New Zealand Journal of Agricultural Research abstracts
The impacts of nitrogen fertilisation and increased stocking rate
on pasture yield, soil physical condition and nutrient losses in
drainage from a cattle-grazed pasture
R. M. Monaghan1
R. J. Paton1
L. C. Smith2
J. J. Drewry1*
R. P. Littlejohn1
1AgResearch
Invermay Agricultural Centre
Private Bag 50 034
Mosgiel, New Zealand
2AgResearch
Woodlands Research Station
RD 1 Invercargill, New Zealand
*Present address: Integrated Catchment Assessment and Management
Centre, The Australian National University, Canberra ACT 0200,
Australia.
Abstract The effects of increasing nitrogen (N)
fertiliser inputs, and associated cattle stocking rates, on pasture
yield and composition, soil physical quality and nutrient losses in
drainage were measured in an experiment on permanent white
clover/ryegrass pastures in eastern Southland, New Zealand. Treatments
were established on hydrologically-isolated replicate plots (900 m2)
where pastures received annual fertiliser N inputs of 0, 100, 200 or
400 kg ha–1 and were grazed throughout spring, summer,
and autumn of each year by non-lactating dairy cattle. Our aim was to
determine if N fertilisation of cattle pastures led to the
deterioration of pasture or soil quality, or to the excessive loss of
nutrients in drainage over the 3–4 years after such land management
started. Pasture and soil monitoring showed that N fertilisation and
increased stocking rate resulted in large, but variable, increases in
pasture yield, with little discernible effect on soil physical
condition, as evidenced by twice-yearly measurements of soil bulk
density, percentage of soil pores >300 µm, soil macroporosity
(volumetric percentage of pores >30 µm), hydraulic
conductivity, and air permeability. A cyclical pattern of spring soil
compaction followed by recovery over summer, autumn, and winter was
evident in the 0–5 cm soil layer within all treatments. Mean
annual pasture responses to applied fertiliser N were 14.8, 12.9, and
9.1 kg DM kg–1 N applied in the 100, 200,
and 400 N treatments, respectively, with greater responses observed in
spring than in autumn in 3 out of 4 years. N fertilisation
significantly increased losses of nitrate-N and Ca in drainage but had
no significant effect on K, Mg, Na, sulphate-S, Cl, and P drainage
losses. Within the context of the potential for enriching groundwater
supplies of domestic drinking water, these losses suggest that annual
fertiliser N inputs should not exceed approx. 170 kg N ha–1 yr–1
at this site. Considered from the perspective of potential surface
water enrichment with P and N promoting nuisance weed and algal growth,
losses of N and P in drainage water exceeded currently accepted
guidelines, especially for N. The responses measured in this study
represent a system that has recently undergone an improvement in soil
fertility along with a change from sheep to cattle grazing. We thus
caution that our findings pertain to short-term changes in soil and
plant responses and may not accurately reflect those in a system that
has been in long-term (>20 years) equilibrium.
Keywords fertiliser nitrogen; cattle stocking
rate; pasture yields; drainage nutrient losses; soil physical
properties
A04075; Received 8 July 2004; accepted 7 April 2005; Online
publication date 30 May 2005
New Zealand Journal of Agricultural Research, 2005, Vol. 48:
227–240
0028–8233/05/4802–0227 © The Royal Society of New Zealand 2005
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