Spring sowing summer-active tall fescue for future pasture production

Transcription

1 Proceedings of the 5 th Annual Conference of the Grassland Society of Southern Australia Inc. 29 Spring sowing summer-active tall fescue for future pasture production Margaret Raeside 1,2, Michael Friend 2,3 and Alister Lawson 4 1 Department of Primary Industries, Hamilton, Vic 33, 2 CRC Future Farm Industries, 3 Charles Sturt University, Wagga Wagga, NSW, 4 Department of Primary Industries, Kyabram, Vic. Introduction Climatic conditions have created a challenge for pasture production in recent years, with long dry spells and large unseasonable rainfall events often resulting in pasture shortfalls at crucial times of the year. Increased climatic variability is likely to continue into the future. Therefore, future pasture systems must be designed to make more efficient use of available moisture, both from rainfall and the soil profile, and convert this moisture into green feed. A pasture species that may improve the productivity of low-lying tracts of land that consist of heavy soils is summer-active tall fescue (Lolium arundinaceum syn. Festuca arundinacea). This is a deep-rooted perennial grass that is able to remain productive into summer by extracting moisture from the soil profile and responding quickly to summer rain (Garwood and Sinclair, 1979; Lawson et al., 27). Summeractive tall fescue is also more heat tolerant than perennial ryegrass (Lolium perenne). Summer-active tall fescue is slow to establish compared with perennial ryegrass, particularly at low temperatures (Brock, 1973; Charles et al., 1991a). Therefore, spring is generally the preferred sowing time (Charles et al., 1991b). This paper presents results from a study into the effect of sowing rate and depth on the establishment of springsown summer-active tall fescue under dryland conditions. Materials and method The experiment was located at the Department of Primary Industries EverGraze site at Hamilton, Victoria (37 o 49 S, 142 o 4 E; altitude 2 m). The region has a temperate climate with mean annual rainfall of 685 mm. The long-term average maximum and minimum daily temperatures in February are 26 o C and 11 o C, and in July are 12 o C and 4 o C, respectively. Monthly rainfall and temperatures are shown in Figure 1. Soil at the site is a grey brown clay loam (Northcote, 1979). Analyses of the top 1 cm found a ph (water) of 5.6, Olsen phosphorus of 24 mg/kg, Skene potassium of 34 mg/kg and CPC sulphur of 8 mg/kg. The paddock had previously been sown to plantain (Plantago lanceolota) and perennial ryegrass. Competition from these species, as well as other weeds, was 158

2 Proceedings of the 5 th Annual Conference of the Grassland Society of Southern Australia Inc. 29 reduced by cutting the paddock for hay in spring 27 to prevent seed set. The paddock was rotationally grazed by sheep until August 28, when it was spray grazed with Roundup at 2 L/ha and Fastac at 1 ml/ha to remove existing herbage and control pests such as cockchafers (Aphodius pseudotasmaniae) and redlegged earth mites (Halotydeus destructor). The paddock was harrowed in September 28 to aerate the soil surface and stimulate further germination of weed seeds which were sprayed grazed again. This weed herbage and any remaining pests were again spray grazed with the same products in October 28. The plots were sprayed in January 29 with 1.2 L/ha of MCPA 5 for control of wild radish, which had invaded areas of the experimental site following summer rain. Rain (mm) Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Temperature ( o C) Figure 1. Mean monthly maximum (%) and minimum (%) temperatures and rainfall (black bars). Long term averages are indicated by the lines and white bars. Seed weight was estimated to be 2.65 grams /1 seeds by a Pfeuffer seed counter; seed germination was 98 %. This was tested by placing 1 seeds on filter paper in each of two glass petri dishes with 5 ml of distilled water. They were incubated at constant temperature of 2 o C in diffuse domestic light. Germination was defined as having taken place when the shoot was 1 mm in length. The site was direct drilled with Quantum summer-active tall fescue on 22 October 28 using a tyne spacing of 15 cm. The site was rolled after sowing. The experimental design was a factorial combination of four sowing depths (5, 1, 2 or

3 Proceedings of the 5 th Annual Conference of the Grassland Society of Southern Australia Inc. 29 mm) and four sowing rates (8, 16, 24 or 32 kg/ha) laid out in a randomised block design with eight replications. Measurements of seedling emergence and seedling density were conducted from sowing until April 29 using five fixed 3 cm drill lengths per plot. Seedling emergence was recorded when the shoot became visible. During this measurement period the plots were not grazed or irrigated. Repeated measures analysis of variance was used to identify differences between treatment means for seedling density using Genstat Version 11 (Payne et al,. 28). Prior to conducting the analysis, the residuals were checked for normality. Results The three-way interaction between sowing depth, sowing rate and sampling date was significant (P<.1) (Figure 2). Discussion There was 13 mm of rain on 2 nd November 28 which prompted emergence from the 5 mm sowing depth, but not from the other sowing depths. However, with no followup rain until 22 mm on 22 nd November 28, many of the seedlings that had emerged from the 5 mm sowing depth died. By the final measurement in early April 29, seedling density from the 5 mm sowing depth was negligible at all levels of sowing rate. Therefore, this experiment has shown that direct drilling at 5 mm in spring in south west Victoria is unwise because of rainfall uncertainty. The 22 mm of rain in late November prompted rapid seedling emergence from the 1, 2 and 35 mm sowing depths. Sowing at 1 or 2 mm depth resulted in the highest seedling density between December 28 and February 29. These sowing depths effectively compromised placing the seed close enough to the soil surface to allow rapid seedling emergence after rain, with placing the seed deep enough to access soil moisture and protect the seed from desiccation and predation by birds, ants and other pests. Therefore, this experiment has shown that sowing at 1 or 2 mm depths maximizes summer-active tall fescue seedling density during a dry season in south west Victoria. The 88 mm of rain that fell in mid-december 28 supported seedling growth over December and January, after which time seedling density progressively declined because there was no further rain until mid-march 29. Seedling survival during this time was highest under the 35 mm sowing depth because the seeds were placed more proximally to soil moisture. Moisture availability generally increases with sowing depth because evaporation losses are greatest near to and at the soil surface. Thus, by the final measurement in April 29, there was no difference in seedling density between the 1, 2 or 35 mm sowing depths. 16

4 Proceedings of the 5 th Annual Conference of the Grassland Society of Southern Australia Inc mm sowing depth mm sowing depth Seedling density (seedlings/m 2 ) mm sowing depth 35 mm sowing depth 1/11/28 1/12/28 1/1/29 1/2/29 1/3/29 1/4/29 Figure 2. Seedling density (seedlings/m 2 ) of summer-active tall fescue sown at 8 (%), 16 (%), 24 (%) or 32 ( ) kg/ha and at sowing depths of 5, 1, 2 or 35 mm. The vertical error bars indicate the sowing depth by sowing rate by sampling date interaction l.s.d (P=.5), with the left bar indicating the between depth by rate l.s.d (4 seedlings/m 2 ) and the right bar indicating the within depth by rate l.s.d (35 seedlings/m 2 ). 161

5 Proceedings of the 5 th Annual Conference of the Grassland Society of Southern Australia Inc. 29 However, a high proportion of the seed sown at 35 mm failed to emerge or had delayed emergence. This was because seeds sown at 35 mm were dependent, for a prolonged period of time, on endosperm reserves to meet their nutrient requirements and in many instances these energy reserves became depleted before the seedling had developed a root and shoot system capable of supplying its nutrient requirements. Therefore, given there were no difference in final seedling densities between the 1, 2 and 35 mm sowing depths, this experiment has concluded that sowing at 35 mm is not justified in south west Victoria, even during a dry season, due to delayed emergence. At the final measurement in April 29, increasing the sowing rate consistently improved seedling density up to the highest tested rate at all levels of sowing depth. However, prior to this, there had been no benefit of sowing more than 24 kg/ha at the 1 and 2 mm sowing depths because of competition between seedlings for moisture. The aim of sward establishment is to maximise seedling density. However, establishment must also be cost-effective. Therefore, this experiment has concluded that a sowing rate of 24 kg/ha sown at a depth of 1 2 mm was optimal for summer-active tall fescue establishment in south west Victoria. Conclusion This experiment has shown that the seedling density of summer-active tall fescue sown during a dry spring in south west Victoria is generally maximised by direct drilling at a rate of 24 kg/ha at a depth of 1 2 mm. This sowing depth was a compromise between placing the seed close enough to the soil surface to facilitate germination and emergence after small rainfall events, and placing the seed closer to soil moisture accessible at depth. Neither the 5 mm nor 35 mm sowing depths achieved this compromise, with seeds sown at 5 mm being prone to desiccation and predation on the soil surface and seeds sown at 35 mm often depleting their energy reserves before they had emerged. A sowing rate of 24 kg/ha was optimal because it achieved a high final seedling density and reflected realistic sowing rates used in the district. The aim of sward establishment is to maximize seedling density. On this basis, sowing at 8 or 16 kg/ha was deemed unproductive due to low seedling density. On the other hand, 32 kg/ha sown at a depth of 1 2 mm only marginally improved seedling density, compared with sowing at 24 kg/ha throughout much of the experiment. References Brock J 1973 Effect of sowing depth and post sowing compaction on the establishment of tall fescue varieties. New Zealand Journal of Experimental Agriculture 1, Charles G, Blair G, Andrews A 1991a The effect of soil temperature, sowing depth and soil bulk density on the seedling emergence of tall fescue (Festuca arundinacea Schreb) and white clover (Trifolium repens L.). Australian Journal of Agricultural Research 42,

6 Proceedings of the 5 th Annual Conference of the Grassland Society of Southern Australia Inc. 29 Charles G, Blair G, Andrews A 1991b The effect of sowing time, sowing technique and post sowing weed competition on tall fescue (Festuca arundinacea Schreb) seedling establishment. Australian Journal of Agricultural Research 42, Garwood E, Sinclair J 1979 Use of water by six grass species. 2. Root distribution and use of soil water. Journal of Agricultural Science 93, Lawson A, Clark S, McKenzie F, Holmes J, O Brien B 27 EverGraze 2. Pasture responses in a dry year. In From the Ground Up, Proceedings of the 48th Annual Grasslands Society of Southern Australia Conference. Murray Bridge, South Australia. p. 11. (Grasslands Society of Southern Australia). Northcote K 1979 A Factual Key for the Recognition of Australian Soils. Rellim Technical Publications: Glenside, South Australia. Payne, RW, Harding, SA, Murray, DA, Soutar, DM, Baird, DB, Glaser, AI, Channing, IC, Welham, SJ, Gilmour, AR, Thompson, R, Webster, R 28 The Guide to Genstat Release 11. Part 2: Statistics. VSN International: Hemel Hempstead, Hertfordshire, UK. 163