High Soil Surface Temperatures Research Articles

Effects of High Soil Surface Temperature on Seedling Survival in Pearl Millet

SummaryA field technique to screen pearl millet genotypes for their emergence and survival at high soil surface temperatures is described. Genetic variation in seedling emergence and survival is shown and it is argued that this variation is largely due to tolerance of high temperatures rather than tolerance of soil moisture deficit, although some interaction occurred. An index for ‘thermotolerance’ is defined and genotypes are ranked accordingly for this trait, which is shown to be highly heritable. The technique is repeatable and allows a large number of genotypes to be screened at the same time.

Atrazine persistence and toxicity in two irrigated soils of Australia

The persistence of atrazine in two contrasting irrigated soils from the Riverine Plain of south-eastern Australia was measured in the laboratory at three constant temperatures. Particularly at lower temperatures atrazine was more persistent, by an order of magnitude, than reported for soils overseas; but in two successive field experiments, encompassing both surface and incorporated applications of atrazine in the heavier soil, residues measured after about 7 months were within the range expected from the literature. The measured residues were 2-6 times smaller than predicted using a simulation model, probably reflecting volatilization and other losses which are not included in the model, but which are expected to be substantial at the extremely high soil surface temperatures observed in the field. Comparative measurements of aged residues in the heavy clay soil showed higher results from chemical analysis of acetonitrile-water soil extracts than by in situ glasshouse bioassay using oats and turnips, demonstrating that only one third of the extractable residue was available to crops. Comparison of soil-based and hydroponic assay using soybeans showed that this soil reduced the effective atrazine concentration in solution by at least 16-fold, but sensitive crops could still be damaged when grown in rotation after tolerant crops, or if irrigated with contaminated water.

Role of Heat Girdling in Early Seedling Death of Sorghum

High soil temperatures (>45 °C) can inhibit the field establishment of sorghum [Sorghum bicolor (L.) Moench.) seedlings in the semi‐arid tropics even when adequate soil moisture is present. The objective of this study was to demonstrate an apparatus for simulating this situation under controlled conditions. The apparatus applies a high temperature localized near the leaf intercalary meristem while maintaining an adequately moist root environment. With this technique, we tested the hypothesis that seedling death may be due to a heat‐girdling, leading to restricted translocation of carbohydrates to the root. Exposure of 10‐d‐old sorghum seedlings to heatgirdling temperatures of 52 ± 2 °C caused complete cessation of leaf elongation. At the same time, shoot carbohydrate concentrations increased while root carbohydrates declined, indicating that phloem transport from the shoot to the root may have been blocked or restricted. During the first 173 h of stress, turgor of both expanded leaves and leaf growing regions (basal 1 cm of leaf tissue) increased, indicating a favorable water balance in the seedlings. After 198 h of heat‐girdling, seedlings died. The apparatus we developed should prove useful for the large scale screening of seedlings for resistance to high soil surface temperatures.

Effect of burial on the softening of hard seeds of subterranean clover

Burrs of eight varieties of subterranean clover (Trifolium subterraneum L.), which had experienced one summer at the soil surface, were placed on the soil surface and at depths of 2, 6 and 10 cm in the soil. The numbers of residual hard seeds were determined after 1, 2 and 3 years. The effects of laboratory treatment at a diurnally fluctuating temperature of 60/15�C on the softening of buried seeds and of seeds stored in the laboratory for 1 and 3 years were determined. Rate of seed softening in all varieties decreased with increasing depth of burial, apparently because the soil insulated the seeds from high soil surface temperatures. Few seeds of the varieties Northam and Geraldton softened during 3 years of burial at 6 or 10 cm; while, at the other extreme, few seeds of Yarloop survived 3 years at any depth. Some evidence was found for microbial decomposition of hard seeds in the field. Seeds softened more readily at 60/15�C (in the laboratory) as the preceding periods of either laboratory storage or field burial increased. Such storage or burial experiences have a preconditioning effect on hard seeds, making them more amenable to softening once they are subjected to wide diurnal temperature fluctuations. The results indicate that soil tillage associated with cropping should build up a useful soil seed reserve of the harder seeded varieties.

The radiation and thermal characteristics of two grasslands in the arid zone of north west India

Micrometeorological observations were made during the winter, summer, monsoon and post-monsoon seasons in grassland at Bikaner (28° 3’ N, 73° 5’ E) and Chandan (26° 55’ N, 70° 55’ E). Profiles of air temperature, radiation penetration, net and total radiation and soil temperatures were recorded over a period of three years. The percentage of net to total radiation was found to be greatest during the growing season and minimal when the grass was dry. Radiation penetration into the mixed grassland at Bikaner was less than at Chandan where the grassland is dominated by a single grass species ( Lasiurus sindicus ). The thermal regimes at Chandan were greatly affected during the non-growing season by the intense radiation, high soil surface temperatures and the presence of only one species of grass. Considerable heat loss through long wave radiation is a common feature of these grasslands in dry weather when surface soil temperatures exceed 50 °C.

Control of the Black Vine Weevil on Concord Grapes in Central Washington1

Four granular insecticides were evaluated during 1962 in replicated plots for control of the black vine weevil, Brachyrhinus sulcatus (F.). Aldrin at 3.2, 3.9, 4.9, and 5.6 lb actual per acre, dieldrin at 3 lb, endrin at 2 lb, and Imidan® (phthalimidomethyl- O,O -dimethyl phosphorodithioate) at 2 lb were applied to the soil surface of a vineyard having 5 different cover-crop cultural practices. Applications were made in late May and early June before the adult weevils had emerged. Aldrin at the 4.9- and 5.6-lb rates was most effective. In another experiment where 5 lb actual aldrin granules was compared with a malathion (2.4 lb) plus aldrin (0.25 lb) dust mixture, the aldrin was most effective. In aldrin-treated vineyards mean cluster injuries were less than 1 per cluster and injured berries were less than 1% compared with mean cluster injuries as high as 25 per cluster and up to 54% injured berries in untreated vineyards or those treated with a malathion-aldrin dust mixture. Contact with aldrin granules disrupts the normal behavior pattern of adult weevils so that rather than hiding by day they are found wandering on the soil surface at mid-morning. Adult weevils were killed in the laboratory when subjected to a temperature of 90°F for several hours. Factors responsible for weevil mortality in the vineyard appear to be a combination of toxic effects of aldrin and high soil-surface temperature. Weevils taken early in the morning from a vineyard treated recently with aldrin were kept at room temperature with adequate food for 30 days, indicating that effects of aldrin alone were not lethal.

High Soil Surface Temperatures Recorded on a Moderately Warm Day

High Soil Surface Temperatures Recorded on a Moderately Warm Day

Soil Temperature Versus Drought as a Factor Determining Lower Altitudinal Limits of Trees in the Rocky Mountains

1. The differing abilities displayed by various Rocky Mountain coniferous trees to extend their ranges downslope into altitudes of increasingly hotter and drier climate has been attributed by some investigators to corresponding differences in the ability of their seedlings to tolerate heat, while others explain the same phenomenon on the basis of drought. In an effort to determine which of these is correct, greenhouse studies were made in which seedlings of trees with different altitudinal ranges have been compared in respect to their tolerance of high soil-surface temperatures and their tolerance of atmospheric and soil drought. 2. In general, it was found that the lower the altitudinal distribution of a species the greater the tolerance of its seedlings for high soil-surface temperatures. However, this factor apparently cannot explain the lower altitudinal limits, since (a) the maximum temperature level which each species can tolerate well exceeds the maximum temperatures obtaining in numerous micro-habitats below its altitudinal range; (b) a number of species, including subalpine fir, can be grown far below their natural lower limits without making compensation for the higher soil-surface temperatures there; and (c) the correlation between altitudinal distribution and temperature tolerance is not absolute, ponderosa pine having no greater temperature tolerance than Douglas fir, although it extends to distinctly lower altitudes. 3. When supplied with abundant soil moisture, even the subalpine trees can tolerate an intensity of atmospheric drought far in excess of that to which they are subjected under natural conditions. Furthermore, all species, regardless of altitudinal range, have approximately equal resistance to atmospheric drought. This aspect of drought therefore is apparently of no direct importance in determining the lower limits of the trees. 4. A distinct variation exists in the length of time over which the seedlings of different species can tolerate a lack of growth water; in general, the lower the altitudinal range the longer the period of soil drought which can be endured. Since all researches to date have indicated that the intensity and duration of drought increase downslope, this factor appears to offer at least a partial explanation of the differences in lower range limits. The significance of this difference among the species to endure soil drought is greatly magnified by the fact that the species of low altitude have the most rapid rates of root penetration. Not only are they better able to endure soil drought, but they are more likely to escape its influence. 5. The accuracy with which uniformity of environmental conditions can be maintained in different parts of the same culture varies in versely with the number of experimental plants used, and therefore conclusions based upon a few carefully tended plants are at least equally as valuable as greater numbers of plants but with conditions less uniform. In the temperature tolerance tests in which the fewest numbers of seedlings were used, the same conclusions may be drawn from either half of the lot of seedlings.