These are the findings of research conducted under the Pastoral 21 Next Generation Dairy Systems programme that aims to provide profitable and proven systems that will lift productivity and reduce nutrient loss.
The programme is managed by AgResearch and is a collaborative venture between DairyNZ, Fonterra, Dairy Companies Association of NZ, Beef + Lamb NZ, and the Ministry of Business, Innovation and Employment.
The research involved scientists from multiple partner organisations with different expertise in plants, soils, animals, and farm systems to identify the best options to help farmers.
Professor Keith Cameron from Lincoln University says this type of research approach is worth its weight in gold because it provides robust science.
In Canterbury, Otago and Southland winter crops – such as swedes, kale and fodder beet – contribute a large proportion of the total nitrogen leached from a dairy farm system. New strategies are needed to ensure farm systems meet the nutrient loss limits that might be implemented by regional councils. These restrictions could reduce crop yields or decrease the number of cows that could be grazed on crop area, which in turn might result in reduced availability of dairy support land and increased wintering costs.
DairyNZ senior scientist Dr Dawn Dalley said the impact of nutrient limits for many regions was still unknown. However in Canterbury some reductions were already in place and Environment Southland would release its proposals in June.
“Farmers are looking at options throughout their farm system to reduce nutrient loss, so if we can find ways to significantly reduce nutrient loss from their wintering system it will give them more flexibility in how they manage the rest of their land area,” Dalley said.
The Pastoral 21 research in Canterbury showed how nitrogen leaching could be reduced in late winter and spring while increasing annual drymatter grown on a winter block through the use of sequence cropping. The research trials compared a kale-only crop with a kale-oats ‘sequence crop’ over a three-year period on the same block of land. Under the sequence cropping regime the kale was sown in early December and grazed off the following winter. The paddock was then lightly cultivated in late August and sown in oats by mid-September. The oats grew over an 80-day period and were baled in late November. The paddock was then sown back into kale by mid-December and the oat balage fed on to the kale crop the following winter.
“Oats were chosen for the catchcrop because they will germinate at soil temperatures of 5-6C which is lower than alternatives,” Peter Carey, a PhD student and part of the Lincoln research team, said.
“Oats have the ability to grow root mass during the cold winter months that quickly develop through the soil profile, so when temperatures start increasing the oats start to take up both the nitrate that is in the soil from the winter grazing and also the water, therefore reducing the leaching loss,” Cameron added.
The sequence cropping system used in the research is outlined in Figure 1. When land lies fallow for three-four months before the next crop is sown there are no plants to take up the nitrogen until late October at the earliest, by which point much of the urinary nitrogen can be leached into drainage water. The principle behind sowing oats as soon as possible after the winter crop is eaten is to catch or mop up some of the excess nitrogen before it is leached below the root zone and lost from the system – hence the term catchcrop.
Research was done over a three-year period on irrigated Balmoral-Lismore stony silt loam soils. Nitrogen loss was measured using lysimeters which are essentially columns of soil that are contained inside a drum sealed on the bottom and sides so drainage water can be collected for analysis.
“We cut down kale on top of the lysimeters (to simulate grazing), collected urine from cows grazing on the kale and applied it at the same rate to each lysimeter, then sowed the oats on different dates,” Cameron said.
Drainage water collected from the lysimeters was analysed for nitrogen content.
The key to a successful sequence cropping programme is to maximise yield and utilisation of the kale crop. The kale crop should be sown from mid-November to early December and once sown would require regular rainfall or irrigation so was only suitable for a summer-safe area or where irrigation was available.
“The risks of not achieving a reasonable kale yield are too high in dryland Canterbury,” Dawn says.
Nitrogen should be applied in two applications of 100kg/ha in the early growth stage to achieve good crop yields. To achieve the optimum sowing timeframes for each crop the paddock selected for sequence cropping should have free-draining soils that are suitable for early cultivation in August-early September.
Oats are a lower priority crop than kale and higher yields from oats should not come at the expense of kale yield. Therefore oats should be sown before September 15 to allow sufficient time from sowing to harvest before the next kale crop needs to be planted between mid-November-early December.
Kale crops should be well-utilised to reduce crop residue, improving conditions for cultivating a good seedbed for the oats.
The sequence cropping research would continue in other regions with different soil types.
“We would like to take these principles and put them into other more challenging environments where maybe soil temperature takes longer to start increasing and on heavier soils that take longer to dry out,” Dalley said.
Different methods of sowing the oats in late winter, such as ‘hoof and tooth’ and aerial sowing, would also be investigated.
“Trying to find practical ways of getting the oats sown into cold, wet soil is part of the challenge,” Carey said.
The sequence cropping research was presented to farmers at a series of DairyNZ workshops throughout Canterbury, Central Otago and Northern Southland and generated a great deal of interest from farmers.
“We have identified a very practical option to help farmers reduce nitrate leaching and there has been a lot of interest in how it can be incorporated into their farm systems,” Cameron said.
For more information on sequence cropping: www.dairynz.co.nz/about-us/research/key-projects/pastoral-21/
