Incomuicardo,

From the World Bank figures, 6.2% of our land area (including islands) is arable. The differences between figures from different sources probably relate to exactly what counts as arable land. Sometimes improved grassland is counted, as with the CIA World Fact Book. The overall picture isn't changed much, however.

Divergence

More land may become more marginal if the cost of diesel and electricity continues to rise. A farmer may have a creek nearby, but the farmer still has to pump water to irrigate.

Certainly the cost of irrigation is a very big cost to farmers in the sugar industry, and a reason why so many farmers have left that industry.

Those who believe agriculture can soak up the vast number of immigrants being brought into the country each year have no idea at all.

It may not even be profitable to subdivide farms in the future. I personally know of a farmer whose farm was no longer profitable, and he wanted to subdivide the farm and join the most powerful industry in Australia, which is selling real estate.

However the cost of subdivision was so great, it was not profitable for him to subdivide his farm and sell it as housing blocks.

So that leaves what as an industry to employ all the immigrants and everyone else?