Hi Louadj.

Iron content of calcareous soils can be low, and iron availability decreases at higher soil pH levels.  However there are many reasons why you will see chlorosis in plant. Iron is one possibility but probably not the first reason I would look for.

John

Hi Louadj.

The high soil pH associated with the presence of calcium carbonate can cause deficiency in a number of micronutrients including iron, but also commonly zinc, copper and manganese that all produce chlorosis (most commonly in new growth). The likelihood of observing chlorosis is also governed by many other factors such as the type of plant, clay content (and CEC), soil OM content (particularly for copper as it readily forms complexes) and nutrient and water availability. You can sometime get chlorosis in these soils with low availability of micronutrients simply because there is not enough moisture to supply micronutrients through mass flow to the root. Likewise if the plant is supplied with high amounts of major nutrients, the induces rapid growth may induce deficiency. There is a plant availability test that has been validated in calcareous soils using DTPA extraction (WL Lindsay, WA Norvell - Soil science society of America J 1978). Many labs do this as a routine now (or as part of a suite). Trying to find a critical test value that is suitable for all applications/crops is more difficult, but there will be published values in the literature. As with all of these availability tests, - its best to make sure you can calibrate a critical level with a response experimentally. Hope this helps. Regards

Andrew

Hi Kenneth

In Addition to the comments by Andrew, chlorosis can also be caused by low sulfur , and nitrogen, as well as other non nutrient possibilities like ozone exposure, herbicide injury ect.  There is a Soil Science Society of America book called "Micronutrients in Agriculture" that may be the quickest place to look for some of the questions you have.

John

Hi Kenneth, certainly iron deficiency is important in calcareous soils, but the point I was making is that it not the only likely issue. Just to be clear for others, the chlorosis I have been referring to is the quite specific interveinal chlorosis seen in young growth which tends to be associated with micronutrients as opposed to more general leaf yellowing or interveinal yellowing on older growth associated with macro nutrients. You can of course, as you mentioned, do a missing nutrient test (where you apply nutrient solutions to plants in pots in your soil of interest) to find out which nutrients are the most limiting (easy to find recipes in literature). On specific work done on iron in the literature. I would say the best area to look at in an agricultural context would be work done right back as far as the 1960's on iron nutrition in citrus in Florida - it was significant issue (made worse by oversupply of copper which is antagonistic in fungicides). The issue is usually managed with chelated iron fertilisers (foliar applied being most effective obviously).  Cheers Andrew

 Hi Louadj

Anecdotal rather than experimental evidence suggested that, in the early days of Swaziland sugar cane industry, excessive P fertilization  on vertic soils caused Fe chlorosis.  A  natural parallel is the acute chlorosis is seen in some P-rich guano  soils on atolls  However those soils consist mostly of comminuted coral, so Ca and Mg are probably the main causes 

Regards  Ian

Hi Louadj

If you want to have a clear cut answer for your case you must did soil and leaves analysis to reveal the nutritional state of  your soil and plant comparing your valuese with critical levels of these nutrient giving you the needed answer.High pH values especially in calcareous soils  related with many  micro nutrient fixation on soil particles(especially iron),so that foliar apply of these elements give you the solution for your case.

Ali Al Hayany 

Interesting discussion . In calcareous soils , there is absolutely no doubt, iron chlorosis is one of the oldest forms of the nutritional disorder , researched worldwide . thereafter , it come the phosphorous  deficiency due to formation insoluble calcium phosphate or secondary orthophosphate . As regards the thresholds of calcium carbonate , it is more important to measure the carbonate reactivity  , governed by the particle size distribution , mineralogy , surface morphology and aggregation with other soil components. Carbonates in clay and fine silts are more dangerous from nutrient availability and plant nutrition point of view. There is also a need to see the carbon stability , more stable carbon will raise the threshold limit of calcareousness. And , such limits are function of crops as well , besides these soil conditions . There is a huge variation  with regard to limits of calcareousness and their tolerance  limits by different crops (PDF enclosed).

 thank you dear Researcher for your valuable answers, and it's an interesting discussion Indeed Dr Kumar Srivastava, thank you for the pdf file that review the calcareous soils and their effects on conifereous trees.

having said that, i agree with you that when we want to study the effect of carbonates calcium on plant developement, it's interesting to measure the reactivity of carbonate instead of total carbonate, or to measure the carbonate content at each fraction, as you said the carbonate content in clay and fine silts are more dangerous, why is it so? may be because of their secondary nature , and their high solubility? when they are in this fraction ( high surface area)?.

and what about  the carbon stability? at my knowledge , one of my feature in calcareous soils in respect to organic matter , is that carbonate will coat onto the organic matter and therefore limit it's mineralisation? is that what you mean by carbon stability,?.

best regards Louadj yacine

Prity interesting argument Louadj . There are reports about the calcium carbonate  playing  role of  stabilizing organic matter from further decomposition .   Coating of calcium carbonate on organic matter and cementation of soil aggregates with CacO3, physically protect the organic matter from decomposition  , stabilizing the source of carbon ?. Persistent carbonate-organic matter coatings may form on coarse fragments and stabilize a substantial portion of organic matter.  

the stabilisation effect of carbonate coating on organic matter in soils are a very interesting topic, because it may be one of the mechanism by which carbon is sequestred in soils.

if we assume that calcareous soils are mostly located in arid and semi arid region , and we know that the organic matter content in these soils are low, but what if this organic matter are protected by carbonate coating so in analysis of these soil, we don't detect a huge amount of this organic matter?.

Back to our inquiry ;  is there a link between  between  high concentration of Calcium from carbonate  in the soil solution and the deficiency of Iron absorption  from the plant tas another way of explaining the phenomena of Chlorosis ( Antagonism effect) ? 

I do not think so about the chlorosis on calcareous soils where Ca from CaCO3 and iron are directly involved to be the causal factor of chlorosis. It is infact the high concentration bicarbonate ions , creating alkalinity along with accumulation of nitrate ions9 accumulation of ammonium is highly unstable in calcareous soils , together playing the pivotal role in chlorosis on calcareous soils . It is frequently observed the concentration of Fe being many time higher in roots than concentration of Fe in leaves. why is it so , it is simply because of the transport of Fe from the apoplast cells to cytosol cells of roots . the transport of Fe is initiated by the plasmalemma located  FeIII -reductase , which is pH dependent . Bicarbonate present in root apoplast will neutralize the protons pumped out of cytosol cells and together with nitrate ( Remember bicarbonate and nitrate act as analogue to each other under such conditions)is taken up by a H/nitrate co-transport high pH levels , blocking further the reduction of FeIII..

Similarly the Fe concentration in chlorotic leaves were observed many time higher than the green leaves ( Non-chlorotic). What is the reason , it is the same phenomenon what operates in roots . This was further confirmed by the negative correlation between leaf apoplast pH and Fe-chlorosis intensity evident from chlorophyll concentration . ( Based on exerpts from work of Prof Menzel ,Plant and Soil 165:275-283). Hope , this explanation provides some insights for further discussion .

thank you for you clear and concise explanation  Dr Srivastava

Interesting point Dr towe 

High soil carbonates influence soil biology as much, if not more, than soil chemistry. All soil organisms need iron and compete for it in varying biological means.

We have a tendency to ignore much the early soil science work by people like Tilsdale and Lippincot because it was done in the 50s. Complexing of elemental compounds in the soil is poorly researched and blatantly ignored by fertilizer companies therefore the universities ignore it because there are no GRANTS involved with research. The commercial-sales answer to every soil pH and chemistry issue is to add salt-type fertilizers. And that answer works...at a further expense of soil microbiology. Huge difference in biological activity when you add Fe EDTA versus iron sulfate.  So the question as to carbonates effecting iron is more suited to be asked as a relationship between iron & biological soil conversion into complexes that can be assimilated by plants.  Further, influence of carbonates on symbiotic soil fungi and, in some cases bacteria, whose functions are shunting Fe via the Hartig Net into plants is also affected in high calciferous/high carbonate soils.

The answer to these questions is too often "this is what you buy" instead of "this is what needs to be done."