Individual study: The effect of tree lupin Lupinus arboreus on the nitrogen status of china clay wastes at Maggie Pie, Cornwall, England
Palaniappan V.M., Marrs R.H. & Bradshaw A.D. (1979) The effect of Lupinus arboreus on the nitrogen status of china clay wastes. Journal of Applied Ecology, 16, 825-831
It is difficult to establish vegetation on sand and mica wastes derived from china clay extraction due to nitrogen (N), calcium and phosphorus deficiencies. In particular, N is a limiting nutrient and regular additions of fertilizer are needed to maintain growth and persistence of grass swards. However, fertilizer additions are expensive and subject to large leaching losses. An alternative approach is to introduce legumes which fix atmospheric nitrogen. The tree lupin (native to western USA) has been deliberately introduced to some waste tips in the UK as it can establish as an early colonist of raw wastes. At the end of its life-span (5-6 years) there is usually a vigorous growth of grasses around the bases of the old lupin plants benefiting from the accumulated N. In this study undertaken at Maggie Pie (National Grid ref. SW 935540), Cornwall (southwest England), the effect of tree lupin on the soil N content of mica wastes was investigated.
The tree lupin colony studied was established on mica waste with very low N content (10-30 pg N/g). Tree lupin tends to occur in large colonies with the oldest at the centre and younger individuals towards the perimeter. A colony was mapped and the ages of all individuals assessed by size and growth ring counts. Two transects were placed through the colony, and soil samples were collected at 150 cm intervals from the centre.
Transects were also laid from individual plants varying from 1-6 years old, and soil samples were collected from the centre of each and radiating out at intervals of 30, 60 and 120 cm. A sample of entire plants of each age class were harvested, oven-dried and weighed. The amount of accumulated litter and yield of companion species under lupin individuals of each age were measured.
Total N increased in the surface soils at the centre of lupine plants (to more than 300 µg N/g after the first year), this increase was confined to a radius of less than 30 cm. At 3 years of age, there was a noticeable increase in N up to 120 cm from the centre with a gradual increase until the fifth year. Under 6-year-old (senescenct) plants, N concentration slightly were slightly lower along the transect compared to 5-year-olds.
Where tree lupins were established, N accumulated at rates of about 180 kg/ha/yr. Concentrations of total, inorganic and mineralizable N increased both in the surface and subsurface soil compared to the raw waste. Non-legume species established under aging lupins, presumably benefiting from the increase in available soil N.
Conclusions: Tree lupin L. arboreus is tolerant of soils with low concentrations of major nutrients (NPK) required by plants. This combined with its ability to fix atmospheric nitrogen, makes it a suitable pioneer species for reclaiming wastes of low fertility (but potential invasiveness must be taken into account).
Note: The compilation and addition of this summary was funded by the Journal of Applied Ecology (BES). If using or referring to this published study, please read and quote the original paper, this can be viewed at: http://links.jstor.org/sici?sici=0021-8901%28197912%2916%3A3%3C825%3ATEOLAO%3E2.0.CO%3B2