Paper Information

Journal:   IRANIAN JOURNAL OF SOIL AND WATERS SCIENCES   2002 , Volume 16 , Number 1; Page(s) 0 To 0.
 
Paper: 

EFFECTS OF ORGANIC MATTER AND MINERAL COMPOUNDS ON SOME CHEMICAL PROPERTIES AND BIOLOGICAL ACTIVITY OF A SODIC SOIL

 
 
Author(s):  ROUSTA M.J., GOLCHIN A., SIADAT H., SALEH RASTIN N.
 
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Abstract: 
In a field experiment, changes in pH, SAR, ECe and biological activity of a sodic soil were studied following the application of organic matter, mineral compounds and combinations of these materials. Experimental design was RCBD with three replicates and the treatments included wheat straw and manure applied at rates of 10, 20 and 40 t/ha, sulfuric acid and gypsum (equivalent to gypsum requirement), cement (5 t/ha), and a combination of wheat straw and manure at a rate of 20 t/ha mixed with gypsum or cement.
Results of the experiment one and four months after application of the treatments showed that both sulfuric acid and gypsum significantly decreased soil pH. Sulfuric acid decreased pH from 8.37 to 7.87 and 7.60 after one and four months, respectively. However, application of gypsum decreased pH to 7.93 after one month and this remained constant thereafter.
Straw (excluding 40 t/ha treatment) manure and cement had no significant effects on soil pH, but application of straw and manure with gypsum, significantly lowered pH after four months. Addition of sulfuric acid to irrigation water, gypsum, and organic matter with gypsum increased ECe and soluble calcium in saturated soil extract significantly.
The highest decrease in SAR was obtained four months after the application of gypsum and sulfuric acid.
Addition of gypsum to soil had better effect on decreasing the SAR than gypsum mixed with organic matter. This suggests that organic matter lowered the positive effects of gypsum in decreasing the SAR of the soil under study.
Following the application of different levels of straw, biological activity (measured as evolved CO2) increased significantly. The highest increases were for 40 t/ha of straw, which raised the biological activity to over 3.5 times compared with the control. This treatment increased evolved CO2 from 46.4 in control to 166.8 mg m-2 h-1. Different levels of manure also increased biological activity, but the effects of manure were much lower. Differences between the rates of manure and straw were statistically significant. Based on these results, it may be concluded that application of plant residues, which have a higher carbon content than manure, is more effective for increasing biological activity of sodic soils.
Furthermore, we found that addition of gypsum to organic matter decreased the rate of carbon mineralization probably due to increasing EC of soil solution. It may be concluded that for the maintenance of organic matter in sodic soils, these materials should be applied in mixture with gypsum.
 
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