The ability of potassium solubilizing rhizo-bacteria isolated from maize rhizosphere for microbial fertilizer

Abstract

Potassium is an essential macro nutrient for plants but most of them are not available because it is fixed in the soil in primary or secondary silicate minerals such as K-feldspar or 2:1 type clay form, so trigger the excessive use of potassium fertilizer that can damage the environment. Potassium solubilizing rhizo-bacteria (KSRB) which is a microbial fertilizer can overcome this problem by changing the non available into available soilpotassium. This is a promising strategy for improving of plant absorption of potassium and reducing the use of chemical fertilizers. The objective of this study was to evaluated the ability of fifteen KSRB isolates that isolated from maize rhizosphere to dissolve potassium. Potassium dissolution activity by KSRB isolate was observed using Khandeparkar’s selection ratio (modified) by measuring the diameter of the clear zone around the colony compared with the colony diameter on Aleksandrov solid medium (K-feldspar powder as sole potassium source) and pH measurement in Aleksandrov liquid medium. All KSRB isolates were capable of solubilizing K-feldspar powder in solid and liquid medium. There was a high negative correlation between Khandeparkar’s selection ratio and pH (r = -0.90**). The highest potassium dissolution activity was shown by RBPK-DHJ3-3150, RBPK-DHJ1-4125, and RBPK-DHJ2-5250 KSRB isolates, which showed Khandeparkar’s selection ratio of 5.97, 5.40, and 4.00 while pH 3.34, 3.28, and 3.64 respectively, so these three KSRB isolates were selected as the superior isolates based on the simple scoring and ranking method.