P (Wittry & Mallarino, 2004). The least profitable situation
for VR strategy was reported to be in fields containing
mainly high and medium STP (Wittry & Mallarino, 2004),
which is similar to the experimental plots used in present
study. In Belgium, STP greater than 30 mg 100 g-1 is
categorised as high level (Vanden Auweele et al., 2000).
Further investigation is needed to compare VR and UR
approaches for very low and medium P because STP in the
present study was in the high and very high level. Fig. 3
shows the relationship between the maize yield and initial
soil Pal within the VR treatment plots. As it can be seen the
yield decreased, when initial soil P increased. Note that the
rate of fertilization decreases as Pal increases and this trend
eventually suggests not applying any P. It seems that the VR
is more efficient, where the initial level of soil Pal is at
intermediate levels (Pal of 35-45 mg 100 g-1). This needs
also further investigation to be conformed. Comparing Fig.
3 with Fig. 4, it can be concluded that the optimum yield
can be reached at soil P levels of 45 mg 100 g-1. Results of
the present research show that for areas with higher levels of
P for which no application is suggested, a small amount of
application is still required to achieve maximum yield. This
finding is inline with another research carried out by Sawyer
and Mallarino (1999 & 2002), who reported from long-term