1. Effects of Legumes-Cassava Intercropping on Cassava Forage and Biomass Production

Authors: Khieu Borin, Frankow-Lindberg, B.E., 2005 .
The Journal of Sustainable Agriculture, 27 (3) 139 - 150

Summary: The experiment was conducted from February 2001 to August 2002 in Cambodia. The experiment was established on 440 m2, of which 270 m2 were used for experimental plots and 170 m2 served as borders between plots and as paths for access. The soil is a sandy loam classified as Sretayen Kampong Speu Province (National Soil Classification) and consists of clay (12.9%), fine silt (10.0%), coarse silt (10.7%), fine sand (27.3%) and coarse sand (38.3%). The experiment included three treatments; cassava alone (C), cassava-D. virgatus (C+Dv) and cassava-G. sepium (C+Gs). Each replicated plot was 30 m2. A short-term variety of cassava, which is commonly grown for root production in Cambodia, was used in the experiment. The experiment was irrigated once daily during establishment (< 30 cm height), thereafter the frequency of irrigation was regulated according to rainfall. The first harvest was done when the cassava had a height of about 150 cm (three months after planting) when all plant material 60 cm above-ground was cut. Thereafter, the plants were harvested every 60 days, and in these harvests all species were present. At each harvest, all cassava plant material was cut and weighed; after this it was manually partitioned into leaves and stems plus petioles, which were dried and weighed separately for the determination of the leaf proportion. Soil samples were taken at the beginning, before planting of the legumes, and at the end of the experiment. An indirect method, ‘a biological test’ used maize to assess soil fertility.

Abstract: 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 soil samples were also analysed 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.