Growth dynamics and nutrient extraction curves of Pennisetum sp. (Maralfalfa)

Abstract

Mathematical models are useful in calculating forage nutrient concentration, nutrient extraction and growth curves. An analysis was done of growth and nutrient content in Pennisetum sp. (maralfalfa) applying Gompertz and Logistic models. Dilution curves for nitrogen, phosphorous and potassium (NPK) were generated using a negative potential model and maximum extraction values were calculated with a second order polynomial equation. Nutrient unitary extraction and nutrient recovery efficiency of NPK were also calculated. The goodness-of-fit models were compared using a completely randomized design with a 2 x 2 factorial arrangement, in which factor A was the two models and factor B was the real-world assay (fertilized treatment vs. control). Nutrient concentration curves were optimized with the Levenberg-Marquart algorithm. Both models’ goodness-of-fit were similar among the study plots, although the Gompertz model better represented biological reality. Maximum growth rate was reached at 21 d after sowing in the control plots and at 56 d in the fertilized plots. The inflection point was reached at 30 ds in the control plots and at 31 d in the fertilized plots. Nutrient concentration decreased over time in both the treatment and control, and dry matter production was highest in the fertilized treatment. Aside from calcium and magnesium, nutrient unitary extraction did not differ between the treatment and control. Nutrient recovery efficiency was 48 % for nitrogen, 39% for phosphorous and 104 % for potassium, suggesting excess nutrient levels.