sweet potatoes storage roots in response to cultivar, growing season and phosphate fertilization

Rendimento e composição nutricional das raízes de armazenamento de batata-doce em resposta a cultivar, época de cultivo e adubação fosfatada

AuthorshipSCIMAGO INSTITUTIONS RANKINGS

    ABSTRACT:

    Sweet potato is an important food security crop, and the world market for this root is on the rise. Based on the physiological changes in plants in response to climatic conditions and fertilization, this study evaluated the effects of the growing season (rainy and dry season) and P2O5 doses (0, 50, 100, 200 and 400 kg ha-1) on total yield, marketable classes yields, as well as chemical composition of storage roots of two sweet potato cultivars. The storage roots yield was greater in the rainy season. The optimum agronomic and economic doses were 128 and 95 kg ha-1 P2O5 for the cultivar Canadense. Cultivar Uruguaiana did not respond to phosphate fertilization, but its storage roots had higher contents of dry matter, lipids, fibers, total and reducing sugars, and starch. Sweet potato cultivation in the rainy season with doses up to 100 kg ha-1 P2O5 increase root yield in marketable size classes in higher economic value and with higher carbohydrate contents. The results can help producers schedule the planting and harvesting of sweet potatoes throughout the year and contribute to the seasonal management of phosphate fertilizer application.

    Key words:
    Ipomoea batatas (L.) Lam; climatic conditions; productivity; chemical composition

    RESUMO:

    A batata-doce é uma cultura importante para a segurança alimentar com mercado mundial em ascensão. Com base nas alterações fisiológicas das plantas em resposta às condições climáticas e à fertilização, este estudo avaliou os efeitos da época de cultivo (período chuvoso e seco) e de doses de P2O5 (0, 50, 100, 200 e 400 kg ha-1) na produtividade total e por classes comerciais, bem como, a composição química das raízes de armazenamento de duas cultivares de batata-doce. A produtividade de raízes tuberosas foi maior na estação chuvosa. As doses ótimas agronômica e econômica foram de 128 e 95 kg ha-1 de P2O5 para a cultivar Canadense. A cultivar Uruguaiana não respondeu a adubação fosfatada, mas suas raízes tiveram maiores teores de matéria seca, lipídios, fibras, açúcares totais e redutores e amido. O cultivo de batata-doce no período chuvoso com doses de até 100 kg ha-1 de P2O5 aumenta a produtividade de raízes em classes de maior valor econômico e com maiores teores de carboidratos. Estes resultados ajudam os produtores a planejarem o plantio e a colheita da batata-doce ao longo do ano e contribui para a gestão da aplicação de fertilizantes fosfatados.

    Palavras-chave:
    Ipomoea batatas (L.) Lam; condições climáticas; produção; composição química

    INTRODUCTION

    The sweet potato originates from Latin America and today is among the most important economic and food security crops in the world. It has a significant contribution as energy supplement and phytochemical source of nutrition (ALBUQUERQUE et al., 2019). This crop is produced on all continents with production in 113 countries, totaling 88.86 million tons in 2021. China is the world’s largest producer (>50%), with most countries with productions below 5 million tons (FAO, 2023).

    Brazilian sweet potato production has been growing in recent years, reaching 847 thousand tons in a harvested area of 58.22 thousand hectares in 2022. The largest production volumes in Brazil are obtained in the northeast (Pernambuco and Paraiba), south (Rio Grande do Sul, Santa Catarina, and Paraná) and southeast regions. In the southeast, the state of São Paulo has the largest commercially cultivated area with sweet potatoes (IBGE, 2023).

    Changes in weather conditions and the increased occurrence of extreme events are being felt more frequently. It is; therefore, critical to understand the effects of these changes on the world’s staple food crops. Studies showed that climatic factors are directly linked to the growth, development, and production of sweet potato storage roots. The growing season is crucial in tuber crops as its effects are of greater magnitude than the effects of the growing years on crop yields; in addition, the genotype and planting season interaction has a greater effect than the genotype-year (ALBUQUERQUE et al., 2019; JANKET et al., 2018; JANKET et al., 2020).

    Accordance with sustainability principles, in intensive agricultural production it has been placed emphasis on increasing productivity with minimal application of fertilizers. For this, plants must have efficiencies of absorption and utilization. Despite the great potential of sweet potatoes to meet the principles of sustainable agricultural production, the average productivity of the crop in Brazil is low (14 tons/ha). It is; therefore, necessary to study cultivars more productive, correct crop management, fertilization and other cultural practices to improve productivity (AZEVEDO et al., 2014; RÓS et al., 2015; CECÍLIO FILHO et al., 2016; VARGAS et al., 2018).

    The sweet potato plant has a branched root system, being highly efficient in absorbing nutrients. However, due to the common deficiency of phosphorus (P) in Brazilian soils, it is necessary to apply it to obtain higher root yields. Phosphate fertilization is essential from the early stages of growth of the sweet potato plant and providing adequate dosages of P allows root development and increased absorption of water and nutrients (CAI et al., 2013). The increases in production are attributed to the beneficial effect of P in activating photosynthesis and in the metabolism of organic compounds, increasing plant growth. Phosphorus is an essential nutrient that plays an important role in plant respiration, energy production and transformation processes, as well as cell division (EL-SAYED et al., 2011; ABDEL-RAZZAK et al., 2013; KAREEM et al., 2018; DUMBUYA et al., 2016; FERNANDES & RIBEIRO, 2020).

    The storage roots are the most important marketable part of the crop and dry matter range from 63.2 to 82.2%. Carbohydrates, proteins, lipids, bioactive compounds, and minerals are present in their composition and makes sweet potato a plant capable of providing several health benefits, such as antioxidant, hepatoprotective, anti-inflammatory, anti-tumor, anti-diabetic action, antimicrobial, anti-obesity, and anti-aging effect. In addition to genetic diversity, the variable chemical composition of the storage roots is attributed to growing conditions, harvesting and post-harvest conditions (WANG et al., 2016; AKOETEY et al., 2017).

    This study evaluated the impacts of the growing season (rainy and dry season), cultivar and doses of phosphate fertilizer on productive parameters and chemical composition of sweet potato storage roots.

    MATERIALS AND METHODS

    Four experiments were carried out under field conditions, in an experimental area of the University located in the city of São Manuel, state of São Paulo, Brazil (22º 77’ S; 48º 34’ W and 740 a.s.l.). The climate of the region, according to the Köppen classification, is of the Cwa type, which is characterized as high-altitude tropical, with dry winters and hot and rainy summers. The experiments were carried out in four adjacent areas with planting in two seasons: planting in March (dry season) and planting in October (rainy season) during the two consecutive years (Figure 1).

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    Figure 1
    Daily rainfall (black bars), maximum (blue line) and minimum (red line) temperatures at the experimental area during the period of sweet potato growing in the field.

    The experimental design used was randomized blocks in a 2×5×2 factorial scheme, with four replications, totaling 20 treatments. The factors consisted of two sweet potato cultivars (Canadense and Uruguaiana), five P2O5 doses (0, 50, 100, 200, and 400 kg ha-1), and two growing seasons.

    The soil of the areas is classified as Dystrophic Typic Hapludox (SOIL SURVEY STAFF, 2014). The soil chemical characteristics, at a 20 cm depth, are shown in table 1. The experimental area, prior to the installation of each experiment, was plowed and harrowed. Subsequently, hills of approximately 30 cm in height were mechanically raised.

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    Table 1
    Soil chemical characteristics at a 20 cm depth prior to the experiments. The data are mean of six samples.

    The branches of the two cultivars were removed from young plants and cut one day before planting and sectioned into pieces of approximately 40 cm in length, containing an average of eight internodes. The branches were buried manually, always at the base, at a depth of 10 to 12 cm.

    The experimental plots consisted of four rows of five-meter-long plants, spaced 1.00 m between rows and 0.30 m between plants. The two central rows of plants were considered as the experimental plot, disregarding 0.5 m at the ends of each row.

    Planting fertilization with nitrogen (20 kg ha-1) and potassium (40 kg ha-1 K2O) followed the recommendations for the crop based on soil analysis (FELTRAN et al., 2022). Ammonium sulfate and potassium chloride fertilizers were used as sources of N and K, respectively. In the planting fertilization, the fertilizers were distributed at a depth of 15 cm in a continuous furrow, opened at the top of the hills. Phosphorus was also applied at planting furrow using triple superphosphate as a source according to the treatments.

    Topdressing fertilization was performed as recommended by FELTRAN et al. (2022), applying 30 kg ha-1 N (urea) and around 50 kg ha-1 K2O (potassium chloride), approximately at 30 DAP (days after planting).

    Root yield and chemical composition of sweet potato roots were determined 165 DAP the seedlings, that is, at the physiological maturation stage of the roots. For the analysis five sequential plants were harvested in two lines, totaling ten plants of each experimental unit.

    After harvest, the uninjured, elongated, and uniform storage roots were classified in the following size classes: 800 to 501 g (Large), 500 to 251 g (Extra A), 250 to 151 g (Extra), 150 to 80 g (Miscellaneous) (MIRANDA et al., 1995). Marketable root yield was obtained from the sum of all classes of storage roots weighing between 80 g and 800 g. Storage roots with injuries and deformed were counted to obtain the incidence of roots with defects. Storage roots with a size greater than 800 g or less than 80 g were counted as unmarketable roots. The number of these roots was subtracted from the total number of storage roots and, thus, the number of marketable roots per plant was obtained. Total root yield was obtained from the sum of all root classes, including unmarketable roots.

    Four samples composed of sweet potato storage roots of marketable classes were separated for analyses of chemical composition of roots. The roots were washed in chlorinated water, allowed to dry in the shade, chopped in an automatic slicer, and then samples were separated to determine the initial moisture content. The remaining slices were dehydrated in an oven with air circulation (55 ºC/36 hours), ground in a knife mill, and stored in polyethylene bags. The dehydrated samples were analyzed for chemical composition following the methodologies of AOAC (2005) for moisture (method 934.06), ash (method 923.03), total sugars (method 968.28), reducing sugars (method 945.66), fiber (method 920.86), protein (method 920.152), lipids (method 923.05), starch (method 996.11). Phosphorus content was determined by atomic absorption spectrophotometry after nitric acid (HNO3) - perchloric acid (HClO4) digestion (MALAVOLTA et al., 1997). The results obtained in the dehydrated samples were converted to the fresh weight of the storage roots.

    Statistical analysis was performed considering the mean values between the years studied. The data were submitted to analysis of variance and the significance of F was tested at the 5% probability level. When significant, the t-test (LSD, P < 0.05) was applied for qualitative factors (cultivars and growing seasons) and regression for the quantitative factor (phosphorus doses). In the regression analysis, the model was defined based on the magnitude of the significant coefficients at 5% probability by the F test.

    The agronomic optimum dose was obtained by estimating the P2O5 dose that reached the inflection point or stabilization of marketable root yield. Using the equation adjusted for marketable root yield, the economic optimum dose was calculated: the P2O5 dose (kg ha-1) in which $ 1.00 of additional P2O5 would return $ 1.00 of sweet potato produced. The economic optimum dose was calculated by equating the first derivative of each equation with the price relationship for phosphate fertilizer and sweet potatoes (FERNANDES et al., 2016). The price relationship was calculated considering the mean price ($ 0.32/kg) of sweet potatoes sold in São Paulo during 2017 and 2018 and P2O5 price of triple superphosphate ($ 2.33/kg). The critical P content in the soil was calculated by the ratio of the initial P content in the soil to reach 95% of the maximum relative storage roots or starch yields (SORATTO et al., 2023).

    RESULTS AND DISCUSSION

    Data analysis showed that there were no differences in storage roots production for the years of cultivation, which was also observed in other studies with sweet potatoes (ANDRADE JÚNIOR et al., 2016; STEFFLER et al., 2022). Storage roots production per sweet potato plant had isolated effects of the factors, as well as the interaction between growing season and phosphate fertilizer doses (Table 2). The cultivar Canadense produced higher total and marketable roots per plant but had a higher percentage of roots with defects. The number of storage roots per plant is an intrinsic characteristic of the cultivar, but it is also affected by growing and environmental conditions. Total storage roots production was higher in the rainy season, with higher marketable losses due to unclassified roots in the dry season.

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    Table 2
    Numbers of total and marketable sweet potato roots per plant, incidence of roots with defects and root yields in each class of root size as a function of cultivar, growing season and phosphorus doses.

    Higher root yields are achieved when reaching the highest number of storage roots per sweet potato plant. Thus, agricultural managements that favor the differentiation of adventitious roots into storage roots at the expense of fibrous roots and pencil roots are important. Soil and air temperatures play an important role in initiating storage roots and crop development. Thus, the nighttime and daytime temperature conditions of the rainy season can have favored early root initiation, with a root system more abundant in storage roots than in the dry season.

    The quality of sweet potato storage roots for marketing is characterized by the occurrence of defects, their severity and quantity. Rot, root sprouting, mechanical damage (injury), pest damage and deformation are analyzed to determine the category of roots for sale. Planting in the dry season intensified the production of deformed roots and with lesions on the peel, due to low rainfall intensity (Figures 1 and 2).

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    Figure 2
    Numbers of total (A) and marketable sweet potato storage roots per plant (B), incidence of roots with defects (C), total yield (D), marketable (E) and yield by classes of storage roots size (F to H) of sweet potato cultivars affected by growing season and/or doses of phosphorus. The square (■) represents the mean values of the two cultivars and the two seasons. The vertical bar in the figure area indicates the LSD value by t-test (P < 0.05). * and **, respectively, are significant at 5% and 1% probability by the t-test.

    The unfolding of the results of the interaction between growing season and phosphorus dose showed that, for all doses studied, cultivation in the dry season resulted in greater losses with unmarketable roots, with an increase in the highest doses of phosphate fertilizer, reaching the maximum at the estimated dose of 220 kg ha-1 of P2O5 (Figure 2). Reductions in total and marketable root yield with high P2O5 doses probably occurred due to the increased shoot growth of the plant, reducing the growth of storage roots.

    Phosphate fertilization increased the yield of marketable storage roots for ‘Canadense’, which overwhelms the negative effects of production of the disqualified roots. Despite being grown under the same conditions, some storage roots reach maturity faster than others. As a result, as the harvest is done for all the roots at the same time, some are collected before reaching their maximum size, which impacts the production of small roots (PAZOS et al., 2022).

    Isolated effects of cultivar and growing season were observed for storage roots yield by size classes (Table 2). The cultivar Canadense had a higher production of medium size roots that have higher marketable value. However, the ‘Uruguaiana’ had lower production of small and large size roots, which may commercially compensate for the difference in the production of medium size roots.

    The yields of medium (251-500g) and large (501-800g) size storage roots were impacted by the growing season, with yields 54.98% and 128% higher than those observed in the dry season for the same size classes. The yield of storage roots with 251-500 g was affected by the isolated factors, and there was a significant interaction between the cultivar and phosphorus fertilization (Figure 2).

    Studies have shown that it is possible to obtain higher storage roots yields in the sweet potato crop using a balanced mineral fertilizer (ABDEL-RAZZAK et al., 2013; KAREEM et al., 2018; FERNANDES & RIBEIRO, 2020). Our study showed that by contrasting the results of the interaction between cultivar and dose of phosphorus for the yield of storage roots with size of 251-500 g, the ‘Canadense’ was superior to ‘Uruguaiana’ at doses of 100 and 200 kg ha-1 P2O5. For each cultivar alone, it was observed that there was no effect on the yield of medium size roots (251-500g) for ‘Uruguaiana’, but at an estimated dose of approximately 100 kg ha-1 P2O5, the yield of this root size class for the ‘Canadense’ increased by 46% compared to the control treatment.

    Growing season influenced sweet potato storage roots yield with increases of 36% and 33% in marketable and total sweet potato root yield in rainy season cultivation, with better yield for ‘Canadense’ (Table 3).

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    Table 3
    Sweet potato root yields as a function of cultivar, growing season and phosphorus doses.

    The cultivar Canadense was more responsive to phosphate fertilization. The phosphate fertilization increased by 30% the marketable root yield of the cultivar ‘Canadense’ up to the optimal agronomic dose of 128 kg ha-1 P2O5, while the optimal economic dose was obtained with 95 kg ha-1 P2O5 (Figure 2). Phosphate fertilizer did not increase the marketable storage roots yield of the cultivar Uruguaiana. The critical soil P content for the rainy season was 6.8 and 6.3 mg dm-3 P for the relative storage roots and starch yields, respectively (Figure 3). However, in the dry season, the critical soil P content was 9.7 and 8.4 mg dm-3 for the relative storage roots and starch yields, respectively. These results indicated that due to low water availability in the dry season (Figure 1), the levels of P available in the soil need to be higher to optimize the yield of sweet potato roots and starch (Figure 3).

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    Figure 3
    Relationship between the relative total storage roots yield (A) and relative starch yield (B) with the initial soil P-resin content. The vertical lines represent the critical values of initial soil P-resin predicted by each growing season. * and **, respectively, are significant at 5% and 1% probability by the t-test.

    Positive effects of phosphate fertilization on sweet potato production were also obtained in other studies. EL-SAYED et al. (2011) in a study with sweet potato cultivation in the summer (EI-Dakahlia Governorate, Egypt) reported that increasing the dose of phosphorus from 15 kg to 45 kg ha-1 led to significant increases in the length of the main stem, dry mass of the canopy, leaf area of the plant, total chlorophyll and carotenoids, as well as tuberous root weight, diameter and percentage of dry matter, and total and marketable storage roots yield.

    CRUZ et al. (2016) in a study with sweet potato cultivation, cv. Beauregard, in soil with low phosphorus availability (São Luis city, Maranhão, Brazil), observed an increase in total root yield with the maximum (2.44 kg m-2) obtained with the estimated dose of 190 kg ha-1 P2O5, which meant an increase of 11.6% in relation to the control. Higher doses of phosphate fertilizer decreased the total and marketable yield of storage roots of cultivar ‘Canadense’.

    The differences observed for the cultivars in relation to fertilization are related to the nutrient use efficiency by the cultivar. SILVA et al. (2013) studied the efficiency of use and response to applied phosphorus in nine sweet potato genotypes. The authors observed that four genotypes were classified as “non-efficient and responsive”, four as “efficient and non-responsive”, and only one was “efficient and responsive”.

    Growing conditions and genetic factors play a crucial role in the concentration of some compounds in sweet potato storage roots (TUMWEGAMIRE et al., 2011; WANG et al., 2016; ROSERO et al., 2020; PAZOS et al., 2022).

    The cultivar Uruguaiana differed from the ‘Canadense’ in the higher levels of dry matter, lipids, fiber, total and reducing sugars and starch in the storage roots. For both cultivars carbohydrates were the main components of the storage roots, followed by protein, ash, and lipids (Table 4).

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    Table 4
    Chemical composition of sweet potato roots as a function of cultivar, growing season and phosphorus doses.

    The results of the present study revealed that the moisture of sweet potato storage roots had isolated effects of cultivars and growing season and corresponded to a range of 75.13 to 80.05 g 100 g-1 (19.05 to 24.87 g 100g-1 of dry matter) (Table 4). The high-moisture content is an indicator of low dry matter and lower storage quality in storage roots. Sweet potato storage roots have a great variation in dry matter content, which is due to not only growing conditions and harvest time but is intrinsically linked to the genotype (ROSE & VASANTHAKAALAM, 2011; SHEKHAR et al., 2015).

    Sweet potato storage roots are transformed into various forms such as roasted, dried slices, cooked puree, powdered and fried products. The dry matter content of the storage roots is the most important character that determines the quality and yield of the products.

    Isolated effects of cultivars, growing season, phosphorus levels and the interaction between cultivar and fertilizer doses were observed for starch content in sweet potato storage roots (Table 4, Figure 4). Starch was the main component of the dry matter, with higher levels in the ‘Uruguaiana’ and in the plants cultivated in the rainy season. Storage roots are important energy sources due to their considerable starch contents (42.5 to 64.9% of dry matter) (WANG et al., 2016).

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    Figure 4
    Chemical composition of storage roots of sweet potato cultivars affected by growing season cultivation and/or doses of phosphorus. The square (■) represents the mean values of the two cultivars and the two seasons. The vertical bar in the figure area indicates the LSD value by t-test (P < 0.05). * and **, respectively, are significant at 5% and 1% probability by the t-test.

    The starch content in the storage roots of the ‘Canadense’ increased with increasing doses of phosphorus (Figure 4). For the ‘Uruguaiana’, there was a decrease in the starch content up to the dose of 200 kg ha-1. LEONEL et al. (2017) observed for potatoes that higher starch contents were observed in tubers when the plants were grown in soil with higher phosphorus availability, which occurs due to the participation of P in a series of key enzymes that are involved in the regulation of starch synthesis.

    The levels of total and reducing sugars in sweet potato storage roots were influenced by all factors and by the interaction between cultivar and fertilizer dose on reducing sugars (Table 4, Figure 4). Storage roots of the ‘Uruguaiana’, as well as those originating from plants grown in the rainy season, had higher levels of sugars. Increasing the dose of phosphate fertilizer led to an increase of approximately 19% in the reducing sugar content up to the estimated maximum dose of 354 kg ha-1 P2O5 for the ‘Uruguaiana’, with no effect for the ‘Canadense’. These results revealed that adequate availability of phosphorus in the soil influenced the production and allocation of assimilates into the storage roots, showing the positive effect of phosphorus on carbohydrate synthesis and the different responses of cultivars to phosphate fertilization.

    ADU-KWARTENG et al. (2014), evaluating the sugar profile of sweet potatoes storage roots, observed variation in the total sugar content from 4.10 to 10.82 g 100g-1 of dry matter, with the highest levels at the end of the growing season (five months). According to these authors, sucrose is the main sugar in cultivars with higher dry matter content, which was also observed in our study for ‘Uruguaiana’ that showed high levels of dry matter and total sugars.

    The sweet taste of sweet potato roots is due to the presence of sucrose, glucose, and fructose. During storage and cooking, maltose is observed resulting from the hydrolysis of starch by α- and β-amylases (WANG et al., 2016). XU et al. (2023) observed in their study with 81 sweet potato varieties that the fructose had average content of 24.64 mg g-1 ranging from 3.42 to 113.50 mg·g-1. The sucrose content varied from 22.50 to 146.41 mg·g-1, with an average value of 86.42 mg·g-1. Average content of glucose was 27.81 mg g-1, with a range of 3.81 to 131.48 mg·g-1.

    The increase in reducing sugar levels with fertilization can be a selection criterion for industrial processing. High levels of reducing sugars can lead to darkening of products subjected to high temperatures, which in most cases is undesirable during processing (LEONEL et al., 2017). Conversely, sugars can be used as substrates for fermentation, having softening effects on baked foods, such as breads and cakes, positively affecting their texture.

    Fibers play an important role in the human diet, and their content in the storage roots of sweet potato cultivars is quite variable. Effects of cultivars, growing season and fertilizer doses on fiber content were observed (Table 4, Figure 4).

    The fiber content in the storage roots of the ‘Uruguaiana’ was 46% higher than that observed for the ‘Canandese’. This characteristic of ‘Uruguaiana’ roots can be valued due to the health benefits of sweet potato fiber which were highlighted by LIU et al. (2020) who observed that sweet potato fibers provided a significant increase in the concentrations of Bifidobacterium and Lactobacillus and a significant decrease in Enterobacillus, Clostridium perfringens and Bacteroides in intestinal flora.

    Sweet potato storage roots harvested from plants grown in the rainy season had 42% more fiber than those grown in the dry season and increasing doses of P2O5 decreased fiber content in the roots. Genotype, root quality and climatic conditions and have been parameters reported in studies as interfering factors for fiber content in sweet potato. PAZOS et al. (2022) highlighted the effect of the genotype and reported for the ‘Arapey’ that the standard roots had a dietary fiber content 54% higher than the unmarketable roots (11.6 and 7.4% d.w., respectively). ROSERO et al. (2022) reported fiber contents in the storage roots from sweet potato cultivars grown in different locations ranging from 3.3 to 6.9% of dry matter and observed the effect of climatic conditions at the planting site, reporting that low accumulated precipitation negatively affected the accumulation of fiber.

    Protein content in sweet potato storage roots varied among the cultivars with a higher level for ‘Canandese’ (Table 4). The protein contents vary widely (1.3 to 9.5% of dry matter) (WANG et al., 2016). The higher availability of phosphorus due to the increase in the fertilizer dose caused a decrease in the protein content in the storage roots (Figure 4), a result also observed by LEONEL et al. (2017) in potato cultivars.

    Data analysis showed that there were isolated effects of cultivars, growing season and phosphorus fertilizer and the interaction between cultivar and P2O5 doses for ash content in sweet potato storage roots. The ash contents ranged from 0.59 to 0.73g/100g w.b., representing the total mineral content in the roots, with the highest levels observed for the ‘Canadense’, rainy season and low levels of phosphate fertilization (Table 4, Figure 4).

    Higher ash content is nutritionally interesting since sweet potato storage roots contain significant amounts of essential minerals for health. Fresh roots of sweet potato harvested at various locations showed contents ranging from 34 to 101 mg 100 g-1 for calcium, 15 to 37 mg 100 g-1 for magnesium, 28 to 58 mg 100 g-1 for phosphorus, 191 to 334 mg 100 g-1 for potassium, 0.62 to 1.26 mg 100 g-1 for iron, 0.37 to 0.69 mg 100 g-1 for zinc, 0.38 mg 100 g-1 for manganese and 0.12 mg 100 g-1 for copper (LAURIE et al., 2015).

    The lipid content in sweet potato storage roots was not influenced by the interaction of the studied factors, but there was an isolated effect of cultivars and phosphorus doses. The ‘Uruguaiana’ had an average of 38% higher lipid content and the increase in phosphorus doses reduced the total lipids content by about 34% up to the estimated maximum dose of 250 kg ha-1 P2O5.

    The phosphorus content in the sweet potato storage roots was higher in the ‘Canadense’, with an increase with the increase in the levels of phosphate fertilization. Regardless of the factors studied, the phosphorus content observed was higher than the levels reported by LAURIE et al. 2015 (28 to 58 mg 100 g-1 for phosphorus). The variation observed for the cultivars indicates differences in the absorption efficiency, and this is important since the use of cultivars with higher phosphorus efficiency is an option for sustainable production in low-P soils.

    The increase in the phosphorus content in sweet potato storage roots can affect the technological properties, given the starch phosphorylation process. The phosphorylation of starch in the plant plays a fundamental role in the remobilization and degradation of starch, which continuously contribute to the flow of carbon during the development of the storage root. Physicochemical and functional properties of starch are closely associated with the degree of phosphorylation of starch (LEONEL et al., 2016; LEONEL et al., 2021).

    CONCLUSION

    In the rainy season the total and marketable root yield were higher than in the dry season. Plants grown in the dry season had higher proportion of roots with defects. The optimum agronomic and economic doses were 128 and 95 kg ha-1 P2O5 for the cultivar Canadense, while the cultivar Uruguaiana did not respond to phosphate fertilization. The storage roots of Uruguaiana cultivar differed from ‘Canadense’ in its higher levels of dry matter, lipids, fiber, sugars, and starch. Higher doses of phosphate fertilizer led to greater accumulation of phosphorus, starch, and sugars in the storage roots. Considering the growing world market for sweet potatoes, this study contributes to production planning with a view to obtaining higher yields of roots with chemical compositions that meet the demands of both the fresh root market and industrial processing.

    ACKNOWLEDGMENTS

    This research was supported by the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) (Grant numbers 302827/2017-0 and 302848/2021-5) and was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), Brasil - Finance code 001.

    REFERENCES

    • CR-2024-0046.R2

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    Publication Dates

    • Publication in this collection
      25 Oct 2024
    • Date of issue
      2025

    History

    • Received
      29 Jan 2024
    • Accepted
      18 June 2024
    • Reviewed
      22 Aug 2024
    Creative Common - by 4.0
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