Alleviation of Soil Acidity Stress In Robusta Coffee By Arbuscular Mycorrhizal Fungi-Containing Biofertilizers
Abstract
Three-month-old Robusta coffee seedlings were raised on soil with a pH level of 4.6 and treated with the microbial fertilizers Mykovam®(consist of 12 arbuscular mycorrhizal species), MykoplusTM (contain arbuscular mycorrhizal species and beneficial bacteria) and BiogroeTM (contain plant growth promoting bacteria) to test the hypothesis that the seedlings’ roots colonized by plant beneficial microorganisms can help in improving plant nutrient absorption by raising pH in the immediate rhizosphere. This study was prompted by the need to utilize marginal soils at medium elevations which are usually strongly acidic. After six months, the bio-efficacy of bio fertilizers were evaluated based on the growth attributes, mycorrhization and nutrient uptake by the coffee seedlings. Mykovam® and MykoplusTM, which contains vesicular arbuscular mycorrhiza, significantly increased stem diameter and shoot dry weight, and improved seedling height by as much as 37% two months after application. More importantly, Mykovam® and MykoplusTM increased root dry weight by 59 and 42%, respectively. The highest percentage of arbuscular mycorrhizal fungi (AMF) occurrence was observed in the roots treated with Mykovam® at 71-94% whereas in MykoplusTM, only 7-11% of AMF was observed. The presence of nitrogen fixing bacteria (6.70E+05) was found in the soil with MykoplusTM treatment. Robusta seedlings treated with Mykovam® and MykoplusTM gained the highest chlorophyll content as measured by SPAD. Plant tissue analysis showed that the highest amount of leaf nutrient concentration (N, P, Ca, Mg, Fe, Zn, Cu and Mn) was found in seedlings treated with Mykovam® while MykoplusTM promoted the highest K uptake. Taken together, the above results can be traced to the pH adjustment in the immediate rhizosphere; pH increased from 4.6 to 4.9 and 5.0 with the application with MykoplusTM and Mykovam®, respectively. Thus, mycorrhiza- containing biofertilizers can be applied in soils with very acidic pH to alleviate the effects of acid stress on coffee plant growth.
