The Diagnosis and Recommendation Integrated System (DRIS) for diagnosing the nutrient status of grassland swards: III practical applications

Perennial ryegrass is the most important species of forage grass in both co ntinental Europe and the British Isles. An investigation was carried out to see if the DRIS model developed for this species was able to diagnose crop nutrient sufficiency status, at harvest time, using data for herbage sampl es collected 2 weeks earlier. A re-evaluation of P fertiliser recommendatio ns for silage, based on the 'Olsen' soil P-test, was then carried out using DRIS diagnoses of P sufficiency status as the criteria with which to judge if swards had been adequately, under, or over-supplied with fertiliser P. The results confirmed that reliable (DRIS) diagnoses of N, P, K and S suffi ciency statuses of silage swards may be made from herbage clippings taken 2 weeks prior to harvest. Current P recommendations for silage swards proved to be excessive for non-basaltic sandy textured soils at first cut, correc t for this group of soils at second cut, and more or less correct for non-b asaltic clay textured soils at both cuts. For basaltic soils, however, P re commendations at both cuts appeared to be unrelated to plant P status, and it was concluded that the 'Olsen' soil P-test had provided an erroneous ass essment of plant available P in these exceptionally iron-rich soils.