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.
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
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