This field investigation near Manhattan, Kansas in 1979 and 1980 includes the influence of irrigation level, N fertilization rate, and plant population density on corn (Zea mays L.) yield (grain and total dry matter) and water use. The soil was Muir silt loam. In 1979, plant population density significantly influenced grain yield, with maximum yield at a population density of approximately 68,910 plants/ha. In 1980, population density did not influence grain yield. Grain yield was not influenced by N rate in 1979, but was increased by N fertilizer applications in 1980. In 1980, corn receiving no irrigation and two irrigations produced I and 69 percent, respectively, as much grain as corn receiving seven irrigations. Seasonal water use was influenced by plant population density each year but not by N fertilization rate either year. Water use increased significantly in 1980 as irrigation level increased. With increasing energy costs and decreasing water supplies available for irrigation, careful management of irrigation water is vital. Corn (Zea mays L.) management practices such as nitrogen (N) fertilization, planting density, and irrigation timing need further examination to determine optimum production levels with limited irrigation resources. Corn grain yield is most sensitive to water deficits during flowering and early ear growth. In a 3-year evapotranspiration (ET) deficit study (Stewart et al., 1975), greatest yields were obtained when little or no ET deficit occurred during pollination. Wright et al. (1980) found that N application rates ranging from 45 to 448 kg N/ha, applied to corn grown on sandy soils, produced various grain yield responses because of different plant population densities. Maximum corn grain production involves a specific plant population density depending on the particular hybrid chosen. Termunde et al. Contribution No. 83-71 -J, Agronomy and Statistics Departments, Kansas Agric. Exp. Stn., Manhattan, Kansas 66506. This content downloaded from 207.46.13.60 on Thu, 21 Apr 2016 07:17:24 UTC All use subject to http://about.jstor.org/terms VOLUME 89, NUMBERS 3-4 111 Table 1. Rainfall and irrigation amounts during the 1979 and 1980 corn growing seasons. Rainfall (mm) Irrigation by month in 1980 (mm) Month 1979 198
Data on hen-housed egg mass, the criterion of selection, and associated egg production traits were obtained from pullets of four strains selected over four generations in intermingled- or separated-family flocks. Data from the foundation stock also were used. Least squares estimates of phenotypic means, components of variance and covariance, heritabilities, and correlations (genetic, environmental, and phenotypic) were computed. Parameter estimates were regressed on generation number. No apparent time trends were found. Evidence was inconclusive for random genetic drift between strains within selection systems. Egg mass is estimated to be a lowly heritable trait (weighted means from sire component analyses ranged from 0.05 ± .03 to 0.16 ± .04). Egg weight is moderately heritable (sire component estimates of 0.32 ± .06 to 0.45 ± .04). Low heritability estimates (mean ranges of .05 to .13) were found for age at sexual maturity, hen-day, and hen-housed rates of lay. Genetic correlation estimates were high and positive between egg mass and rates of lay (sire component estimates ranged from .82 to 1.0). Egg mass and egg weight were moderately correlated genetically (.31 to .73). Genetic correlation estimates were low between age at sexual maturity and egg weight with mean ranges for estimates of −.06 to .12. Moderately large and negative genetic correlation estimates were obtained between age at sexual maturity and rates of lay.
Lasalocid, monensin or thiopeptin was administered intraruminally each at .33, .65 or 1.3 mg/kg body weight and evaluated for its effectiveness in preventing experimentally induced lactic acidosis in cattle. Four rumen-fistulated cattle were used for each dosage level and the design was a 4 × 4 Latin square with each animal receiving lasalocid, monensin, thiopeptin or no antibiotic. Acidosis was induced by intraruminal administration of glucose (12.5 g/kg body weight). Control cattle exhibited the typical drop in rumen pH and concurrent increases in L(+) and D(−) lactate concentrations commonly observed in cases of lactic acidosis. Alkali reserves were depleted in the control cattle as evidenced by a decrease in blood bicarbonate and a negative shift in base excess. In all three trials, cattle given lasalocid had higher rumen pH and lower lactate concentrations than did control cattle or cattle given monensin or thiopeptin. Cattle given monensin had a significantly higher rumen pH and a lower lactate concentration than the controls only at the .65 and 1.3 mg/kg body weight dosages, whereas thiopeptin was effective only at the 1.3-mg dosage. Concentrations of total VFA in rumen fluid decreased in the controls but remained unchanged in cattle given antibiotics. A significant reduction in the molar proportion of acetate and an increase in the molar proportion of propionate were observed in the rumen fluid of the cattle given antibiotics. Colony counts of Streptococcus bovis and Lactobacillus were significantly reduced in rumen fluid of cattle given 1.3 mg antibiotic/kg body weight. Counts of lactate-utilizing bacteria increased in both control cattle and cattle given antibiotics. Cattle given antibiotics showed no evidence of lacticacidemia, hemoconcentration or change in acid-base balance.
