Removing the seed heads through grazing or mowing results in more tillers being produced by the grass plants and the leaves start growing again. The net effect is that the pasture quality is partly restored to its previous levels.
So how do we control pastures on-farm over spring? The conclusion is that either the demand of the farm needs to be increased or the supply of pasture reduced.
Methods of increasing feed demand are increasing animal performance or buying additional livestock. Options to decrease pasture supply are removing supplements, spraying areas for crops (or summer fallowing), mechanical topping, deferred grazing and chemical topping. These options are discussed in greater detail below.
The aim should always be to “push” the feed surplus to better contoured areas of the farm where it can be dealt with easily. If pasture covers on the steeper areas of the farm are allowed to build-up a mass of dead material in the sward they can take years to recover.
Increasing feed demand: The options available to increase feed demand within a season are limited to either increasing animal performance or increasing stock numbers.
Increasing animal intake by increasing animal performance is a double-edged sword. This occurs because the optimum post-grazing pasture residuals for high animal growth rates are greater than those required to clean up emerging seed head.
For cattle to grow at near optimum, they need a post-grazing residual of at least 1800kg/DM/ha (4-5cm). Sheep on the other hand require a post-grazing residual of 1600kg/DM/ha (3cm) to achieve the best per head performance. At these levels, sheep and cattle will avoid grazing the emerging seed head leaving “clumps” in the pasture.
One method that has been used with good success is to have a “flying mob” of mature cattle. These graze a paddock within a rotation that has been intentionally skipped by the mob on rotation with a pre-grazing of greater than 2500kg/DM/ha. This mob grazes the paddock down until the seed head “clumps” are removed. Often this mob will have higher growth rates than comparable mobs kept on their rotations.
The aim should be to have all livestock fully fed before buying additional livestock when targeting to reduce a feed surplus.
Increasing stock numbers: Once pastures have started to reseed, the store market is often nearing its peak. This limits the short-term trades such as two-year-old cattle which have the ability to consume large amounts of lower quality feed and still perform.
An alternative option is to step down to yearling cattle. These can be summered with the primary objective of maintaining feed quality and making a sufficient return to recover their direct expenses and interest on capital.
A yearling bull bought on November 1 at 280kg LW and grown to 400kg LW on May 1 needs to return a margin of $45/head to break even. A yearling steer bought on November 1 at 300kg LW and grown to 400kg LW on May 1 needs to return a margin of $49/head to break even.
The option of summering yearling cattle will depend on your risk of a summer dry and feed profile.
Making supplements: Making supplements is a straightforward option provided you have contour suitable to making hay and silage. This requires that areas of the farm are shut up before feed surpluses begin to appear. The supplements are either used in next winter’s feed plan or sold on the open market.
Table 1 shows the costs for making various supplements. These prices will vary depending on contour, access and location. Note that these figures do not allow for the cost of replacing the nutrients removed if the supplements are sold off-farm.
Spraying for crops: Another option for farms with suitable contour is spraying and planting crops. These crops need to have a purpose before they are sown such as cash crops, feeding lambs, or winter feed reserves.
A few of the common forage options are outlined in Table 2 but no allowance has been made for the cost of regrassing (about $650/ha). The cost of regrassing is planned to be recovered from the new pastures.
Mechanical topping: Using a mower is a good way of ensuring that pastures that are beginning to get out of control remain in a vegetative state. Although definitive, pasture topping can be expensive involving tractor running costs, labour and wear on the machinery. Topping costs between $50 to $80 a hectare including labour.
Pastures should ideally be mechanically topped in November to January as seed heads becomes evident. Topping will also help control mature weeds.
Deferred grazing: This is the concept of consolidating surplus pasture into one area while maintaining the pasture quality on the rest of the farm. The area selected will be one that can easily be fed off to mature stock behind an electric wire when needed. The paddock should be grazed once reseeding is completed (from February on).
By deferring an area of the farm, natural reseeding occurs and once cleaned off the pastures perform better than before being shut up. DairyNZ research has shown that pasture production in the year following deferred grazing is increased by 15%.
Deferred grazing should be avoided in paddocks containing low-fertility grasses (ie, Browntop) and a high proportion of weeds (eg, scotch thistles).
Chemical topping: This involves the use of a light rate of glyphosate to check grasses and has been used successfully in hill-country pastures. Clovers are unaffected by the spraying and provide a high-quality feed source for lambs. Chemical topping costs $30-$40/ha and needs to be timed with seed head emergence (usually during October/November).
The only difficulty with chemical topping is the suggestion that it is encouraging glyphosate resistance in grasses.
Summary: The goal over late spring is to keep the pastures in the optimum growing conditions so as to provide a high-quality feed to maximise stock performance.
The plan you adopt will likely be a combination of the factors outlined earlier. Ensuring you have a plan for the coming months will guarantee that you will keep the farm pasture cover under control.
Brendan Brier, Brier Ag Consultancy Ltd, 0800 4 BRIER
