Two field experiments were conducted during 1981-1982 to determine the feasibility of using midday canopy temperatures, measured with an infrared radiation thermometer, for irrigation scheduling in ‘Oregon 1604’ and ‘Galamor’ snap beans (Phaseolus vulgaris L.) Treatments which allowed various levels of positive canopy minus air temperature differences [stress-degree-days (SDD)] to accumulate between irrigations were evaluated along with a treatment irrigated at 4 growth stages, a dry treatment, and a control treatment which was irrigated at -0.06 MPa soil water potential (SWP). Diurnal measurement of canopy and air temperatures indicated that the greatest differences between canopy and air temperature occurred near solar noon. In 1981, all treatments irrigated by an accumulation of positive SDD had reduced yields compared to the control SWP treatment. In 1982, under higher rainfall and lower air saturation vapor pressure deficits (VPD) than in 1981, yields of the SDD irrigated treatments were comparable to those obtained with the SWP treatment. Accumulation of positive SDD values to schedule irrigations was adequate when midday VPD values were low. However, when high VPD occurred, SDD values were always negative. A model is presented in which SDD values can be adjusted for environmental variability to more accurately schedule irrigations. Measurements of air temperatures within the canopy were made and compared to surface canopy temperatures measured with an infrared thermometer. Regression analysis showed that canopy temperature could be predicted using the air temperature within the canopy (R2 = 0.89). The sum of SDD values for the season was used to estimate canning maturity pod yield (R2 = 0.65).
Field experiments were conducted to evaluate the effects of differential irrigation treatments on the yield and pod quality of ‘Oregon 1604’ and ‘Galamor’ snap beans (Phaseolus vulgaris L.) in 1981 and 1982. Treatments in which various levels of positive canopy minus air temperature differences [stress-degree-days (SDD)] accumulated between irrigations were evaluated along with irrigation at 4 growth stages, a dry treatment which received only one irrigation to establish plants, and a control treatment irrigated at -0.06 MPa soil water potential (SWP). In both seasons, yield was related strongly to the average soil water potential from planting to harvest. Yields in 1982 were at least 5 MT/ha greater at a given average soil water potential than in 1981. Yields of ‘Oregon 1604’ and ‘Galamor’ were similar under adequate irrigation, but under greatest water stress, yield of ‘Oregon 1604’ was higher than for ‘Galamor’. Pod number was reduced only in the dry treatment. Percentage of set pods, pod length, and number of seeds per pod were all reduced by low irrigation, while fiber content of pods and weight per seed were increased by low irrigation.
Two field experiments were conducted to evaluate the effects of differential irrigation on plant growth, development, and water status of 2 snap bean cultivars, ‘Oregon 1604’ and ‘Galamor’ (Phaseolus vulgaris L.). Plants were grown at various irrigation levels ranging from a well-watered control to a dry treatment which received only one irrigation to establish plants. Measurements on plants sampled weekly at 6 times during the growing season showed that total plant dry weight, total leaf dry weight, total leaf area, average area per leaf, and number of leaves per plant were reduced by water deficits in both cultivars. Also, for both cultivars, total leaf area per plant was reduced more by a decrease in area per leaf than by a reduction in leaf number. Specific dry leaf weight was higher in the drier treatments. During each year, a significant difference between treatments occurred earlier in the season for total leaf area per plant than for total plant weight. At predawn, leaf water potential (ψ) always was more negative in the dry treatment than in the control. Early in the season, there was no significant difference in midday ψ between the control and dry treatment. Later, as soil water became limiting, the dry treatment had a more negative ψ than the control. Near the end of the season, after the dry treatment had been subjected to a long period of water stress, midday ψ was more negative in the control than in the dry treatment. Although some osmotic adjustment occurred in the dry treatment, leaf turgor potential (ψp) was generally lower than in the control throughout the day. As ψ decreased from early morning through midday, transpiration rates increased due to an increase in evaporative demand on the leaves. Leaf diffusive resistance also increased with decreasing ψ but a “threshold value” for stomatal closure was not demonstrated.
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.
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.
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.
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 (r2 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 (r2 ranged from 0.82 to 0.93), but differences in these relationships between years and experiments indicate that CWSI measurements must be improved.
Yield variables of mainstem nodes 6 (terminal) and 2 (that of the first trifoliate leaf) of ‘Oregon 1604’(Phaseolus vulgaris L.) were evaluated at 2 irrigation regimes × 2 plant populations in a warm (1978) and a moderate (1979) season. A single inflorescence formed at node 6, whereas up to 4 inflorescences were borne on branches at node 2. After emergence, crops were irrigated either when the soil water potential reached −0.06 MPa (high) or −0.25 MPa (low). High and low plant populations were, respectively, 45 vs. 18 plants/m2 in 1978 and 54 vs. 33 plants/m2 in 1979. Yield per unit area was increased significantly from 38–54% by high plant population and 40–120% by high irrigation. On a per plant basis, plant population failed to have a significant effect on total yield or yield variables at node 6. At node 2, however, high plant population reduced the number of inflorescences in 1978 and decreased the number of flowers, number of pods formed and harvested, and percentage set and reduced pod yield by about 50% in both years. Per unit area yields of node 2 at high and low plant population differed by less than 13–18%. Since the productivity of node 6 was not influenced by density, per unit area yields at this node more directly reflected plant population. Nodes 2 and 6 responded similarly to the low irrigation regime, which in 1978 significantly decreased the number of pods formed, percentage set, and pod yield at both nodes. Irrigation effects on individual yield parameters at each node generally were less in the cooler 1979 season. No significant irrigation–plant population interactions occurred for any measured yield variable in either season.
‘Jubilee’ sweet corn (Zea mays L.) was grown under conventional and strip tillage in 1982 and under conventional tillage, strip tillage, and no-till culture in 1983. Stand establishment was decreased by strip tillage in 1982, but was lower only in the no-till treatment in 1983. Midseason plant height in strip tillage was slightly less than in conventional tillage both years, whereas the no-till plants were much shorter than in other treatments the second year. Yields of husked ears from strip tillage were 7% and 16% lower than from conventional tillage in 1982 and 1983, respectively. In 1983, yield from the no-till treatment was 31% lower than from conventional tillage. The percentage of kernel moisture always was higher from plants in strip tillage and no-till, indicating these treatments had ears that were more immature at time of harvest than in conventional tillage. Average daily soil temperatures at the 5 cm depth for the first 30 days after planting in 1983 were highest for conventional tillage, followed by strip tillage and no-till.
Leaves at nodes 4 or 8 of greenhouse grown beans, Phaseolus vulgaris L., cv. Puelba 152, were briefly exposed to 14CO2 at 35, 48, 63, or 70 days after planting. Prior to flowering, over 85% of the recovered 14C-activity translocated in 24 hours from node 4 was in roots, nodules, and lower stem. At flowering, radioactivity translocated to the lower stem decreased but correspondingly increased in nodules. Roots sequestered 45% of translocated-14C throughout the life of the node-4 leaf. About 80% of the 14C-activity exported from node 8 at flowering was in middle and upper stem sections, but during pod-fill over 85% moved into the pods and less than 1% to the nodulated root system. Starch concentration in the lower stem increased continuously from flowering, but in other plant parts declined after early pod-fill. At mid pod-fill, the concentration of soluble sugars in nodules and roots declined and reached a common value in stem sections. Nitrogen (C2H2) fixation decreased rapidly after peaking at early pod-fill. This decline, which was accompanied by loss of lower leaves, occurred in the presence of a high concentration of starch in the stem.