Nitrogen uptake and nitrate (NO-3)
leaching below 1.1 m was estimated under phalaris, cocksfoot, and annual
ryegrass pastures and under bare fallow in a 4-year field experiment under
control and high N (500 kg N/ha) treatments in north-eastern Victoria (693
mm/year rainfall for the study period). The perennial grasses,
particularly phalaris, took up more N in herbage than annual ryegrass. High
concentrations of NO3-N were measured at 1 m depth
below all treatments, suggesting that NO3- losses from
pastures have potential to contaminate streams and/or groundwater.
Perennial pastures were only able to reduce NO3-
leaching compared with annuals in drier than average years. Values calculated
for acid addition due to NO3-leaching resulted in a net
annual input of approximately 1 kmol H +/ha.year
under the phalaris pasture compared with 2 kmol H
+/ha.year under annual ryegrass. Adding these
figures to carbon cycle addition data of 1 kmol
H+/ha.year (measured in a previous study)
corresponds to a lime rate of 100 and 150 kg lime/ha.year being required
to stop further acidification under these pasture types. A 1 unit pH decline
to 30 cm depth was estimated to take 42 years under annual pasture or 67 years
under perennial grasses. Whilst perennial pastures have a role in reducing
soil acidification, lime application is the most important management option
in balancing soil acidification caused by agriculture.
In-Field Observation of Root Growth and Nitrogen Uptake Efficiency of Winter Oilseed Rape
