The effect of nitrogenous fertilizers on the calcium status of soil

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Abstract
The results of an experiment, conducted over one cycle of a four-course rotation to study the effects of nine nitrogenous fertilizers on crops and soil, are described. All the crops gave fairly good responses to nitrogen but in no case was there a significant difference between the effects of the various nitrogenous fertilizers. The “recovery” of added nitrogen was about 40–50 % with all the fertilizers. Figures are given for the changes in exchangeable CaO content of the soil. The results confirm Crowther and Basu's deduction that “the loss of calcium exceeds that for equivalent nitrogen added as nitrate by an amount equivalent to the excess of anions over the cations in the added fertilizer, all added nitrogen being regarded as nitrate and all carbon and phosphates being ignored”. The fact that phosphate should be ignored is shown by results for mono- and diammonium phosphates. Precipitation of phosphates in the soil almost certainly involves removal of calcium from the exchange complex but the calcium in such precipitated phosphates is exchangeable. Since phosphate has no effect on calcium status, it is clear that fertilizers based on ammonium phosphates remove less calcium from the soil than do mixtures based on ammonium sulphate and superphosphate.