The previous posts have focused on the need to cater for a continuous supply of nitrogen from the atmosphere by nitrogen-fixing plants and how much nitrogen these plants can contribute under idealized conditions. In this post we'll get a little closer to reality and look at the factors that influence nitrogen fixation scope.
The main factors proves (in addition to good access to water) phosphorus- and potassium content in the soil. Phosphorus and potassium are the other nutrients that are important for healthy growth and all of the nitrogen in the world will not help unless it also is enough phosphorous and potassium to meet the plants' other needs. If there is a shortage of phosphorus and potassium in the soil can kvävefixerarna not assimilate nitrogen from the bacteria and pulling down on fixation. Is there much phosphorus and potassium in the soil increases nitrogen fixation to the growth rate of plants generally becomes higher, ie they can produce more green mass and thus increase the photosynthesis ability, which in turn allows them to distribute more sugar to the bacteria that helps with nitrogen fixation .
Another important factor that comes into play is the nitrogen content in the soil. Is there much nitrogen in the soil initially draws the nitrogen-fixing plants down on costly food distribution of their bacterial friends. Furthermore, in such a situation, no need to resubmit nitrogen from fixeraren to non-fixeraren because mushrooms have it more difficult to establish symbiosis with trees in the nitrogen-rich conditions.
Making use of nitrogen-fixing plants is worth it then especially if it is short of nitrogen in the soil, and when there are plenty of phosphorus and potassium. I detta kan ideally, 10-20% nitrogen needs of the non-nitrogen-fixing plant covered by nitrogen fungi collect from the surplus produce kvävefixerarna . You can find out your potential by observing the existing vegetation. The growth rate is high and the plants look lush and prosperous like you probably have a fertile soil and when needed it is perhaps not so many kvävefixerare. Is the growth, however weak it may be worthwhile to submit a soil sample at the lab, to find out if there is a shortage of one or more nutrients in the soil.
A quite natural question in this context is how many nitrogen-fixing plants needed to reach these levels. Funnily enough answer this question is not at all in most of the research that I found. I had to dig quite a long time to find a report from 1989 a samplantering of black walnut (Juglans nigra) and Elaeagnus umbellata (Elaeagnus umbellata) and alder (Alnus glutinosa)  which states planteringstätheter on 1100 nitrogen-fixing plants per hectare, more than twice as many as the number of walnut trees. In Putt Myra forest garden we have in the current situation around 200 nitrogen-fixing trees and shrubs, which corresponds to a planting density of just over 300 plants per hectare, Thus only just over a quarter of the density proposed in the literature. Meanwhile, our soil samples proved that we have the right low nitrogen content in the soil and good values for phosphorus and potassium, so we will in the coming season to plant many more kvävefixerare between the existing plants.
Although it now seems that it takes the right special conditions and very many plants to get up to significant amounts of nitrogen applied to the forest garden through nitrogen fixation from the air, it is important to again point out the difference between kvävefixerarna and non-kvävefixerarna. The latter recovers only nitrogen already in the soil, while the former brings new nitrogen from the atmosphere to the cycle that occurs in the Earth, which means that even a little nitrogen is fixed makes a difference to the total in circulation.
In conclusion we can say that it requires good access to water, phosphorus and potassium to kvävefixerarna be able to make a significant contribution to the forest garden nitrogen budget - and it needed many nitrogen-fixing plants per unit area. The smaller the nitrogen present in the soil from the beginning, the greater the difference will kvävefixerarna to do. If you have limited space and good access to relatively nitrogen rich material and manure, compost or urine can in good conscience cut down on the number kvävefixerare.
In the next post, we look with new eyes at list of kvävefixerare I uploaded a couple of years ago to the nitrogen-fixing plants that are the best in our climate. And last but not least: Merry Christmas and a Happy New Year!
 Ekblad, A.L.F. and K. Huss-Danell, Nitrogen fixation by Alnus incana and nitrogen transfer from A. incana to Pinus sylvestris influenced by macronutrients and ectomycorrhiza. NPH New Phytologist, 131(4): p. 453-459, 1995.
 Paschke, M.W., J.O. Dawson, and M.B. David, Soil nitrogen mineralization in plantations of Juglans nigra interplanted with actinorhizal Elaeagnus umbellata or Alnus glutinosa. Plant Soil Plant and Soil : An International Journal on Plant-Soil Relationships, 118(1-2): p. 33-42, 1989.