Long-term effects of improved legume fallows on soil invertebrate macrofauna and maize yield in eastern Zambia

Though improved fallows have been widely promoted as low-input technologies suitable for soil fertility replenishment in smallholder agriculture in southern Africa, their interaction with soil invertebrates has not been studied. In the present study we compared the population of soil macrofauna in maize grown in gliricidia (Gliricidia sepium), leucaena (Leucaena leucocephala), Leucaena diversifolia, sesbania (Sesbania sesban) and acacia (Acacia anguistissima) and continuously cropped monoculture maize. The objectives of the study were to determine (1) the effect of the type and length of fallows on soil macrofauna communities and functional groups, and (2) the long-term effect of legume fallows on maize yield. The number of invertebrate orders per sampling unit was significantly influenced by the type of fallow but not by the length of fallow period. Maize grown in legume fallows had more numbers of invertebrate orders than monoculture maize. Among the soil invertebrate macrofauna, centipede and millipede populations were significantly influenced by fallow type. The density of earthworms varied with both the type and length of fallow practice. Earthworm populations under maize grown in gliricidia fallows were significantly higher than those under fully fertilized monoculture maize. The population densities of other invertebrate orders and functional groups did not significantly differ between maize grown continuously in monoculture and in legume fallows. The highest maize grain yield (3.0–6.0 t ha−1) was recorded in fully fertilized monoculture. Maize grown in gliricidia and leucaena fallows consistently gave 2.0–4.0 t ha−1 throughout the study period, while maize grown without fertilizer yielded less than 2 t ha−1. These legumes produced 0.4–2.9 t ha−1 of re-sprout biomass annually, which released nutrients contributing to higher maize yields over a long period of time. It is concluded that these legume fallows can improve maize yields in addition to their positive impact on the diversity and functions of soil invertebrates.