Low Moisture Levels Research Articles

Physical and sensory characteristics of processed cheeses manufactured by extrusion technology

AbstractBACKGROUND: Not much work has been reported on use of extrusion technology for manufacturing processed cheese. The main goal of this study was to determine whether processed cheese of acceptable quality could be manufactured by extrusion technology. Two extrusion temperatures (80 and 90 °C), two moisture levels (440 and 480 g kg−1), and two emulsifying salt levels (10 and 15 g kg−1) were studied (eight experimental samples). Instrumental measures (moisture and texture profile analysis), descriptive analysis, and consumer acceptability for the processed cheese samples were carried out.RESULTS: The instrumental measures and descriptive analysis showed differences among the samples. The major difference was a result of the moisture content. The lower‐moisture cheeses were firmer/chewier in texture, and had more Cheddar flavor note. Consumers found the lower‐moisture cheeses extruded at 80 °C to be more acceptable.CONCLUSION: It could be concluded from this study that processed cheeses that were extruded at lower temperature with lower moisture levels might be better suited for manufacturing using extrusion technology. Copyright © 2009 Society of Chemical Industry

Evaluation of functional diversity in rhizobacterial taxa of a wild grass ( Saccharum ravennae) colonizing abandoned fly ash dumps in Delhi urban ecosystem

Metal rich fly ash dumps may serve as repository of ecologically useful multi-functional rhizobacteria having potential use in the development of vegetation at the dumps. Therefore, in the present study bacteria from the rhizosphere of a wild perennial grass colonizing Indraprastha and Badarpur fly ash dumps of Delhi region were purified, identified and functionally characterized. The fly ash had low levels of nutrients, moisture and organic matter coupled with toxic levels of heavy metals (As, Cd, Cr, Cu, Hg, Ni, Pb and Zn). Both the dumps were mostly barren except for a few patches of Saccharum ravennae and some weedy species. Sixty five dominant, morphologically distinct rhizobacteria were purified, which belonged to 18 genera and 38 species. Gram-positive bacteria were dominating in the fly ash environment. Bacillus spp. and Paenibacillus spp. were common at both the dumps. Multi-metal tolerance was shown by diverse bacterial taxa. The minimum inhibitory concentration (MIC) was highest for As (12.5–20.0 mM) and Pb (7.5–10.0 mM), although many rhizobacteria also possessed significant tolerance to Cr, Zn, Ni, Cu, Co and Cd. The tolerance profiles of rhizobacteria to different metals may be ranked in the decreasing order as As > Pb > Cr > Zn > Ni > Cu > Co > Cd > Hg. Majority of rhizobacteria showed good siderophore activity. Multiple-metal tolerance was also coupled with high siderophore production in some of the isolates ( Microbacterium barkeri IPSr74, Serratia marcescens IPSr90 and IPSr82, Enterococcus casseliflavus BPSr32, Bacillus sp. IPSr80, Pseudomonas aeruginosa BPSr43 and Brochothrix campestris BPSr3). Most of the bacteria could grow on nitrogen-deficient medium. However, the dominant nitrogen-fixers reported from the rhizosphere of other Saccharum species were not detected. S. marcescens IPSr90 was the only rhizobacterium, which showed ACC-deaminase (ACCD) activity. Proportion of phosphate-solubilizing bacteria was high. Considerable improvement in the seedling establishment, plant weight and shoot length in rhizobacterial inoculated plants of S. ravennae in fly ash environment indicated the significance of rhizobacteria in its colonization and spread to the dumps. Representative rhizobacteria, with high MIC (for most of the metals) and good plant growth promoting (PGP) traits comparable to commercially useful bacterial inoculants were identified as S. marcescens IPSr82 and IPSr90, P. aeruginosa BPSr43, Paenibacillus larvae BPSr106, Arthrobacter ureafaciens BPSr55, Paenibacillus azotofixans BPSr107 and E. casseliflavus BPSr32. S. ravennae and some of these rhizobacteria may be potentially useful for the development of inoculation technologies for conversion of barren fly ash dumps into ecologically and economically productive habitats.

Water regime shifts in the active soil layer of the Qinghai–Tibet Plateau permafrost region, under different levels of vegetation

Soil moisture and water cycling in a permafrost active layer are affected in a synergistic manner by both the sequence of soil temperature and changes in vegetative cover. Between 2004 and 2007, the dynamics of soil water content and water movement in the active layer of alpine meadow soils were monitored at sites located in the permafrost region of the Qinghai–Tibetan Plateau, China for four years to examine the synergistic effects of freeze–thaw cycles and levels of vegetation cover. The analysis of variations in monthly and seasonal soil moisture, soil-desiccation index, and soil available indicated that soil moisture exhibited a relatively stable and consistent pattern over the growing season (July–September), independent from the vegetation cover. Greater soil moisture was present in the upper root zone and at the bottom of the soil profile, whereas lower moisture levels occurred in the middle portion of the profile. Irrespective of soil depth, the lower the vegetation cover, the quicker the increase in soil liquid water during the thaw initiation period (May and June), and the quicker its decrease during the freeze initiation period (October and November). In addition, the greater the vegetation cover, the greater the available water content of the upper root zone and the less the water content of the soil layer at 0.60−0.70 m depth below the root zone. Both the soil hydraulic parameters and the spatiotemporal distribution of the water content were subject to the synergistic action of the freeze–thaw cycle and the extent of vegetation cover. The variances in active soil heat transmission and heat-water coupling relationship under the different vegetation covers were considered the main driving factors in the distribution and dynamics of the active soil water regime. The permafrost supports the development of alpine frost meadow ecosystems, and well-ordered, high-cover alpine meadow vegetation favors the protection of permafrost from degradation.

Control of discontinuous gas exchange inSamia cynthia: effects of atmospheric oxygen, carbon dioxide and moisture

The evolution of discontinuous gas exchange (DGE) in insects is highly controversial. Adaptive hypotheses which have obtained experimental support include a water savings mechanism for living in dry environments (hygric hypothesis), a reduction in oxidative damage due to a high-performance oxygen delivery system (oxidative damage hypothesis), and the need for steep intratracheal partial pressure gradients to exchange gases under the hypercapnic and/or hypoxic conditions potentially encountered in subterranean environments (chthonic hypothesis). However, few experimental studies have simultaneously assessed multiple competing hypotheses within a strong inference framework. Here, we present such a study at the species level for a diapausing moth pupa, Samia cynthia. Switching gas conditions from controlled normoxic, normocapnic and intermediate humidity to either high or low oxygen, high or low moisture, elevated carbon dioxide, or some combination of these, revealed that DGE was abandoned under all conditions except high oxygen, and high or low gas moisture levels. Thus, support is found for the oxidative damage hypothesis when scored as maintenance of DGE. Modulation of DGE under either dry or hyperoxic conditions suggested strong support for the oxidative damage hypothesis and some limited support for the hygric hypothesis. Therefore, this study demonstrates that the DGE can be maintained and modulated in response to several environmental variables. Further investigation is required using a strong-inference, experimental approach across a range of species from different habitats to determine how widespread the support for the oxidative damage hypothesis might be.

Effects of post-harvest silviculture on use of boreal forest stands by amphibians and marten in Ontario

Much of the southern boreal forest is composed of second-growth stands that have been subjected to a variety of silvicultural treatments ranging from cut and leave to scarification, planting, and tending with herbicides. We have limited understanding of the effects that these treatments may have on wildlife species, as a result of changes to forest structures and species composition. Forest amphibians, generally, and the American marten (Martes americana) are species for which there has been long-standing concern about the effects of forest management. We examined the long-term effects at stand and landscape scales of a range of silviculture intensities on these species by comparing the relative abundances of some amphibians and habitat use by marten in forests that were about 32 to 50 years old. American toads (Bufo americanus) appeared to be unaffected by long-term changes in habitat structure and composition owing to silvicultural techniques. We observed lower relative abundance of wood frogs (Rana sylvatica) in treated stands 20 to 30 years old than in all other stands including uncut old forests. However, abundance in treated stands more than 32 years old did not differ from untreated or uncut stands. This effect may have resulted from lower moisture levels in treated young stands. Marten seemed to positively respond to post-harvest planting and tending treatments, suggesting that basic silviculture provided habitat attributes, notably a higher conifer content, which was favourable to marten. Key words: post-harvest silviculture, marten, wood frog, American toad, herbicide, boreal, woody debris, Ontario

Global Soil Moisture Patterns Observed by Space Borne Microwave Radiometers and Scatterometers

Within the scope of the upcoming launch of a new water related satellite mission (SMOS) a global evaluation study was performed on two available global soil moisture products. ERS scatterometer surface wetness data was compared to AMSR-E soil moisture data. This study pointed out a strong similarity between both products in sparse to moderate vegetated regions with an average correlation coefficient of 0.83. Low correlations were found in densely vegetated areas and deserts. The low values in the vegetated regions can be explained by the limited soil moisture retrieval capabilities over dense vegetation covers. Soil emission is attenuated by the canopy and tends to saturate the microwave signal with increasing vegetation density, resulting in a decreased sensor sensitivity to soil moisture variations. It is expected that the new low frequency satellite mission (SMOS) will obtain soil moisture products with a higher quality in these regions. The low correlations in the desert regions are likely due to volume scattering or to the dielectric dynamics within the soil. The volume scattering in dry soils causes a higher backscatter under very dry conditions than under conditions when the sub-surface soil layers are somewhat wet. In addition, at low moisture levels the dielectric constant has a reduced sensitivity in response to changes in the soil moisture content. At a global scale the spatial correspondence of both products is high and both products clearly distinguish similar regions with high seasonal and inter annual variations. Based on the global analyses we concluded that the quality of both products was comparable and in the sparse to moderate vegetated regions both products may be beneficial for large scale validation of SMOS soil moisture. Some limitations of the studied products are different, pointing to significant potential for combining both products into one superior soil moisture data set.

Oxygen Embrittlement and Time-Dependent Grain-Boundary Cracking of ALLVAC 718PLUS

This study focuses on the time-dependent intergranular cracking of a newly developed Ni-base superalloy ALLVAC 718PLUS. Grain-boundary (GB) cracking is due to the penetration of oxygen down grain boundaries and subsequent oxidation of GB particles, i.e., carbides and possibly delta phase present at the grain boundaries. The GB oxidation and subsequent brittle intergranular failure of this material is highly dependent upon moisture level in the testing atmosphere. With increasing moisture level in the test atmosphere, it is demonstrated that hydrogen may become dominant over oxygen as the embrittling species. The degree of susceptibility to time-dependent intergranular cracking is also highly dependent upon microstructure. The behavior exhibited by ALLVAC 718PLUS is common to a wide range of Ni- base superalloys when tested in air or other aggressive environments. A six-step model for the grain-boundary cracking mechanism is presented. The model is presented for hydrogen in high-moisture environments but is equally applicable to oxygen at lower-moisture levels, as well. Structures which provide increased resistance to time-dependent intergranular cracking are also discussed.

Moisture measurement using porous aluminum oxide coated microcantilevers

Abstract Two types of aluminum oxide (Al 2 O 3 ) modified microcantilevers (MCLs) were tested for their sensitivity and reproducibility for detection of low levels of moisture. Aluminum was sputtered on the MCLs and oxidized to Al 2 O 3 through thermal oxidation (Method I) and anodization method (Method II). Both deflection and frequency change of the MCLs were investigated. Thermally treated MCLs showed a 16 ± 2 nm deflection and a 25 Hz change in resonant frequency, i.e., a mass change of 1.85 × 10 −11 g, to a 200 ppm level of moisture. MCLs from Method II showed a 95 ± 5 nm deflection and a 340 Hz change in resonant frequency, i.e., a mass change of 41.76 × 10 −11 g, to the 200 ppm level of moisture. The MCLs’ response time to moisture was less than 3 min using the deflection mode, and less than 25 s using the frequency method. The MCLs prepared by Method II demonstrated a higher sensitivity toward moisture measurement due to the larger surface area of the porous Al 2 O 3 coating. The comparison also suggests that the frequency responses of microcantilever sensors to moistures are much faster than the deflection responses. These sensors were stable for months stored under ambient conditions. The bending amplitudes and frequency change were proportional to the moisture level, and the detection of moisture was not affected by alcohols in the environment.

Varying Hydric Conditions during Incubation Influence Egg Water Exchange and Hatchling Phenotype in the Red‐Eared Slider Turtle

Environmental conditions within the nest, notably temperature and moisture of substrate, exert a powerful influence during embryogenesis in oviparous reptiles. The influence of fluctuating nest temperatures has been experimentally examined in different reptile species; however, similar experiments using moisture as the key variable are lacking. In this article, we examine the effect of various substrate moisture regimes during incubation on different traits (egg mass, incubation length, and hatchling mass) in a chelonian species with flexible-shelled eggs, the red-eared slider turtle (Trachemys scripta elegans). Our results show that the rate of water uptake by the eggs was higher in wet than in dry substrate and varied across development. More important, during the first third of development, the egg mass changes were relatively independent of the soil moisture level; they became very sensitive to moisture levels during the other two-thirds. Moreover, hydric conditions exerted a strong influence on the eggs' long-term sensitivity to the moisture of the substrate. Even short-term episodes of high or low levels of moisture modified permanently their water sensitivity, notably through modification of eggshell shape and volume, and in turn entailed significant effects on hatchling mass (and hence offspring quality). Such complex influences of fluctuating moisture levels at various incubation stages on hatchling phenotype better reflect the natural situation, compared to experiments based on stable, albeit different, moisture levels.

Belowground Chemical Signaling in Maize: When Simplicity Rhymes with Efficiency

Maize roots respond to feeding by larvae of the beetle Diabrotica virgifera virgifera by releasing (E)-beta-caryophyllene. This sesquiterpene, which is not found in healthy maize roots, attracts the entomopathogenic nematode Heterorhabditis megidis. In sharp contrast to the emission of virtually only this single compound by damaged roots, maize leaves emit a blend of numerous volatile organic compounds in response to herbivory. To try to explain this difference between roots and leaves, we studied the diffusion properties of various maize volatiles in sand and soil. The best diffusing compounds were found to be terpenes. Only one other sesquiterpene known for maize, alpha-copaene, diffused better than (E)-beta-caryophyllene, but biosynthesis of the former is far more costly for the plant than the latter. The diffusion of (E)-beta-caryophyllene occurs through the gaseous rather than the aqueous phase, as it was found to diffuse faster and further at low moisture level. However, a water layer is needed to prevent complete loss through vertical diffusion, as was found for totally dry sand. Hence, it appears that maize has adapted to emit a readily diffusing and cost-effective belowground signal from its insect-damaged roots.

Thermoplastic Processing of Proteins for Film Formation—A Review

Increasing interest in high-quality food products with increased shelf life and reduced environmental impact has encouraged the study and development of edible and/or biodegradable polymer films and coatings. Edible films provide the opportunity to effectively control mass transfer among different components in a food or between the food and its surrounding environment. The diversity of proteins that results from an almost limitless number of side-chain amino-acid sequential arrangements allows for a wide range of interactions and chemical reactions to take place as proteins denature and cross-link during heat processing. Proteins such as wheat gluten, corn zein, soy protein, myofibrillar proteins, and whey proteins have been successfully formed into films using thermoplastic processes such as compression molding and extrusion. Thermoplastic processing can result in a highly efficient manufacturing method with commercial potential for large-scale production of edible films due to the low moisture levels, high temperatures, and short times used. Addition of water, glycerol, sorbitol, sucrose, and other plasticizers allows the proteins to undergo the glass transition and facilitates deformation and processability without thermal degradation. Target film variables, important in predicting biopackage performance under various conditions, include mechanical, thermal, barrier, and microstructural properties. Comparisons of film properties should be made with care since results depend on parameters such as film-forming materials, film formulation, fabrication method, operating conditions, testing equipment, and testing conditions. Film applications include their use as wraps, pouches, bags, casings, and sachets to protect foods, reduce waste, and improve package recyclability.

Diversity and distribution of entomopathogenic nematodes (Nematoda: Steinernematidae, Heterorhabditidae) and their bacterial symbionts (γ-Proteobacteria: Enterobacteriaceae) in Jordan

Until now, only a few systematic surveys of entomopathogenic nematodes (EPN) have been conducted in Middle Eastern countries. Many of the recovered EPN species in this region have shown to own distinctive qualities that enable their survival in unique environments, such as high temperatures and low moisture levels tolerance. These new species and strains, with unique environmental tolerances, are more suitable for their consideration in pest management programs in xerophytic regions. With this background in mind, we recently conducted a survey of EPN in Jordan. This study records for the first time the diversity and distribution of these nematodes and their bacterial symbionts in this country. Jordan’s three geographic regions: (1) the highlands, (2) Jordan valley and (3) the desert region were sampled. Within each region, natural habitats and agricultural regions characteristic to each region were considered for sampling purposes. Four EPN species including three Steinernema and one Heterorhabditis were recovered. Nematodes were identified using a combination of molecular markers and classic morphological diagnostic tools. Bacterial symbionts were identified by analysis of 16S rRNA sequences. Abiotic characteristics such as soil type, soil pH, and elevation were also recorded. We herein report the diversity of EPN species in Jordan and discuss their potential in Biocontrol and IPM programs for this country.

Mechanisms linking plant productivity and water status for a temperate Eucalyptus forest flux site: analysis over wet and dry years with a simple model.

A simple process-based model was applied to a tall Eucalyptus forest site over consecutive wet and dry years to examine the importance of different mechanisms linking productivity and water availability. Measured soil moisture, gas flux (CO2, H2O) and meteorological records for the site were used. Similar levels of simulated H2O flux in 'wet' and 'dry' years were achieved when water availability was not confined to the first 1.20 m of the soil profile, but was allowed to exceed it. Although the simulated effects of low soil and atmospheric water content on CO2 flux, presumably via reduction in stomatal aperture, also acted on transpiration, they were offset in the dry year by a higher vapour-pressure deficit. A sensitivity analysis identified the processes that were important in wet versus dry years, and on an intra-annual timeframe. Light-limited productivity dominated in both years, except for the driest period in the dry year. Vapour-pressure deficit affected productivity across more of each year than soil moisture, but both effects were larger in the dry year. The introduction of a reduced leaf area tended to decrease sensitivity in the dry year. Plant hydraulic architecture that increases plant available water, maximises productivity per unit water use and achieves lower sensitivity to low soil moisture levels should minimise production losses during dry conditions.

Persistence of Shiga toxin-producing Escherichia coli O26 in various manure-amended soil types

To evaluate the behaviour of Shiga toxin-producing Escherichia coli (STEC) O26 strains inoculated in manure-amended soils under in vitro conditions. Four green fluorescent protein (GFP)-labelled STEC O26 strains were inoculated in duplicate (at 10(6) CFU g(-1)) in three different manure-amended soil types, including two loam soils (A and B) and one clay loam soil (C), and two incubation temperatures (4 and 20 degrees C) were tested. STEC counts and soil physical parameters were periodically monitored. STEC O26 cells were able to persist during extended periods in soil even in the presence of low moisture levels, i.e. less than 0 x 08 g H2O g(-1) dry soil. At 4 and 20 degrees C, STEC could be detected in soil A for 288 and 196 days, respectively, and in soils B and C for at least 365 days postinoculation at both temperatures. The ambient temperature (i.e. 20 degrees C) was significantly associated with the highest STEC count decline in all soils tested. The temperature and soil properties appear to be contributory factors affecting the long-term survival of STEC O26 in manure-amended soils. This study provides useful information regarding the ecology of STEC O26 in manure-amended soils and may have implications for land and waste management.

Al2O3-coated microcantilevers for detection of moisture at ppm level

Abstract We have demonstrated that the Al 2 O 3 -modified microcantilevers (MCLs) can be used to detect low level of moisture. The detection limit for moisture in nitrogen was 10 ppm. The MCLs’ response time to moisture was less than 3 min. The sensors were stable for months stored under ambient conditions. The bending amplitudes were proportional to the moisture level and temperature, and the detection of moisture was not affected by alcohols in the environment.

Hospedeiras de Struthanthus flexicaulis (Loranthaceae) em campos rupestres ferruginosos no Quadrilátero Ferrífero, Minas Gerais

Parasitic plants constitute an interesting study template for several botanical and ecological in the studies. In Brazil, about 100 species of Loranthaceae have been described, among which several in the genus Struthanthus, aerial hemiparasites characterized by an haustorial root system. We evaluated the host specificity of S. flexicaulis Mart. in a 9-ha area of high-altitude ironstone fields in the “Iron Quadrangle”, MG. The plant community develops over canga couraçada, a compact substrate rich in heavy metals, with low levels of moisture and organic matter. Of the 85 vascular plant species that occur in the area, 44, distributed among 19 families, are parasitized by S. flexicaulis, and one is used only as support. Phanerophytes were the most common host life-form. The lack of specificity is common to other Loranthaceae, and appropriate for a resource-heterogeneous environment, where host specificity would not be advantageous.

Soil strength response of select soil disturbance classes on a wet pine flat in South Carolina

Harvest operations conducted under conditions of high soil moisture on a wet pine flat in South Carolina resulted in a high degree of soil surface disturbance. Less soil surface disturbance occurred when soil moisture content was lower. Soil strength varied by soil disturbance class in wet harvested locations and highly disturbed areas were associated with low soil strength and elevated levels of soil moisture. Soil strength levels in untrafficked locations were significantly higher than more disturbed classes including ruts greater than 0.20 m and puddled soils. The application of bedding to both wet and dry harvested locations lowered soil strength to less than 1.0 MPa in the upper 0.40 m. Mole plowing, in general, did not appear to have a significant impact on soil strength under the conditions of this study. However, soil strength of untrafficked areas increased when subjected to mole plowing. This may be the result of lowering soil moisture status and subsequently increasing soil strength in response to drier soil conditions. Further elaboration on the relationship among soil strength, disturbance conditions and machine trafficking is necessary to fully understand this complex interaction.

Actinomycete growth in conditions of low moisture

Actinomycete communities demonstrated a replacement of the generic composition in time as a function of soil moisture. Representatives of the genera Streptomyces, Micromonospora, Actinomadura, Saccharopolyspora, and Microbispora were repeatedly isolated from soil under different moisture conditions (field capacity, maximum molecular capacity, and maximum adsorption capacity). Representatives of some rare genera (Thermomonospora and Kibdelosporangium) were isolated from soil with low moisture levels inhibiting growth of more hydrophilic actinomycetes and bacteria. Spores of some actinomycetes could grow at low relative air humidity (RH) (50 and 67%). The complete growth cycle of all actinomycetes starting from spore germination to sporulation was observed only at RH of 98%.

Influence of moisture on the vital activity of actinomycetes in a cultivated low-moor peat soil

It was found that the actinomycetal complex of a cultivated low-moor peat soil is characterized by a high population density and diversity of actinomycetes; representatives of eleven genera were isolated from this soil: Streptomyces, Micromonospora, Actinomadura, Saccharopolyspora, Microbispora, Microtetraspora, Streptosporangium, Nocardioides, Saccharomonospora, Kibdelosporangium, and Thermomonospora. Some genera were isolated from the soil under all the studied levels of soil moisture. The so-called rare (rarely occurring) genera (Saccharomonospora, Kibdelosporangium, and Thermomonospora) were isolated upon the low level of soil moisture, which ensured an absence of competition from the more abundant actinomycetes. Spores of all the studied actinomycetes could germinate under the low moisture level (a w = 0.67). The level of moisture a w = 0.98 was found to be optimal for the development of the actinomycetes. The complete cycle of the development of all the actinomycetes up to spore formation occurring was only observed under the high moisture level (a w = 0.98).

Response of potato (Solarium tuberosum) tuber yield components to gel‐polymer soil amendments and irrigation regimes

Two field experiments were conducted to investigate the effects of two gel‐polymer formulations (pure and fertiliser‐fused) and moisture stress on yield and quality of potato (Solanum tuberosum). The experiments were carried out at the Hatfield Experimental Farm of the University of Pretoria, South Africa. Six gel‐polymer rates, consisting of pure gel polymer at 1.5kg/m3 of soil, with 85% and 70% fertiliser rate of the control, and fertiliser‐fused gel polymer at 1.5, 2, and 3kg/m3 soil, and control (without gel polymer) were assigned to the subplots. Four maximum allowable moisture depletion (MAD) levels, 25%, 40%, 55%, and 70% of the plant available soil moisture, were allocated to the main plots. Rate of phosphorus (P) was the same for all treatments (168kg/ha). Total nitrogen (N) and potassium (K) budget for the treatments (except one pure gel‐polymer treatment received 85%) were balanced to 70% of the control. The fertiliser‐fused gel polymer showed no substantial improvement in tuber yield parameters for all rates. The pure gel polymer, especially at higher fertiliser rate, improved total and marketable tuber yield. Marketable tuber number and yield, and total tuber mass showed declining trend with an increase in MAD. Significant reduction in tuber fresh and dry mass was observed at the 55% and 70% MAD irrigation levels. Both high and low soil moisture levels reduced tuber specific gravity. Incidence of common scab was inversely related to the irrigation frequency.