Analysis of the productivity of upland rice and cover crops in relay intercropping systems using a mechanistic competition model

Abstract

Relay intercropping systems with rice cultivars (WAB450-24-3-2-P18-HB (V4) and WAB56-50), the competitive Cajanus cajan and the weakly competitive Stylosanthes hamata were evaluated in the tropical savanna zone in Cote d\'Ivoire. The INTERCOM model for competition served for data analysis and understanding of the system based on phenological, physiological and morphological characteristics of the species. Relationships between accumulated legume biomass and yield loss (YL) in rice showed that rice yield was reduced up to 63 % and 100 % by S. hamata and C. cajan respectively, depending on the introduction time. At low levels of YL both legumes performed similarly. At higher levels of rice YL, C. cajan performed better as it produced higher amounts of biomass. Differences in legume biomass at a specified level of rice YL were mainly created in the growth period following rice maturity, which is restricted by water availability. The lesser performance of S. hamata in that period was attributed to the difference in phenology, combined with the short-duration character of the species. The combination of early introduction and short growth duration of this species prevented a rapid leaf canopy development after rice harvest, resulting in the relatively poor biomass production. Options to improve legume biomass production in relay systems should focus on the period following rice maturity. Les systemes de culture relais avec les varietes de riz (WAB450-24-3-2-P18-HB (V4) et WAB56-50), les especes competitives Cajanus cajan et faiblement competitive Stylosanthes hamata, ont ete evalues en zone savane tropicale de Cote d\'Ivoire. Le modele de competition INTERCOM a servi a l\'analyse et a la comprehension du systeme sur la base des caracteres phenologiques, physiologiques et morphologiques des especes. La relation entre la production en biomasse des legumineuses et les pertes en rendement (PR) du riz ont montre que les rendements en riz ont ete reduits de 63 % et 100 % par S. hamata et C. cajan, respectivement, en fonction de la date de semis. A de faibles niveaux de PR en riz, les deux especes de legumineuses se comportent de facon similaire. A des niveaux eleves de PR, C. cajan est plus performant en produisant des quantites de biomasse plus importantes. Les differences de production en biomasse a un niveau specifie de perte de rendement en riz apparaissent principalement pendant la periode suivant la maturite du riz et qui est restreint par la disponibilite en eau. La faible performance de S. hamata pendant cette periode est attribuee a la difference de phenologie, associee au caractere cycle court de cette espece. La combinaison entre le semis precoce et le temps de croissance reduit n\'a pas permis un developpement rapide de la canopee apres la recolte du riz, entrainant une production relativement mauvaise de la biomasse. Des options pour ameliorer la production de biomasse des legumineuses dans les systemes de culture relais doivent se focaliser sur la periode suivant la maturite du riz Keywords : Legumes, cropping systems, yield loss, Cote d\'Ivoire. Agronomie Africaine Vol. 18 (3)006: pp. 285-298