horse manure vs multipurpose compost - growing seedlings

Hello,

I'm doing comparison test between seedlings growing in 8 months old horse manure and the regular multipurpose compost.
I've planted clover, lupin, nasturtium, mustard (Horse manure on the left and multipurpose compost on the right).
What I've noticed is slower growth in horse manure and lower germination rate for all plants (might be because it is lumpy).
I'm yet to do ph test of both but what I wonder is why nasturtium and mustard have red/purple stems and outline of leaves, do you think it might be some kind of deficiency like phosphorous ?

http://s14.postimg.org/nc0oip1dt/IMG_20160221_072943.jpg
http://s28.postimg.org/y92tzes31/IMG_20160221_072831.jpg
http://s21.postimg.org/rbu9tdpav/IMG_20160221_072845.jpg

Thanks
Raf

I know in some plants they gain reddish pigments when they've absorbed toxic concentrations of nitrates.

Thanks for the answer I've been more and more puzzled by this, it seems that symptoms indicate lack of nutrients but might be caused by to many nutrients...not sure why is that need to learn more about it. I also have noticed the leafs are purple underneath.

http://s10.postimg.org/k1t6tbuvd/IMG_20160224_200401.jpg