Effect of defoliation on root development of star‐grass under greenhouse conditions

Abstract

Plant height above the stubble (PH) and stubble height (SH) are known to affect stargrass (Cynodon nlemfuensis Vanderyst var nlemfuensis) yield, quality, and persistence. However, little is known of PH and SH on root development. A greenhouse study was conducted comparing the effect of PH (15 and 30 cm) and SH (5 and 15 cm) cutting combinations to an uncut control on depth of rooting (DOR) and root dry matter (RDM) production of ‘Florico’ stargrass. Other response variables were herbage dry matter (HDM) yield, crude protein (CP) content and yield, and total nonstructural carbohydrate (TNC) content of the crown (5.0 cm stem base plus 7.5 cm root). Transparent plastic tubes 15 cm in diameter and 100 cm long were used as pots for soil columns. Root dry matter was reduced 97%, 90%, 70%, and 36% compared to the uncut control (16.6 Mg/ha by PH/SH combinations of 15/5, 30/5 15/15, and 30/15, respectively. The 15/15 PH/SH combination produced high total HDM yield (18.9 Mg/ha with high CP content (135 g/kg). Delaying harvest until PH reached 30 cm reduced CP content to 99 g/kg with only slight (P>0.05) increase in total HDM yield. These suggest that forage yield, CP content, and root development need to be considered simultaneously when deciding on a harvest management for Florico stargrass. Cutting treatments also reduced TNC content of the crown. Root DM yield and TNC content were highly correlated (r = 0.994, P<0.01).