Jj. Varco et al., TILLAGE EFFECTS ON LEGUME DECOMPOSITION AND TRANSFORMATION OF LEGUME AND FERTILIZER N-15, Soil Science Society of America journal, 57(3), 1993, pp. 750-756
The inclusion of legumes in cropping systems raises questions about th
eir effectiveness as a N source. The objective of this study was to de
termine the effects of tillage on legume cover crop decomposition and
transformation dynamics of legume and fertilizer N-15. Nitrogen-15-lab
eled hairy vetch (Vicia villosa Roth.) residue or fertilizer was added
to soil cores contained in open-ended Plexiglas tubes placed in the f
ield. Vetch residues were either placed on the soil surface for no-til
lage (NT), or mixed with the soil for conventional tillage (CT). In 19
84, (NH4NO3)-N-15-N-15 was applied at rates of 0 and 100 kg N ha - 1 a
nd, in 1985, ((NH4)2SO4)-N-15 was applied at rates of 0 and 150 kg N h
a - 1 to both NT and CT cores with a history of winter fallow. Fertili
zer N-15 was applied in solution to the soil surface. Within 30 d, 77%
of the original vetch residue weight was lost with CT, compared with
45% with NT. Nitrogen lost from the residue by 30 d averaged 89% with
CT and 60% with NT. At 15 d in 1985, soil inorganic N-15 recovery for
fertilizer was 78% with CT and 57% with NT, and for vetch it was 47% w
ith CT and 12% with NT. Vetch N-15 immobilization averaged 2.3 times g
reater than fertilizer N-15 with CT and 1.7 times greater with NT. The
results indicate that N availability as measured by soil inorganic N
is less from vetch residue than fertilizer due to both greater vetch N
immobilization and the dependence of vetch N mineralization on decomp
osition rate.