Effects of phosphorus fertilization on a low input meadow

We assessed the evolution of the yield, the nutritive value of the herbage and the botanical composition of a low input permanent meadow that received different amounts of mineral fertilizer during 11 years. In the long run, a negative effect on the yield and the P content of the herbage was observed when the level of P fertilization was lower than about one third of the average crop P offtake. In the plots receiving no P fertilizer but fertilized with N and K, the P content of the herbage was already in the second experimental year significantly lower than in the plots receiving 40 or 53 kg P2O5 per hectare and year. A significant difference between the yield of the plots receiving no P fertilizer and the plots receiving the highest rates of P fertilizer appeared after 7 years. In the plots where no nutrients at all were applied, we observed an important decrease in yield from the second experimental year onward. The proportion of grasses in the sward of the unfertilized plots was 63 % whereas it was between 71 % and 79 % in the other treatments. The proportion of legumes seems to have slightly deceased when no P fertilizer was applied. These results show that the P content of the herbage of low input meadows can quickly decrease when the level of P fertilization lies below the crop P offtake.