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A 3-year irrigation scheduling study on carrots (Daucus carota L.) was conducted at the Colorado State Univ. Horticulture Research Center near Fort Collins to determine the irrigation schedule that produced the best combination of high water use efficiency and marketable yields with the least amount of water and fewest irrigations. This study used an irrigation scheduling program developed by the U.S. Department of Agriculture/Agricultural Research Service with crop coefficients calculated for carrots. Maximum carrot production and water use efficiency were obtained when the scheduling program simulated a 30-cm rooting depth at planting, increasing linearly to 60 cm in 75 days. Best yields and water use efficiency were attained by irrigating whenever 40% of the available water in the root zone had been depleted. The computer program for irrigation scheduling is available on diskette from the authors.
Roots of acorn squash were washed from soil cores, dried and weighed. The cores were taken in a pattern about individual plants to reflect the roots present in each selected zone at different periods during the season. A different plant was sampled at each period so that there would be no effect from previous sampling. The root weights were multiplied by factors commensurate with the volume of soil represented by each core sample. Two years data have indicated that irrigation level effects the size of the root system but not its distribution. Density of roots was always greatest in the top 15 cm of soil and this zone of the greatest density progressively moved out from the center of the plant with time. Pattern of root distribution was not effected by plastic mulch, bare ground, trickle or furrow irrigation treatments. Root distribution was the same on all sides of the plant.
Abstract
Two onion (Allium cepa L.) irrigation scheduling procedures were compared in field studies over a 3-year period. The McSay–Moore model uses volume of distilled water evaporated from calibrated Bellani atmometers as a basis for predicting irrigation. This model tells when to irrigate, but not how much to apply. The ARS/USDA model uses energy and aerodynamic equations to make estimates of evaporation rates from meteorological data. This model not only predicts when to irrigate, but also the amount to apply. Given the conditions for these experiments, onion yields and water use efficiencies were greater with the ARS/USDA than with the McSay–Moore model.
An irrigation scheduling program has been developed for zucchini squash that produced high yields and high water use efficiency with, a minimum number of irrigations. The irrigation program is based upon a soil water balance model developed by the USDA. This irrigation program is available in diskette form and may be used with any IBM compatible personal computer provided wind run, temperature, solar radiation, humidity and precipitation data are available.
Abstract
Cucumber (Cucumis sativus L.) irrigation scheduling was studied during the 4 years of 1983-1986. Tensiometers were used during the first year to determine when to irrigate, and the USDA irrigation scheduling program was used to determine the amount of water to apply. The data from the first year’s study indicated that the plants had not been stressed; therefore, the following year, estimates of the available water depletion were made with the USDA irrigation scheduling program, with tensiometers used only for comparison. After 4 years of study, we concluded that the best combination of high yield, high water use efficiency, and fewest number of irrigations was obtained if cucumbers were irrigated when the original scheduling program determined that 40% of the available water was depleted, applying only 70% of the water that the program indicated was required. This signaled that the program was overestimating the rate at which water was being depleted. Therefore, as a final step, a revised set of cucumber coefficients that approximated daily evapotranspiration (ET) more closely was determined. When using the revised coefficients, cucumbers should receive the exact amount of water called for by the irrigation program.
Squash (Cucurbita pepo L. var. pepo) plants were grown on black polyethylene mulch or on bare ground, with trickle or furrow irrigation, and received only natural rainfall, or natural rainfall plus half or all of the estimated supplemental irrigation water required as determined by an irrigation scheduling program. The squash roots predominate in the upper 6 inches of soil throughout the season, with no less than 60% of the root mass located in this layer. The proliferation of roots increased as they extended horizontally from the vertical center line of the plant from 0 to 24 inches. Neither the irrigation treatments nor black polyethylene mulch had any influence on the pattern of root development. Water stress, however, reduced the size of the root system and the crop yield. Yields were not influenced by either furrow or trickle irrigation on the short rows that were used in this study. However, black polyethylene mulch and full irrigation offered the best chance of maximizing squash yields under the conditions of this study.