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Abstract
Abstract The objective of this study was to determine the mean duration and the interannual variability of phenological subperiods and total soybean development cycle for 11 sowing dates in the humid subtropical climate conditions of the state of Rio Grande do Sul. Daily meteorological data were used from 1971 to 2017 obtained from the Pelotas agroclimatological station and from 1968 to 2017 from the main climatological station of Santa Maria. The soybean development simulation was performed considering three sets of cultivars of relative maturity groups between 5.9-6.8, 6.9-7.3 and 7.4-8.0, with intervals between the sowing dates of approximately 10 days, comprising September, 21 to December, 31. The data of phenological subperiods duration and total development cycle were subjected to the exploratory analysis BoxPlot, analysis of variance and mean comparison by the Scott-Knott test, with 5% of probability. The development cycle duration is greater in Pelotas than in Santa Maria. There was a decrease in soybean cycle duration from the first to the last sowing date for both locations. The R1-R5 subperiod duration is decreasing from October to December due to photoperiod reduction.
Highlights
Soybean is the most important aleuro-oleaginous crop in the world, being the crop with the largest area sown in Brazil (36.8 × 106 ha) during the 2019/2020 agricultural crop
The mean values of development cycle duration of the three relative maturity groups (RMG: 5.9-6.8; 6.9-7.3; 7.4-8.0) decreased among all 11 sowing dates, except by RMG 7.4-8.0 for Santa Maria in which there was a shorter duration for sowing in September than in October (Fig. 1)
For RMG 7.4-8.0, there were small differences in cycle duration between Santa Maria and Pelotas for sowing dates performed in November and December (Fig. 1), as well as in relation to data obtained by Zanon et al (2018)
Summary
Soybean is the most important aleuro-oleaginous crop in the world, being the crop with the largest area sown in Brazil (36.8 × 106 ha) during the 2019/2020 agricultural crop. In Rio Grande do Sul, the third largest Brazilian producer state, 5.9 million hectares were cultivated, with an average yield of 3.15 t ha-1 in this agricultural year (CONAB, 2020). Despite the technological advance in the soybean production system, the yield difference between years is significant, which is directly related to the interannual and spatial variability of the meteorological conditions. The main abiotic factors that influence soybean crop development are air temperature and photoperiod. Considering that soybean is a short-day plant, reduced development rate occurs when the plants are subjected to longer photoperiod conditions. Increased development cycle is expected in regions more distant from the equator line, and alterations in function of sowing date, as well as the thermal time variability among years
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