In my short gardening experience I have discovered that organic matter is the most important aspect of soil for successful vege gardening. Organic matter provides nutrients and improves soil structure. In my garden, the main source of organic matter is the mulch (also used to retain moisture and keep the roots cool) and fresh manure for our steers (thanks boys!). I also keep a compost bin for all vege and garden scraps.
Our compost bin and weed/manure tea drum, the tomato is an added bonus!
I have kept a compost bin in the past when living in the city, and it was never very successful, so I was little nervous about starting one for the garden, but it is working well so far. I think the mistake I made in the past was not having the right ratio of wet/dry matter. I just chucked in all scraps and grass clippings and the compost just went a bit slimy and didn’t ferment properly. Now that I have access to some compost activators (micro-organisms and nutrients that are added to a compost pile to speed up the breakdown of fruit and vegetable scraps) and a wider range of compostable material, it seems to be working better. The compost activators include comfrey and manure, although this website also recommends urine! I throw in all scraps and garden cuttings, and grass clippings/hay if the compost is looking low. I put in manure and comfrey every couple of weeks. I put in a bucket of water or two if its looking too dry (or if I see a mouse living in there!).
I purchased a cheap commercial compost bin due to laziness, but you can build something fairly cheaply. At our last property we used a 44 gallon drum with both ends cut off. You could just tip it over a bit to get the mature compost out of the bottom.
My other source of nutrients for the garden is “weed tea”/”manure tea” (for a good description see here). We have a 44 gallon drum with tap welded near the top (thanks to my clever husband). I keep the drum filled with water and occasionally top it up with nutrient rich goddies like manure, comfrey leaves and any other weeds with deep tap roots, like thistle, that I pull out from the garden or paddocks. Every few weeks I pour out some tea into my watering can and tip it over the garden. Its supposed to be diluted, but I don’t bother unless it looks really strong. The tea is very rich in nitrogen, so I put it mainly on the leafy veges, like silver beet and lettuce and seedlings that I want to get a bit bigger and stronger before they flower. I avoid putting it on flowering or root veges, as they need more potassium than nitrogen to produce fruit and will get too leafy if they have the tea. You really only need a bag of manure every few months, so if you don’t have access to animals of your own, you can probably buy some to get you started and it won't work out too expensive. You can also just make weed tea instead with lots of weeds (mine grow better than my veges, so I always have a good supply). Do you use compost? weed tea? Any advice? More about my worm farm here.