Augmentation of mineral fertilizer with organic nutrient sources to improve soil quality and nutrient use efficiency in cocoa landscape in Ghana

Abstract

Integrating organic nutrient sources with mineral fertilizers offers a promising approach to address the challenges associated with conventional fertilizer management practices in cocoa production systems. This study evaluated the effect of augmenting mineral fertilizer with organic nutrient sources on soil health and nutrient use efficiency in cocoa landscapes in Ghana. The study consisted of two factors: shade systems (no shade and medium shade) and soil amendment (no amendment (T1), mineral fertilizer alone (T2), mineral fertilizer + biochar (T3), ½ mineral fertilizer + compost without rock phosphate (RP) (T4) and ½ mineral fertilizer + compost with RP (T5). The results reveal that these factors affected soil temperature and water, with medium-shade systems generally exhibiting lower temperatures and higher water contents. Soil chemical properties such as pH, soil organic carbon (SOC), total N, available P, and cation exchange capacity were significantly impacted by shade system and soil amendment, particularly in enhancing SOC and N levels. Furthermore, adding compost to mineral fertilizer improved microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), and microbial biomass phosphorus (MBP), indicating the positive effect of organic amendment on microbial activity. Plots treated with T5 showed significant improvement in Nitrogen use efficiency (NUE), Phosphorus use efficiency, and Potassium use efficiency (KUE). The importance of RP in improving the availability of N, P, and K for plant uptake was highlighted. The regression revealed that soil N was the most important driving force for NUE and KUE with a 1% increase in soil N resulting in a 79 and 111% increase in NUE and KUE respectively.