Allen, Vivien G.

Kemp, David R.

Michalk, David L.

English

University of Kentucky

University of Kentucky UKnowledge International Grassland Congress Proceedings 21st International Grassland Congress / 8th International Rangeland Congress Can We Really Understand Our Grasslands with Short-Term Experiments? Vivien G. Allen Texas Tech University David R. Kemp Charles Sturt University, Australia David L. Michalk Department of Primary Industries, 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/21/9-1/14 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 ]30　 瞯 　 Multifunctional Grasslands in a Changing World 　 Volume Ⅱ 　Grasslands/Rangelands Production Systems——— Livestock Production SystemsCan we really understand our grasslands with short‐term experiments ?V .A llen1 ,D .K emp 2 ,D .M ichalk 31 Department o f Plant and Soil Science ,Texas Tech University ,L ubbock ,TX ,79409‐2122 ,USA ; 2 School o f A griculture andW ine Science ,Charles Sturt University ,Orange ,NSW ,A ustralia 2800 ; 3 Orange A gricultural Institute ,NSW Department o fPrimary Industries ,Orange ,NSW A ustralia 2800 . E‐mail : v iv ien .allen＠ ttu .eduKey words : grazing research ,grazing systems ,long‐term experimentsIntroduction Grasslands are complex ecosystems comprising natural , exotic and imposed elements over many scales . Thebehaviour of these components can appear chaotic but when investigated in detail ,a deeper order often emerges with time alongwith a clearer understanding of the mechanisms driving production and ecosystem outcomes e .g . the Park Grass Experiment atRothamsted .Too often interpretations from grassland studies are based on guessing likely longer‐term trends derived from onlya few years of observation as funders are reluctant to make long‐term commitments .This often leads to erroneous conclusionsbecause the behavior of the system has not had time to express itself .Grasslands research ,of necessity large scale and expensivein terms of land ,labour and capital ,is faced with a dilemma .Yet the longer better designed and resourced experiments aremonitored the greater the return in information gained .USA example A １０‐year ( １９９７‐２００７ ) ,３‐paddock ,field‐scale integrated cotton/ forage/ grazing system for stocker steers wascompared with a cotton ( Gossy p ium hirsutum L .) monoculture on the Southern High Plains ,Lubbock ,Texas .Both systems (３replications) were subsurface drip irrigated .The grazing system included the perennial C４ grass ,Bothriochloa bladhii ( Retz) S .T .Blake while cotton was grown in a ２‐paddock rotation with grazed wheat ( T riticum aestivum L .) and rye ( Secale cerealeL .) .In years １ to ５ ,the grazing system consistently required ２３％ less irrigation water ,４０％ less nitrogen ( N ) fertilizer ,andwas ９０％ more profitable than the cotton monoculture ( Allen et al . ,２００５ ) .However ,from year ６ ,weather patterns changed .Profitability of cotton increased as new cotton technologies increased yields ,though water and N fertilizer use remained lowerfor the grazing system .Wheat became non‐viable in the rotation due to suppression by allelopathic chemicals .Herbicide‐tolerantweeds increased ,especially in the cotton monoculture .Both systems had shif ts in soil microbial populations and in soil organiccarbon relating to both current and past vegetation cover and to grazing effects .Results obtained during years １ to ５ would nothave predicted results obtained in subsequent years .Australian examples Over a ２４‐year period ,the grazing management of native perennial grassland at T rangie in western NewSouth Wales was investigated ( Michalk and Robards ,１９９３ ) .After ５ years ( １９６７‐７１ ) perennial basal area declined from ～ ２ .８％ to ０ ,suggesting that even the lowest stocking rate ( ２ .５ sheep/ ha) was unsustainable .By year ８ ,basal area was ＞ ８％ at thelowest stocking rate and ～ ４％ at the highest rate (４ .９ sheep/ ha) .After ２４ years (１９９０) basal cover at the high stocking ratewas ～ ２％ ,the same as the starting value in １９６７ .The study concluded that effects of weather patterns which had a significanteffect on vegetal change ,could not be predicted by a ４‐５ year grazing study .A small paddock , sheep grazing experiment using four pasture systems : natural grassland ( C３ and C４ species ) ; naturalgrassland plus phosphate fertiliser ; sown fertilized perennial temperate pasture species ; chicory forage system) and two grazingtreatments ( continuous grazing and a tactical grazing / reduced stocking rate designed to increase the content of perennial grassspecies when required) was done over ７ years at Carcoar in central New South Wales ( Michalk et al .２００３ ) .It took the firstthree years from the start of the study ( the normal time for funding projects) for each treatment to function in some consistentway .Pressure was exerted by funding bodies ( resisted by the researchers) to impose grazing on some treatments before plantswere adequately established which would have only produced results that reflected early system behaviour .The next three yearswere reasonably consistent behaviour ,but then a drought and the effects of grazing treatments had important effects on speciescomposition ; Dacty lis glomerata was replaced in the sown pasture by Phalaris aquatica ,while Themeda australis ( nativegrass) and Echium p lantagineum ( weed ) became more dominant spatially in native pasture paddocks .The treatment andreplicate layout was initially based on botanical and soil surveys across the whole site to ensure that there were no major initialdifferences between treatments and replicates . However , by year ７ landscape effects were emerging that could not beinvestigated further as funds had finished .Current recommendations to farmers are then limited in how best to use these variableresources .ReferencesAllen ,V .G . ,C .P .Brown ,R .Kellison ,E .Segarra ,T .Wheeler ,P .A .Dotray ,J .C .Conkw right ,C .J .Green ,and V .Acosta‐Martinez . ２００５ .Integrating cotton and beef production to reduce water withdrawal from the Ogallala Aquifer in the SouthernHigh Plains .A gron .J . ９７ :５５６‐５６７ .Michalk ,D .L . ,Dowling ,P .M . ,Kemp ,D .R . ,King ,W .McG . ,Packer ,I .J .Holst ,P .J .Priest ,S .J .Millar ,G .D .Brisbane ,S . ,and Stanley ,D .F .(２００３) .Sustainable grazing systems for the Central Tablelands of New South Wales .A ustralian J .Ex per .A gric . ４３ ,８６１‐８７４ .Michalk D .L . ,and Robards ,G .E .(１９９３) .Stability of windmill grass pastures by sheep for ２４ years in semi‐arid south‐easternAustralia .Proceed .XV I I Internat .G rassl .Cong . , ３２０‐３２１ .

Can We Really Understand Our Grasslands with Short-Term Experiments?

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Can We Really Understand Our Grasslands with Short-Term Experiments?

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