There is an incredible difference between soils in Tasmania and soils in, for instance, river deltas like the Nile delta or Bangladesh where regular floods refresh and replenish the land at least once a year. An island like Java has young incredibly fertile soils because of regular volcanic activity.
In comparison, Tasmania has very old soils that have provided nutrition to native vegetation for millennia and have been subject to leaching and other weather influences for a very long time.
Tasmanian gardeners may believe that adding compost, manure and blood and bone to their garden is all that is needed to provide the nutrition their food crops need, but let's consider this for a moment.
The compost you use is most likely to come from your own garden. Elements and trace elements that healthy food crops need and that come in the form of zinc, magnesium, potassium, iodine, iron etc. etc. in your soil, will not be added to your soil as compost if they were not in your garden soil in the first place because plants use these elements if they are in the soil, but they do not manufacture them.
Manure from Tasmanian sheep or cattle is also unlikely to have sufficient quantities of these elements because they would be lacking in the soil the sheep or cattle graze on.
Blood and bone produced in Tasmania or on the mainland most likely will also not have enough of them either, because there will be insufficient quantities of them is the soils and therefore the animals.
Steve Solomon discusses these issues in his book Growing Vegetables South of Australia. It is not the easiest of reads at times, but it is a very good guide for Tasmanian food-gardeners, as it is specifically written for Tasmanian soil and climate conditions.
Steve Solomon argues that the only way we can make our food crops really healthy and therefore optimally nutritious is to use a 'complete organic fertilizer'. Based on years of experience he provides a number of options and choices. I took his advice and began to use my own mix based on his recommendations. I am in no doubt that this has made a big difference to the health of my crops.
Here are the ingredients and quantities of the complete organic fertiliser I use:
Blood and bone 1, Lime 1/2, Kelp 1/2, Dolomite 1/2, Seedmeal 3
The result is this:
I got myself six large tubs, 5 for the ingredients, and one for the mix. I wrote the quantity on the lid of each tub because I can never remember the formula. With a measuring can I put each ingredient in the mixing tub and then mix well. The mix is a potent one. I do not use it liberally everywhere all the time.
In my garden I use a 3-year crop rotation (Legumes, then Leaves, then Roots). I apply a little bit of the mix before sowing my Legumes, a lot when sowing/planting my Leave crops and nothing at all when sowing root vegetables.
Ingredients such as kelp are not necessarily cheap or easy to get, and, as usual, the bigger the quantity you buy, the more cost-effective it becomes. I realise you may wish to try this before buying too much, but buying small quantities is not very economic. Hardware stores and nurseries sell some of the ingredients. The Roberts store near the ABC roundabout has some ingredients. Hollander Imports along the Brooker Highway (opposite TAFE) is, in my opinion, a really good supplier with competitive prices.
In his book Steve Solomon is not afraid to give his opinion about things. He argues, for instance, that improving sandy soils is 'doable', but improving heavy clay soils is not worth the years and effort it takes. Well, I chose not to believe him when I tried to work with a heavy clay soil in part of my garden. I gave up after nine years and brought in good soil from elsewhere.
Google 'Steve Solomon gardening' and you will find a lot more information on this subject. There is even a YouTube video. The book is available at good bookshops in Hobart.
In conclusion I like to say 'soils ain't soils'. We can not all expect to grow the same things with the same rate of success because our soils are not the same. Making sure that our fertilizers contain what plants need is the way to success.