Information collected includes daily grazing and supplementary feed records, application levels of effluent, fertiliser and irrigation and stock and feed movements. This will help determine the effects of management on crop and pasture yield and quality, the farm's nutrient budget, and profit.
Dairy pastures frequently contain a higher concentration of N than dairy cows require, and most of the excess is excreted in urine. Urinary N is concentrated in a small area and is more than plants can use, so much of it is prone to leaching into the ground water. Some enters waterways, posing an environmental threat. The FRNL scientists are looking at ways to develop pasture and cropping systems that are more efficient at reducing N in urine and at capturing N from the soil.
Three scientists; John de Ruiter and Edmar Teixera at Plant & Food Research, and Garry Waghorn at DairyNZ, are working on different but inter-linked areas of crop research for the FRNL programme.
Low nitrogen feed and forages
At Plant & Food Research, John de Ruiter is analysing data on a wide range of feeds to identify relationships between forage type, nutritive value and crop management. The aim is to find low N forages and conserved feeds with high fibre or high total carbohydrate content that may lower urinary N excretion when fed. So far, more than 3000 entries have been analysed.
He is checking what's out there in terms of different crops, their chemical composition, how they metabolise and what adjustments to quality can be made by using specific crop management practices on-farm. These include variables like cultivar choice, time of sowing, fertiliser and irrigation effects, and how all of these might affect the composition of the plant. He is fine-tuning the database to pick trends among forage types and identify regional differences.
Field trials in Waikato with rape, fodder beet, maize, chicory and oats have looked at different N and Potassium (K) application rates and different sowing rates to see how quality varies. Similar plot trials in Canterbury compared fodder beet and kale with maize and cereals. When crops were managed for high yield, there was surprisingly little variation in the quality. When conditions are suboptimal for plant growth, the effects on quality were more pronounced.
New Zealand is unique in terms of wintering cows on crops, unlike many other parts of the world where animals are often fed inside and where there is opportunity to collect effluent.
"High yielding crops are more cost effective. But the higher the yield, the higher the stocking density and the higher the amount of N return per unit area in the paddock. Reducing the yield target is one option to reduce N loading, but a more sensible option might be to manage or select feeds that achieve lower urinary N concentrations. We could adopt cut and carry systems or feed crops for shorter periods and then move stock to standoff areas. I think a mix of these approaches may be required for best economic use of standing feed and with lower environmental impacts," says John.
Nitrogen-absorbing crops
Plant & Food researcher Edmar Teixera is running a series of computer simulated experiments to test the impacts of different management practices -- in this case sowing dates -- on N leaching.
Latest research shows that although the effect of winter cover crops such as Italian ryegrass or oats are often positive, the magnitude of leaching reduction varies from one year to another. To understand the causes the Plant & Food Research team is modelling various scenarios.
"With the model, it is possible to simulate the effect of different management options (e.g. contrasting cover crop sowing dates) and soil types across multiple years," says Edmar.
First published in Inside Dairy
