Sowing date changes phenological development, plastochron index, and grain yield of soybeans under Cerrado conditions1 1 Research developed at Selvíria, MS, Brazil

Épocas de semeadura alteram o desenvolvimento fenológico, índice de plastocrono e produtividade de soja em condições de Cerrado

João W. Bossolani Hugo H. A. Meneghette Izabela R. Sanches Fabiana L. dos Santos Lucas F. Parra Edson Lazarini About the authors

HIGHLIGHTS:

Delayed sowing causes detrimental effects on the development and grain yield of extra-early and early cycle cultivars of soybeans.

Delayed sowing increased the plastochron index and reduced the crop cycle and growth of soybean cultivars.

In the region of Selvíria-MS, sowing in November was the most suitable for soybean.

ABSTRACT

The sowing date is a crop management practice that affects soybean development and grain yield, and is directly related to the genotype and cycle type. Our objective was to evaluate phenological development as a function of photoperiodic responses, plastrochron index, and grain yield in three soybean cultivars with different growth cycles sown on three sowing dates. The study was conducted in Selvíria, Mato Grosso do Sul State, Brazil, using a split-plot design with the main plots arranged in blocks with four replications. The main plots included three sowing dates, 15 days apart, beginning on November 15, and the subplots were composed of three cultivars: BMX Turbo RR (extra-early cycle), BMX Potência RR (early cycle), and TMG 1180 RR (medium cycle). Delayed sowing increased the plastochron index and reduced the growth cycle duration, plant height, node number of the main stem, and pod number per plant. We found that cultivars with longer cycles were more suitable for delayed sowing, had improved vegetative and reproductive development, and had higher grain yields than those with shorter periods. The second sowing date was most suitable for soybean cultivation in this region.

Key words:
photoperiod; Glycine max L.; phenological stages; delayed sowing

RESUMO

A época de semeadura é a prática de manejo cultural com maior interferência no desenvolvimento e na produtividade de grãos de soja, e está diretamente relacionada com o genótipo e tipo de ciclo da cultura. Nosso objetivo foi avaliar o desenvolvimento fenológico em função das respostas fotoperíodicas, índice de plastocrono e produtividade de grãos de três cultivares de soja com ciclos diferentes, semeadas em três épocas distintas O estudo foi realizado em Sevíria, Mato Grosso do Sul e utilizou um delineamento de parcelas subdivididas com as parcelas principais dispostas em blocos com quatro repetições. As parcelas foram compostas por três épocas de semeadura com intervalo de 15 dias, a partir de 15 de novembro, e as subparcelas foram compostas por três cultivares: BMX Turbo RR (ciclo extra-precoce), BMX Potência RR (ciclo precoce) e TMG 1180 RR (ciclo médio). A semeadura tardia aumentou o índice de plastocrono e reduziu a duração do ciclo de crescimento, altura da planta, número de nós no caule principal e número de vagens por planta. Nossos resultados demonstram que cultivares com ciclos mais longos são mais adequadas para semeadura tardia, apresentam melhor desenvolvimento vegetativo e reprodutivo e maior rendimento de grãos. A segunda época de semeadura foi a mais adequada para o cultivo da soja na região.

Palavras-chave:
fotoperíodo; Glycine max L.; estádios fenológicos; semeadura tardia

Introduction

Many soybean cultivars are grown in tropical regions, and several others are introduced to the market every year (Nath et al., 2017Nath, A.; Karunakar, A. P.; Kumar, A.; Nagar, R. K. Effect of sowing dates and varieties on soybean performance in Vidarbha region of Maharashtra, Indian. Journal of Applied Science, v.9, p.544-550, 2017. https://doi.org/10.31018/jans.v9i1.1227
https://doi.org/10.31018/jans.v9i1.1227...
). The evaluation of the development and adaptation of soybean cultivars to different edaphoclimatic conditions and the determination of the optimum sowing date (SD) are essential for improving the efficiency of soybean production and harvest planning (Streck et al., 2008Streck, N. A.; Paula, G. M. D.; Camera, C.; Menezes, N. L. D.; Lago, I. Estimativa do plastocrono em cultivares de soja. Bragantia, v.67, p.67-73, 2008. https://doi.org/10.1590/S0006-87052008000100008
https://doi.org/10.1590/S0006-8705200800...
; Zanon et al., 2015Zanon Junior, A.; Winck, J. E. M.; Streck, N. A.; Rocha, T. S. M. da; Cera, J. C.; Richter, G. L.; Lago, I.; Santos, P. M. dos; Maciel, L. da R.; Guedes, J. V. C.; Marchesan, E. Desenvolvimento de cultivares de soja em função do grupo de maturação e tipo de crescimento em terras altas e terras baixas. Bragantia , v.74, p.400-411, 2015. https://doi.org/10.1590/1678-4499.0043
https://doi.org/10.1590/1678-4499.0043...
).

Higher agricultural yields can be obtained by understanding the dynamics of the production chain (Matoso et al., 2018Matoso, A. O.; Soratto, R. P.; Guarnieri, F.; Costa, N. R.; Abrahão, R. C.; Tirabassi, L. H. Sowing date effects on cowpea cultivars as a second crop in Southeastern Brazil. Agronomy Journal, v.110, p.1-14, 2018. https://doi.org/10.2134/agronj2018.01.0051
https://doi.org/10.2134/agronj2018.01.00...
). The most important management practices for increasing grain yield (GY) are the determination of the optimum sowing date (SD) and selection of genotypes adapted to the agroclimatic region (Ezeaku et al., 2015Ezeaku, I. E.; Mbah, B. N.; Baiyeri, K. P. Planting date and cultivar effects on growth and yield performance of cowpea (Vigna unguiculata (L.) Walp). African Journal of Plant Science, v.9, p.439-448, 2015. https://doi.org/10.5897/AJPS2015.1353
https://doi.org/10.5897/AJPS2015.1353...
).

The optimum theoretical period for sowing soybeans is 30-45 days before the summer solstice because these plants are sensitive to the photoperiod and prefer shorter days (Slafer et al., 2015Slafer, G. A.; Kantolic, A. G.; Appendino, M. L.; Tranquilli, G.; Miralles, D. J.; Savin, R. Genetic and environmental effects on crop development determining adaptation and yield. In: Sadras, V. O.; Calderini, D. (eds.) Crop physiology: Applications for genetic improvement and agronomy. Amsterdam: Elsevier, 2015. p.285-319.; Zanon et al., 2015Zanon Junior, A.; Winck, J. E. M.; Streck, N. A.; Rocha, T. S. M. da; Cera, J. C.; Richter, G. L.; Lago, I.; Santos, P. M. dos; Maciel, L. da R.; Guedes, J. V. C.; Marchesan, E. Desenvolvimento de cultivares de soja em função do grupo de maturação e tipo de crescimento em terras altas e terras baixas. Bragantia , v.74, p.400-411, 2015. https://doi.org/10.1590/1678-4499.0043
https://doi.org/10.1590/1678-4499.0043...
).

Plant emergence rate and the node number per plant (NNP) are essential parameters of plant development (Martins et al., 2011Martins, J. D.; Radons, S. Z.; Streck, N. A.; Knies, A. E.; Carlesso, R. Plastochron and final node number of soybean cultivars as a function of sowing date. Ciência Rural, v.41, p.954-959, 2011. ) that can be estimated by measuring the time necessary for the appearance of two successive nodes in the same stem, and the thermal sum of the period (Jing et al., 2017Jing, Q.; Huffman, T.; Shang, J.; Liu, J.; Pattey, E.; Morrison, M.; Jégo, G.; Qian, B. Modelling soybean yield responses to seeding date under projected climate change scenarios. Canadian Journal of Plant Science, v.97, p.1152-1164, 2017. https://doi.org/10.1139/cjps-2017-0065
https://doi.org/10.1139/cjps-2017-0065...
). In dicotyledons, this interval is known as the plastochron index (PI) (Rockenbach et al., 2016Rockenbach, A. P.; Caron, B. O.; Souza, V. Q.; Elli, E. F.; Oliveira, D. M. de; Monteiro, G. C. Estimated length of soybean phenological stages. Semina: Ciências Agrárias, v.37, p.1871, 2016. https://doi.org/10.5433/1679-0359.2016v37n4p1871
https://doi.org/10.5433/1679-0359.2016v3...
).

The objective of this study was to evaluate the photoperiodic responses related to phenological development, PI, and GY in three soybean cultivars with different growth cycles sown on three sowing dates.

Material and Methods

The study was conducted over two years in an experimental area located in Selvíria, Mato Grosso do Sul State, in the central-west region of Brazil (51º22’ W 20º22’ S; 335 m.a.s.l.). The soil of the experimental area was characterized as Typic Haplorthox (USDA, 1999USDA - United States Department of Agriculture. Soil Taxonomy: A basic system of soil classification for making and interpreting soil surveys. Washington, DC, Agriculture Handbook, 2.ed. 1999. 886p.). The rainfall, and maximum and minimum temperatures of the air at the study site are presented in Figure 1.

Figure 1
Data of rainfall, maximum and minimum temperatures of the air in the experimental area at Selvíria, Mato Grosso do Sul State, Brazil, during 2015/2016 (A) and 2016/2017 (B)

The sowing system was no-tillage, and the experiments were performed in the same area in spring and summer. In the last 12 years, the experimental area has been cultivated with maize in the off-season (fall/winter) and soybean during the growing season (spring/summer). This sequence of cultivation is most commonly used in Brazil.

Before the installation of the experimental plots, the 0-0.20 m layer of the soil was sampled for chemical analysis according to the methodologies described by van Raij et al. (2001van Raij, B. V.; Andrade, J. C. de; Cantarella, H.; Quaggio, J. A. Chemical analysis to evaluate the fertility of tropical soils. Campinas: Instituto Agronômico. 2001. 285p.), and presented the following characteristics: phosphorus (Presin): 22 mg dm-3; soil organic matter (SOM): 21 g dm-3; pH (CaCl2): 5.5; exchangeable potassium (K+): 1.8 mmolc dm-3; exchangeable calcium (Ca2+): 22 mmolc dm-3; exchangeable magnesium (Mg2+): 19 mmolc dm-3; potential acidity at pH 7 (H + Al): 22 mmolc dm-3; base saturation (BS): 42.8 mmolc dm-3; cation exchange capacity (CEC): 64.5 mmolc dm-3; and base saturation (BS, %): 66%.

The granulometric characteristics of the 0-0.20 and 0.20-0.40 m layers were 545 and 513 g kg-1 for clay, 347 and 360 g kg-1 for sand, and 108 and 127 g kg-1 for silt, respectively.

The soil physical properties (0-0.20 m layer) were as follows: microporosity (34.6%), macroporosity (8.2%), total porosity (42.8%), soil bulk density (1.6 kg dm-3), water retention at field capacity (0.35 g g-1), and permanent wilting point (0.08 g g-1).

The study used a split-plot design with the main plots arranged in blocks with four replications. The main plots included three SDs, and the subplots were composed of three cultivars.

The main plots included November 15, 2015 (1st SD), November 30, 2015 (2nd SD), and December 15, 2015(3rd SD) for the first year; and November 15, 2016 (1st SD), November 29, 2016 (2nd SD), and December 14, 2016 (3rd SD) for the second year. The subplots were composed of three cultivars (BMX Turbo RR [C1], BMX Potência RR [C2], and TMG 1180 RR [C3], Cambé-PR, Brazil).

The first SD corresponded to the commonly recommended time for on-site geoclimatic conditions, while the second SD was considered a marginal period for sowing, and the third SD was considered incompatible with the regional conditions (Ferrari et al., 2015Ferrari, E.; Paz, A. da; Silva, A. C. da. Déficit hídrico e altas temperaturas no metabolismo da soja em semeaduras antecipadas. Nativa, v.3, p.67-77, 2015. https://doi.org/10.31413/nativa.v3i1.1855
https://doi.org/10.31413/nativa.v3i1.185...
). Each experimental plot consisted of seven 10 m rows with an inter-row spacing of 0.45 m.

This study was conducted over two consecutive years (2015/2016 and 2016/2017). The same amounts of agricultural inputs were used for both years to minimize the random effects. A total of 20 kg ha-1 of N, 60 kg ha-1 of P2O5, and 60 kg ha-1 of K2O were used for fertilization at sowing (Ambrosano et al., 1997Ambrosano, E. J.; Tanaka, R. T.; Mascarenhas, H. A. A.; van Raij, B.; Quaggio, J. A.; Cantarella, H. Leguminosas e oleaginosas. Recomendações de adubação e calagem para o Estado de São Paulo, v.2, p.187-203, 1997.).

The plant density per hectare for cultivars C1 and C2 was 380 000, and 360 000, respectively, and 320 000 for C3. Seeds were treated with fungicides (Carboxin + Thiram, each at 100 mL a.i. 100kg-1 seeds) before inoculation and sowing. Phytosanitary treatments were performed according to the requirements of soybean crops (Seixas et al., 2020Seixas, C. D. S.; Neumaier, N.; Balbinot Junior, A. A.; Krzyzanowski, F. C.; Leite, R. D. C. Tecnologias de produção de soja. Londrina: Embrapa Soja-Sistema de Produção (INFOTECA-E). 2020. 347p. ).

The phenological development of soybean cultivars was monitored at each SD using the scale proposed by Fehr et al. (1971Fehr, W. R.; Caviness, C. E.; Burmood, D. T.; Pennington, J. S. Stage of development descriptions for soybeans, Glycine max (L.) Merrill. Crop Science, v.11, p.929-931, 1971. ), and phenological changes were determined in plots containing 10 plants. The observations were made using the same plants, and the dates of each phenological stage were recorded.

The meteorological data were collected daily from an agrometeorological station located 2 km from the study site and were used to construct graphs of the duration of each phenological stage as a function of the photoperiod.

The daily photoperiod was calculated according to latitude and date. The critical photoperiod for soybean in tropical regions was 13.5 h (Câmara et al., 1997Câmara, G. M. S.; Sediyama, T.; Dourado-Neto, D.; Bernardes, M. S. Influence of photoperiod and air temperature on the growth, flowering and maturation of soybean (Glycine max (L.) Merrill). Scientia Agricola, v.54, p.149-154, 1997. https://doi.org/10.1590/S0103-90161997000300017
https://doi.org/10.1590/S0103-9016199700...
).

In the plants marked for quantification of the phenological stages, the NNP visible in the main stem was counted three times a week, as proposed by Munger (1997Munger, P.; Bleiholder, H.; Hack, H.; Hess, M.; Stauss, R.; van den Boom, T.; Weber, E. Phenological growth stages of the soybean plant (Glycine max L. Merr.): codification and description according to the BBCH scale. Journal of Agronomy and Crop Science, v.179, p.209-217, 1997. https://doi.org/10.1111/j.1439-037X.1997.tb00519.x
https://doi.org/10.1111/j.1439-037X.1997...
). The growing degree-days (GDDs) for each cultivar at each SD were calculated considering 10 °C as the baseline temperature for the emission of nodes on the main stem (Silva et al., 2018aSilva, C. M. da; Mielezrski, F.; Chaves, D. V.; Lima, E. de A.; Costa Filho, J. H. da; Silva, A. V. da. Sowing seasons maturity groups on quantitative traits in soybean. African Journal of Agricultural Research, v.13, p.7-13, 2018a. https://doi.org/10.5897/AJAR2017.12717
https://doi.org/10.5897/AJAR2017.12717...
).

For each repetition, linear regression between the NNP in the main stem and GDDs from plant emergence were obtained (Baker & Reddy, 2001Baker, J. T.; Reddy, V. R. Temperature effects on phenological development and yield of muskmelon. Annals of Botany, v.87, p.605-613, 2001. https://doi.org/10.1006/anbo.2001.1381
https://doi.org/10.1006/anbo.2001.1381...
; Streck et al., 2005Streck, N. A.; Tibola, T.; Lago, I.; Buriol, G. A.; Heldwein, A. B.; Schneider, F. M.; Zago, V. Estimation of plastochron in melon (Cucumis melo L.) cultivated in plastic greenhouse at different times of the year. Ciência Rural, v.35, p.1275-1280, 2005.; Zanon et al., 2015Zanon Junior, A.; Winck, J. E. M.; Streck, N. A.; Rocha, T. S. M. da; Cera, J. C.; Richter, G. L.; Lago, I.; Santos, P. M. dos; Maciel, L. da R.; Guedes, J. V. C.; Marchesan, E. Desenvolvimento de cultivares de soja em função do grupo de maturação e tipo de crescimento em terras altas e terras baixas. Bragantia , v.74, p.400-411, 2015. https://doi.org/10.1590/1678-4499.0043
https://doi.org/10.1590/1678-4499.0043...
). The plastochron index (°C day node-1) was considered the inverse of the slope of the linear regression between the NNP and GDDs (Baker & Reddy, 2001). The PI was determined for each replicate (Streck et al., 2005).

At phenological stage R2 (full flowering), samples (2 m rows per subplot) were collected to determine the shoot dry matter. The plants were dried in a forced-air oven at 65 °C for 72 hours and weighed to determine the dry matter yield per hectare.

At the end of the growth cycle, 10 plants were randomly collected manually from one row in each plot, and plant height (PH) and insertion height of the first pod (IHFP) were measured and expressed in centimeters. The number of lateral branches per plant (NLBP) and NNP was also determined.

Plants from the plots were harvested at the end of the growth cycle. The pods were dried on a concrete floor, impurities were removed, and the grains were threshed and cleaned using a stationary mechanical thresher.

The 100 grain weight (100 GW) was determined by randomly collecting and weighing four samples per subplot, and the values were adjusted to a moisture content of 130 g kg-1 of water. The grains obtained by threshing were weighed. GY was transformed into Mg ha-1 at a moisture level of 130 g kg-1 of water.

The results were subjected to Anderson-Darling normality tests, and homogeneity was evaluated using Levene’s test and analysis of variance [F-test (p ≤ 0.05)]. Data were analyzed separately for each year because the weather conditions varied between the years and there was a significant interaction between the years and the effects of treatment. All blocks and block interactions were considered random effects. The SDs and cultivars were considered fixed effects. Differences between treatments were compared using the LSD test (p ≤ 0.05).

Results and Discussion

Many agricultural factors influence the development of soybean crops, but SD is the strongest contributor (Sediyama et al., 2015Sediyama, T.; Silva, F.; Borém, A. Soy: From planting to harvesting, 1. ed. Viçosa, MG. 2015. 333p.) and determines the length of plant exposure to climate variations. Therefore, the incorrect choice of sowing period in relation to the cultivar may result in lower GY and crop loss (Silva et al., 2018bSilva, D. R. O. da; Aguiar, A. C. M. de; Basso, C. J.; Cutti, L.; Soriani, H. H. Impact of the competition duration on light and soil resources between soybean and volunteer corn. Scientia Agraria, v.19, p.78-85, 2018b.).

In this study, delayed sowing (DS) reduced the time required for the plant to change its phenological stage (Table 1). The total GDD tended to decrease until flowering when sowing was delayed (Table 1). Moreover, the GDDs of the extra-early cultivars were strongly affected by SD. Cultivars with longer growth cycles were more sensitive to the duration of phenological stages than those with shorter cycles.

Table 1
Duration in calendar days of each phenological subperiod and growing degree-days (GDD) required for flowering (R1) and physiological maturity (R7) of soybean cultivars as affected by three sowing dates

The accumulation of GDDs tended to decrease as sowing was delayed up to stage R1; however, when observing the accumulation of degree days until the end of the cycle, the results did not show a clear trend, which suggests that the thermal unit approach did not accurately describe the phenological development of soybean. Several other factors, such as air humidity, thermal amplitude, and photoperiod, were likely the more determining factors (Awasthi et al., 2017Awasthi, R.; Gaur, P.; Turner, N. C.; Vadez, V.; Siddique, K. H.; Nayyar, H. Effects of individual and combined heat and drought stress during seed filling on the oxidative metabolism and yield of chickpea (Cicer arietinum) genotypes differing in heat and drought tolerance. Crop and Pasture Science, v.68, p.823-841, 2017. https://doi.org/10.1071/CP17028
https://doi.org/10.1071/CP17028...
).

There was a significant effect of SD and cultivar on PI (Table 2). C3 presented the highest PI, independent of the SD. Furthermore, additional GDDs were necessary for the emission of nodes when sowing was later, and this result was observed in all cultivars in both growing seasons (Table 3).

Table 2
F values and averages for plastochron index (°C day node-1) according to the treatments
Table 3
Interactions between cultivar and sowing dates for plastochron (°C day node-1) in first and second year

Early-cycle cultivars had smaller PIs, and SD further decreased this index regardless of the cultivar. The PI of cultivar BMX RR Power was more stable in the last two SDs. Later sowing may occur in periods with low regularity of rainfall, which can also influence the development of soybean plants (Silva et al., 2018bSilva, D. R. O. da; Aguiar, A. C. M. de; Basso, C. J.; Cutti, L.; Soriani, H. H. Impact of the competition duration on light and soil resources between soybean and volunteer corn. Scientia Agraria, v.19, p.78-85, 2018b.). This fact could also be one of the hypotheses of developmental delay (greater plastochron), agreeing with Ma et al. (2021Ma, L.; Fang, Q. X.; Sima, M. W.; Burkey, K. O.; Harmel, R. D. Simulated climate change effects on soybean production using two crop modules in RZWQM2. Agronomy Journal, n.113, p.1349-1365, 2021. https://doi.org/10.1002/agj2.20548
https://doi.org/10.1002/agj2.20548...
), that the water deficit in the soil, even if slight, delays the vegetative development of soybean.

The analysis of the relationship between the photoperiod and the duration of the phenological stages indicated that the phenological cycle was reduced and flowering occurred sooner with late sowing than early sowing, regardless of the cultivar and year of cultivation (Figure 2). Furthermore, floral induction occurred earlier as the photoperiod was reduced, approaching the critical value for the study region (13.5 h).

Figure 2
Influence of photoperiod in the experimental site in relation to soybean growth stages, for extra-early maturing cycle soybean in 1st (A), 2nd (B) and 3rd (C) sowing dates, for early maturing cycle soybean in 1st (D), 2nd (E) and 3rd (F) sowing dates and medium maturing cycle soybean for 1st (G), 2nd (H) and 3rd (I) sowing dates during two consecutive years (2015/2016 and 2016/2017)

In the case of late sowing, the photoperiod conditions for the vegetative growth of soybean were still favorable, although as the sowing date approached the summer solstice (December 21 for the Southern Hemisphere), the period above the critical photoperiod had a shorter duration than when sowing was performed earlier, which can cause early flowering induction in greater or lesser intensity, depending on the sensitivity of the cultivar (Martins et al., 2011Martins, J. D.; Radons, S. Z.; Streck, N. A.; Knies, A. E.; Carlesso, R. Plastochron and final node number of soybean cultivars as a function of sowing date. Ciência Rural, v.41, p.954-959, 2011. ).

According to Rockenbach et al. (2016Rockenbach, A. P.; Caron, B. O.; Souza, V. Q.; Elli, E. F.; Oliveira, D. M. de; Monteiro, G. C. Estimated length of soybean phenological stages. Semina: Ciências Agrárias, v.37, p.1871, 2016. https://doi.org/10.5433/1679-0359.2016v37n4p1871
https://doi.org/10.5433/1679-0359.2016v3...
), the shortening of the cycle and the precocity for flowering are characteristics that occur due to the reduction of the photoperiod and the occurrence of high temperatures, as observed in the years studied, mainly in the vegetative growth phase.

In the first SD, floral induction occurred when daylight hours increased. Floral induction occurred earlier in the first SD than in the two later SDs, that is, flowering began when the number of daylight hours began to decrease, although the daylight period was longer than the critical photoperiod.

The cultivar C3 had the most pronounced change in the duration of the phenological stages relative to the other cultivars; in the first and second SDs (Figures 2G and H), the plants reached growth stage V7, whereas in the third SD (Figure 2I), flowering occurred after V5, resulting in the shortening of the growth cycle. Changes in the vegetative period as a function of the SDs were observed only for this cultivar, which had a comparatively longer growth cycle.

Regarding the duration of the phenological stages, cultivars with longer cycles were more sensitive to the duration of subperiods than those with shorter cycles (Rockenbach et al., 2016Rockenbach, A. P.; Caron, B. O.; Souza, V. Q.; Elli, E. F.; Oliveira, D. M. de; Monteiro, G. C. Estimated length of soybean phenological stages. Semina: Ciências Agrárias, v.37, p.1871, 2016. https://doi.org/10.5433/1679-0359.2016v37n4p1871
https://doi.org/10.5433/1679-0359.2016v3...
). This variation was more evident from the vegetative period to the beginning of grain filling (VE - R5.1). For the other subperiods, this change was not as evident. The same was true for the other materials during the three study periods.

The PI decreased when sowing was delayed, that is, the rate of node production increased at the later sowing dates. The decrease in the PI with SD may be a response to the duration of daylight hours, because the increase in the rate of plant development in shorter photoperiods is a typical response of short-day plants (Lu et al., 2017Lu, S.; Zhao, X.; Hu, Y.; Liu, S.; Nan, H.; Li, X.; Cao, D.; Shi, X.; Kong, L.; Zhang, F.; Wang, Z.; Yuan, X.; Cober, E. R.; Liu, B.; Hou, X.; Tian, Z.; Su, T.; Li, S.; Weller, J.; Kong, F. Natural variation at the soybean J locus improves adaptation to the tropics and enhances yield. Nature Genetics, v.49, p.773-779, 2017. https://doi.org/10.1038/ng.3819
https://doi.org/10.1038/ng.3819...
). Furthermore, soybean crops sown late may undergo periods of irregular rainfall, which may affect plant development.

There was clearly an increasing tendency in the PI in the medium-cycle cultivar (C3), while the extra-early and early cultivars alternated their responses between the two years. The growth cycle is not a reliable indicator of the PI because the development of soybean is not affected by the rate of development of nodes, but by the final number of nodes (Streck et al., 2008Streck, N. A.; Paula, G. M. D.; Camera, C.; Menezes, N. L. D.; Lago, I. Estimativa do plastocrono em cultivares de soja. Bragantia, v.67, p.67-73, 2008. https://doi.org/10.1590/S0006-87052008000100008
https://doi.org/10.1590/S0006-8705200800...
).

The relationship between the photoperiod and the duration of phenological stages demonstrates that the vegetative growth of soybean in the first and second SDs was within the period in which the average amount of daylight was greater than the critical photoperiod. This condition is considered optimal for the crop because it allows the plants to reach maximum PH with as many nodes as possible (Streck et al., 2008Streck, N. A.; Paula, G. M. D.; Camera, C.; Menezes, N. L. D.; Lago, I. Estimativa do plastocrono em cultivares de soja. Bragantia, v.67, p.67-73, 2008. https://doi.org/10.1590/S0006-87052008000100008
https://doi.org/10.1590/S0006-8705200800...
).

The photoperiodic conditions for the vegetative growth of soybeans were still favorable for DS. However, as the date of sowing was close to the summer solstice in the Southern Hemisphere, the favorable amount of daylight above that of the critical photoperiod was smaller than that with early sowing, which may lead to a greater or lesser extent of early flowering, depending on the sensitivity of the cultivar (Martins et al., 2011Martins, J. D.; Radons, S. Z.; Streck, N. A.; Knies, A. E.; Carlesso, R. Plastochron and final node number of soybean cultivars as a function of sowing date. Ciência Rural, v.41, p.954-959, 2011. ).

This factor, together with high temperatures during the soybean harvest period, increases the risk of early flowering.

In the first year, cultivar C3 plants were taller than those of the early cultivar, which in turn were taller than plants from the extra-early cultivar (Table 4). The NNP in both years was different between the cultivars and followed the same trend as that of PH.

Table 4
F values and averages for plant height (PH), insertion height of the first pod (IHFP), number of nodes per plant (NNP) and number of lateral branches per plant (NLBP) according to the treatments

The NNP was highest in cultivar C3 and lowest in cultivar C1. Furthermore, in the second year, SD resulted in the development of plants with a small NNP in the main stem, indicating that SD affected the NNP and, consequently, PH.

There were significant differences in the NLBP between the cultivars, but only in the second year, and the mean NLBP was comparatively higher in the first and second SDs. C1 presented the highest NLBP, followed by C2 and C3.

The lowest values of PH and the IHFP were obtained with later SDs, which was directly associated with the shorter vegetative period, as observed by Câmara et al. (1997Câmara, G. M. S.; Sediyama, T.; Dourado-Neto, D.; Bernardes, M. S. Influence of photoperiod and air temperature on the growth, flowering and maturation of soybean (Glycine max (L.) Merrill). Scientia Agricola, v.54, p.149-154, 1997. https://doi.org/10.1590/S0103-90161997000300017
https://doi.org/10.1590/S0103-9016199700...
). The climatic conditions during the vegetative stage, especially the shorter photoperiod and higher temperature, reduced PH and the phenological cycle, which directly affected vegetative growth and biomass accumulation.

Although cultivars C2 and C3 had longer growth cycles relative to C1, and were consequently more sensitive to photoperiodic variations, their juvenile period was longer than that of extra-early cultivars, which was compensated for with increased vegetative growth and accumulation of plant biomass.

Shoot dry matter was higher in the first year in cultivars C2 and C3 than in C1 (Table 5). However, there were no significant differences in this variable between the SDs and cultivars in the second year. In both growing seasons, the NNP was significantly higher in the second SD than in the third SD. Moreover, in the second year, the NNP was higher in cultivars C2 and C3 than in C1.

Table 5
F values and averages for aboveground dry matter (ADM), number of pods per plant (NPP), 100-grain weight (100GW) and grain yield (GY) according to the treatments

GY was affected by the interaction between SDs and cultivars (Table 6). GY was comparatively higher in the second SD, and cultivar C2 presented the highest GY in both years. SD reduced the GY of all three cultivars, regardless of the duration of the growth cycle. Nonetheless, GY in the early and medium-cycle cultivars was higher than that in the extra-early cultivar (C1).

Table 6
Interactions between cultivar and sowing dates for weight of 100 grains (100GW) and grain yield (GY) in first and second growing season

Similarly, for this cultivar, GY was highest in the second SD, especially in the second year, when GY was similar to that of C2 and higher than that of C3. SD strongly compromised GY in this cultivar, and should not be performed in practice. In contrast, long-cycle cultivars were more indicated for DS, as was the case for C2 and C3 in both growing seasons.

Among the sowing dates in our study, accumulated rainfall during the growth cycle was reduced as sowing was delayed, independent of the year (Figure 2), and was more pronounced in early- and medium-cycle cultivars, especially between the first and third SD.

Cultivars with longer growth cycles remained in the field for longer than early cycle cultivars and, consequently, had a higher capacity to recover from abiotic stresses, including water stress, leading to higher GYs (Silva et al., 2018aSilva, C. M. da; Mielezrski, F.; Chaves, D. V.; Lima, E. de A.; Costa Filho, J. H. da; Silva, A. V. da. Sowing seasons maturity groups on quantitative traits in soybean. African Journal of Agricultural Research, v.13, p.7-13, 2018a. https://doi.org/10.5897/AJAR2017.12717
https://doi.org/10.5897/AJAR2017.12717...
).

High temperatures occurred during soybean development, especially in the flowering and grain filling periods with late sowing, which may increase the probability of pod abortion (Awasthi et al., 2017Awasthi, R.; Gaur, P.; Turner, N. C.; Vadez, V.; Siddique, K. H.; Nayyar, H. Effects of individual and combined heat and drought stress during seed filling on the oxidative metabolism and yield of chickpea (Cicer arietinum) genotypes differing in heat and drought tolerance. Crop and Pasture Science, v.68, p.823-841, 2017. https://doi.org/10.1071/CP17028
https://doi.org/10.1071/CP17028...
) and photorespiration, ultimately leading to a decrease in the net concentration of photoassimilates directed to grain filling.

Conclusions

Our results demonstrated that delayed sowing changed less the phenological development of longer-cycle cultivar, being more indicated for late sowing. Regardless of the cultivar, the duration of the phenological cycle was strongly reduced by sowing dates and affected the plastochron index. The second sowing date was the optimum period for soybean cultivation in the studied latitude, resulting in higher grain yield.

Acknowledgements

The authors would like to thank the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for financial support to the first author (#grant 35612).

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  • 1 Research developed at Selvíria, MS, Brazil

Publication Dates

  • Publication in this collection
    20 Apr 2022
  • Date of issue
    July 2022

History

  • Received
    18 Oct 2021
  • Accepted
    25 Jan 2022
  • Published
    09 Feb 2022
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