Humification and N mineralization of crop residues in semi-arid Argentina

Crop residues in the soil play a fundamental role in organic matter dynamics and have effects on numerous beneficial soil properties. The humification of residues depends on soil nutrient status and physical and meteorological conditions. The prediction of the humification rate and of the size and decomposition of fresh and humified soil organic matter has been attempted with equations and models which require several constants. To simplify the procedure, Janssen developed an equation which utilizes only one constant, allows to calculate the young (fresh) and old (humified) soil organic matter pools and predicts the production of available or mineralized nitrogen. The validity of Janssen's equation was tested in three production systems (a crop rotation and two tillage procedures) in a sandy-loam textured, thermic, entic Haplustoll soil in the pampean semi-arid region of Argentina. The model produced results compatible with actual field data, but information on soil available water was essential for fitting and interpreting the organic matter dynamics.

Galantini J.A., Rosell R.A., Andriulo A.E., Miglierina A.M., Iglesias J.O. 1992. Humification and N mineralization of crop residues in semi-arid Argentina. The Science of the Total Environment (Netherlands), 117/118: 263-270.
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Effect of sorghum residues on wheat productivity in semi-arid Argentina

Effect of sorghum residues on wheat productivity in semi-arid Argentina. 1. Stover decomposition and N distribution in the crop.

Humification and residual effects of three month-fallowed sorghum residues on the productivity of winter wheat in a petrocalcic Haplustoll soil in semi-arid Argentina were studied. ¹⁵N-labelled urea was applied at sorghum harvesting-mulching (or beginning of fallow, F), wheat seeding (S) and tillering (T). Sorghum residues interacted strongly with N added to the soil. Total aerial plant dry matter (TADM) was lowest (4.94 Mg ha^-1) when N was added at the beginning of fallow thus indicating a strong N immobilization, and highest (8.30 Mg ha^-1) when N was incorporated at S. The N uptake followed a similar pattern. The percentage of N derived from fertilizer and that of recovery as well as the N content of the TADM increased from F to S to T. These data suggest that the sorghum residues immobilize larger amounts of N when it is applied at the beginning of fallowing than when it is incorporated at a later time such as seeding and tillering.

Rosell R.A., Galantini J.A., Iglesias J.O., Miranda R. 1992. Effect of sorghum residues on wheat productivity in semi-arid Argentina. I. Stover decomposition and N distribution in crop. The Science of the Total Environment (Netherlands), 117/118: 253-261.
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