Partitioning of Nutritive Value in Crotalaria Juncea L. (Sunn Hemp).

Sunn hemp (SH; Crotalaria juncea L.) is a fast-growing, warm-season tropical legume that can provide high quality forage during summer when cool-season forages are less productive. However, results from our lab indicate that nutritive value of SH declines rapidly with maturity. Our objective was to determine how leaves and stems (Type) contribute this decline. We measured crude protein (CP), fiber (ADF, NDF), and digestibility (IVTD, NDFD) of SH leaves and stems at 35, 45, and 55 days after planting (DAP). We observed a Type x DAP interaction (P<0.0005) for all variables. CP was greater in leaves than stems (266 and 98.4 g/kg, respectively) at all DAP. Stem CP decreased with DAP from 34 to 45 but not 45 to 55 DAP. Stem NDF was greater than leaf NDF (662.8 and 273.7 g/kg, respectively) at all DAP and increased with DAP for both plant parts. ADF of stems was greater than leaves (580.4 and 219.9 g/kg, respectively) for all DAP and was stable in leaves and stems from 35 to 45 but increased from 45 to 55 DAP. IVTD of leaves was greater than stems (90.6 and 58.4%, respectively) at each DAP. However, IVTD of leaves was stable from 35 to 45 DAP, whereas that of stems decreased with DAP. NDFD was greater for leaves than stems (95.6 and 93.8%, respectively) for each DAP. Stem NDFD decreased from 35 to 45 but not from 45 to 55 DAP. Overall, nutritive value of leaves was greater than stems and both decreased with maturity. Our results suggest that SH stems contributed to the rapid decline of nutritive value with maturity and that SH should be harvested prior to 45 DAP for optimal nutritive value.