Improving the value & sustainability of Esperance port zone grain growers.

After the Fire – Points for Consideration


By Phil Smyth and Ben Curtis, Farmanco


Background

The events of Tuesday the 17th of November 2015 near Cascade, Grass Patch and Scaddan have left widespread damage and destruction and left many growers wondering how to deal with the already apparent threat of wind and water erosion over the summer period.

At present the main objective for all growers is to concentrate on the immediate task of completing what’s left of harvest in a timely fashion. Once this is complete and grain is delivered the focus will shift to getting away from the farm and having some well-earned and needed time off.

There is however some concern over a relatively large area of land that has now become prone to erosion given the nature of the soil.

The following does not attempt to give a direct action plan as we identify that each situation may be quite unique, rather it attempts to put options on the table for careful consideration.

Identifying soil types that are prone to wind erosion will prioritise areas of concern. Heavy soil types should be the least concern and can be left in their current state for next season. The light sands are the highest priority.

It is important to note traffic on these areas should be avoided all together even down to utes and motorbikes. Leaving traffic marks creates a point of least resistance for wind to start to shift the soil.

Nutrition

Straight after the fire it may look like a lot of topsoil is blowing away. The fine ash is easily moved by wind. Only a small proportion of nutrients are in this ash with the majority still in the soil.

Although there will be some patches that scour, depending on the soil type there will probably be only up to a few millimetres of soil that will be removed. This will be only a tiny fraction of the total soil volume so most of the soil nutrient bank and soil biology will remain in place.

In terms of nutrient loss:

·         Phosphate is the major nutrient that is stored in the soil. Most of the phosphate is evenly spread through the soil and in some cases it can concentrate in bands at depth. Losing the top few millimetres of soil will cause some small phosphate losses but the majority of it will still be left behind.  

·         It will be similar for potassium, which is a mobile nutrient and once added as fertilizer moves down through the soil profile.

·         The biggest potential losses will be for nitrogen through the loss of organic carbon which can concentrate at the surface. Our modern farming practise is good at supplying the crop with fertiliser nitrogen during and after seeding, so this can be managed.

There is also a consideration of the lost nutrients contained in the grain and/or stubble that has been totally removed.Table 1. shows potential losses from a 5 t/ha wheat stubble. The stubble was analysed for nutrient composition just before burning and highlights the need to consider background soil nutrient levels for next season’s crop and the requirement for early tissue testing.



Table 1.                                Nutrient loss from Burning a 5t Wheat Stubble

Nutrient 

Wheat stubble nutrients (analysed 24/05/2004)  

% Loss 

kg/ha of Nutrient loss for 5 t/ha of Stubble
 


 Nitrogen

 .63%

 80

 25

 Phosphorus

 .05%

 44



 Potassium

 .31%

 40

 6

 Sulphur

 .08%

 80

 3

 Magnesium

 .10%

 47

 2

 Carbon

 48%

 80

1920

Source:  Adapted from Maize Stubble Management Survey summary of results, Robinson and Kirkby CSIRO Land and Water Technical Report 13/02, January 2002.

Previous experience from growers that have had extreme fire events is that the damage can look worse than it is. The crop sown in the following year can achieve its normal potential as long as the nutritional needs of the crop are met.

Soil Preservation

We do know however that if areas of deep sand are moving now they can be gouged out over time and then become extremely non wetting and unproductive due to loss of organic matter.

Deciding on a course of action will depend on whether there is any burnt material or root material left on the paddock that will act to slow and hold the soil in place. If this is the case leaving the paddock untouched could prove the best option. The answer to this is likely ‘no’. October and November rainfall has been below average however moisture can be found in the lighter soils types within 10cms. Losing stubble will mean less pathways for moisture entry and the nature of the light soils will mean a degree of non-wetting making it hard to water to easily enter the profile.

Waiting for a rainfall event may be the best bet to avoid additional wind erosion caused by sowing and then seed depth issues caused by furrow fill resulting in a poor germination. Once the region receives a summer rainfall event, temporarily wetting up the profile, ideally a quick growing low cost crop like barley or millet should be planted. Avoid sowing with fertiliser as cover is required not yield. If sowing barley 50kg/ha should suffice or 2kg/ha of millet. Seed should be sown very shallow in case furrow fill occurs. Creating a furrow will act to slow wind movement across the soil surface and help to harvest water.

Another idea is to spread seed via a plane so as to avoid trafficking paddocks altogether. The plane is able to accurately spread at 50kg or 2kg if required. This would best be done prior to rainfall as some soil movement may help bury seed a little along with rain splash having the same effect.

Unfortunately given summer temperature conditions the top soil will dry out quickly so it will come down to the amount of rainfall required to germinate enough seeds perhaps a minimum of 20mm is required for this to work effectively. A delay in rainfall once grain is spread may also mean the seed could move around in wind events so this should be timed with forecast rainfall however precision spreading is really not the key here its ground cover.

Worry around creating a green bridge is of the lowest concern. Once your cover crop becomes established desiccating this crop around early stem elongation is advised. This will give enough cover, minimise stored summer moisture loss and should create enough of a gap for a winter crop to be planted with minimal green material present.

If you have access to the necessary machinery and clay nearby consider claying or delving the most susceptible areas. This is obviously going to depend on the amount of area affected.

When planning for next season ensure some thought is given to how the fires have affected long term rotations which may need modifying as particularly canola becomes hard to establish in this scenario. There may be a need for additional nutrients and early plant testing will be paramount to ensure deficiencies are rectified.

Each situation will be unique. If you require any advice tailoring your plan of action please give Phil, Ben or Gerard a call at Farmanco Esperance.