EFFECTS OF PLASTIC FILM COVERS ON DRY-MATTER PRODUCTION AND EARLY TUBER YIELD IN POTATO CROPS

摘要

Three experiments, conducted in 1988, 1989 and 1990, examined the effects of date of removal of a clear, perforated (200 x 10 mm holes m(-2)), plastic film cover on the growth and early yield of potato crops. Results confirmed that the highest early yields were achieved when the cover was removed 2 wk after 50% crop emergence and the resulting yield increase over a non-covered control varied from 6-14 t ha(-1). Later removal reduced the benefit from covering and in some cases eliminated any advantage. Covering increased mean soil and air temperatures by 2.9 degrees C and 3.2 degrees C respectively (mean of three experiments), thereby advancing crop emergence by between 3 and 5 days. The number of day-degrees accumulated between planting and emergence was very similar in covered and non-covered treatments within a season but varied between seasons from 190 degrees C to 293 degrees C day (> 0 degrees C). Delaying removal resulted in an increased physical restriction to canopy expansion and reduced the capacity of the crop to intercept solar radiation. Total dry-matter yield was determined largely by the amount of radiation intercepted by crops (R(2) - 0.98). Plastic covering had relatively little effect on partitioning of dry matter to tubers but reduced tuber dry-matter percentage at early harvests when removal occurred later than 3 wk after crop emergence.