SYSTEMS FODDER BEET SCIENCE
Fodder beet pulling nitrogen out of the soil A study by Lincoln University Bachelor of Agricultural Science honours graduate Alexander Koops has found that fodder beet roots will soak up nitrogen. Anne Lee reports.
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Lincoln University study is pointing towards a surprising catch crop for fodder beet – itself. The study found that following even a high yielding, intensively grazed crop with another crop sown without nitrogen inputs will result in a lower yielding crop that can be lifted but importantly will take up all of the nitrogen deposited in winter plus some. It’s raising more questions over the validity of a cut-off date for sowing a catch crop after winter grazing and again prompts the query – is the nitrogen that moves below 60cm really lost? Bachelor of Agricultural Science honours graduate Alexander Koops carried out his study last year under the supervision of Lincoln University’s Dr Jim Gibbs, before travelling to Germany to undertake a Masters in Dairy Science at ChristianAlbrechts-Universität zu Kiel (CAU of Kiel), while working also on a top German dairy farm called “Milchhof Rodenwalde KG”. The research project systematically worked through some of the key characteristics of what makes a good catch crop, checking off how fodder beet stacks up. He then used robust modelling to determine what a double cropping system could achieve. Firstly, he looked at what was going on in the early growth phase of both fodder beet and oats – given oats is already used as a proven nitrogen catch crop because of its ability to get established soon after a winter crop and to grow in cooler temperatures. 50
Lincoln University honours student Alexander Koops is in Germany embarking on a masters in dairy science.
Alexander applied two different nitrogen fertiliser application rates (200 or 350kg N/ha) to fodder beet plants to mimic common establishment methods. He then measured the rooting depth of the fodder beet plants as well as the rooting depth of oats, established using standard industry practice. They were all grown under cooler ambient temperatures and the measurements took place at 75-days post sowing, so just 2.5 months into the crops’ growing phase. The oat roots made it down to 1.5m in that time but what may be surprising to many is that the fodder beet did too. Alexander’s findings are in line with similar international results for 50 years that have measured beet tap root depth right down to 3m in some cases. “Fodder beet roots can extend a long way down past the bulb with that taproot structure,” he says. He found the oats and fodder beet sown using 200kg N/ha had similar root mass but when 350kg N/ha had been applied the fodder beet root mass almost doubled. Those roots aren’t just good at quickly
getting to depth - Alexander’s research showed fodder beet roots appear to be hungry foragers for nitrogen. He used a nitrogen isotope – N15 – to monitor the plant’s uptake of nitrogen from three depths – 75cm, 35cm and 0cm. “We only allowed the 75 day old plants a seven-day period in which to pick up the N15 and didn’t look below 75cm in this study but we found the fodder beet took up 60% of the N15 at each depth. “In the normal crop situation the plants have months to pick up nitrogen. So it’s likely it would have taken up much more if the pick-up period was extended,” he says. He then went on to use modelling to find out what was likely to happen to nitrogen and organic matter levels after a large fodder beet crop, grown using 300kg N/ha, was grazed and then followed by one of four different scenarios where the catch crops were grown using no fertiliser
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fodder beet scenarios
The four scenarios that followed winter grazing of a large fodder beet crop were:
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Sow another fodder beet crop as a catch crop and then graze it.
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Sow another fodder beet crop as a catch crop and then harvest it.
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Sow an oats crop as a catch crop and graze it.
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Sow an oats crop as a catch crop and harvest it.
Dairy Exporter | www.nzfarmlife.co.nz | August 2021
