0.007) effects for two dung applications and quadratic (P = 0.048) effects for three applications
(Fig. 4-7). This response is similar to that for DM harvested because there was no effect of dung
on herbage N concentration. Thus, as observed for DM harvested, an important factor affecting
the N harvested response appears to be physical interference of dung in Ring 1 that reduced both
DM and N harvested (Figs. 4-3 and 4-7). This effect was most pronounced when dung was
applied two or three times per year.
The effect of application frequency within a level of ring number was assessed to
determine how far from the center of application dung affected N harvested. There were a linear
(P = 0.055) and cubic (P = 0.047) effects of application frequency for Ring 1. Linear effects
reveal the general pattern of decreasing N harvested with increasing numbers of excreta
applications. The cubic effect was significant because two dung applications actually depressed
N harvested more than three applications. The biological significance of the cubic effect is not
clear. There were no effects of application frequency for Rings 2 (P > 0.441) or 3 (P = 0.194)
indicating that dung application had no effect on the N harvested response outside of the
immediate 15-cm radius circle to which it was applied. The minimal positive impact of dung,
despite containing high amounts of N, is attributed to the slow physical breakdown of the dung
pats and low mineralization rates of organic N in dung (Deenen and Middelkoop, 1992).