Microclimatic and crop responses to center pivot sprinkler and to surface irrigation

Over 1 million hectares are irrigated with center pivot sprinklers in the Great Plains, USA. Microclimatic conditions under center pivot systems will be affected somewhat by periodic sprinkling, but the extent of microclimatic modification to be expected from sprinkling in the High Plains region and the physiological implications have not been reported. We compared the leaf temperature, canopy air temperature, vapor pressure deficit, vapor pressure, soil temperature, and soil heat flux in a corn (Zea mays L.) canopy under center pivot sprinkler and surface irrigation. The crops were grown at Garden City, Kansas, in 1980, a hot, dry year, and in 1981, a relatively cool, wet year. Leaf and air temperatures in 1980 were significantly cooler undder sprinkler irrigation than under surface irrigation. Maximum, minimum, and mean daily leaf temperatures were reduced by 2°, 2°, and 1° C, respectively; and maximum, minimum, and mean canopy air temperatures were reduced by 3°, 1.5°, and 1.5° C, respectively. Leaf and minimum canopy air temperature reductions were significant at the 1 % level. Shorter irrigation intervals may explain the reduced stress on the sprinkled plots. We observed small, nonsignificant temperature reductions under the sprinkler in the 1981 season. No significant effects of irrigation type on vapor pressure deficit or on vapor pressure in the canopy were observed in 1980 or 1981. Analysis of the 1981 data indicated that most of the day-to-day variability in leaf and canopy temperatures is related to ambient air temperature and that canopy vapor pressure deficit and vapor pressure are related to both ambient temperature and ambient vapor pressure deficit. Soil temperatures were significantly reduced and soil heat flux increased under sprinkler irrigation. The diurnal response to sprinkler irrigation cycles was pronounced during early stress periods of the 1980 growing season. Leaf and canopy air temperature and vapor pressure deficit were all significantly lower throughout the day in recently irrigated areas compared to areas that were sprinkled one or two days earlier. Responses to sprinkling during nonstress periods of 1980 and 1981 only persisted while the leaves were wetted; after, conditions returned to levels found in the rest of the field.