Repairing pastures damaged by drought

An unavoidable consequence of drought is damage to many pastures, and the negative affect this has on future production. After a prolonged drought period, most damaged pastures will not recover to their state prior to the drought, because the gaps in pastures at the end of the drought get filled with low-producing weeds (eg. thistles) and grasses (eg. poa annua, browntop), which also have lower feed value. Finances will prevent many farmers repairing all pastures immediately after the drought, so well considered thought and planning is needed to ensure the money that is spent, gives the greatest return.

Where to start?

To make good decisions it is important to have good information. The first step is to assess the state of all your pastures at the end of the drought, and the likelihood of them recovering. Assess the density of the sown grass(es), and whether these plants are large/strong or small/weak. Match the degree of damage with the potential each paddock has to contribute to overall farm production and rank them in order of priority (eg. badly damaged pasture on flats with good soil will have a high priority).

The next step is to work out a plan of attack for the next 1-2 years, including details on which paddocks to start with, what crop or pasture to sow in them and when, and the costs involved. It helps to involve all family and staff when making this plan, to seek advice from a seed retailer with good pasture and crop experience, and in some cases banks will be interested.

What are the options?

Where the grass and clover has thinned drastically, and is not yet replaced by weeds, it is an option to drill grass straight into the paddock to fill these bare gaps without the need for herbicide application (undersowing). This works best for sowing Italian or other short term ryegrasses. Experience in previous droughts however has shown that for sowing a perennial grass there is almost always an advantage to spray the old pasture before drilling (spray-drilling) because this reduces the invasion of weeds in the replacement pasture.

For many pastures, it is not ideal to try to re-establish a perennial pasture immediately. If there has been an increase in hard-to-kill weeds and weed seed during the drought, this can swamp new pastures. Pastures that are likely to have a lot of weed and undesirable grasses should go through a crop or short-term grass phase before being planted in perennial pasture (Table 1). An advantage of these crops is that they usually generate more feed in the short-term than perennial pastures, which is important following a drought because of lower pasture growth and low supplementary feed reserves.

Table 1
Summary of break-crop options when repairing drought-damaged pasture.

What crops can be grown?

There are a number of crop types that can be planted in spring following a drought. With current demand for animal and human feeds, there are several profitable options for cash crops, as well as feed crops utilised on the farm (Table 2). The area of grain crop that can be grown on livestock farms may be limited by on-farm grain storage facilities, or harvesting infrastructure.

Table 2
Summary of spring-planted crop options.

What perennial pastures to plant?

A perennial pasture can be planted successfully after 1-2 crops, either in the spring or autumn, depending on when the final crop is harvested. Most farmers will plant perennial ryegrass and clover pastures. They should make notes on what types of ryegrass and which endophytes have survived best during this drought, as a guide for what will be most sustainable on their farm.

Many farmers will now be aware of the costs of having pastures that do not survive drought, and will be looking for an alternative to ryegrass. Tall fescue is the drought-tolerant grass most similar to ryegrass for growth and quality, and other options include cocksfoot, pasture brome, lucerne, chicory, plantain, and sub-clover.

Hill country

The options are more limited on country that cannot be cultivated or drilled. For farms that have both hill country and arable land, the arable land should be fully repaired first because the costs and failure rates on hills are often higher.

A lower cost option on hills is to just spray for broadleaf weeds (eg. thistles) to prevent their spread and further loss of pasture production. If the area is to be re-established with grasses, this is best done in late-autumn in the North Island and spring in the South Island. Badly damaged pastures that are to be oversown next autumn can be sprayed with glyphosate before November, and again in autumn 5-7 days before oversowing, as this will improve establishment success.

Another alternative is to oversow just clover seed in early-spring (often following a thistle spray), with an aim to get the nitrogen cycle going again and thereby encouraging the regeneration of ryegrass from surviving plants and buried seed. Coated seed is recommended, for its better ballistic qualities, and soil-seed contact this gives.

Grazing management of pastures recovering from drought

Where it is not possible to repair pastures, or for those that are only partially damaged, careful management can enhance their recovery. Surviving plants should have good access to nutrients (N for grass, P, K and S for clovers) and extra fertiliser applications in early-spring may be of benefit to plants and also feed production. Rotational grazing should be practiced because repeated close grazing of plants will restrict their growth and spread. A rotation should be started at the end of the drought to allow most of the plants on the farm time to replace root reserves, which will enhance future re-growth.

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