Quinoa with yellowing leaves

[kathycam]

Hi, its almost a year since I got my allotment and I've developed a taste for unusual crops, so not sure if anyone would have tried this. I'm growing quinoa and the tops are looking healthy, I can see grain forming and each plant has several "heads". But the bottom of the leaves are turning yellow and some leaves in the middle section have yellow speckss. I've increased the amount of water I give them and added some feed (chicken pellets/ seaweed). Not made a difference. Is this just one of the stages it goes through? What else should I be doing. It's a raised bed with various layers including, straw, cardboard, leaves, compost, manure, rotting veg. Below are a few pics!

[kathycam]

Actually I looked, seems the yellowing may be part of the process.It just it looks so dramatically different to the top! Lets hope it works out.