Replacing Nitrogen

We're on the cusp of having animals out in our fields but I'd like to raise them organically.  However, I've just had a big discussion with someone who has worked for many years on grassland research and he says that it's very difficult to replace the nitrogen that the animals eat in the form of grass.  I guess that means poor pasture after a while.  Is that why you see farmers flicking vast quantities of stuff (presumably nitrogen) onto what appears to be 'just grass'.  How does one maintain the nitrogen level without resorting to adding chemicals? 

(He challenged me - that nitrogen occurs naturally anyway so how is it unnatural to add it as farmers do?  I respect his opinion and I know that he plays devil's advocate sometimes but I'm often stumped how to reply  ops:)

I wonder what your acquaintance has been doing wrong all these years.

Commercial nitrogen fertilizers are synthesized using fossil fuels. These resources are limited, and we are running out of them. Their synthesis accounts for a significant percentage of greenhouse gas emissions, and over time it ruins the land because commercial fertilizers don't include the micronutrients or support the microrganisms that are necessary for healthy soil. Commercial fertilizers run off into the local waterways and cause algal blooms, which use up all the oxygen and then kill everything else in the water. This happens because they're ultra-concentrated, but also because they are just applied to the surface of the soil where they will be washed away by the first hard rain. Healthy soil has plant roots, animals, and fungus working to fix nitrogen below the surface 24/7/365.

I don't think organic methods of replacing nitrogen are as difficult as your acquaintance says—they involve the use of cover crops and allowing the animals to trample their urine (which is naturally nitrogen-rich) and manure into the soil. Even better results can be obtained by managing a diversified perennial grassland with rotational grazing, or through Joel Salatin's methods. This short blog post skims the surface and might give you an idea where to look: Permaculture Gardening and Rotational Pasture (Grass) Farming You might get even more information from ATTRA, here.

Don't panic, I think your friend is talking about intensive agriculture !

The simple approach to having good healthy pasture is to avoid overstocking.

Let your browsing goats on the land first then put the close grazers on. Horses or donkeys are ideal because they complement sheep and goats in the sense that they ingest the internal parasites of each other and "clean" the land. 

Then allow your chickens to peck the grass and eat the other animals' parasites at the same time contributing their nitrogen-rich droppings.  Rest the land or if possible use it for a crop, for growing a green fertiliser or for cutting hay.

Repeat.

very interesting Irene.  I have never heard of this.  So the worms that inhabit goats get killed if they are eaten by a horse? How about a cow?  Where can I find more information on this. 
It seems everything is wormy in this day and age.  animals, apples,  there is something that will bite on it.  When I grew up we never wormed, ever.  But our meadows grew a big variety of plants.  I remember when farmers started planting hayfields to get rid of all the "needless' plants.  I think that did it.  Modern agriculture probably has fostered the proliferation of parasites by crowding out natural antidotes.

Elfriede B,

I think the same applies to cows but since horses nibble the grass right down (Where the worm larvae tend to stay because they need the humidity) I'd imagine they'd be more effective.

Resting the pasture for two months is also very effective because it breaks the life-cycle of the parasites. That's why it's better to have several smaller fields and rotate the animals - even keeping them inside on hay for a while during the winter or during lambing/kidding can help to de-worm them and rest the pasture. 

I've got a lot dreadful memory for the names of books I'm sure there's loads about this on the internet. I'll have a look for some links. (I'm on lambing duty so I'm on the internet a lot between contractions and ensuring the wee ones have colostrum.)

I've found one or two references :

Internal parasites have adapted themselves to the internal environment of their host animal and have become host-specific. Horse parasites can only exist in horses, this means that cross grazing with either cattle or sheep can actually assist to reduce the worm burden on your pasture. Although Cattle and Sheep are also affected by worms, those which affect horses do not affect cattle or sheep and if ingested can not mature, thereby breaking the life cycle. This can be a useful factor when considering parasite control.

This was taken from : http://www.horseconnections.co.uk/pages/worming.cfm

The use of clean or safe pastures will help to control parasite problems. A clean or safe pasture is one in which sheep or goats have not grazed for 6 to 12 months. A pasture grazed by cattle and/or horses is also considered safe, since sheep/goats and cattle/horses do not share the same parasites. Pastures that have been renovated or rotated with row crops are clean, as are pastures in which a hay or silage crop has been removed.

This was taken from :

http://www.sheepandgoat.com/articles/IPM.html

It makes sense to have mixed farms - but I'm sure you know that already !

That's really interesting about the multi-animal approach.  I had wanted to do this but thought that maybe I was taking on too much - now it seems they look after each other to some extent 

And Kerrick, I'll no longer be tongue tied. 

I'm now off to look at these sites that you guys quoted.  You are a wonderful and enlightening source of knowledge. Thanks

"Just grass" is probably a recipe for disaster, I agree.

Natural vegetation usually has some broad-leaf plants mixed in, and among these are, quite often, some plants that host nitrogen-fixing bacteria. These bacteria serve the same function as the Fischer-Tropsch chemical plants that most farmers rely on, in that they take in a cheap and available form of energy plus nitrogen from the air, and put out ammonia.

As others have pointed out, the supply of clover is a little easier to secure in the long run than the supply of natural gas. Unless by "secure," you mean "corner the market on." The quote I use in my profile is from the Supreme Court's ruling that nitrogen-fixing symbiotic bacteria could not be patented. It makes sense for businesses to promote sources of nitrogen that they can control centrally, rather than more grassroots (well, clover root nodules) solutions.

With enough clover, lupine, etc. in your pasture, nitrogen won't be a problem. Most of the agricultural workhorses in the effort to replace soil nitrogen are in the legume family (fabacae/rhizobium), but alder, lichen, azolla, and a host of others have their own nitrogen-fixing symbiotic arrangements, with varying degrees of similarity to the way legumes work.

There are other elements than nitrogen to worry about depleting, though. Organic farmers often buy greensand and other minerals to replace things like phosphorus, potassium, etc. If you test your soil and find that something is lacking, this forum might be a good place to ask about the most-sustainable way of making up the deficit.

Excellent info Joel,

It's a fascinating subject and the more you learn, the more you realise you need to know.

In France you can take a few samples of your soil to your nearest agricultural college and they'll do an analysis for you free of charge.

If you're lucky they may also have students who would like to use your land as a project and you'll get help deciding what animals and crops would be suitable for your situation. You can then make your on mind up.

Yes Joel, my friend was also mentioning phosphorus and saying that that was the BIG one to watch for.  He was only half-joking when he said that folk might want to leave their body to agriculture rather than medical science in the future!

Irene, your sentence faded out - has a lamb just popped out???

Ooops, something happened and I pushed the wrong button just before I went out then went back to edit the post !

You must have posted just as I was doing that.

Sorry ! 

Thanks a bunch. 

Adding lots of nitrogen (whether from natural or industrial sources) is a quick way to boost yields, but it has some negative effects. Ask your friend if he denies that high nitrogen applications will deplete organic matter from the soil and negatively impact structure and C.E.C.  And many industrial sources of nitrogen also have a dramatic lethal effect on worms, insects, and other components of the soil ecosystem.

Phosphorous can be a limiting factor in some pastures - one way to deal with this is to encourage fungi. Many fungi are very good at solubilizing phosphorous and transporting through the soil - when plants give them a little protein and sugar, and they will more than payback the plant in phosphorous. Mycorrhizal fungi do this, as do free-living fungi.  We are looking at rapid depletion of highly concentrated phosphate deposits ('peak phosphorous') ... but most soils contain a huge amount of dilute phosphorous in their mineral matrix. That poses an insolvable problem if we use the soil as an inert hydroponic media, but not if we manage soil-based  ecosystems and coax out the existing phosphate. The prairie ecosystems of the world were pretty productive before we came along, and they supported high plant productivity and huge herds of buffalo or other grazing animals.

One of the things we do to aid this process on the fields near the house where the goats spend a lot of time is to feed the goats branches of shrubs and trees cut while we're clearing the garden.

We throw clippings over the fence and the goats help themselves to the leaves and soft woody stems. The larger branches stay where they are protecting the ground from the animals to allow weed seeds to take root. When the animals are moved to other fields or into the woods to browse for their own food we add more wood chippings and they and the branches gradually rot down.

Fresh tree chips are highly regarded by the French as a mulch called BRF. (Bois Raméal Fragmenté) which helps introduce the elements necessary to make good humus, aiding soil conservation due to the water retention capacity of humus content and the capacity of water accumulation and management by soil organisms.

BRF also encourages highly-mycorrhized root systems, higher phosphorus, potassium and magnesium content.

http://www.sbf.ulaval.ca/brf/regenerating_soils_98.html

I've used a more intensive system of BRF for a few years in several plots in the vegetable garden and so far the results have been good. I'll try to find a few more links in English and post them - so far most of the information I have is in French.

Another thing we do is move our goats in the evening. They spend all day browsing on the rich land in the valley, so we herd them up to the top of the hill to count and check on them. They sleep outside where it's dryer so our grazing is improved for the winter months with their rich droppings. 

How would pigs fit in to this rotational grazing bit?

Polyculture!

Looking at that pic, I would not put animals on that pasture until there was more to eat.  And it needs lots and lots of trees and shrubs.

And there is a difference (IMOO) between grass and pasture.  Pasture is more likely to be a polyculture:  plants helping plants helping plants.  So some plants are gonna be great at bringing in excess N.  Some are gonna accumulate P and/or K.  Some or gonna share water.  Etc. 

Trees, bushes, mycelium, bacteria ....  permaculture!

And pulse grazing results in five times more growies in an area (not of all plants, but quite a few!)

Did I mention TREES! 

Paul the sheep aren't grazing in that field. We cut hay then horses have been in there for the past couple of weeks.

The sheep (and our goats) have access to 60 acres of hundreds of varieties of trees, shrubs, shade and water from a stream in the valley. We encourage all our animals to come up to the fields at the top of the house in the evenings for a small ration of cereal which we feed for about 6 weeks before and after lambing or kidding. The chicken clear up the last of the cereal left on the ground and also eat a lot of ticks and other parasites (sometimes straight off the animal). We count the sheep to make sure they're all there, look at them to make sure they're OK and they sleep near the house to make our lives easier.

If they stayed in the forest and margins all night they would lose lambs through birthing problems or to dogs, badgers and foxes.  This is about half of our land and will give you an idea what I'm talking about.

heninfrance,

Pigs don't graze as you probably know and destroy pasture for any grazing animal. But as they are great diggers you can use that to your advantage in rotating land. Two of our young pigs cleared an acre here in about ten days and really enjoyed themselves in the process !.



We left this field to regenerate naturally and after two years it has a wonderful mixture of all sorts of plants - which is exactly what goats need.

They'll clean a space filled with gorse, bracken and brambles and eat anything edible they find. In the spring and summer we feed ours near the house from our veg plot. In autumn, we've several fenced-off areas in the woods where they eat tree leaves, bushes, acorns, chestnuts, to their hearts' content. (We don't put them in our best Cep areas though ! )

Pigs have the added advantage that unless you want to breed your own, you can kill them in the winter when there's not much to eat then buy weaners in spring. 

Providing you've enough food for them, they are much easier to keep than goats and sheep !

Paul hits the nail squarely talking about microbes and fungi...

Your nitrogen in a healthy soil is found in bacteria. Your phosphorus is a combination of soil content and fungi. Maintain these two populations in a healthy fashion and you need NEVER worry about either nutrient.

Introducing biologies to depleted soils (which could be from acid rain, previous chemical use of everything from fertilizers to pesticides, flood, fire, etc.) is as easy as a good compost tea; it distributes evenly through the soil profile and each organism finds its happy place and STAYS there, unlike chemical nitrogen that washes away with the next available moisture into our streams, rivers and ocean. We do NOT need any more dead zones; we have plenty and they are growing... Aerated Compost Teas (ACT) are non-invasive to soils, utilize local biology when made form local compost, and do not replace existing ecology but supplement it.

In particular the additional protozoa are the key component to additional plant available nitrogen. These higher predators eat vast amounts of bacteria, releasing their inherent nitrogen (Bacteria are VERY high in nitrogen with a C:N ration of 5:1; protozoa and humans are about 30:1). This continual release happens directly in the zones around plant roots, as plants exude polysaccharide compounds (called root exudate) to attract bacteria and fungi.

So we have a natural system that both stores and releases nitrogen in a controlled fashion directly on target for plants, that we can support in a non-invasive manner with sustainable renewable inputs. What's not to like? Who needs to add anything once it is well established and self-sustaining?

We simply need to look at our soil biologies as smarter than we are about how to do this, and at least get the hell out of their way if we can't work with them... 

Jeff Lowenfels and Wayne Lewis have written a great book on this topic called Teaming with Microbes; we are currently discussing the book with Jeff here. Join in, it's a central tenet of permaculture to build your soil, so you should get to know your workforce... 

S

Scott Reil wrote:
Your nitrogen in a healthy soil is found in bacteria.

The whole soil food web topic deserves more attention.
Good introduction straight from the queen of SFW Elaine Ingham

The key is "in a healthy soil".  I suspect lack of organic matter or poor gas exchange due to compaction can so undermine soil ecology that subtle manipulation of biota is moot.

Secondarily... if microsites and forage are capable of supporting biota, then why is introduction warranted?  Is dispersal of soil biota that slow?  Is the compost tea effect actually from a change in biotic composition, or just the pulse of easy to decompose organics?

On that last bit, some of both Paul... 

I'd agree there are situations that warrant extreme measures, and low humus levels are probably the key indicator for a depleted soil, but it is amazing what the addition of just a few microbes and fungi can do for soil structure and tilth. With as little as 2% humic content you can establish some decent soil biology where none existed (chemical depletion, dehydrated soil) and yes a,dding back some more humus along with the biology is just smart (I don't go camping without a tent, so we ought to send these guys along with somewhere to live, and all soil biology lives in the humic content of soils.

So a good tea is both humic content and biology; "food" values are superfluous. They are part of the biology, which also assists with leaching mineralized nutrients from the parent material (rocky part of soil). Plants feed the biology as well, keeping them close by the roots. It's a system that is complex in design, but it is very elegant in its simplicity of concept. Plants feed biology, biology feeds plants. Why we ever got explosives mixed up in this process is beyond me. 

S

Irene Kightley wrote:

Fresh tree chips are highly regarded by the French as a mulch called BRF. (Bois Raméal Fragmenté) which helps introduce the elements necessary to make good humus, aiding soil conservation due to the water retention capacity of humus content and the capacity of water accumulation and management by soil organisms.

BRF also encourages highly-mycorrhized root systems, higher phosphorus, potassium and magnesium content.

Irene, BRF - do they make thi with a shredder type thing?  Around here they seem to burn all the very small branches/twigs.  We have a whole host of branches and twigs that I could REALLY do with as mulch but our pathetic electric shredder is doing a crap job and just using up mega watts of power.

most pigs dig and root, but not all and some do a little digging but not a lot

there are pigs that do well on just grass

is it really true that 2 young pigs turned up an entire acre to leave no vegetation like in this picture in only 1 week?

from what i have been led to believe this doesn't work, at least when you are planning on planting in to where they were digging.

there is a growing number of people producing pasture raised pork, the thought process that pigs must be kept in pens has been abandoned, i hope it stays that way haha!

I'm given to understand that Kune Kunes are more of a grazer.

We now have 2 British Lop x Large Black 13 week old sows and they are in a paddock that's about 1/4 of an acre.  We have had them for 3 weeks and they have lifted the 'turf' in a couple of patches but mostly lay about the place.  Maybe we're feeding them too much?  I'll continue that in my other thread about Keeping/Feeding Pigs.  I'm hoping that they DO dig cos wer hoping to move them on to the next 1/4 acre and plant this one up.

Yes Kune Kunes tend to be grazers but the older outdoor varieties like Berkshires and GOS dig all day if you let them.

asmileisthenewak47 wrote:from what i have been led to believe this doesn't work, at least when you are planning on planting in to where they were digging.

there is a growing number of people producing pasture raised pork, the thought process that pigs must be kept in pens has been abandoned, i hope it stays that way haha!

Our experience is that they are wonderful at preparing new land. They clear everything !

I hope it stays that way too !

I know Jeff! Every couple of years I make it to his fantastic July 4th party.

More on topic, Yes, nitrogen does exist as NH[sub]3[/sub] (well NH[sub]4[/sub]OH) and NO[sub]3[/sub][sup]-[/sup] in the soil, and you can add it, but quantity matters. For instance, there are minute amounts of water in your lungs, if not they would have the consistency of styrofoam (dried lungs are so cool!) however it is not wise to fill your lungs at the bottom of the pool.

One of the benefits of organic matter, even with out the associated microbes, is that there are big complex and hairy molecules that will grab on to and hold onto those fertilizer chemicals, but only in fairly low concentrations. In high concentrations you have them floating in the soil as a salt, where they kill many of the organisms you want and your soil looses the ability to hold many of the nutrients it once did. Some nitrogen is incorporated in the living animal, but the manure contains most of it. If you supplement feed you may actually bring in more nitrogen in the feed than you loose to the meat hair and hide. Add to this the nitrogen fixation off of leguminous components of your pasture flora and you have a recipe for sustained production. How does your friend think that the prairies survived for so many thousands of years?

And don't forget that if the amount of urine that exits your body in one year is strategically placed in that depleted field it will potentially N-fertilize 3,000-9,000 square feet.
    And you can always get a bunch of lentils, esp. the little black organic montana lentils (more seeds per pound) that you can buy in bulk at the Good Food Store in Missoula and many other places , dip them in appropriate bacteria, then broadcast them over that land., let 'em go to seed and die back into the soil.

So lots of natural additions of nitrogen listed here, none of which kill off biology (which the ammonia salt fertilizers will), pollute the air with CO2 in their production (the Haber-Bosch process burns four gallons of fuel for every fifty pounds, and that's before they ship it across the country to get to you), won't compress soil (chemical compaction takes place as fungal structure that holds voids in the soil dies off from the chemical assault. This decreases aeration, water retention, and fertilizers associations that help plants with water, gas, and nutrient uptake).

Chemical fertilizers are a hundred year old experiment based on "What do we do with these leftover explosives?" It was a stupid idea then, and it remains a stupid idea...

HG

Seth, that's an interesting idea about the lentils.  Appropriate bacteria?  Please can you expand on that one.  Plus what sort of climate do they need to thrive?  Could some of them feed my chooks (I have half an acre to plant up with animal food)

Rhizobium sp.  innoculant They have different strains for beans and peas but I'd imagine any would work You can find it at most garden centers. If you want I'll find you some online.

Salts are all right, and even needed, it is a matter of concentration. A very light application of Nitrogen salt fertilizer will be 100% Okay, because the plants will snap it up before it causes problems. Urine is very salty, but you don't soak the whole field in it repeatedly all at once. you leave a little here, and a little there, etc.

Emerson White wrote:
Rhizobium sp.  innoculant They have different strains for beans and peas but I'd imagine any would work You can find it at most garden centers. If you want I'll find you some online.

Salts are all right, and even needed, it is a matter of concentration. A very light application of Nitrogen salt fertilizer will be 100% Okay, because the plants will snap it up before it causes problems. Urine is very salty, but you don't soak the whole field in it repeatedly all at once. you leave a little here, and a little there, etc.

it depends by what you mean by nitrogen salt fertilizer

Ammonium Nitrate, that's a good one, lets go with that; Ammonium Sulfate for basic soils.

hrmm... pretty sure this is the permaculture forum...

those chemicals require more energy to produce than they give you

the idea that there is a safe level to use and that we have any idea what it is is somewhat laughable

not to  mention all the "inert" chemicals that are added to bags of fertilizer

we need to rely upon auto fertility, we need to wean ourselves of soil inputs, don't you know there is no hope for us if we don't?

My point is not that we should be doing this, just that it isn't necessarily something with out a place in the world.

Emerson White wrote:
My point is not that we should be doing this, just that it isn't necessarily something with out a place in the world.

I have read of people doing such things to get a green manure crop going in areas that would not be very possible without some input

That would probably be the number one instance where it would be useful. The problem with salts is that they accumulate in the soil and the osmotic pressure kills organisms and they drive down the solubility of some chemical species. Low concentrations of Nitrogen salts get locked up in complex organic molecules and become biomass, which we can then use for permaculture processes. That process is highly unsustainable at high concentrations, but that doesn't necessarily mean that they don't have a place. Scotts turf builder doesn't have a place, anywhere, especially not in a lawn; some of these vilified inorganic salts may have a place in permaculture.

I am strongly of the belief that out of hand dismissal of something true drives people away from a movement. I don't think it is worth it to pretend something false is true in order to lure supporters in, but I think that there is almost always a strong case to be made for moderation.

  You can tell your freind that lots of chemical nitrogen kills burns the life in the soil bacteria fungi mites algi actomycetes alsorts of busy things insects worm so you get dead earth where before there was accordin to one account more living organisms in a spade full of soil than humans on the earth.
  Without life in the soil there is nothing to break down organic matter and organic matter greatly increases the water retaining properties of the earth and the passing down of water to deeper layers in the soil, so if he wants to do more watering his crops thats his affair and it does not seem to be a very water responsible and so socially responsible one, It does not seem to be a sensible answer. I hope farmers have to pay for water, they use more htan anyone, i woudl not mind so much if i did not believe that they grow crops that are not the right ones for the climate.

  As said above in other answers in this forum the micro organisms in the soil hep with plant health. Look up the thread -bacterial endophytes!!- started by jonathon byron who says that these bacteria protect plants from parasitic fungi, increase growth rates and production of essential oils.
  Paul Cereghino says in the same thread that these bacteria stimulate plant defenses against disease, something also said of mycorrhizal fungi, and give hormonal stimulation and enhance nutrient uptake in plants. The bacteria and other forms in the earth killed by chemical fertilisers have a lot of functions to go putting nitrogen need in front of other plant needs and as also said above you can get nitrogen from plants that have nitrogen fixing bacteria on their roots, also from plants with deep roots which get nitrogen that has been washed down into the ground that they bring up and with their leaf fall leave on the surface of the ground.
You can certainly make sure your farming methods don't ruin the soil for future generations by refraning from using chemical sources for the nitrogen in you soils even if it does mean a slight lose of income and according to quite a few sources it does not  things jsut about draw even with the two methods in ht ehands of good farmers. anything can happen with bad ones and i would probably belong to the last category. agri rose macaskie.

There was a time and it was in the eighteenth century, that is nearly two hundred years ago! when they found out that plants eat inorganic matter, nitrogen and phosfates and such and so they decided that the thing was to give them as much of these things as possible , now they know more about the complex interelations of plants with other living organisms and it is probable that you can get better crops manipulating all these facts than just pouring chemicals on to the soil for plants to eat is in fact the testimony of a lot of organic and such farmers. look what sepp holzer grows.. Heninfrance your friend is in the soil science plant pathology dark ages still.
      Also there are now a lot of  have factory farming in which the number of cattle no longer bares any relation to the food produced on the farm because feeds are bought in this mweans no abono where you grow your hay and too  much were you keep your cows.
  I have read there are common market regulation against mixed animal farming it is a problem for the Spainish farming system the dehesea. 
   

  Overgrazing produces such loss of nutrients that the application some might be necessary.
IIf soil has been badly over pasyrised it may so lsck nitrogen that it needs some for any plant however miserable just to grow there.
Over grazing means the destruction of plants eaten everytime they try to recover. that means that there are no polants to lleaving rotting plant matter in the earth and no plants to entertain livestock who dejection fertilize the ground and no p'lants to stop wind erosion so anyway all the soil gets blown or washed away. THe result soils with no nutrients and need for a jump start nutrients applied so there can start to be organic material.

    Old fashioned meadows are spoilt by the application of manure. I know from a book i have on meadows, the proper old fashioned meadows, that too much nitrogen does for the meadow plants. Maybe it causes more grass to grow an dmeadow plants get suffocated.
 
The application of manure can mean little need to grow many roots or deep roots less organic build up in soils.
      Darrel doherty gives as a reason for a organic farm having after years only a thin layer of top soil that they used their cowmanure on the feilds and that meant the the roots of the plants did not have to grow deep inot the ground in search of nutrients so the remediation that the organic farming bought to the land did not create good top soil to any great depth. agri rose macaskie.

webpage Try visiting this site before making sweeping statments.

Irene Kightley wrote:heninfrance,

Pigs don't graze as you probably know and destroy pasture for any grazing animal. But as they are great diggers you can use that to your advantage in rotating land. Two of our young pigs cleared an acre here in about ten days and really enjoyed themselves in the process !.



We left this field to regenerate naturally and after two years it has a wonderful mixture of all sorts of plants - which is exactly what goats need.

They'll clean a space filled with gorse, bracken and brambles and eat anything edible they find. In the spring and summer we feed ours near the house from our veg plot. In autumn, we've several fenced-off areas in the woods where they eat tree leaves, bushes, acorns, chestnuts, to their hearts' content. (We don't put them in our best Cep areas though ! )

Pigs have the added advantage that unless you want to breed your own, you can kill them in the winter when there's not much to eat then buy weaners in spring. 

Providing you've enough food for them, they are much easier to keep than goats and sheep !