Modeling dry matter production in Panicum maximum grasses

Abstract Text: The achievement of DM production models for tropical grasses is almost absent in literature, despite the importance for livestock production, especially when considering climate chances, and it has effects on rain and temperature distribution. Models could be used as tools to adjust stocking rate and strategic planning for pasture during the year. The Panicum maximum grasses have high DM production (DMP), 30 ton of DM/ha.year on average, and that’s why their use is becoming more common in tropical countries. The objective was to determinate a DMP model, using three cultivars of Panicum maximum (Mombaça, Colonião and Sempre-verde), and weather variables.A database was used (N=180) based on pre-defoliation criteria as 95% of light interception, and 50% of height residue. Data were collected between December of 2012 and January of 2014. The variables minimum temperature (^oC, MIN), MIN², average temperature, maximum temperature, insolation (hours of light/d), precipitation (PCT, mm/d) and fertilizer (FTZ, kg of Nitrogen/d) were tested by Stepwise procedure (P<0.010) to determinate the variables that better determinate DMP. Afterwards, the effect of cultivars on selected variables were also tested. The variables MIN², FTZ and PCT were chosen by the procedure Stepwise, and they were affected by the cultivars (P<0.040). The intercept was also affected by cultivar (P = 0.042). The adjusted equations are: DMP_Mombaça (kg/d) = -92.88 + 0.56×MIN² + 10.55×FTZ + 3.52×PCT (r² = 0.73, MSE = 1198, AIC = 566); DMP_colonião (kg/d) = -35.44 + 0.42×MIN² + 15.67×FTZ + 0.27×PCT (r² = 0.51, MSE = 1809, AIC = 570); DMP_sempre-verde (kg/d) = -69.33 + 0.46×MIN² + 7.03×FTZ + 4.21×PCT (r²= 0.63, MSE = 1562, AIC = 694). Colonião was the cultivar most responsible to fertilizer, less sensitive to temperature and had the greater DMP, whereas Sempre-verde was the most responsive to precipitation, which shows that their production is more distributed throughout the year in tropical countries. Finally, Mombaça was the most responsive to temperature, with a production strongly affected by weather condition. Nevertheless, despite Colonião having greatest DMP, data from literature shows that it has a small leaf/steam relationship. This variation on morphological components affects their nutritive value, and that’s why it's important to develop models capable of stratifying their components for purpose of complementing DMP models. In conclusion, this model is capable to predicting DMP and it is strongly affected by cultivar. 

Keywords: Colonião, Mombaça, Sempre-verde