Abstract
The urochloa grass (Urochloa mosambicensis) is a perennial grass, C4 plant, with a high photosynthetic rate and CO2 fixation, persistent to water deficit, adapted to a wide diversity of soils and hot climate regions. Thus, the objective was to evaluate the urochloa grass growth and define the best models to estimate plant height as a function of nitrogen and phosphate fertilization. The experimental design was completely randomized, in the 2 x 2 factorial design (presence and absence of nitrogen presence and absence of phosphorus), with four replications. Was used a dose of nitrogen and phosphorus equivalent to 100 kg.ha-1 of N and 150 kg.ha-1 of P2O5, respectively. The following models were used: linear, power, gamma andlogistic to estimate plant height as a function of the following explanatory variables: days after planting, nitrogen and phosphorus doses. The criteria used to determine the best model(s) were as follows: higher adjusted coefficient of determination, lower Akaike information criterion, lower sum of square of residuals and high Willmott index. The plant height in the absence of nitrogen and phosphorus and when applied 100 kg.ha-1 of N and 150 kg.ha-1 of P2O5 was estimated more accurately by the Gamma model with high power of explanation. The adoption of the Gamma model allows to estimate the U. mosambicensis plant height, in a non-destructive manner, with high precision, speed and low cost, depending of age plant and nitrogen and phosphate fertilization.
Highlights
Urochloa grass (Urochloa mosambicensis) is a perennial grass originating of the African continent, C4 plant, with a high photosynthetic rate and CO2 fixation, persistent to water deficit, adapted to regions with a minimum mean annual rainfall of 500 mm and a wide diversity of soils (LEITE et al, 2017).The Brazilian soils, for the most part, contain low levels of phosphorus, one of the elements that most limits the productivity of forages
In order to obtain sustainable crops and high forage yields in these soils, it becomes necessary and essential phosphorus fertilization, as well as nitrogen fertilization, which plays an important role in plant morphogenesis, promoting increase in the metabolism and rates of enzymatic reactions (BEZERRA et al, 2017)
The behavior of the U. mosambicensis plant height in the absence of nitrogen and phosphorus was best estimated by Gamma model, since it presented greater power of explanation ( =99.2%) and Willmott index (d=0.998) and smaller sum of squares of residuals (SSR=16.67) when compared to linear, power and logistic models, while the Akaike information criterion presented best performance for the power model
Summary
The Brazilian soils, for the most part, contain low levels of phosphorus, one of the elements that most limits the productivity of forages. In order to obtain sustainable crops and high forage yields in these soils, it becomes necessary and essential phosphorus fertilization, as well as nitrogen fertilization, which plays an important role in plant morphogenesis, promoting increase in the metabolism and rates of enzymatic reactions (BEZERRA et al, 2017). Nitrogen is the mineral element that plants require in larger quantities, under conditions of disability, nitrogen is the main limiting factor to plant growth and can significantly affect forage grasses productivity (MARTINS et al, 2008; MARTUSCELLO et al, 2015)
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