Ballantrae Research Farm is located near Woodville in the Hawke’s Bay region of NZ (NZMS sheet 2 1988 Ltd Rev). The experimental site is situated c. 200
to 350 a.s.l. on steep (c. 5 - 45º, Figure 3.3) heavily dissected hill country (Zhang et al. 2006). The experimental block design was unbalanced as treatment levels 0, 200,
and 400 kg N/ha.y were replicated in all three blocks and the 100, 300, 500, and 750 kg N/ha.y treatments were replicated in two of the three blocks only (hence 17 paddocks in total). Paddocks ranged in size from 0.2 to 0.5 ha and were blocked according to proximity to each other. The trial began in June 2004 and ended in June 2008.
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Figure 3.3 Photographs of some of the experimental hill country paddocks on Ballantrae Farm in the North Island
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Paddocks were rotationally grazed year round by hoggets and dry two tooths as herbage mass reached approximately 2,000 kg DM/ha in autumn, winter and early spring, and 2,500 kg DM/ha in late spring and summer. Stock numbers were adjusted as appropriate to graze paddocks down to a residual herbage mass of approximately 1,000 kg DM/ha within a 3 to 4 day grazing period.
At the start of the trial the site supported a mixture of 53 % HFRG (Lolium perenne, Anthoxanthum odoratum, and Poa Spp.) and 41 % low fertility tolerant grasses
(LFTG, Agrostis Spp., Cynosurus cristatus and Festuca rubra), which moved towards
a higher but not significantly different proportion of HFRG by the end of the trial period. Legume contribution (Trifolium Spp.) remained low (<5 %) for the duration
of the trial (Stevens et al. 2008). Mean annual net herbage accumulation from the
control sites (0 kg N/ha.y) over the trial period was approximately 10,658 kg
DM/ha.y. Mean response to fertiliser N was 7 kg DM/kg N applied with a response range of 3 to 20 kg DM/kg N applied.
The farm block is described as summer moist country (Lambert et al. 1983). The
relatively mild winter soil temperatures and high seasonal rainfall totals at this site are conducive to year round denitrification activity (Table 3.5). The high rates of
potential evapotranspiration in summer, and the rapid uptake of water by plants during spring however may result in soil moisture deficits over prolonged periods at these times. Highest N2O emissions may therefore be expected to occur during autumn
when water losses are smaller and soil temperatures are still warm enough to support denitrification activity.
Table 3.5 Annual and seasonal climate data summary for Ballantrae from Tait et al. and Tait and Woods (2006; 2007) with s.e.m in parenthesis, for the period 1975 - 2008
Spring median Summer median Autumn median Winter median Annual median Rainfall mm 322 (13.2) 260 (17.1) 290 (11.5) 358 (17.6) 1209 (40.7) Soil temperature °C 10 cm depth 11.3 (0.1) 16.8 (0.2) 12.4 (0.1) 6.7 (0.1) 11.8 (0.1) Potential evapotranspiration mm 239 (2.5) 373.3 (3.9) 158.8 (2.3) 58.3 (1.6) n/a Solar radiation MJ/ m2. d 15.4 (0.1) 19.4 (0.2) 11.7 (0.2) 7.7 (0.3) 13.7 (0.1)
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Experimental sites were situated on predominantly Wilford hill silt loam, which is a Mottled Argillic Pallic Soil (Hoogendoorn et al. 2008). The parent material is bluish
grey mudstone of the Waitotaran age (late Tertiary). The ranges for the soil parameters measured in Table 3.6 at this site were similar to values measured at Ballantrae and reported by Lambert et al, (2000). The minimum value measured for
soil pH in Table 3.6 may inhibit denitrification activity, although there is evidence for adaptation to local soil conditions by denitrifiers (Haynes 1986).
44 Table 3.6 Mean physical and biochemical properties of soils in trial paddocks at Ballantrae Research Farm (0-75 mm depth) with sed. Ranges are reported in parenthesis
pH Organic C % Total N % C:N ratio Olsen P mg/kg soil
Bulk density g/cm3
Pore size distribution <30 µm 30-300 µm >300 µm 5.7 (4.7-6.6) 5.0 (3.5-7.8) 0.4 (0.3-0.7) 12.5 (10.7- 15.6) §25 (18-35) 0.97 (0.78- 1.11) n/d n/d n/d SED 0.08 0.12 0.02 0.27 0.02
§values are from year 1 of the Wise N Use Trial for the Ballantrae site
in Stevens et al. (2008) n/d: no data
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Wilford hill soils are classed as weakly gleyed, weakly to moderately leached intergrades between central yellow-brown earths and yellow-grey earths (mottled argillic pallic soils). Soils were formed from Tertiary sandstone, siltstone, and mudstone but with some loess influence in areas. The mottling is a sign of impeded drainage which makes this soil vulnerable to increased and/or prolonged
denitrification activity at times of heavy rainfall. These soils are characterised by heavy textured firm subsoils with a weakly developed prismatic structure breaking to blocky structure. A profile from a weathered cutting on the Saddle Road on a
northerly facing slope of 25° is given by Cowie (1983) below:
A1 10-15 cm brown silt loam; friable; moderately developed fine and medium nutty structure; abundant roots; distinct, irregular boundary with much worm mixing,
B1 13 cm brownish yellow heavy silt loam; firm; weakly developed coarse prismic structure breaking to moderately developed medium blocky structure; some roots; indistinct boundary,
B2 25 cm pale yellow brown clay loam; very firm to slightly hard; weakly developed medium prismic breaking to moderately developed coarse blocky structure; many faint pale grey and yellowish brown mottles; darker brown coatings on prism faces; few roots indistinct boundary. (This horizon stands out as a pan in cuttings)
C1 on grey silty mudstone, very firm; some yellowish mottles in top few inches; strongly developed blocky structure
Subsoil textures range from silty clay loam to clay loam and the numbers of mottles in the subsoil is variable. On shady faces subsoils are more friable, browner in colour and less mottled. These soils are Andic Distrochrepts, Typic Distrochrepts, and Typic Eutrochrepts in the USDA classification (Lambert et al. 1983).