Crop models can be used to explain yield variations associated with management practices, environment and genotype. This study aimed to assess the effect of plant densities using CSM-CROPGRO-Soybean for low latitudes. The crop model was calibrated and evaluated using data from field experiments, including plant densities (10, 20, 30 and 40 plants per m2), maturity groups (MG 7.7 and 8.8) and sowing dates (calibration: 06 Jan., 19 Jan., 16 Feb. 2018; and evaluation: 19 Jan. 2019). The model simulated phenology with a bias lower than 2 days for calibration and 7 days for evaluation. Relative root mean square error for the maximum leaf area index varied from 12.2 to 31.3%; while that for grain yield varied between 3 and 32%. The calibrated model was used to simulate different management scenarios across six sites located in the low latitude, considering 33 growing seasons. Simulations showed a higher yield for 40 pl per m2, as expected, but with greater yield gain increments occurring at low plant density going from 10 to 20 pl per m2. In Santarém, Brazil, MG 8.8 sown on 21 Feb. had a median yield of 2658, 3197, 3442 and 3583 kg/ha, respectively, for 10, 20, 30 and 40 pl per m2, resulting in a relative increase of 20, 8 and 4% for each additional 10 pl per m2. Overall, the crop model had adequate performance, indicating a minimum recommended plant density of 20 pl per m2, while sowing dates and maturity groups showed different yield level and pattern across sites in function of the local climate.
The degree-days or thermal time theory has been widely used to simulate crop development because of its simplicity; in addition, it represents a good indicator of crop phenological evolution compared with the days after sowing scale. We investigated the development and thermal requirements of soybean (Glycine max (L.) Merrill), BRS Tracajá cultivar, grown in an agricultural border area of advance in eastern Amazon. The field experiment was carried out in the 2007 and 2008 growing seasons in the municipality of Paragominas, Pará state, in a completely randomized experimental design at six sowing dates with three replicates. The soybean thermal time required, from emergence to flowering, at cardinal temperatures of 10, 31 and 40 °C was 642±70 degree-days and the thermal time of the Ve-R8 stage was 1,753±16 degree-days. RESUMO: A teoria dos graus-dia ou tempo térmico tem sido amplamente utilizada para simular o desenvolvimento de culturas pela simplicidade do método, além de representar um bom indicativo da evolução fenológica da cultura quando comparado à escala de dias após a semeadura. Avaliaram-se o desenvolvimento e a necessidade térmica da soja [Glycine max (L.) Merrill], cultivar BRS Tracajá, em uma área de avanço de fronteira agrícola na Amazônia Oriental. O experimento foi realizado durante a safra de 2007 no município de Paragominas-PA, usando-se um delineamento inteiramente ao acaso em três datas de semeadura com três repetições cada. O tempo térmico necessário para a soja atingir o florescimento em Paragominas-PA, considerando-se as temperaturas cardinais de 10, 31 e 40 °C, foi de 642±7 graus-dia e, para completar o ciclo total, foi de 1.753±16 graus-dia.
This study investigated whether gas exchange and the present content of antioxidant compounds can contribute to the survival of Euterpe oleracea plants in environments of frequent waterlogging. A factorial randomised, experimental design included two distinct water conditions (waterlogging and control) and five evaluation times (0, 6, 12, 18, and 24 d). Gasexchange parameters, leaf temperature, electrolyte leakage, and contents of antioxidant compounds were measured. Waterlogging did not promote significant alterations in net photosynthetic rate and transpiration, and stomatal conductance was reduced only after 18 d. Malondialdehyde and glutathione contents did not significantly change during waterlogging. Additionally, electrolyte leakage was significant only after 18 d of waterlogging. Thus, this study revealed that maintenance in gas exchange and antioxidant compounds might contribute to the survival of E. oleracea plants in environments exposed to waterlogging.
RESUMO 2018). However, a lack of knowledge regarding the interaction of soybean crops with the Amazonian environment has created inconsistent information about the attainable potential of soybean crops in this region.An approach about the potential yield and yield gaps could help to understand the interactions of the soybean production system with the Amazon agro-ecosystem and, at the same time, develop suitable strategies to improve the yield of a crop (Sentelhas et al. 2015). However, identifying the
The objective of this work was to evaluate the effi ciency of soybean (Glycine max) in intercepting and using solar radiation under natural fi eld conditions, in the Amazon region, Brazil. The meteorological data and the values of soybean growth and leaf area were obtained from an agrometeorological experiment carried out in Paragominas, Pará state, during 2007 and 2008. The radiation use effi ciency (RUE) was obtained from the ratio between the above-ground biomass production and the intercepted photosynthetically active radiation (PAR) accumulated to 99 and 95 days after sowing, in 2007 and 2008, respectively. Climatic conditions during the experiment were very distinct, with reduction in rainfall in 2007, which began during the soybean mid-cycle, due to the El Niño phenomenon. An important reduction in the leaf area index and biomass production was observed during 2007. Under natural fi eld conditions in the Amazon region, the values of RUE were 1.46 and 1.99 g MJ -1 PAR in the 2007 and 2008 experiments, respectively. The probable reason for the differences found between these years might be associated to the water restriction in 2007 coupled with the higher air temperature and vapor pressure defi cit, and also to the increase in the fraction of diffuse radiation that reached the land surface in 2008. Efi ciência do uso da radiação solar pela soja em condições de campo na região AmazônicaResumo -O objetivo deste trabalho foi avaliar a efi ciência da soja (Glycine max) em interceptar e usar a radiação solar em condições naturais de campo, na região Amazônica do Brasil. Os dados de crescimento e área foliar da soja e dados meteorológicos foram obtidos em um experimento agrometeorológico realizado em Paragominas, PA, em 2007 e 2008. A efi ciência do uso da radiação (ERU) foi obtida pela razão entre a produção de massa de matéria seca da parte aérea e o acúmulo da radiação fotossinteticamente ativa interceptada (RFA), até os 99 e 95 dias após a semeadura, em 2007 e 2008, respectivamente. As condições climáticas durante o experimento foram muito distintas, com redução na precipitação em 2007, iniciada na metade do ciclo de cultivo de soja, em consequência do fenômeno El Niño. Observou-se uma importante redução no índice de área foliar e na produção de massa de matéria seca durante 2007. Em tais condições de campo na região Amazônica, os valores de EUR foram de 1,46 e 1,99 g MJ -1 RFA, nos experimentos de 2007 e 2008, respectivamente. A provável razão para as diferenças encontradas entre os anos pode estar associada à redução de água em 2007, em conjunto com a elevada temperatura do ar e o defi cit de pressão de vapor, e também ao aumento na fração de radiação difusa que atingiu a superfície do solo em 2008.Termos para indexação: Glycine max, região Amazônica, índice de área foliar, interceptação da radiação.
RESUMO A condutância estomática (gs) é uma variável fisiológica que faz referência ao fluxo gasoso (CO2 e H2O) entre folha e atmosfera, portanto, representa um processo fundamental para as pesquisas agrometeorológicas. O objetivo deste estudo foi ajustar e validar um modelo descritivo, para quantificar o efeito das variáveis meteorológicas que modulam a gs como: temperatura do ar (T), irradiância solar (Io), déficit de pressão de vapor no ar (DPV) e umidade no solo. O modelo, proposto neste estudo foi calibrado com dados experimentais realizados em blocos casualizados. A gs potencial (gsp) (condições ótimas de água no solo) foi estimada a partir do produto das variáveis meteorológicas (T×DPV×Io -1). Na sequência a gsp foi corrigida para a condição atual de água no solo, utilizando um fator de estresse hídrico. As estimativas de gs obtidas pelo modelo foram comparadas com dados experimentais independentes. Os testes de validação indicaram que o modelo foi satisfatoriamente sensível às variações meteorológicas e aos teores de água disponíveis no solo, a julgar pelo baixo erro absoluto médio das estimativas (<15%) e pela alta concordância entre os dados observados e simulados (d = 0,82).
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