Hunt, L. P.

Petty, S. R.

Poppi, Dennis P.

White, Andrew I.

English

University of Kentucky

University of Kentucky UKnowledge International Grassland Congress Proceedings 21st International Grassland Congress / 8th International Rangeland Congress Grazing Management for the Tropical Savannas of Northern Australia: Utilisation Rates and Timing of Spelling Andrew I. White Heytesbury Beef, Australia L. P. Hunt CSIRO, Australia S. R. Petty Heytesbury Beef, Australia Dennis P. Poppi The University of Queensland, Australia Follow this and additional works at: https://uknowledge.uky.edu/igc  Part of the Plant Sciences Commons, and the Soil Science Commons This document is available at https://uknowledge.uky.edu/igc/21/9-2/15 The 21st International Grassland Congress / 8th International Rangeland Congress took place in Hohhot, China from June 29 through July 5, 2008. Proceedings edited by Organizing Committee of 2008 IGC/IRC Conference Published by Guangdong People's Publishing House This Event is brought to you for free and open access by the Plant and Soil Sciences at UKnowledge. It has been accepted for inclusion in International Grassland Congress Proceedings by an authorized administrator of UKnowledge. For more information, please contact UKnowledge@lsv.uky.edu. 瞯 ]82　 瞯 　 Multifunctional Grasslands in a Changing World 　 Volume Ⅱ 　Grasslands/Rangelands Production Systems——— Livestock Production SystemsGrazing management for the tropical savannas of northern Australia :utilisation rates and timingof spellingI .A .W hite 1 ,2 ,3 , L . P . H unt3 , S . R . Petty 1 and D . P . Pop p i2 . Hey tesbury Bee f 1 , University o f Queensland2 , CS IROSustainable Ecosystems3 PMB 44 W innellie ,N T ,A ustralia 0822 .andrew .i .white＠ csiro .auKey words : tropical savannas ,grazing systems ,spelling ,utilisation ratesIntroduction The survival and continuing productivity of native perennial grasses are the foundation of sustainability for thecattle industry in northern Australia . Cattle have grazed the Victoria River District of the Northern Territory for almost １３０years ,and the current thrust is for production intensification to meet the increasing cost price squeeze . Year‐round set stockingis the commonly used grazing system ,but there is interest in alternatives that incorporate spelling with higher utilisation rates toenhance both productivity and ecological sustainability . This paper reports the preliminary results of a study to investigateoptimum spelling and utilisation rates for three key native perennial grass species .Materials and methods T reatments were spelling for the early ,late or full wet season ,and utilisation rates of : ０％ ( control) ,２０％ ,３０％ ,４０％ ,５０％ and ６０％ of the leaf height of each plant . Twenty plants of each of the desirable hoop Mitchell grass( A strebla elymoides ) and curly bluegrass ( Dichanthium f ecundum ) ,and of the non‐preferred feathertop wiregrass ( A ristidalati f olia) were subjected to the １８ different treatment combinations at two locations during the ２００５‐０６ and ２００６‐０７ wetseasons . Defoliation was achieved by repeated clipping of individual plants to the desired height . Prior to the treatments beingimposed all plants were cut to a standard height of １０ cm and again at the end of the growing season . Plant mortality ,basalarea ,yield ,leaf height and incidence of flowering were all recorded at the time of clipping .Rainfall during the ２００５‐０６ wetseason ( October to April) was １０６９ mm ,with the smallest monthly totals being ５７ and ５５ mm in November and February . Inthe shorter ２００６‐０７ wet season ５５７ mm fell between December and March ,with December recording １５ mm and February １２mm .Results Results were generally similar between species , but varied between seasons and some treatments , although someconsistent trends emerged . Across all species ,full wet season spelling consistently promoted higher yields compared with partwet season spelling ( Figure １ ) ,w ith basal area either increasing or its decline being lessened . Consistent with seasonalconditions ,higher yields were evident in ２００５‐０６ for utilisation rates up to ４０％ for all spelling treatments . An increase in theutilisation rates from ０ to ６０％ produced an almost linear decline in basal area ,for ２００５‐０６ R２ ＝ ０ .９６ ,P ＜ ０ .００１ and for ２００６‐０７R２ ＝ ０ .９２ ,P ＜ ０ .００１ ( Figure ２ ) . Higher plant mortalities occurred in ２００６‐０７ but this was not consistent across thetreatments . Contrary to expectations based on rainfall ,basal area either increased ,or declined less ,in ２００６‐０７ ( Figure ２ ) .While the reasons for this are not clear ,in ２００６‐０７ the mean basal area of wiregrass in each treatment increased from ３％ to９４％ compared with changes for the other species of between‐５１％ to ＋ １６％ . Wiregrass basal area declined between ２６％ to６１％ in ２００５‐０６ .Figure 1 Y ield per p lant ( ± SE) f or all speciescombined ,f or di f f erent spelling treatments .　 　 　 　 　 　Figure 2 Change in basal area w ith di f f erentutilisation rates .Conclusions The data suggests that to promote a favourable species mix and maintain productivity of the native perennialgrasses ,grazing management should include spelling for a full wet season and maximum utilisation of ４０％ of the individualplant leaf height . Full wet season spelling promotes increased pasture yield in both good and bad wet seasons ,while theadoption of lower utilisation rates seems more important for maintaining pasture condition in good seasons .

Grazing Management for the Tropical Savannas of Northern Australia: Utilisation Rates and Timing of Spelling

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Grazing Management for the Tropical Savannas of Northern Australia: Utilisation Rates and Timing of Spelling

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