Soil Moisture Treatments Research Articles

Moisture Effects on Development and Survival of the Plum Curculio (Coleoptera: Curculionidae)

Laboratory-reared larvae of Conotrachelus nenuphar Herbst were exposed to three soil moisture treatments in pots containing a mix of soil and vermiculite, whereby pots were either watered daily (wet treatment) or watered to saturation when matric potential reached threshold values of −160 and −800 kPa for the intermediate and dry treatments, respectively. Adult emergence began at approximately the same time in the 3 treatments, but peak emergence (occurring ~1 month after the start of the experiment and within 2 wks of the beginning of emergence) was much more pronounced in the intermediate moisture treatment than in the wet and dry ones. In addition, cumulative emergence in the intermediate moisture treatment (corresponding to >40% of the initial number of larvae used in the experiment) was higher than in the wet (~30%) and dry (~20%) treatments. Approx. 25% of the adults that emerged from the dry treatment were underdeveloped and/or malformed. In a separate set of experiments, the effect of air humidity on survival of laboratory-reared plum curculio adults was investigated. Survival analysis revealed a significant (P< 0.0001) effect of vapor pressure deficit on adult longevity. As vapor pressure deficit decreased from ~2.8 to 0.009 kPa, median life expectancy increased from 1.1 to 9.0 d for insects without food supply and from 7.0 to 30.5 d for insects feeding on apples. Longevity correlated with cumulative water loss from the insects, which was lowest in a saturated atmosphere and greatest for insects exposed to a vapor pressure deficit of ~2.8 kPa. Cuticular permeability of C. nenuphar to water was calculated as 185.8 μg cm−2 kPa−1.

Growth and development of bambara groundnut ( Vigna subterranea) in response to soil moisture : 2. Resource capture and conversion

A study was conducted in controlled environment glasshouses to investigate the effects of soil moisture on resource capture and conversion of three landraces (DipC, S19-3 and UN from Botswana, Namibia and Swaziland, respectively) of bambara groundnut ( Vigna subterranea (L.) Verdc.). The study was conducted under two soil moisture treatments: an irrigated control and a drought treatment where irrigation was withheld from approximately flowering to final harvest. Drought reduced the mean fractional intercepted radiation ( f) from 0.8 to less than 0.7 across landraces. The mean light extinction coefficient (=0.46) was not affected either by landrace or watering regime, while cumulative intercepted radiation ( S ci) reduced under drought because of the reduction in f. Drought reduced total transpiration ( E c) only in DipC while it had no effect on the other two landraces. Crops under irrigation extracted most of the water from the top 50 cm of the profile while those under drought extracted water down to 90 cm. The conversion coefficient for intercepted radiation ( ɛ s; g MJ −1) was reduced by 32%, from 1.51 to 1.02 g MJ −1. Similarly, drought reduced the dry matter/transpired water ratio ( ε w ; g kg −1) by 20% from 2.05 to 1.65 g kg −1.

On-line screening of soil VOCs exchange responses to moisture, temperature and root presence

The exchanges of volatile organic compounds (VOCs) between soils and the atmosphere are poorly known. We investigated VOC exchange rates and how they were influenced by soil moisture, temperature and the presence of plant roots in a Mediterranean forest soil. We measured VOC exchange rates along a soil moisture gradient (5%–12.5%–20%–27.5% v/v) and a temperature gradient (10°C–15°C–25°C–35°C) using PTR-MS. Monoterpenes were identified with GC-MS. Soils were a sink rather than a source of VOCs in both soil moisture and temperature treatments (−2.16 ± 0.35 nmol m−2 s−1 and −4.90 ± 1.24 nmol m−2 s−1 respectively). Most compounds observed were oxygenated VOCs like alcohols, aldehydes and ketones and aromatic hydrocarbons. Other volatiles such as acetic acid and ethyl acetate were also observed. All those compounds had very low exchange rates (maximum uptake rates from −0.8 nmol m−2 s−1 to −0.6 nmol m−2 s−1 for methanol and acetic acid). Monoterpene exchange ranged only from −0.004 nmol m−2 s−1 to 0.004 nmol m−2 s−1 and limonene and α-pinene were the most abundant compounds. Increasing soil moisture resulted in higher soil sink activity possibly due to increases in microbial VOCs uptake activity. No general pattern of response was found in the temperature gradient for total VOCs. Roots decreased the emission of many compounds under increasing soil moisture and under increasing soil temperature. While our results showed that emission of some soil VOCs might be enhanced by the increases in soil temperature and that the uptake of most soil VOCs uptake might be reduced by the decreases of soil water availability, the low exchange rates measured indicated that soil-atmosphere VOC exchange in this system are unlikely to play an important role in atmospheric chemistry.

Different soil moisture conditions change the outcome of the ectomycorrhizal symbiosis between Rhizopogon species and Pinus muricata

The outcome of species interactions often depends on the environmental conditions under which they occur. In this study, we tested how different soil moisture conditions affected the outcome of the ectomycorrhizal symbiosis between three Rhizopogon species and Pinus muricata in a factorial growth chamber experiment. We found that when grown in 7% soil moisture conditions, ectomycorrhizal plants had similar biomass, photosynthesis, conductance, and total leaf nitrogen as non-mycorrhizal plants. However, when grown at 13% soil moisture, ectomycorrhizal plants had significantly greater shoot biomass, higher photosynthetic and conductance rates, and higher total leaf nitrogen than non-mycorrhizal plants. The differences in plant response by mycorrhizal status in the two soil moisture treatments corresponded with evidence of water limitation experienced by the fungi, which had much lower colonization at 7% compared to 13% soil moisture. Our results suggest that the outcome of the ectomycorrhizal symbiosis can be context-dependent and that fluctuating environmental conditions may strongly affect the way plants and fungi interact.

Drought Survival and Recuperative Ability of Bentgrass Species Associated with Changes in Abscisic Acid and Cytokinin Production

Abscisic acid (ABA) and cytokinins are two groups of plant hormones that play important roles in regulating plant responses to decreases in soil water availability. The primary objective for this study was to determine whether species variability in drought survival and recovery for colonial bentgrass (Agrostis capillaris L.), creeping bentgrass (A. stolonifera L.), and velvet bentgrass (A. canina L.) were related to changes in ABA and cytokinin content. Plants of ‘Tiger II’ colonial bentgrass, ‘L-93’ creeping bentgrass, and ‘Greenwich’ velvet bentgrass were subjected to two soil moisture treatments: 1) well-watered controls, irrigated three times per week; and 2) drought, irrigation completely withheld for 16 days. For recovery, previously drought-stressed plants were rewatered and irrigated three times per week to evaluate the recovery potential for each species. Drought stress resulted in significant declines in turf quality (TQ), shoot extension rates, canopy net photosynthetic rate (Pn), daily evapotranspiration rate (ET), and cytokinin content, and significant increases in ABA content for all three bentgrass species. Velvet bentgrass exhibited less severe drought injury, as exhibited by higher TQ, Pn, and daily ET rate compared with colonial bentgrass and creeping bentgrass. Velvet bentgrass also had significantly less ABA accumulation, which could allow for continued gas exchange and sustained plant survival during drought stress compared with colonial bentgrass and creeping bentgrass. Upon rewatering after drought stress, colonial bentgrass exhibited more rapid recovery in turfgrass growth and water use compared with creeping bentgrass and velvet bentgrass. The higher recuperative ability of colonial bentgrass could be associated with its more rapid decline in ABA content and increases in cytokinin content compared with creeping bentgrass and velvet bentgrass.

Morpho-anatomical changes and photosynthetic metabolism of Stenocereus beneckei seedlings under soil water deficit

Characteristics developed by Cactaceae for adaptation to climates where water is limited include crassulacean acid metabolism (CAM), a thick cuticle, and spines and trichomes that intercept a proportion of solar radiation. A few studies consider morpho-anatomical and physiological characteristics of Cactaceae seedlings, which may help understand their establishment, growth, and eventual reproduction. In this study, photosynthetic metabolism (titratable protons) and morpho-anatomical features of Stenocereus beneckei seedlings were examined under limiting water conditions. Soil moisture treatments consisted of -0.03, -0.5, -1.5, and -3.0 MPa, and seedling samples were taken at 3 h intervals on one day at 7 and 9 months of age with three replicates per treatment. The results show irregular fluctuations in acidity concentrations during the first 6 and 7 months of age; at 9 months, an increase in titratable proton values was observed during the night, and it seems that soil moisture does not determine CAM expression. Seedlings from smaller seeds are less tolerant to water stress, they had poor growth in all treatments, and at -3.0 MPa after 3 months of drought none survived. Anatomical observations show collapsed cells associated with a high accumulation of calcium oxalate crystals and starch grains, as a response to water deficit. Titratable acidity concentration increased with seedling age, and CAM expression did not accelerate with soil water deficit.

Effects of Slash, Machine Passes, and Soil Moisture on Penetration Resistance in a Cut-to-length Harvesting

Multiple entries into forest stands are often needed for fire hazard reduction and ecosystem restoration treatments in the Inland-Northwest U.S.A. region. However, soil compaction occurring from mechanized harvesting operations often remains for many years and may contribute to a decline in long-term site productivity. A controlled experiment on a silt loam soil was conducted to determine (a) the effectiveness of logging slash to buffer compaction, (b) the influence of the number of machine passes, and (c) the contribution of soil moisture to changes in penetration resistance during a cut-to-length harvest in northern Idaho. Penetration resistance was measured at three soil depths (10, 20, and 30 cm) for three different moisture contents (low, medium, and high) and slash amounts (none, light, and heavy) after each of 12 machine passes (one pass each with a harvester and an empty forwarder, and 10 passes with a fully-loaded forwarder). At all three soil depths the main effect of moisture content and machine passes on penetration resistance was significant, but slash amounts alone did not significantly affect penetration resistance. After 12 passes, we measured the greatest penetration resistance in the medium soil moisture treatment at 5 to15 cm of soil depth. When evaluated at similar moisture contents after harvesting, the soil that was driest during machine traffic (low moisture treatment) had the lowest penetration resistance. Slash was important for protecting the soil against compaction in the medium and high soil moisture treatments. Penetration resistance did not significantly increase after the second pass of a fully-loaded forwarder (31,752 kg) at any moisture content or slash level. Managing felling operations to take advantage of dry soil conditions or using slash when soils are moist may help reduce ruts and avoid long-term compaction impacts on this soil type.

Osmotic Adjustment Associated with Variation in Bentgrass Tolerance to Drought Stress

Osmotic adjustment (OA) is a major physiological mechanism associated with maintenance of cell turgor in response to dehydration stress. The objectives of this study were to examine changes in capacity for OA in relation to plant tolerance to drought stress for two cool-season turfgrass species, creeping bentgrass (Agrostis stolonifera L.) and velvet bentgrass (A. canina L.), and to determine major solutes contributing to OA in these grass species. Plants of `L-93' creeping bentgrass and `Greenwich' velvet bentgrass were grown in a growth chamber in polyvinyl chloride (PVC) tubes (5 cm diameter, 40 cm high) filled with a 1:3 (v/v) sterilized mixture of sand and sandy loam soil. The experiment consisted of two soil moisture treatments: 1) well-watered control, irrigated three times per week to maintain soil moisture near pot capacity; and 2) drought stress, irrigation completely withheld. Velvet bentgrass exhibited higher drought tolerance compared to creeping bentgrass, as manifested by higher visual turfgrass quality (TQ) and leaf relative water content (RWC) under drought stress. Both creeping bentgrass and velvet bentgrass exhibited OA in response to drought stress; however, velvet bentgrass exhibited 50% to 60% higher magnitude of OA, which could be related to the maintenance of higher leaf RWC and TQ for greater drought duration compared to creeping bentgrass. OA for both creeping bentgrass and velvet bentgrass was associated with accumulation of water soluble carbohydrates during the early period of drought and increases in proline content following prolonged period of drought; however, inorganic ion content (Ca2+ and K+) did not considerably change under drought stress and did not seem to contribute to OA in these species.

Effects of soil water on seed production and photosynthesis of pink smartweed (Polygonum pensylvanicum L.) in playa wetlands

Soil moisture is frequently manipulated by wetland managers to achieve a desired composition and production of plant species. Pink smartweed (Polygonum pensylvanicum) is a species valued by wetland managers because of its potential seed production and food base for migrating and wintering waterbirds. To improve ability to manage pink smartweed, we measured the influence of four growing-season soil moisture regimes (flooded, field capacity, prescribed moist-soil management, and continuously dry) in playa wetlands of the Southern High Plains of Texas. We used xylem water potential as an index of soil moisture available to the plants and compared vegetation and seed production among the four moisture treatments. Daily net photosynthesis was measured in each playa at 0900, 1200, and 1700 hours. The continuously-flooded wetland had the lowest absolute xylem water potential value (−0.294 MPa), followed by the playa at field capacity (−0.446 MPa), moist-soil managed playa (−0.758 MPa), and dry playa (−1.039 MPa). Vegetation biomass (F3,40 = 97.7, P < 0.001) and seed production (F3,40 = 54.3, P < 0.001) of pink smartweed differed among soil moisture treatments. Conducting moist-soil management (x = 6816 kg/ha) increased vegetation biomass by 44% over the dry treatment (x = 4706 kg/ha). As soil moisture increased to field capacity (x = 9010 kg/ha) vegetation increased by 32% above the moist-soil treatment. Maintaining standing water in a playa maximized vegetation production (x = 12497 kg/ha) of pink smartweed. Seed production was greatest when soil moisture was maintained at field capacity (x = 695 kg/ha). There was no difference in seed production between the moist-soil managed (x = 492 kg/ha) and flooded playas (x = 514 kg/ha), which was 28% lower than the field capacity treatment. Seed production in the dry treatment (x = 377 kg/ha) was 46% lower than the field capacity treatment and 25% below the flooded and moist-soil managed treatments. Net photosynthesis and xylem water potential decreased throughout the day in all treatments except continuously flooded, which corresponded to the increased vegetation production in this treatment. Slight increases in water stress relative to the continuously flooded treatment resulted in a redistribution of resources from vegetation to seed production. Managers should consider maintaining wetland soils at field capacity to increase seed production of pink smartweed.

Allyl Isothiocyanate and Carbon Dioxide Produced during Degradation of Brassica juncea Tissue in Different Soil Conditions

A study was conducted to quantify volatiles generated from Indian mustard (Brassica juncea L. Czerniak) tissue incorporated into soils under controlled conditions. Mustard residues were incorporated into noncovered and covered soils that varied by texture, temperature, moisture, pH, or sterility (autoclaved or nonautoclaved). Sandy loam soil had 38% more allyl isothiocyanate (AITC) than clay loam soil. AITC concentration in 45 °C soil was 81% higher than in soil at 15 °C, and 56% higher in covered compared to noncovered treatments. The microbial catabolism of AITC was suggested by the result that AITC concentration in autoclaved soils was over three times that measured in nonautoclaved soils. The highest AITC level detected (1.71 μmol·L–1) occurred in the autoclaved covered soil. Several factors also influenced CO2 evolution. At 30 or 45 °C, CO2 concentration was at least 64% higher than at 15°C. The covered soil had over twice the CO2 found in the noncovered soil, and the nonautoclaved soil treatment yielded twice the CO2 measured in the autoclaved soil. There were no main effect differences among soil moisture, soil pH, and soil texture treatments for CO2 concentrations. This information could be helpful in defining ideal soil conditions for field scale experiments. Additionally, this study demonstrates a sampling technique for testing fumigation potential of biofumigation and solarization systems that may have the potential to replace methyl bromide.

Respiratory substrate availability plays a crucial role in the response of soil respiration to environmental factors

We examined the response of the temperature coefficient ( Q 10) for soil respiration to changes in soil temperature and soil moisture through a laboratory incubation experiment. Two types of soils differing in vegetation and moisture status were collected and incubated under two temperatures (10 and 30 °C) and two soil moisture regimes (35 and 75% of water holding capacity, WHC) for 5 weeks. Before and after the incubation experiment, the temperature coefficient of soil respiration was measured using soda-lime method by changing temperature in a water bath. For both soils, the mean Q 10 values of the respiration rate were 2.0 in the 30 °C and 2.3 in the 10 °C soil treatments. Higher temperature with lower soil moisture treatment significantly decreased the Q 10 value, whereas lower temperature with higher soil moisture treatment significantly enhanced the Q 10 value (ANOVA, p < 0.05). These results indicate that soils became less sensitive to temperature when incubated under higher temperature with higher moisture conditions, and more sensitive in lower temperature with higher moisture conditions. There was a significant correlation ( r 2 = 0.67, p < 0.05) between water-soluble carbon (WSC) and soil respiration rate. However, the correlation between soil respiration rate and microbial biomass carbon (MBC) was weak ( r 2 = 0.27, p > 0.05). Although incubation temperature and moisture accounted for 40 and 29% (as r 2 × 100%), respectively, of variations in Q 10, soil water-soluble carbon content alone could have explained 79% of the variation, indicating that the availability of respiratory substrate, rather than the pool of soil microorganisms, played a crucial role in the response of the temperature coefficient to environmental factors. These results suggest that biotic factors should also be taken into consideration when using the Q 10 function to predict the response of soil respiration to global warming.

Effects of Hydroperiod and Iron on Typha latifolia Grown in a Phosphorus-Enhanced Medium

This study was designed to mimic a phosphorus-(P)-enhanced environment and focused on the effects of hydroperiod and dissolved iron (Fe) concentrations on Typha latifolia. The physiological responses and nutrient uptake capabilities of plants were quantified. The research was conducted in a greenhouse utilizing a factorial design with three soil-moisture treatments (permanently flooded, periodically flooded, drained) and three Fe levels (0 mg Fe L − 1, control; 1 mg Fe L − 1; 10 mg Fe L − 1). All treatments also received P at 0.2 mg l − 1. Plant gas exchange, growth, biomass, and tissue Fe and P concentrations were measured. Permanent flooding enhanced height growth, shoot weight, and root weight, and led to high Fe concentrations in the roots. Plants receiving the 10 mg Fe L −1 treatment had taller shoot heights compared with those receiving the control and 1 mg Fe L −1 treatments. It appeared that a concentration of 10 mg Fe L − 1 did not significantly affect T. latifolia under moderately reduced soil conditions. However, low soil-redox potential levels below +70 mV and iron levels of 10 mg L − 1 may eventually lead to a photosynthetic decline in T. latifolia. Results highlighted two important findings: (1) Fe treatment and moisture regimes, as tested, did not affect tissue P concentrations and thus the ability to uptake and sequester P, and (2) a treatment of 10 mg Fe L − 1 may have led to some initial beneficial effects in T. latifolia, such as producing the greatest shoot growth, but a photosynthetic decline was noted in the last week as redox potential levels fell below +100 mV. This effect potentially hinders the use of Fe to aid P retention in wetlands, due to the possibility of inducing physiological dysfunction in some species, such as noted in T. latifolia.

Performance of Perennial Cool‐Season Forage Grasses in Diverse Soil Moisture Environments, Southern High Plains, USA

A continuing need exists to evaluate grasses for irrigated pastures in new and marginal environments. Persistence and yield of Altai wildrye, Leymus angustus (Trin.) Pilg.; beardless wildrye, L. triticoides (Buckley) Pilg.; creeping foxtail, Alopecurus arundinaceus Poir.; grazing bromegrass, Bromus stamineus E. Desv.; intermediate‐pubescent wheatgrass, Elytrigia intermedia (Host) Nevski; meadow bromegrass, B. riparius (Rehmann); meadow fescue, Festuca pratensis (Huds.); orchardgrass, Dactylis glomerata (L.); prairie bromegrass, B. willdenowii (Kunth), syn. B catharticus Vahl var. catharticus; reed canarygrass, Phalaris arundinacea L.; RS wheatgrass, E. repens var. repens L. Desv. ex B.D. Jackson × Pseudoroegneria spicata (Pursh) A. Love; Russian wildrye, Psathyrostachys juncea (Fisch.) Nevski; smooth bromegrass, B. inermis Leyss.; tall fescue, F. arundinacea Schreb.; tall wheatgrass, E. elongata (Host) Nevski; and western wheatgrass, Pascopyrum smithii (Rybd.) A. Love, sown in late summer 1997, were measured from 1999 to 2001 at Tucumcari, NM. Soil moisture treatments were (i) furrow irrigated once before each harvest, which is typical management; (ii) typical irrigation plus irrigated monthly during winter; and (iii) poorly drained, saline/sodic soil, irrigated less than once per cutting. Russian wildrye, RS wheatgrass, tall fescue, tall wheatgrass, and western wheatgrass maintained ground cover across soil moisture treatments. Stand development by Altai wildrye and smooth bromegrass was inconsistent across soil moisture treatments, but eventually complete. Beardless wildrye established stands only in poorly drained soil, while intermediate‐pubescent wheatgrass and meadow bromegrass did not establish well in that soil. No other species established or maintained satisfactory stands after 3 yr in any soil moisture treatment. Winter irrigation increased early‐season yield of intermediate‐pubescent wheatgrass, but decreased late‐season yields of several species, especially Altai wildrye. Distribution of tall wheatgrass and Altai wildrye yield appear complementary, and a binary mixture might provide uniform season‐long yields in this region.

Phenotypic plasticity in vegetative and reproductive traits in an invasive weed, Lythrum salicaria (Lythraceae), in response to soil moisture

In colonizing species, high phenotypic plasticity can contribute to survival and propagation in heterogenous adventive environments, and it has been suggested as a predictor of invasiveness. Observation of natural populations of an invasive species, Lythrum salicaria salicaria, indicated extensive variation in its growth and reproductive traits. Phenotypic plasticity of different life history traits of L. salicaria was investigated using vegetative clones of each of 12 genotypes from one population in Ontario, Canada. We chose soil moisture as the treatment factor because of its importance in wetland species and raised all 12 genotypes in each of four soil moisture treatments. We examined an array of vegetative and reproductive traits, including root and shoot mass, shoot and inflorescence length, total seed set, floral mass, and morphometric variables. All observed vegetative as well as reproductive traits demonstrated significant phenotypic plasticity in response to soil moisture treatment. Even the stigma-anther separation involved significant genotype by environment interactions, suggesting that soil moisture may modify the relative positions of anthers and stigma. Compared to vegetative traits, most reproductive traits demonstrated crossing reaction norms, implying that the average differences in those traits among genotypes vary with the environment maintaining the genetic variation in a population.

Liquid Swine Manure Can Kill Verticillium dahliae Microsclerotia in Soil by Volatile Fatty Acid, Nitrous Acid, and Ammonia Toxicity

ABSTRACT In previous studies, liquid swine manure (LSM) was sometimes shown to reduce Verticillium wilt of potato caused by Verticillium dahliae. We also observed that microsclerotia of this fungus died within 1 day, or between 3 and 6 weeks, after addition of LSM to some acid soils and within 1 week in some alkaline soils. In this study, we demonstrated that a volatile fatty acid (VFA) mixture with an identical concentration of VFAs as that found in an effective LSM reduced germination in an acid soil (pH 5.1) to the same extent as the LSM after 1 day of exposure. Germination was reduced by 45, 75, and 90% in the 10, 20, and 40% ([wt/wt] soil moisture) treatments, respectively, with the latter being equivalent to an application of 80 hl/ha. Addition to this acid soil of 19 LSMs (30% [wt/wt] soil moisture) collected from different producers resulted in complete kill of microsclerotia with 12 manures. Effective manures had a total concentration of nonionized forms of VFAs in soil solution of 2.7 mM or higher. In some acid soils (pH 5.8), addition of LSM (40% [wt/wt] soil moisture) did not kill microsclerotia until 3 to 6 weeks later. Here, a reduction in viability of microsclerotia was attributed to the accumulation of 0.06 mM nitrous acid in the soil solution at 4 weeks. When an LSM was added (40% [wt/wt] soil moisture) to an alkaline soil (pH 7.9) where VFAs are not toxic, microsclerotia germination was reduced by 80% after 1 week. Here the pH increased to 8.9 and the concentration of ammonia reached 30 mM in the soil solution. An ammonium chloride solution having an equivalent concentration of ammonium as the manure was shown to have the same spectrum of toxicity as the manure in assays ranging from pH 7 to 9, both in solutions and above the solutions. At pH 9, the concentration of ammonia reached 18 mM and 100% mortality of microsclerotia occurred. Thus, in acid soils, LSM can kill microsclerotia of V. dahliae by VFA and/or nitrous acid toxicity and in alkaline soils by ammonia toxicity. In order to take advantage of these mechanisms for disease reduction, the manure chemical composition, rate of addition, and soil characteristics need to be determined for each instance of use.

Reproductive and vegetative responses of different accessions of Microlaena stipoides (Labill.) R.Br. to nitrogen applications and supplementary irrigation in southern Australia

Native grasses such as Microlaena stipoides (Labill.) R.Br. have the potential to play an important role in pastures, revegetation and as turfgrasses, but their use to date has been limited by seed supply. The purpose of this study was to investigate, (i) the effect of nitrogen fertilisation on M. stipoides seed production, (ii) the effect of irrigation on seed production, and (iii) the variation among accessions in response to these 2 factors. Microlaena stipoides accessions responded to added nitrogen with an increase in shoot growth, total amount of dry matter produced per plant and in reproductive characters at the end of the harvest season. Higher yields were recorded for high (split) nitrogen treatments in comparison to nil (control) or low nitrogen treatments, with added nitrogen extending seed production. Higher soil moisture regimes produced significantly more reproductive culms, more spikelets per culm, and more seeds per plant when compared to low soil moisture treatments. The frequency of irrigation had more effect on seed yield than the amount of water applied. Microlaena stipoides appears to have a 2–step mechanism for regulating the yield of its summer inflorescences namely; the plant initially responds to a high frequency of rainfall or irrigation events by initiating culms. Numbers of culms and florets per culm that reach maturity are dependent on the volume of water applied. Such a mechanism would assist in the adaptation of this grass to a southern Australian climate, which often exhibits an erratic summer rainfall. While there were differences among the accessions for both reproductive and vegetative characters, they gave a uniform response to the different nitrogen treatments. The responses of 3 accessions to different irrigation treatments were somewhat different but with respect to total number of spikelets produced per plant, they all responded in the same way. Different irrigation management schedules may be required for different cultivars for commercial seed production.

Gender-specific responses to winter defoliation of greenhouse-grown Atriplex canescens clones under contrasting soil moisture regimes

A greenhouse experiment with female, male and monecious clones (36 of each, 108 total) of tetraploid Atriplex canescens (Pursh) Nutt. (fourwing saltbush) was conducted to determine gender-specific responses to simulated herbivory under contrasting conditions of soil moisture. We imposed three levels of winter defoliation (control, 40%, and 70% stem removal) and two soil moisture treatments (control and water stress). Gender-related responses to defoliation were context-specific. Defoliated female clones produced significantly less shoot biomass than male or monecious clones when soil moisture conditions were not limiting. All genders produced similar amounts of shoot biomass under conditions of soil moisture stress. Root biomass responses exhibited the opposite trend. With adequate soil moisture all defoliated clones produced similar amounts of root biomass, but water-stressed defoliated females usually produced less root biomass than their male and monecious counterparts. Leaf gas-exchange measurements indicated that females were less efficient than males in the use of water. Monecious clones outperformed both females and males when conditions of stress were greatest. Defoliated female shrubs may be at a competitive disadvantage regardless of the environmental context, and could therefore be expected to be the shrub gender most negatively affected by herbivory.

Influence of Tillage and Mulching Systems on Soil Water and Tomato Fruit Yield and Quality

ABSTRACT Many growers have interests in using mulches, cover crops, and conservation tillage systems in tomato production, but also have concerns about the effect of soil moisture fluctuations on fruit quality. Percent soil moisture and ‘Fabulous’ tomato (Lycopersicon esculentum Mill.) fruit production in response to different mulching/tillage systems within wheat (Triticum aestivum L.) and winter rye (Secale cereale L.) cover crops were evaluated. Treatments applied following the mowing of the cover crops were: (1) conventional tillage (CT); (2) black polyethylene plastic over conventional tillage (BP); (3) no-tillage with cover crop killed with 1.5% glyphosate one week prior to transplanting (NT); (4) strip-tillage with cover crop killed with a 1.5% glyphosate one week prior to transplanting (ST); (5) no-tillage in which the cover crop was mowed periodically during the growing season [NT-Lm (living mulch)]; and (6) strip-tillage with the cover crop mowed and treated similar to treatment 5 (ST-Lm). Generally, there were no differences (P < 0.05) between winter rye and wheat cover crops with respect to tomato quality or yields. Large amounts of cull fruit were produced in both years, regardless of moisture; however, blossom-end rot was more severe across treatments during 1999. Under drought conditions (1999 growing season), all conservation tillage treatments had higher soil moisture readings 24 hrs after rainfall than other treatments, but BP had higher moisture levels than all other treatments under times of excessive water depletion. Under a condition of sufficient soil moisture (2000 growing season), black plastic resulted in higher soil moisture early in the season than CT or conservation tillage systems, a response associated with greater total marketable yields. Comparisons between the various conservation tillage treatments for soil moisture and tomato yields were inconclusive, but with adequate and consistent soil moisture, conservation and conventional tillage treatments produced similar marketable yields.

Physiological Adaptation of Kentucky Bluegrass to Localized Soil Drying

This study was designed to investigate effects of surface soil drying (SD) on water relations, gas exchange, growth characteristics, and abscisic acid (ABA) content of leaves and roots for Kentucky bluegrass (Poa pratensis L.), and to examine whether physiological adaptation to SD is associated with hydraulic or chemical regulation. ‘Award’ and ‘Nuglade’ were subjected to three soil moisture treatments in a growth chamber: (i) well‐watered control; (ii) SD (0–20 cm); and (iii) full soil profile (0–40 cm) drying (FD). Under SD, turf quality (TQ), relative water content (RWC), photosynthesis, and cell membrane stability remained the same as the controls, but stomatal conductance (gs) declined by 35 and 45%, and shoot growth rates were reduced by 50 and 40% for Award and Nuglade, respectively. Root DW decreased in 0‐ to 20‐cm dry soil, but increased compared with controls in the 20‐ to 40‐cm wet soil under SD. The ABA content increased by four to sixfold in roots at 0‐ to 20‐cm drying soil and did not change in the 20‐ to 40‐cm wet soil under SD conditions. The ABA content was also higher in leaves of SD plants. The results suggested Kentucky bluegrass adapted to localized soil drying by maintaining TQ, photosynthesis, leaf water status (WS), and root growth using water in the deeper soil profile. Decline in gs and shoot growth was independent of leaf WS, and could be hormonally controlled, which could help maintain favorable WS in leaves by reducing water loss under SD conditions.

Radish (Raphanus sativus) as a Model System for the Study of Soil Moisture Effects on the Glucosinolate-myrosinase Complex

Clarifying the influence of abiotic environmental factors on the glucosinolate-myrosinase complex in vegetables of the Brassicaceae is an important step in understanding physiological processes that affect crop quality. Previous related work in this lab has shown that irrigation timing in the field may influence physical-, chemical- and sensory-based indicators of cabbage quality. The objective of this study was to record glucosinolate concentrations and myrosinase activity in crop tissues from plants subjected to varying soil moisture levels, employing radish as a model. Plants of cv. Belle Glade were grown in a controlled environment system designed at the Ohio Agricultural Research and Development Center in Wooster, Ohio for maintenance of target soil moisture levels. Pots were maintained at three soil moisture ranges, 40% to 60% (A), 20% to 30% (B) and 10% to 20% (C) volumetric soil moisture content at 30 °C. Preliminary observations revealed that treatments A, B and C corresponded to soil tensions which were not stressful, moderately stressful, and severely stressful to plants, respectively. Pot evapotranspiration, leaf stomatal conductance and plant size followed the order A&gt;B&gt;C, while canopy temperatures followed the order C&gt;B&gt;A. In leaves, glucosinolate concentrations and myrosinase activity were about 15% greater in treatments B and C than in A, while glucosinolate levels and myrosinase activity were 28 and 50% lower in hypocotyls and roots, respectively, in C than in A. It is hypothesized that changes in enzyme and substrate synthesis and translocation within the plant in response to sub-optimal soil moisture levels may explain the differential response of tissue glucosinolate concentrations and myrosinase activity to soil moisture treatments.