Pasture Persistence

It is perfectly normal that pastures don’t last forever - or more accurately, their performance declines with time. The underlying reason for this is that when we plant new pastures, we are introducing exotic species into environments where other naturalised plants are better adapted to tolerate insects, climate, soil conditions, drought, low soil fertility or pugging.

We choose these exotic species because, unlike the naturalised plants (eg. weeds), they are palatable, productive, grow well in the crucial seasons of the year, and produce good animal performance.

So we need to accept that if we choose to battle against nature, sometimes nature will win. However, there are things you can do to greatly improve persistence.

There are many specific causes of pasture deterioration. A common cause is a loss of plants associated with wet soils, leading to pugging damage and/or suffocation due to water logging. This is a major problem on some dairy farms, particularly now with high stocking rates and larger herd sizes. Careful grazing management is important, and for areas with prolonged wet periods, feeding pads should be considered.

The next main cause is weed invasion. Grass (eg. browntop, old ryegrass, summer grass) and broadleaf (eg. buttercup, chickweed) weeds can establish from buried seed and spread to dominate pasture. The more weed you have the less the pasture you will grow, and what animals eat is lower in palatability and quality. Weed invasion can be caused simply by poor soil fertility, so soil test and ensure levels are adequate. Another reason for weeds is poor paddock preparation pre-sowing, and this is where crops (e.g. brassicas) can have a great place in ‘cleaning’ ground prior to sowing a new pasture. Finally, weeds can be just a symptom of poor persistence, due to a range of possible problems.

There are many insects that damage ryegrass and clover, resulting in death or poor plant vigour, which then allows weeds to take over from buried seed. Of course, pastures in lower rainfall areas also suffer from droughts, which kill or suppress our preferred plants and allow weeds to dominate.

Grazing management can compound the problems caused by these other stresses. Most often it is not the drought alone that kills pastures, but the combination of dry conditions plus grazing. The plants reserves in grasses are above the ground, in the bottom 2 cm of a pasture. Hard and frequent grazing weakens the plant, its root system and ability to re-grow, so exacerbates pressure from insects or drought. The key to get pastures through the dry, so when rain comes your system recovers as soon as possible, is to reduce pressure on pastures through policies such as destocking early, summer crops and supplements.

Regional differences

The most likely cause of deterioration in pastures varies between regions, and even between farms and paddocks. The further north you go the more insect species you will find, and their populations and damage are more severe. For example, in Northland, insects (eg. black beetle) are a major cause of poor pasture persistence.

In East coast regions, hot and dry summers constantly damage ryegrass and clover pastures, and are often finished off with the combination of insects.

In West coast regions, droughts and insects are less common, and most damage is done with frequent pugging/treading damage while soils are wet, and the subsequent invasion of weeds.

On the Southland plains, ryegrass pastures can persist for decades because of the lack of insect or drought pressure combined with fertile soils and good grazing management.

If you can prevent all of the causes of pasture deterioration, you will have good pasture persistence. Unfortunately, most people farm in environments where this is just not possible, particularly with today’s high stocking rates, so they must accept that pastures don’t last forever.

This leads into the question often posed, “Why is it some of my new pastures only last 3-5 years when paddocks my Dad planted here 30 years ago still look good?”.

It is quite likely that what happened to your pasture was exactly what happened to those your Dad planted. The difference is that your Dad did not re-plant those pastures, and they were quickly filled with grass plants establishing from buried seed in the gaps left by the sown grass.

If you look carefully at a 30 year-old pasture, usually you find few of the original plants sown. So the seed he planted may be no more persistent than what you have used.

Endophytes

There are some exceptions to this, where the blame for poor pasture persistence can be laid on the seed that is used. Prior to the late 1980’s, most ryegrass seed had high levels of standard endophyte, which protected the plant from several insects, but caused ryegrass staggers and other health issues. In the 1990’s, farmers started using seed with no endophyte, and then in the 2000’s using AR1 and other novel endophytes. Plants grown from ryegrass seeds without endophyte are damaged by all insects, and therefore, with the exception of Southland, often have very poor persistence.

AR1 is a great technology for farmers, as pasture is safe for animals and it does not reduce performance, but persistence in some cases has been disappointing (eg. in parts of northern New Zealand with black beetle damage), and some dryland environments (eg. surviving combinations of dry summers and insects). The choice of endophyte can have a greater impact on persistence than the variety of perennial ryegrass you choose.

In this second instance we believe a main factor of this is the much better palatability of AR1 over the old standard endophyte, meaning AR1 pastures are easier to overgraze.

Plant breeders have also responded to farmer’s requests for ryegrasses with better palatability and feed value, as well as production. They have delivered significant improvements for animals. Unfortunately, there is a tendency for these higher quality ryegrasses to be more susceptible to overgrazing, drought, wet soils and insects. Some farmers may have used these in the wrong environments when they should have been using more robust types.

Choosing the correct species is also important for persistence. Perennial ryegrass is not naturally suited to many environments in New Zealand. Other species (eg. tall fescue, cocksfoot) are better able to tolerate drought, insects and wet soils, so are therefore more persistent.

So, farmers who want good persistence from their pastures should prepare the paddock thoroughly (removing weeds and their seed) before planting, ensure soil fertility is adequate, choose species/endophytes/cultivars best suited to their environment, avoid pugging, and minimise as much as possible all the stresses that ryegrass can suffer from – particularly through summer dry periods using destocking and other strategies.

Pastures often revert to old naturalised grasses because those species are better adapted to surviving the environment and management.

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