New Zealand : how much nitrogen does asparagus need?
Experts say nitrogen fertiliser should be applied in the establishing years for asparagus, but thereafter, only the nitrogen removed during harvest needs to be replaced. Anecdotally, asparagus has been considered a low nitrogen crop, but grower practices in New Zealand don’t always reflect this. For example, a 2019 survey of grower practice in Waikato suggested an extremely wide range of application rates with typical applications exceeding crop exports.
Lack of nitrates guidelines specific to NZ asparagus crops
A few years ago, LandWISE, an organisation promoting sustainable land management, worked with vegetable growers in Levin amid concerns they were losing nitrogen to Lake Horowhenua. It developed a simple nutrient budget template that suits most crops. But when LandWISE manager Dan Bloomer heard asparagus growers were also keen to use it, he realised no reliable data or guidelines were available for their green asparagus. Thus, after talks with the NZ Asparagus vest needs to be replaced. Anecdotally, asparagus has been considered a low nitrogen crop, but grower practices in New Zealand don’t always reflect this. For example, a 2019 survey of grower practice in Waikato suggested an extremely wide range of application rates with typical applications exceeding crop exports.
Lack of nitrates guidelines specific to NZ asparagus crops
A few years ago, LandWISE, an organisation promo-ting sustainable land management, worked with vegetable growers in Levin amid concerns they were losing nitrogen to Lake Horowhenua. It developed a simple nutrient budget template that suits most crops. But when LandWISE manager Dan Bloomer heard asparagus growers were also keen to use it, he realised no reliable data or guidelines were available for their green asparagus. Thus, after talks with the NZ Asparagus Council, and funding via the Rural Professionals Fund from NZ’s Our Land and Water National Science Challenge, a nitrate management trial started.
Some farmers replace a lot more nitrogen than is removed at harvest
Unfortunately grower input was limited by a Covid-19 lockdown and brutal season in 2021, but despite the difficulties, some insights were gained. So far, a wide range of nitrogen management practices have been identified, indicating no agreed industry best practice. Bloomer said grower comments varied from, “I don’t put any nitrogen on my asparagus, I save it up and put it on my broccoli”, through to putting it on “because Dad did”. “So there isn’t an industry standard practice,” he said. Some farmers were found to be applying nitrogen at rates much higher than were likely being exported in the harvested crop. The researchers estimated that the amount of NO3-N exported in the harvested crop is about 12–13 kg NO3-N/ha while rates of 24, 55 and 69 kg NO3-N/ha were used by those growers in the trial who reported applying nitrogen fertilisers.
Sources :
Project report: Collaborative Research Towards Best Practice Nitrogen Management in Asparagus Cropping: Final report.
