early yellowing

I am at the beginning of the 5th week of flowering and I have a marked yellowing on the leaves... in this phase should I increase the nitrogen or is it better to let the thing proceed as it is? (harvest 8/9 wk) ... increased nitrogen? do I push with grotek npk 18-36-1 and then continue with the normal fertilization program?

Have any pictures? where are you located? Is it raining alot? are these plants in a greenhouse or are they in the weather? If i was you i would probably start a flush and get ready for harvest, but its depending on your conditions , i wouldn't be loading nutes into my plants if they were that close to finish, you'll have a hard time flushing later and could potentially run into worse damage to plants from burning.

I'm not in a greenhouse. The weather for now is still quite decent

They look pretty damn happy, i would say they are approaching ripeness keep an eye on them the next couple weeks and you should be done, i wouldn't put anymore nutes in unless a DRASTIC change happens, a flush should be starting soon they look great

it seems to me that the plant is still behind with the ripening of the flowers for having already begun to turn yellow...
this year I had an early yellowing in almost all the plants... next year if I keep the same soil recipe I will have to remember to do a top-dress at the beginning of pre-flowering

in these photos maybe you can see better

Oh is this soil used previously ? Then you probably have run a deficiency.

Don't worry about it at all.. That is not what i would consider a little yellowing, that's almost none considering its week 5 of flower. Start cutting out the nutes slowly or don't add anymore ammendments. I like to go with a slow flush and by week 5 of flower they should not be that dark green in my opinion, but thats just me. I find my smoke is always smooth and the terps are amazing, i always consider my long slow flush to be apart of that.