COWPEA PRODUCTION IN RICE-BASED CROPPING SYSTEMS OF THE PHILIPPINES -EXTRAPOLATION BY SIMULATION

There is a growing interest in cultivating cowpeas (Vigna unguiculata (L.) Walp.) in the tropics to meet the protein requirements of small f armers, forage requirements of ruminants, and to attain more sustainab le agricultural systems. A mechanistic crop growth model was used to e stimate yields of partially irrigated and strictly rainfed crops of IT 82D-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 t able before and after the growth of rice (Oryza sativa) in various par ts of the Philippines. Long-term simulation results indicated that the yield of TVX1948-012F varied from 100 to 2250 kg ha-1, and that of IT 82D-889 varied from 50 to 1600 kg ha-1 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 increa sed long-term biomass compared with those for strictly rainfed situati ons 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 two maturity classes of cowpea cultivars appear to have somewhat differen t extrapolation domains. The study demonstrates that mechanistic simul ation modelling can be a useful tool to delineate the extrapolation do mains of crops and cultivars.