CALCIUM IN FERTILIZERS

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Abstract
The average mixed fertilizer contained about 15.5% CaO in 1900 and 17% in 1946. In recent yrs. about 85% of the total CaO in commercial mixtures was derived from superphosphate, 10% from dolomite, 1% from Ca cyanamide, 1% from natural organics, and 3% from all other materials. The av. CaO content of various grades of superphosphate is as follows 18% grade 27.09, 20% grade 28.72, 45% grade 19.71, and run-of-pile 28%. Dolomite contains 30.5% on the av. The CaO content of mixed fertilizers is related to the P2O5 and N, but not to the K2O content. The relationship between CaO and P2O5 is expressed by the equation y[long dash]7.29691 + 1.55098x - 0.05585x 2 where y = CaO and x = P2O5 content. When x = 0, y = 7.29; x = 8, y = 16.13; x = 13.89, y = 18.06 (max. value); x = 24, y = 12.35; and x = 31.87, y = 0. These theoretical values agree fairly well with actual detns. on 520 samples. Ordinarily mixed fertilizers of less than 22% total plant food contain 1.45% of CaO for each 1% P2O5 and 1.14% CaO for each 1% N. Fertilizers supply almost as much Ca to crops as they do of the other 3 nutrients combined. The quantities of fertilizer Ca applied to crops in 1944 varied from 6 lbs. per acre for hay to 118 lbs. for tobacco with an av. of 13 lbs. for all crops. The harvested portions of crops remove from the soil more Ca in some cases and less in others than is applied on the av. in fertilizers.

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