During my recent trip to the southern coast of Western Australia I learned about something I didn’t even know existed: non-wetting soils.
The coastline in this part of Australia is exquisitely beautiful with white powder sandy beaches and turquoise blue water. This beautiful white sand is also what makes this area so challenging to farm. The sand is perfectly eroded by water to be a round particle, so it not only compacts easily but also has become non-wetting, especially in the top layer.
Non-wetting soils occur when organic matter decomposes and forms a hydrophobic layer around each soil particle. As a result, following precipitation, water is repelled by the soil and runs off rather than infiltrating into the profile.
I visited with Laura Bennett, junior assistant manager at Lobethal Farm, a 13,000-hectare property east of Esperance.
The land around Esperance is some of the last to be converted into cropland. It was originally thought that this land was only suitable for sheep farming. In the past, some who have tried to farm this land abandoned it due to high winter rainfall, minimal summer rainfall and low-productivity pastures. In the past 15 years, a change in mindset has resulted in a change in farming practices in the area, resulting in the amelioration of the soils. What was once deemed to be “livestock only” country has started producing some amazing crops.
The Lobethal farm
At Lobethal, crops grown include wheat, barley and canola, with some legumes such as lupins, field peas and faba beans included in the rotation recently. Legumes have been included to limit diseases that were arising due to the previous continuous wheat-canola rotation. The typical current rotation is a five-year sequence of a legume followed by canola-wheat-canola-barley.
Blackleg in canola has been the biggest disease issue at Lobethal. Australia is the first place in the world where agronomists have seen blackleg in the upper canopy, on leaves and pods post-flowering. Other diseases in the area are crown rot and take-all in wheat, net blotches in barley and sclerotinia in canola. Given that this is only the 10th crop that has been grown on some of this land, the high level of disease pressure is a concern. An increase in the number of break crops in the rotation was inevitable.
This is one of very few “crop only” farms in the area, where owners do not use the land to feed livestock for a few years to decrease disease pressure.
Another challenge apparent on my visit at harvest time was barley heads snapping at the neck. This phenomenon is known as “brackling,” and is due to strong sea breezes.
Because the area is very sandy, the soils are severely deficient in potassium, which means crops have difficulty dealing with heat stress in spring due to the lack of stomatal control.
In Western Australia, the non-wetting soil is mostly in the top layer. Techniques that invert the soil layer result in significant increases in yield potential. Lobethal has started implementing soil-inversion technology techniques including spading and deep ripping as well as the VRT application of lime and gypsum to improve soil structure against compaction and pH. Out of the 13,000 hectares in this block, most have been deep-ripped in the past five years. Around 3,000 hectares have been ripped twice and 9,000 hectares have been spaded. Trials are being conducted to see how many years the benefits in extremely sandy soils like this will last. They are expecting the benefits will last about five years.
The other challenge with soils like this is compaction. The hard compaction layer in this area is around 20 centimetres deep. Lobethal has implemented controlled traffic farming with all of its equipment. Currently, everything is set up on three-metre centres. This practice has benefits in terms of weed germination. Weeds germinate evenly so they can be sprayed at the appropriate timing. And, in the wheel tracks there is so much compaction that weeds do not grow and are not a problem even if the soil is bare. The majority of weed seeds are also confined to the wheel tracks as all combines are fitted with “chaff decks” which lay the chaff only on the wheel tracks during harvest.
Bennett manages multiple fertility trials every year, as well as variety trials, soil amelioration trials and general agronomy trials. Due to soils being inherently low in fertility, every nutrient required for plant growth must be applied in the right amount, in the right place at the right time. Nitrogen is applied via direct drill at seeding and then spread broadacre twice during the season. Phosphorous is also applied at seeding at a flat rate, while potassium is applied with VRT at seeding. Gypsum is applied at variable rates for both soil compaction and to meet sulphur requirements. Areas that do not need gypsum that grow canola will get sulphur in the first broadacre spread of nitrogen. Trace minerals including zinc, copper, magnesium and manganese are applied foliar with fungicides.
For Lobethal, this has been one of the driest years on record with only 350 millilitres of precipitation. So far average canola yields are 2.5 tonnes per hectare, with wheat and barley coming in at 5.5 tonnes per hectare.