Hi Gen, it has been a while from your last post. Legumes such as white clover, are capable of extracting nitrogen from the air and converting it to a usable form of nitrogen,. Clover collects nitrogen in nodules in its root system. However, I don't believe it is available to other non-legumes unless the clover is killed and degrades through common agricultural systems such as tilling the clover crop under. We grow yellow clover here on the farm as a cover crop, which is turned under as a green manure. However, if the clover in the citrus container is alive and growing, I do not think its nitrogen is available to the citrus tree. - Millet