Nitrogen mineralization in tropical soils amended with crop residues

Continuous incorporation of crop residues after harvest can contribute to restoring the health of the soil. A 12-week aerobic incubation study was carried out with the objective of determining N mineralization in five tropical soils and in soils amended with groundnut (Arachis hypogaea) haulm and maize (Zea mays) stover. Plant materials (4 t ha(-1)) were mixed with the topsoil of five soil series, namely, Bungor sandy clay loam (Typic Paleudult), Munchong clay (Haplorthox), Rengam sandy clay (Typic Paleudult), Selangor silty clay (Typic Aquept), and Serdang sandy clay loam (Typic Paleudult). Nitrogen mineralization rates of indigenous soil organic matter (SOM), were 0.024 mg N kg(-1), 0.051 mg N kg(-1), 0.064 mg N kg(-1), 0.052 mg N kg(-1), and 0.042 mg N kg(-1) week(-1) for the five series, respectively. In these soil series, 9 mg N to 15 mg N kg was potentially mineralizable. After 12 weeks of incubation, net N mineralization was observed only in the Bungor series (24 mg N kg(-1) soil from the groundnut haulm and 13 mg N kg(-1) from the maize stover). In the other soil series, immobilization was observed ranging from 6 m N to 94 mg N kg(-1) in soils amended with groundnut haulm and 15 mg N to 105 mg N kg(-1) in soils amended with maize stover. The soil texture had little effect on N mineralization in soils amended with crop residues. Generally, by the end of the incubation period, the soil pH values increased (P less than or equal to 0.05) from 0.26 to 1.44 due to amendments with plant residues.