Sn. Nguluu et al., EFFECT OF TISSUE PHOSPHORUS CONCENTRATION ON THE MINERALIZATION OF NITROGEN FROM STYLO AND COWPEA RESIDUES, Plant and soil, 191(1), 1997, pp. 139-146
Laboratory studies were conducted to investigate the effect of phospho
rus concentration in residues of cowpea (Vigna unguiculata, L. Walp) a
nd style (Stylosanthes hamata, L., cv Verano) on their rate of nitroge
n mineralisation when incubated in a soil whose P status was deficient
for plant growth. Residues with a range of P concentrations were obta
ined by applying varying rates of P to soil in which the plants were g
rown in the field or the glasshouse. Variations in P concentration of
field- or glasshouse-grown residues were not accompanied by variations
in other chemical components (C:N ratio, lignin and polyphenol concen
trations). Both lignin and polyphenol concentrations were higher in th
e field-grown than in the glasshouse-grown residues. Lignin concentrat
ion was greater in cowpea than in style, but polyphenols were higher i
n style. Cowpea residues mineralised N less rapidly than style. N mine
ralisation from residues with low P concentration was consistently les
s than from those of higher P concentration; reduced mineralisation wa
s observed for P concentration in the residues below 1.6 g kg(-1). Whe
n inorganic P was added to the residue-soil systems, N mineralisation
from the residues was increased, though no interaction between the eff
ects of adding inorganic P and P concentration in the residues was obs
erved.