Fjölrit RALA - 05.12.1999, Page 140

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BIOMASS AND SOIL NUTRIENT POOLS IN NEWZEALAND
Table 4. Weight of elements in biomass and soil pools with 13 years afforestation with Pinus con-
torta at Craigiebum and with 13 years revegetation with Lupinus polyphyllus at Hakatere each
compared with element pools in weedy short grassland at same sites.
Soil
0 to 200 to
Above-ground 200 400
Locality Element Ecological stage Live Dead Roots tnm mm Total
Craigiebum C (tha'1) Pinus contorta 67.4 11.4 20.6 52.1 19.4 170.9
N (kg ha~‘) Weedy short grassland 1.7 0.8 8.2 12.2 19.8 102.7
Pinus contorta 550 244 90 2980 1649 5513
P(kgha-‘) Weedy short grassland 30 8 107 3953 1322 5420
Pinus contorta 106 16 22 788 695 1627
Weedy short grassland 6 1 16 1633 622 2278
K(kgha-’) Pinus contorta 454 43 86 125 110 -
Ca (kg ha"1) Weedy short grassland 41 3 67 259 87 -
Pinus contorta 304 159 66 590 87 -
Weedy short grassland 22 5 52 882 248 -
Hakatere C (t ha“l) Lupinus polyphyllus 3.0 3.3 12.9 98.0 53.5 170.7
N (kg ha"1) Weedy short grassland 0.4 0.5 5.0 98.3 56.5 160.7
Lupinus polyphyllus 138 85 248 7204 5162 12837
Weedy short grassland 7 4 68 7304 5410 12793
P (kg ha"1) Lupinus polyphyllus 11 6 28 1411 1322 2778
Weedy short grassland 1 1 8 1543 1475 3028
K(kgha-') Lupinus polyphyllus 70 16 162 190 77 -
Ca (kg ha"1) Weedy short grassland 25 4 58 216 86 -
Lupinus polyphyllus 75 92 124 1267 246 -
Weedy short grassland 19 2 97 1044 260 -
Table 4 also presents summary comparative data for nutrient pools 16 years after
the most degraded grassland site in the Hakatere montane sequence was revegetated
with lupins.- At this site, several different legumes had been sown with differential
levels ofphosphate in 1979 (Davis 1991). Biomass levels and nutrient concentrations
were determined after 16 years without grazing or additional fertiliser in Lupinus
polyphyllus plots with minimal initial P treatment (6.25 kg ha_I).
Substantial changes occurred in nutrient pools in biomass compartments, both
above and below ground, after herbaceous revegetation, without being reflected in any
directly discemible change in soil pools. Nutrient pools in lupin roots clearly exceeded
corresponding pools in the root mass of degraded grassland, whereas the nutrient
pools in pine roots did not always greatly surpass those of the Craigiebum weedy
grassland. In above-ground live and dead compartments, the increases in nutrient
pools with lupins are considerable, but do not match the dramatic changes in nutrient
pools occurring at Craigiebum in above-ground live and dead biomass compartments,
following afforestation with Pinus contorta.
Soil analyses themselves do not reveal increase in nutrient pools under pine forest
or lupins, even though there has been substantial carbon fixation in both cultural de-
velopment regimes (and under the lupins, substantial N2-fíxation) for more than a dec-
ade. We have argued elsewhere (O’Connor and Nordmeyer 1996) that to make such
comparisons validly, we would have to survey land surfaces carefully and sample to
uniform depth from a fixed benchmark, to take account of soil growth through root