Cassava growth and productive performance at different planting times in the Agreste of Alagoas, Northeastern Brazil¹

Crescimento e desempenho produtivo da mandioca em diferentes épocas de plantio no Agreste de Alagoas, Nordeste do Brasil

ABSTRACT

The aim of this study was to evaluate the influence of different planting times and meteorological variables on the productive performance of industrial cassava in the Agreste region of Alagoas state, Brazil. The treatments were five planting dates, 25 days apart: D₁ - April 10, D₂ - May 5, D₃ - May 30, D₄ - June 24 and D₅ - July 19. The experiment was conducted from April 2021 to September 2023 (two cultivation cycles), using randomized blocks, with four replicates. The variables analyzed were agrometeorological data, crop growth and yield. In the Agreste region of Alagoas, the average daily ET₀ varies from 2.9 to 4.7 mm between the rainy and dry seasons, respectively. The average temperature of 24.3 °C meets the thermal demands of cassava cultivation. Although annual rainfall is sufficient to guarantee cassava production, it is seasonal, with a dry period from spring to summer, which compromises subsequent plantings. In the Agreste region of Alagoas, the best time to plant cassava is from April 10 to May 5, which is the beginning of the rainy season and ensures better vegetative canopy height (3.2 m), stem diameter (2.8 cm), leaf area index (3.0), maximum root length (43.1 cm), number (6.6) and yield (72.8 t ha^-1), total biomass (145 t ha^-1) and starch content (34.3%).

Key words:
Manihot esculenta Crantz; evapotranspiration; planting dates; root biomass; water deficit

HIGHLIGHTS:

Planting cassava at the beginning of the rainy season promotes normal growth and increases root starch content and yield.

Late cassava planting is not advisable, since it causes a greater risk of water stress during the plant’s critical period.

Rainfall seasonality affects cassava growth and yield.

RESUMO

O objetivo desta pesquisa foi avaliar a influência de diferentes épocas de plantio e variáveis ​​meteorológicas no desempenho produtivo da mandioca industrial na região do Agreste de Alagoas. Os tratamentos foram cinco datas de plantio, com espaçamento temporal de 25 dias entre elas: D₁ - 10 de abril, D₂ - 05 de maio, D₃ - 30 de maio, D₄ - 24 de junho e D₅ - 19 de julho. O período experimental foi de abril de 2021 a setembro de 2023, dois ciclos de cultivo. Utilizou-se o delineamento em blocos casualizados, com quatro repetições. As variáveis analisadas foram: dados agrometeorológicas e de crescimento e produção da cultura. Na região do Agreste de Alagoas, entre as estações chuvosa e seca, a ET₀ média diária varia de 2,9 a 4,7 mm, respectivamente. A temperatura média do ar é 24,3 °C e atende as demandas térmicas da cultura da mandioca. A precipitação anual é suficiente para garantir a produção de mandioca, porém, há sazonalidade nas chuvas, com período seco da primavera ao verão, o que prejudica plantios mais tardios. Na região do Agreste de Alagoas, o melhor período para o plantio da mandioca é de 10 de abril a 5 de maio, que é o início do período chuvoso da região e garante melhores resultados em: altura do dossel vegetativo (3,2 m), diâmetro do caule (2,8 cm), índice de área foliar (3,0), comprimento máximo (43,1 cm), número (6,6) e rendimento de raízes (72,8 t ha^-1), biomassa total (145 t ha^-1) e teor de amido (34,3%).

Palavras-chave:
Manihot esculenta Crantz; evapotranspiração; datas de plantio; biomassa de raízes; déficit hídrico

Introduction

Scientific advances led to exponential growth in the world population in the late 20th century. It is estimated that by 2100, there will be around 11 billion people on the planet, pressuring agricultural production systems and food security (UNDESA, 2015). In this respect, cassava (Manihot esculenta Crantz) stands out for its lower production costs, since it is commonly a rainfed crop in Brazil. However, under these conditions its yield is strongly influenced by planting date, soil type, and physical-hydric properties (Djaman et al., 2022; Enesi et al., 2022).

Rain is the water source for about 80% of the world’s agricultural lands, and approximately 60% of global food production comes from rainfed crops. As rainfall patterns become more uncertain, yields tend to decrease, affecting the global population (Howeler et al., 2013). Choosing the appropriate planting date is key to increasing cassava yield in rainfed conditions, given that the crop is most susceptible to water deficits in the first five months after planting (Conceição, 1981; Alves, 2002; Silva et al., 2021a).

In this context, a research project aimed at maximizing rain use, especially in semi-arid regions, is crucial (Moustakis et al., 2022). Understanding the planting date that minimizes water deficit during cultivation and maximizes cassava yield under different soil and climate conditions is relevant for combating hunger and generating income in rural areas. Although worldwide studies on the productive responses of cassava to more suitable planting dates show the benefits of planting on these dates, such as increased root and shoot yield and starch content (Enesi et al., 2022; Van Laere et al., 2023), few studies have analyzed cassava growth and yield as a function of planting dates in Northeast Brazil. As such, the aim of this study was to evaluate the influence of different planting seasons and meteorological variables on the productive performance of industrial cassava in the Agreste region of Alagoas, Brazil.

Material and Methods

The two field experiments were carried out from April 2021 to September 2023, in Arapiraca county, Agreste, in Alagoas state, Northeast Brazil (9° 46’ 07” S, 36° 33’ 41” W, 324 m). The local climate is AS (tropical), with average annual rainfall and temperature of 800 mm and 25 °C, respectively. The rainy season is from autumn to winter, and the dry period from spring to summer (Barros et al., 2012). The soil is classified as Argissolo Vermelho-Amarelo (Santos et al., 2018), which is equivalent to Ultisol, with a sandy loam texture. Soil chemical and physical-hydric properties in the 0.0 to 0.2 m layer are summarized in Table 1.

Table 1
Soil physical-hydric and chemical attributes in the study area

Chemical attributes	Value	Unit	Physical-hydric attributes	Value	Unit
pH	5.70	-	Field Capability	24.0	%
P	22.0	mg dm-3	Permanent wilting point	12.0	%
K+	0.27	cmolc dm-3	Available water capacity	93.0	mm
Ca2+	1.40	cmolc dm-3	Soil density	1.30	g cm-3
Mg2+	0.80	cmolc dm-3	Total porosity	52.0	%
Al3+	0.03	cmolc dm-3	Effective root depth	60.0	cm
Na	0.10	cmolc dm-3	Coarse sand	372	g kg-1
Cation exchange capacity	2.60	-	Fine sand	466	g kg-1
Base saturation	49.0	%	Total sand	838	g kg-1
Organic matter	0.70	%	Silt	18	g kg-1
			Clay	144	g kg-1

The experimental design used was randomized blocks, with four replicates. The industrial cassava was planted under rainfed conditions, on five dates: D₁ - April 10, D₂ - May 5, D₃ - May 30, D₄ - June 24 and D₅ - July 19, in 2021 and 2022, and harvested, respectively, on June 10, July 5, July 29, August 26 and September 19 of the following year. These dates were selected because the rainy season is concentrated in these months, when harvesting and replanting begins. The experimental plots measured 4.0 × 4.0 meters (16.0 m²).

The Caravela cassava cultivar, widespread in the region and characterized by high yield, was used (Silva et al., 2021b). Soil was harrowed five days before planting, with spacing of 1.0 × 0.5 m (20,000 plants per hectare). Base fertilization consisted of 40 kg ha^-1 of P₂O₅ and nitrogen fertilizer (40 kg ha^-1 of N) was added 45 days after planting (DAP). The sources of phosphorus (P) and nitrogen (N) used were simple superphosphate (18% of P₂O₅) and urea (45% of N), respectively, based on Alvarez et al. (1999). After planting, a pre-emergent herbicide based on Flumioxazin (200 g c.p. ha^-1, 400 L of spray ha^-1) was applied.

The following meteorological variables were assessed: minimum (T_MIN), average (T_AVE) and maximum (T_MAX) air temperature, average relative air humidity (RH_AVE), wind speed at 2.0 meters high (U₂) and rain, collected daily at an automatic meteorological station (Datalogger - CR-1000, Campbell Scientific, Logan, Utah) installed 50 meters from the experimental area.

The 10-day water balance of the crop was carried out using the Thornthwaite and Mather method, according to Pereira et al. (2002). Effective rainfall during cultivation was calculated by subtracting excess water, determined by the crop’s water balance, from total rainfall. Daily reference evapotranspiration (ET₀ - mm per day) was calculated using Eq. 1, standardized by Hargreaves & Samani (1985):

$$E{T}_0=a\times \frac{R_a}{2.45}\times {\left(T_{MAX}-T_{MIN}\right)}^b\times \left(T_{AVE}+c\right)$$ (1)

where:

R_a - extraterrestrial solar irradiation (MJ m^-2 per day);

T_MAX - maximum air temperature (°C);

T_MIN - minimum air temperature (°C); and,

T_MED - average air temperature (°C).

The values of a, b and c are adjustment coefficients of the equation, with a = 0.0023, b = 0.5 and c = 17.8.

Solar global irradiation at the top of the atmosphere (MJ m^-2) and correction of the relative earth-sun distance, was estimated by Eq. 2 and 3.

$$R_a=37.6\left(\frac{d}{D}\right)\left[\left(\frac{\pi }{{180}^o}\right)hn sen\Phi sen\delta +\cos \Phi \cos \delta senhn\right]$$ (2)

$${\left(\frac{d}{D}\right)}^2=1+0.033 \cos \left(NDA360/365\right)$$ (3)

where:

Φ - local latitude (degrees);

δ - solar declination (degrees);

hn - hour angle at sunrise (degrees); and,

d/D - correction of the relative earth-sun distance and NDA the number of the day of the year or Julian day.

Stem diameter (SD), plant height (PH) and leaf area index (LAI) were measured on eight plants per plot, at bimonthly intervals, characterizing plots subdivided over time, at two-month intervals, from the date of planting until harvest (14th month). Plant height was measured with a tape measure. Stem diameter was measured 0.3 m above ground level with a caliper. When determining the LAI, the leaf area (LA - cm²) was obtained, according to Gabriel et al. (2014), using Eq. 4.

$$LA=0.1774\times X^{2.4539} \left(R^2=0.96\right)$$ (4)

where:

X - Is the length of the largest leaf lobe (cm).

The sum of the value per leaf resulted in the LA_TOTAL of the plant. On sympodial branches, the LA of the stems was considered equal; thus, the LA of the stem was measured by multiplying the number of stems on each branch. This count considered the primary and secondary branches of the plant. Measurements were taken on all the leaves of each branch. Next, the LAI was determined by the ratio between the soil area occupied by the plant and the vegetative canopy coverage. During the cassava harvest, carried out at 14 months after planting (MAP), the following were measured in eight plants from the central rows of the experimental unit: maximum length (RL - cm) and diameter (RD - mm) of the roots, number (NR) of roots, root yield (RY - t ha^-1), stump yield (STY - t ha^-1), stem yield (SY - t ha^-1), leaf yield (LY - t ha^-1), shoot yield (stem + leaf, SHY - t ha^-1), total biomass (root + stump + stem + leaf, TB - t ha^-1), harvest index (HI) and root starch content (SC - %). The partitioned mass of the plant was obtained on a digital scale (Milla, China), with precision of 0.01 kg. Commercial roots were those longer than 10 cm and greater than 2 cm in diameter, according to Tironi et al. (2015). Root length and diameter were obtained with a tape measure and caliper, the latter measured in the central part of the roots. The harvest index was determined by the ratio of root mass to total plant mass, according to Silva et al. (2021b). Root starch content was determined using the hydrostatic balance method, according to Grossmann & Freitas (1950). SC data were only obtained in the second year of cultivation, due to equipment problems.

Individual variance analysis was carried out for each cultivation cycle, in addition to joint statistical analysis of the experiments. The magnitudes of the mean squares of the residues (MS Residues) were also analyzed and since they were homogeneous (the relationship or ratio between the largest and the smallest mean square (MQ) residues is not greater than 4.0) the two cultivation cycles were included in the joint analysis. The growth variables analyzed over time, at two-month intervals, from the planting date until the fourteenth month, when the harvest took place, were submitted to regression analysis, applying the t test (p ≤ 0.05). The means of the other variables were compared using the Scott-Knott test (p ≤ 0.05) (Ferreira, 2018).

Results and Discussion

The average minimum daily temperature during the first and second experiments was 20.8 (±1.6) and 20.9 (±0.9) °C, respectively. The lowest minimum temperature (16.1 °C) during the entire period (April 2021 to September 2023), occurred on August 16, 2021. The average maximum daily temperature was 28.8 (±2.6) and 29.0 (±2.4) °C, respectively, with the highest maximum temperature (35.9°C) recorded on November 6, 2021. The average daily temperature throughout the research was 24.3 (±1.5) °C.

Regions with temperatures ranging from 16 to 38 °C are ideal for cassava cultivation (Alves, 2002). Silva et al. (2021b) found normal cassava growth and development in Alagoas at an average temperature of 25.1 °C. Based on the above, the temperature of the Agreste region of Alagoas lies in the ideal thermal range for cassava cultivation with planting on all the dates studied. The average daily relative humidity throughout the research was 80.2 (± 6.3) %. The average relative humidity during the dry (spring and summer) and rainy (autumn and winter) was 74.1 (± 5.1) and 84.1 (± 5.6) %, respectively (Figure 1). The average wind speed in the dry and rainy periods was 1.6 (± 0.2) and 1.1 (± 0.3) m s^-1, respectively, with an overall mean of 1.4 (± 0.3) m s^-1.

Figure 1
Minimum (T_MIN), average (T_AVE) and maximum (T_MAX) daily air temperature and average relative air humidity (RH_AVE), in the Agreste region of Alagoas, Brazil, from April 2021 to September 2023

The average daily reference evapotranspiration (ET₀), regardless of the planting season, was 4.0 (± 0.8) mm. In the dry season, the average daily ET₀ was 4.7 (± 0.5) mm, while in the rainy period it was 2.9 (± 0.7) mm (Figure 2).

Figure 2
Decennial rainfall and reference evapotranspiration (ET₀) in the Agreste region of Alagoas, Brazil, from April 2021 to September 2023

Total rainfall during the first and second experiments, which includes all planting dates (April 2021 to September 2022 - 1st cycle and April 2022 to September 2023 - 2nd cycle), was 2,716 and 3,052 mm, respectively (Figure 2). Silva et al. (2021b) found that cassava can obtain a high root and shoot yield with 900 mm of water, well distributed throughout the cycle. This shows that the Agreste region of Alagoas receives enough rainfall to meet the plant’s water needs. However, given rainfall seasonality, as shown in Figure 2, determining the ideal planting date is important to prevent plant stress due to water deficit during the critical period.

In the 2021/22 cycle, the planting carried out on July 19 received the highest total rainfall (2,119 mm), a value relatively close to that of the other treatments. However, the plantings on this date received less than the other treatments, during the critical period of the crop (320 mm). Areas planted on April 10 received the highest total rainfall in the critical period (702 mm), 125% higher than that obtained on July 19. In the 2022/23 cycle, the May 5 planting received the highest total rainfall (2,618 mm). The July 19 planting had the lowest accumulated rainfall for the critical period (841 mm), while its April 10 counterpart received the highest (1,755 mm), 107% higher than the lowest value observed (Table 2).

Table 2
Total rainfall (R_T), in the plant’s critical period (P_CP) and effective rainfall (R_EF) in the cassava production cycles with different planting dates, in the Agreste region of Alagoas, Brazil, from to April 2021 to September 2023

Planting dates	Cycle 2021/22			Cycle 2022/23
	RT	PCP	REF	RT	PCP	REF
	mm
April 10	1,964	702	950	2,601	1,755	1,197
May 5	2,030	499	1,008	2,618	1,639	1,013
May 30	2,064	400	1,014	2,302	1,177	1,130
June 24	2,112	275	982	1,933	961	1,154
July 19	2,119	320	996	1,806	841	1,222

The high accumulated rainfall in the second cycle (2022/23) was due to the strong interference of the atmospheric-oceanic phenomenon known as ‘La Niña’. According to Oliveira (1999), this phenomenon is characterized by the abnormal cooling of the surface waters of the tropical Pacific Ocean and typically causes above-average rainfall in Northeast Brazil. This favored higher total rainfall during the critical cassava period on all planting dates of the second cycle (Table 2), compared to the first (2021/22). However, rainfall between the second ten days of September and the end of October 2022 was only 47 mm, which probably impacted the later planting on July 19, 2022, while the rainfall of the other treatments was better distributed throughout the plant’s critical period.

Figure 3 shows the water balance over the experimental period for the 2021/22 and 2022/23 cycle.

Figure 3
Decennial water balance, with emphasis on water deficit and surplus, in the Agreste region of Alagoas, Brazil, from April 2021 to September 2023

Soil water deficit in the April 10 plantings was 653 and 440 mm, in the first and second cultivation cycle, respectively. Water surplus was 1,014 and 1,404 mm and effective rainfall 950 and 1,197 mm. This is the water that was available to the plant, a value also equivalent to the real evapotranspiration (ET_R) of cassava. In the May 5 plantings, a water deficit of 645 and 429 mm, water surplus of 1,022 and 1,606 mm and effective rainfall of 1,008 and 1,013 mm, respectively, were observed. The water deficit in the May 30 plantings was 644 and 431 mm, in the first and second cultivation cycle, respectively, water surplus 1,050 and 1,171 mm and effective rainfall 1,014 and 1,131 mm. Planting on June 24 generated a water deficit of 645 and 433 mm, and on July 19, 650 and 449 mm, respectively. The water surplus was 1,130 and 779 mm, for June 24, and 1,223 and 584 mm, for July 19. In these areas planted later, the effective rainfall was 982 and 1,154 mm, for plantings on June 24, and 996 and 1,222 mm, for those on July 19.

Several researchers (Conceição, 1981; El-sharkawy, 2007; Silva et al., 2021a) reported that prolonged water deficits up to the fifth month after planting (critical period) compromise cassava establishment in the field, since it affects vegetative canopy formation and root differentiation, which reduces the number of storage roots, photosynthetic capacity, and photoassimilate accumulation. Thus, it is confirmed that planting cassava on April 10, the beginning of the rainy season in the Agreste region of Alagoas, ensures more uniform water distribution in the critical phase of the crop, as can be seen in Table 2. This guarantees normal root growth and, consequently, greater yield, as reported by Connor et al. (1981). This is confirmed in the topics to follow.

The different planting dates produced a significant difference in relation to all variables studied, except for root diameter. The regressions and discussions of the variables plant height, stem diameter and leaf area index were generated from the average values ​​of the cultivation cycles, since the years × months interaction was not significant. The highest cassava plant height (PH) was 3.2 m, observed in April 10 and May 5 plantings, 14 months after planting (MAP) (Figure 4A). Plantings on May 30, June 24 and July 19 obtained PH values of 2.7, 2.7 and 2.8 m (Figure 4C, D and E), respectively, 15% lower than the highest PH obtained. Rainfed plantings on dates that maximize the use of rainfall tend to guarantee higher cassava PH and, consequently, higher shoot yield. Furthermore, they favor initial plant growth without water stress and the formation of successful cultivation areas, thereby reducing invasive plant infestation and competition for water and solar radiation (Albuquerque et al., 2012), characteristics that were confirmed in this study, as will be discussed later.

Figure 4
Plant height of cassava planted on April 10 (A); May 5 (B); May 30 (C); June 24 (D) and July 19 (E), in the Agreste region of Alagoas, Brazil, as a function of months after planting

A linear adjustment of the variable stem diameter (SD) was observed on all planting dates. The highest SD (2.8 cm) occurred at 14 MAP in plants from areas planted on April 10, which is 11% higher than the lowest value obtained (2.5 cm), observed in the June 24 planting. In relation to the year factor, April 10 plants obtained a higher average SD in the two cultivation cycles studied, namely 2.0 and 2.3 cm, in 2021 and 2022, respectively (Figure 5). Albuquerque et al. (2012) and Pereira et al. (2022) reported that SD indicates whether stress has occurred in the phenological cycle of a plant, and higher SDs tend to be obtained in crops where the plants grew without significant stress, while crops under water stress and competition from invasive plants tend to exhibit lower SD. This confirms the data from this research, since later plantings (June 24 and July 19), under lower accumulated rainfall, obtained a lower SD because they are more susceptible to water stress and lower yields, as reported by Wang et al. (2017).

Figure 5
Stem diameter of cassava planted on April 10 (A); May 5 (B); May 30 (C); June 24 (D); July 19 (E) as a function of months after planting and means for the interaction between planting dates and years of cassava cultivation (F), in the Agreste region of Alagoas, Brazil, from April 2021 to September 2023

The highest maximum leaf area index (LAI) was estimated for planting carried out on April 10 (3.0), 8.3 MAP (Figure 6A). In later planting areas, the lowest maximum LAIs were observed in June 24 and July 19 plants (1.4 and 1.6), 9.3 and 10 MAP, respectively (Figures 6D and E). These values are 53 and 46% lower than the highest maximum LAI observed.

Figure 6
Leaf area index of cassava planted on April 10 (A); May 5 (B); May 30 (C); June 24 (D); July 19 (E) as a function of months after planting and means for the interaction between planting dates and years of cassava cultivation (F), in the Agreste region of Alagoas, Brazil, from April 2021 to September 2023

Santanoo et al. (2020) found that planting cassava on dates that maximize rainwater produces greater LAI and photosynthetic capacity, which produces more photoassimilates and guarantees higher yields. Conceição (1981) observed that cassava exhibits abundant leaf mass from the sixth to the tenth month after planting, since at this stage of the phenological cycle maximum photoassimilate accumulation occurs in the plant’s root system. In light of the above, planting at the beginning of the rainy season (April 10) in the Agreste of Alagoas ensures normal cassava growth and development, higher LAI in a shorter time frame and in an important phenological phase for increased root mass, when compared to later plantings (June 24 and July 19). The lower LAI in June 24 and July 19 plantings is linked to the fact that the dry season begins in September in the region (Figure 2), thereby impacting the cassava phenological cycle, which has yet to undergo the most critical growth stage (1 to 5 MAP), entering physiological rest with little leaf mass, thereby compromising its photosynthetic capacity and yield.

In terms of the year factor, a higher cassava LAI was observed in areas planted on April 10, with average values of 2.0 and 2.3, in 2021 and 2022, respectively (Figure 6F). The higher LAI on April 10 is probably related to the more uniform rainfall distribution for plantings at the beginning of the rainy season, since in both cycles (2021/22 and 2022/23), a higher accumulation of uniform rainfall (702 and 1,755 mm) was observed during the critical period, which ensured greater leaf mass when compared to later planting dates (June 24 and July 19). It should be noted that despite the greater rainfall accumulation (961 and 841 mm) in the second cycle (2022/23) on later dates during the critical period, the distribution was irregular (Figure 2), which delayed the increase in leaf mass in the phenological phase, characterized by vegetative canopy establishment (Figure 6D and E).

Plantings from April 10 to May 30 exhibited the greatest root length (RL), with an overall average of 43.1 cm. Areas planted on July 19 generated the lowest RL (29.3 cm), 32% lower than the highest value obtained (Figure 7A). With respect to the year factor, there was a greater number of roots (NR) for plantings on April 10th and May 5th, with an overall average of 6.6 roots per plant. An average NR of 3.6 was observed for the other planting dates (Figure 7C). Thus, plantings at the beginning of the rainy season tend to guarantee greater length and number of roots in cassava crops, in contrast to later plantings. This was because planting at the beginning of the rainy season ensures better rainfall distribution during the plant’s critical period, without water deficit, as shown in Table 2, which, according to Conceição (1981) and Alves (2002), guarantees greater root length and a larger number of storage roots.

Figure 7
Means for planting dates, regardless of the cultivation year for root length (A) and root yield (B), and means for the interaction between planting dates and cultivation year for number of roots (C); stump (D), stem (E), leaf (F), shoot (G) total biomass (H) yield and cassava harvest index (I), in the Agreste region of Alagoas, Brazil, from April 2021 to September 2023

The highest cassava root yield (RY) was observed in areas planted on April 10 and May 5, with an overall average of 72.8 t ha^-1, while the lowest RY was obtained in areas planted on July 19 (32.6 t ha^-1), a value 55% lower than the highest RY obtained (Figure 7B). Fagundes et al. (2010) and Coelho Filho (2020) found that planting cassava on dates that maximize rainwater, such as the beginning of the rainy season, guarantees plant establishment in the field, with the formation of a larger number of storage roots and LAI, which tends to ensure greater final harvest yield, since water availability is highest in the critical period for cassava, from the 1 to 5 MAP. This explains the higher RY in plantings carried out from April 10 to May 5, since the rainy season begins in autumn, which guarantees greater water availability for cassava during its critical period.

In general, cassava planted on April 10 had the highest overall average stump yield (STY) (6.3 t ha^-1) in both cultivation cycles (Figure 7D). The highest average stem yield (SY) in the 2021 cycle was obtained in planting carried out on April 10 (49.1 t ha^-1), while in 2022, planting on April 10 and May 5 were equal and obtained the highest SY, with an average of 69.2 t ha^-1. Plantings carried out from May 30 to July 19 had an average of 25.6 and 31.1 t ha^-1 in 2021 and 2022, respectively, values 48 and 55% lower than the highest SY observed (Figure 7E).

In 2021, leaf yield (LY) did not differ between planting dates, obtaining an average of 7.6 t ha^-1. However, in the 2022 cycle, planting on April 10 generated the highest LY (9.5 t ha^-1), while those from May 30 to July 19 performed worse, with an average of 4.9 t ha^-1, which is 48% lower than the highest value (Figure 7F). The highest average cassava shoot yield (SHY) in the 2021 and 2022 cycle, was 57.9 and 78.1 t ha^-1, respectively, with planting on April 10, but in the latter cycle, planting on May 5 was practically equal to that of April 10, with an SHY of 77.6 t ha^-1. In both cycles, planting on July 19 generated the lowest SHY, with an average of 29.1 t ha^-1 (Figure 7G).

The highest cassava total biomass (TB) was produced in areas planted on April 10 and May 5, with an overall average of 121.9 and 167.7 t ha^-1, in 2021 and 2022, respectively. The lowest TB value in both cycles was observed in plantings on June 24 and July 19, with averages of 80.5 and 70.3 t ha^-1, respectively, 34 and 58% lower than the highest values observed (Figure 7H).

Uniform water availability during the cassava cycle is essential for higher yields of commercial roots and shoots, and greater rainfall during the plant’s critical period tends to favor more vigorous shoots, since the vegetative canopy forms faster, thereby increasing the plant’s capacity to tolerate adverse weather conditions (Pereira et al., 2022). This confirms the data reported here, whereby April 10 plants had greater water availability in the 2021 and 2022 cycles (702 and 1,755 mm, respectively), during the critical period, which ensured greater growth and biomass production. Furthermore, the higher biomass production in 2022 is probably linked to the fact that above-average rainfall occurred in the region due to the strong interference of ‘La Niña’.

In relation to the harvest index (HI), a significant difference was found only for the 2022 cycle, with the highest HI obtained in planting areas on May 30 and June 24, with an overall average of 0.55, which is 66 % higher than the lowest HI (0.33), obtained with the July 19 planting (Figure 7I). Souza et al. (2010) and Silva et al. (2021b) observed cassava HI between 0.37 and 0.48, under rainfed conditions in the Brazilian Northeast. According to these researchers, prolonged water deficits, soil conditions and the cultivar used can affect the plant’s source-sink relationship and impact the shoot or root biomass production, which can affect cassava HI. Thus, the later cassava planting in the Agreste of Alagoas, on July 19, generates a lower HI, because shoot biomass production is higher and root mass lower.

The different planting dates generated a significant difference (p ≤ 0.05) in terms of cassava starch content (SC) evaluated in the 2022 cycle. The highest cassava SC was 34.3%, obtained in areas planted on April 10. Performance on the other planting dates was lower or equal, with an overall average SC of 26.9%, which is 21% lower than the highest observed (Table 3).

Table 3
Average cassava starch content at different planting dates in 2022, in the Agreste region of Alagoas, Brazil

Planting dates	Starch content (%)
April 10	34.37 a
May 5	28.98 b
May 30	26.52 b
June 24	25.85 b
July, 19	24.10 b
CV (%)	9.58

• CV - Coefficient of Variation. Means followed by the same letter do not differ according to the Scott-Knott test (p ≤ 0.05)

Morais et al. (2016) evaluated industrial cassava genotypes in the Agreste of Alagoas, observing an average starch content of 31.1% with the Caravela variety, planted in June, a value 9.0% lower than the highest SC found here. According to these researchers, cassava genotypes have little influence on starch content when submitted to different growing conditions or environments. However, adequate crop management, free from pest attack and diseases, competition with invasive plants and planting on suitable dates that reduce the risk of deficit, can maximize Cassava SC and guarantee greater agro-industrial yield. That said, planting cassava on April 10 in the study region is more favorable for cassava and when combined with adequate management, can yield a higher starch content.

Conclusions

1. In the Agreste region of Alagoas, the average daily reference evapotranspiration (ET₀) varies from 2.9 to 4.7 mm, between the rainy and dry seasons, respectively. The average temperature of 24.3 °C meets the thermal demands of cassava cultivation.

2. Annual rainfall is sufficient to guarantee cassava production; however, it is seasonal, with a dry season from spring to summer, which compromises later plantings (July 19).

3. The best period for planting cassava in the Agreste region of Alagoas is from April 10 to May 5, which results in higher growth and yield.

Literature Cited

• Albuquerque, J. A. A.; Sediyama, T.; Silva, A. A.; Alves, J. M. A.; Finoto, E. L.; A. Neto, F. D.; Silva, G. R. Desenvolvimento da cultura de mandioca sob interferência de plantas daninhas. Planta Daninha, v.30, p.37-45, 2012. https://doi.org/10.1590/S0100-83582012000100005
  » https://doi.org/10.1590/S0100-83582012000100005
• Alvarez, V. V. H.; Ribeiro, A. C.; Ribeiro, A. C.; Guimarães, P. T. G.; Alvarez, V. V. H. Recomendações para o uso de corretivos e fertilizantes em Minas Gerais: 5ª aproximação. Viçosa, MG: Comissão de Fertilidade do Solo do Estado de Minas Gerais-CFSEMG. 1999. 359p.
• Alves, A. A. C. Cassava botany and physiology. In: Hillocks, R. J.; Thresh, J. M.; Bellotti, A. C. Cassava: Biology, production and utilization. 2002. Cap. 67-89. New York: Wallingford. https://doi.org/10.1079/9780851995243.0067
  » https://doi.org/10.1079/9780851995243.0067
• Barros, A. H. C.; Araújo Filho, J. C.; Silva, A. B.; Santiago, G. A. C. Climatologia do estado de Alagoas. Recife: Embrapa, 2012. 32p.
• Coelho Filho, M. A. Irrigação da cultura da mandioca. Cruz das Almas: Embrapa, 2020. 12p.
• Conceição, A. J. A mandioca. São Paulo: Nobel, 1981. 382p.
• Connor, D. J.; Cock, J. H.; Parra, G. E. Response of cassava to water shortage I. Growth and yield. Field Crops Research, v.4, p.181-200, 1981. https://doi.org/10.1016/0378-4290(81)90071-X
  » https://doi.org/10.1016/0378-4290(81)90071-X
• Djaman, K.; Allen, S.; Djaman, D. S.; Koudahe, K.; Irmak, S.; Puppala, N.; Angadi, S. V. Planting date and plant density effects on maize growth, yield and water use efficiency. Environmental Challenges, v.6, e100417, 2022. https://doi.org/10.1016/j.envc.2021.100417
  » https://doi.org/10.1016/j.envc.2021.100417
• El-Sharkawy, M. A. Physiological characteristics of cassava tolerance to prolonged drought in the tropics: Implications for breeding cultivars adapted to seasonally dry and semiarid environments. Brazilian Journal of Plant Physiology, v.19, p.257-286, 2007. https://doi.org/10.1590/S1677-04202007000400003
  » https://doi.org/10.1590/S1677-04202007000400003
• Enesi, R. O.; Hauser, S.; Pypers, P.; Kreye, C.; Tariku, M.; Six, J. Understanding changes in cassava root dry matter yield by different planting dates, crop ages at harvest, fertilizer application and varieties. European Journal of Agronomy, v.133, e126448, 2022. https://doi.org/10.1016/j.eja.2021.126448
  » https://doi.org/10.1016/j.eja.2021.126448
• Fagundes, L. K.; Streck, N. A.; Rosa, H. T.; Walter, L. C.; Zanon, A. J.; Lopes, S. J. Desenvolvimento, crescimento e produtividade de mandioca em diferentes datas de plantio em região subtropical. Ciência Rural, v.40, p.2460-2466, 2010. https://doi.org/10.1590/S0103-84782010001200004
  » https://doi.org/10.1590/S0103-84782010001200004
• Ferreira, P. V. Estatística experimental aplicada às Ciências Agrárias. Viçosa: UFV, 2018. 588p.
• Gabriel, L. F.; Streck, N. A.; Roberti, D. R.; Chielle, Z. G.; Uhlmann, L. O.; Silva, M. R.; Silva, S. D. Simulating cassava growth and yield under potential conditions in Southern Brazil. Agronomy Journal, v.106, p.1119-137. 2014. http://dx.doi.org/10.2134/agronj2013.0187
  » http://dx.doi.org/10.2134/agronj2013.0187
• Grossmann, J.; Freitas, A. C. Determinação do teor de matéria seca pelo peso específico em raízes de mandioca. Revista Agronômica, v.14, p.75-80, 1950.
• Hargreaves, G. H.; Samani, Z. A. Reference crop evapotranspiration from temperature.Applied Engineering in Agriculture, v.1, p.96-99, 1985. http://dx.doi.org/10.13031/2013.26773
  » http://dx.doi.org/10.13031/2013.26773
• Howeler, R.; Lutaladio, N.; Thomas, G. Save and grow cassava: a guide to sustainable production intensification. Rome: FAO, 2013. 142p.
• Morais, L. K.; Santiago, A. D.; Cavalcante, M. H. B. Avaliação de genótipos de mandioca tipo indústria no Estado de Alagoas. Aracaju: Embrapa, 2016. 24p.
• Moustakis, Y.; Fatichi, S.; Onof, C.; Paschalis, A. Insensitivity of ecosystem yield to predicted changes in fine‐scale rainfall variability. Journal of Geophysical Research: Biogeosciences, v.127, e2021JG006735, 2022. https://doi.org/10.1029/2021JG006735
  » https://doi.org/10.1029/2021JG006735
• Oliveira, G. S. O El Niño e você: o fenômeno climático. São José dos Campos: Transtec, 1999. 116p.
• Pereira, A. R.; Angelocci, L. R.; Sentelhas, P. C. Agrometeorologia: Fundamentos e aplicações práticas. Guaíba: Agropecuária, 2002. 478p.
• Pereira, L. F. M; Santos, H. L.; Zanetti, S.; Oliveira, B. I. A.; Santos, T. L. R.; Rodrigues, T. M.; Almeida, S. M. Morphology, biochemistry, and yield of cassava as functions of growth stage and water regime. South African Journal of Botany, v.149, p.222-239, 2022. https://doi.org/10.1016/j.sajb.2022.06.003
  » https://doi.org/10.1016/j.sajb.2022.06.003
• Santanoo, S.; Vongcharoen, K.; Banterng, P.; Vorasoot, N.; Jogloy, S.; Roytrakul, S.; Theerakulpisut, P. Canopy structure and photosynthetic performance of irrigated cassava genotypes growing in different seasons in a tropical savanna climate. Agronomy, v.10, e2018, 2020. https://doi.org/10.3390/agronomy10122018
  » https://doi.org/10.3390/agronomy10122018
• Santos, H. G.; Jacomine, P. K. T.; Anjos, L. H. C.; Oliveira, V. A.; Lumbreras, J. F.; Coelho, M. R.; Almeida, J. A.; Araújo Filho, J. C.; Oliveira, J. B.; Cunha, T. J. F. Sistema Brasileiro de Classificação de Solos. Brasília: Embrapa, 2018. 356p.
• Silva, R. B.; Teodoro, I.; Souza, J. L.; Ferreira Junior, R. A.; Magalhaes, I. D.; Santos, M. A.; Lyra, G. B.; Moura Filho, G.; Souza, R. C.; Silva, L. K. S.; Santos, J. V.; Oliveira, J. D. S. Physiological and productive aspects of cassava under different irrigation levels. Bragantia, v.80, e5321, 2021a. https://doi.org/10.1590/1678-4499.20200501
  » https://doi.org/10.1590/1678-4499.20200501
• Silva, R. B.; Teodoro, I.; Souza, J. L. D.; Magalhães, I. D.; Morais, M. A. F. D.; Teodoro, I. P. D. O.; Santos, W. M. D. Growth, yield and viability of irrigation in cassava crop in the Alagoas Coastal Plateaus. Ciência Rural, v.52, e20210145, 2021b. https://doi.org/10.1590/0103-8478cr20210145
  » https://doi.org/10.1590/0103-8478cr20210145
• Souza, M. J. L. D.; Viana, A. E. S.; Matsumoto, S. N.; Vasconcelos, R. C. D.; Sediyama, T.; Morais, O. M. Características agronômicas da mandioca relacionadas à interação entre irrigação, épocas de colheita e cloreto de mepiquat. Acta Science, v.32, p.45-53, 2010. https://doi.org/10.4025/actasciagron.v32i1.720
  » https://doi.org/10.4025/actasciagron.v32i1.720
• Tironi, L. F.; Uhlmann, L. O.; Streck, N. A.; Samboranha, F. K.; Freitas, C. P. O.; Silva, M. R. Desempenho de cultivares de mandioca em ambiente subtropical. Bragantia, v.74, p.58-66, 2015. https://doi.org/10.1590/1678-4499.0352
  » https://doi.org/10.1590/1678-4499.0352
• UNDESA - United Nations Department of Economic and Social Affairs. Population division world population prospects: the 2015 revision, key findings and advance tables. New York: UNDESA, 2015.
• Van Laere, J.; Munyahali, W.; De Bauw, P.; Dercon, G.; Kintche, K.; Merckx, R. Early planting of cassava enhanced the response of improved cultivars to potassium fertilization in South Kivu, Democratic Republic of Congo. Field Crops Research , v.296, e108903, 2023. https://doi.org/10.1016/j.fcr.2023.108903
  » https://doi.org/10.1016/j.fcr.2023.108903
• Wang, X.; Meng, Z.; Chang, X.; Deng, Z.; Li, Y.; Lv, M. Determination of a suitable indicator of tomato water content based on stem diameter variation. Scientia Horticulturae, v.215, p.142-148, 2017. https://doi.org/10.1016/j.scienta.2016.11.053
  » https://doi.org/10.1016/j.scienta.2016.11.053

• ¹ Research developed at Universidade Federal de Alagoas, Arapiraca, AL, Brazil

Supplementary documents

• There are no supplementary documents.

Financing statement

• There was no funding for this research.

Edited by

• Editors: Ítalo Herbet Lucena Cavalcante & Walter Esfrain Pereira

Data availability

There are no supplementary documents.

Publication Dates

• Publication in this collection
  03 Feb 2025
• Date of issue
  June 2025

History

• Received
  16 Apr 2024
• Accepted
  10 Dec 2024
• Published
  16 Dec 2024