Effect of Compost Rates Combined with Mineral Fertilizers in Microdose on the Growth and Productivity of Amaranth (Amaranthus cruentus L.) under Soilless Cultivation in Mali

Abstract

In the Sahel, declining soil fertility and pressure on urban land increase the need for resource-efficient vegetable production systems. This study evaluated integrated organo-mineral fertilisation for soilless production of amaranth (Amaranthus cruentus L.) variety ‘A2004’ in Samanko, Mali. Four compost rates (0%, 25%, 50% and 66.6%) were combined with a constant mineral microdose of 12 g NPK and 6 g urea per growing bag. Trials were conducted over two annual cycles under open-field and greenhouse conditions during rainy and dry seasons, using a randomised complete block design. Compost rate significantly affected growth and yield parameters across production environments. The 50% compost treatment (T2) produced the highest marketable leaf yields in all environments, reaching 65.87 t·ha⁻¹ under open-field rainy-season conditions, 40.54 t·ha⁻¹ under greenhouse rainy-season conditions, 36.77 t·ha⁻¹ under open-field dry-season conditions and 75.10 t·ha⁻¹ under greenhouse dry-season conditions. Plant height also peaked under T2 in each environment, while stem collar diameter generally increased with compost rate and reached the highest values under T3. The 66.6% compost treatment reduced marketable yield relative to T2, suggesting that excessive organic loading constrained foliar productivity. These findings indicate that a 50% compost rate combined with a fixed mineral microdose is an effective strategy for improving soilless amaranth production under the tested conditions in Mali.