Easy, low-cost solutions make a difference

An AgResearch study in South Otago has indicated that simple and low cost management techniques can significantly reduce overland flow and contaminant losses from grazed winter forage crop paddocks.

With the growth of dairy farming in Otago and Southland, there has been a corresponding increase in environmental concerns, particularly regarding losses of nutrients, faecal microbes and sediment to waterways.

​Winter forage grazing paddocks are believed to contribute a disproportionately large part of annual farm nutrient and sediment losses as a result of intensive stock grazing on soils with high moisture content.

A paired catchment study, which is part of the Pastoral 21* programme, was led by AgResearch Invermay-based scientists Ross Monaghan and Seth Laurenson and Research Associate Tom Orchiston.

The study was established at Telford Dairy Farm, just outside Balclutha. It has been investigating the effect of grazing strategy on overland flow and water quality when paddock soil type, topography, drainage and stock management were taken into account.

It was thought that strategic grazing of cows in a winter forage crop paddock could reduce overland flow and thus sediment and nutrient losses.

In the test two different types of management were used. There was a control group, with cows starting at the bottom of the hill and then strip grazing up the hill. There was no back-fencing and the gully was unfenced and unprotected.

In the treatment catchment the cows entered at the top of the paddock, then strip grazed in a downward direction. There was protection of the gully, back-fencing every four to five days, and finally restricted grazing of the area surrounding the stream if conditions were suitable, effectively offering the ‘last bite’ of winter when conditions allowed.

Ross Monaghan says the trial has shown that strategic grazing of dairy winter forage paddocks can considerably reduce volumes of overland flow.

“By reducing overland flow, the yields of sediment and nutrients carried in the flow were also reduced considerably,” he says.

“The strategic grazing method was a combination of protecting the critical source area (CSA) from stock by fencing, and grazing the least risky areas first and grazing towards the higher risk areas. This effectively left the most vulnerable areas with minimal soil damage for as long as possible throughout the winter season.

“Protection of the CSA, gullies and areas prone to soil saturation is a key part to reducing overland flow and sediment loss. Grazing the CSA can still occur, but only when soil conditions allow. These grazing managements are relatively simple to implement and low cost.”

In 2013 the managements of each catchment were swapped to see if the differences between the control and treatment grazing strategies continued.  Results confirmed findings from 2012 and demonstrated even greater benefits from implementing the strategic grazing practices. Averaged over the two treatment years, strategic grazing and careful management of the CSAs reduced losses of sediment and phosphorus (P) by 80-90%.

*Pastoral 21 is a collaborative venture between DairyNZ, Fonterra, Dairy Companies Association of New Zealand, Beef + Lamb NZ and the Ministry of Business, Innovation and Employment. Its goal is to provide accessible systems-level solutions for profitably increasing pastoral production while reducing farms’ environmental footprint.