Mineral Ntesting to be improved
PROBLEMS identifying how much mineralised nitrogen is contained in silt soils could soon be unravelled, according to Kemira Agricultures Jim Welson.
Research carried out by the company analysing soil samples taken down to a depth of 120cm could provide the basis for an accurate prediction model of mineralised N availability in silts.
"In normal mineral soils, about 55% of mineral N is in the top 30cm, 35% in the next 30cm and 10% down to 90cm," he says. "But this percentage is almost inverted in silt soils."
One example is a deep core test sampled after lettuce and going into wheat, where 102kgN/ha was measured, 61kg of which was contained in the 90-120cm layer.
Testing to 90cm does not measure all available mineral N in silt soils, says Mr Welson. "Most crops will pick up the majority of mineral N, even down to 120cm, so its important to estimate how much is there. There could also be environmental implications."
Levels of mineral N are very variable and depend on previous cropping, but Mr Welson is confident that a couple more seasons of deep core sampling should build up an extensive database which growers will be able to use to predict total mineral nitrogen availability from shallower samples. *