EXTRACTABLE SOIL BORON AND ALFALFA UPTAKE - CALCIUM-CARBONATE EFFECTSON ACID SOIL

Since soil tests for B in fine-textured soils give inconsistent predic tions and the amendment of acidic soils with CaCO3 is a common practic e, the suitability of extractants for plant-available B in a CaCO3-ame nded clayey soil was studied. This research investigated the pH effect on B adsorption, the changes in the amounts of hot-water-extractable B (HW-B), mannitol-extractable B (MANN-B), and soil solution B (SOLN-B ) as a result of B and CaCO3 addition to a silty clay soil (a clayey, mixed, mesic Typic Humaquept) with an initial pH of 4.2. The relations hip between the amounts of extractable B and B uptake by alfalfa (Medi cago sativa L.) was also studied. Amounts of extractable B in soil wer e in the order HW-B > MANN-B > SOLN-B, decreasing with increasing pH a nd after growth of alfalfa. Addition of 2.5 and 5.0 g CaCO3 kg(-1) inc reased alfalfa dry matter yield; whereas addition of 0.5 and 1,5 mK B kg(-1) had no effect. In the absence of added B, the B concentration i n alfalfa shoots decreased with increasing pH. Linear correlations bet ween B concentration in alfalfa shoots and extractable B in soil were significant for all three cuts and for all three extractants. Total up take of B was significantly correlated with all forms of extractable B except HW-B for the third cut only. Inclusion of pH improved the rela tionship for the other cuts. The dilution of B in plant shoots by CaCO 3-stimulated growth may result in B deficiency.