c-ray
05-18-2012, 08:30 PM
from http://soilminerals.com/information.htm#iron
Iron is second only to aluminum in the list of abundant metals. It makes up about 5% of the earth's crust, so it is rarely absent from soils, although it may not be present in an available form.
For garden soil we like to see 50-200ppm of iron on a standard soil test. Above 250 ppm usually indicates something out of balance.
What does iron do in the plant? Paraphrasing Arden Andersen, "Iron draws energy to the leaf by absorbing heat from the sun; it makes the leaf darker, thus absorbing more energy. It will increase the waxy sheen of the crop. Iron is necessary for the maintenance and synthesis of chlorophyll and RNA metabolism in the chloroplasts. It increases the thickness of the leaf, [which] increases nutrient flow geometrically, resulting in a production increase geometrically." Science in Agriculture p236
Iron is needed by nitrogen fixing bacteria.
So iron is a good thing, in most cases. Below we have a couple of different views on just how good it is and how much we want:
Both iron and manganese become less available at pH 7 and above and in the absence of organic matter and water. These conditions are found in some arid parts of the western United States. High calcium soils also tend to have low available iron, particularly if they are also low in organic matter. In a calcareous soil, most of the potentially available iron is tightly bound to organic matter. Some plant roots have been shown to have the ability to obtain iron from these sources by chemically reducing ferric iron (Fe+++) to ferrous iron (Fe++). High phosphorus soils may also have low available iron, as any free iron will chemically bind to from iron phosphate....Correcting an iron deficiency may be difficult because the problem is not a lack of iron in the soil, but that it is chemically bound. Lowering the pH, if practical, is the surest method. Foliar iron sprays are also effective. Foth and Ellis Soil Fertility pp146-147
Here's an excerpt from an interview with Gary Zimmer "In our dairy work we are looking at phosphorus as a key element. We want phosphate uptake for sugars and energy and digestibility and plant health. If I have high iron in my soils, usually from over-tillage, excessive use of caustic materials or too much nitrogen use, I'm not happy. On a dairy farm, I scream and holler if they buy a single pound of commercial nitrogen. If they buy nitrogen, I want to know why. They had better use their manures and alfalfa and rotation, because I don't want iron buildups. Iron binds with phosphate within the plant . Many people who don't feed cattle don't notice this difference. You see, the phosphorus may be in the plant, but when you bind it to iron, it becomes unavailable. Iron has a triple-positive charge and phosphorus has a triple-negative charge, so they will bond very easily. If your feed is high in iron, then the cow is starved for phosphorus. We are fanatical about trying to get our iron down, just so we have better phosphate availability . In high iron soils I don't think our soil tests give an accurate idea of phosphate availability to the plant." [emphasis added] Graeme Sait Nutrition Rules pp187-188. Gary Zimmer works mostly with neutral or alkaline pH soils in the upper Midwestern US, and we don't know offhand what he considers high iron.
The info above brings up some interesting questions about iron supplements in general, don't you think? I wonder what connection there might be between the high iron intake recommended for women and high incidences of osteoporosis? Fallon and Enig have this to say about one type of iron supplementation "Recently, researchers have warned against inorganic iron used to supplement white flour. In this form, iron cannot be utilized by the body and its buildup in the blood and tissues is essentially a buildup of toxins. Elevated levels or inorganic iron have been linked to heart disease and cancer." Nourishing Traditions p44.
Charles Walters has this to say about signs of iron deficiency in plants "When iron deficiency is serious, the entire leaf will turn yellow, leaving only the veins to stand out like road maps....Chlorosis (white leaves that should be green) is possible even in the presence of iron. Lime can complex iron, and yet in the human being calcium and copper must be present for iron to function properly. In order to free iron, the farmer must complex calcium in this case, and this means using either iron sulfates or iron chelates, or substituting a proper foliar blend." Eco-Farm p196.
At soil minerals.com we have seldom seen a soil test that showed a lack of iron. and as we usually are working with gardens and fields of a few acres and smaller, our approach is to bring the pH down below 7 which will make iron (as well as the other cations) more easily available. The alternative, if one cannot lower the pH with minerals because of size, expense, highly calcareous soils, or other constraints, is to increase the biological activity in the soil. As noted above in the excerpt from Foth and Ellis' Soil Fertility, in a calcareous soil most of the iron is tied up with organic matter. Increasing the organic matter content of such soils will provide more holding points for iron, and increasing the biological activity, through the addition or seeding of beneficial bacteria and fungi, should make more Fe available to the plants.
Iron is second only to aluminum in the list of abundant metals. It makes up about 5% of the earth's crust, so it is rarely absent from soils, although it may not be present in an available form.
For garden soil we like to see 50-200ppm of iron on a standard soil test. Above 250 ppm usually indicates something out of balance.
What does iron do in the plant? Paraphrasing Arden Andersen, "Iron draws energy to the leaf by absorbing heat from the sun; it makes the leaf darker, thus absorbing more energy. It will increase the waxy sheen of the crop. Iron is necessary for the maintenance and synthesis of chlorophyll and RNA metabolism in the chloroplasts. It increases the thickness of the leaf, [which] increases nutrient flow geometrically, resulting in a production increase geometrically." Science in Agriculture p236
Iron is needed by nitrogen fixing bacteria.
So iron is a good thing, in most cases. Below we have a couple of different views on just how good it is and how much we want:
Both iron and manganese become less available at pH 7 and above and in the absence of organic matter and water. These conditions are found in some arid parts of the western United States. High calcium soils also tend to have low available iron, particularly if they are also low in organic matter. In a calcareous soil, most of the potentially available iron is tightly bound to organic matter. Some plant roots have been shown to have the ability to obtain iron from these sources by chemically reducing ferric iron (Fe+++) to ferrous iron (Fe++). High phosphorus soils may also have low available iron, as any free iron will chemically bind to from iron phosphate....Correcting an iron deficiency may be difficult because the problem is not a lack of iron in the soil, but that it is chemically bound. Lowering the pH, if practical, is the surest method. Foliar iron sprays are also effective. Foth and Ellis Soil Fertility pp146-147
Here's an excerpt from an interview with Gary Zimmer "In our dairy work we are looking at phosphorus as a key element. We want phosphate uptake for sugars and energy and digestibility and plant health. If I have high iron in my soils, usually from over-tillage, excessive use of caustic materials or too much nitrogen use, I'm not happy. On a dairy farm, I scream and holler if they buy a single pound of commercial nitrogen. If they buy nitrogen, I want to know why. They had better use their manures and alfalfa and rotation, because I don't want iron buildups. Iron binds with phosphate within the plant . Many people who don't feed cattle don't notice this difference. You see, the phosphorus may be in the plant, but when you bind it to iron, it becomes unavailable. Iron has a triple-positive charge and phosphorus has a triple-negative charge, so they will bond very easily. If your feed is high in iron, then the cow is starved for phosphorus. We are fanatical about trying to get our iron down, just so we have better phosphate availability . In high iron soils I don't think our soil tests give an accurate idea of phosphate availability to the plant." [emphasis added] Graeme Sait Nutrition Rules pp187-188. Gary Zimmer works mostly with neutral or alkaline pH soils in the upper Midwestern US, and we don't know offhand what he considers high iron.
The info above brings up some interesting questions about iron supplements in general, don't you think? I wonder what connection there might be between the high iron intake recommended for women and high incidences of osteoporosis? Fallon and Enig have this to say about one type of iron supplementation "Recently, researchers have warned against inorganic iron used to supplement white flour. In this form, iron cannot be utilized by the body and its buildup in the blood and tissues is essentially a buildup of toxins. Elevated levels or inorganic iron have been linked to heart disease and cancer." Nourishing Traditions p44.
Charles Walters has this to say about signs of iron deficiency in plants "When iron deficiency is serious, the entire leaf will turn yellow, leaving only the veins to stand out like road maps....Chlorosis (white leaves that should be green) is possible even in the presence of iron. Lime can complex iron, and yet in the human being calcium and copper must be present for iron to function properly. In order to free iron, the farmer must complex calcium in this case, and this means using either iron sulfates or iron chelates, or substituting a proper foliar blend." Eco-Farm p196.
At soil minerals.com we have seldom seen a soil test that showed a lack of iron. and as we usually are working with gardens and fields of a few acres and smaller, our approach is to bring the pH down below 7 which will make iron (as well as the other cations) more easily available. The alternative, if one cannot lower the pH with minerals because of size, expense, highly calcareous soils, or other constraints, is to increase the biological activity in the soil. As noted above in the excerpt from Foth and Ellis' Soil Fertility, in a calcareous soil most of the iron is tied up with organic matter. Increasing the organic matter content of such soils will provide more holding points for iron, and increasing the biological activity, through the addition or seeding of beneficial bacteria and fungi, should make more Fe available to the plants.