Decomposition of a Green Manure Mixture of Field Peas and Oats As Affected By Particle Size and Crop-Induced Priming.

Green manures are a source of nitrogen (N) after the residues undergo decomposition and mineralization. Residues with smaller particle size will mineralize faster than those with larger particle size due to the greater surface area for microbial colonization, solubilization and enzymatic hydrolysis. Crop-induced priming of root-associated microorganisms is also expected to stimulate N mineralization of green manure residues, but how this phenomena affects the breakdown of residues with different physical size is unknown. The objective was to investigate the interactive effect of residue particle size and crop-induced priming on the decomposition and N mineralization from green manure residues.  This greenhouse experiment was done in pots (10.5 cm diam. by 13 cm depth) containing (1000 g) of loam soil. The residue, a mixture of field pea (Pisum sativum L.) and oat (Avena sativum L.), was harvested after 5 weeks and ground to pass through sieves, resulting in residue size treatments of no residue (control with bare soil), 0.5-1 mm and 2-4 mm particle sizes. The crop-induced priming treatment included a control (no plant), arugula (Eruca sativa L.) and glucose addition (0.25 to 6 mg glucose kg^-1 added every 3 d to simulate arugula root exudation). The experiment was designed as a factorial (3 residue sizes x 3 crop-induced priming treatments), replicated 4 times for a total of 36 pots. Soil and plant measurements were taken for 6 weeks. The soil mineral N concentration (soluble NH₄-N and NO₃-N pools) showed a greater concentration of IEM- NO₃-N with smaller residue size than larger residue size and bare soil. Glucose and arugula stimulated N mineralization, as determined from the IEM-NO₃-N concentration and crop N uptake.  We conclude that plant root had a great effect than glucose, influencing the decomposition of residues at 0.5 -1 than 2-4 mm, subsequently impacted IEM-NO₃-N concentration.