The phosphate field experiment IB 0013; annual report of the IMPHOS experiment; the ninth year: 1999

The results of the ninth year of the Dutch IMPHOS field trial IB 0013 are presented. In 1999 spring barley was grown. The first stages of the growth of spring barley were positively affected by phosphorus fertilization. The more phosphorus was given, the better the crop responded. The soil structure was rather poor. Phosphorus fertilization could not compensate the yield loss due to the poor soil structure. The heterogeneity of the crop did not allow for robust comparison of the different treatments.At final harvest phosphorus fertilization had increased the grain yield but the maintenance treatments (M) were similar in grain and straw yields or in uptake of phosphorus and nitrogen. The treatment without phosphorus fertilization yielded 89.3% of theM treatments. In this situation maintenance fertilization of spring barley is profitable. Based on the average total phosphorus uptake by spring barley, the maintenance phosphorus fertilization for the next crop, i.e. sugar beet in 2000, is set at 13.7 kg of P per ha (M treatment = 31.4 kg of P2O5 per ha). Phosphate fertilization increased the phosphorus status of the soil, but the differences are small. Compared to the results of 1998 the phosphorus status of the soil layer 0-25 cm declined for all four treatments due to the relatively low quantities of fertilizer that were used in 1998 and 1999