The interactive influence of climate and management factors on leaf area index (LAI) of soybean yield potential has not been investigated in subtropical environments. Such information can help in optimizing current soybean management practices to increase seed yield and efficiency of resource use. The objective of this study was to identify the optimum leaf area index for attaining yield potential in modern soybean cultivars grown in a subtropical environment. A large soybean yield, LAI, and phenology database collected from a combination of on-farm and research-station experiments conducted during four soybean growing seasons (2011)(2012)(2013)(2014)(2015) in southern Brazil was used. The database represented a wide range of weather conditions, soil types, sowing dates, and cultivar maturity groups (MGs). A boundary function was derived for the relationship between soybean yield and LAI at R1 and R5 developmental stages for cultivars of determinate and indeterminate growth habit, and for both types combined. An increase in yield was in line with the increase of LAI for experiments with a small yield gap (soybean yield more than 4.5 Mg ha -1 ). In this case, optimum LAI at R1 growth stage (LAI R1, opt ) to reach the soybean yield potential was between 3.4 (indeterminate) and 4.5 (determinate) whereas the optimal maximum LAI (LAI max,opt ) is between 6.0 and 6.5 for indeterminate and determinate cultivars, respectively. These results suggested that management practices for soybean crops that involve the LAI and high yield potential must be adjusted according to the maturity group, growth habit and sowing date in a subtropical environment.
ResumoOs objetivos neste trabalho foram quantificar a contribuição das ramificações e a evolução do índice de área foliar em cultivares modernas de soja com diferentes grupos de maturação, tipos de crescimento, semeadas em diferentes épocas e regiões produtoras de soja no Rio Grande do Sul. Experimentos de campo foram conduzidos durante o ano agrícola 2013/2014 em Santa Maria, Júlio de Castilhos e em três lavouras comerciais de soja nos municípios de Restinga Sêca, Tupanciretã e Água Santa. Avaliaram-se (data de ocorrência) os estágios reprodutivos e a determinação do índice de área foliar total, máximo, da haste principal e das ramificações em treze cultivares de soja. O índice de área foliar das ramificações contribui com cerca de 31%, 12,3% e 11% do índice de área foliar total nas cultivares determinadas, e com 20,2%, 11,8% e 9% do índice de área foliar total nas cultivares indeterminadas nas semeaduras de setembro, novembro e fevereiro, respectivamente, em Santa Maria. A maioria das cultivares apresentou uma redução no índice de área foliar total, máximo, da haste principal e das ramificações com o atraso da época de semeadura, independentemente do grupo de maturação e tipo de crescimento.Palavras-chave: Glycine max, época de semeadura, tipo de crescimento. Branches contribution and leaf area index evolution in modern cultivars of soybean AbstractThe purposes of this study were to quantify the branches contribution and the leaf area index evolution in modern cultivars of soybean with different maturity groups, stem termination, sowing in different dates and producing regions of soybean in Rio Grande do Sul. Field experiments were conducted during the growing season 2013/2014 in Santa Maria, Júlio de Castilhos and in three soybean crops on the municipalities of Restinga Sêca, Tupanciretã and Água Santa. It were carried out analysis (occurrence date) of reproductive stages and determination total, maximum, of main stem and of branches of leaf area index in thirteen cultivars of soybean. The leaf area index on the branches contributes with about 31%, 12.3% and 11% of the total leaf area index on the determinate cultivars and with 20.2%, 11.8% and 9% of the total leaf area index on the indeterminate cultivars sowing in September, November and February, respectively, in Santa Maria. Most cultivars showed a reduction on total leaf area index, maximum, of main stem and of branches with the delay on planting date, independently of the maturity group and stem termination.
ranged with the type of growth, maturity group, location, and sowing date.
Little is known about the relationships between soybean [Glycine max (L.) Merr.] maturity grouping and the yield-limiting factors in the subtropics. This information can be used to estimate soybean potential yield (Yp) and the water-limited yield (Yw) and to optimize current soybean management practices to improve yield and resource use efficiency. The objectives were (a) to estimate the Yp, Yw, and yield gaps (YGs) of soybean in subtropical Brazil and (b) to identify the biophysical and management factors which potentially explain the YG. The CSM CROPGRO model that was calibrated with data collected between 2011 and 2019 was used to estimate the influence of sowing date and maturity group (MG) on yield potentials and water efficiencies. Yield varied from 6.1 to 7.2 Mg ha −1 and from 2.5 to 5.1 Mg ha −1 between buffer zones (BZs) for Yp and Yw, respectively. The YG caused by water deficit (YGw) ranged from 26% (1.8 Mg ha −1 ) to 62% (4.1 Mg ha −1 ) of the Yp and the YG caused by management (e.g., sowing date, MG, final density) ranged from 9% (0.6 Mg ha −1 ) to 39% (2.7 Mg ha −1 ) of the Yp. The main management factor of the YG was sowing date. The potential yield was higher in the early MGs, showing greater water use efficiency in MG ≤ 5.5 (9.6 kg ha −1 mm −1 ) than in high MGs (MG ≥ 5.6). Findings from this study can be used by agronomists in subtropical regions to optimize soybean yields.
-The objective of this work was to evaluate soybean cultivation in a hydromorphic or nonhydromorphic soil, with or without supplemental irrigation. Field experiments were carried out with the TECIRGA 6070RR and A 6411RG cultivars in highlands (nonhydromorphic soils) and lowlands (hydromorphic soils), which are traditionally cultivated with irrigated rice. The following parameters were determined in both soybean cultivars: leaf area index, developmental stages, dry matter partition, and leaf gas exchange. Low water stresses, which commonly occur either by deficit or excess in soybean areas cultivated in hydromorphic soils, do not affect the development and partitioning of dry matter; however, they cause reductions in stomatal conductance, photosynthetic rate, and leaf area evolution. Growing soybean in lowlands exposes plants to water stress, even in years with well-distributed rainfall during the growing season, due to the low water storage capacity of these soils.Index terms: Glycine max, gas exchange, irrigation, lowlands. Desempenho da soja cultivada em solo hidromórfico e não hidromórfico com ou sem irrigaçãoResumo -O objetivo deste trabalho foi avaliar o cultivo de soja em solo hidromórfico ou não hidromórfico, com ou sem irrigação suplementar. Experimentos em campo com as cultivares TECIRGA 6070RR e A 6411RG foram realizados em terras altas (solos não hidromórficos) e em terras baixas (solos hidromórficos), que são tradicionalmente cultivadas com arroz irrigado. Determinaram-se, nas duas cultivares de soja, os seguintes parâmetros: índice de área foliar, estágios de desenvolvimento, partição de matéria seca e quantificação das trocas gasosas em nível foliar. Pequenos estresses hídricos, que comumente ocorrem por deficit ou excesso em áreas de soja cultivada em solo hidromórfico, não influenciam o desenvolvimento e a partição de matéria seca; porém, provocam reduções da condutância estomática, da taxa fotossintética e da evolução da área foliar. O cultivo de soja em solos hidromórficos faz com que as plantas sejam expostas ao estresse hídrico, até mesmo em anos com precipitação de chuvas bem distribuída ao longo da estação de crescimento, em razão da baixa capacidade de armazenamento de água desses solos.Termos para indexação: Glycine max, trocas gasosas, irrigação, terras baixas.
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