How does green manure shape up against orthodox forms?

[ourarka]

I have a big plot, and have been using green manure the past couple of seasons. I primarily use phacelia as it germinates readily and digs in easily. I use it primarily during long periods of no crop (rather than brief interludes). I really like the idea of green manure as, for a big plot, is is MUCH cheaper and easier than spreading tons of manure, or other soil additives and it doesn't form a nice, pungent 'all you can eat' buffet for my two dogs!!

Many places laud it as just as good, and I understand its ability to add organic matter/improve soil structure when dug in, and to prevent leaching of nutrients during the winter. What I don't understand though is how it can ADD nutrients, like manuring will. Surely, all it has to go on are the nutrients of the present soil? As crops (and the green manure) deplete them over time, they have to be re-added somehow or other? Or can the green manure add fresh nutrients, by taking them from winter rains etc?

[Kristen]

Good question, and I too will be interested in the answers

Implicit in what you said, but any nutrients that would have been leached, that are taken up by the Green Manure, are in effect "added". Nitrogen-fixers have that ability too, so that might help specifically with Nitrogen (although I read conflicting things about how well a follow-on crop can utilise the Nitrogen fixed in root-nodules on legume crops ...)

Personally I've never seen Green Manure as a substitute for Farm Yard Manure, and I use both. But I am intrigued by your concept that Green Manure is easier to apply etc. as lugging barrow loads of manure from the roadside to my plot is quite a strenuous task ...

[Shadylane]

Well there's the nutrients the plant makes using photosynthesis I think. I've never really used it properly and for long enough to say whether it is a suitable substitute, although there are people on here who will tell you that you don't need farmyard manure and green manure and compost is sufficient. I'm trying it on one of our plots for a few years. Haven't mucked it this year or last, but I haven't really done green manure 'properly' in that I always forget to sow it in time. I have used weeds and left them on the surface.

On our other plot I didn't muck the greenhouse and the toms have been nowhere near as good this year, but then I didn't muck it last year either. I compost everything possible but there's still no where near enough to spread on the beds and the greenhouse/polytunnel, so I am going to use muck on that this year if I get some in time.

[Noosner]

I'm trying gm for the first time this year too and would be also be interested to know more. Transporting muck to my plot is tricky as a truck can't get anywhere near. A local manure supplier gave me a hand last year but he wasn't interested in doing it again this year. He kept making excuses about not being able to deliver, until the penny finally dropped, and I stopped pestering him!.

[solway cropper]

The point of green manure, farmyard manure and compost is to add organic matter which helps the soil structure. None of them have a lot in the way of nutrients although FYM generally has more than GM. You will need to add fertilizer from another source, either organic or otherwise. I use seaweed and BFB along with home-made liquid feeds which has been doing the trick for donkey's years.

[Dorothy rouse]

How does green manure shape up against orthodox forms?

I've just used green manure in small raised bed this year, I used more last year and found it really hard work to dig in/turn over. I also used farmyard manure, seemed to produce a lot of weeds, and also emptied contents of compost bins , which wasn't really composted at all, covered some beds, covered this with black weed membrane until the Spring, this seemed to help the soil best, so will be doing the same this year. Also use chicken manure pellets. So for me def a mixture.

[Kristen]

None of them have a lot in the way of nutrients although FYM generally has more than GM.

I wonder about this. Horse manure, from pampered-animal stables, is probably just droppings ... maybe a bit of straw but bedding from over wintered cow sheds will have as little straw as the farmer can get away with and will be saturated with urine / slurry etc. I wonder if after a hard winter, when the animals have to indoors for longer, whether the manure will be more urine-rich so to speak? (more straw will be used too of course)

[Penellype]

Horse manure will be a mixture of poo, which is basically chewed up hay/grass partly digested and mixed with gut bacteria, and soiled bedding, which will contain urine. The urine contains far more nitrogen than the poo, but the poo contains plenty of bulky organic matter so it is also good for the soil.

Green manure can add nutrients in several ways. It prevents leaching, it adds organic matter created in part from photosynthesis (so water + CO2 from the air is converted into sugars), and deep rooted green manures can also draw up minerals from deep in the soil and make them available to future crops.

With regard to leguminous plants fixing nitrogen, the bacteria that live in the root nodules have a symbiotic relationship with the plant, providing it with a built in fertilizer. When the plant dies they will probably die too, but the nitrogen they have absorbed from the air and converted to usable nitrogen compounds will remain in the soil, either released by the bacteria or from the decaying plant material from the green manure.

[Feral007]

Our horses are paddocked, so no mixed straw/urine in it. So prob not comparable. I use the manure in the water barrel for manure tea. Last year, not so much manure tea and the plants not so good. The year before lots of manure tea and the plants went gangbusters.

So more manure tea brewing as we speak.

We used green manure winter before last. Was good to keep ground covered, and moist. Not sure that it made things fabulous in spring, but it did help in winter. We were reclaiming paddock to fruit forest and that worked for us.

[bravo2zero]

I started using them in earnest last year using phacelia and red clover mainly during summer, rye and tare overwinter and mustard all 4 seasons. I try to rotate them as much as i can and consider the benefits to crops after like mustard before tatties for it biofumigant properties tare prior to leafy/stalky crops etc and always to alleviate erosion and leaching throughout the year. ive even gone as far to sow it in 20mm cell trays to plant out as soon a crop is cleared. With regards to adding nutrients i think a status quo is struck over time and the benefits of added goodness to the soil takes years of constant use and vigilant rotation, think about it, a green manure will not deplete nutrient levels as its waste product is oxygen the rest of it is dug back in adding humus when it composts down.This year ive closed 2 beds and will only used green manure and garden compost and will monitor over the next 5 yrs. For those who run a no dig plot chop it down into small pieces with shears and cover with plastic, membrane or carpet until the worms have dragged it down. Ive even this year let a bed of mustard go to seed and collected it for next year.

[KevinM67]

Great post - bravo2zero