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Just Accepted
This article has been peer reviewed and accepted for publication. It is in production and has not been edited, so may differ from the final published form.
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Changes in botanical composition on three farmlets subjected to different pasture and grazing management strategies
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Libuseng
Shakhane,
James
Scott,
Bob
Murison,
Colin
Mulcahy,
Geoff
Hinch,
Amber
Morrow,
Duncan
Mackay
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Abstract
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As part of the Cicerone Projectâs farmlet experiment, conducted on the Northern Tablelands of NSW, Australia, between July 2000 and December 2006, this study assessed the effects of varying soil fertility, pasture species and grazing management on the botanical composition of three 53 ha farmlets subjected to different management strategies. Starting with the same initial conditions, the farmlets were managed to reach different target levels of soil phosphorus (P) and sulfur (S); farmlet A aimed at 60 mg/kg of Colwell P and 10 mg/kg S (KCl40) whereas farmlets B and C both aimed at 20 and 6.5 mg/kg of P and S respectively. Pastures were renovated on 6 out of 8 paddocks on farmlet A, but only one paddock of each of farmlets B (typical management) and C (intensive rotational grazing) was renovated. Flexible rotational grazing was employed on farmlets A and B (each of 8 paddocks) whilst farmlet C used intensive rotational grazing (IRG) over its 17 major paddocks which were further subdivided into 37 sub-paddocks. This paper focuses on the botanical composition dynamics observed across all three farmlets and the explanatory variables associated with those changes.
Eight assessments of botanical composition were carried out at approximately annual intervals across each of the 37 major paddocks distributed across the farmlets and the results for each of 49 species were aggregated into 7 functional groups for analysis. The strongest correlation found was a negative curvilinear relationship between sown perennial grasses (SPG) and warm season grasses (WSG). The most significant factors affecting the functional group changes were soil phosphorus, sowing phase, paddock and date. These factors led to significant increases in SPG and correspondingly lower levels of WSG on farmlet A compared to farmlet B. Farmlets B and C experienced similar, declining levels of SPG, and increasing levels of WSG suggesting that intensive rotational grazing did not lead to substantial changes in botanical composition, compared to flexible rotational grazing, in spite of the fact that IRG had much longer grazing rests and shorter graze periods than the other two farmlets. Soil phosphorus levels were also significantly associated with levels of cool season annual grasses (CAG), legumes (LEG) and herbs (HRB), especially on farmlet A.
In general, the largest differences in botanical composition were between farmlet A and the other two farmlets; these differences were most closely associated with those plants categorised as sown, introduced, C3 pasture species. The levels of legume were generally low on all farmlets, due largely to the dry seasons experienced over most of the trial. Efforts to increase the legume composition on all farmlets were more successful on farmlet A than on the other two farmlets due, presumably, to higher soil fertility on farmlet A. Farmlet C, with its long rest periods and short graze periods, had a small proportion of legumes, due to the competitive effects of the accumulated tall grass herbage between grazings. The âtypicalâ management of farmlet B also resulted in low levels of legume as well as increased âpatchinessâ of the pastures and increased numbers of thistles.
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| AN11177 Accepted 20 March 2012 |
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| © CSIRO 2012 |
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