Potato ( Solanum spp.) in the hot tropics V. Intercropping with maize and the influence of shade on tuber yields

Abstract

The influence of various shade treatments on tuber yield of potato in three hot tropical sites (5–12°S, 180–800 m a.s.l.) within Peru was evaluated. Shade treatments comprised (a) artificial screens imposed throughout the season of the potato crop; (b) relay-cropping with maize for a short (10–30-day) period following planting of potato; and (c) planting maize and potato simultaneously such that maize shaded potato from 40 days after planting onwards. Variables tested included periodicity of shading throughout the day, duration of shade, and density of shade, the last-mentioned accomplished by variations in population and rectangularity of maize plantings. Artificial shade (50% reduction of light transmission) during midday or in the afternoon favoured tuber yield more than morning shade, and shaded plants were in general 35–39% more efficient than non-shaded plants in their conversion of available solar energy to tuber fresh weight. When relay-cropped with maize, potato plant population at harvest was superior to that of a sole crop of potato, an effect mediated through faster emergence and achievement of a greater maximum population and not through differential survival of shaded or sole potato plants. Enhanced final population was often offset by reduced individual yield per plant, particularly at dense or extended periods of shade, and shade for 20 days appeared optimal, although during the dry season 30-day periods were not always detrimental to yield. Tuber yields of relay-cropped plots ranged from +89% to −53% those of sole potato plots, the latter following a 31-day period of shade at a density of 4.76 maize plants m −2 during the rainy season. Yields of maize increased with increase of maize planting population, and at a given population were greater for square than for rectangular plantings. Tuber yield of potato planted simultaneously with maize was not significantly less than potato yield of sole crops until maize population exceeded 0.6 plants m −2, i.e. the population reducing transmission by more than 30% to the understory potato crop. In a replacement-series experiment, at the hottest site, tuber yield was greater in mixed than in sole plots at 1:11 and 1:9 maize:potato proportions (375 and 391 g m −2 vs 273 g m −2 for sole plots) and the maximum reduction in tuber yield at the densest maize population (1:6) at any site was 34% (1030 and 1563 g m −2 for mixed and sole plot). However, land equivalent ratios always exceeded unity since maize yield in mixtures was disproportionally greater than yield based on per-plant yields of sole-maize plots. In relay cropping treatments, and those in which maize and potato were simultaneously planted, a delicate balance existed between the ability of shade to reduce air and soil temperatures, without causing reductions in tuberization and photosynthesis. Our results indicate that there would appear to be potential for intercropping potato and maize in the hot tropics.