DIAGNOSIS OF NUTRIENT LEVEL FOR PERMANENT GRASSLANDS IN SPRING - BUILDING MODELS

The pattern of nitrogen, phosphorus and potash uptake was studied in 4 permanent grasslands during the spring. These grasslands differed in their soil fertility level. Experimental treatments consisted of nitrogen (spread on the land each year at different places N1 = 120 kg.ha-1, No = 0)), phosphorus (52 kg.ha-1 or not) and potassium (208 kg.ha-1 or not) spread on the land over a period of 4 years in the same place. Mineral uptake and mineral content were compared to aerial dry matter yield. Comparison between plots and treatments allowed us to define upper curves for which mineral content increased without dry matter yield increasing. Deviations from these curves were used to diagnose the herbage nutrition level. In order to simplify the method, the relationships between N content and P or K content were analyzed. A slight deviation occurred with the second method in the case of nitrogen stress. A nutrient index has been described as the ratio between the observed mineral content and the potential content of the same mineral.