Mineralisation of chicory and lucerne residues under field conditions

The incorporation of chicory into phased farming systems requires an understanding of N mineralisation of chicory residues and the supply of N to subsequent crops. A field experiment was conducted to determine the relative rates of N mineralisation from chicory, chicory/subclover and lucerne/subclover residues. Existing pastures were removed by spraying with herbicide in either spring or autumn and mineral N was measured at the time of spraying, and then 6 and 12 months later. Chicory/subclover had the greatest mineralisation rate during the first 6 months after spraying in either spring (0.54 kg mineral N/ha/day) or autumn (0.64 kg mineral N/ha/day), whilst lucerne/subclover had the lowest at 0.07 and 0.08 kg mineral N/ha/day for spring and autumn, respectively. However, 12 months after spraying, the mineralisation rate increased for lucerne/subclover, but began to slow for chicory and chicory/subclover. Compared to chicory alone, growing chicory with subclover significantly increased the release of mineral N by 28 and 47 kg N/ha, 6 and 12 months after pasture removal, respectively. The mass of N mineralised 12 months after pasture removal was similar for chicory/subclover (219 kg N/ha) and lucerne/subclover (234 kg N/ha). However, as high rates of mineralisation occurred for chicory treatments within the first 6 months after spraying, chicory-based pastures could potentially be sprayed out later (eg autumn) than lucerne pastures allowing more grazing time without the risk of N deficiency to the following crop. Therefore chicory/subclover pastures are well suited to phased farming systems, particularly where pasture phases are shorter, as the N benefit can be readily utilised by following crops.