Observations indicate that Spanish‐type peanuts (Arachis hypogaea L.) are more tolerant of dehydration than Virginia types under severe water stress. However, physiological reasons for differences in tolerance to water deficits among peanut genotypes have not been established. The objective of this study was to evaluate peanut genotypes for their response and relative resistance to severe water deficits. A Spanish type (‘Comet’), Virginia type (‘Florunner’), and a Spanish ✕ Virginia selection (OK‐FH15) were grown in situ under irrigated (IRR) and rainfed (RF) conditions. Leaf water potential (ψw), osmotic potential (ψπ), turgor potential (ψp), relative water content (RWC) and its apoplastic water fraction (Aw) were determined weekly between 1300 and 1500 h, and diurnally on selected days. Yields were determined at 149 days after planting (DAP). Ratios (RF/IRR) genotype ψw, ψπ, and RWC showed significant differences among genotypes between 50 and 63 DAP, a critical period of peanut growth and development. The ψw and RWC ratios were maximum for all genotypes at 63 and 70 DAP, respectively. The maximum ψπ ratio occurred on 56 DAP for Comet (1.25), 63 DAP for OK‐FH15 (1.32), and 70 DAP for Florunner (1.18). Regression analysis of 1/ψw vs. RWC showed a biphasic cubic polynomial function best fit the data for all genotypes. The data indicated that as RWC declined, Comet ψw tended to decrease more rapidly than either OK‐FH15 or Florunner. Conservative estimates of ψπ, changes between 95 and 55%R WC were highest for Comet, lowest for Florunner, and OK‐FH15 was intermediate. Aw was calculated for each genotype and plotted against ψp to determine its contribution to hydration maintenance. At high ψp, maximum Aw, was 7.1, 12.1, and 25.2%f or Florunner, OK‐FH15, and Comet, respectively. Florunner Aw, decreased to zero at 0.16 MPa ψp, and the Aw of OK‐FH15 decreased with ψp to the origin. Comet had much greater Aw at low ψp and was the only genotype with appreciable Aw at zero ψp. These results indicate that Aw varies in peanuts and may be genotype specific. Comet showed significantly higher yield, grade, and dollar value than either Florunner or OK‐FH15 under rainfed conditions. The lower ψw, greater change in ψπ, and higher Aw and yield of RF Comet suggests greater resistance to dehydration when high soil moisture deficits and evaporative demand conditions occur.
Peculiar stomatal action has been suggested as one causal factor for observed differences in water use between peanuts (Arachis hypogaea L.) grown in narrow and wide rows. This study was designed to characterize stomatal action in narrow‐ and wide‐row plantings on a Udic Argiustoll soil. Measurements of stomatal diffusive resistance (Rs) and leaf‐water potential (Ψw) were made daily at half hour intervals on irrigated peanuts grown in narrow‐row (NR) and wide‐row (WR) spacings during periods of flowering to pod development in 1979,1981, and 1982. Measurement days were classified as low, moderate, and high evaporative demand days according to respective daily meteorological conditions. In both NR and WR treatments the relationship between Rs and Ψw was generally linear. On certain days, however, NR‐Rs increased to much higher values earlier in the afternoon at a given Ψw than WR‐Rs. The effect was most pronounced on high evaporative demand days and was never noted on low evaporative demand days. Data for 3 years reveal the NR stomatal closure effect was real and repeatable.
Efficient water application for crop productivity requires knowledge of the plant/soil water balance. The objectives of this research were to determine how peanut (Arachis hypogaea L.) leaf water content responds to soil water content and to examine the soil water content‐ΨS relationship for predicting limiting levels of soil water relative to crop water status in the field. Few field data describing peanut internal water balance responses to soil water are available. In the present study, available soil water content is defined as water content minus water content at −1.5 MPa divided by water content at −0.01 MPa minus water content at −1.5 MPa. This approach. normalizes water content to the fraction available. It is analogous to leaf relative water content (LRWC) and is expressed as soil relative water content (SRWC). The objectives of this research were to: (i) define the relationship between SRWC and LRWC of peanut grown under rainfed and irrigated conditions, and (ii) use SRWC to predict limiting levels of soil water relative to crop water status. Plants were grown on a Teller loam soil (fine, mixed, thermic Udic Argiustoll). Weekly midday (1130 to 1300 apparent solar time) measurements of LRWC were made between 40 and 100 d after planting (DAP). Weekly SRWC values were interpolated to correspond to LRWC measurement days. Above 50% SRWC, the mean LRWC was about 85%, and appeared to be affected more by evaporative demand than by SRWC. Below 50% SRWC, LRWC was highly correlated with SRWC. The predicted SRWC when turgor pressure potentials approached zero was about 45%. This SRWC threshold occurred under rainfed conditions in the 3 yr studied at 59, 56, and 64 DAP during flowering and pod formation. It is concluded that the SRWC vs. soil water pressure potential curve of Teller soil may be useful for predicting limiting levels of soil water for peanut and that limiting levels of soil water may occur well above the classically defined lower limit of soil water availability.
Soil matric potential controls plant growth. Yet it is difficult to determine the effect of soil matric potential, by itself, on plant water relationships and growth. One way to isolate matric potential is to split roots between soil and nutrient solution because the soil has a matric potential while the nutrient solution has a matric potential of zero. Therefore, in this study, leaf water potential, stomatal resistance, rate of water use, leaf area, plant height, and root length of winter wheat (Triticum aestivum L. em. Thell. cv. Osage), grown with and without wind, and with roots split between soil:soil, soil: nutrient solution (soln), and soln:soln were measured to determine the effect of soil matric potential on wheat water relationships and growth. During the first 16 days of the 38‐day experiment, the soil (Kirkland silt loam, Udertic Paleustoll) was well‐watered. Water was withheld from all soil treatments after the 16th day. Plants were grown with and without wind, and with and without soil drought, because, in the Great Plains, wind and drought, or a combination of the two, are the main causes of crop loss. Leaf water potential and stomatal resistance of plants with roots in soi1:soln were usually between those of plants with roots in soil:soin and soln:soln. Plants with all roots in nutrient solution had the highest leaf water potential and lowest stomatal resistance. Plants with all roots in well‐watered soil lost 2.5 times less water, but grew as well as plants with all roots in solution. Plants with roots split between solution and well‐watered soil lost the same total amount of water as plants with all roots in solution. But the plants with roots in soil:soln lost 7 and 11 times more water from the solution side than from the soil side of the split root containers for the wind and no‐wind treatments, respectively. Nonstressed plants (no wind, no drought) with roots split between soi1:soln were taller and had a larger leaf area than plants with roots all in soil or all in solution. The results showed that growth of wheat was increased if part of its root system was in media with zero matric potential (nutrient solution) and part in soil.
Induced stomatal closure behavior of irrigated peanut (Arachis hypogeoe L. cv. Comet, a bunch type) as related to row spacing and evaporative demand has been previously demonstrated as real and repeatable. The objective of this research was to determine the magnitude of evaporative demand that induced stomatal closure in narrow-row plantings. Stomates in wide rows tended to show far less closure on the same days. The differences were not noted on days with low evaporative demand. Concurrent measurements of net radiation, dry-and wet-bulb temperature, and horizontal wind velocity were made every IS min. Estimates of environmental evaporative demand were made. No distinct peak or cumulative evaporative demand levels were found that separated stomatal differential action days from nonaction days. However, analysis of the cumulative advective energy component of cumulative evaporative demand showed a threshold above which stomatal closure responses were noted. This threshold was 8.S MJ m-2 • Further detailed analysis of the factors involved in the cumulative advective energy component indicated stomatal closure was dominated by neither horizontal wind velocity, integrated over time, nor integrated vapor pressure deficit.Additional index words: Evapotranspiration, Advective energy.
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