31 Dec 05

|

05 Dec 05

|

21 Nov 05

|

31 Oct 05

|

05 Oct 05

|

19 Sep 05

|

05 Sep 05

|

15 Aug 05

|

01 Aug 05

|

25 Jul 05

31 December 2005

After the rain at the beginning of December, the main trend in the data was wetting of the soil at the shallower depths. Only at the 1 m depth in the wedgetail (ungrazed) did any drying continue past this date. As the crop was mature when the rain fell, this continued drying probably reflects a slow response time of that sensor. The treatments were harvested on 15th December.

Drying occurred in all treatments to 1.2 m, with some indication of a small amount of drying at1.4 m. Treatment differences in the dryness of the profiles at harvest were small, and had no consistent pattern. It is concluded that grazing had no long term effect on the water use of whistler wheat.

A summary report and analysis of the year's results will be available from this website by early February.

05 December 2005

After another couple of dry warm weeks (until the storms on 2 December which produced 27 mm at Coolamon Post Office), the effect of drying of the soil profile by the crops are even more pronounced (compare profiles from early December with that from 15 November).  All treatments have dried the soil to the lower limit of the soil water sensor (200 kPa) at 0.2 and 0.4 m (although there was some re-wetting following the rain on Dec 2) and almost to 200 kPa at 0.6 and 0.8 m. Grazed Whistler has overtaken Diamondbird as the most strongly drying treatment, with it approaching 200 kPa at 1.0 m as well. At 0.8 m and above, drying seems to be slowing down in all treatments, but it is still accelerating at 1.0 and 1.2 m. The maximum depth from which water is being extracted is 1.2 m in all treatments. There is still no sign of the subsoil running out of water and failing to meet crop demand.

21 November 2005

After a pretty dry November, except for the very patchy storms on 7 November which seem to have bypassed the area (only 9 mm at Coolamon), the crops have continued to dry the soil profile. All treatments have dried the soil to the lower limit of the soil water sensor (200 kPa) at 0.2 and 0.4 m and are drawing water from deeper depths. Diamondbird continues to dry the soil more effectively than the other treatments, although the grazed Whistler is matching it at some depths. There is no sign yet of either the subsoil running out of water or the demand for water by the crops slowing down. The maximum depth from which water is being extracted appears to be between 1 and 1.2 m.

31 October 2005

In the last three weeks crop water use has accelerated, particularly in the Diamondbird treatment which has outstripped the other two treatments. The differences between the grazed Whistler and ungrazed Wedgetail decreased and had disappeared (as far as can be seen without the missing measurements at 0.4 and 0,8 m in the Wedgetail) by mid October. Visual inspection of the trial on 21 October indicated that the Diamondbird is further advanced and had a greater leaf area than the other two treatments, which were very similar. The Diamondbird and Whistler treatments are showing evidence of water use down to 1 m, while the effect of Wedgetail is shallower to date. Wetting of the profile at depth has stopped; the apparent wetting at the two deepest depths are attributed, because of their gradual nature and their timing, to the temperature effect. The continuing rainfall (65 mm for October at the Coolamon Post Office) has probably contributed to keeping the soil wetter at 0.2 m than 0.4 m under the Diamondbird treatment.

05 October 2005

Since 19 September the differences between the grazed and ungrazed treatments has become accentuated; even a month after the end of grazing, the effect on water use remains. There is still not much difference between the treatments at 0.2 m depth (presumably because of regular top-ups of rain), but the gap at 0.4 m has grown, while at 0.6 and 0.8 m it has remained about the same. At 1.0 m depth, wetting has continued under the Whistler (grazed) treatment whereas under the two ungrazed treatments, the soil has started to drain to the depths below. As explained on 19 September, this is because the capacity of the soil to store the rainfall close to the surface was smaller in the grazed treatment, thus forcing the water deeper.

There are several interesting comparisons with last year's grazing wheat trial:

	2005	2004
Depth of wetting	1.2 m Continuing to wet at 1.2 m in October	0.8 m Wetting ceased in September
Persistence of wetting	The soil above the wetted depth has remained quite wet (wetter than 40 kPa)	The soil above the wetted depth dried quickly after each rainfall event, and by October was drier than 80 kPa at 0.2 and 0.4 m, and drier than 60 kPa at 0.6 and 0.8 m.
Effect of grazing	In both years, grazing reduced the water use compared with the ungrazed treatments, and the effect lasted until October.

19 September 2005

The two main features in the data that have become clear since 5 September are (a) the differences between the grazed and ungrazed treatments, and (b) the effect of the significant rainfall on 10 - 11 September  (40 mm at Coolamon ).

(a) Following the heavy grazing at the end of August, the Whistler (grazed) treatment responded by drying less slowly than the ungrazed treatments, which continued to follow each other closely. This effect was not seen at 0.2 m, but is particularly evident at 0.4 m. This observation is consistent with the observations in the 2004 Marrar Grazing Wheat Trial, in which the grazed treatments also experienced a decrease in water use following grazing relative to the ungrazed treatments. It is a consequence of the decreased leaf area of the crop as a consequence of grazing.

(b) The 40 mm of rainfall had an effect down to about 0.6 m in the ungrazed treatments and 0.8 m in the grazed one. The deeper penetration of this wetting front in the Whistler (grazed) treatment is explained by the soil at 0.4 m being wetter under that treatment, as described above, so that the capacity of the soil to store the rainfall close to the surface was smaller in that treatment, thus forcing the water deeper.

The soil has started to drain at 1.0 m but continues to wet at 1.2 m under all treatments.

05 September 2005

The rain on 19 August (13 mm at Coolamon) caused a small spike in the soil water potential at 0.2 m, briefly interrupting a drying trend. Drying has continued since then, and was unaffected by the 10 mm of rain on 30 August. At 0.2 m, the soil is now drier than at any time since the winter rains started in June, indicating that the roots of the crops are now probably extracting water from this depth.

Drying has also commenced at 0.4, 0.6 and 0.8 m, but this is very slow and attributable to draining of water to deeper depths rather than uptake by the crops. This is consistent with the continued wetting observed at 1.0 and 1.2 m. The upward trend in the data at 1.4 and 1.6 m could also be wetting, but is more likely to be the temperature effect, as the coldest time of the year has been passed and soil temperatures, even at these depths, are starting to increase.

15 August 2005

The rain on 3 August (23 mm at Coolamon) topped up the soil profile, and although that on 9 August (8 mm at Coolamon) did not have as much effect, the soil remains at or near "drained upper limit" throughout the top 0.8 m. At 1 m "drained upper limit" has been reached in the Wedgetail (ungrazed) treatment, and is being approached rapidly in the other two treatments. Wetting continues at 1.2 m.

Since mid-July, there has been some drying at 0.2 m, temporarily reversed by the rainfall on 3 August. The Whistler (grazed) treatment has tended to dry slightly faster than the other two treatments, but it is not clear whether this represents a significant difference at this stage.

The "rogue" sensors at 0.4 and 0.8 m in the Wedgetail (ungrazed) treatment are continuing to recover, and appear to have reached equilibrium with the soil, but at a soil water potential value that does not appear real. It is still unclear what has caused this unrepresentative response by these sensors.

01 August 2005

Wetting has now commenced at 1.2 m in all treatments. At 0.2 m, soil water potential has now dropped below "drained upper limit", suggesting that water use by the crop, and perhaps evaporation from the soil surface, has increased over the last week or so and is starting to draw on water from that depth. Values at depths of 0.4, 0.6 and 0.8 m remain constant, while at 1.0 m the soil continues to wet.

The "rogue" sensors at 0.4 and 0.8 m in the Wedgetail (ungrazed) treatment are continuing to recover, but have not yet reached equilibrium with the soil.

Date :	16 June	21 June	30 June	10 July	15 July
Cumulative rainfall (mm) :	45	64	84	118	127
Maximum depth of wetting (m) :	0.2	0.4	0.6	0.8	1.0