Monday, February 06, 2006

A little discussion has developed on the topic of nitrogen fertilizers, in the comments to my January 25th post "Reason Unbound." Back40 has given a quite detailed comment, and I thought it worth bringing up here so it won't be missed.


Update - don't miss Eleutheros' comments to this post, either. This is getting too easy - the commenters are doing all the work! Thanks, everyone.


Anonymous said...

I'd overlooked this so I read the comments on the original post and the blog article (Crumb Trail) from which it came.

I found Back40's comment to be most useful. I am thinking about applying it liberally to my corn field this year. The article that is becuase it is quite rich in organic fertilizer.

It's the same lame argument used for solar power and such. If you could cut back your energy use until you only used as much as solar power would produce, you wouldn't have to have the solar power to start with. The proposal is that synthetic nitrogen in quantities that could be supplied by sustainable means and in quantites not high enough to harm the soil overcomes the main objections to their use. But as GC points out, if you are using that little nitrogen, just use the manure and be done with it.

That, of course, if it was just a matter of chemical nitrogen. It isn't.

A great deal of nitrogen in the form of chemical salts available to plants is NOT a good thing. It makes them grow rank but imbalanced. Vegetables grown on chemically fed soils are less nutrive than those grown on organic soils. For a plant (even, or especiall grass) to grow at Nature's pace and develop the maximum health an nutrition, it requires nitrogen to be released to the plant slowly and over time. Manure and organic material in the soil feed the microbal life, bacteria, but not just backteria, all manner of fungi and soil dwelling orgnaisms.

Applying manure permanently affects the soil. The nutrition and fertility are built up slowly. Burn out a field with chemical nitrogen salts for a few years and then one year apply nothing. The field will be nearly sterile and support almost no plant growth. Put on manure for several years and then the next year apply nothing and you will get just about as good a crop as you always have. The use of chemical salts is short sighted, looking only at this year's yield. The application of organic material is a long sighted approach in which the material applied this year will yield benefits twenty and fifty years down the road.

The notion that chemical synthetic nitrogen is better for a field than manure is like saying that when you go out to work the field, a breakfast of a Coca-Cola is better for you than whole wheat toast. After all, the human body does work by burning sugar (no matter what the original form) and the soda has more direclty available sugar than does the toast which must release it's starch-bound sugar slowly through the day.

Chemical fertilizers make it look as if they are giving higher yields because they in part make up for some of the shortcomings of industrial agriculture: monocropping, mechanizaiton, marginal financing, etc. But as a botanical reality, they are inferior. I've gardened on the same ground now for more than 15 years and have built up the soil fertility with organic material alone for all that time. I would invite Back40 or anyone to put in a plot right beside my garden using chemical methods and try to match my per/square-foot yield. You can't do it.

And furthermore, from milk and eggs to potatoes and carrots, put your food on the table side by side with mine and even a jaded palate can tell the difference.

Anonymous said...

I've thought that this as an addition to the discussion might put some of the ideas into perspective.

The idea that organic manures contain little "available" nitrogen and inorgaic salts contain huge amounts more of "available" nitrogen is misleading.

In healthy organic soils to which organic material is regularly added there is a complex, self-regulating system of delivering useable nitrogen (in the form
of nitrates) to plants. Several different classes of bacteria work in conjuction to accomplish and reglate the process.

Organic nitrogen compounds are acted upon by certain bacteria which produce nitrites as byproducts. With the addtion of organic matter to the soil, these
bacteria begin to increase in number and raise the amount of nitrites in the soil. Another class of bacteria injest the nitrites and give off nitrates as
byproducts. The rise in numbers of the latter class of bacteria helps check the growth of the former. The Plant roots absorb the nitrates as they become available. If the amount of nitrates becomes so large that the plants cannot readily absorb them, the presence of the excess nitrates gives rise to yet a
third class of bacteria that take in nitrates and give off nitrogen compounds in the from of atmospheric gases such as nitrous oxide and amonium and also
help check the numbes of the nitrate emitting bacteria. Thus it is a self-regulating system
which works to make present in the soil just the right amount of absorbable nitrates the plants need and keeping to a minimum the amount of nitrogen that is leached away as soluable nitrates or lost through coversion to
atmospheric gasses.

The longer this process has been established in a plot of soil, the more efficiently it works. It is much more complex than this, however. There are also cycles
of bacteria which fix phosphorous and sulphur in compounds that the
plants can use and the humic acids formed from the bacterial interactions greatly
facilitate the absorbtion of nitrates by the plants in addtion to breaking down minerals from rock particles present in the soil. And it is much more complex
than this still in that the bacteria interact with fungi, enzymes, insects, and all
manner of other things in the soil.

When chemical nitrates are added to the soil as fertilizer, the nitrogen may well be "available" to the plants, but this is misleading. It doesn't mean the plants in practice absorb or use it. A great percent of it leaches down below the rhizoshpere where the plant roots and bacteria are and enters the groundwater. With a lack of organic material on which to feed, the nitrite
producing bacteria decrease in number, and then, of course, the bacteria that convert nitrites into nitrates diminish. With no competition from crowding by these other bacteria and huge amounts of food to support them, the nitrate eating bacteria increase expodentially. They then compete with the plant roots for the nitrates and convert huge amounts of them into atmospheric gases such as nitrous oxide, a major greenhouse gas.

As time goes by the soil becomes sterile of most of its types of bacteria, humic acid disappears making nitrogen absorbtion by the plants even less efficient and requiring the addition of minerals to replace those once dissolved by the acids. The soil deteriorates and errodes. It then takes more and more added synthetic nitrates to get the same result.