Soil Moisture Tension Research Articles

Yield and Seed Growth at Various Canopy Locations in a Determinate Soybean Cultivar1

AbstractThe purpose of this study was to investigate yield and seed growth in various parts of the canopy of a determinate soybean [Glycine max(L.) Merr.] cultivar. ‘Braxton’ soybeans were grown in a Cecil sandy loam soil (clayey, kaolinitic, thermic Typic Hapludults) with irrigation (I) applied when soil moisture tension exceeded 0.02 MPa and no irrigation (NI). Row width was 0.96 m, with intrarow spacings of 51, 102, and 152 mm in 1982 and 51 mm in 1983. Pods sampled during reproductive growth were separated into nine groups on the basis of pod location in one of three strata (based on canopy height) with a further separation into main stem pods or pods on lower, middle, or upper branches. Plot yields averaged 3068 and 1400 kg ha−1for the I and NI treatments, respectively. Intrarow spacing did not significantly influence yield. Yield in the upper canopy stratum increased from 33% of total crop yield in the NI treatment to 42% in the I treatment. With an increase in intrarow spacing from 51 to 152 mm, the relative yield contribution of main stems decreased from 31% of total yield to 15% while that of lower branches increased from 48 to 66%. Most pod groups did not differ in single seed weight, seeds per pod, or seed growth rate. These averaged 151 mg seed−1, 2.02, and 3.97 mg seed−1day−1, respectively. It was concluded that both irrigation and intrarow spacing influenced distribution of yield on branches and that yield increases in I soybeans were associated with increases in pod number and in percentage of total crop yield in the upper canopy.

Repeated Load Triaxial Testing of Frozen and Thawed Soils

Abstract This paper describes the equipment and methodology used to determine the resilient properties of granular soils that exhibit thaw-weakening behavior. Such soils suffer a significant loss in stiffness as the result of freezing and thawing and subsequently experience an increase in stiffness during a recovery phase. The recovery phase results from gradual desaturation of the thawed soil and is characterized by an increase in the soil moisture tension level. We have developed a means to simulate this freeze-thaw-recovery process in the laboratory that calls for testing specimens several times at soil moisture tension levels corresponding to field observations. We have designed test cells with removable bases to facilitate this sequential testing procedure. A given specimen remains on one cell base throughout the course of testing, thus avoiding excessive handling and allowing the material to remain in contact with a porous element built into the base. The porous element is part of a tensiometer system that continuously monitors the moisture tension level of the soil. The cells are equipped with axial and radial displacement transducers and a load transducer, which, along with the other cell components, are assembled about each mounted specimen to be tested. All transducers are interchangeable between our larger and smaller triaxial cells. The cells receive 152.4-mm-diameter, 381-mm-long specimens and 50.8-mm-diameter, 127-mm-long specimens, respectively.

Water Management of Greenhouse Tomatoes

Abstract Crack-susceptible and crack-resistant tomato (Lycopersicon esculentum L. Mill.) cultivars were grown in soil beds and in bags filled with a peat-vermiculite mix. Plants in soil were drip-irrigated 1 or 4 times daily, or hand-watered every day or as needed based on soil moisture tension. Plants in bags received only drip-irrigation treatments. Genotype had the greatest effect on fruit cracking, with 3.8% by weight cracked fruit in the crack-resistant compared to 35.3% in the crack-susceptible cultivar. Growing plants in bags reduced the weight and the percentage of cracked fruit per plant, but, in both cultivars, total and No. 1 fruit weights were greatest from the soil treatments with drip-irrigation. Irrigation frequency and method did not affect fruit weight except in the crack-resistant cultivar grown in bags where increasing irrigation frequency increased weights. Cracking was decreased by 22% in tomatoes irrigated manually every day, compared to those irrigated only when needed. In the soil treatment, raising the irrigation frequency significantly decreased cracking in the susceptible, but not in the resistant cultivar. In the soilless treatment, frequent irrigation increased cracking in both cultivars.

Variation in Seedbed Moisture Correlated with Growth ofPinus taedaSeedlings

SYNOPSIS Seedlings of P. taeda were grown in a seedbed under the open-rooted system to obtain growth data to regress against variations in soil moisture tension. From July through October, frequent rains kept soil moisture levels high and made irrigation unnecesary. Variations of mean soil moisture tension within the seedbed ranged from 3 to 11 kPa. Seedling growth was measured by destructive sampling in October. Root collar diameter, total height, and dry weight of shoots all increased with increasing mean soil moisture tension. This study indicates that growth of P. taeda seedlings may be reduced when soil is kept in a saturated condition (mean soil moisture tension < 10 kPa for this study).

Recovery from drought-induced desiccation at the vegetative growth stage in direct-seeded rainfed rice

Abstract Prolonged soil moisture stress causes desiccation of leaf and other plant parts of most cultivated annual crops. The ability to recover from desiccation during vegetative growth is important to the productive capacity of rice. A study conducted in the 1981 and 1982 dry seasons showed that after 36 days of imposed drought, soil moisture tension (SMT) at 20-cm depth reached 10 bars in Maahas clay soil (Andaqueptic Haplaquolls). At that SMT, drought-susceptible rice lines were desiccated and drought-tolerant varieties averaged 50% dead leaves. Seven days after sprinkler-irrigation to relieve soil moisture stress, the desiccated rice lines did not show recovery but stand recovery in those with partial leaf drying was up to 100%. A significant relationship between drought tolerance, as indicated by degree of desiccation, and percentage recovery was observed. Results suggest that farmers in rainfed areas should grow drought-tolerant modern rice lines with good recovery ability. During dry spells, the visual degree of desiccation at the vegetative growth stage permits the farmer to estimate potential plant recovery upon relief of soil moisture stress.

Varietal comparison on the responses of photosynthetic rate and leaf water balance at different soil moisture tensions in rice.

Differences in the photosynthetic activity and related leaf water balance were studied in eight rice varieties subjected to various levels of soil moisture tensions, i.e, flooded condition, values of 10, 20, 40 cbar and values at which leaf rolling began (50-62 cbar depending on the variety). The materials consisted of two lowland (IR 8 and Bosque), three tropical upland (Moroberekan, IAC 1246 and Batatais), two Japanese upland (Sensho and Rikuto Norin 24) and one dwarf mutant (Daikoku 1) varieties, respectively. The parameters observed were the photosynthetic rate (P), transpiration rate (T), leaf water potential (LWP), leaf diffusive conductance (1/r1) and leaf water content (W). The P decreased with the decrease in soil moisture with a concomitant decrease of T, LWP, 1/r1 and W, suggesting that the leaf water balance directly affects the P. Based on the responses of these parameters to soil-water stress, the material varieties were differentiated into four types. The lowland varieties performed high P and good leaf-water balance under fiooded condition. But they were very sensitive to the changes of the soil moisture, showing remarkable decreases of these parameters under moderate and severe drought. The tropical upland varieties showed rather low P under flooded condition, but they kept relatively good performance of P and leaf-water balance under moderate and severe drought conditions. The Japanese upland varieties showed intermediate values between the formers under flooded and moderate levels of the soil moisture tension (10-20 cbar), but under severe drought they showed sharp decrease of the values of these parameters as the lowland varieties did. The dwarf mu.tant Daikoku 1 performed comparatively high values of these parameters at every level of the soil moisture tension. The characteristics of these four types were discussed in view of their adaptation and plant-types.

Effect of defoliation on the photosynthetic parameters and yield components under flooded and drought conditions in rice varieties.

Defoliation treatment (clipping half of every leaf blade) was applied to rice varieties under drought and flooded conditions to determine its effect on the photosynthetic parameters, water balance, yield components and drought response of the plants. In the first experiment, photosynthetic and related leaf water parameters were measured in three upland varieties, (Moroberekan, IAC 1246 and Sensho), two lowland varieties (Bosque and IR 8) and one dwarf mutant variety (Daikoku 1). Under flooded condition, the defoliation treatment increased the photosynthetic and transpiration rates with a concomitant increase of the leaf water content and leaf diffusive conductance. The effect particularly pronounced in the tall upland varieties. When the water supply was restricted, the defoliation retarded the loss of soil moisture and accordingly the varieties maintained a high photosynthetic rate for a longer period. However, when the soil moisture tension reached a value of 40 cbar, the photosynthetic rate and leaf diffusive conductance became similar in magnitude in both the defoliated and nondefoliated plants. The decrease of photosynthetic rate by water shortag'e was the smallest in the dwarf mutant and the largest in the lowland varieties. In the second experiment, the effect of defoliation on yield components was examined in the early upland varieties (Sensho and Rikuto Norin 24), one early lowland variety (Bosque) and one dwarf mutant variety (Daikoku 1). Under flooded condition, the defoliation treatment decreased the yield components except for the tiller number of the tall varieties, resulting in a decrease of grain weight per plant in every variety. However, under drought condition, defoliation alleviated the decrease of several yield components, resulting in a lower decrease of grain weight per plant except for the dwarf mutant. It was concluded that defoliation was effective in preventing drought damage in tall varieties with large leaves. It was postulated that the lowest decrease of the photosynthetic rate under drought condition in the dwarf mutant was associated with the presence of short and thicker leaves, and that such a short-leaved plant was able to avoid drought damage.

Moisture characteristics of irrigated Mallee soils in South Australia

The soil moisture characteristics of undisturbed samples of Mallee soils, taken from typical profiles of the Riverland district neat Berri in South Australia, were determined. Samples were grouped according to texture and bulk density and, for each group, the moisture storage between matric potentials was derived. Over the usual range of soil moisture tensions (-0 to 40kPa) these showed only small variation between soil groups since, while moisture storage at field capacity and at wilting point does vary with texture; 50 to 60 mm/m is available between field capacity (-7 kPa) and the re-irrigation point (-30 to 40kPa) in all soils.

Effect of soil moisture regimes on the yield and water use of lentil (Lens culinaris Medic)

The effect of soil moisture regimes on the grain and straw yield, consumptive water use (Cu) and its relation with evaporation from free water surface (Eo), water use efficiency and soil moisture extraction pattern of lentil was studied in a field experiment conducted at the Indian Agricultural Research Institute, New Delhi during the fall-spring season of the crop years 1979–1980 and 1980–1981. The grain and straw yield, consumptive water use rate, Cu/Eo ratio and water use efficiency increased with an increase in irrigation frequency. Consumptive water use rate increased as the crop season advanced and reached its peak value during flowering and grain filling stage. The Cu/Eo ratio attained its minimum values 35 and 105 days after sowing at branching and grain filling stages. Depletion of soil moisture was most from the top 0–30 cm soil layer followed by 30–60 cm soil layer and was least from 90–120 cm soil layer. The pattern of soil moisture depletion was also influenced by soil moisture regime. During the vegetative and flowering stage the percent contribution from the top 0–30 cm soil layer decreased and that from the lower soil layers (30–60, 60–90, and 90–120 cm) increased with an increase in the soil moisture tension, however, the actual amount of moisture depleted from all the soil layers was always higher under low soil moisture tension regime than under high soil moisture tension regime. During the grain development stage the soil moisture treatment had no significant effect on the relative contribution from different soil layers under low and high soil moisture tension as the crop was irrigated at the same time under both these treatments. However, with no irrigation, the percent contribution from top soil layer continued to decrease, and from lower soil layers continued to increase, as the crop advanced from flowering stage to grain development stage.

Effect of Soil Moisture Tension on Pod Retention and Seed Yield of Beans

Abstract Two bean cultivars and one breeding selection with different pod-retention characteristics were grown at mean soil moisture tension (MSMT) of 0.05 and 0.1 MPa in 2 separate plantings. In the 5 May planting, flower buds developed during the 1st 3½ weeks of flowering, were dated and counted, and those developing mature pods were identified. Sixty-five percent to 90% of all pods that reached full maturity were from floral buds that reached anthesis during the 1st 2 weeks of flowering. The percentage of pods reaching maturity varied among cultivars. About 40% of the floral buds that developed on the determinate bean selection were retained to full pod maturity. Only 20% to 25% of the floral buds developed on each of the indeterminate cultivars were retained to full pod maturity. An increase in the MSMT from 0.05 to 0.1 MPa in the 23 June planting reduced the number of pods and seeds/plant and total seed weight/plant by 20% to 40%, but the number of seeds/pod and weight/seed was not influenced by MSMT or by number of pods produced on either of the dry bean cultivars or the breeding selection.

Soil oxygen and moisture in relation to Russet Burbank potato yield and quality

On a Declo loam, rooting density, final yield and quality of potatoes (Solanum tuberosum cv. Russet Burbank) showed no significant differences among conventional planting, ripping along the row, or forced aeration 30 cm below the top of the row. There were significant relationships between oxygen diffusion rate (ODR) and soil moisture tension (matric potential) at the 30 and 40 cm depths, but these relationships were not significantly different among treatments. In a complementary experiment, sprinkler irrigations at negative soil water matric potentials of 30-40 (wet), 40-50 (intermediate) and 50-60 kPa (dry, i.e., 0.5-0.6 bar tension) produced no differences in total yield. However, the wet treatment gave significantly more knobby and undersized tubers < 113 g (4 oz.) and a lower percentage of U.S. #1 tubers than the intermediate and dry treatments. Premium sized tubers > 284 g (10 oz.) were significantly higher in the dry than in the wet treatment. Fertilizer N was applied periodically during the season and petiole NO?-N levels indicated adequate levels with no differences among treatments in either experiment. So much attention has been given to the effects of drought and high temperature stress on the quality of Idaho Russet Burbank potatoes, that some growers may now over-irrigate. Results of this research indicate that attention should also be directed to the effects of excess moisture on the size and quality of tubers.

WATER REQUIREMENTS OF IRRIGATED SOYBEANS IN SOUTHERN ALBERTA

Field experiments were conducted from 1979 to 1982 in southern Alberta to determine the seasonal water use of soybeans. Soil moisture was determined every 5–6 days throughout the growing season and irrigation water was applied when soil moisture tension in the top 30 cm reached −40 kPa, with an additional treatment of −60 kPa for 1980 and 1981. Seasonal water use in a year of normal growth (1980) varied from 426 to 482 mm for the drier and wetter treatments, respectively. The drier treatments in 1980 and 1981 resulted in more efficient use of water. Low early-season water use with peak use after full pod development (R4) was defined. Water use peaked in late July to early August with a requirement of 7 mm/day. Small changes in seed quality, tending towards higher protein and lower oil under wetter conditions, are corroborated in the literature. The possibility of integrating crop and cultivar selection with appropriate irrigation management to improve production efficiency in southern Alberta is discussed. The late-peak water requirement of soybeans combines well with the early-peak use of cereal crops to ensure efficient seasonal irrigation management.Key words: Glycine max (L.) Merr., évapotranspiration, seed protein, seed oil

Kinetics of the Microbial Degradation of 2,4‐D in Soil: Effects of Temperature and Moisture

AbstractThe effects of soil moisture tension and temperature on the kinetics of the degradation of (2,4‐dichlorophenoxy)acetic acid (2,4‐D) in an Ascalon sandy loam were studied under laboratory conditions to develop a simulation model. Degradation occurred by a slow, first‐order reaction (slow phase) which, under some conditions, was followed by a rapid, first‐order reaction (fast phase). The optimum temperature and moisture tension were 27°C and 0.1 bar, respectively. Degradation rates under optimum conditions were 0.230 and 2.234 µg g−1 soil for the slow and fast phases, respectively. At temperatures above the optimum, no fast phase was observed. The activation energy (EA) values increased from 22.96 to 45.46 kcal mole−1, with increasing soil moisture tension in the range from 0.1 to 1.0 bar. The rate of decomposition of 2,4‐D decreased with increasing soil moisture tension for temperatures between 20 and 35°C. This decrease was a result of the reduced activity of the 2,4‐D‐degrading microorganisms arising from decreased water availability and increased 2,4‐D solution concentration.

Effect of soil moisture tension and preplant treatments on early growth of hybrid Populus hardwood cuttings

A growth room study indicated that bud opening of hybrid Populus hardwood cuttings began sooner as soil moisture tensions decreased up to at least −0.05 bar (1 bar = 105 Pa). Subsequent shoot elongation also increased with decreasing soil moisture tension. Warming and soaking cuttings to the stage of imminent root emergence also accelerated early shoot growth. Effects of soil moisture tension and warming–soaking treatments on rooting were generally similar to the effects on shoot growth. The three clones tested were of diverse parentage, but all showed a strong positive response to the treatments. In establishing field plantations, cuttings should be warmed and soaked to near the point of root emergence and then planted in moist soil.

Effects of Irrigation Practices on Vine Growth, Yield, and Quality of Muskmelons1

Abstract Higher yields, larger fruit size, and earlier maturity were achieved in muskmelons (Cucumis melo L.) by irrigating when soil moisture tensions at the 25-cm depth reached 50 and 75 kPa compared with tensions of 25 kPa. More fruits were culled in the wet treatment due to decay while the drier treatments produced more fruits with growth cracks. Melons from the drier treatments were higher in soluble solids. Irrigation did not affect the other storage and shipping quality factors measured. A prethinning irrigation caused restricted root development, vine growth, fruit size, and yield.

Field Study of the Fate of Fall‐Applied 15N‐Labelled Fertilizers in Three Alberta Soils1

AbstractFall application of N fertilizers is often less effective than spring application in increasing yields of cereal crops in portions of the Prairie Provinces of Canada. This paper reports on five field experiments (and involving three soils) using 15N‐labelled fertilizers to determine the amounts of mineral N lost over the winter by denitrification, leaching, and immobilization. The labelled N fertilizers were applied at 112 kg N ha−1in October in 1974–1975 experiments and in December in 1975–1976 experiments. The plots were sampled to a depth of 120 or 150 cm in late May. In the two 1974–1975 experiments (Malmo sicl soil), KNO3 and urea were mixed into the 0 to 12 cm depth of soil, and (NH4)2SO4 was placed in a band. Recovery of the labelled fertilizer N found in the total soil N was lowest for KNO3 (60 %), next for urea (71 %), the highest for (NH4)2SO4 (84%). The addition of 50 mm of water to the soil, which reduced the soil moisture tension of the 0 to 15 cm depth to less than 33 KPa on fall freezing, decreased the recoveries of KNO3 and urea in the total soil N to 26 and 54%, respectively. There was no leaching below the 60 cm depth. For the three fertilizers, from a 10th to a third of applied N was immobilized. In the three 1975–1976 experiments, the three soil types were, Demay 1, Malmo sicl, and Falun 1. The fertilizers were placed in bands 5 cm deep into the frozen soil. There was little loss of the labelled N from the total soil N for (NH4)2SO4, but very large losses for KNO3. As in the experiments from 1974–1975, the experiments for 1975–1976 showed no 15N below 60 cm depth for KNO3, and below 30 cm depth for (NH4)2SO4. The percent of applied N which became immobilized range from 7 to 49%, with the highest value for (NH4)3SO4 on a Malmo sicl soil. In summary, substantial losses of late fall‐applied l5N‐labelled fertilizers occurred over the winter, with field experiments that were started in 2 different years. These losses from the soil averaged 67% for KNO3 (five experiments, range of 40 to 87%), 38% for urea (two experiments, range of 29 to 46%), and 10% for (NH4)2SO4 (five experiments, range of 1 to 18%). The overwinter loss of fall‐ or winterapplied N was not through leaching, but through denitrification which apparently took place in early spring. The amount of immobilization of the labelled fertilizers varied from experiment to experiment.

Effect of Salinity on Rhizobium Growth and Survival

This study examines the effect of salinity on the growth and survival of Rhizobium spp. in culture media and soil. Eleven isolates from saline and nonsaline environments were compared. The growth (mean doubling time) of all strains and species tested decreased when the electrical conductivity of the culture medium (yeast extract-mannitol) was raised from 1.2 mS cm to 6.7 mS cm (15% seawater equivalent) or to 13.1 mS cm (28% seawater equivalent). Three of eleven strains failed to grow at 13.1 mS cm. Although growth was affected by salinity, four strains selected from the growth rate study could survive in extremely high concentrations of salt. Two strains with growth rates sensitive to salt and two strains with growth rates relatively unaffected by salt were inoculated into solutions with electrical conductivities of up to 43.0 mS cm (92% seawater equivalent). Not only did all four strains survive the initial osmotic shock (at 5 h after inoculation), but it was not until 27 days after inoculation that the sensitive strains exhibited a significant reduction in viable numbers. The salt-tolerant strains survived for more than 65 days with no reduction in viable counts. The interaction between soil moisture tension and soil salinity in relation to Rhizobium survival in gamma-irradiated soil was also examined. Six treatment combinations were used, ranging from -0.1 bars and 0.2 mS cm to -15 bars and 12 mS cm. Sensitive strains declined from 10 to 10 organisms per g of soil after 84 days of incubation at -15 bars and 12 mS cm. Tolerant strains survived for the same period with no loss in viable numbers. The results of these experiments indicate that many strains of Rhizobium can grow and survive at salt concentrations which are inhibitory to most agricultural legumes. The emphasis of research concerning the effects of salinity on symbiotic nitrogen fixation should, therefore, be directed to aspects of the symbiosis other than the survival of the Rhizobium spp.

The effect of water potential on soil‐borne diseases of wheat seedlings

SUMMARYUnder glasshouse conditions, Fusarium culmorum caused more injury to wheat seedlings in soil at 33% saturation (approximately – 1 bar) than at 66% (–0·1 bar). The same effect occurred with inoculated seeds raised on soil moisture tension tables at –0·1 and –0·5 bar, at 20° and at 15°C. In controls, spontaneous infection by soil‐borne F. culmorum was unaffected by soil water potential. Inoculated F. nivale, at 127deg; and at 15°C, showed a similar, but smaller, effect to that with inoculated F. culmorum. Water potential in this range did not affect disease incidence with inoculated Gaeumannomyces graminis, but disease was more severe in the drier soil. On tension tables, seedlings did not consistently develop faster under wetter conditions, and factors other than host growth rate probably played a part in limiting fungal attack.

An evaluation of carbon disulphide as a sulphur fertilizer and as a nitrification inhibitor

There was little release of extractable SO4-S during four weeks from CS2 applied by injecting into two S-deficient soils. In this incubation experiment, the rate of CS2 was 30 μg S g−, placement was injection at 9 cm depth, soil temperature was 20°C, and soil moisture tension was 33 kPa. The yield of barley forage after seven weeks in the greenhouse showed only small increases from 10 or 30 μg S g−1 of CS2 as compared to Na2SO4, on the two soils.

Trafficability Factor in a Silty Clay Loam Soil

ABSTRACT SUBSURFACE drainage systems affect spring and fall trafficability, the timeliness of planting and subse-quent crop harvest and yield on a silty clay loam marine soil. Drainage effectiveness and trafficability response were evaluated by mercury tensiometers for soil moisture, a cone penetrometer for soil strength and by a subjective walk-on trafficability index (TI). Soil moisture and penetrometer resistance measurements were taken over the shallow drains spaced at 3, 6 and 12 m, at the mid-point between drains and at two comparable random locations in undrained plots. Trafficability was found to develop more rapidly in the spring on a slowly permeable representative silty clay loam soil with drainage than on undrained plots. However, we did not observe any clear differences be-tween any of the three drain spacing treatments. A good correlation existed between soil moisture tension and soil strength in the 0-15 cm soil depth which could be match-ed to soil readiness and thus to workday or trafficable conditions. Corn yields vs. drainage for 1980, a year characterized by a dry spring, showed no significant difference between drainage and no drainage. Alfalfa in 1981, when drained plots were ready for cultivation 3 wk earlier than un-drained plots, gave yields significantly greater for the drained over no drainage from two cuttings. There was no difference between drained treatments.