Soil allelochemical residue effects in a tomato cowpea rotation – nodulation and productivity of cowpea and nematode suppression

Soil allelochemical residue (SAR) effects from nemarioc-AL phytonematicide in a tomato–cowpea (Vigna unguiculata) succession system were investigated on nodulation of Bradyrhizobium japonicum, productivity of cowpea and suppressive capabilities of Meloidogyne species. Following a tomato (Solanum lycopersicum) crop which was subjected to five concentrations (CCs) and five application interval (AI) levels of nemarioc-AL, the cowpea var. Eureka was raised on spots previously occupied by tomato plants, without reapplying the treatments. SAR effects due to CC × AI consistently inhibited B. japonicum nodulation in 96% factorial pairwise combinations, while CC alone increased soil pH and seed yield, but reduced Meloidogyne incognita numbers. Similarly, AI alone increased dry shoot mass and reduced Meloidogyne species. Overall, at high CCs and repeated AIs, cowpea var. Eureka was not suitable for immediate use as successor crop in botinemagation systems where Meloidogyne species were managed using nemarioc-AL phytonematicide in tomato production.