Why does My new Zeland spinach looks SO sad?

Hi, it's the first time i'm growing new Zeland spinach and i'm in The Amazon jungle . The plant has 4 months aproximately . The pot it's 25 liters. But it looks like it's not growing well. Is it normal that it generate yellow leaves? What do You think?

Any advice?

Looks kinda like a pH problem.  I'm not an expert on new Zealand spinach or the Amazon, but i did try growing it in Missouri once and it died.  

First whats it growing in?

A quick search says new Zealand has acid soil.  Could be your soil is too basic?
Have you fertilized?  Extremely poor soil would look similar and a drowning plant can too

My advice is gently pull it out of it's pot, if the roots have grown all the way to the bottom, add fertility, if not change your soil out.  You don't need potting mix, regular Amazon dirt should do

Plant too big container too small?

Overwatering?

for the size of the pot, i'd say your plant looks about right. i have a garden full of this. the few yellow leaves are all old, at the bottom of the stems. they're going to fall off.
It does very well in clay soil, I would also put it in the ground. it looks like it's very leggy (straining towards light)... it can do fine in full sun. I'd pinch off a few branches and let it focus its growth on the remainder.
it also looks like your plant is full of buds, so it may be focusing more on reproduction. another reason to remove a few branches. most people i know who grow these regularly prune them and they tend to bush out.

The leggy habit is normal. When I've grown this in the garden it trails all over the place. It's tough, too. The best examples I've seen of it in the wild were along a beach in the southern part of the South Island. It was growing profusely mixed in with grasses and brush in the dunes, exposed to unceasing wind and salt spray. That was also the tastiest bunch I ever tried, maybe because of the salt. This is one of the greens I'd like to eat more of but always gives me that irritation in my throat that I associate with oxalates. I suppose cooking it would fix that problem.

Phil Stevens wrote:This is one of the greens I'd like to eat more of but always gives me that irritation in my throat that I associate with oxalates. I suppose cooking it would fix that problem.

Yes, around here it is our least favorite spinach-type green because of that, and even cooking doesn't get rid of that scratchiness. My kid likes it but to put it in food we basically have to blend it and mix it with something else to get rid of that feeling.

the curled leaves make me think it's over-watering but it could be a lot of different things.

I think it looks stretched out and etiolated, trying to find light.

I grew it for a couple of seasons but as others mentioned, I found something slightly unpleasant in the taste. To me it was kind of a metallic taste or something. Not fully unpleasant but not really nice. Sometimes boiling it and discarding the water before cooking it with oil and onions etc helped and it came out fine, and sometimes even that didn't make it good. Maybe once it starts forming those little flower buds, flowers or seeds, its flavor goes that way?

I grew it in the ground in a greenhouse, and it was very productive. In winter it would die back to the ground or close, but in spring it would rebound. And yes, the older leaves turned yellow and fell off on their own as part of the normal growth habit.