CHANGES IN DRY-MATTER AND NUTRIENT YIELDS DURING THE RESTORATION OF SPECIES-RICH GRASSLANDS

Abstract. In two moderately productive grasslands that had been withdrawn from agricultural use, one on humic sandy soil and one on heavy clay, the decrease in dry matter, N‐, P‐ and K‐yields were measured for 14 and 11 years respectively, after fertilization had been stopped. The grasslands were mown twice a year. The yields and concentrations of nutrients were compared with those of already unproductive grasslands under the same growing conditions. On sandy soil, the annual dry matter yield decreased from 10.2 to 6.5 ton / ha in four years. After nine years, the dry matter (4.1 ton / ha) and K (20.5 kg / ha) yields were as low as those of the unproductive grassland. At that time yields and concentrations of N and P were still greater. The low K‐ concentration of 0.50 % and the lack of response upon N fertilizing indicate that the supply of K limits biomass production. On clay, during the first three years, the dry matter yield decreased from 10.2 to 5.0 ton / ha, after 6 yr the production increased again. The low N‐concentration of 1.52 % after 10 yr indicates that N is likely to limit biomass production, but the low P‐concentration of 0.14% indicates that P shortage can also be expected. In the lower productive grassland on sand the number of species that invaded was higher. 1990 IAVS ‐ the International Association of Vegetation Science