Tall fescue is a naturally persistent plant, provided it is used in a suitable environment and managed correctly. Survival of pastures consisting of new tall fescue cultivars depends largely on management. For tall fescue to persist well, it must be established at a high density and without weeds and other grasses in the first year (see Chapter 5). Soils should be tested and limestone applied 6 to 12 mo before sowing to increase pH to at least 5.8 (water test) or 4.9 (CaCl test) and decrease Al to <2%, particularly if legumes are to be sowed also. While tall fescue has good tolerance of acid soils, most clovers and Rhizobium N-fixing bacteria do not, so the pH needs to be adjusted to ensure N fixation. Producers should consult their district agronomist or agricultural industry representative for appropriate local recommendations.
Low soil fertility or insufficient fertilizer applications are common causes of lack of persistence of tall fescue stands. The soil on sites intended for tall fescue should be tested before the decision is made to use the species. Minimum target levels of nutrients for soils to be sown in tall fescue are presented in Table 7-3. Soil fertility should be corrected before or at the time of sowing. If this cannot be done, there should be a commitment to fertilizer above maintenance levels, twice a year, until soil nutrient levels are adequate.
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Tall fescue requires higher amounts of maintenance fertilizer than cocksfoot or perennial ryegrass because of its greater forage production. Recommended maintenance P requirements are presented in Table 7-4, but requirements will vary with stocking rates and production levels. If pastures are harvested for silage or hay, the fertilizer rates will need to be increased. The quantity of N, P, and K to be supplied from fertilizer will depend on soil fertility reserves, as measured by soil tests. Failure to fertilize sufficiently will compromise pasture production and persistence. The levels suggested in Table 7-4 may seem high when compared to the average amount of maintenance fertilizer applied in the past on most enterprises. However, when lower rates have been used, tall fescue persistence can be reduced (Milne, 2001a). Tall fescue survival in drought periods will be enhanced by P applications (Keys, 1996). In addition, where soils are derived from volcanic materials, 4 to 8 kg/ha of P will be required in addition to normal annual maintenance requirements.
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Nutrients removed from the paddock should be replaced with fertilizer. To ensure proper management, the amount of grazing on each paddock should be recorded. As a general guide, 1.2 to 1.5 kg P/ha/yr should be applied for every dry sheep equivalent (DSE = 45-kg wether) carried on each hectare. In some regions, the new tall fescue pastures will carry 20 or more DSE/ha, so applications of 30 or more P/kg/ha are required each year. Phosphate applications in early spring can produce a rapid increase in tall fescue production and also increase Mg and Ca levels in the herbage (Blevins, 1997).
Phosphorus, S, and K, which encourage legume growth and legume N fixation, are only part of the requirements of tall fescue. When legume growth is restricted, low amounts of N will be fixed, necessitating frequent applications of N fertilizer for active tall fescue growing periods. The lack of N results in weeds becoming more dominant, thereby reducing persistence of tall fescue. The need for N can be assessed roughly by leaf color or plant vigor and by color differences between urine/dung patches and nonurine patches. Applications of N fertilizer just before normal growth spurts or when there are few or no legumes in the stand also can be used to increase tiller density, particularly from autumn to early spring. Higher rates of N fertilizer can boost tiller density by 16% (Mazzanti et al., 1989). Tall fescue will respond to N at any time of the year when there are adequate soil moisture and temperature for growth, but particularly in autumn, when tiller production is stimulated and the ability of tall fescue to compete with winter weeds is improved. Early spring applications also can be valuable, but mid-spring (November) applications should not be used because they will stimulate stem growth. Nitrogen fertilizer is essential for the survival of tall fescue sown on sandy soils, or where legume growth is poor, a common occurrence in low rainfall (400-500 mm) regions of New Zealand, where clovers die 2 to 3 yr after planting. In soils with very low N, as much as 150 kg N/ha may be needed. In soils with moderate legume growth and medium levels of N availability, one application of 30 kg N/ha in late autumn may be sufficient to maintain the pasture. Care should be taken when livestock is grazing pastures that have received recent large applications of N fertilizer, to forestall nitrate poisoning if no rainfall has occurred.
Trace elements are indirectly important to tall fescue, as they have a greater effect on clover growth than on grass growth. Regular applications of trace elements may be needed where deficiencies occur in the companion clover plants.
Repeated grazing of continental tall fescue cultivars that are drought-stressed will deplete plant populations severely and is likely to kill the pasture completely. Mediterranean cultivars are likely to be more tolerant of grazing during drought, but grazing at such times still should be avoided.
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