Soil Moisture and Weather Station paddock report - 24 November 2017

View the monthly report below (or download a printable version).


Growing season rainfall (Apr-Nov):
Estimated available soil water capacity:
Soil type: Sandy loam over clay
Pasture type: Phalaris/ryegrass/clover based pasture
Current pasture status
(see photos below)
Composition: Phalaris 45%, Ryegrass 35%, Other grasses 10%, Clover 10%
Estimated Feed on Offer (FOO): 5400 kg DM/ha
Paddock and grazing management 250 ewes and lambs at foot grazed the paddock for two days in early November (1-3/11/17).
Narrative The soil moisture levels at this site could be described as marking time. The pasture remains green particularly due to the perennial phalaris component continuing to utilise the available moisture.  Even though we saw a batch of hot weather – with daily evapotranspiration figures of over 6mm on Nov. 21st and 22nd, rainfall has maintained moisture levels in the profile. This provides us with a good opportunity to compare actual water use against the weather based evapotranspiration model.

For the 7 days to Nov. 24th the net change in plant available water (PAW) was close to 0 and rainfall totalled 12.4mm. From this you could assume that the plants used about 12mm of water for the week or a bit under 2mm/day.

The 7-day reference crop evapotranspiration (ETo) was 28.4 mm (4mm/day) and using the suggested monthly Crop Coefficient  (Kc) of 0.74, modelled pasture evapotranspiration (Etc = ETo X Kc) would have been 20.7mm (3mm/day). Given that we now have enough data to be confident in our PAW figures, the discrepancy is likely to come from (1) water held in the top 10cm – where we don’t have a sensor – and (2) the Crop Coefficients. The latter are only available on a monthly basis and further, we do not have them for each pasture variety/combination. But what the above is telling us is that the Kc for the week 18-24 Nov. is likely to be closer to 0.5 or 0.6.

One month ago (26 October 2017)

Now (23 November 2017)


Growing season rainfall (Apr-Nov):
Estimated available soil water capacity:
Soil type: Red loam over clay
Pasture type: Annual grass and sub-clover based pasture, including some phalaris
Current pasture status
(see photos below)
Composition: Silver grass 45%, Barley Grass 45%, Wild oats 10%
Estimated Feed on Offer (FOO): 1700 kg DM/ha
Paddock and grazing management The paddock was last grazed by 1000 wether lambs (stocking rate of approximately 7 DSE/ha) from 24/10-7/11/17.

This site has recorded nearly 21mm of rain in the two weeks to Nov. 24th (20mm then 0.8mm). This has increased the plant available water (PAW) from 17 to 27mm (i.e. 10mm increase over this period). The pasture is not using moisture at this site, so where has the extra rain gone?

There are a couple of likely causes: the winter annual grasses which dominate the paddock have died off, while some moisture will gather on the stalks and more again will be held at ground level and in the top 10 cm of soil. Given that our uppermost soil moisture sensor is at a depth of 15cm, we can’t see the moisture at the surface. In bare soils, this evaporates quickly, but with established pasture/crops, the moisture is retained. Some will no doubt be lost to evaporation, but the rest will either stay where it is, or will infiltrate deeper into the profile. If the pasture is cut or heavily grazed, evaporation rates will rise and much of this would be lost again.

The PAW at this site is low so the profile fills and empties quite quickly. Pasture and grazing management decisions thus play a big role in making the most of the water.

One month ago (26 October 2017)

Now (23 November 2017)


Growing season rainfall (Apr-Nov):
Estimated available soil water capacity:
Soil type: Red brown earth
Pasture type: Oats / vetch
Current pasture status
(see photos below)
Composition: Oats 35%, Trash 55%, Bare 10%
Estimated Feed on Offer (FOO): 1700 kg DM/ha (not including the bales)
Paddock and grazing management After being cut for hay on 16/10/17 the paddock was baled in early November and yielded approximately 5.5t/ha. As there was still soil moisture in the profile after the paddock was cut, the oats started to regrow, with there now being 1700 kg DM/ha of FOO.

The photos below clearly show the regrowth in the oats in this paddock, but the accompanying water use is not visible on the graph. This is because the rain received has been well in advance of the water used. From Nov 11th to the 24th, the PAW increased by 11mm; rainfall totalled 45mm; ETo was 55mm and estimated ETc was 46mm.


Further analysis shows the top soil moisture sensor (15cm) is close to saturation and water has been moving quickly to 25cm and even caused a small spike at 35cm. With so much water available at the top of the profile, the oats are not experiencing any water stress therefore they will grow freely and plant dry matter will continue to increase.


December is just around the corner and the ‘on again, off again’ spring is likely to turn into a hot dry summer. But with 40% of PAW still on hand, this paddock should be able to hang on for quite a while and provide some handy ‘out-of-season’ livestock forage.

One month ago (26 October 2017)

Now (23 November 2017)

Thanks to Adelaide and Mount Lofty Ranges NRM Board and SA Murray Darling Basin NRM Board and TOIP Pty Ltd.

Disclaimer: this report has been prepared by BIGG and TOIP Pty Ltd. It is for information only and any actions or decisions made by readers from it are at their sole discretion.

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