No reason for the straw or hay to be there other than bedding and feeding purposes.The hay can have seed in it as well.So watch for the weeds and grass to grow around ya plants.Soon as moisture is applied to the aged manure you got all those sorts of thing wanting to grow.They rob all nutrients from ya grow.Composted cow manure would have gone through a heat and made all those weed seed sterile,and they would have decomposed!But your on the right path with the manure! Keep up the growing! Good luck!

Ga Grown