Abstract
This study aimed to fit the Gompertz and Logistic growth models to evaluate the description of fresh and dry masses of shoot as a function of accumulated thermal sum and accumulated solar radiation, to compare the fittings, and to indicate which one best describes the growth of two sudangrass cultivars at four sowing times. Eight uniformity trials were conducted with the sudangrass crop. Five plants were collected from each trial for weighing of fresh and dry shoot masses. These evaluations were carried out three times a week starting from 15 days after plant emergence. The Gompertz and Logistic models were fitted to the masses as a function of accumulated thermal sum and accumulated solar radiation. The parameters and their confidence intervals were estimated. The points of maximum acceleration, inflection, maximum deceleration and asymptotic deceleration, and fit quality indicators were calculated. The intrinsic nonlinearity and the parameter-effects nonlinearity were quantified. The independent variables accumulated thermal sum and accumulated solar radiation can be used to fit the models. Both models satisfactorily describe the growth of fresh and dry shoot masses of cultivars BRS Estribo and CG Farrapo. The Logistic model is more accurate.
Highlights
In the no-till system, cover crops are used in rotation with cash crops to control losses of soil, water, and nutrients by water erosion (Cardoso, Silva, Carvalho, Freitas, & Avanzi, 2012), to promote nutrient cycling, and to increase soil organic matter contents (Pacheco et al, 2013).Sudangrass [Sorghum sudanense (Piper) Stapf.] is among the many species that have been investigated as alternative cover crop options
It is possible to observe that the fresh shoot mass (FSM) and the dry shoot mass (DSM) as a function of accumulated solar radiation (ASR), showed dispersion in the sigmoidal shape, justifying the fit of the Gompertz and Logistic models
After to fit the models, the residuals analyses carried out to evaluate assumptions of normality, homoscedasticity, and independence of the errors of the models fitted for fresh and dry shoot masses as a function of accumulated thermal sum (ATS) and ASR showed that all assumptions were met, with p-values greater than 0.05 (p > 0.05) obtained from the Shapiro-Wilk, Bartlett, and Durbin-Watson tests, respectively
Summary
In the no-till system, cover crops are used in rotation with cash crops to control losses of soil, water, and nutrients by water erosion (Cardoso, Silva, Carvalho, Freitas, & Avanzi, 2012), to promote nutrient cycling, and to increase soil organic matter contents (Pacheco et al, 2013).Sudangrass [Sorghum sudanense (Piper) Stapf.] is among the many species that have been investigated as alternative cover crop options. Sudangrass belongs to the family Poaceae, develops well in regions with hot and dry climate, and tolerates acid and low fertility soils It yields high amounts of biomass, reaching 84.3 t.ha-1 of fresh mass and 15.8 t.ha-1 of dry mass (Arenhardt et al, 2016) and providing good soil cover and high weed suppressive effect (Borges, Freitas, Mateus, Sá, & Alves, 2014). It has good nutritional quality and can be used in animal feed (Mattos, 2003). Reports on the growth and development of this species are scarce, indicating the need for studies to obtain more information on this process
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