Marco Teórico

4 . 2 . 1 . RANGF FINDING STUDY

PRELIMINARY FINDINGS

T h e initial range f i n d i n g t e s t c o n d u c t e d during a dry period of w i n t e r s h o w e d a s u b s t a n t i a l d i f f e r e n c e in soil moisture b e t w e e n the unburnt Themeda site and t h e u n b u r n t Nassella site ( f i g u r e l 2 ) , w i t h the u n b u r n t Themeda obviously having a m u c h higher soil m o i s t u r e c o n t e n t t h a n the unburnt Nassella. This w a s also t h e case f o r t h e b u r n t Themeda site. This w a s observed at all 3 levels t h a t samples w e r e t a k e n at.

Also o b s e r v e d w a s t h e f a c t t h a t the moisture c o n t e n t for the Nassella d o m i n a t e d sites w a s generally closer to t h a t of the bare ground (Atrazine treated) site, f r o m w h i c h m o s t v e g e t a t i o n had been removed years ago.

This s u g g e s t e d t h a t perhaps the mature stands of Nassella had the e f f e c t of s i g n i f i c a n t l y l o w e r i n g the soil moisture c o n t e n t of the soils f r o m their previous values.

STATISTICAL ANALYSIS OF DATA

Initial s t a t i s t i c s c o n d u c t e d on these result are s h o w n in tables 1, 2, & 3. These w e r e o b t a i n e d using M i n i t a b t o c o n d u c t a t w o - w a y analysis of variance, as a t h r e e - w a y t e s t w a s not available. All data u n d e r w e n t an Arcsine t r a n s f o r m a t i o n t o normalise i t ^ „ S t a t i s t i c a l significance w a s t a k e n at the 0 . 0 5 level. W h e n statistical significance has been d e t e r m i n e d it w a s a l w a y s s h o w i n g t h a t the soil moisture under t h e Nassella w a s l o w e r t h a n t h a t of t h e Themeda sites, and t h a t the burrvt sites had lower values t h a n

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t h e u n b u r n t . A d d i t i o n a l statistics were c o n d u c t e d for all d i f f e r e n t studies using t h e M a n n - W h i t n e y (non-parametric) t e s t , but none of the data collected in the initial s t u d y w a s f o u n d t o be s i g n i f i c a n t by this method as too f e w replicates w e r e t a k e n (3 o n l y ) . j

The t w o - w a y analysis of variance (table ^ s h o w s t h a t the only statically significant d i f f e r e n c e in soil nnoisture values in this limited study were obtained in the 1 - 4 c m TV

- layer, and o c c u r e d due to the different species of grass g r o w i n g on the soil. W i t h the

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3 sites having significantly lower values than the r/7e/77ec/a. A t t h e 5-8 c m level ^ ^ there w a s no statistically significant differences in values. The species of grass

^ g r o w i n g w a s also f o u n d to be statistically significant at in 1 5-1 8 c m layer, and here, ^ ^ t h e i n t e r a c t i o n b e t w e e n t h e t w o factors w a s f o u n d to be significant.

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5 ^ history w a s not determined to be significant for this initial s t u d y even t h o u g h the O ' i t h e species was. This could be due to t h e small n u m b e r of i k replicates t a k e n (tables 1, 2, & 3).

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A f t e r t h e initial s t u d y , problems w i t h the m e t h o d for the determination of soil moisture w e r e addressed - section 3 . 3 .

4 . 2 . 2 . DETAILED FOLLOW UP OF MOISTURE UNDER THEMEDA A N D NASSELLA

Detailed sampling of soil moisture was undertaken to f o l l o w up the initial s t u d y . This occured after a day of fairly heavy rain w h i c h might account for the raise in

soil moisture levels at the surface, above those initially determined.

The data f o l l o w e d t h e same general pattern of the range-finding t e s t , w i t h the u n b u r n t

Themeda site being substantially higher in soil moisture than the u n b u r n t Nassella, or i n f a c t any of t h e other sites (1-4cm). Soil at 1 - 4 c m under the burnt Themeda also had a substantially higher value than the u n b u r n t Nassella. The burnt Nassella had an - average soil moisture value of b e t w e e n the burnt and unburnt Themeda.

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S t a t i s t i c ^ c o n d u c t e d on this study by a t w o - w a y analysis of variance (tables 4, 5, & s h o w e d t h a t there w a s a statistically significant difference in the soil moisture in me -

Statistical analysis conducted using the Mann-Whitney test showed a statistically significant difference b e t w e e n the t w o Themeda sites w i t h different fire histories, but

no difference b e t w e e n the Nassel/a sites f o ^ c ^

T w o - w a y analysis of variance also showed a highly significant effect at this level to t h e t w o d i f f e r e n t g r a s s e s [Themeda triandra and Nassella trichotoma) g r o w i n g o n t h e site.

For the soil moisture of the t w o different grasses growing on the unburnt site, the M a n n - W h i t n e y test determined that there was a highly significant difference. This w a s not the case for the recently burnt site.

The interaction of these t w o factors, given by the t w o - w a y analysis of variance was also higly significant and showed that these factors contribute to the difference in soil moistures b e t w e e n sites. ^

A t the 5-8 c m and the 15-18 cm levels the fire history was not determined to be statistically significant using the t w o - w a y analysis of variance, and the only statistically significant difference determined by the Mann-Whitney test was in the 5-8 c m level.

These samples did s h o w statistical significance regarding diiferences in the soil moisture between the t w o different species. At both levels the combined effect of fire history and species present produced a statistically significant result using both the t w o - w a y analysis of variance and the Mann-Whitney test.

EFFECTS OF ROOTS ON SOIL MOISTURE

As part of this study the effects of roots in the soil samples on the soil moisture determination using the gravimetric method were investigated. These are discussed below.