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- Author or Editor: William S. Braunworth Jr. x
Abstract
Sweet corn (Zea mays L.) was irrigated using randomized complete block and line source experimental designs in 1984 and 1985 on a mixed, mesic Cumulic Ultic Haploxeroll soil. Irrigations were scheduled when ≈50% of the available water was depleted in the root zone of the 100% treatment to refill the root zone to 0% to 100% of field capacity (five irrigation levels). Four yield parameters were measured for all plots: yield of all ears before husking, yield of good husked ears, kernel yield (fresh), and total dry matter production of plants and ears. Maximum relative total unhusked ear yield and near-maximum evapotranspiration (ET) were obtained at 85% of maximum water applied, indicating that high yields can be maintained with deficit irrigation. Without irrigation, only 44% of maximum yield was obtained. Maximum water use efficiency (WUE), defined as the total unhusked ear yield in kg·ha−1·mm−1ET, occurred between 407 and 418 mm of ET. The maximum WUE corresponded to ≈313 mm water applied (WA); maximum yield, however, occurred within the range of 449 to 518 mm WA. Irrigation treatments to achieve maximum WUE were predicted to result in a 10% yield reduction.
Abstract
The crop water stress index (CWSI) may be useful for optimal irrigation timing. This preliminary study evaluates the relationships between the CWSI and evapotranspiration (ET) and yield. The CWSI was also characterized on an hourly basis. Once-daily CWSI measurements after full ground cover was established and hourly CWSI measurements on 4 days were made in sweet corn (Zea mays L. ‘Jubilee’) irrigation experiments in 1984 and 1985. The gradient of water applied included five irrigation levels established from 0% to 100%, with the 100% level intended to refill the root zone to field capacity, after 50% depletion of available water, at each irrigation. CWSI values, obtained hourly throughout the day, were highest between 1000 and 1700 hr. CWSI values tended to be higher in the less-irrigated plots (40% and less) than in those that received greater amounts of water (57% to 100% treatment levels). Seasonal average CWSI values (midday measurements) were closely related to the seasonal ET deficit (r 2 ranged from 0.45 to 0.96), but there was not the expected 1:1 relationship of CWSI and ET deficit. The yield deficit of good, husked ears was also closely related to CWSI (r 2 ranged from 0.82 to 0.93), but differences in these relationships between years and experiments indicate that CWSI measurements must be improved.
Abstract
Accurate irrigation scheduling for sweet corn can reduce irrigation costs and ensure meeting of yield goals. Three scheduling methods, evaluated in a 2-year study, included: a) irrigation when 46% and 57% of available water was depleted in 1984 and 1985, respectively, as measured by a neutron meter; b) irrigation when 50% of available water was depleted as estimated by the Food and Agriculture Organization modified Penman equation; and c) irrigation at three growth stages. Irrigation water applied for the neutron meter, modified Penman, and growth stage method was 367, 279, and 269 mm, respectively, in 1984 while in 1985 these methods resulted in application of 500, 368, and 366 mm of irrigation water. Yields of total unhusked ears in 1984 for the growth stage and modified Penman methods were significantly lower than the yields of the neutron meter method but were not significantly different from one another. In 1985, there were no significant differences in total unhusked or husked processable ear yields among the three scheduling methods. Quality factors, which included ear length, kernel moisture content, and ear weight did not vary significantly with irrigation scheduling methods. Since total unhusked, husked processable yields, and quality differences were minor, irrigation scheduling by any of these methods would appear to be satisfactory.
Abstract
The yield and quality response of sweet corn (Zea mays L.) to variable water supply was evaluated in 1984 and 1985. Irrigation depths were established with sprinklers at five intervals from 0% to 100%, with the 100% treatment intended to refill the root zone to field capacity. The other treatments were considered as deficit irrigation. Irrigations were scheduled when 47–57% of the available water was depleted in the root zone of the 100% treatment level plots. Yields were similar when irrigation depths were 50% or greater in 1984 and 1985, although water application depths varied between years. Water balance measurements indicated very little deep percolation. Deficit irrigations of about 50% and 70% saved water and maintained yield. Yield, ear weight, and kernel weight decreased in the nonirrigated treatments or when water application depths were about 25%. Nonirrigated sweet corn tended to be more mature at harvest then irrigated corn.
Evapotranspiration (ET) of three perennial ryegrass (Lolium perenne L.) cultivars and one cultivar each of colonial bentgrass (Agrostis tenuis L.) and tall fescue (Festuca arundinacea L.) was measured in the field. Soil water depletion was measured with a neutron probe. Under minimal maintenance (i.e., no irrigation and infrequent mowing), ET was not significantly different for five perennial grasses. All grasses used more water than the bare-ground treatment. Soil water uptake was greatest in the upper soil layer (O to 25 cm) and decreased with depth. Few differences in water uptake were noted among grasses within each soil layer.