Anne M. Parkhurst

Changes in soil microbial community structure with tillage under long-term wheat-fallow management

Fatty acid methyl esters (FAMEs) were used to ‘fingerprint’ soil microbial communities that evolved during 25 years of wheat-fallow cropping following native mixed prairie sod at Sidney, Nebraska, USA. Total ester-linked FAMEs (EL-FAMEs) and phospholipid-linked FAMEs (PL-FAMEs) were compared for their ability to discriminate between plots remaining in sod and those cropped to wheat or left fallow under no-till, sub-till or plow management. Cropped plots were higher in microbial biomass than their fallowed counterparts, and did not diAer significantly with tillage for the 0‐15 cm depth. Under fallow, microbial biomass was greatest in no-till and least in plow. Both cluster and discriminant analysis of PL- and EL-FAMEs clearly separated the remaining native sod plots from the existing wheat-fallow plots. This separation was particularly pronounced for the EL-FAMEs and was largely driven by high amounts in sod of a single FAME, C16:1(cis11), which has been cited as a biomarker for arbuscular mycorrhizal (AM) fungi. Within wheat-fallow, C16:1(cis11) declined significantly from no-till to plow, which supports the origin of C16:1(cis11) from extraradical mycelium and spores of AM fungi known to be sensitive to soil disturbance. Although discriminant analysis of PL- and EL-FAMEs diAerentiated wheat and fallow systems by tillage, discrimination among tillage treatments was expressed most strongly during fallow. FAME profiles from fallow plow were most dissimilar from cropped soils which suggests a relationship between tillage management and the long-term resiliency of the microbial community developed under the wheat crop. 7 2000 Elsevier Science Ltd. All rights reserved.

Effect of farnesol on a mouse model of systemic candidiasis, determined by use of a DPP3 knockout mutant of Candida albicans.

ABSTRACT This work extends our previous observation that the fungus Candida albicans secretes micromolar levels of farnesol and that accumulation of farnesol in vitro prevents the yeast-to-mycelium conversion in a quorum-sensing manner. What does farnesol do in vivo? The purpose of this study was to determine the role of farnesol during infection with a well-established mouse model of systemic candidiasis with C. albicans A72 administered by tail vein injection. This question was addressed by altering both endogenous and exogenous farnesol. For endogenous farnesol, we created a knockout mutation in DPP3, the gene encoding a phosphatase which converts farnesyl pyrophosphate to farnesol. This mutant (KWN2) produced six times less farnesol and was ca. 4.2 times less pathogenic than its SN152 parent. The strain with DPP3 reconstituted (KWN4) regained both its farnesol production levels and pathogenicity. These mutants (KWN1 to KWN4) retained their full dimorphic capability. With regard to exogenous farnesol, farnesol was administered either intraperitoneally (i.p.) or orally in the drinking water. Mice receiving C. albicans intravenously and farnesol (20 mM) orally had enhanced mortality (P < 0.03). Similarly, mice (n = 40) injected with 1.0 ml of 20 mM farnesol i.p. had enhanced mortality (P < 0.03), and the onset of mortality was 30 h sooner than for mice which received a control injection without farnesol. The effect of i.p. farnesol was more pronounced (P < 0.04) when mice were inoculated with a sublethal dose of C. albicans. These mice started to die 4 days earlier, and the percent survival on day 6 postinoculation (p.i.) was five times lower than for mice receiving C. albicans with control i.p. injections. In all experiments, mice administered farnesol alone or Tween 80 alone remained normal throughout a 14-day observation period. Finally, beginning at 12 h p.i., higher numbers of C. albicans cells were detected in kidneys from mice receiving i.p. farnesol than in those from mice receiving control i.p. injections. Thus, reduced endogenous farnesol decreased virulence, while providing exogenous farnesol increased virulence. Taken together, these data suggest that farnesol may play a role in disease pathogenesis, either directly or indirectly, and thus may represent a newly identified virulence factor.

NITRATE LEACHING IN IRRIGATED CORN AND SOYBEAN IN A SEMI-ARID CLIMATE

Nitrate-nitrogen leached from the root zone of land in intensive corn production is a major groundwater contaminant in some of the intensively irrigated regions of the western Cornbelt, including central and western Nebraska. To obtain a clearer understanding of the amount and timing of nitrate leaching losses from irrigated crops, 14 monolithic percolation lysimeters were installed in 1989-1990 in sprinkler irrigated plots at the University of Nebraska’s West Central Research and Extension Center near North Platte, Nebraska. The lysimeters were used to provide a direct measure of leachate depth from continuous corn and a corn-soybean rotation. Both cropping systems were sprinkler irrigated and used current best management practices (BMPs) in the region for water and nitrogen management. Leachate was collected from 1990 through 1998 and analyzed for nitrate-N concentration. Results for the period 1993- 1998 are reported here. In the semi-arid climate of West-Central Nebraska, the interaction of rainfall patterns with the period of active uptake of water by crops played a major role in defining leaching patterns. Careful irrigation scheduling did not eliminate leaching during the growing season. There was no significant difference in drainage depth between continuous corn and the corn-soybean rotation. The average drainage depth among the lysimeters was 218 mm yr–1. This was more than expected, and in part resulted from above normal precipitation during several years of the study. No water quality benefit was found for the corn-soybean rotation as compared to continuous corn. Nitrate-N concentration in the leachate from continuous corn averaged 24 mg L–1, while that from the corn-soybean rotation averaged 42 mg L–1. Total yearly nitrate leaching loss averaged 52 kg ha–1 for continuous corn and 91 kg ha–1 for the rotation. This represents the equivalent of 27% and 105% of the amount of N fertilizer applied over the six years of study. In calculating N fertilizer needs for corn in Nebraska, the recommended legume N credit of 50 kg ha –1 for a preceding crop of soybean may be too low under irrigated production.

EVAPORATION FROM SOIL INFLUENCED BY CROP SHADING, CROP RESIDUE, AND WETTING REGIME

ABSTRACT Soil evaporation (E) was measured with mini-lysimeters 225 mm deep and 150 mm in diameter over the growing season in 1986 and 1987. Mini-lysimeters were placed in com field plots under dryland, limited irrigation and full irrigation water regimes, with or without canopy shading and with or without straw mulch. Soil water content in the mini-lysimeters was periodically matched to that in the surrounding field. Mean daily E was calculated and the effects of canopy shading and straw mulch were analyzed. No significant differences in E between mini-lysimeters at different row positions under the corn canopy were observed. Shading by the corn canopy significantly reduced E 0.3 to 0.5 mm d-i under dryland, 0.6 to 0.7 mm d-i under limited irrigation, and 1.2 mm d-i under full irrigation. The presence of a straw mulch significantly reduced E 0 to 0.1 mm d-l under dryland, 0.5 mm d-i under limited irrigation, and 0.9 to 1.1 mm d-i under full irrigation. The crop canopy played a more important role in reducing soil E than straw mulch under dryland. Under limited or full irrigation the crop canopy and straw mulch contributed equally to E reduction. Combined reduction of mean daily E by the crop canopy and straw mulch was approximately 0.5, 1.0, and 2.0 mm d-l for dryland, limited irrigation, and full irrigation wetting frequencies, respectively. KEYWORDS. Soil evaporation, Lysimeters.

Evaluation of Serotonin as a Feedback Inhibitor of Lactation in the Bovine

Serotonin (5-HT), a neurotransmitter synthesized from tryptophan, has been proposed as a feedback inhibitor of lactation. We determined that the gene coding for tryptophan hydroxylase 1, the rate-limiting enzyme for 5-HT synthesis, is expressed in bovine mammary epithelial cells in vitro and is upregulated by prolactin. In addition, 5-HT reduced the expression of alpha-lactalbu-min and casein genes in vitro. Furthermore, inhibiting 5-HT synthesis with p-chlorophenylalanine or blocking the 5-HT receptor with methysergide (METH) increased milk protein gene expression. We then evaluated effects of intramammary 5-HT or METH infusion on production and milk composition in 6 multiparous Holstein cows. Cows were assigned to a repeated measures design of contralateral intramammary infusions of METH (20 mg/quarter per d) or saline for 3 d followed by a 7-d washout period before administering 5-HT (50 mg/quarter/d) or SAL for 3 d. For each udder half, milk yield was recorded twice and composition was determined once per day. Blood samples were harvested each day for plasma to determine glucose and nonesterified fatty acid concentrations. Evaporative heat loss, respiration rate, left and right udder temperatures, and rectal temperatures were obtained after each milking to evaluate possible systemic effects of infusions. During METH and saline infusions milk yield increased 10.9%. During 5-HT and saline infusion milk yield decreased 11.1%. Milk yield and physiological responses suggested intramammary 5-HT and METH doses were high enough to cause systemic effects. Infusing saline, METH, and 5-HT increased milk SCC. Infusing 5-HT tended to reduce mean lactose concentration (4.3 vs. 4.6%) relative to saline. Milk protein content was decreased by METH and SAL (2.0%) and was increased (5.8%) by 5-HT followed by a 33% decrease postinfusion. Infusion of METH increased evaporative heat loss 11%, which decreased 11% postinfusion. Infusions of 5-HT or METH did not affect plasma nonesterified fatty acid or glucose concentrations, respiration rate, or milk fat content. We conclude 5-HT infusion reduced milk synthesis, whereas blocking the 5-HT receptor with METH increased milk synthesis. Doses of 5-HT and METH used in this study likely resulted in systemic effects. These data support the concept that 5-HT is a feedback inhibitor of lactation in the bovine.

Asian Salted Noodle Quality: Impact of Amylose Content Adjustments Using Waxy Wheat Flour

ABSTRACT Fourteen flour blends of two natural wild-type wheat (Triticum aestivum L.) flours, ‘Nuplains’ and ‘Centura’, blended with one waxy flour sample were characterized and processed to Asian salted noodles. The flour amylose content range was <1–29%. Damaged starch contents were 10.4, 7.0, and 6.6% for the waxy wheat, Nuplains, and Centura, respectively. The waxy flour farinograph water absorption was as high as 79.5%, ≈20% higher than the wild-type flours. Because two types of starch granules (wild-type and waxy) existed in the flour blends, two peaks at 82°C (waxy) and 95°C (wild-type) were found in the RVA pasting curves. Reduced amylose content caused high flour swelling volume and power and low falling number. Significant effects of flour amylose content on noodle processing and textural (eating) qualities were found in the study. Noodle qualities, as reflected in covariate analysis, were not significantly affected by the flour blends protein content, SDS-sedimentation volume, mixograph dough d...

On-farm experiment designs and implications for locating research sites

Research plots that are large enough to accommodate regular farm machinery are thought to contain too much field variation to allow reliable interpretation of experimental results. This study was conducted to determine whether experimental error was controlled on a wide variety of agricultural field trials that used plots larger than normally used by researchers. The investigation included trials conducted on an experiment station and trials conducted on actual commercial farms. The planning and management of the experiments ranged from those completely conducted by university researchers to those completely done by farmers. The level of experimental error in all the trials was well within the limits normally accepted by researchers in agronomy. Plots ranging in length from 125 to 1200 feet and as wide as one or two passes of standard farm machinery gave experimental results that were statistically sound. Statistical requirements for randomization and replication were all met. The ability to use large plots and farmer participation enhances the testing of new technology on farms. This leads to new opportunities to test crop production factors in a systems setting under actual farm conditions. The statistical reliability of the on-farm designs analyzed in this study should increase cooperation among researchers, extension workers, and farmers in research activities.

Design, Installation, and Performance of Percolation Lysimeters for Water Quality Sampling

Lysimeters are the primary research tool for measuring percolation and water quality. Monolithic percolation lysimeters were evaluated for measuring the quantity and quality of leachate from the root zone of irrigated crops. Six percolation lysimeters were installed in a continuous corn (Zea Mays, L.) cropping system near North Platte, Nebraska, during the fall of 1988 and spring 1989. The lysimeters were 0.9 m in diameter and 2.4 m deep. They were filled with undisturbed soil using a hydraulic pull-down method. Porous stainless steel extractors were installed vertically upward into the lysimeter bottoms, and leachate was extracted from the unsaturated soil. Leachate volume, volumetric soil water content, soil temperature, and soil bulk density were measured. Isolation of a large soil monolith in the lysimeter did not significantly affect plant growth, soil bulk density, or temperature. Soil water content near the lysimeter bottoms was greater than in the surrounding field after a wet spring in 1991. However, extractors removed most excess water and adequately matched unsaturated drainage in the field. Though leachate varied among lysimeters, they behaved similarly over time. Results will help relate irrigation management and scheduling strategies to potential leaching of soil water and associated chemicals into groundwater.

Relationships among grain sorghum quality factors

ABSTRACT Correlations among grain sorghum quality factors (proximate composition, physical properties, and water absorption properties) were evaluated. Samples of 46 commercial hybrids (24 and 22 from crop years 1993 and 1994) were analyzed for starch, protein, crude free fat, test weight, absolute density, 1,000 kernel weight, percent kernel abraded, water absorption index, initial water absorption rate, and moisture saturation point. Test weight, absolute density, and percent kernel abraded were positively correlated among themselves (r > 0.5). Protein was negatively correlated with both test weight and absolute density (r < -0.5), while moisture saturation point showed negative correlations with test weight, absolute density, 1,000 kernel weight, and percent kernel abraded (r < -0.4). Principal component factor analysis through the covariance matrix explained 95% of the total variation of quality factors among hybrids (two factors), and, through the correlation matrix, 85% of the total variation (five ...

Wheat tortilla quality: Impact of amylose content adjustments using waxy wheat flour

ABSTRACT Amylose content is closely related to wheat flour pasting or thermal properties, and thus affects final food qualities. Fourteen flour blends with amylose content ranges of <1 to 29% were used to study tortilla production and quality parameters. Reduced amylose contents decreased dough stickiness and pliability; low amylose doughs were also very smooth in appearance. Very low flour amylose content was associated with earlier tortilla puffing and poor machinability during baking, darker color, low opacity, larger diameters, and reduced flexibility after storage. Tortilla texture analysis indicated that lowering amylose content gave fresh tortillas higher extensibility; after three or more days storage, however, low amylose flours required more force to break the tortillas and the rupture distances became shorter. These results, as reflected in covariate analysis, were not significantly affected by the flour blends protein content, swelling volume/power, SDS-sedimentation volume, mixograph dough d...