Capturing the benefits of catch crops

// Forage Cropping

With the right timing and a bit of patience, catch crops can reward growers with high yielding supplementary feed crops which can generate gross margins of over $1,000/ha.

cattle grazing

Sown in the wake of intensively grazed winter forage crops, catch crops such as oats and Italian or hybrid ryegrasses capture and utilise the nitrogen (N) left in soil from urine patches and turns it into drymatter.

The four-year ‘Catch Crops for Cleaner Freshwater’ programme, which has been run by Plant & Food Research soil scientist Dr Brendon Malcolm in conjunction with AgResearch, is part of the Ministry for Primary Industries Sustainable Land Management and Climate Change – Freshwater Mitigation programme.

Now in its final year, Catch Crops for Cleaner Freshwater has identified and demonstrated best-practice management of catch crops through trials sites established on commercial farms in Southland, Canterbury and the West Coast.

Trial work in Canterbury has shown catch crops can effectively reduce N leaching by up to 60%, but they can also reduce the potential for soil and phosphate losses.

The key to successful catch crops is timing and Dr Malcolm says these crops should be sown as soon as practicable after the paddock has been grazed.

Cereals such as oats can germinate in soil temperatures as low as two-degrees, but Dr Malcolm says they recommend sowing when soil temperatures are four to five degrees, particularly if soils are heavy or very wet.

In their experience, soil temperatures very rarely drop below this for a significant period of time.

In Southland, one-pass Spader drills are ideal for drilling in heavier and wetter soils, but in other regions, drilling should take place as soon as the tractor can get on the paddock.

Higher than normal sowing rates of 110-120kg/ha are recommended to achieve target plant populations of 300 plants per square metre. The greater the plant density, the more light is intercepted and the higher the crop yield and N uptake. In very wet soils, Dr Malcolm says Italian or hybrid ryegrasses should be included with cereals.

While the seeds will germinate, establish roots and capture N at these low temperatures, the seedlings may take four to five weeks to emerge when sown in winter, and this is where the patience comes in.

“If you are patient enough to wait until the crop gets to the green-chop stage then the returns are good.”

In a Canterbury trial, a catch crop of oats sown after a kale yielded 10t DM/ha and at a value of 20c/kgDM, this generated a gross margin of over $1,500/ha.

While sowing as early as July is not always practical, Dr Malcolm says sowing in August and into early September can still significantly reduce N leaching.

“Treat the catch crop as a main crop, even when sown late, it will still pay.”

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