Nitrate losses in subsurface drainage from a corn-soybean rotation as affected by fall and spring application of nitrogen and nitrapyrin.

Substantial amounts of NO3 from agricultural crop production systems on poorly drained soils can be transported to surface water via subsurface drainage. A field study was conducted from the fall of 1993 through 2000 on a tile-drained Canisteo clay loam soil (fine-loamy, mixed, superactive, calcareous, mesic Typic Endoaquoll) to determine the influence of fall vs. spring application of N and nitrapyrin [NP; 2-chloro-6-(trichloromethyl) pyridine] on NO3 losses from a corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] rotation. Four anhydrous ammonia treatments (fall N, fall N + NP, spring preplant N, and spring N + NP) were replicated four times and applied at 135 kg N ha(-1) for corn on individual drainage plots. Drainage occurred in all seven years. Seventy-one percent of the annual drainage and 75% of the annual NO3 loss occurred in April, May, and June. Fifty-four percent of the NO3 lost in the drainage occurred during the corn phase and 46% during the soybean phase. Annual flow-weighted NO3-N concentrations for the fall, fall + NP, spring, and spring + NP treatments averaged 14.3, 11.5, 10.7, and 11.3 mg L(-1) during the corn phase but annual NO3-N concentrations were still > or =10 mg L(-1) in three of six years for the spring preplant treatment. Averaged across the six rotation cycles, flow-normalized NO3-N losses ranked in the order: fall N > spring N + NP > fall N + NP > spring N. Under these conditions, NO3 losses in subsurface drainage from a corn-soybean rotation can be reduced 14% by spring N and 10% by late fall N + NP compared with fall-applied N. Nitrate losses were not appreciably reduced by adding NP to spring preplant N.

Nitrate losses in subsurface drainage from a corn-soybean rotation as affected by time of nitrogen application and use of nitrapyrin.

Subsurface drainage, a water management practice used to remove excess water from poorly drained soils, can transport substantial amounts of NO3 from agricultural crop production systems to surface waters. A field study was conducted from the fall of 1986 through 1994 on a tile-drained Canisteo clay loam soil (fine-loamy, mixed, superactive, calcareous, mesic Typic Endoaquoll) to determine the influence of time of N application and use of nitrapyrin [NP; 2-chloro-6-(trichloromethyl) pyridine] on NO3 losses from a corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] rotation. Four anhydrous ammonia treatments [fall N, fall N + NP, spring preplant N, and split N (40% preplant and 60% sidedress)] were replicated four times and applied at 150 kg N ha(-1) for corn on individual drainage plots. Sixty-two percent of the annual drainage and 69% of the annual NO3 loss occurred in April, May, and June. Flow-weighted NO3-N concentrations in the drainage water were two to three times greater in the two years following the three-year dry period compared with preceding and succeeding years. Nitrate N concentrations and losses in the drainage from corn were greatest for fall N with little difference among the other three N treatments. Nitrate losses from soybean were affected more by residual soil NO3 following corn than by the N treatments per se. Averaged across the four rotation cycles, flow-normalized NO3-N losses ranked in the order: fall N > split N > spring N = fall N + NP. Under these conditions NO3 losses from a corn-soybean rotation into subsurface drainage can be reduced by 13 to 18% by either applying N in the spring or using NP with late fall-applied ammonia.

EPIC tile flow and nitrate loss predictions for three Minnesota cropping systems.

Subsurface tile drains are a key source of nitrate N (NO3-N) losses to streams in parts of the north central USA. In this study, the Erosion Productivity Impact Calculator (EPIC) model was evaluated by comparing measured vs. predicted tile flow, tile NO3-N loss, soil profile residual NO3-N, crop N uptake, and yield, using 4 yr of data collected at a site near Lamberton, MN, for three crop rotations: continuous corn (Zea mays L.) or CC, corn-soybean [Glycine max (L.) Merr.] or CS, and continuous alfalfa (Medicago sativa L.) or CA. Initially, EPIC was run using standard Soil Conservation Service (SCS) runoff curve numbers (CN2) for CC and CS; monthly variations were accurately tracked for tile flow (r2 = 0.86 and 0.90) and NO3-N loss (r2 = 0.69 and 0.52). However, average annual CC and CS tile flows were underpredicted by -32 and -34%, and corresponding annual NO3-N losses were underpredicted by -11 and -52%. Predicted average annual tile flows and NO3-N losses generally improved following calibration of the CN2; tile flow underpredictions were -9 and - 12%, whereas NO3-N losses were 0.6 and -54%. Adjusting a N parameter further improved predicted CS NO3-N losses. Predicted monthly tile flows and NO3-N losses for the CA simulation compared poorly with observed values (r2 values of 0.27 and 0.19); the annual drainage volumes and N losses were of similar magnitude to those measured. Overall, EPIC replicated the relative impacts of the three cropping systems on N fate.

Nitrate nitrogen in surface waters as influenced by climatic conditions and agricultural practices.

Subsurface tile drainage from row-crop agricultural production systems has been identified as a major source of nitrate entering surface waters in the Mississippi River basin. Noncontrollable factors such as precipitation and mineralization of soil organic matter have a tremendous effect on drainage losses, nitrate concentrations, and nitrate loadings in subsurface drainage water. Cropping system and nutrient management inputs are controllable factors that have a varying influence on nitrate losses. Row crops leak substantially greater amounts of nitrate compared with perennial crops; however, satisfactory economic return with many perennials is an obstacle at present. Improving N management by applying the correct rate of N at the optimum time and giving proper credits to previous legume crops and animal manure applications will also lead to reduced nitrate losses. Nitrate losses have been shown to be minimally affected by tillage systems compared with N management practices. Scientists and policymakers must understand these factors as they develop educational materials and environmental guidelines for reducing nitrate losses to surface waters.

Seepage from deep bedded and poultry litter systems.

The work reported indicates that there could be a potential of ground water pollution by NO3-N from turkey facilities built on both sandy and clay soils. At four different depths (30.54, 61.08, 91.62, and 122.16 cm), the NO3-N levels for the clay soil were 1572, 497, 66, and 28 ppm, and those for the sandy soil were 293, 425, 324, and 164 ppm, respectively. No significant P increases were observed but there did exist a significant increase of K in the topsoil for both clay and sandy turkey structures. The results show that swine hoop houses with less than three or four years of age may not pose a threat to groundwater pollution due to the leaching of nutrients. The only dairy feedlot sampled in this study, although it has been used for more than 20 years, did not show leaching of NO3-N and P. However, it did show a significantly elevated concentration of potassium in the topsoil, as compared to the background sample. More sites should be investigated to verify this.

Cytokine-mediated inhibition of erythropoietin synthesis by dexamethasone.

The effect of inflammatory cytokines on the in-vitro synthesis of erythropoietin by HepG2 cells was evaluated. Monocyte-conditioned medium, and the cytokines interleukin-1 beta, interleukin-6 and tumour necrosis factor-alpha all reduced synthesis of erythropoietin. The steroidal anti-inflammatory drug, dexamethasone, did not affect cytokine-mediated erythropoietin inhibition. Dexamethasone did cause a reduction in the secretion of erythropoietin inhibitory cytokines from monocytes. These results point to a possible therapeutic approach in the treatment of anaemia caused by suppression of erythropoietin synthesis by monocytic cytokines.

Elevated serum progesterone values at the time of ovulation induction in luteal leuprolide acetate-down-regulated GIFT cycles are associated with decreased clinical pregnancy rates.

PURPOSE: The effects of premature luteinization of ovarian follicles as detected by elevated progesterone values on the day of human chorionic gonadotropin induction of ovulation were evaluated in 38 consecutive gamete intrafallopian transfer (GIFT) retrieval cycles. MATERIALS AND METHODS: All patients received leuprolide acetate beginning in the midluteal phase of their prior menstrual cycle, followed by gonadotropin stimulation of folliculogenesis. At least four oocytes were transferred in each cycle. RESULTS: No significant differences in gonadotropin dosage, total number of days of gonadotropins, age, number of prior pregnancies, years of infertility since last pregnancy, total number of eggs retrieved, mature residual oocytes, fertilization of mature residual oocytes, or primary etiology of infertility were observed between groups; however, estradiol concentrations were significantly higher in the group with elevated progesterone values (2573 +/- 216 pg/ml) compared to the lower progesterone group (1925 +/- 202 pg/ml, P = 0.035) and the total number of oocytes transferred was greater in the high progesterone group (7.5 +/- 0.5) vs the low progesterone group (6.3 +/- 0.3, P < 0.038). P4 concentrations < or = 0.8 ng/ml were associated with significantly higher pregnancy rates (11/19; 57.9%) compared to progesterone concentrations > 0.8 ng/ml (5/19, 26.3%; P = 0.050). CONCLUSIONS: Premature luteinization may occur in luteal leuprolide acetate-down-regulated patients and progesterone values > 0.8 ng/ml are associated with significantly lower pregnancy rates in GIFT cycles.

Synergy between tumor necrosis factor and endotoxin decreases early embryo development in vitro.

The purpose of the present study was to investigate the individual and combined effects of low levels of endotoxin and physiological levels of tumor necrosis factor on in vitro fertilization and preimplantation embryo development. B6D2F1 mice were superovulated by utilizing pregnant mare serum gonadotropin and human chorionic gonadotropin. Oocyte-cumulus complexes (3221 oocytes) were collected, pooled, and randomized into control and treatment groups. Sperm were collected from the caudae epididymides of mature male mice and allowed to capacitate. Treatments included culture media supplemented with increasing amounts of endotoxin (0.5, 1.0, and 2.0 ng/ml; sp act, 3000 IU/ng) and/or tumor necrosis factor (1, 10, and 50 pg/ml; sp act, 0.01 IU/pg) throughout the fertilization and preimplantation development process. Percentage cleavage and percentage expanded blastocyst formation were evaluated. No significant effects were observed for percentage cleavage or percentage expanded blastocyst formation in either the endotoxin (E) or the tumor necrosis factor (TNF) groups. The combination of endotoxin and tumor necrosis factor at any of the levels tested did not significantly decrease cleavage; however, percentage blastocyst formation was decreased with any combination of TNF and E (P less than 0.05-P less than 0.001). We conclude that TNF and E exert significant synergistic effects which are detrimental to in vitro preimplantation embryonic development.

Prolactin enhances uteroglobin gene expression by uteri of immature rabbits.

The effect of prolactin on uteroglobin production by immature rabbits was studied with neonatal (1 day old) and juvenile (14 days old) does. The animals were divided into 11 treatment groups for each age category and exposed to a 9-day injection protocol. Each day the animals received a subcutaneous injection of oestradiol-17 beta and/or ovine prolactin and/or progesterone, or were sham-injected. Juvenile animals, which received 100 micrograms oestradiol/kg 24 h-1, plus progesterone or plus prolactin and progesterone, produced detectable amounts of uteroglobin in the uterine secretions (0.034 +/- 0.010 mg uteroglobin/mg total protein and 0.098 +/- 0.03 l mg uteroglobin/mg total protein, respectively). None of the animals in the other juvenile treatment groups or any of the neonatal groups produced uteroglobin. From this survey it was apparent that uteroglobin secretion could be induced by exogenous oestradiol and progesterone in rabbits treated as early as 14 days of age, and that the added supplementation of prolactin enhanced the response to the ovarian steroids. As a result, additional juvenile animals were injected with 100 micrograms oestradiol +/- prolactin + progesterone and the effects of these two treatments were quantitated as follows: uteroglobin mRNA levels by slot-blot hybridization; endometrial surface area by computerized image analysis; and oestrogen, progesterone and prolactin receptors by immunocytochemistry. Prolactin modified the response of the juvenile rabbit uterus to oestradiol + progesterone for all parameters tested.

Isolation, in vitro maturation, and fertilization of germinal vesicle oocytes obtained from the intact murine ovary.

The purpose of this investigation was to attempt to develop a process, utilizing a murine model, which would allow more efficient harvesting from the intact ovary and maturation in vitro of germinal vesicle (GV) oocytes. The recovery process yielded 25.5 +/- 4.5 (mean +/- SE) cumulus-free GV oocytes per animal. Treatment groups included culture medium (CM) supplemented with either estradiol (E2), follicle stimulating hormone (FSH), human chorionic gonadotropin (hCG), or prolactin (PRL). Among the hormone-free controls 83.2 +/- 1.6% of oocytes underwent GV breakdown, whereas 25.3 +/- 2.6% developed to the first polar body stage (PB-1) following 18 hr of incubation (n = 29 trials). Oocytes progressing to the PB-1 stage were inseminated in vitro. In vitro fertilization (IVF) of pooled in vitro matured (IVM) PB-1 oocytes (judged by two-cell formation) was 19.9%, which was significantly lower than in the group of in vivo matured oocytes (74.4%). E2 significantly increased the percentage of GV breakdown (control, 76.8 +/- 2.5%; E2 at 10 ng/ml, 92.9 +/- 2.5%, P less than 0.001; E2 at 100 ng/ml, 93.7 +/- 2.1%, P less than 0.001; and E2 at 1 micrograms/ml, 86.7 +/- 3.3%, P less than 0.05) but not PB-1 formation. Neither FSH nor hCG significantly increased GV breakdown or PB-1 formation.(ABSTRACT TRUNCATED AT 250 WORDS)

Preimplantation murine embryos are more resistant than human embryos to bacterial endotoxins.

Bacterial endotoxins have been correlated with increased fragmentation of early cleavage-stage human embryos and decreased pregnancy rates in human in vitro fertilization programs. The purpose of the present study was to test the direct effects of increasing concentrations of endotoxins on in vitro fertilization and development of mouse embryos to the blastocyst stage. Sexually mature B6D2F1 female mice were superovulated and oocytecumulus complexes were collected from the oviducts and randomized into control and treatment groups. Oocytes (n = 867) were inseminated with capacitated sperm. Treatments included Ham's F-10 supplemented with 3 mg/ml bovine serum albumin and increasing amounts of endotoxin (0.35, 0.64, 0.92, 1.5, 2.08, 3.21, 6.07, and 11.79 ng/ml). Percentage cleavage, percentage fragmentation at the four-cell stage, and percentage expanded blastocyst formation (of cleaved embryos) were evaluated. Statistically significant decreases in cleavage at 6.07 ng/ml (P less than 0.05) and blastocyst formation at 11.79 ng/ml (P less than 0.05) of endotoxin were observed. Fragmentation at the four-cell stage was significantly increased at 3.21 ng/ml (P less than 0.05) of endotoxin. We conclude that the levels of endotoxin necessary to decrease murine preimplantation development significantly is higher than that reported for human embryos.

Nitrate-N in the soil profile and tile drainage water as influenced by tillage.

Conservation tillage systems facilitate the infiltration of greater amounts of precipitation into the soil profile by reducing surface runoff. Concern has developed among some scientists because higher infiltration and percolation rates are often linked to potentially higher leaching losses of agricultural chemicals. Soil samples were taken in 1 foot increments to a depth of 5 feet to ascertain the accumulation and distribution of nitrate-nitrogen (NO3-N) in the soil profile as influenced by tillage. Two long-term tillage studies on fine-textured, clay loam soils were sampled in July and November 1977 following 2 years of limited rainfall. Nitrate-N accumulation in the 0 to 3 foot profile in late July was reduced by 75% (no tillage) to 38% (chisel plow) compared with the conventional moldboard tillage system in this 8-year-old study. Accumulation in the 0 to 5 foot profile after harvest was 751, 546, 345, and 198 lb NO3-N/A for the moldboard plow, chisel-plow, disk-, and no-tillage systems, respectively. Another 3 year study showed accumulations of 625, 619, 468, and 391 pounds NO3-N/A after harvest with the moldboard plow, ridge-plant, chisel-plow, and no-tillage systems, respectively. These data indicate that tillage can have substantial effects on the accumulation of NO3 in soils and that additional research is needed to determine the mechanisms responsible for these differences.

Blood pressure and plasma renin activity responses to chronic stress in the borderline hypertensive rat.

The purpose of this study was to examine the systolic blood pressure and plasma renin activity (PRA) responses to chronic stress in normotensive rats and in rats with one hypertensive parent. Twenty-four male Wistar-Kyoto (WKY) and 24 male F1 offspring of spontaneously hypertensive and WKY rats (BHR) were randomly assigned to 3 groups of 8 each. Experimental (E) animals were subjected to 2 hr daily of shock-shock conflict. Each response produced a 0.2 sec, 0.2-0.4 mA cutaneous electric shock. Failure to respond in 10 sec resulted in a train of 5 shocks (0.2 sec each sec). Yoked animals (Y) received the same shocks as E but had no control over their presentation. Finally, a control group (C) for maturation received no shocks. The E and Y animals were subjected to 14 weeks of conflict and were then monitored an additional 14 weeks in the absence of shock. All animals had their tail cuff blood pressures taken weekly except for 3 times when bloods were obtained for PRA assays. Analysis of blood pressure data revealed that:(1) BHR animals showed more of a blood pressure response to shock than WKY animals; (2) Y animals showed more of a response to conflict than E, especially for the BHR group; and (3) BHR shocked animals remained permanently elevated compared to BHR control animals even in the 14 week post-conflict period during which no shocks were given. Although PRAs for BHR animals were significantly higher than for WKY at the beginning of study, the stress-induced hypertension was associated with either normal or suppressed PRA values, suggesting that the hypertension in these animals is not a high renin hypertension.