The current EEE farmlet trial on the Stratford Demonstration farm aims to determine the economics, efficiency of feed use and environmental effects of two widely different dairy farm systems.
While the economics and efficiency of feed use are relatively easy to determine once the actual physical results are obtained, the environmental effects are very difficult to measure.
For this we have used the Overseer nutrient budget computer model for calculations and estimates of environmental effects based on the physical data on inputs and outputs and management used. Current results of this evaluation are showing that the high-stocked, high-feed input system, as run on the farm, has generally higher environmental effects on a per-hectare basis, but lower or no worse effects on a per kg/milk solids basis compared to the low-input, no brought-in feed system.
The Stratford Demonstration farm is currently run as two farmlets. One is a low-stocked, self-contained system on all grass feeding, with no brought-in supplements except what replacement stock are grazed off. This is system one under the DairyNZ classification system.
The aim is to be lower stocked at 2.8 Jersey cows per hectare to make use of modern genetics and good feeding to achieve high production with a very profitable system and low environmental effects per hectare.
The other farmlet is a high-stocked, high-input system at 4.1 Jersey cows per hectare with high levels of brought-in feed. The aim is to use most of the pasture grown by milking cows, buy in feed to achieve high per cow production and very high per hectare production, along with a high profit, while minimising environmental effects especially on a per kg/milk solids basis.
This is classified as system four under the DairyNZ system.
For this season the high-input herd has had high use of a covered feed pad and winter stand-off pad with a wood chip floor for absorbing effluent.
This is then spread over the farmlet later in the season when leaching is not a problem. The farm has a standard two-pond effluent system for milking shed effluent.
On this basis the model calculates and estimates that, on a per hectare basis, the much higher producing high-stocked, high-input system has similar nitrogen-leaching losses and soil water nitrogen concentrations, 21 per cent higher phosphorus losses to waterways, a higher nitrogen conversion efficiency and much higher green house gas emissions as the low-input system.
However, on a per kg/milk solids basis, the greenhouse gas emissions are similar but nutrient losses much lower. The high-input system could improve more if the fertiliser value of brought-in feeds could be better utilised.
Calculated nitrogen losses to water on both farmlets were 64kg of nitrogen per hectare per year on the milking area. This is very high compared to national averages and to targets of 25 kg N/ha/yr or less in some regions.
This is partly due to the high production off the farm, but mainly due to the high Stratford rainfall. Estimated soil water nitrogen concentrations of 4ppm are low due to the dilution from lots of rain. The high-stocked high-input system is able to match the low-input system due to the intensive use of the covered wintering pad.
A similar effect could be obtained by a high level of winter grazing off, but this would just be transferring the problem to another area.
Calculated phosphorus losses to water were 1.5kg P/ha/year from the low-input system and 1.9kg P/ha/year from the high-input system.
A high proportion of the losses are from the effluent pond systems, so more milkers theoretically equals more losses.
Calculated green house gas emissions were 10.3kg per kg/milk solids for both systems.
The high-input system produced less methane due to the use of PKE and maize silage feeding, but had higher nitrous oxide production with the stand-off pad use. On a per hectare basis, the high-input system has nearly 50 per cent higher emissions due to 50 per cent higher milk production per hectare.
Interestingly the calculated green house gas emissions from the low stocked high per cow production system were no different than the calculated levels for the farm's traditional moderate stocked moderate per cow production system as both produced a similar total milk production.
The environmental effects of the two farmlet systems will continue to be evaluated and will change over time as we continue to try to minimise environmental effects for each system where practical and affordable.
Graeme is farm management consultant to the Stratford Demonstration Farm.