Aeschynomene afraspera

Cultivation Details

Aeschynomene afraspera is found at elevations from sea level to 900 metres in tropical areas with a distinct dry season and a monomodal rainfall distribution^[1]. Succeeds in a wide range of soils, from pure dune sands along rivers to peat soils in mangrove swamps so long as there is sufficient plant-available phosphorus (at least 10 ppm). Soil reaction can range from alkaline in salt flats to highly acidic in acid sulphate soils^[1]. The plant occasionally appears as a weed in rice fields^[1]. A fast-growing plant, though initial growth until the fifth leaf has been produced is slow^[1]. With the onset of stem nodulation and/or closure of the canopy the plant then grows rapidly, and can reach a height of 60 - 150cm within 2 months^[1]. In the Philippines the plant starts flowering 65 days after sowing during the short-day season, and after 80 days when daylength exceeds 12 hours. With prolonged soil flooding, the otherwise short flowering period can extend to over 2 months^[1]. Fruit ripening causes drying and brown discolouration of leaves and stems, ending the growth cycle^[1]. An 8-week-old crop grown in a pure stand can accumulate a dry biomass of 4 - 6 tonnes per hectare, with a corresponding nitrogen yield of 80 - 200 kilos, provided sufficient water and soil P are available; 70% or more of this may be the result of biological nitrogen-fixation. As an intercrop, 35 - 60 kilos of nitrogen per hectare can be accumulated^[1]. Reported increases in rice grain yield due to the incorporation of a 6 - 8-week-old green manure range from 0.8 - 3.2 tonnes per hectare^[1] This species has a symbiotic relationship with certain soil bacteria; these bacteria form nodules on the roots and fix atmospheric nitrogen. Some of this nitrogen is utilized by the growing plant but some can also be used by other plants growing nearby^[2]. The most distinctive characteristic of Aeschynomene afraspera is the presence of nitrogen-fixing nodules, not only on the roots but also on predetermined, sub-epidermal primordia of adventitious roots on stems and branches. Upon infection with rhizobia via rain splash or insect activity the root primordia can develop into nitrogen-fixing nodules. Since root nodules are scarce under anaerobic conditions in flooded soils, the plant has to rely on stem nodules to fix atmospheric nitrogen. Root primordia on stems become visible in 2-week-old plants, and profuse stem nodulation is apparent 3 - 5 weeks after germination. Up to 400 nodules can be found on the stem of a 2-month-old plant and 70 - 80% of the nitrogen in the biomass is reportedly derived from biological nitrogen fixation, indicating the high efficiency of the symbiosis in stem nodules^[1].