Subject: Mulching/Reseeding

From: jack rowe <[email-masked]>
Date: 03 Feb 97 12:34:54 EST

A basic answer to the question of when to cut green manures for greatest
fertility contribution versus reseeding is that a green manure will typically
have the highest levels of nutrients in its tissues, and the highest weight (not
counting seeds), when it is in the beginning of full bloom. As seeds are formed,
nutrients pass from the plant to its seeds, which are, as a result, excellent
concentrated sources of N, P, K, and minerals (that's why they're so good for us
to eat). Plants which have gone to seed are not so great as N-P-K-style
fertilizers, though they can still make a significant carbon contribution,
important for humus formation. Just don't let the carbon get way ahead of the
nitrogen if you are planning for production, as microbia will tie up the
existing nitrogen while working on decomposing the carbon -- growing plants
cannot compete with the efficiency of the microbia and will suffer nitrogen
deficiency. This is why you'll see that grass growing through sawdust mulches
(very high C:N ratio) will have yellowed blades and poor, spindly growth. 

When to cut for max fertility contribution also depends on whether plants can be
expected to regrow, or to die back upon cutting. Ryegrass, for instance, will
stand several cuttings if cut when young, but will typically die back if cut
just as seeding begins. The single cutting at seeding will weigh more than the
smaller cuttings individually, but not cumulatively. Not only will several
cuttings give a higher total dry weight (up to over 5,000/acre or 5,000 kg/ha),
but it will also be richer in terms of nitrogen. For plants which do not regrow
after cutting, there is in general no advantage to cutting before flowering
begins -- some weight gain would be lost. The grasses, in general, make
excellent nitrogen recovery crops for following crops in a rotation, and often
enough N remains after cropping that the total N captured by ryegrass can meet
or exceed the amount which would be produced by a leguminous green manure crop.
This because, although the legume will have double the tissue analysis for N,
the ryegrass will have double the total weight -- plus the added carbon
contribution and the capture of the other-wise wasted existing nitrogen. 

Jack Rowe
Seeds of Texas Seed Exchange
[email-masked]