If the soil has more than 50 ppm available S, what will be the impact on rice plant? What is the permissible limit of soil available S for rice plant? It is notable that soil pH is >5.8 and texture is clay loam.
Some very interesting feedbacks. . I would like to add one more point , that S-toxicity due to redox-induced reduction in oxidised sulfur com is at a very low redox potential somewhere -400-600mv depending upon nature and properties of the soil to really experience S-toxicity.
First thing is that Sulfur toxicity is not very common in rice. But 50 ppm is high level of excessive content of sulfur, therefore in this condition, sulfur reduces nutrient uptake of plants by reducing root respiration and then may be other nutrients, especially nitrogen deficiency appears and rapidly plant vigor will be diminish. Plant parts could be burns.
Dear M.N. Islam,
8 to 10 mg/kg of mono-calcium-phosphate extractable S has been reported as the soil critical limit (Ponnamperuma, 1981). During soil submergence, hydrogen sulfide (H2S) is produced by sulfate reduction and the anaerobic decomposition of organic matter. In normal soils, hydrogen sulfide (H2S) is removed from the solution phase as insoluble iron sulfide (FeS). But in soils low in iron, such as bleached sandy soils and some peaty soils, hydrogen sulfide (H2S) may be present in amounts (more than 10-6 M) toxic to rice. Thus H2S toxicity may arise in submerged soils low in iron.
Ref: Ponnamperuma F.N. (1981) Properties of tropical rice soils. Text of a series of lectures prepared for delivery to Graduate Students at the Tropical Agriculture College, H. Cardenas, Tabasco, Mexico. July 23-25, 1981.
Some very interesting feedbacks. . I would like to add one more point , that S-toxicity due to redox-induced reduction in oxidised sulfur com is at a very low redox potential somewhere -400-600mv depending upon nature and properties of the soil to really experience S-toxicity.
As I understand 50 ppm sulphate-S, though on higher side ,may not be toxic to rice plant.However,at high sulphur levels in soil, Mo nutrition may be affected,especially if soil Mo status is low.Only under highly reduced conditions one may encounter the problem of sulphide toxicity.Sulphate adsorption may not be problem in your soil as the pH is more than 5.0.Soil is a clay loam and so SO4-S leaching also may not be problem.I could locate a reference from your own institute for critical limit of soil SO4-S.Thecritical level of soil available S by calcium phosphate extractant was established at 12 ppm for rice(Islam and Bhuiyan,1988).12-20 ppm may be medium and more than 20 ppm high( From the second reference below).
Islam,M.M. and Bhuiyan,N.I.1988.Evaluation of various extractants for available sulphur in wetland rice(Oryza sativa) soils of Bangladesh.Indian J.Agri.Sci.58(8):603-606.
Bhuiyan,N.I.1991. Sulphur fertilization for rice and non-rice crops of Bangladesh agriculture.In:Proceedings of the international symposium of sulphur.magnesium and micronutrients in balanced plant nutrition.Sichuan Academy of Agricultural Sciences,China pp.1-418.
I agreed with the statement of Dr.Anup and Dr.Annagi.
For giving me a new vision.
Mr.Islam,you may also check the S concentration in rice plant parts to see if S is in excess.The following are some critical levels of S in rice in India.
Rice /Rajasthan 0.16% S at tillering.
Rice/Bihar 0.1% S at 60 days.
Rice leaves at 50 days 0.20% S sufficiency and 0.15%S mild deficiency and 0.12% severe deficiency.
Dr. Dilip Kumar Kundu has refered a good work. Drs. Anoop Kumar Srivastava and Annangi Subba Rao have further elaborated it. However, in submerged rice chances of toxicity are there although may not be very severe. I think there will be indirect effects of high S through some adverse interactions with other nutrients before any toxicity of S in witnessed. And these are at places and times may result in lower rice yield.
No one is talking what is the difference in effect of excess sulphur as sulphide versus sulphate in rice plants ?
It decreases nutrient uptake by reducing root respiration thus adversely effecting on metabolism. There will be interveinal chlorosis of emerging leaves and dark brown to black root system etc..
When you say 50 ppm available S, you must also tell what availability index of S you have used.
Respectable Bijay Singh sir
In Bangladesh, soil available S (AvS) is extracted with calcium dihydrogen phosphate extrractant. The critical limit (CL) of soil available S for wetland rice is 10 ppm. We classify the soil available S as very low (AvS 375% of CL).
Thats the most missing point Dr Bijay Singh sir, we hardly attach any value to this . Soil test value comes out of a given soil test method , and that varies as per methodology followed. My compliments to Dr Aminul. This is what we should stress upon the most..
In wetland situation sulfide toxicity is not very common. Some times S deficiency arise in reduced or water logged condition. However, if the soil is low in Fe content sulfide toxicity may develop. According to IRRI, "no critical levels have been established to test Sulfide toxicity."
Above information is for normal soil. But in saline soil, behavior of S may be different.
at 50ppm " available S" you shall not expect toxicity effects in this soils.
Better check the S staus of the plants by tissue analysis: soil analysis for "available" S is always a wild goose chase!
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