Small paddocks key to dual-purpose crops

With good management, the period of grazing can increase net crop returns by up to $600 per hectare and have a range of system benefits including widening sowing windows, reducing crop height, filling critical feed gaps and spelling pastures.

The indicative stock density used to achieve the above profit was about 2000 dry sheep equivalent (DSE) grazing days per hectare, for example, 40dse/ha for 50 days of grazing.

David Harbison, director of DR Agriculture which specialises in crop and pasture research, said over the past 20 to 30 years cropping machinery has been getting bigger and more efficient and as a consequence many paddocks were now too large to graze efficiently.

"Achieving grazing return relies heavily on good management, with time of sowing, stock number, grazing management, crop growth (both pre-grazing and recovery), water supply and other factors all critical to a successful outcome," Mr Harbison said.

"Water points are often minimal and of lesser quality and quantity, or the number of stock required to provide efficient grazing can be very large - creating its own sub-set of management issues."

While there is no ideal paddock size, or available grazing area, Mr Harbison's experience was that smaller paddocks/areas (under 40 to 50ha) are likely to be far easier to manage and have more manageable water points than much larger paddocks.

"Getting the most from the grazing dry matter (DM) requires eating more of what is on offer, over a shorter period of time and leaving a critical residual biomass to allow significant crop regrowth before the second (and potentially third) grazing," Mr Harbison said.

"Understanding crop growth rates and what drives them, from planting to first graze (autumn) and into winter, enables farmers and advisers to predict likely stock numbers and DM production."

Stock number and predicted consumption determines how long a set amount of DM will last and in general a larger paddock will proportionally increase the stock number needed to optimise grazing efficiency.

Water is also a significant limitation to larger paddocks as it's usually the most difficult infrastructure to accommodate in the dual purpose crop system.

Many issues surround good stock water supply, including distance to, temperature and cleanliness of water, dam versus trough and other factors, which all impact on animal intake and performance.

Mr Harbison said the Department of Primary Industries and Regional Development publication 'Water quality for livestock', guides farmers in the water needs of livestock.

"Stock avoid warm water, so deeper or shaded water sources will generally be preferred, while pipes carrying water above ground to moveable troughs may deliver hot and undrinkable water, pending time of the year and location," he said.

"While trough systems have many benefits, if the mob size is too large or inflow rates too low, stock will walk off with less and sometimes nil, water intake.

"Allowing at least one metre of trough per 130 sheep is their advice."

Dams are still very valuable and often the only option for many, but stock will always decrease the quality of dam water, often by urine and faeces contamination and most commonly just by mud and foot disturbance.

Mr Harbison said if the water quality was poor, livestock may drink less than they need, or rarely, may stop drinking altogether.

"Lower water intake decreases DM intake, thus resulting in decreased animal performance," he said.

"Many experiments have demonstrated the benefits of cleaner trough water over dam water, but it is not available to all."

Understanding plant growth, time to first graze and regrowth rates is the most effective way of predicting how much stock and of what class, will be required during the season.

Mr Harbison said DM utilisation was the amount of DM consumed by the animal as a percentage of total on offer.

"For cereals, I estimate 60 to 70pc utilisation pending row spacing and I am aware of data showing higher utilisation rates in canola," he said.

"The caution here is not to over-estimate potential DM on offer, as running out of crop DM is far worse than having more left in the paddock than first planned.

"It takes experience - and lots of it - as no two seasons are the same and growth rates can change rapidly in response to dry spells, frosts and nutrient deficiencies to list a few."

The second variable to consider before stocking is how much residual DM to aim for to enable speedy recovery/regrowth.

Mr Harbison said the best regrowth occurred when there was 1000 to 1400 kilograms DM remaining, typically 10 to 12 centimetres high in cereals.

"Eating below this range restricts regrowth rates for a period, thus decreasing overall DM available for consumption during the season," he said.

"Not leaving enough residual biomass after the last grazing is very damaging in terms of grain recovery".

Overall, paddock size, or available grazing area, is key to maximise grazing efficiency, while water sources must be of good quality and well located within each paddock.

Also, identifying the class of stock and their indicative weight and consumption needs before sowing is necessary to determine the likely area of grazing crop needed.