“It seems to take a whole season to get the roots down to that nitrogen,” she said.
For the trial 800kg nitrogen/ha was applied in June, simulating a urine patch following removal of a mixed swede-kale crop.
By the following May barely 100kg N/ha remained where a chicory-clover mix had been sown in October, significantly less soil mineral nitrogen than where ryegrass-clover pasture was sown (about 140kg N/ha) or barley (about 155kg N/ha remaining).
However, about 400mm of drainage occurred between the urea application and the end of September when drainage was calculated to have ceased, so only about 360kg N/ha of the 800kg N/ha applied remained in the top 90cm of the soil profile at sowing of the crops, with half of that below 30cm.
Barley took up the most nitrogen initially but little following its January harvest owing to drought and little regrowth, even of weeds.
Lucci et al suggested that if triticale had established successfully it might have offered a second harvest opportunity and hence been able to access nitrogen deeper in the soil.
Chicory’s success in recovering nitrogen was attributed to its deeper roots, which favoured it during the November-January drought in the trial region, and the plant’s slightly higher nitrogen content.
Nonetheless, barley produced the highest total yield over the growing season to early May, at 6.8 tonnes drymatter (DM)/ha, compared to 4.9t DM/ha of chicory and 3.6t DM/ha of pasture.
That was despite little regrowth of barley or weeds after its harvest in January.
“Cereal roots don’t seem to get so deep but they do get in early,” Lucci said.
Challenged by a conference delegate as to whether such modest differences between crops in their nitrogen uptake was worth pursuing, given the 800kg N/ha deposited in a typical urine patch, Lucci acknowledged that it was a good question but research still had to be done to answer it.
“The urine patch is the big problem,” she stressed.
- Lucci’s paper is published in the Journal of NZ Grasslands 77. Go to www.grassland.org.nz.
