Porcentaje total de transmisión de la luz visible de las LIOs

Experiments 1 and 2 showed that over-drilling subterranean clover into established perennial ryegrass based pastures can increase dry matter yields and clover content in early spring. However, subterranean clover growth was visually patchy at both experiments, and yields were low. This raises the question of whether over-drilling subterranean clover was profitable in terms of increased revenue vs costs.

6.1.1 Profitability

For successful farmer uptake of any new farming practice, it needs to be shown to be profitable. Yield increases need to be shown to be sufficient to generate a substantial increase in animal production. The subsequent increase in revenue needs to cover costs (e.g. sowing costs), and also generate extra profit to make the concept worthwhile. Table 6.1 shows the theoretical increase in revenue and costs associated with over-drilling subterranean clover.

Table 6.1: Theoretical revenue and costs for over-drilling subterranean clover into dairy pastures. Assumptions are shown below

Sub clover yield (kg DM/ha)

189 320 1000

Revenue $ $ $

Milk solids increase/ha

($6/kg MS) 90.7 153 480 Nitrogen fixation/ha 5.48 9.28 29 96.2 162 509 Less costs Seed cost 100 100 100 Labour + machinery 40 40 40 140 140 140 Profit/loss per ha ($) -43.7 22.8 369

 Milk solid response = 80 g MS/kg DM (Dalley et al., 2005)  Nitrogen fixation = $29/ t DM (Section 2.2.3)

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The dry matter yields in Table 6.1 are from the ‘Woogenellup’ yields in Experiment 2 (189 kg DM/ha), the greatest yield in Woolshed 5 (320 kg DM/ha), as well as a proposed goal of 1000 kg DM/ha. The profit shown in Table 6.1 is subject to variation, mostly from dry matter yields, milk solid response and milk solid payout. The maximum subterranean clover yield measured in Experiment 1 & 2 (320 kg DM/ha) would result in a profit of $22.80/ha. This profit may be too small for it to be worthwhile for farmers to over-drill sub clover. If the average subterranean clover yield of ‘Woogenellup’ from Experiment 2 (189 kg DM/ha) is used for the same calculation, the result is a loss of $44/ha. In contrast, if subterranean clover produced 1000 kg DM/ha, it would generate $369/ha. If 20% of the average NZ dairy farm (144 ha) produced an extra 1000 kg DM/ha from over-drilling subterranean clover, this would result in $10,627 of extra profit. Given the variation in the calculations (e.g. milk payout, production response to extra dry matter), producing an extra 500-1000 kg DM/ha from over-drilling subterranean clover should consistently be profitable. Further research needs to be carried out to see if it is possible to consistently produce an extra 500-1000 kg DM/ha from annual clovers.

6.1.2 Leaf size

In both experiments, ‘Woogenellup’ and ‘Antas’ were superior to ‘Denmark’ in terms of dry matter production, which appeared to be related to leaf size. This was also apparent in Experiment 3, where the large leaved cultivars ‘Narrikup’, ‘Antas’, and ‘Woogenellup’ produced greater dry matter yields than small leaved cultivars. This suggests that to achieve a target of 1000 kg DM/ha of subterranean clover, large leaved cultivars would be most appropriate for use in perennial ryegrass pastures. This inference can be supported by the use of large leafed white clover cultivars in dairy pastures. These have greater ability to elongate their petioles and put leaflets above the ryegrass canopy, therefore intercepting more light than small leafed clovers.

6.1.3 Does over-drilling work?

Based on this research, over-drilling was not proven to be a reliable and profitable method for increasing spring dry matter yields and clover content. Both experiments

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were damaged by extremely high rainfall in July (Section 3.4). However the concept of using subterranean clover to increase spring dry matter yields and clover content was shown to be an area that needs to receive further research before being accepted or rejected.

6.1.4 Further research

Further research needs to be carried out to investigate if producing 500-1000 kg of extra DM from adding subterranean clover to dairy pastures is realistic. Higher than average rainfall (Section 3.4) and pest damage (Section 3.1.7) are likely reasons for the low subterranean clover yields in Experiments 1 & 2. It is likely that subterranean clover yields could have been greater if experimental sites were treated with slug bait prior to sowing, and soils were not waterlogged. If this experiment was replicated, the choice of a more suitable experimental area may result in greater subterranean yields. A sowing rate of 15 kg/ha, using a large leaved cultivar such as ‘Woogenellup’, should allow sufficient seedling establishment. Pastures with no insect pressure, particularly from slugs, grass grub and clover root weevil, with low white clover content at the time of sowing would create a favourable environment for subterranean clover establishment. Pastures should also be relatively open to allow maximum light interception to establishing seedlings. Irrigation would reduce the risk of establishing seedlings being exposed to water stress. Spray irrigation (e.g. pivots, fixed grid etc.) would be preferable rather than flood irrigation, as this can simulate a temporary waterlogging effect which may inhibit root growth of establishing seedlings. Soils should be free draining, with a pH of >6.0 and Olsen P of 35+. Adding subterranean clover into a seed mix and sowing conventionally could also be investigated, as this could reduce competition from perennial ryegrass and also reduce sowing costs.

Another area for further research is the use of different annual clovers, particularly balansa clover. Balansa clover is a winter annual, with some similarities in its life cycle to subterranean clover (Monks, 2009). However, balansa clover is tolerant of waterlogged or poorly drained soils which may make it more suitable for moist dairy pastures.

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6.2 Experiment 3 - Gibberellic acid on pure subterranean clover.