90-day Intervals Research Articles

歯の生理的移動についての実験的研究 : 近遠心的移動について

Although it is generally known that human teeth must have drifted after eruption toward the mesial direction, little has been reported on the physiologic tooth drift. The purpose of this study is to reseach the influence of the forces presumed to be participating in the physiologic tooth drift over the alveolar bone (cheeks, tongue, antagonists, neighbours and gingival fibers group) histopathologically. Twenty-two adult dogs with permanent dentitions were selected. The upper right 1st, 2nd and lower 3rd molars, and lower right distal root of 1st molars were extracted. A cheek-and-tongue guard for lower 2nd molar was applied with the mesial section of lower 1st molar as the abutment tooth. Four experimental groups with 3 dogs or more per group were investigated at 7-, 30-, 60-, and 90-day intervals after appliance setting. Other 5 dogs were used as the control without extractions and appliance setting for the 90-day period. Uppon completion of the experimental period, the changes occurring in the right and left 2nd molars and in the periodontal tissues were investigated histopathologically and compared with those of controls. The results obtained were as follows : 1. Setting the appliance to eliminate the antagonists, neighbour teeth, soft tissues and cutting the gingival fibers group displaced the teeth on the experimental side and caused changes in the periodontal tissues but did not displace obviously in the non-experimental side. 2. The direction of the tooth drift was mainly distal and elongation on the experimental side. 3. The tooth drift was observed at 7 days histopathologically and the tooth drift due to elimination was observed at 30 days in the fluorescent findings after appliance setting. 4. The peak of alveolar bone changes to adapt to the tooth drift was observed at 30 and 60 days after the appliance setting, and stabilization of the alveolar bone in the new tissue environment was not yet observed at 90 days after appliance setting. The above results histopathologically substantiate that some or all forces presumed to be participating in physiologic tooth drift (the soft tissues, antagonists, neighbour teeth and gingival fibers group) have something to do with the tooth drift as the inhibitory force. The results also prove histopathologically that the forces from these factors are indispensable to the stability of tooth position after orthodontic treatment.

Histologic, morphometries, and biochemical evolution of vein bypass grafts in a nonhuman primate model: I. Sequential changes within the first three months

The objective of this study was to define the histologic and morphometric evolution that accompanies the increase in cholesterol content of vein bypass grafts in a nonhuman primate model. Cephalic vein grafts were interposed bilaterally in the femoral arteries of 15 stump-tailed macaque monkeys (Macaca arctoides), which were fed a diet that sustains plasma cholesterol levels of approximately 225 mg/dl. Grafts were excised from five animals for analysis on each of postoperative days 3, 7, 14, 30, 60, and 90. Cholesterol content increased from 69 +/- 24 micrograms/100 mg (mean +/- standard deviation) in ungrafted vein to 473 +/- 122 micrograms/100 mg in grafts 90 days after implantation (p less than 0.05). By stepwise regression analysis, cholesterol content was best predicted by abundance of foam cells (r2 = 0.82). Intima comprised 13% +/- 5% of the total cross-sectional area of the wall in ungrafted vein and 59% +/- 11% at day 90 (p less than 0.001). With cholesterol content excluded from the stepwise regression, intimal area was best predicted by the presence of foam cells (r2 = 0.39). There was consistently an increase in the prevalence of polymorphonuclear leukocytes on the luminal surface and in both the intima and media during the first 14 days after grafting. Vasa vasorum, which were always present in ungrafted vein, were sparse at 3 days but reappeared by day 7. Medial fibrosis occurred in grafts, and in the 30- to 90-day interval it was directly correlated with the number of adventitial vasa vasorum present (r = 0.64, p less than 0.05). Immunohistochemistry revealed prominent staining for both platelet factor VIII and fibronectin during the first month, with a gradual decline in staining intensity thereafter. The evolution of changes in vein bypass grafts documented in this report are in general agreement with graft changes observed in humans and support the validity of our model in evaluating the histologic correlates of increased graft cholesterol content.

Testing for a Pulse in Seasonal Event Data

Most tests for seasonal clustering are sensitive to the peak in incidence in some season (90-day interval) followed by a trough 6 months later. We present two statistics sensitive to a relatively sharp increase in disease incidence for a season superimposed on a constant incidence over the entire year: the ratchet scan, based on the maximum number of events in k consecutive months, and the continuous circular scan, the maximum number of events in d consecutive days. We tabulate the tail distribution of the ratchet scan for N less than or equal to 35 and k = 2 and 3, and find the asymptotic distribution which is applicable for N greater than or equal to 50 when k = 2 or 3. We evaluate an approximation for the distribution of the continuous scan. The statistics are applied to investigate seasonal clustering of adolescent suicide in the United States. An illustration is given of the application of the circular scan, and a small simulation study and the example are used to compare the statistics with others proposed in the literature.

Recovery of Hormone Secretion after Chronic Gonadotropin-Releasing Hormone Agonist Administration in Women with Polycystic Ovarian Disease*

Persistent suppression of gonadotropin and ovarian steroid production can be achieved in women with polycystic ovarian disease (PCO) by daily administration of a long-acting GnRH agonist (GnRHa). This study was designed to determine the patterns of recovery of clinical responses and hormonal secretion after chronic GnRHa administration in women with PCO. Six women with PCO were treated with daily sc injections of [D-His6(imBzl),Pro9-NEt]GnRHa (100 micrograms) for 6 months. Blood samples were obtained at the time of and three times weakly for 90 days after discontinuation of agonist therapy. In five women who did not ovulate, the suppressed serum FSH levels rose to pretreatment values within 10 days. In contrast, a gradual and progressive increase in serum LH (as measured by bioassay and immunoassay) was apparent by day 18. The LH increase coincided with progressive increases in serum estrone (E1), androstenedione, and testosterone. Serum estradiol (E2) began to rise on day 28. All hormones returned to their pretreatment baseline values within the 90-day recovery interval, with the exception of E2. Trend analysis of the slopes of recovery revealed that the incremental secretion patterns of E1, E2, androstenedione, and testosterone differed significantly from that of FSH, but not from those of bioactive or immunoactive LH. Serum progesterone, dehydroepiandrosterone sulfate, and cortisol did not change after withdrawal of GnRHa. One woman ovulated spontaneously on day 52 before which her hormone secretion patterns were indistinguishable from those of the other women. In summary, 1) during recovery after discontinuation of chronic GnRH agonist therapy the patterns of FSH and LH release suggested resumption of endogenous GnRH action on the pituitary with greater release of FSH than LH, a pattern that would be expected in the absence of ovarian steroid influence; 2) the lack of early estrogen production despite the increase in serum FSH concentrations suggests inadequate FSH secretion, abnormal ovarian responsiveness to FSH, or impaired FSH bioactivity; 3) androgen secretion was provoked by the increase in LH secretion; 4) per unit LH measured by bioassay, greater ovarian androgen secretion was stimulated in PCO than ovulatory women; and 5) the likelihood of spontaneous ovulation during recovery was minimal.

Development and monte carlo analysis of an oyster bioaccumulation model applied to biomonitoring data

Routine operations of the Calvert Cliffs Nuclear Power Plant (CCNPP) include almost daily releases of low levels of radionuclides to the Chesapeake Bay. A biomonitoring program involving quarterly collection of oysters ( Crassostrea virginica) maintained in the effluent of the CCNPP was initiated in 1978 to monitor the radionuclide concentrations in oysters. In this paper, the application of an oyster bioaccumulation model to the radionuclide biomonitoring data is presented. The model represents radionuclide concentrations in oysters as dependent on the processes of uptake, biological excretion, physical (radioactive) decay, and oyster growth. Driving variables in the model are daily water temperature and the magnitudes of daily plant releases of radionuclides. The model was calibrated and verified to concentrations of Ag-110m and Co-58 measured in oysters. Monte Carlo simulation involving the variation of model parameters, driving variables and initial conditions was performed to: assess the consequences of alternative plant release scenarios on radionuclide concentrations in oysters, and evaluate alternative sampling frequencies in the biomonitoring program for their ability to capture temporal variability of radionuclide concentrations in oysters. Results showed that releases restricted to the winter resulted in the lowest radionuclide concentrations in oysters on an annual basis, and releases restricted to the spring resulted in the lowest concentrations during the period of the year of commercial and recreational oyster harvest (fall and winter). Results also showed that the estimates of the probabilities of exceeding given radionuclide concentrations with the 90-day sampling interval presently used in the biomonitoring program are similar to estimates based on more frequent sampling (i.e., have relatively small bias). However, an increase in the sampling frequency to three samples per quarter (i.e., 30-day intervals) resulted in a substantial in the uncertainty (coefficient of variation) associated with the estimated probabilities. The general modeling approach is appropriate for other biomonitoring situations with known point source discharges.

Lasting Remissions in Patients Treated for Graves’ Hyperthyroidism With Propranolol Alone: A Pattern of Spontaneous Evolution of the Disease*

Twenty-six patients with Graves' hyperthyroidism treated only with propranolol for 1-21 months have been followed up to 5 years. The patients were evaluated before treatment, at 15, 30, and 90 days during treatment, and then at 90-day intervals during propranolol treatment by clinical examination and measurement of serum free T3, free T4, rT3, TSH, and sex hormone-binding globulin concentrations and serum anti-thyroglobulin, antithyroid microsomal, antithyroid peroxidase, and thyroid-stimulating autoantibodies. Eighteen patients who had no biochemical improvement during propranolol therapy or relapsed after initial improvement were treated conventionally. In contrast, eight patients had a biochemical remission, which has lasted 30-48 months after propranolol withdrawal. The biochemical values before and during treatment did not differ among the two groups of patients, except for the initial serum free T3 levels which were significantly higher in the patients who had no remission. Serum TSH levels returned to normal only in patients who had a long-lasting remission. While thyroid autoantibodies decreased or disappeared during follow-up, the evolution of thyroid-stimulating autoantibody values was grossly related to the clinical outcome. Long-lasting remissions may occur in patients with hyperthyroidism due to Graves' disease not given ablative or antithyroid drug therapy. Since propranolol is devoid of antithyroid and immunosuppressive actions, these remissions are probably spontaneous. Although they tended to occur in patients with less severe disease, no biological parameter was found that predicted the outcome.

Root perforations dressed with calcium hydroxide or zinc oxide and eugenol

Root perforations were experimentally made at the furcation level in 15 maxillary and mandibular dog's premolars. A group of these perforations were dressed with an aqueous paste of calcium hydroxide and iodoform; another group was dressed with zinc oxide and eugenol; and in a third group (control) the perforations were kept open. After a 90-day postoperative interval, the dogs were killed and their teeth and neighboring structures processed for histopathological analysis. In those teeth dressed with calcium hydroxide, necrosis in front of the perforation and different levels of cementum hyperplasia were observed. The specimens dressed with zinc oxide and eugenol showed inflammatory reactions with abscess formation and resorption of the alveolar crest. In the opened perforations these same phenomena were also frequently seen. Root perforations were experimentally made at the furcation level in 15 maxillary and mandibular dog's premolars. A group of these perforations were dressed with an aqueous paste of calcium hydroxide and iodoform; another group was dressed with zinc oxide and eugenol; and in a third group (control) the perforations were kept open. After a 90-day postoperative interval, the dogs were killed and their teeth and neighboring structures processed for histopathological analysis. In those teeth dressed with calcium hydroxide, necrosis in front of the perforation and different levels of cementum hyperplasia were observed. The specimens dressed with zinc oxide and eugenol showed inflammatory reactions with abscess formation and resorption of the alveolar crest. In the opened perforations these same phenomena were also frequently seen.

Histopathological study of pulpal irritation of dental adhesive resin. Part 1. Panavia EX

This histopathological study was undertaken to investigate the pulpal irritation of Panavia EX in adult dogs at the intervals of 3, 7, 14, 30, 60, 90 and 120 days after filling. The results were as follows:1. At the 3-day and 7-day postoperative intervals many cases showed the pulpal changes, however, its degree was not severe, but moderate.2. At the 14-day and 30-day postoperative intervals few cases showed changes and yet its degree was mild. The number of the cases with reparative dentin formation was very few.3. At the 60-day, 90-day and 120-day postoperative intervals many cases showed no pulpal changes, the number of the cases with changes gradually decreased and its degree became mild. The number of the cases with reparative dentin formation was reparatively few and also its amount was scanty.4. As a result of this study, it can be considered that Panavia EX was less irritative to the pulp.

Histopathological study of pulpal irritation of dental adhesive resin. Part 2. Super Bond C & B

This histopathological study was undertaken to investigate the pulpal irritation of Super Bond C & B in adult dogs at the intervals of 3, 7, 14, 30, 60, 90 and 120 days after filling. The results were as follows:1. At the 3-day and 7-day postoperative intervals more than half cases showed the pulpal changes directly under the cavity, however, its degree was not severe, but moderate.2. At the 14-day and 30-day postoperative intervals few cases showed the changes. Its degree was mild with a tendency of decreasing the changes.3. At the 60-day, 90-day and 120-day postoperative intervals many cases showed no pulpal changes. The number of the cases with reparative dentine formation was reparatively few.4. As a result of this study, it can be considered that Super Bond C & B was less irritative to the pulp.

SUPPLEMENTARY COPPER FOR GRAZING BEEF CATTLE — INJECTABLE COPPER GLYCINATE, AND COPPER SULFATE IN FREE-CHOICE MINERAL SUPPLEMENTS

Eight herds of beef cattle from Northwestern Manitoba were selected for Cu supplementation trials during the 1974 and 1976 grazing season (four herds in each season). Supplementary Cu was provided as injectable Cu glycinate or as CuSO4 in a free-choice mineral supplement. The treatments were a combination of: (1) one dose of injectable Cu at the start of the pasture season; (2) two doses of injectable Cu, at an interval of approximately 90 days, with the first dose as in (1); (3) CuSO4 added to mineral supplements to provide 0.25 or 0.50% Cu; and (4) injectable Cu, one or two doses during the pasture season, plus 0.25% Cu as CuSO4 in the mineral supplement. Within each herd a cow and her calf were treated as a cow-calf unit. The concentration of Cu in blood serum was used as an indicator of the Cu status of cattle. Forage samples were analyzed for Cu, Mo and total sulfur, and absorption coefficients for Cu and available Cu were calculated. One dose of injectable Cu at the start of the pasture season, or the inclusion of 0.25% Cu as CuSO4 in the mineral supplement, was effective as a Cu supplement where dietary Mo and total S were less than 3 mg/kg and 3 g/kg dry matter, respectively. When Mo and total S concentrations were higher than 3 mg/kg and 3 g/kg dry matter, respectively, doses of injectable Cu provided at a 90-day interval or a Cu concentration greater than 0.25% in the mineral supplement were effective. More than 0.50% Cu, as CuSO4, was required where Mo and total S in forages were in excess of 10 mg/kg and 3 g/kg dry matter, respectively. Inclusion of CuSO4 in the mineral supplement was adequate as a supplement for cows, but the calves did not appear to consume adequate mineral. Injectable Cu was equally effective for cows and calves. An inadequate transfer of Cu via milk was indicated when a cow, but not its calf was provided with injectable Cu. The beneficial influence upon serum Cu of injectable Cu as opposed to Cu in the mineral supplement, depended upon whether the Cu requirement of the cow or its calf was to be met. The level of supplementation to prevent a drop in serum Cu over the pasture season depended upon the concentrations of dietary Mo and S, and their effect upon the coefficient of absorption for Cu. Key words: Supplementary Cu, grazing cattle, injectable Cu glycinate, dietary CuSO4, free-choice mineral supplements

Multinational comparative clinical trial of long-acting injectable contraceptives: Norethisterone enanthate given in two dosage regimens and depot-medroxyprogesterone acetate. Final report: Who special programme of research, development and research training in human reproduction

Final results are presented from a two-year WHO multinational comparative trial of three regimens: depot-medroxyprogesterone acetate (DMPA) given at 90-day intervals, norethisterone enantate (NET-EN) given at 60-day intervals for the entire study period (NET-EN (60-day)), and NET-EN given at 60-day intervals for six months and thereafter at 84-day intervals (NET-EN (84-day)). 1587 DMPA subjects were observed for 20,550 woman-months, 789 NET-EN (60-day) subjects were observed for 10,361 woman-months, and 796 NET-EN (84-day) subjects were observed for 10,331 woman-months. This clinical trial represents the largest clinical trial undertaken on injectable contraceptives. After two years, the pregnancy rate with NET-EN (84-day) was 1.4 (±0.6 S.E.) per 100 women, as compared with the two-year rates of 0.4 (±0.3 S.E.) per 100 women observed with DMPA and 0.4 (± 0.2 S.E.) with NET-EN (60-day). Both discontinuation rates for amenorrhea and the prevalence of amenorrhea lasting more than 90 days were significantly higher with DMPA than with either NET-EN regimen. Terminations for bleeding problems were similar with the three treatments, despite a better cyclic pattern for the first six months with the NET-EN regimens. The three treatments were comparable with respect to discontinuation rates for other medical or personal reasons, and for all reasons combined. For family planning programs, NET-EN (60-day) has the advantage of low pregnancy rates compared to NET-EN (84-day), and a schedule of administration that does not change. Both NET-EN regimens produce less amenorrhea than DMPA. However, the NET-EN (60-day) regimen has the logistic and economic disadvantage of requiring more frequent injections. All three injectable regimens compare favourably with oral contraceptives in terms of pregnancy and total continuation rates observed in clinical trial settings.

Pulses of cholinergic receptor escape from atropine blocking reflect major natural periodicities

1. Semi-lunar variation in cardiac response to applied acetylcholine was reconfirmed. 2. Atropine completely blocked the effects of acetylcholine on the heart except for brief pulses of escape at 12-hr intervals which began at moonset and progressed through midday at 10 to 14-day intervals. 3. The direction of escape, i.e. inhibition or acceleration, reversed at the winter solstice and at both equinoxes. 4. Cholinergic receptors in the cardiac preparation seem to reflect the following: 12-hr intervals beginning at moonset, 24.8 hr, 10 to 14-day intervals, 14.8-day intervals and the equinoxes and solstices, 90-day intervals.

NUTRITIVE VALUE OF GROUND AND/OR AMMONIATED CORN STOVER

Corn stover stacks were harvested and a portion of these were treated with anhydrous ammonia at a level of 3% of dry matter (DM) and left covered with plastic for at least 30 days during the fall of 1977. In the spring, both treated and untreated corn were chopped through a forage harvester. A portion of each was then ground through a 1.3-cm screen. Treatments were: untreated chopped, untreated ground, ammoniated chopped, ammoniated ground. Treatments were evaluated with eight Hereford-Angus yearling steers in a double 4 × 4 latin square design. In addition to the stover, rations contained 10% molasses, 6% soybean meal, and 2.3% mineral mix. Urea was added to the untreated rations at the level of 1.6% to make rations isonitrogenous. Steers were injected with vitamins A, D and E at 90-day intervals. With both control and ammoniated rations, grinding increased (P < 0.001) intake on a body weight raised to the 0.75 power basis (MBW) of DM, digestible energy (DE) and digestible DM by 47%, 39%) and 39%), respectively. With both chopped and ground stover rations, ammoniation increased (P < 0.001) intake of digestible DM and DE and increased (P < 0.01) intake of DM all on a MBW basis by 22%, 31% and 12%), respectively. However, grinding decreased digestibilities of DM and neutral detergent fibre (NDF) (P < 0.001) and of organic matter (OM) (P < 0.01) by 5%, 10% and 5%, respectively. With both chopped and ground stover rations, ammoniation increased (P < 0.001) digestibility of DM, OM, and NDF by 9%, 9% and 14%, respectively. Ammoniation plus grinding increased (P < 0.01) intake (MBW) of DM, digestible DM and DE by 64%), 71% and 85%), respectively, over untreated chopped rations. Grinding increased (P < 0.01) rumen acetate 0.5 h preprandially but did not significantly affect other rumen parameters measured preprandially or 2 h postprandially. Ammoniation increased (P < 0.01) rumen propionate 0.5 h preprandially but did not significantly affect the remaining rumen parameters. Before versus after feeding levels of rumen metabolites did not differ except for an increase (P < 0.01) in ammonia-N and total VFA postprandially. No significant treatment interactions were present.

Serial lateral hypothalamic destruction with various interlesion intervals

Mature male or female albino rats sustained unilateral lateral hypothalamic area (LHA) destruction, and 30, 60, or 90 days later, sustained destruction of the intact contralateral LHA, thereby producing bilateral LHA destruction (serial 30, 60, and 90). Other rats sustained either simultaneous bilateral LHA destruction (one-stage), two lesions of the same LHA separated by 60 days (multistage), or unilateral LHA damage followed 60 days later by thalamic-hippocampal damage on the side of the brain opposite the original LHA lesion (thalamic). After brain damage, food and water intakes, body weight, and sensorimotor behaviors were measured. The multistage and thalamic rats displayed only minor and short-term deficits on the variables measured. The one-stage bilateral LHA rats were adipsic and aphagic, and displayed body weight loss, sensory neglect, hypoactivity, and gastric pathology. The serial rats (30-, 60-, and 90-day interlesion intervals) also displayed severe and persistent deficits. The serial rats were equivalent to the one-stage rats for duration of adipsia-aphagia, body weight loss, sensory neglect, hypoactivity, and gastric pathology. The results show that bilateral LHA destruction sustained in two operations (separated by 30, 60, or 90 days) produced behavioral deficits equivalent to deficits produced when the LHA was bilaterally destroyed in a single operation.

Blood levels of medroxyprogesterone acetate after multiple injections of DepoProvera or CycloProvera

Mean levels of MPA in blood taken 90 days after injection were not significantly different between women who had received a single injection of DepoProvera and those who had received eight injections at 90-day intervals. There was a wide variation in plasma MPA concentration in the two groups of women. In women who had received 31 to 45 injections of CycloProvera, plasma levels of MPA 28 days after injection were significantly higher than those of women who had received a single injection. The levels were also higher than those found in women 90 days after injection of DepoProvera. The results suggest that the dose of MPA in CycloProvera could be reduced.

Effects of Delayed Hand Weeding on Sole-crop Cassava in Sierra Leone

SUMMARYThe effects of delayed hand weed control at 30-, 45-, 60-, 90-day intervals, and no weeding, on sole-crop cassava, was studied in two experiments on the upland soils of Sierra Leone. Timing and frequency of weeding were important in influencing root number and root yield, and delayed weed control depressed both attributes. The critical period of competition was in the 45-day weeding interval, with six weedings in a 14-month growing period. Rottboellia exaltata was the predominant species amongst the permanent grasses on the no-weeding plots.

Response of anamnestic IgA-producing cells in the mouse gut after repeated intragastric immunization.

1) Repeated intragastric immunization after a 90-day interval results in a local immunologic memory. 2) Repeated intragastric immunization does not induce the same circulation of gut lymphocytes as does the initial oral immunization. 3) Measurement of circulating antibodies is a poor criterion for gauging the local immune status. 4) A gastric intubation dose of 4 X 10(9) SRBC given daily for 4 days appears to be suboptimal for the induction of a local immune response.

Soluble immune complexes in sera of patients with nephritis

Binding of radioactively labeled C1q was used to detect soluble antigen-antibody complexes in sera collected at the time of renal biopsy from 104 patients with immunofluorescent findings consistent with immune-complex disease. In comparison with data obtained with sera from 85 healthy donors, significantly elevated C1q binding activity was demonstrated in sera from 22 patients. C1q binding was elevated in all four patients whose dominant histologic finding on bright field microscopy was an intense interstitial mononuclear cell infiltrate. High C1q binding activity was found preferentially in sera from patients who had diffuse rather than focal histologic abnormalities by light microscopy, heavy glomerular deposits of C4 and C3 by immunofluorescence and elevated serum creatinine concentrations. However, there were many patients with similar immunofluorescent and bright field microscopic changes in whom circulating complexes were not detected and there was no correlation between the pattern of glomerular localization of immune complexes and the C1q binding activity of the sera. Serial measurements of C1q binding activity in the sera from three patients over a 90-day interval emphasized that immune complexes may be demonstrated by this technique only intermittently in the sera of some patients with renal biopsy evidence of immune-complex disease. Nevertheless, these observations suggest that the C1q binding test may be a useful tool to monitor disease activity in patients with immunologically mediated renal disease.

Título en español.

Se estudió el efecto de aplicaciones de nitrógeno que variaban entre 0, y 1,600 libras por cuerda por año y de intervalos de corte de 40, 60, y 90 días, en el rendimiento y composición de la yerba Guinea (Panicum maximum), y en la acidez del suelo durante 2 años consecutivos. Los rendimientos aumentaron con niveles de nitrógeno hasta 800 libras por cuerda por año. El contenido y rendimiento de proteína aumentó con niveles de nitrógeno hasta 1,600 libras por cuerda por año. Se recuperó en el forraje aproximadamente la mitad del nitrógeno aplicado hasta 800 libras por cuerda, pero la eficiencia de utilización expresada en términos de forraje seco producido por cada libra de nitrógeno disminuyó según se aumentaban los niveles de nitrógeno. El contenido de fósforo disminuyó, pero el de lignina aumentó al aumentar los niveles de nitrógeno. El contenido de calcio, potasio, y magnesio en el forraje no se afectó con las aplicaciones de nitrógeno. Los rendimientos de forraje seco y el contenido de lignina aumentaron al alargarse los intervalos de corte. Sin embargo, el contenido de proteína, fósforo, calcio, magnesio, y potasio disminuyó según se alargaron los intervalos de corte. Un intervalo de corte de 60 días y de 400 a 800 libras de nitrógeno por cuerda por año dependiendo de la abundancia de lluvia parece ser el tratamiento óptimo con 800 libras de nitrógeno al año, la yerba Guinea produjo 32,738 libras de materia seca (como 73 toneladas de forraje verde) por cuerda por año, con un contenido de proteína de 9.6 por ciento. Con este tratamiento, la yerba extrajo del suelo 500 libras de nitrógeno, 330 libras de potasio, 286 libras de calcio, 169 libras de magnesio, y 70 libras de fósforo por cuerda por año. El rendimiento no varió apreciablemente durante los 2 años de experimentación, pero la producción varió considerablemente durante distintas épocas del año. La aplicación de 800 libras de nitrógeno, en forma de sulfato amónico, por cuerda por año durante 2 años, redujo el pH de las 6 pulgadas de superficie en 2.1 unidades y acarreó una pérdida de 5.4 miliquievalentes de bases intercambiables por cada 100 gramos de suelo.

Título en español.

Se estudió el efecto de aplicaciones de nitrógeno que variaban entre 0 y 1,600 libras por cuerda por año, y de intervalos de corte de 40, 60, y 90 días, en el rendimiento y composición de la yerba Para (Panicum purpurascens). Los rendimientos aumentaron con niveles de nitrógeno hasta 800 libras por cuerda por año. El contenido y rendimiento de proteína aumentó con niveles de nitrógeno hasta 1,600 libras por cuerda por año. Se recuperó en el forraje aproximadamente la mitad del nitrógeno aplicado hasta 800 libras por cuerda, pero la eficiencia de utilización expresada en términos de forraje seco producido por cada libra de nitrógeno disminuyó según se aumentaban los niveles de nitrógeno. El contenido de fósforo disminuyó, pero el de lignina aumentó al aumentar los niveles de nitrógeno. El contenido de calcio, potasio, y magnesio en el forraje no se afectó con las aplicaciones de nitrógeno. Los rendimientos de forraje seco y el contenido de lignina aumentaron al alargarse los intervalos de corte. Sin embargo, el contenido de proteína, fósforo, calcio, magnesio, y potasio disminuyó según se alargaron los intervalos de corte. La producción varió considerablemente durante distintas épocas del año. Con un intervalo de corte de 60 días y 800 libras de nitrógeno por cuerda por año la yerba Para produjo 30,841 libras de materia seca (como 70 toneladas de forraje verde) por cuerda por año, con un contenido de proteína de 9.5 por ciento. Con este tratamiento, la yerba extrajo 469 libras de nitrógeno, 524 libras de potassio, 120 libras de calcio, 77 libras de magnesio, y 52.4 libras de fósforo por cuerda por año. No debe aplicarse nitrógeno en más de 400 libras por acre al año en tiempo de sequía.