Relating particulate organic matter-nitrogen (POM-N) and non-POM-N with pulse crop residues, residue management and cereal N uptake

摘要

Particulate organic matter nitrogen (POM-N) was evaluated as an indicator of crop residue source ( pulse versus cereal) and residue management (no-tillage [NT], stubble burned [SB] or stubble mulched [SM]) on soil quality and subsequent crop productivity in a continuous cropping experiment in northern New South Wales ( NSW), Australia. The relative contributions to POM of pulse versus cereal, and shoots versus roots, were studied using in situ N-15 shoot labelling. Under NT, a greater proportion of organic N was found in POM-N > 250 mum (5.5% versus 3.5% [SM] and 2.7% [SB]) and POM-N > 53 mum (10.3% versus 9.7% [SM] and 8.7% [SB]). Pulse residues ( particularly roots) contributed 2-7 times more N to POM and 20-4 times more N to non-POM-N than barley (N-15 data), but this increased contribution was not detectable with non-isotopic analysis. POM-N was sensitive to residue management, but was not a reliable measure of N inputs from pulse versus cereal residues, nor a useful tool for predicting subsequent crop N uptake.