Narrowing the agronomic yield gap with improved nitrogen use efficiency: a modeling approach.

Improving nitrogen use efficiency (NUE) in the major cereals is critical for more sustainable nitrogen use in high-input agriculture, but our understanding of the potential for NUE improvement is limited by a paucity of reliable on-farm measurements. Limited on-farm data suggest that agronomic NUE (AE(N)) is lower and more variable than data from trials conducted at research stations, on which much of our understanding of AE(N) has been built. The purpose of this study was to determine the magnitude and causes of variability in AE(N) across an agricultural region, which we refer to as the achievement distribution of AE(N). The distribution of simulated AE(N) in 80 farmers' fields in an irrigated wheat system in the Yaqui Valley, Mexico, was compared with trials at a local research center (International Wheat and Maize Improvement Center; CIMMYT). An agroecosystem simulation model WNMM was used to understand factors controlling yield, AE(N), gaseous N emissions, and nitrate leaching in the region. Simulated AE(N) in the Yaqui Valley was highly variable, and mean on-farm AE(N) was 44% lower than trials with similar fertilization rates at CIMMYT. Variability in residual N supply was the most important factor determining simulated AE(N). Better split applications of N fertilizer led to almost a doubling of AE(N), increased profit, and reduced N pollution, and even larger improvements were possible with technologies that allow for direct measurement of soil N supply and plant N demand, such as site-specific nitrogen management.

Mechanisms of nitrogen retention in forest ecosystems: a field experiment.

Intensive forest management led to elevated losses of nitrogen from a recently harvested loblolly pine plantation in North Carolina. Measurements of nitrogen-15 retention in the field demonstrated that microbial uptake of nitrogen during the decomposition of residual organic material was the most important process retaining nitrogen. Management practices that remove this material cause increased losses of nitrogen to aquatic ecosystems and the atmosphere.

Exchange of materials between terrestrial ecosystems and the atmosphere.

Many biogenic trace gases are increasing in concentration or flux or both in the atmosphere as a consequence of human activities. Most of these gases have demonstrated or potential effects on atmospheric chemistry, climate, and the functioning of terrestrial ecosystems. Focused studies of the interactions between the atmosphere and the biosphere that regulate trace gases can improve both our understanding of terrestrial ecosystems and our ability to predict regional-and global-scale canges in atmospheric chemistry.

Agricultural intensification and ecosystem properties.

Expansion and intensification of cultivation are among the predominant global changes of this century. Intensification of agriculture by use of high-yielding crop varieties, fertilization,irrigation, and pesticides has contributed substantially to the tremendous increases in food production over the past 50 years. Land conversion and intensification,however, also alter the biotic interactions and patterns of resource availability in ecosystems and can have serious local, regional, and global environmental consequences.The use of ecologically based management strategies can increase the sustainability of agricultural production while reducing off-site consequences.

Biological Invasion by Myrica faya Alters Ecosystem Development in Hawaii.

The exotic nitrogen-fixing tree Myrica faya invades young volcanic sites where the growth of native plants is limited by a lack of nitrogen. Myrica quadruples the amount of nitrogen entering certain sites and increases the overall biological availability of nitrogen, thereby altering the nature of ecosystem development after volcanic eruptions.

Reproductive physiology of the female greater bilby (Macrotis lagotis Thylacomyidae): evidence for a male-induced luteal phase.

Endocrinology of the oestrous cycle, pregnancy and early lactation was investigated in captive Western Australian greater bilbies (Macrotis lagotis). Initially, six females were monitored for changes in urogenital cytology, plasma progestogen, pericloacal and pouch morphology in the absence of a male. This was followed by the introduction of a male and a reproductive assessment through mating, gestation and early lactation. In the absence of a male, there was no cyclical pattern of urogenital cytology, pericloacal or pouch development, and progestogen concentrations remained basal. Within 5 days of the introduction of a male, all females had a karyopycnotic index of 100%. Spermatozoa were present in the urogenital smear within 3 days of male introduction in all five females that gave birth. Five to 9 days after the introduction of a male, there was an increase in plasma progestogen concentration that remained elevated for 14-19 days. Six of the seven females gave birth approximately 3 days after reaching peak plasma progestogen concentrations. Gestation length ranged between 14 and 17 days. Plasma progestogen concentrations of the postpartum and early lactation period were lower (P < 0.0001) than during gestation, but greater (P < 0.0001) than those recorded before the introduction of a male. One female that gave birth early in the study that was examined until weaning of the pouch young showed a cyclical pattern of plasma progestogen secretion that ended at weaning. This study provides evidence that the luteal phase in the greater bilby is induced by the presence of a male. Similar to female reproductive physiology in the Peramelidae, elevated progestogen concentration in the greater bilby was extended into lactation.

Eosinophilia-myalgia syndrome. Natural history in a population-based cohort.

BACKGROUND: To determine the natural history of eosinophilia-myalgia syndrome, we followed up all patients with eosinophilia-myalgia syndrome reported to the Oregon Health Division, Portland, during the recent epidemic caused by contaminated tryptophan. METHODS: Patients were interviewed by telephone from 1 to 5 months after illness onset and again at least 12 months after onset. Symptoms (type, onset, and duration), overall disability, treatment, and tryptophan lot and dose were assessed for each patient. RESULTS: Information was obtained for 55 (96%) of 57 case-patients: 53 patients completed interviews and two patients had died. For the 53 patients who were interviewed, symptoms with onset more commonly during the first 3 months of illness included severe myalgias, fatigue, generalized weakness, edema, and rash. Symptoms with later onset included paresthesias, muscle cramps, extremity weakness, and alopecia. At 12 months, 41 patients (77%) continued to report fatigue, 36 (68%) weakness, and 34 (64%) myalgias; 26 patients (49%) had difficulty climbing stairs, 23 (43%) had difficulty getting up from a chair, and 15 (28%) had difficulty holding a cup. Higher doses of tryptophan were correlated with more severe disability, both initially (rs = .33) and at follow-up (rs = .42). Although most patients reported improvement in symptoms at 12 months, only 14 (26%) patients reported that they were able to perform all normal daily activities. CONCLUSIONS: Most patients with eosinophilia-myalgia syndrome in this population-based cohort are still symptomatic 1 year after onset, primarily with the complaints reported early in the illness. The association between degree of disability and daily tryptophan dose suggests that ingestion of varying amounts of contaminant may be responsible, in part, for the severity of symptoms experienced by individual patients.

Cardiac effects of standard-dose halofantrine therapy.

The antimalarial drug halofantrine hydrochloride has been associated with cardiac arrhythmias. This is a report of a study on the cardiac effects of standard-dose halofantrine (24 mg/kg) on a sample of 48 patients selected from a group of 402 Dega (Montagnard) refugees treated for Plasmodium falciparum infection. Prolongation of the rate-corrected QT interval (QTc) on the electrocardiogram (ECG) was used as an indicator of risk for halofantrine-associated cardiac arrhythmias. We found that standard-dose halofantrine was associated with a lengthening of the mean QTc from 0.04 sec(1/2) to 0.44 sec(1/2). Two patients had a QTc increase of greater than 25%, but none had a follow-up QTc of more than 0.55 sec(1/2), an interval length generally considered to be a risk factor for ventricular arrhythmias. Regression analysis indicated that pretreatment ECGs were poorly predictive of QTc lengthening during therapy, although pretreatment ECGs may be useful to evaluate patients with pre-existing cardiac conditions. The manufacturer has recommended that the halofantrine dose not exceed 24 mg/kg and revised the list of medication contraindications to include some cardiac conditions. Clinicians should weigh a patient's risk, including history of cardiac disease and availability of alternative therapy before use of halofantrine.

Imported malaria in Montagnard refugees settling in North Carolina: implications for prevention and control.

In the winter of 1992, some 402 Southeast Asian refugees were resettled in North Carolina. They received very limited medical screening before immigration and many arrived in the United States with significant health problems, including several tropical infectious diseases. These refugees had lived for many years in remote areas along the Vietnam-Cambodia border, where there is intense transmission of malaria, including Plasmodium falciparum resistant to most antimalarial drugs available in the United States. Of 322 refugees screened after arrival in North Carolina, 187 (58%) were infected: 33% with P. falciparum, 23.5% with P. vivax, 23.5% with P. malariae, and 2.1% with P. ovale. Most infected persons were asymptomatic and infections with multiple species were common. Because of the documented high infection prevalence and the probable presence of many subpatent infections, all nonpregnant refugees were treated with halofantrine; those with P. vivax or P. ovale infections were given primaquine as well. This group accounted for the largest cluster of malaria cases reported in the United States in the last 50 years. Their rapid relocation, with minimal medical screening prior to arrival, resulted in a significant burden to the refugees and to the health-care system. Coordination between immigration agencies, the public health community, and medical workers in communities where the refugees are settled is critical for U.S.-based management of imported tropical diseases.

The treatment of infertility associated with endometriosis by in vitro fertilization.

In vitro fertilization and embryo transfer (IVF-ET) was performed on women with tubal disease only (28 women, 40 cycles), endometriosis grade I (15 women, 24 cycles), grade II (25 women, 37 cycles), grade III (26 women, 36 cycles), or grade IV (31 women, 52 cycles). Rates of oocyte recovery and fertilization were not affected by the presence of endometriosis. Pregnancy rates per cycle were similar to that of the tubal group (18%) for women with grade I (13%) or grade II (14%) endometriosis, lower in women with grade III endometriosis (6%) and significantly reduced in women with grade IV (2%, P less than 0.05).

Delay in the application of the cover glass is a potential source of error with the Makler Counting Chamber.

OBJECTIVE: To determine the effect of delaying the application of the cover glass of a Makler Counting Chamber (Sefi Medical Instruments, Haifa, Israel) on the apparent concentration of sperm or Dynabeads (Dynal Pty Ltd, Carlton, Victoria, Australia). DESIGN: Systematic alteration of the time taken to apply the cover glass. SETTING: Comprehensive infertility service. PATIENT(S): Fresh semen from a patient or washed sperm from a donor. INTERVENTION(S): For the Makler Counting Chamber, a 5-microL drop of the sperm or bead suspension was placed in the center of the lower platform and the cover glass was applied either immediately (0 seconds) or after a delay of 5, 10, or 30 seconds. MAIN OUTCOME MEASURE(S): The concentration of beads or sperm counted using an Improved Neubauer Hemocytometer or a Makler Counting Chamber. RESULT(S): There was a progressive increase in sperm concentration with a longer delay in applying the cover glass when sperm was suspended in either seminal plasma or culture medium. Repeating the experiments with Dynabeads resuspended in phosphate-buffered saline, serum, or seminal plasma showed the same trend, although the suspension of beads in serum seemed to settle the least over the first 10 seconds. CONCLUSION(S): Delay in the application of the cover glass is a potential source of error with the Makler Counting Chamber and should be avoided.

Hormonal profiles and embryo quality in women with severe endometriosis treated by in vitro fertilization and embryo transfer.

A study was undertaken comparing the outcomes of 30 women with infertility due to untreated severe (grade IV) pelvic endometriosis with a comparable series of 28 women whose infertility was caused solely by irreversible tubal disease. There were no significant differences in either the follicular phase or luteal phase hormonal profiles of estradiol and progesterone, but there was a significantly reduced pregnancy rate in those women with severe endometriosis. In part, this was due to the recovery of fewer oocytes from the endometriosis patients (P less than 0.001) despite the fact that the peak estradiol levels and ovarian accessibility were similar in the two groups. However, there were no significant differences in the proportion of oocytes that fertilized or the number that demonstrated normal embryo growth and high-grade embryo quality. There also appears to be an implantation inhibitory factor in patients with severe endometriosis as the pregnancy rate/embryo transferred and number of gestational sacs identified/embryo transferred were significantly reduced (P less than 0.05).

The use of biosynthetic human growth hormone to augment ovulation induction with buserelin acetate/human menopausal gonadotropin in women with a poor ovarian response.

The present study has demonstrated the usefulness of GH in augmenting buserelin acetate/hMG to stimulate the rate of growth of follicles in women regarded as poor responders. The PR achieved was extremely encouraging in a group of patients whose prognosis was otherwise poor. Further studies are required to confirm these preliminary data.

Early luteal serum progesterone concentrations are higher in pregnancy cycles.

In a consecutive series of 167 patients reaching the stage of embryo transfer after in vitro fertilization and embryo transfer, 19 clinical pregnancies ensued. The serum progesterone (P) levels were significantly greater on the first and second (P less than 0.01) and third (P less than 0.05) postaspiration days for those who conceived. Higher circulating levels of P were achieved on days 1, 2, and 3 (P less than 0.05) by the daily injection of P, 50 mg in oil, given for 5 consecutive days, beginning immediately after follicle aspiration. Both pregnancy and nonpregnancy cycles demonstrated high circulating P levels, but the study implies that relatively higher levels are required for conception, and such levels can be achieved by the use of intramuscular P.

The in vitro fertilization of supernumerary oocytes in a gamete intrafallopian transfer program.

Gamete intrafallopian transfer (GIFT) was performed on a series of 42 couples in whom four oocytes were replaced into the fallopian tubes and the remaining oocytes were inseminated with 100,000 motile spermatozoa. Fertilization in vitro was assessed 16 to 20 hours later. An overall pregnancy rate after GIFT of 40.0% (12/30) in normospermic couples and 16.7% (2/12) in oligospermic couples was seen. Supernumerary oocytes were submitted to in vitro fertilization (IVF) and the findings related to the likelihood of pregnancy. No correlation between IVF and the likelihood of GIFT pregnancies was found in either the oligospermic or normospermic couples. A similar proportion of pregnancies was seen in couples with or without evidence of fertilization of the supernumerary oocytes in both the oligospermic and normospermic couples. However, a high proportion of normospermic couples with no evidence of fertilization had only one oocyte remaining for insemination. These results suggest that the failure of low numbers of supernumerary oocytes to fertilize in vitro after GIFT relates to oocyte selection criteria and does not mean a reduced chance of conception in that treatment cycle.

Pregnancies following pronuclear stage tubal transfer.

Pronuclear stage tubal transfer (PROST) is a technique that involves in vitro fertilization (IVF) of oocytes, followed by the transfer of pronuclear oocytes into the fallopian tubes. It has been developed for its prognostic value of confirming fertilization in couples with oligospermia or asthenospermia and enabling fertilization in cases with antispermatozoal antibodies (ASAB). PROST has provided useful diagnostic information in the management of couples who have failed to conceive in other treatment programs and has particular advantages over IVF for those receiving fresh donated oocytes for ovarian failure. Fourteen pregnancies resulted from 52 transfers, providing a pregnancy rate of 27% per transfer. The pregnancy rates were higher than a matched IVF series in the male factor and female ASAB groups and reached statistical significance for the ovum donation group. It is anticipated that both pregnancy rates and fetal wastage will be improved over conventional IVF and embryo transfer for the described infertility groups.

The role of gamete intrafallopian transfer (GIFT) in the treatment of oligospermic infertility.

Gamete intrafallopian transfer (GIFT) was used to treat 32 couples where the male partner was oligospermic (less than 12 X 10(6) motile spermatozoa per milliliter of semen). Initially, 100,000 motile spermatozoa were transferred per fallopian tube and no pregnancies were achieved in 11 cases. The technique was then modified so that a maximal number of motile spermatozoa were transferred (range, 0.11 to 0.90 X 10(6) spermatozoa) and 6 of 21 (29%) pregnancies resulted, with 325,000 spermatozoa being the lowest number associated with pregnancy. It appears that the modified GIFT technique, whereby an increased number of motile spermatozoa are replaced with the oocytes, is an effective therapy in the treatment of oligospermic infertility.

Cryopreservation of human embryos at the pronucleate, early cleavage, or expanded blastocyst stages.

Supernumerary embryos following treatment by IVF or GIFT were cryopreserved at the pronucleate, early cleavage or expanded blastocyst stages. The success of embryo cryopreservation at these stages was evaluated in terms of (i) the proportion of embryos surviving the freeze/thaw procedure; (ii) the proportion of patients reaching embryo replacement; and (iii) the incidence of pregnancy per replacement. Significantly more embryos survived when frozen/thawed at the pronucleate (44/61; 72%) or early cleavage stages (48/80; 60%), than at the expanded blastocyst stage (13/34; 38%). A significantly higher proportion of patients had embryo replacements when embryos were frozen/thawed at the pronucleate (17/19; 89%) or early cleavage stages (21/24; 88%), than at the expanded blastocyst stage (9/17; 53%). Following replacement of frozen/thawed pronucleate and early cleavage stage embryos, clinical pregnancy rates of 8/17 (47%) and 3/21 (14%) clinical pregnancies were achieved, respectively. No pregnancies were achieved following replacement of frozen/thawed expanded blastocysts.