Nitrogen Use Efficiency of 15 N‐labeled Poultry Manure

The timing between poultry manure N mineralization and crop N uptake as influenced by manure application time (winter or spring) and bedding material [barley ( Hordeum vulgare L.) straw, wood chips, or no bedding] was investigated with 15 N‐labeled poultry manure. Reference plots received either a high or low dose of 15 N‐labeled mineral fertilizer in spring or were without manure and fertilizer N. The 15 N recovery was measured for 1 yr in spring barley and for the two following years in perennial ryegrass ( Lolium perenne L.). Barley grain yield and N uptake were significantly higher when poultry manure had been applied in spring compared with application in winter. The barley 15 N recovery was 15% for winter‐applied manure and 38% for manure applied in spring. The recovery of manure 15 N from spring‐applied poultry manure corresponded to 82% of what was taken up by barley in the fertilizer‐amended soil, where 15 N recovery averaged 46%. Bedding in poultry manure had no effect on crop 15 N uptake. Ryegrass recoveries of 15 N from manure and fertilizer were 4 to 6% in the second year and 1 to 2% in the third year. After 3 yr, 94% of 15 N of spring‐applied poultry manure and 88% of mineral fertilizer were recovered in crops plus soil. Total recovery of 15 N from winter‐applied poultry manure averaged 56%. The bedding had no influence on total 15 N recovery. It is concluded that although poultry manure contains bedding with high C:N ratios which potentially could immobilize N for a period, optimum time for manure application is in the spring.