Is reseeding a realistic goal?
Published 29/08/2012 | 06:00
So far 2012 has challenged farmers' grassland management to the limit and grazing plans and objectives have had to be changed a number of times.
Many farmers have had aspirations to reseed paddocks, initially in April, which changed to June and now possibly to late August/September. Some farmers will have to postpone reseeding to next year.
There are plenty of farmers who have burnt off paddocks and still haven't got to cultivate them. If farmers have paddocks burnt off, then it is important they are sown in the coming weeks, providing weather and soil conditions allow.
For those that have not burnt off ground yet, it would be advisable to hold off until next year. However, planning can begin now by getting soil tests carried out and identifying the poorest-performing paddocks from 2012, which can be reseeded in spring/summer 2013.
Is there a difference in performance between reseeding methods?
How paddocks are prepared for reseeding comes down to soil type, amount of underlying stone and machine/contractor availability. There are essentially two methods of preparing the seedbed, ploughing and/or minimal cultivation. In recent years, there has been more focus on minimal cultivation techniques.
Ploughing is the most expensive method. Pests, thrash and native competitors are all buried with ploughing and it can also help the soil drainage. It can provide the basis for a sound seedbed and more level surface. Deep ploughing (>15 cm) can bury the top layer of most fertile soil. After ploughing the objective is to develop a fine, firm and level seedbed. Minimal cultivation techniques allow perennial ryegrass to be introduced into swards without ploughing. Most techniques involve spraying the existing vegetation -- the seedbed is then prepared using shallow cultivation equipment.
Soil disturbance is minimised, so the more fertile soil remains at ground level for use by the young seedlings, as well as providing better support for both machinery and animals at the early stages of pasture establishment. This is a fast and simple method of reseeding. It is important that the sward is grazed tightly if minimum cultivation techniques are to be used, as surface thrash will not be buried. As this thrash (dead organic matter) decays, it releases organic acids which may inhibit seed germination. Applying about 2t of lime/acre before cultivation will help neutralise this effect. With minimum cultivation, more weeds may appear, making the use of a post-emergence spray even more critical.
In Moorepark, a number of reseeding methods were compared in an area that was reseeded during the autumn, the techniques compared were as follows: (i) Control - permanent pasture, (ii) Direct drill, (iii) Discing plus one pass, (iv) One pass, (v) Plough plus level plus one pass.
All swards were initially sprayed with Roundup except the control. The swards were subsequently grazed with maiden heifers and dry matter production was measured.
Mean grass DM production over the two years for the treatments were Control sward 10.4t DM/ha; Direct drill - 12.4t DM/ha; Discing + one pass - 12.6t DM/ha; One pass - 11.9t DM/ha; Plough + level + one pass - 11.2t DM/ha. Table 1 (right) shows the individual values for the two years.
Little difference was found between reseeding methods, once the seed bed is clean and firm, minimum cultivation techniques work very well.
While the control sward had nearly 50pc perennial ryegrass, all reseeded swards increased their DM production capacity. Additional DM yield benefits from reseeded swards (i.e. high N response) can be expected in subsequent years compared to the non reseeded area.
Timing of reseeding
Historically most of the reseeding in Ireland takes place in autumn. This may make sense from a feed budget point of view, but it does have some negative consequences especially as you go later into the autumn.
Conditions deteriorate as autumn progresses -- lower soil temperatures can decrease seed germination and variable weather reduce the chances of grazing the new sward.
Table 2 (below) outlines the effect of autumn sowing date on seedling and tiller population and grass availability in spring.
As the sowing date moved to early October from early September, there was both a 50pc reduction in seedling survival and DM production in the October sown sward next spring.
Given good soil conditions and soil temperatures successful reseeding can take place up to mid September.
Our experiences of sowing paddocks in late Sept-ember/early October are extremely mixed and have generally delivered poor swards, full of annual meadow grass.
Once pastures establish poorly, it is very difficult to rectify poor establishments.
The target turnaround time in which to get a reseed back into production (spray off to first grazing) should be 50-60 days. However, 2012 has been an exception to this. Farmers are slow to reseed pastures because they believe paddocks are out of production for too long. The time that the sward is out of production can be minimised by cultivating 7-10 days after spraying the old sward.
Reseeding is a medium-term investment (Table 3, below).
It is an important investment and -- if conditions are right -- then it should be undertaken. Swards renovated in 2012 can be expected to last for 6-10 years or longer if correctly managed. Such swards will be required to sustain production over that time period.
When looking at the full costs of reseeding, it must be remembered that costs can vary, because a range of different reseeding systems exist and some costs are lower on farms depending on machine availability and the amount of work that is completed by the farmer.
In general, farmers estimate the cost of reseeding at €500/ha, which is realistic, because some of the costs outlined are carried in the overall management of the farm.
Increasing the amount of cultivations will only increase the cost of the operation. The best time to control docks and all other weeds is in the post-emergence phase of growth. By using a post-emergence spray, seedling weeds can be destroyed before they properly develop and establish root stocks.
Survey information shows that only 50pc of farmers are applying a post-emergence spray, resulting in more than 90pc of surveyed farms having problems with dock infestations.
To ensure a post-emergence spray can be applied, reseeding should be targeted for early autumn, when establishment conditions are much more suitable and the opportunity for weed control is guaranteed.
The post-emergence spray should be applied approximately six weeks after establishment, just before the first grazing takes place.
Michael O'Donovan and Phil Creighton work with the Animal and Grassland Research and Innovation Centres at Teagasc Moorepark and Athenry.
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