Levels Of Soil Water Potential Research Articles

Arbuscular mycorrhizal fungi inoculation and phosphorus application improve growth, physiological traits, and grain yield of rice under alternate wetting and drying irrigation

Climate change and agricultural malpractices are exacerbating drought in many parts of the world causing a substantial agricultural production loss. The improvement of drought tolerance in rice is crucial for maintaining productivity and ensuring global food security. Alternate wetting and drying (AWD) irrigation along with plant-microbe interaction through arbuscular mycorrhizal fungi (AMF) is a potential approach for enhancing rice production through AMF-induced up-regulation of tolerance and resilience against drought stress. Therefore, the ameliorative role of AMF inoculation and phosphorus (P) application on growth, physiological traits, and grain yield of rice was evaluated under water stress imposed through AWD irrigation. A factorial experiment consisting of four fertilizer treatments where the P percentage varied along with the recommended dose of nitrogen (N) with or without AMF inoculation (P100 as the control, P100 + AMF, P75 + AMF, and P50 + AMF), three soil water potential levels (0, −15, and −30 kPa), and two cultivation methods (wet direct seeding and transplanting) was conducted in a polyhouse. The subscript values of 100, 75, and 50 under P represent 100%, 75%, and 50% of the recommended field application dose. Data were collected on selected growth parameters, physiological traits, levels of mycorrhizal colonization, yield and its components, and water productivity of rice. The results revealed that P100 + AMF inoculated plants had 11%, 14%, 74%, and 54% higher leaf greenness, leaf relative water content, net photosynthetic rate, and grain yield, respectively, for wet direct-seeded plants at reduced soil water potential (−30 kPa) compared with non-inoculated plants (P100). Free proline accumulation gradually enhanced with decreasing soil water potential, and it was maximized by 77% at −30 kPa compared with 0 kPa for P50 + AMF (for transplanted plants). Free proline accumulation was also higher with decreasing soil water potential in AMF-inoculated plants than non-inoculated plants regardless of cultivation methods. Leaf osmotic potential was reduced by −0.5 to −1.2 MPa at −30 kPa compared with 0 kPa under different fertilizer doses. However, AMF inoculation (P100 + AMF and P75 + AMF) improved leaf osmotic potential of plants under severe water stress (−30 kPa) maintained through AWD irrigation resulting in better osmotic adjustment than non-inoculated plants. AMF inoculation improved the response of most of the evaluated physiological traits of rice and enhanced grain yield with higher P availability (even with a 25% reduction in its recommended dose) in the rhizosphere under drought stress. Thus, it can be concluded that AMF inoculation coupled with judicious P management is a promising approach for improving physiological and biochemical traits, grain yield, and water productivity of rice under AWD irrigation regardless of cultivation methods.

Mitigating the accumulation of arsenic and cadmium in rice grain: A quantitative review of the role of water management

Arsenic exposure through rice consumption is a growing concern. Compared to Continuous Flooding (CF), irrigation practices that dry the soil at least once during the growing season [referred to here as Alternate Wetting and Drying (AWD)] can decrease As accumulation in grain; however, this can simultaneously increase grain Cd to potentially unsafe levels. We modelled grain As and Cd from field studies comparing AWD and CF to identify optimal AWD practices to minimize the accumulation of As and Cd in grain. The severity of soil drying during AWD drying event(s), quantified as soil water potential (SWP), was the main factor leading to a reduction in grain total As and inorganic As, compared to CF. However, lower SWP levels were necessary to decrease grain inorganic As, compared to total As. Therefore, if the goal is to decrease grain inorganic As, the soil needs to be dried further than it would for decreasing total As alone. The main factor driving grain Cd accumulation was when AWD was practiced during the season. Higher grain Cd levels were observed when AWD occurred during the early reproductive stage. Further, higher Cd levels were observed when AWD spanned multiple rice growth stages, compared to one stage. If Cd levels are concerning, the minimum trade-off between total As and Cd accumulation in rice grain occurred when AWD was implemented at a SWP of −47 kPa during one stage other than the early reproductive. While these results are not meant to be comprehensive of all the interactions affecting the As and Cd dynamics in rice systems, they can be used as a first guide for implementing AWD practices with the goal of minimizing the accumulation of As and Cd in rice grain.

Growth, yield and water productivity of rice as influenced by seed priming under alternate wetting and drying irrigation

ABSTRACT Seed priming is a vital seed enhancement tool used for mitigating various biotic and abiotic stresses, improving seedling growth and enhancing crop productivity. Alternate wetting and drying (AWD), a water-saving technique, reduces irrigation water input in rice production without compromising yield. A factorial experiment consisting of seven priming treatments (non-primed control, hydropriming, Trichoderma, silicon dioxide, salicylic acid, potassium nitrate, abscisic acid) and three soil water potential levels maintained through AWD irrigation (0, –15, –30 kPa) was conducted to explore potential benefits of seed priming in mitigating water-deficit stress. Grain yield was not significantly different between 0 and –15 kPa regardless of priming treatments. However, it was reduced at –30 kPa under all treatments, except for Trichoderma. Seed priming with Trichoderma resulted in 52%, 68% and 77% higher grain yield and 52%, 70% and 66% higher water productivity at 0, –15 and –30 kPa, respectively, than the control. Rice can be safely grown with AWD irrigation level up to –15 kPa. However, seed priming with Trichoderma is recommended where frequent irrigation is difficult to practice and soil water potential drops below –15 kPa. Seed priming with potassium nitrate is also a promising option when soil water potential drops below –15 kPa.

A Dynamic Model for Strategies and Dynamics of Plant Water-Potential Regulation Under Drought Conditions.

Vegetation responds to drought through a complex interplay of plant hydraulic mechanisms, posing challenges for model development and parameterization. We present a mathematical model that describes the dynamics of leaf water-potential over time while considering different strategies by which plant species regulate their water-potentials. The model has two parameters: the parameter λ describing the adjustment of the leaf water potential to changes in soil water potential, and the parameter Δψww describing the typical ‘well-watered’ leaf water potentials at non-stressed (near-zero) levels of soil water potential. Our model was tested and calibrated on 110 time-series datasets containing the leaf- and soil water potentials of 66 species under drought and non-drought conditions. Our model successfully reproduces the measured leaf water potentials over time based on three different regulation strategies under drought. We found that three parameter sets derived from the measurement data reproduced the dynamics of 53% of an drought dataset, and 52% of a control dataset [root mean square error (RMSE) < 0.5 MPa)]. We conclude that, instead of quantifying water-potential-regulation of different plant species by complex modeling approaches, a small set of parameters may be sufficient to describe the water potential regulation behavior for large-scale modeling. Thus, our approach paves the way for a parsimonious representation of the full spectrum of plant hydraulic responses to drought in dynamic vegetation models.

Effects of drought and rewatering on growth and transpiration in European beech seedlings late in the growing season

Drought stress is one of the most important environmental factors affecting plant growth and survival. To date, most studies aim at understanding of post-stress physiological and anatomical adaptation to drought stress; however only few studies focus on plant recovery. In the present study, transpiration, shoot water potential, and anatomical and morphological measurements were performed on 4-year-old European beech seedlings with fully developed leaves. The seedlings were exposed to three levels of soil water potential (well-watered, moderate drought stress and severe drought stress) and followed by rewatering under greenhouse conditions. Reduced transpiration rates were observed in the stressed seedlings as a response to drought stress, whereas anatomical and morphological variables remained unchanged. Three days after rewatering, transpiration rates in both moderately and severely stressed seedlings recovered to the levels of those of well-watered seedlings. Drought stress promoted leaf budding, resulting in higher shoot dry mass of stressed seedlings. Our findings indicate that anatomical and morphological adaptations of European beech seedlings to drought stress are visibly limited during late-season growth stages. These results will help us to further understand factors involved in drought adaptation potential of European beech seedlings faced with expected climate-related environmental changes. To complete our findings, further experiments on plant recovery from drought stress should be focused on different periods of growing season.

Extruded seed pellets: a novel approach for enhancing sagebrush seedling emergence

Small or low-vigor species can be susceptible to being planted at depths that prevent seedling emergence. As an example, sagebrush ( Artemisia spp. L. [Anthemideae]) seed is often prone to being planted at depths where the seedlings cannot emerge from the soil. We evaluated a potential solution to this problem that incorporates seed within an extruded pellet that is designed to enhance seedling emergence through the swelling action of the pellet creating conduits for the emerging seedlings to follow. We quantified the swelling capacity of the extruded pellet and evaluated how the technology improves seedling emergence and plant growth of Wyoming big sagebrush ( Artemisia tridentate Nutt. ssp. wyomingensis Beetle & Young), over a range of seeding depths (5, 10, and 15 mm [0.2, 0.4, and 0.6 in]), within silt-loam and sandy-loam soils. Swelling capacity of the pellets in the silt-loam soil was approximately twice that of the sandy-loam soil. At all planting depths, pellets improved seedling emergence between 2.3- to 10.0-fold in the silt-loam soil. In the sandy-loam soil, no treatment effect occurred for seedling emergence at the 5 mm and 15 mm depths, but pellets enhanced emergence at the 10 mm depth by 3.1-fold. Some indications suggest that seedlings produced from the extruded pellets had greater growth than untreated seed. This technology opens up the possibility for sagebrush (and potentially other smallseeded species) to be seeded at deeper soil depths where soil water potential levels are more conducive for seed germination and seedling survival. Future development and field testing are merited.

Greenhouse gas emission from direct seeded paddy fields under different soil water potentials in Eastern India

In the anticipated water scarcity and global warming scenario; it is imperative to identify suitable irrigation scheduling strategy in paddy fields for increasing water productivity and mitigating greenhouse gas (GHG) emissions. We conducted a two year (dry season of 2014 and 2015) field experiment for irrigation scheduling based on tensiometric measurement of soil water potential (SWP) in order to quantify temporal and seasonal variations in GHGs emissions and their trade off relationship at five levels of SWPs viz. SWP 1 (−20kPa), SWP 2 (−30kPa), SWP 3 (−40kPa), SWP 4 (−50kPa) and SWP 5 (−60kPa), in addition to the traditional practice of growing flooded rice (CF). Fluxes of methane (CH4) and nitrous oxide (N2O) during the growing period were measured using manual closed chamber-gas chromatograph and the carbon dioxide (CO2) flux was measured using an infrared CO2 analyzer. A significant decrease in seasonal cumulative CH4 emission (30–60.2%) was recorded at different SWPs as compared to CF. In contrast, emission of CO2 and N2O increased by 12.9–26.6% and 16.3–22.1% respectively at SWPs 1 and 2; conversely, a significant decrease in emissions of these gases were observed at higher SWPs (SWPs 3–5). Among different SWP treatments, irrigation scheduling at SWP 2 maintained yield at par with CF with water saving of 32.9–41.1% and reduced CH4 emission (43–44.1%). However, due to increase in CO2 and N2O emission at SWP 2, there was no significant reduction in global warming potential (GWP) as compared with CF. Among different rice growth stages GHGs emission were predominant during vegetative growth stage. Regression relationship of GHGs emission with key soil parameters was employed to predict seasonal emissions of GHGs from paddy field. The results of this study suggest that scheduling irrigation at SWP 2 can be an effective strategy in order to save water, maintain rice yield and mitigate CH4 emission from direct seeded paddy fields in eastern India, however further research is needed to identify suitable management strategy for reducing CO2 and N2O emissions at SWP 2 in order to reduce the GWP.

The potential for primed acclimation in papaya (Carica papaya L.): Determination of critical water deficit thresholds and physiological response variables

Priming is a strategy that potentiates a plant’s response to stress. Primed acclimation (PA) in crop irrigation scheduling is the use of a temporary period of regulated deficit irrigation (RDI), imposing mild or moderate deficits, to evoke a primed state, after which full evapotranspiration replacement is resumed. Although little has been reported regarding physiological impacts of PA, the technique has been used to maintain or improve yields in agronomic crops in drought-prone regions. The first objective of this study was to test a plant-based approach to determine the appropriate level of soil water potential needed to evoke a primed response in papaya plants. This was done through a substrate (potting medium) dry-down experiment with one group of plants irrigated to field capacity and a second group of plants for which the soil was allowed to dry gradually. Physiological responses were assessed to determine at what point a mild to moderate level of stress was reached. The second objective was to test the effects of a priming stress (the level set in the first objective) on leaf gas exchange (net photosynthesis [A], stomatal conductance [gs], transpiration [E]) and chlorophyll fluorescence in papaya as compared to a control treatment in which soil water content was maintained at field capacity. The most sensitive variable in the dry-down experiment was gs, which was used to select a soil water potential target of −30kPa for subsequent priming treatments. Priming treatments using this predetermined target resulted in increased A and leaf chlorophyll index (SPAD) during the period when irrigation to field capacity was restored. According to OJIP analysis, primed plants had increased fluorescence performance indices, reduced antennae size per Photosystem II reaction center, and increased fluxes and efficiencies from plastoquinone A through Photosystem I. Thus, increased A as a result of priming had both stomatal and photochemical components. However, increased A due to priming of papaya appeared to be temporary. These results show that papaya has the capacity to reach a primed state and provide the soil water potential levels that could be utilized to achieve the appropriate level of water deficit for priming. This vital information can be used in the development of management techniques to capitalize on papaya’s priming ability under commercial irrigation management schemes.

梨枣在果实生长期对土壤水势的响应

Pear jujube(Ziziphus jujuba Mill.grafted on wild jujube) is widely cultivated in the Loess Plateau region of China.However,pear jujube culture has been constrained by the wasteful use of limited water supplies that characterizes traditional irrigation,which has restricted the development of local agriculture.Thus,there is a need to develop new irrigation scheduling techniques that optimize water use.This paper aimed to determine a suitable soil water potential measure based on pear jujube tree responses to different soil water potentials during the fruit development period in the Loess Plateau.Fruit development is divided into two periods,i.e.,the slow-growing fruit stage,where the main fruit process is cell differentiation,and the fast-growing fruit stage,when the cells expand.Four soil water potential levels were tested with four-year-old pear jujube trees.It was found that the maximum daily trunk diameter increased slowly during the slow-growing fruit stage while high soil water potential decreased the proportion of fruit abscission.The fruit abscission rate decreased significantly when the soil water potential was higher than-84 kPa.The maximum daily trunk diameter and relative leaf water content indicated the pear jujube water content during the fast-growing fruit stage.Thus,higher soil water potential resulted in a greater maximum daily trunk diameter and increased relative leaf water content.Furthermore,the percentage of fruit abscission was negative,i.e.,fruit set number exceeded fruit abscission,when the soil water potential varied in the range of-41 kPa to-51 kPa during the fast-growing fruit stage.Fruit setting occurred in treatments where the soil water potential was higher than-84 kPa,whereas trees did not set fruit after receiving full irrigation that produced a soil water potential of-461 kPa in early experiments.However,fruit that set during the fast-growing fruit stage were always small because they had less time to grow.Thus,the single fruit weight with a full irrigation treatment was lower than other treatments.The soil water potential was similar to the control treatment after drought stress(-461 kPa),but leaf photosynthetic function and chlorophyll content were affected,i.e.,the leaf photosynthetic function was decreased and the chlorophyll content was the lowest among all treatments.The low chlorophyll content decreased the leaf photosynthetic function.We found that mild controlling the soil water content could increase the single fruit weight with no effect on production.This study showed that a suitable soil water potential during the fruit development period was-41 kPa to-84 kPa,because this treatment increased the leaf water use efficiency and the single fruit weight,which compensated for the lower number of fruit.

Effects of water deficit in two phenological stages on production of japanese cucumber cultived in greenhouse

The experiment was performed in the experimental area of the Engineering Department Federal University of Lavras, Minas Gerais State, Brazil. It aimed at identifying the adequate irrigation management of the greenhouse-cultivated Japanese cucumber (Cucumis sativus L.). complete randomized design, with four levels of soil water potential (15; 30; 60 e 120 kPa) at two phenological phases (vegetative and reproductive), and 5 replications. Overall, the results showed decrease of yield according to increase of soil water potentials. During the reproductive stage, Japanese cucumber plants were more sensitive to water deficit, resulting in further decrease in yield compared to applied water deficit during the vegetative stage of the culture.

Influence of egg aggregation and soil moisture on incubation of flexible-shelled lacertid lizard eggs

Many oviparous terrestrial species deposit flexible-shelled eggs into the soil. These eggs are sensitive to the hydration level of the nest environment. Among other factors, water exchange of eggs during incubation may be affected by the soil water potential. To evaluate whether egg aggregation influences embryonic development, we incubated flexible-shelled Schreiber's green lizard (Lacerta schreiberi) eggs under three levels of soil water potential (wet: –150 kPa; intermediate: –650 kPa; dry: –1150 kPa) and under two levels of aggregation (aggregated: in groups of six eggs with physical contact among them; isolated: groups of six eggs each 1 cm apart). The availability of water during egg incubation influenced egg mass and hatchling size. Eggs incubated in dry soils absorbed less water and produced smaller hatchlings. The selected levels of soil water potential did not influence incubation duration or hatching success. When soil was wet or dry, we did not find any effect of egg aggregation in embryonic development. However, when soil water potential was intermediate, aggregated eggs absorbed less water and their embryos hatched at smaller sizes compared with isolated eggs. Moreover, variability and range of egg water absorption and hatchling size were higher among aggregated eggs than among solitary ones when access to water was restricted. In these cases, eggs competed with different success for water, a limited resource in the nest environment.

Postanthesis Water Deficits Enhance Grain Filling in Two‐Line Hybrid Rice

Two‐line hybrid rice (Oryza sativa L.) is a hybrid from a thermosensitive genetic male sterile line and its corresponding restoring line. This hybrid rice shows strong heterosis but a slow grain‐filling rate, as a result of unfavorably delayed senescence. This study investigated the possibility that a moderate water deficit imposed during grain filling may enhance plant senescence, and therefore facilitate the remobilization of reserve C to the grains and improve grain filling. Two two‐line indica hybrids were grown in both the pot and field. Three levels of soil water potential, well watered (WW), moderate water deficit (MD), and severe water deficit (SD), were imposed from 9 d after anthesis to maturity in both pot and field experiments. Results showed that Chlorophyll content and photosynthetic rate of the flag leaves declined more quickly as plants approached maturity for MD and SD plants than for WW plants, indicating the water deficits enhanced senescence. The remobilized C reserve and reallocation of pre‐fixed 14C from stems to grains increased by 1.5‐ to 2‐fold and 55 to 67%, respectively, for water deficit plants, when compared with WW plants. The water deficit treatments shortened the grain‐filling by 5 to 17 d and increased the grain‐filling rate by 0.09 to 0.27 mg d−1 grain−1 The grain yield of MD plants in both experiments was increased by 8.2 to 10% but that of SD plants in the pot was reduced. We conclude that if water deficit is properly controlled during the grain filling, whole‐plant senescence is enhanced. The enhanced senescence can facilitate remobilization of C reserves, accelerate grain filling, and increase grain yield in the two‐line hybrid rice.

Carbon Remobilization and Grain Filling in Japonica/Indica Hybrid Rice Subjected to Postanthesis Water Deficits

Poor grain filling, as in unfilled grains, and unused carbohydrate in straws are two major problems in japonica/indica (J/I) hybrid rice (Oryza sativa L.). This study investigated if an early senescence, induced by controlled postanthesis soil drying, could enhance the remobilization of reserved C to the grains, and therefore improve the grain filling. Two J/I hybrids and one indica/indica (I/I) hybrid were field‐grown. Three levels of soil water potential (ψsoil)—well watered (ψsoil = 0), moderate water deficit (ψsoil = −0.025 MPa), and severe water deficit (ψsoil = −0.05 MPa)—were imposed 9 d after anthesis to maturity. As a result of water deficit treatment, chlorophyll concentrations and photosynthetic rates of flag leaves declined more quickly, indicating an enhanced senescence. The remobilized C reserve from the culm and sheath during grain filling was increased by 47 to 61% for the J/I hybrids and 12 to 26% for the I/I hybrid. Partitioning of 14C from the flag leaves to the grains was increased by 18 to 28%. Active grain‐filling period was shortened by 2.7 to 8.7 d, and grain‐filling rate increased by 0.14 to 0.36 mg d−1 grain−1. Water deficits reduced the grain yield of the I/I hybrid by 2.9 to 16.4% but increased that of the two J/I hybrids by 4.4 to 13.3%. We conclude that if water deficit is properly controlled for J/I, the gain from enhanced remobilization of stored C may outweigh the loss due to shortened photosynthetic duration, leading to a fast grain filling and high grain yield in cases where senescence is unfavorably delayed.

Water deficit stress effects on N2 fixation in cowpea inoculated with different Bradyrhizobium strains

The objectives of this experiment were to select strains of Bradyrhizobium sp. resistant to water stress, envisaging an increase in N2 fixation in cowpea (Vigna unguiculata [L.] Walp.), and to verify the plant's adaptive physiological responses to water stress. The experiment was carried out in greenhouse conditions using random complete blocks subdivided into plots adjusted to soil water potential levels of −6.0, −75.0, and −85.0 kPa, and subplots containing strains of Bradyrhizobium sp. (SEMIA 6145, 6086, 6002 and NFB 700), with four blocks. The soil was a Yellow Latosol with pH 6.3. The crop used was cowpea cv. IPA 204. Stress was applied continuously beginning 15 d after planting, by the control of water potential through a porous cup. Various parameters were evaluated every 7 days, until final harvest at 45 d. There was significant interaction between Bradyrhizobium strains and water stress. At the more negative ψm, plants inoculated with the SEMIA 6145 had higher LHb concentration, ureide-N, ψw and root dry matter, forming associations of greater symbiotic efficiency, while plants inoculated with SEMIA 6086 were not resistant to stress. LHb concentration apparently was not inhibited at ψw −1.0 MPa in cowpea. The Bradyrhizobium strains may have affected the metabolism of N assimilation and/or transport. Key words: Bradyrhizobium, N2 fixation, porous cup, Vigna unguiculata, water stress, Yellow Latosol

The effect of water stress on the yielding capacity of potato crops and subsequent performance of seed tubers

The effect of water stress on yielding capacity of potatoes was studied in 3 years using four different levels of soil water potential (0.7, 1.9, 3.4 and 7.8 atm.) in experiments in specially adapted structures that excluded uncontrolled water supply. Seed tubers from these crops were planted in the following years to investigate effects of water stress on their subsequent performance.

Water use and soil moisture depletion by olive trees under different irrigation conditions

12 year old cv Kalamon olive trees irrigated at soil water potential ranges of −0.02 to −0.06 MPa (ψP0.2) and −1 to − 1.5 MPa (ψ15) were compared with non-irrigated (NON-IRR) trees. Irrigation water was applied by two drip laterals per row (DR2) or a microtube-fed basin at each tree (BAS) for ψ0.2 and one drip lateral per row (DR1) or a microtube-fed basin at each tree for ψ15. Soil moisture depletion in the non-wetted areas of the irrigated treatments was greater than that of the wetted ones, but about the same as the non-irrigated treatment. Soil moisture depletion in the non wetted areas of the irrigated and non irrigated treatments occurred mainly during May–June. Soil moisture reached wilting percentage at the end of September in the non-wetted areas of the ψ0.2, at the end of August in the non-wetted areas of ψ15 and at the end of July in the non-irrigated treatment. Total soil moisture reserve depletion was generally greater in the upper soil layers of the wetted and non-wetted areas. The amount of irrigation water used was higher at the ψ0.2 than at the ψ15 treatment, but it was not noticeably different between the drip and basin irrigation methods within the same soil water potential levels. Evapotranspiration of irrigated trees during May–September period was met mainly from irrigation water (75–90%), less from the reserves of the soil moisture (10–20%) and lesser still from the rainfall of the respective period (2.5–5%). Crop coefficient, expressed as an evapotranspiration to class “A” pan evaporation ratio, increased from 0.4 to 0.65 for the ψ0.2, maintained at about 0.3 to 0.4 for the ψ15 and decreased from 0.2 to 0.05 for the non irrigated treatment. Crop coefficients were not markedly different between drip and basin methods within the same soil water potential levels.

Growth promotion of rotation crop species by a sterile fungus from wheat and effect of soil temperature and water potential on its suppression of take-all

Two temperatures (15 and 20 °C) and two levels of soil water potential (−0·0015 MPa and −0·001 MPa) were used to test the ability of a sterile red fungus (SRF) to protect wheat ( Triticium aestivum cv. Gamenya) and rye-grass ( Lolium rigidum cv. Wimmera) from infection by the take-all fungus ( Gaeumannomyces graminis var. tritici (Ggt)). The SRF protected wheat and rye-grass plants from infection by Ggt at both levels of soil moisture and temperature. The SRF promoted the growth of wheat and rye-grass in both the SRF alone and SRF + Ggt treatments at −0·0015 MPa and −0·001 MPa, and 15 and 20°. Shoot and root weights were greatest at −0·001 MPa and 15° for wheat, and −0·001 MPa and 20° for rye-grass, in all treatments. At both temperatures the percentage of dead plants of wheat or rye-grass was greater at −0·0015 MPa than at −0·001 MPa in the Ggt-alone treatment. The reduction of shoot and root weights of wheat and rye-grass by the take-all fungus was most severe at −0·0015 MPa and 20°. The SRF promoted the growth of the barley ( Hordeum vulgare cv. Stirling), great brome ( Bromus diandrus ), chick pea ( Cicer arientinum cv. Opal), lupins ( Lupinus angustifolius cv. Yandee), medic ( Medicago polymorpha L. cv. Santiago), oats ( Avena saliva cv. Swan), peas ( Pisum sativum cv. Dundale) rape ( Brassica napus cv. Wesbrook), rye-grass ( Lolium rigidum cv. Wimmera) and subterranean clover ( Trifolium subterraneum cv. Nungarin) which are used as rotation crops with the wheat. Although the roots of all these plants were found to be infected and covered by the SRF, the recovery of the SRF was more frequent from the roots of wheat, rye-grass, oats, barley and great brome than peas, lupins, medic subterranean clover and chick pea.

Genetic Variability for Characters Affecting Stand Establishment in Crested Wheatgrass

Genetic Variability for Characters Affecting Stand Establishment in Crested Wheatgrass

Effect of Soil Water Potential of Two Soils on Soybean Emergence1

AbstractRapid, uniform emergence of seedlings from the soil is an important factor in crop production. A greenhouse study was conducted to evaluate the effect of different levels of soil water potential on rate and percentage of soybean [Glycine max (L.) Merr.] emergence from two soil types. ‘Tracy’ soybeans were planted in Sharkey clay (Vertic Haplaquept, very fine, montmorillonitic, thermic) and Dubbs silt loam (typic Hapludalf, fine‐silty, mixed thermic) soils equilibrated to soil water potentials (SWP) of −0.1 to −0.7 bar in 0.1 bar increments. Emergence counts were made through 14 days after planting, and each emerging seedling was rated for morphological abnormalities.Plants emerged from the Sharkey clay at a faster rate and over a wide range of SWP's than from the silt loam soil. Total emergence from the clay soil after 14 days was not significantly different over the range of SWP's used, and exceeded 81% in all treatments. However, significantly fewer plants emerged from the −0.1 and −0.7 bar potentials of the silt loam soil than from the −0.4 to 0.6 bar levels. The range of emergence from the silt loam was 31.7 to 90.0%. The trends for percentage of normal plants that emerged at each SWP level within each soil were the same as those for total emergence.Based upon these results, rapid and uniform emergence of soybean seedlings can be expected if SWP of a fine‐textured soil such as Sharkey clay is between −0.1 and −0.7 bar and that of a medium‐textured soil, such as Dubbs silt loam is between −0.4 and −0.6 bar. The range is apparently more critical for the latter soil.

Effect of Abscisic Acid at Different Levels of Soil Water Potential on the Transpiration of Zea mays

AbstractThe effect of different levels of both exogenous abscisic acid (ABA) and soil water potential on transpiration from intact maize leaves was studied in growth chamber experiments. The transpiration rate showed a more consistent decrease with decreasing soil water potential than with increasing concentration of applied ABA. The effect of exogenous ABA on the transpiration rate was markedly lower at low than at high levels of soil water potential.