Evaluation of Sodium Tetraphenylboron (NaBPh4) as a Soil Test of Potassium Availability

Abstract

Non-exchangeable potassium (Knex) contributes to soil K availability and several extractants are used to access its contribution. This study evaluated sodium tetraphenylboron (NaBPh₄) as a soil test of K availability in 20 soils from Northern Greece. Winter wheat (Triticum aestivum L. var. 'Yecora') was sown in a greenhouse pot experiment and five cropping cycles were carried out until K-depletion. Soils were analyzed with NH₄OAc and NaBPh₄ (1 and 5 min incubation periods). Critical levels of K ranged between 130-140 and 330-340 mg K/kg of soil for NH₄OAc and NaBPh₄ (1 min incubation period), respectively, and between 32 and 35 g K/kg of wheat dry matter. NaBPh₄-K (1 min) related better with K concentration and uptake compared to NH₄OAc for each cropping cycle (r² = 0.45-0.83 and 0.44-0.89) and for all soils (r² = 0.58 and 0.51). Similar results obtained in soils low in exchangeable K (r² = 0.41 and 0.39). Correlation between NH₄Oac- and NaBPh₄-extractable K was weaker among soils below the critical level (r = 0.70) compared to those above (r = 0.93). Inclusion of illitic K and cation exchange capacity in a multiple linear regression between NH₄OAc- and NaBPh₄-extractable K showed that they significantly contributed to NaBPh₄-extractable K.

Bilias, F & Barbayiannis, N 2017, 'Evaluation of Sodium Tetraphenylboron (NaBPh4) as a Soil Test of Potassium Availability', Archives of Agronomy and Soil Science, vol. 63, no. 4, pp. 468-476. doi:10.1080/03650340.2016.1218479