The productivity of East African highland (EAH) banana cropping systems is declining, particularly in areas with low inherent soil fertility. Soil fertility management requires knowledge of nutrient flows at the interface between the soil surface and the soil system. The magnitude of soil fertility dynamics and nutrient depletion was studied for a short-term banana plant density trial in three contrasting agro-ecological sites of Rwanda (Kibungo low rainfall with medium soil fertility, Rubona high rainfall with low soil fertility and Ruhengeri high rainfall with high soil fertility) using nutrient stock and partial nutrient balance calculations. Plant density did not influence significantly nutrient mass fractions in plant parts (fruit, leaves and pseudostems) but nutrients contained through shredded leaves and pseudostems and those removed through bunch dry matter increased with plant density. Plant density responses to variation in soil fertility and partial nutrient balances seemed to depend on diversity in climate and soil type. Partial N and K balances (kg ha(-1) year(-1)) were estimated to be strongly negative at Rubona and Ruhengeri while Ca and Mg were positive at Kibungo and Ruhengeri but negative at Rubona. This study showed that partial nutrient balances associated with soil nutrient stocks can provide the first order of magnitude of nutrient depletion in low input EAH banana cropping systems. This brings attention from agricultural researchers and farmers to develop options that can improve the productivity of these systems, where resource availability for improved nutrient management is scarce.
