Root and inorganic nitrogen distributions in sesbania fallow, natural fallow and maize fields.

摘要

A field study was conducted on a Kandiudalfic Eutrudox in the highlands of western Kenya to measure rooting characteristics and distribution of inorganic N and water in three land-use systems (LUS): (a) Sesbania sesban fallow, (b) uncultivated natural weed fallow and (c) unfertilized maize monoculture. The maximum rooting depth was 1.2 m in (c), 2.25 m in (b) and >4 m in (a). Total root length was 1.26 km m-2 for (c), 5.98 km m-2 for (b) and 4.56 km m-2 for (a). Root length to 1.2 m was greater for(b) than (a) or (c). A considerable portion of the S. sesban root length to 4 m was in the subsoil; 47% was at 1.2 to 4 m and 31% was at 2.25 to 4 m. Deep rooting of S. sesban coincided with lower soil water below 2 m in the S. sesban fallow than the natural fallow. Soil nitrate-N, but not ammonium-N, to 4 m was affected by LUS. Total soil nitrate to 4 m was 199 kg N ha-1 for (c), 42 kg N ha-1 for (b) and 51 kg N ha-1 for (a). Soil nitrate in (c) was highest at 0.3 to 1.5 m depth on this Oxisol with anion sorption capacity. No such accumulation of subsoil nitrate was present under S. sesban or natural fallow.