Can you afford not to reseed?

Published 28 June 10

 

Reseeding is not a cheap exercise," says DairyCo extension officer, Chris Duller.  "Add up the costs of spraying off the old sward, ploughing, secondary cultivations, seed and drilling and it is easy to reach a figure of around £400/ha (£160/acre).

"Factor in the time that ground is out of production and the potential costs of subsequent weed control and it is easy to understand why reseeding has taken a backseat on many dairy farms." However, there are many reasons why reseeding is a very sound business investment.

"From the first day a new ley is established there is a continual decline in the percentage of sown species as weed grasses and broad leaved weeds move into the sward," Chris explains.  "Even under good management it is likely that after six years a medium term ley based around intermediate perennials could contain less than 60% ryegrass.

"The impact of declining ryegrass content is a drop in both yield and quality. A young perennial ryegrass ley should yield well in excess of 10tDM/ha/yr in the first few years of its life - and if managed correctly should maintain quality above 11.5 ME and 20% crude protein.

"Much of this yield and quality is driven by a high response to applied nutrients; for every kilogram of nitrogen applied (from bag/slurry or clover) expect to get back 25-30kgDM of grass.  With this level of response grass is a cheap forage.

Chris continues: "Old leys may struggle to produce 6tDM/ha/yr and quite often because of poor response rates they may need greater nutrient inputs to achieve even that. The net result is less, poorer quality and more expensive grass.

"The speed of decline in leys is highly variable. Late perennials will survive longer than intermediate varieties and far longer than hybrids, which will struggle to make five years in most leys. Grass breeders are continually selecting for persistency - so even between varieties there is significant variability. Add to this variability the vagaries of soil type and climate and then mix in different management systems and it becomes clear that there is no simple 'time rule' to apply to decide when a ley has become worn out and an expensive source of grass.

"The decision on when to reseed generally needs to be governed by when ryegrass falls to below 50% of the sward. Ideally this observation would be backed up by production data; either some measure of stock performance on the ley (level of milk production or number of grazing days) or ideally, records of grass yield and quality from plate measurements and analysis.

Table 1 below shows how a typical silage ley based on a hybrid and perennial ryegrass mix can decline in productivity and quality as the hybrid ryegrass component drops and the content of weed species increase. The economic threshold is year five when the differential between the performance of the existing ley and a reseed (£637/ha) is significantly higher than the costs of a reseed at £400/ha. If you try and stretch the life of the ley an extra year then costs start to increase rapidly.

Table 1 - Example of the loss of productivity from a typical silage ley.

Age of Ley

Yield

T DM/ha/yr

Cost

p/kgDM

Average
quality

ME

Total energy produced
(yield x quality)
'000 MJ/ha

Difference in energy
'000 MJ/ha

Cost to replace energy with concentrates (£/ha)

1

13

10

12

156

 

 

2

12.5

10.4

11.8

147

9

127

3

12

10.8

11.6

139

17

240

4

11

11.8

11.5

127

29

410

5

9.7

13.4

11.4

111

45

637

6

8.4

15.5

11.3

95

61

864

7

7

18.5

11.2

78

78

1105

Chris continues: "While a full plough and reseed is the most expensive option it does provide an opportunity for weed control and the correction of any soil structural problems.

"Sward renovation through oversowing, either using grass rakes or a slot seeder, is undoubtedly a cheaper option but cannot alleviate any soil compaction. If poor soil structure was one of the reasons that ryegrass had disappeared from the original sward then oversowing is unlikely to provide a long term solution to sward improvement.  If soil conditions are suitable then oversowing can reinvigorate a sward successfully, but is unlikely to compete with the yield and vigour of a completely new ley.

"Cutting variable costs has been a reoccurring message to dairy producers over recent years and as a consequence expensive reseeding operations have frequently been put off or replaced with periodic sward renovation. To produce high quality and lost cost forage reseeding needs to be recognized as a highly profitable investment with a very short payback period. So take a close look at your swards - are they really up to the job?" he concludes.

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