We need chemical fertilizers mostly because we practise monoculture as our modern agricultural model. Nutriments needed to grow a crop need to be replaced chemical fertilizer arean easy way to do this. There is no way that you could produce the volume of compost needed to do this.
There are however, many alternative methods of agriculture that do not require the use of fertilizers or the addition of compost, many of these can be found in the traditional agricultural societies in the developing world.

Yes growing food takes nutrients from the soil which must be replaced if the soil is to remain viable. Composted plant material is the best means of replenishing the soil. Assay the soil periodically to determine what it needs and supplement it with an appropriate compost or other soilI amendment to maintain a good balance of nutrients.

Crop rotation with nitrogen-fixers like lentils can do the job, from what I hear.

nature uses animal and leaf waste but there are so many fucking humans we have to change how our food even grows ie genetically modified. we have to make loads of man made stuff to then keep creatures under control and then fertilise it. balance has all gone.

While crop rotation can replace nitrogen in the soil unless you let the whole crop rot on the site you are removing phosphorus, sulphur, calcium, iron and the micronutrients every time you harvest 9or take animals away to slaughter. If they are being removed then they need to be replaced by otherwise the soil becomes deficient and crops fail or do not have the nutrients required to sustain animal life (eg. the plant survives but anything relying on it for food fails.) The only exception is flood plains where the soil is replaced anually.
Natural systems rely on the breakdown of rock to release minerals and trace elements for uptake by plants, and the death and decay of animals and plants to return nutrients to the system but once you start removing food from the system it is no longer self-sustaining.

I never spray chemicals on my garden. Yeah we need to fertilise.

How much food do you want/need to grow?
Many soils lack various nutrients, plants need 16 elements to grow,
soil and climate conditions are not suitable for all plants, if you want to grow plants not native to an area you may need to add,
also if growing crops continually in theone place you will definately need to add stuff.
Human poo, humanure is in short supply in China.

Yes we need.
We are extracting energy from the plants in a speed much faster that they evolve to do. This drains the soil as natural fungi and bacteria can't recover it.
That's why we need to pump this extra energy into the soil using fertilisers.
Crop rotation could avoid it, but the rotation crops are not as productive as the huge ones.
Our food source is based on corn, wheat and soya, and those 3 will drain the same kind of nutrients, other crops are waaaaaaaay less productive and the net output would be order of magnitude smaller if you do the rotation.
We are way too many on the planet and we need the technology to sustain this amount.
Without these technologies maybe we could sustain 2 or 3 billion max.

The "green revolution" back in the 30-60s showed that chemical fertilizers worked and were able to allow the population to grow. It increased production, but not without cost. Some interesting arguments listed on the wiki article: [en.wikipedia.org] (and as I alway encourage, support Wikipedia with some funds).

Yes and no. We absolutely need advanced fertilizers and composts to grow food at the rates necessary to feed the planet’s population. However, the way in which we create those fertilizers and composts could use some changes. Current industrial fertilizers contain far too much nitrate-nitrogen and are causing major problems to our water systems.

You can mke your own compost easily enough seawwd is good if you live near the coast.

I want to add another point: in the 50s, a study was published on fertilizer methods - artificial and "green"fertilizers to detect a relationship to the incidence of Multiple Scerosis. AT that time, in Europe and England, artificial fertilizers were used almost exclusively and the rate of MS was 80/100,000 while in China, where green fertilizers were used almost exclusively, the rate was something like 1.6 out of 100,000. Green fertilizers are plants that are grown after harvest , then plowed back into the soil. Nothing was ever done with this study, results were published but not followed up because... my own bias here... the big chemical companies in Europe and America were not letting a small study hinder their huge financial success in any way.
My friend Oonagh ( from England) died a miserable death from MS. I am still convince that the agriculture in England added to her death.

Last year my garden was sad sight, it was our first garden in our new home. This year I added steer manure into the soil, after I get it going I will see if I can get some photos going. Unfortunately I had forgotten to take photos of last years garden disaster.

We use natural compost inorue home gardens. Works just fine.

Nope the organic farmers can do it with rot water and love

Only to produce the same crops year after year on the same ground to the abundance needed to justify the expense of inputs. In reality nature provided us with what we need in natural fertilzation methods and if everyone had the time, space and ability to put up a garden and preserve their harvests we wouldnt need large commercial growers for many of fruits and vegetables and even our grains. We live in a world that is unbalanced in its resource distribution. People in Africa starve for the lack of basic nutrition meanwhile those of us in the west throw out and waste enough food to save those same lives.

Well you don't need fertilisers at all.Maybe initially to save time but on any reasonable soil NOTHING IS NEEDED. And yes I can prove it.Just look at weeds and trees growing with no help.

1. Collect all the weeds you can instead if spraying them.This is the catch as it takes a lot.
   2.keep all rows well mulched or at least enough to keep surface microzoa alive
   3 Roll regularly with metal rake to disturb and harvest weeds.Don't dig on rows.Worms will do all the work from here to harvest.
   No machines no expense just three or for basic tools.