Cowpea production in rice-based cropping systems of the Philippines - extrapolation by simulation

A mechanistic crop growth model was used to estimate yields of partially irrigated and strictly rainfed crops of IT82D-889, an early maturing cowpea cultivar and TVX1948-012F, a medium maturing cowpea cultivar. Average yield and yield stability of these cultivars were determined for fields with a shallow and a deep water table before and after the growth of rice in various parts of the Philippines. Long-term simulation results indicated that the yield of TVX1948-012F varied from 0.1 to 2.25 t/ha and that of IT82D-889 varied from 0.05 to 1.60 t/ha for fields with a shallow water table and for partially irrigated conditions. Yields were greater for the post-rice than for the pre-rice season. Partial irrigation increased long-term biomass compared with those for strictly rainfed situations by 30% in the pre-rice season and by 104% in the post-rice season. Yields were more stable at Davao than at Los Banos or Iloilo. The 3 maturity classes of cowpea cultivars appeared to have somewhat different extrapolation domains. It was concluded that mechanistic simulation modelling can be a useful tool to delineate the extrapolation domains of crops and cultivars