Effects of potato cultivation on soil pH _KCl and exchangeable calcium under organic and conventional management

The study was conducted at the Estonian University of Life Sciences during the second cycle of a long-term crop rotation trial. We investigated the effects of potato cultivation in organic and conventional systems on soil pHKCl and exchangeable Ca. The five-field rotation included barley undersown with red clover, red clover, winter wheat, pea, and potato. Soil samples were collected before and after potato cultivation to measure pH (1 M KCl, 1:2.5) and exchangeable Ca. Three organic treatments were applied: Org 0 followed crop rotation only; Org I included winter cover crops; and Org II combined cover crops with composted cattle manure. Four conventional treatments used increasing nitrogen fertilisation: N0 (control), N50, N100, and N150. The between-system difference in soil pHKCl was small (0.09 units) and statistically non-significant (P > 0.05), whereas exchangeable Ca was moderately higher under mineral-input management (by 13.9%). In conventional treatments, pHKCl tended to decrease with higher N rates, while Ca showed no consistent change. Correlation analysis indicated that the preceding crop influenced pHKCl, and regression suggested weaker pHKCl responsiveness to Ca dynamics under organic than under conventional management.