Crescimento, desenvolvimento e produtividade de cultivares de soja em Alagoas

Abstract

Grain cultivation in the Zona da Mata of the state of Alagoas is seen as a promising alternative. Among grains, soybean production has been increasing, however, production rates are still low, especially when comparing the productivity of Alagoas with other producing regions in the Northeast of Brazil. For this reason, and in order to analyse the growth, development and productivity of soya cultivars in the Zona da Mata of Alagoas, two field experiments were set up on the Agrarian Sciences Campus (CECA) of the Federal University of Alagoas (UFAL): one irrigated, during the dry season, and the other under rainfed conditions during the rainy season. The experimental design was of randomised blocks with five replications, with the treatments comprising six soya cultivars (M 6210, M 6410, BMX-Potência, AS 370, M 8349 and BRS-9383). The production variables under analysis in the two experiments were height of the first pod insertion, number of pods per plant, 1000-grain weight, harvest index, water productivity and grain yield. The growth variables were plant height, plant dry matter and leaf area index. Development was monitored based on the duration of the phenological phases. The physiological variables analysed were the net photosynthetic rate, internal CO2 concentration, transpiration, stomatal conductance, instantaneous water use efficiency, instantaneous carboxylation efficiency, the potential quantum yield of photosystem II and the SPAD index. The mean air temperature during each study was 26.5°C and 24°C, mean relative humidity was 72% and 75%. In the first study, the irrigation depths totalled 345.30 mm, rainfall was 375 mm, and there was an increase in the water available to the crop, as seen from the sum of the rainfall and irrigation of 720 mm, with only 547 mm in the rainfed crops. The accumulated reference evapotranspiration (ETc) was 589 mm and 422 mm. In the irrigated experiment, the maximum height of the first pod insertion was 19.30 cm (M 8349), the greatest number of pods per plant was 118 units (BRS-9383), the greatest 1000-grain weight was 209.5 g (M 8349), with a harvest index of 45 (BMX-Potência), water productivity of 1.30 kg m-3 (AS 3730), and maximum grain yield of 6,180 (AS 3730) kg ha-1. The maximum growth variables were a plant height of 110.35 cm, plant dry matter of 66 g, and LAI of 7.68. Development lasted a maximum of 140 days after sowing, with 2,331 accumulated degree- days. The maximum physiological variables were a photosynthetic rate of 28.40 μmol CO2 m- 2 S -1 , a transpiration rate of 8.20 μmol H2O m-2 s -1, stomatal conductance of 1.04 μmol H2O m- 2 S -1 , internal CO2 concentration of 395 μmol m-2 s -1 , maximum effective quantum efficiency of 0.75, and maximum SPAD index of 41.86. For the rainfed crops, the maximum height of the first pod insertion was 16.80 cm (M 8349), the greatest number of pods per plant was 72.0 units (BRS-9383), the greatest 1000-grain weight was 176.0 g (AS3730), with a harvest index of 51.0 (BMX-Potência), water productivity of 0.86 kg m-3 (AS 3730), and maximum grain yield of 3,600 (M 6410) kg ha-1. The maximum growth variables were a plant height of 62.91 cm, plant dry matter of 40 g, and LAI of 6.34. Development lasted a maximum of 130 days after sowing, with 1,832.4 accumulated degree-days. The maximum physiological variables were a photosynthetic rate of 15.40 μmol CO2 m-2 s -1 , transpiration rate of 4.22 μmol H2O m- 2 S -1 , stomatal conductance of 0.48 μmol H2O m-2 s -1 , internal CO2 concentration of 200.61 μmol m-2 s -1 , maximum effective quantum efficiency of 0.73, and maximum SPAD index of 40.05. In general, irrigating soya cultivars generates greater production and growth components in the region of Rio Largo, Alagoas. Keywords: Glycine max (L.) Merrill; irrigation; water balance; agricultural productivity.