Balanced phosphorus fertilization on grassland in a mixed grazing and mowing system; results after 18 years

In the Netherlands the P application standard including animal manure and P fertilizer has decreased to
balanced P fertilization since 2015. Moving towards balanced P fertilization might affect grassland yield
and quality, because soil processes might influence the P availability for plant uptake. In the short term,
balanced P fertilization is not expected to limit dry matter (DM) production of grass on soils with a
sufficient to high soil P. Decreases in P content and P offtake of grass are, however, expected directly after
decreasing P fertilization. In the longer term decreases of herbage yield can be foreseen. With balanced P
fertilization, annual DM yield and P content of alternately grazed and mown grassland were lower than
at a surplus of 9 or 18 kg P ha-1 yr-1 on sand and peat. However, differences between P treatments in DM
yield and P content remained constant over the whole period. On the marine clay soil, no differences in
DM yield were found between P treatments, but P content in the herbage were lower with balanced P
fertilization than with surplus P fertilization. The risk of yield reduction seems to be related to uneven
distribution of dung patches and the P buffering capacity of the soil.