Potato (Solanum spp.) in an isohyperthermic environment V. Intercropping with maize

Seven experiments were conducted at 14°N latitude and 150 m a.s.l. in the Philippines. Various maize plant populations, spatial planting configurations and planting time of maize (from 0 to 30 days after planting potato) were evaluated to assess their influence on light transmission to the intercropped potato and its effect on growth and yield of potato and maize. With synchronous planting of potato and maize, there was no shading of the potato for the first 25 days after planting (dap) resulting in no advantage in rate or percentage emergence, time of tuber initiation and tuber number plant−1. Low levels of shading (less than 25% from 50 to 60 dap potato) did not improve per plant tuber yield in any experiment. Potato tuber yields were significantly reduced when the solar radiation levels reaching the potato canopy dropped to less than 10 MJ m−2 day−1 during the middle of the bulking period (50–60 dap). Maize pulations of 30 000 plants ha−1 in a planting configuration where maize rows were 1.2 to 2.4 m apart transmitted more than the critical light requirement of 10 MJ m−2 day−1. Maize at 43 000 plants ha−1, planted up to 20 dap potato, delayed shading of the intercropped potato but resulted in shade levels exceeding 50% from 55 dap potato, which detrimentally affected potato yields in two experiments, and to a lesser extent in a third experiment. Potato yields ranged from 16 to 23 t ha−1 for the monocropped and best intercropped treatments across all experiments. Maize populations of 30 000 plants ha−1 along with 56 000 potato plants ha−1 improved land-equivalent ratios up to 1.4.