Carbonates are the natural components of the soil in many areas of the world and their distribution and quantity greatly influence the soil function. The presence of a high amount of carbonates in soil affects the physical and chemical properties of soil creating a lot of problems for soil fertility and plant nutrition. Besides, the type and quantity of lime in soil affect its physical characteristics such at aeration and permeability. Numerous methods have so far been developed to measure the amount of carbonates in soil and scientists are still trying to find an easy, rapid, accurate, and low cost approach for carbonate measurement in soil. The objectives of this investigation were: (i) to compare and eva‎luate titration and calcimetry methods in carbonates determination, and (ii) to study the feasibility of replacing the analytical grade acid with a waste acid in the titration method to reduce the cost of lime determination in different soils. A total of 139 soil samples were collected from different climatic and ecological regions of Iran including 50 soil samples from Isfahan region, 45 soil samples from Charmahal-Bakhtiary Province, and 44 soil samples from Gilan and Mazandaran Provinces representing highly calcareous, moderately calcareous, and least calcareous or non-calcareous soils. Descriptive statistics of physico-chemical properties of the soil samples confirmed their diversity. The amount of calcium carbonate equivalent (CCE) was determined in all the soil samples with 3 replications using titration method with an analytical grade acid (Merk, Germany) and calcimetry method with Merk acid and also with a waste acid. Furthermore, the effect of different size fractions of lime particles with 15, 40, and 60% of CCE on lime measurement accuracy was studied by LSD test at the probability level of 5%. There was no subjective judgmental error in the final point of measurement in the calcimetry method which is the case in the titration approach. Also, the determination process was much faster in the calcimetry method as compared to that of the titration technique. Results of CCE measurement in all the samples and also in samples from three different climatic areas indicated that there was no statistically significant difference at 1% probability level between the titration and calcimetry methods using the analytical grade acid. There was also no statistically significant difference between the results obtained from calcimetry method using a waste acid and those from both titration and calcimetry methods using the Merk acid. Therefore, it seems that calcimetry method using waste acids could be successfully employed to measure CCE in most Iranian soils. This would save us a lot of time and money. The effect of different-sized lime in soil on the CCE measurement accuracy indicated that there was no statistically significant difference in the results obtained for samples containing 15, 40, and 60% carbonates analyzed by the titration method. CCE measurement by calcimetry method using the Merk acid in soils having 15% of carbonates with different sizes showed no statistically significant difference. But, CCE values obtained for soils containing 40% coarse-sized lime (0.1-0.5 mm) were statistically different from that obtained for soils having the same amount of lime but with the size less than 0.05 mm. Besides, CCE values obtained for soils containing 60% coarse-sized lime (more than 0.1mm) were statistically different from that obtained for soils having the same amount of lime but with the size less than 0.05 mm and also the size of 0.1-0.5 mm. It seems that the titration method of measuring carbonates in soil could be well replaced with the waste acid based calcimetry approach as a rapid and reasonably accurate technique for determining carbonates in Iranian soils. Grinding the soil samples before carbonates determination would certainly provides better results, particularly in coarse textured soils.

حسين خادمي

حسين شريعتمداري

شمس اله ايوبي، عليرضا گوهري