THE EFFECT OF FERTILIZER NITROGEN ON THE SOLUBILITY AND RUMEN DEGRADABILITY OF DRY-MATTER AND NITROGEN IN WHEAT-GRAIN

Seventy-four samples of wheat grain (c.v. Mercia) grown under a variet y of different fertiliser nitrogen (N) regimes were milled through a 3 mm screen. The rumen degradation characteristics of dry matter (DM) a nd N were estimated using the polyester bag in situ technique and DM a nd N solubility in water was estimated in the laboratory. The values d etermined in situ for the immediately soluble (a) fraction for N (16.9 +/- 3.81%) and the rate (c) of N degradation (0.128 +/- 0.0178 h(-1)) were both considerably lower than in previous reports in the literatu re. The N content of the grain. exhibited a strong curvilinear relatio nship with the total amount of N applied as fertiliser. Increasing fer tiliser N and the resulting increase in grain N contents tended to red uce and increase (P < 0.01) the immediately soluble and insoluble but degradable N fractions respectively, although the relationships only a ccounted for about 10% of the variance. For both statistical and theor etical reasons these relationships may not be applicable to other samp les of wheat. The work also showed that the water soluble DM measured in the laboratory was about ten times lower than the immediately solub le DM measured in situ. A similar, but less pronounced effect was seen for N where soluble N was on average only about 0.4 of the in situ ze ro hour loss (21.2 +/- 4.49%) and about 0.5 of the fitted a value (16. 9 +/- 3.81%) This suggests that the in situ technique can seriously ov erestimate the immediately soluble DM and N fractions of wheat and pro bably other cereal grains. (C) 1997 Elsevier Science B.V.