Growth, nitrogen accumulation and nitrogen transfer by legume species established on mine spoils

Summary

Nitrogen deficiency may often limit plant growth on many types of mine and mineral spoil. One method of overcoming this is to use legume species which are able to accumulate nitrogen in the substrate. The growth, nitrogen accumulation and nitrogen transfer to a companion grass species was compared for 22 legume species established on sand waste derived from the extraction of china clay at Maggie Pie (National Grid ref. SW 935538), near St Stephen, Cornwall, southwest England.

Trials of the legume species were established in April 1977 on a bed of 2 m deep sand tipped on to a mica tailings dam.

Lime and fertilizer addition: To the sand was added ground limestone at a rate of 1 t/ha, and nitrogen (N), phosphorus (P) and potassium (K) at 30 kg N (ammonium nitrate), 40 kg P (triple superphosphate) and 40 kg K/ha (potassium sulphate) fertilizers.

Experimental design: Twenty-two legume species (a mix of natives and non-natives) were sown in 1 x 0.5 m plots in a randomized block design with three replicates. The species  were:

Annuals: white lupine Lupinus alba, blue lupine L.angustifolius, yellow lupine L.luteus, serradella Ornithopus sativus, lesser trefoil Trifolium dubium, subterranean clover T.subterraneum,large yellow vetch Vicia grandiflora, common vetch V.sativa;

Biennials: black medick Medicago lupulina, white melilot Melilotus alba ribbed melilot M.officinalis;

Perennials: kidney vetch Anthyllis vulneraria, crown vetch Coronilla varia, broom Cytisus scoparius, lucerne Medicago sativa, bird’s-foot trefoil Lotus corniculatus, greater bird's-foot trefoil L.uliginosus, Lupinus perennis, Trifolium hybridum, red clover T.pratense, white clover T.repens, gorse Ulex europaeus.


Legume seeds were inoculated with appropriate Rhizobium strains to assist establishment, and sown at 50 kg/ha. Bent-grass Agrostis castellana (cv. ‘Highland’) was sown with each legume at 30 kg/ha, and also in monoculture at 80 kg/ha. P was reapplied at 40 kg/ha in March 1979.

Harvesting: Vegetation was sampled in September 1977, September 1978 and May 1979, 5, 17 and 25 months after sowing. On each date, 625 cm² subsample was clipped to 2-3 cm in height. Different areas of the plots were sampled at each harvest. Material was dried and separated into legume and grass and weighed. Stubble and soil cores (7.5 cm diameter, 7 cm deep) were taken, air-dried and sieved to remove the stubble and roots. The roots were washed, dried and weighed. Bulk density of the sand and total nitrogen was determined.

At the first harvest the annuals L.angustifolius, L.luteus and O.sativus were the most productive species (yields 4.5-8 t dry wt/ha). Despite seed production at the end of the first season, annuals were very scare or absent in the second year. Small-seeded species (e.g. O.sativus, T.dubium and T.subterraneum) faired best in areas harvested the previous year, the associated soil disturbance perhaps providing sites for establishment. The biennials also did poorly in the second year.

Yields of forage perennials conventionally used in agriculture were low (0.7 to 1.5 t dry wt/ha). At the second and third harvests Lotus corniculatus and L.uliginosus appeared best suited to the sand waste (maintaining yields between 1- 2 t dry wt/ha, as other forage species progressively declined). Of the ‘non-forage’ perennials, Lupinus perennis performed very well; establishment was slow and yield quite low at first, but it became the highest yielding species with 7.9 and 14.2 t dry wt/ha at the second and third harvests. The only two woody shrubs in the trials, broom and gorse, were slow to establish but grew throughout the experimental period, with a progressive increase in biomass except for broom at the final harvest, which declined due to frost damage.

At first harvest Agrostis yield was about equal for all the legume species, and was not significantly different from the monoculture. The monoculture became moribund by the second harvest but biomass was maintained. Agrostis sown with some of the legumes, e.g. L.corniculatus, L.uliginosus and T.repens, was greener than the monoculture, but no legume species had any significant effect on grass yield. At the third harvest the Agrotis monoculture yield fell. In contrast that sown with L.corniculatus, L.uliginosus, M.alba, M.officinalis, O.sativus, T.dubium, T.hybridum, T.pratense and T.repens increased and was significantly greater than for the monoculture.

The total N content of the legume shoots reflected the pattern of dry matter production. At the first harvest the N content of the most productive annuals was high but because of the failure of establishment subsequently N content of the roots and sand declined. The N content of the shoots of the forage legumes declined after the first season, but these species had a more persistent effect on N content of the roots and sand. The most effective species was L.perennis which increased in total N content and had substantial N accumulation.

Agrostis N content was unaffected by any legume species at the first and second harvest. Differences became apparent at the third harvest with the N content when grown with L.corniculatus, L.uliginosus, M.alba, M.officinalis, T.hybridum and T.repens being significantly greater than that of the monoculture. This was greatest with L.corniculatus and M.officinalis where Agrostis shoots had a N content of 35 and 36 kg/ha respectively, compared with only 5 kg/ha in the monoculture.

Conclusions: The legumes trialed, especially perennials, were effective in accumulating N in the sand waste with rates as high as 295 kg N/ha/yr being measured for Lupinus perennis. N transfer from legumes to the companion grass was also apparent. This study shows that a wider range of legume species than conventionally used may be useful in reclamation of such wastes.

 

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%28198112%2918%3A3%3C945%3AGNAANT%3E2.0.CO%3B2-2