HEMATOCRITO NIÑAS

Invermay Research Farm is located near Mosgiel in the Otago region of NZ. The experimental site is situated c. 90 – 150 m above sea level (a.s.l, NZMS 260 I44),

on rolling land (c. 8-15 º, Figure 3.2). In the Wise N Use trial, paddocks were

blocked according to pasture age; block 1 >20 y, block 2 c. 10 y, and block 3 <3 y old

pastures and ranged in size from 0.7 to 1.05 ha (Appendix 1). The trial began in June 2004 and ran until June 2007.

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Paddocks were rotationally grazed with breeding ewes and hoggets during which time pasture mass between 2,500 and 3,000 kg DM/ha was grazed down to a residual target between 1,000 and 1,800 kg DM/ha. From lambing to lamb weaning, pastures were set stocked and maintained between 1,500 and 2,500 kg DM/ha using a put and take system to alter grazing pressure as required. Grazing stock normally moved from low through to high N application paddocks and were held off for 24 h if moving from high to low N application paddocks (Stevens et al. 2008).

The site supported a mixture of high fertility responsive grasses (HFRG, Lolium perenne, Anthoxanthum odoratum, and Poa Spp.) and white clover (Trifolium repens). Weedy species were <5 % of pasture composition (Stevens et al. 2008).

Mean annual herbage yield for the control sites (0 kg N/ha.y) over the trial period was approximately 12,680 kg DM/ha.y and the mean N response rate was 21 kg DM/kg N applied with a response range of 4 to 32 kg DM/kg N applied (Stevens et al. 2008).

The farm block is described as summer dry, rolling country (Stevens et al. 2008). The

low winter soil temperatures (4.6 - 5 °C) and low summer rainfall combined with high potential evapotranspiration rates would not be expected to be conducive for

denitrification activity in the soils during these seasons (Table 3.2). Highest N2O

emissions may therefore be expected to occur during spring and autumn when soil moisture and soil temperatures are most suitable for denitrification activity at this site.

Table 3.2 Annual and seasonal climate data summary for Mosgiel from Otago Regional Council (2006). Data are the median values for the period 1970 – 2001

Spring median Summer median Autumn median Winter median Annual median Rainfall mm 201-250 181-200 201-250 201-250 801-900 Soil temperature °C 10 cm depth 11-1-11.5 13.6-14.0 6.1-6.5 4.6-5.0 9.1-9.5 Potential evapotranspiration mm ¥_171-180 ¥_161-170 ¥_66-70 ¥_{91-95 n/a} Solar radiation MJ/ m2. d 19-1-20.0 17.1-18.0 5.1-6.0 7.1-8.0 12.1-13.0

¥ _{Seasonal median values are from one month of each season only for the period 1970 - 2001}

The trial was situated on predominantly Warepa silt loam, a strongly mottled phase soil (Campbell 1977), and is classified as a Mottled Fragic Pallic Soil (Hewitt 1998). The parent material is loess. The ranges for the soil parameters measured at this site

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reported in Table 3.3 were similar to those measured for the Warepa silt loam reported by Campbell (1977), McDowell et al. (2004), Otago Regional Council (2006), and

38 Table 3.3 Mean physical and biochemical properties of soils in trial paddocks at Invermay Research Farm (0-75 mm depth) with sed. Ranges are reported in parenthesis

pH Organic C % Total N % C:N ration Olsen P mg/kg soil

Bulk density g/cm3

Pore size distribution % <30 µm 30-300 µm >300 µm 6.2 (5.7-6.9) §4.89 (4.87- 5.1) § .41 (.38-.44) 11.3 §26 (22-29) 0.90 (0.5–1.0) 50.1 8.1 8.0 SED 0.05 0.01 0.58 0.42 0.66

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Warepa soils are imperfectly drained due to perching of water on a dense fragipan, evidenced by mottling, making them susceptible to prolonged denitrification activity in times of high rainfall. Soils have a 15 to 25 cm deep topsoil that has moderately developed structure and good root distribution. Subsoil structure is moderate to weak in the upper subsoil, abruptly changing in the lower subsoil to the massive structure of the fragipan at c. 60 cm depth, which provides a barrier to root development (Table

3.4). Identified phases that experimental plots were situated on include Warepa deep silt loam, rolling (Wr0zR), Warepa moderately deep silt loam, rolling (Wr1zR) and Warepa deep silt loam, hilly (Wr0zH). Some characteristics of these soil phases are given in Table 3.4. The impeded drainage characteristics and structural vulnerability of this soil type (Table 3.4) renders it vulnerable to increased and/or prolonged denitrification activity and therefore gaseous N2O emissions in wet conditions.

Table 3.4 Attributes of the Warepa Soil phases Wr0zR, Wr1zR and Wr0zH within the Wise N Use Trial area described by Otago Regional Council (2006)

Soil phases

Wr0zR Wr1zR Wr0zH

Slopes Rolling (8-15º) Rolling (8-15º) Hilly (16-25º)

Potential rooting depth

40-80 cm 30-60 cm 40-80 cm

Rooting barrier Pan Pan Pan

Topsoil stoniness Stoneless Stoneless Stoneless

Soil texture Silt loam Silt loam Silt loam

Drainage class Imperfectly drained Imperfectly drained Imperfectly drained Permeability profile Moderate over slow Moderate over slow Moderate over slow Water logging

vulnerability – irrigated

High High High

Structural vulnerability

High High High

Drought vulnerability – not irrigated

Moderate Moderate Moderate

A detailed soil profile of the Warepa silt loam is described by (McIntosh 1985):

A 0-15 cm very dark greyish brown (10YR 3/2) silt loam; friable; strongly developed fine nut with crumb and granular structure; many roots and bracken rhizomes; indistinct boundary,

A/B 15-26 cm light yellowish brown (2.5Y 6/4) clay loam with profuse mottles of greyish brown (2.5Y 5/2) and dark greyish brown (10YR 4/2); Mn/ Fe

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concretions; friable; strongly developed nut and blocky structure; many roots; indistinct boundary,

Bg1 26-47 cm greyish brown (2.5Y 5/3) clay loam with mottles of yellowish brown (10YR 5/6); moderately developed prismatic structure; few roots; indistinct boundary,

Bg2 47-80 cm yellowish brown (10YR 5/6) silty clay loam with net gammate veins, light brownish grey (2.5Y 6/2); firm; strongly developed coarse blocky structure and platy fracture; few roots; diffuse boundary,

Cx 80-100+ cm brownish yellow (10YR 6/6) clay; extremely firm; strongly developed coarse prismatic structure; prisms separated by white (2.5Y 8/2) gammations

These are Typic Fragiudalf soils in the USDA taxonomy (McDowell et al. 2004).