Effects of legumes-cassava intercropping on cassava forage and biomass production

A sweet short-term variety of cassava was harvested for forage every 60 days during 18 months on a sandy loam soil near Phnom Penh in Cambodia. Treatments were cassava intercropped with Desmanthus virgatus (C + Dv) or Gliricidia sepium (C + Gs), and cassava alone (C) was the control. The harvested biomass was weighed and samples for the determination of dry matter (DM), nitrogen (N), crude protein (CP), and leaf proportion were taken. Soil fertility was assessed by a 'biological test' with maize grown in soil samples from the cassava plots and sod samples were also analyzed for the determination of chemical composition at the beginning and the end of the experiment. Intercropping did not affect cassava DM and CP yields but total DM and CP yields were increased by 43% and 39% in D. virgatus and G. sepium intercrops, respectively. Intercropping increased leaf proportion in the cassava DM. The total CP yield ranged from 0.1 to 0.5, from 0.4 to 0.6 and from 0.3 to 0.6 tons harvest occasion(-1) in treatments C, C + Dv, and C + Gs, respectively. The CP content ranged from 21.1-29.3% and 8.3-10.8% in the cassava leaf and stems plus petioles, respectively, while the CP contents in D. virgatus and G. sepium were 14.8% and 15.6%, respectively. It was estimated that D. virgatus and G. sepium fixed 1/3 and 1/2 of the N amounts removed in the cassava forage, respectively. In this experiment all biomass produced was removed from the plots and soil fertility declined.