• Nitrogen and row spacing on Digitaria eriantha production and digestibility

      Gargano, A. O.; Adúriz, M. A.; Busso, C. A.; Amela, M. I. (Society for Range Management, 2003-09-01)
      Research on the effects of the rate and method of fertilizer application or row spacing on dry matter yield and digestibility of perennial forage crops either is scarce or has produced contradictory results. The objective of this study was to determine the effects of various rates of N fertilization, method of fertilizer application and row spacing on dry matter yields and in vitro dry matter digestibility (IVDMD) in the cultivated, perennial forage grass Digitaria eriantha Steud. subsp. eriantha cv. Irene. Field studies were conducted on a petrocalcic Ustipsament, sandy loam soil. The total annual N fertilizer (0, 50 or 100 kg ha-1) was applied once (in early spring) or split (half in early spring, half in early summer) on rows 0.3 or 0.5 m apart. Plants were clipped, leaving 50 mm of stubble, whenever they reached 260-280 mm height during the 1998-1999 and 1999-2000 growing seasons. All fertilized treatments produced higher (P < 0.05) dry matter yields than unfertilized controls. Averaged across both seasons, annual dry matter yields were 3.5, 5.2, and 6.0 Mg ha-1 for 0, 50, and 100 kg ha-1 N treatments, respectively. Dry matter yields during summer were greater (P < 0.05) under split than single application. Row spacing did not affect dry matter yield. Although small, increases in IVDMD due to fertilization were significant (P > 0.05). Mean IVDMD was 602, 633, and 656 g kg-1 for N fertilization rates of 0, 50, and 100 kg ha-1. It is suggested that N application should be between 50 and 100 kg ha-1 for D. eriantha, and that this application should be split rather than applied at one time in early spring.
    • Effects of aeration on phenolic amine content of guajillo

      Windels, S. K.; Hewitt, D. G.; Forbes, T. D. A. (Society for Range Management, 2003-09-01)
      Aeration is a common range management technique used in southern Texas and northern Mexico to reduce shrub cover and increase biomass of more palatable forages. Guajillo (Acacia berlandieri Benth.) is an important forage plant for deer and domestic livestock throughout its range in northeastern Mexico and southern Texas. It responds to top removal, such as by aeration, by producing large numbers of juvenile sprouts which can have higher total leaf nitrogen content up to 6 months after treatment. However, the concentration of phenolic amines, potentially toxic secondary plant chemicals, may also increase. We compared concentrations of tyramine and N-methyl-phenethylamine (NMP), 2 prominent phenolic amines that can negatively affect reproduction in herbivores, between juvenile (regrowth) and mature stems of guajillo in areas that had been aerated and also between mature stems in aerated and control sites. Aeration increased NMP but not tyramine concentrations in mature stems. Juvenile stems had higher total nitrogen concentration than mature stems but also had higher amine concentrations until about 1 year after aeration. A greater percent of total nitrogen was incorporated into amines in juvenile stems (2.5-6.0%) than mature stems (1.8-4.2%). Amine concentrations peaked in summer and early autumn, a period when herbivores may rely heavily on browse because forbs are scarce. Our results suggest that while aeration may result in higher nitrogen concentrations in guajillo, increases in amines may limit benefits to herbivores.