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

Abstract

Matching plant residue mineralisation rate to plant nutrient demand is one way of increasing the efficiency of nutrient cycling. A glasshouse experiment was conducted in a Soloth soil with a C₄d¹³ C signature using drained pots to examine the effect on the yield of Japanese millet (Echinochloa frumentocea) and the fate of ¹⁵ N, ³⁵ S, and C (using d ¹³ C shift) from the C ₃ plants Flemingia macrophylla, Medicago truncatula hay, and wheat (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 medic hay had been added (13.7 g/pot) and lowest where wheat straw was used (11.5 g/pot). Recovery of ³⁵ S by the millet was highest in the wheat straw and medic hay treatments (mean 11.5%), whilst recovery of ¹⁵ N was highest from medic hay (15.8%). Leaching losses of ³⁵ S were highest in the Flemingia and medic treatments (mean 8.1%), and ¹⁵ N loss in leachate was highest in the medic hay treatment (6.6%). A maximum of 1.5% of the C added in residues was recovered in the leachate of the medic hay treatment.