Recovery of nitrogen by spring barley following incorporation of ¹⁵N-labelled straw and catch crop material

The recovery by spring barley (Hordeum vulgare L.) of nitrogen mineralized from N-15-labelled straw and ryegrass material was followed for 3 years in the field. The effects of separate and combined applications of straw and ryegrass were studied using cross-labelling with N-15. Reference plots receiving (NH4NO3)-N-15-N-15 were included.

Plant samples were taken every second week until maturity during the first growing season and at maturity in the two following years. Incorporation of plant material had no significant influence on the above-ground dry matter yield of the barley. The barley recovery of N derived from straw was not significantly different whether straw was incorporated alone or in combination with ryegrass material.

The mean recovery of straw N was 4.5% in the first barley crop and 2.7% and 1.1% in the second and third crop. During the first growing season, recovery of ryegrass N in the barley was higher when the catch crop material was incorporated without straw, but the differences were only significant at one sampling date.

At maturity 7.8% and 10.2% of the ryegrass N was recovered in the barley crop, when ryegrass was incorporated with or without straw, respectively. Mean recoveries of ryegrass N were 2.3% in the second year and less than 1% in the third year after incorporation. Recovery of mineral fertilizer in the year of application was relatively low (29-40%), probably due to long periods of spring drought in all 3 years.

The recovery of N from residual mineral fertilizer was in the second and third barley crop similar to the recovery of N from incorporated plant residues.