La trazabilidad como instrumento de garantía alimentaria

3.3.3.1 Pre- and post-grazing herbage mass, herbage accumulated and herbage harvested

Pre-grazing herbage mass (HM) above 3.5 cm was determined by cutting two strips per

paddock (1.2 m × 10 m) with a motor Agria mower (Etesia UK Ltd., Warwick, UK;

Figure 3.1) and taking the average of the two harvests similar to Kennedy et al. (2009)

and McEvoy et al. (2010). The herbage yielded from each cut strip was collected,

weighed and sampled, and a sub-sample (100 g) was dried overnight at 90ºC in a forced-draught oven to determine DM content. Ten grass-height measurements were recorded before and after harvesting on each cut strip using a folding pasture plate meter

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Zealand; Earle and McGowan, 1979). Based on the above measurements, sward density (kg DM/ha per cm >3.5 cm) was calculated by dividing ore-grazing HM above 3.5 cm by compressed pasture height.

Pre-grazing HM below 3.5 cm was measured within each cut strip using a 0.5m×0.2m quadrat and scissors (Figure 3.1) and all collected material was washed to remove any

soil contamination and dried overnight at 90oC in a forced-draught oven to determine

DM content. Total HM was then calculated by adding pre-grazing HM above and below 3.5 cm. Post-grazing HM above 3.5 cm was determined after grazing by cutting a 20-m strip per paddock, following a similar procedure to pre-grazing HM.

(a) (b)

Figure 3.1 (a) Herbage mass measurement above the 3.5-cm horizon and (b) herbage mass measurement below the 3.5-cm horizon.

Herbage accumulated between grazings was calculated as the pre-grazing HM less the

post-grazing HM of the previous rotation. Herbage harvested (kg DM/hautilised; above

3.5 cm) was calculated as the pre-grazing HM less the post-grazing HM within the same rotation. Total herbage accumulated and harvested during each period and over the entire grazing season was calculated as the sum of all herbage accumulated and harvested. Pre- and post-grazing sward heights were measured with the rising plate meter, taking 35 measurements across the diagonals of each paddock. Finally, the proportion of available herbage utilised (harvesting efficiency) was calculated on an individual paddock and grazing event basis as the proportion of the pre-grazing HM

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which is harvested. The proportion of available herbage utilised reflects the grazing severity of an individual grazing event (and approaches 1.00 when paddocks are grazed to 3.5 cm).

3.3.3.2 Sward structure, sward morphology and tiller density

Extended tiller height (ETH) and extended sheath height (ESH) were measured on 200 random primary tillers immediately pre- and post-grazing across the diagonals of each paddock using a graduated ruler (Figure 3.2). The ETH was measured from ground level to the highest point of the tiller. The ESH was measured from ground level to the point of the highest ligule (longest leafed sheath). Free leaf lamina (FLL) was then

calculated by subtracting the ESH from the ETH, as described by Gilliland et al. (2002).

The proportion of rejected area or those areas laxly grazed due to the presence of faecal and urine deposits, was visually assessed using a 1m×1m quadrat placed randomly at 10 points along the diagonal of each paddock, when ETH and ESH were measured (Figure 3.2). The number of tillers that were selected from rejected (taller grass) or non-rejected areas (grazed at the expected grazing height) to measure ETH and ESH was consistent with the proportion of rejected area previously measured with the quadrat.

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Figure 3.2 (a) Sampling with hand shears; (b) assessment of grazing rejected areas; (c) extended tiller height measurement and (d) sampling procedure for morphological measurement.

The morphological composition of the herbage was determined before each grazing. Twenty grab samples (approx. 80 g in total) were cut at random to ground level with scissors in each paddock (Figure 3.2). By securing the sample with an elastic band and

(c) (d) (a) (b)

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placing it in a bag, the vertical structure of the cut sward was preserved. A 40-g sub-

sample was selected from the sample while fresh and separated into two portions –

above and below 3.5 cm. Each portion was subsequently separated into leaf, stem (including true stem, pseudo-stem and flower head, if present) and dead material. Each

component was dried overnight in an oven at 90oC to determine morphological

composition on a DM basis. The DM weight of each component was divided into the total DM weight of the sample to estimate the proportion of each component in the sample. Leaf, stem and dead yields were estimated using the proportion of each component from the herbage accumulated. To estimate tiller density, 10 turves per paddock (10 cm × 10 cm) were taken on 5 February, 17 June and 2 November. The

tillers were separated into PRG or other-grass species (Poa pratensis, Poa trivialis and

Agrostis stolonifera) and counted, and then multiplied by 100 to estimate number of

tillers/m2 (Jewiss, 1993). The daily net change in tiller density was calculated for each

treatment as the difference between the number of tillers on measurement dates divided by the number of days between measurements.

3.3.3.3 Sward quality

Herbage, representative of that removed by animals during grazing was sampled weekly from each paddock with hand shears (Accu 60, Gardena International GmbH, Ulm, Germany; Figure 3.2), taking cognisance of the previous defoliation height recorded from each treatment, i.e., after careful observation of post-grazing residuals of previous

grazing. A sub-sample was dried at 40°C for 48 hours and subsequently milled through

a 1-mm screen prior to chemical analysis, which consisted of ash, neutral-detergent fibre (NDF; Ankom Technology, Macedon, New York, USA), organic-matter digestibility (OMD; Fibered Systems, Foss, Ball mount, Dublin, Ireland) and crude protein (CP) analyses (Lecco FP-428, Lecco Australia Pty Ltd., Castle Hill, New South Wales, Australia).