Tracing the nitrogen, sulfur, and carbon released from plant residues in asoil/plant system

Matching plant residue mineralisation rate to plant nutrient demand is one way of increasing the efficiency of nutrient cycling. A glasshouse experime nt was conducted in a Soloth soil with a C-4 delta(13)C signature using dra ined pots to examine the effect on the yield of Japanese millet (Echinochlo a frumentocea) and the fate of N-15, S-35, and C (using delta(13)C shift) f rom the C-3 plants Flemingia macrophylla, Medicago truncatula hay, and whea t (Triticum aestivum) straw applied at 3 t/ha in the presence of N and NPKS fertiliser. The yield of Japanese millet at 91 days was highest where medi c hay had been added (13.7 g/pot) and lowest where wheat straw was used (11 .5 g/pot). Recovery of S-35 by the millet was highest in the wheat straw an d medic hay treatments (mean 11.5%), whilst recovery of N-15 was highest fr om medic hay (15.8%). Leaching losses of S-35 were highest in the Flemingia and medic treatments (mean 8.1%), and N-15 loss in leachate was highest in the medic hay treatment (6.6%). A maximum of 1.5% of the C added in residu es was recovered in the leachate of the medic hay treatment.