Phosphorus in Hawaiian kikuyugrass pastures and potential phosphorus release to water.

Pasture systems in Hawaii are based primarily on kikuyugrass (Pennisetum clandestinum Hochst. ex Chiov.). Relationships among kikuyugrass P concentration, animal P requirements, and various soil P determinations are needed to help identify source areas for implementing pasture management strategies to limit P loss via overland flow. A total of 51 rotationally stocked kikuyugrass pastures (>20 yr old) with contrasting soil chemical properties were sampled. A satisfactory predictive relationship between modified-Truog (MT)-extractable phosphorus (P(MT)) and dissolved (<0.45-mum pore diameter), molybdate-reactive phosphorus (DRP) desorbed from soil in a water extract (DRP(WE)) was found when 0- to 4-cm-depth data for the soil orders with medium to high DRP(WE) (two Mollisols and an Inceptisol) were pooled separately from those with low DRP(WE) (five Andisols, three Ultisols, and an Oxisol). The oxalate phosphorus saturation index (PSI(ox)) procedure was the best predictor of DRP(WE) across soil orders when oxalate-extractable molybdate-reactive phosphorus (RP(ox)) was used to calculate PSI(ox) (PSI(ox)RP) rather than when total oxalate-extractable phosphorus (TP(ox)) was used (PSI(ox)TP). There was little DRP(WE) until PSI(ox)RP exceeded 6% or PSI(ox)TP exceeded 8%. A more empirical dilute-acid phosphorus saturation index (PSI(MT)) was also calculated using P(MT) and MT-extractable iron (Fe(MT)) and aluminum (Al(MT)). The PSI(MT) procedure showed some utility in predicting DRP(WE), was positively related to the PSI(ox) procedures, and can be more readily performed in agronomic soil testing laboratories than PSI(ox). The present research suggests that while Hawaiian kikuyugrass pastures tend to be sufficient to high in forage P, potential soil P release to water only appeared to be a possible environmental concern for the Mollisol and Inceptisol sites.

Dairy heifer and bermudagrass pasture responses to rotational and continuous stocking.

During 1990 and 1991, pastures of 'Callie' bermudagrass [Cynodon dactylon (L.) Pers.] located near Gainesville, FL (29 degrees 60' N latitude) were used to determine the effects of three grazing methods on performance of 250-kg Holstein heifers (Bos taurus) and forage nutritive value and botanical composition. The grazing methods were rotational stocking (15 paddocks) with short grazing periods (1.5 to 2.5 d/paddock), rotational stocking (three paddocks) with long grazing periods (10 to 14 d/paddock), and continuous stocking. Average daily gain across years did not differ among methods (.50 +/- .04 kg), partially because average in vitro digestible OM concentration of herbage varied little (558 +/- 12 g/kg of OM). Across years, rotational stocking with short grazing periods had a greater average stocking rate (3520 kg of liveweight/ha per d) than did rotational stocking with long grazing periods (2980 kg/ha per d), but no differences occurred in heifer gain among the three grazing methods (697 +/- 30 kg/ha). Under the conditions of our 2-yr study, effect of grazing method on heifer performance was slight, but the potential for long-term differences exists because 'Callie' stand longevity is greater under rotational stocking.

Impact of Grazing Management on Soil Nitrogen, Phosphorus, Potassium, and Sulfur Distribution.

Little information is available directly comparing soil nutrient distribution under different defoliation managements. During 1990 (116 d) and 1991 (141 d), 'Callie' bermudagrass (Cynodon dactylon var. aridus Harlan et de Wet) pastures grazed by Holstein heifers (Bos taurus) were used to determine the effects of two rotational stocking methods and continuous stocking on lateral and vertical distribution of extractable N, P, K, and S. A hay management also was included to compare soil responses under grazing and clipping. Nutrient distribution and concentration in the Ap1 horizon (0- to 15-cm soil depth) did not differ among grazing methods, but N, P, and K accumulated in the third of the pastures closest to shade, water sources, and supplement feeders (lounging areas where cattle tend to congregate or rest). Similar observations were made with K in the Ap2 horizon (15- to 30-cm soil depth). Nutrient concentrations were lower or tended to be lower in the Ap1 horizon of the hay management than in grazed pastures because of nutrient removal in harvested herbage. Across defoliation managements, greater extractable N, P, and K concentrations were observed in the Ap1 horizon in 1991 than in 1990. For N and K, this was attributed to fertilizer inputs in all managements and partially to supplemental feed inputs in grazed pastures. Increases in extractable P appeared to be associated primarily with flooding of the experimental site in late 1991. This study suggests that grazing method of well-managed pastures may have little effect on short-term (2 yr) soil nutrient distribution, especially when grazing occurs during months when temperatures are high.

Structure of phage P22 gene 19 lysozyme inferred from its homology with phage T4 lysozyme. Implications for lysozyme evolution.

The amino acid sequence of the lysozyme from phage P22 is shown to be homologous (26% identity) with the lysozyme from bacteriophage T4. The sequence correspondence suggests that the structure of P22 lysozyme is similar to the known structure of T4 lysozyme within the "core" of the molecule, including the active site cleft. However, P22 lysozyme appears to lack two surface loops present in T4 lysozyme. It is possible that P22 lysozyme may provide an "evolutionary link" between the phage-type lysozymes and the goose-type lysozymes.