Mycorrhizal inoculant and bamboo biochar amendment promoted mycorrhizal population and soil nutrients for sustainable cacao farming

Poor soil nutrient levels and acidity negatively impact the production of high value crops that constitute the food economy and security background in most countries. Arbuscular mycorrhizal fungi (AMF) are proven to have biological activities that improve soil fertility and productivity of many crops, including cacao (Theobroma cacao). In this study, the long-term effects of AMF and biochar applied singly or in combination on rhizosphere mycorrhizal population was investigated. Grafted cacao seedlings (var UF18, K1, and K2) bought from an accredited cacao grower were inoculated with AMF (MYKORICH®, coded as MR) during transfer into bigger polybags filled with 1.5 kgs of soil sand mixture (1:1 v/v) and grown in a nursery of UPLB-BIOTECH. Field planting was done after six months where biochar was added as a treatment. The initial mycorrhizal spore level and soil fertility were assessed during field planting. Rhizosphere soil samples were collected every 12 months for over 5 years to assess any improvement of mycorrhizal population and soil fertility. Overall, MR+/-BB significantly improved the mycorrhizal sporulation as compared to its uninoculated counterparts, especially in K1 variety. In addition soil physico-chemical properties in UF18 and K2 varieties significantly improved two years after inoculation. Correlation analysis showed the significant positive effects of MR+/-BB to mycorrhizal population build up and to soil fertility. Moreover, regression analysis showed that AMF density predicts the variation in soil nutrients. Increase in AMF a year after inoculation has contributed to overall significant impact on soil physico-chemical characteristics and nutrients in the succeeding years. AMF density significantly (p<0.0001) predicted 87% in the variation of soil pH (F=74.28, b=0.433); 90% of OM (F=94.48); 89% of N (F=86.4); 71% of P (F=26.94); and 89% of soil CEC (F=85.78). Results show that mycorrhizal inoculant can enhance soil fertility even under stressed environmental conditions. Findings support the value of the technology as a renewable biological solution to agricultural problems arising from soil nutrient deficiency and acidity. Results must be verified in other high value crops and in other ecosystems with similar structure to demonstrate and establish the effectiveness of the technology for wider use by various sectors.