Soil Moisture Tension Research Articles

Application of Soil Water Flow Theory in Field Simulation

A numerical model based on a finite difference approximation of the basic differential equation for soil water flow is described. The equation includes a sink term representing moisture extraction by root systems, and allowance for evaporation from the soil surface is made too. Estimation of these terms is based on a potential transpiration calculated from Penman-Monteith's equation, on a potential evaporation calculated from Ritchie's equation and in both cases on relations to soil moisture status over various soil depths. The model simulations are compared with field observations of moisture content and soil moisture tension. Further, the model has been applied in evaluating how irrigation treatment effects the increases in evapotranspiration and deep percolation.

Leaf Rolling and Unrolling Behavior in Relation to Soil Moisture Tension and Climatic Factors

Leaf Rolling and Unrolling Behavior in Relation to Soil Moisture Tension and Climatic Factors

Water relations of cassava: water content, water, osmotic and turgor potential relationships

The water content, water potential, osmotic potential, and turgor pressure relationships of two cultivars of indoor-grown cassava (Manihot esculenta) were examined. The two cultivars (CMC9 and MCOL113) represent low and high starch yielding varieties, respectively.Leaf water potentials were measured insitu with a dew-point hygrometer. A pressure chamber was used to estimate ψL in excised leaves. Relative water content (RWC) of intact leaves was measured with a beta-gauge but was calculated from the pressure chamber data for excised leaves. Osmotic potentials at water contents between 0 and 100% were calculated and the corresponding turgor pressures were obtained by difference.At low soil moisture tension, RWC and ψL dropped to minimum values during the day but recovered considerably at night. Osmotic potentials of turgid leaves were −970 kPa in cv. CMC9 and −1000 kPa in cv. MCOL113. Diurnal variations ψπ were small in both cultivars. However, daily fluctuations in ψP were larger and paralleled changes in ψL. A marked hysteresis was evident in the water content-potential and the water content-turgor pressure data obtained during the drying cycle. However, when water potentials and turgor pressures were changed rapidly by switching the lights off and on at short-time intervals, no hysteresis was observed in the data.

Nitrogen Transformations in Sewage Sludge—Amended Soils as Affected by Soil Environmental Factors

AbstractThe objectives of this study were to determine the effects of soil pH, soil moisture tension, sludge application rate, incubation temperature, and nitrification inhibitor on N transformations in soils amended with an 15N‐labeled sewage sludge. Less than 0.1% of added sludge‐N was lost from any of the samples due to NH3 volatilization. Nitrification rates were faster in sludge‐amended soils as compared to nonamended acidic soils treated with NH4+‐N. Adding calcareous sewage sludge to acid soils produced a more favorable pH for nitrification. Nitrification was faster in sludge‐amended soil having an initial pH of 7.5 than in samples at pH 6.0 or 5.3. Nitrite‐N accumulated to levels of 100 µg/g in sludge‐treated soils with high pH values (∼ 7.5). Nitrification proceeded at a faster rate in sludge‐amended soils adjusted to −0.25 and −0.5 bar moisture tension than in soils at −1 bar. Nitrification rates were not greatly affected by sludge application rate, although more time was required for complete nitrification of greater quantities of NH4+‐N. Nitrapyrin inhibited nitrification for 112 days, after which nitrifying ability recovered. Temperature was the only factor evaluated which markedly affected mineralization of sludge‐organic N and immobilization of added inorganic‐N. The rates of both mineralization and immobilization increased as temperatures increased. At the end of 168 days of incubation at 21°C, 40% of added sludge‐organic N was mineralized in silt loam soils, but up to 26% of added NH4+‐N was immobilized. There were only small net changes in inorganic‐N concentrations in sludge‐amended soils after 168 days of incubation.

Establishment of Sod‐seeded Alfalfa at Various Levels of Soil Moisture and Grass Competition1

AbstractAlfalfa (Medicago sativa L.) establishment in competition with grass sods is not always successful, especially under conditions of soil moisture deficiency. Our objective was to evaluate the effect of soil moisture concentration and grass competition on alfalfa establishment and yield when it was interseeded into perennial grass sods.In a greenhouse experiment, alfalfa was seeded into Kentucky bluegrass (Poa pratensis L.) or smooth bromegrass (Bromus inermis Leyss.) sods which had been sprayed with 0, 0.6, and 2.2 kg/ha glyphosate [N‐(phosphonomethyl)glycine]. Three soil moisture regimes were established by watering to field capacity when soil moisture tensions reached 0.1, 1, and 12 bars. Grass‐shading treatments were also applied.At two field locations alfalfa was seeded into an unimproved Kentucky bluegrass, smooth bromegrass, and quackgrass (Agropyron repens L.) pasture and into a smooth bromegrass pasture. The soil at both locations was a Waukegan silt loam (Typic Hapludoll). Three levels of grass suppression were obtained by spraying with 0, 0.8, and 3.3 kg glyphosate/ha. Soil moisture regimes consisted of watering to field capacity when soil moisture tension reached 1 and 15 bars.Under shaded conditions in the greenhouse and with low grass suppression (no glyphosate) in the field, moisture did not significantly affect alfalfa establishment or dry matter yield. However, when shading was eliminated or grass suppression increased, low soil moisture tensions resulted in increased legume yields.In the greenhouse, alfalfa dry matter yields and root weights were generally greater when it was seeded into Kentucky bluegrass compared to smooth bromegrass. Smooth bromegrass was more tolerant of glyphosate application than Kentucky bluegrass. When seeded into smooth bromegrass, alfalfa yields from low and medium moisture level treatments were not significantly different, but when seeded into Kentucky bluegrass yields from high and medium moisture levels were significantly greater than for the low moisture treatment.Our results show that both adequate soil moisture and reduced grass competition for light are important for successful alfalfa sod‐seeding.

Relationship between Root Dostribution of Upland Crops and their Yield : III. Influence of soil moisture levels on root distribution and root dry matter of upland-cultured paddy rice, crossbred rice of paddy rice and upland rice, and upland rice

This experiment was conducted to clarify the effects of different soil moisture levels on the root distribution and root dry matter of upland-cultured paddy rice (cv. Myojoo, Kochihibiki), crossbred rice of paddy rice and upland rice (cv. Ishioka glutinous No.10, Mizuhatamochi), and upland rice (cv. Norin No. 12, Norin No. 21). In the first experiment (1977), the root distribution and dry matter was investigated on the six cultivars which were cultivated under irrigation and nonirrigation. The irrigation treatments were begun at July 18. The soil moisture tension of the two irrigation plots were at pF 2.5 and pF 2.0 at l0 cm depth, respectively. During July 24 to August 8, the soil moisture tension of nonirrigation plot was over pF 2.9 and in the range of pF 2.5 to 2.9, at 10 cm and 30 cm depths, respectively. Therefore, the soil moisture of nonirrigation plots reached to first permanent wilting point at l0 A.M., August 4. Top dry matter, root dry matter and root distribution were investigated at maturity. The investigation of the root distribution was practiced by excavating soil masses, which were sectioned by 7 cm increments up to 35 cm depth. The second experiment (1978) was set up in cylindrical plastic pots of 30 cm height and 25 cm inner diameter using four cultivars (Myojoo, Mizuhatamochi, Norin No. 12, Norin No. 21). Soil moisture treatments composed by two levels of high and low were begun at July 10. That is, high soil moisture plot was irrigated by each pots every day. While, low soil moisture plot was irrigated when every time the soil moisture became to first permanent wilting point. The treatments were continued for 58 days. The results showed that root distribution of the rice plants was effectively influenced by different soil moisture levels. The roots of rice plants distributed in the shallow layer under irrigation, while the roots distributed in the deeper layer under nonirrigation. Root distribution of upland-cultured paddy rice and crossbred rice of paddy rice and upland rice distributed in the shallow layer than that of upland rice. Also, root dry matter was influenced by different soil moisture levels. The root dry matter was increased in drier soil condition, where rice plants proliferated numerous branches to gather a small amount of soil water. The root dry matter of upland rice cultivar 'Norin No. 12' was increased conspicuously in surface layer under nonirrigation. It is suggested that high growth rate of root weights in water stressed rice plants was correlated with drought resistance, because high growth rate of root weight was obtained by upland rice which has drought tore-lance. R-T ratio was increased in drier treatments, because root dry matter was increased and top dry matter was decreased by water stress.

Nitrogen Mineralization in Florida Histosols

AbstractThe N‐mineralization rates of several Florida Histosols and the effects of soil moisture tension and organic C amendments on these rates were measured in the laboratory with an 15N‐tracer technique. An enhancement of microbial activity by crop residues was exhibited by greater N mineralization in cropped vs. uncropped soils. Nitrogen mineralization was not affected by soil moisture tension over the range of 0.1 to 3.0 bar. Exogenous C supplies such as glucose or St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntz] stimulated mineralization of native soil organic matter. Mineralization of soil organic N was increased by 91% in glucose amended soil samples. The N‐mineralization rate for a 75‐cm profile of Pahokee muck was estimated to be 686 kg N/ha for each centimeter of soil lost to microbial oxidation.

Frost heave in an instrumented soil column

Thermocouples, electrical resistivity gages and tensiometers were installed at various depths in a column of Fairbanks silt 100 cm long and about 14 cm in diameter. The water level was maintained at a depth of 45 cm below the surface and the volume of water taken up during the freezing process was monitored. Three freezing tests were conducted, two with a surcharge equivalent to about 35 cm of water pressure and one with a surcharge equivalent to about 350 cm of water. The upper 15 cm of soil was frozen at a rate of about 1 cm/day. The soil moisture tension increased (became more negative) throughout the length of the sample when the first ice was nucleated. All three samples exhibited a similar behavior. The amount of frost heave at the end of the tests was 6.0 and 2.1 cm for the two samples with the small surcharge and 3.2 cm for the sample with the higher surcharge. During freezing the two samples with the small surcharge took up 615 and 410 cm 3 of water while the sample with the larger surcharge took up 490 cm 3 of water.

Environmental Correlates of Emergence in Spadefoot Toads (Scaphiopus)

In arid habitats surface activity of spadefoot toads (Scaphiopus) is restricted to short periods following rains; the rest of the year is spent inactive underground. Therefore the perception of favorable conditions for emergence is critical to their survival. The environmental factors that may influence the emergence of Scaphiopus couchi and S. multiplicatus were studied. Low frequency sound (probably below 100 Hz) was the only primary emergence cue we identified for S. couchi. This stimulus alone was sufficient to elicit emergence from dormancy in deep burrows as well as from shallow summer burrows. These toads were extremely sensitive: less than 0.5 mm (0.02 in) of rain elicited 95% emergence from shallow summer burrows in roofed enclosures where no water reached the soil. Vibration from an electric motor consistently induced nearly 100% emergence from dormancy under very arid conditions-15% relative humidity, 30?C air and soil temperatures, and -15 atmospheres soil moisture tension. The only other factor that had a discernible effect on emergence was soil temperature below about 20?C, which inhibited the response to sound. Increasing soil temperature and wetting the soil to less than saturation failed to break dormancy in the absence of a sound stimulus.

Calculation of water balance in the crop root zone by computer

A computer programme was developed which computes the daily evapotranspiration as a residue from the water balance equation. Moisture profiles from field observations of soil moisture tensions are used as an input into the model. Further, the programme evaluates the effects of rainfall or irrigation during the periods of observation and also calculates the water loss from deep drainage. It takes care of the limitation in the availability of data due to occasional skipping of records for two or more days at a stretch. The additional features of this programme include the procedures for the computation of infiltration and the moisture flow. The model was applied to actual field data and the results are presented.

Kinetics of ammonia volatilization of anhydrous ammonia applied to a vertisol as influenced by Farm Yard manure, sorbed cations and cation exchange capacity

Abstract In laboratory experiments, effects of added Farm Yard Manure (FYM), sorbed cations and cation exchange capacity (CEC) on NH3 volatilization of anhydrous ammonia applied to a Vertisol were studied at 0.3 bar soil Moisture Tension and 25 ± 1°C. On addition of FYM or with increase in CEC the volatilization of retained ammonia was reduced while the effect of the sorbed cations was in the order : K‐Soil > Na‐Soil > Ca‐Soil > Mg‐Soil. The results suggest that the volatilization of retained NH3 followed First order reaction kinetics, with a rapid rate of volatilization in the initial 8 to 10 h followed by a retarded rate up to 144 h.

Fluctuations of the soil environment and fine root growth in a young Sitka spruce plantation

From soil cores extracted at 5 day intervals from 3 May to 6 August it was found that the biomass of fine roots in a Sitka spruce plantation, 14 years old, fluctuated with maxima in late May and mid July. The earlier peak coincides with increasing soil temperatures during a period of high incident precipitation and the latter developed when the soil profile was rewetted. Fine root biomass and soil moisture tension (SMT) were significantly and negatively correlated in three of four soil horizons. Root mortality occurred whenever incident precipitation failed to maintain soil moisture tension near zero. In the very open pored horizons the critical SMT for root death was unexpected small, <0.1 bars; in the peat horizons it wasc 0.2 bars.

Irrigation and Tillage Effects on Soybean Yield in a Coastal Plain Soil1

AbstractTillage‐induced pans in many Atlantic Coastal Plain soils restrict soybean (Glycine max L. Merr.) rooting. Consequently, one or more drought periods may reduce soybean yields. This study determined tillage and irrigation effects on soybean yields in one of these soils in a dry year.‘Ransom’ soybeans were planted on 19 May 1977 on Wagram loamy sand (Arenic Paleudult) which has a traffic induced pan at 25 cm. One half of each plot was conventionally tilled (moldboard plus three diskings); the other half was subsoiled to 45 cm and bedded. The date at which irrigation began was considered the whole plot and was replicated four times in a randomized block design. Irrigations were scheduled using tensiometers whenever the soil moisture tension in the 15 to 30‐cm depth reached 0.8 bars. A gradient with respect to the amount of water applied was established across each plot; no irrigation water reached the far side of the plots. Dates at which irrigation began were 23 June (early), 29 July (after flowering began), and 1 September (after pod set started). Once irrigation was initiated, each treatment was irrigated as needed throughout the growing season.Yields of conventionally tilled soybeans were 1,728, 2,063, 2,124, and 1,686 kg/ha for no irrigation and for full irrigation initiated on 23 June, 29 July, and 29 September, respectively. No significant yield increase or decrease was observed for the irrigated, subsoiled plots, regardless of the date irrigation began. Average yield of the subsoiled treatment was 37% higber than the 1,802 kg/ha overall average yield for conventionally tilled soybeans.The fact that the irrigated, conventionally tilled treatments did not achieve yields equal to those of the nonirrigated, subsoiled treatment suggest that some other benefit(s) accrue from the subsoil and bedding operation in addition to increasing water availability.

Dry soil mulching in tropical rice

Abstract Soil moisture was conserved through the dry season (January to April) by generation of a soil mulch after the end of the previous wet season. Soil moisture tension under the dry soil mulch did not exceed 0.3 bar at a 15-cm depth, whereas under a weedy falIow the tension rose to 5 bars. With a weed-free fallow the tension reached 3 bars at the same depth. Land preparation at the end of the previous wet season enabled crop establishment 3 weeks earlier than by preparation at the beginning of the following wet season. Up to 6 weeks of potential growing time was lost when the rice crop was transplanted. It was concluded that in regions with a distinct dry season a dry soil mulch would be a valuable cultural practice for securing an early establishment of the dry-seeded rice crop.

Establishment of Pine (Pinusspp.) Transplants in Perennial Grass Stands with Atrazine

Atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] applied as a preplant treatment at rates of 2.24 to 8.96 kg/ha was evaluated for the control of perennial grasses and the establishment of jeffrey (Pinus jeffreyiGrev. &amp; Balf.) and ponderosa (Pinus ponderosaLaws.) pine transplants. The most consistent and effective rates of atrazine (6.72 and 8.96 kg/ha) reduced grass herbage biomass an average of 72% over a 3-yr period and increased average final survival of transplants from 1% on the control to 66% with treatment. These rates also gave continued grass control for at least 3 to 4 yr after treatment. Stem diameter and top growth tended to be greater on the most effective treatments. High survival and increased growth of transplants on these treatments were attributed to low soil moisture tensions and increased NO3-N accumulation throughout the summer to depths of 30 cm during the year of planting and subsequent years.

Influences of Irrigation Practices on Spider Mite 1 Densities on Field Corn 2

Field corn plants grown with seasonal irrigations of 70 cb or less soil moisture tension, applied every furrow, supported fewer mites ( Oligonychus pratensis (Banks) and Tetranychus cinnabarinus (Boisduval)) and showed lower levels of plant stress than plants in plots kept dry (200 cb) at some time during the growing season. Mite densities remained low before tassel and began increasing rapidly prior to soft dough. Prolonged rain and thunder-storms at tassel caused reduced mite density. It was concluded that rain and/or instrument controlled irrigations of ≤ 50 cb can limit the growth and severity of spider mite populations on corn.

Rate of hydrolysis of urea as influenced by thiourea and pellet size

Two incubation experiments and a number of field experiments were conducted to determine the effect of soil moisture tension, pellet size and addition of thiourea to urea on the rate of urea hydrolysis. In the incubation experiments at 20°C, the rate of hydrolysis of urea increased from 15 bar to 1/3 bar soil moisture tension, with the largest change (doubling) occurring from 15 bar to 7 bar moisture tension. Increasing pellet size reduced the rate of urea hydrolysis by about 12% with urea pellets weighing 0.21 g as compared to 0.01 g urea pellets after 114h. When thiourea (a metabolic inhibitor) was pelleted with urea in a ratio of two parts urea and one part thiourea, the rate of hydrolysis was halved. In a field experiment, the addition of thiourea to urea and increasing pellet size suppressed the rate of urea hydrolysis considerably for 8 days. The amount of urea hydrolyzed with urea+thiourea (2∶1) pellets weighing 2.51 g was one-fourth of the amount of urea hydrolyzed with 0.01 g pellets of urea alone. In the other six field experiments which were set out in October, only 22% to 39% of urea +thiourea (2∶1) was hydrolyzed at two weeks after application, while almost all of the urea was hydrolyzed when it was mixed into the soil without an inhibitor. Unter our field conditions, we would estimate that the hydrolysis of urea can be inhibited for at least one week. The inhibition of urea hydrolysis appears to be great enough that the problems encountered from the rapid hydrolysis of urea, wherever these occur, may be reduced by combined use of thiourea and either increased pellet size or band placement.

Germination and Seedling Development of Canada Thistle (Cirsium arvense)

Optimum germination of Canada thistle [Cirsium arvense(L.) Scop.] occurred at alternating temperatures of 20 to 30 C and 30 to 40 C and at a constant temperature of 30 C. Osmotic pressures of 7 bars and greater reduced germination, but 2% of the seeds germinated at 15 bars. Canada thistle seeds (14%) were able to germinate in NaCl concentrations of 20,000 ppmw. Light was important in seed germination, however, its effect could be overcome by adding GA3(gibberellic acid) to the germination medium. Optimum pH for germination was between 5.8 and 7.0. Depth of planting influenced emergence; the highest percentage of seedlings emerged from depths of 0.5 to 1.5 cm. Canada thistle seedlings tolerated average soil moisture tensions of 1.3 bars and continued to grow. Canada thistle seedlings 19 days old and with two true leaves were able to resprout after top-growth removal. Regrowth was evident on 8% of the clipped plants 4 days after initial top-growth removal.

Studies on Tobacco Culture in the Subtropical Conditions : IV. Effects of wind on rooting and growth of tobacco in its early stage

In order to investigate the effects of wind on rooting and growth of tobacco in its early stage, potted seedlings of flue-cured tobacco (variety; Coker 319) were grown under the condition of the constant wind (3 m/s). The results were obtained as follows; 1. The soil of the wind plot lost moisture from its surface faster than that of control plot under ventilating air current only, especially near the surface of soil. The.soil temperature became lowered by the wind slightly in daytime, while scarcely in nighttime. 2. The rate of leaf emergence of tobacco was apparently depressed by the wind. Its stem length, leaf area and dry leaf weight were distinctly less than those of control tobacco (grown under ventilating air current only), and dry root weight of the wind-treated tobacco was slightly inferior to that of control tobacco. 3. Because of the poor growth of top caused by the wind, the smaller T/R ratio was resulted in the wind-treated tobacco as compared with that in control tobacco. The roots of the former grew longer and reached deepcr in soil than of the latter. 4. When the influence of soil moisture loss on the growth of tobacco in the wind plot was excluded by adjusting the soil moisture tension of the both plots at the same level ( l2 mmHg at 7-9 cm in depth), the growth of top of tobacco in the wind plot was still kept poor as mentioned above, even though it was only slightly improved by the treatment. It was concluded that the windy weather in Okinawa can possibly be the major cause of the poor rooting and growth of tobacco in its early stage in the field there which had been considered to be a typical tendency of tobacco growing in the district of Okinawa.

Water-Manometer Tensiometers Installed and Read from the Land Surface

Abstract Soil-moisture tension has been measured beneath an artificial-recharge basin in Suffolk County, Long Island, N.Y., with water-manometer tensiometers that can be installed and read from the land surface. The manometer-tensiometer unit is buried at the desired depth, and soil-moisture tension is measured from the land surface with a simple wire probe and electrical circuit that detect the level of water in the manometer. The water manometer is more sensitive than other common methods for determining unsaturated pressure head or soil-moisture tension over small ranges and is most helpful in situations where small changes in soil-moisture tension can reflect significant changes in hydraulic conductivity. Although the configuration may not be appropriate for installation at great depth (&amp;gt; 6 m) or in extremely coarse or fine soils, it provides rapid, reliable measurement of soil-moisture tension.