Articles
STRATEGIES FOR DETERMINING OPTIMUM NITROGEN SUPPLY TO ONIONS
Article number
571_21
Pages
181 – 185
Language
English
Abstract
Onions (Allium cepa L.) are mainly grown in Sweden on light soils with a high risk of nitrogen leaching.
This may, especially after heavy rains, result in large losses and yields will consequently decrease if extra nitrogen is not supplied.
With the aim of avoiding low yields, many growers apply more nitrogen than recommended.
This may lead to negative environmental effects and decreased product storage ability.
One strategy to minimise the nitrogen supply to onion crops, fertilised with inorganic nitrogen, has been to split the nitrogen applications and to adapt the amounts to the content of mineralised nitrogen in the soil (Nmin). Target values for Nmin demand under Swedish conditions have been established experimentally for yields of at least 60 tons per hectare.
Target values for five dates during the season are available, but growers do not accept the requirement for so many soil analyses.
During most years, the main nitrogen supply is given before sowing and in the middle of June.
We therefore recommend growers to make soil analyses on these two dates and to supply nitrogen according to the appropriate target values.
If the weather conditions indicate a large risk for leaching, growers may make additional analyses and give an extra nitrogen dose according to the target values.
This will only rarely be necessary, but may be decisive for the yield in these cases.
According to experimental data, this fertilisation strategy ensures a high yield even in rainy years and in years with low mineralisation.
During years with normal weather conditions, the strategy results in a lower level of nitrogen fertilisation.
This may, especially after heavy rains, result in large losses and yields will consequently decrease if extra nitrogen is not supplied.
With the aim of avoiding low yields, many growers apply more nitrogen than recommended.
This may lead to negative environmental effects and decreased product storage ability.
One strategy to minimise the nitrogen supply to onion crops, fertilised with inorganic nitrogen, has been to split the nitrogen applications and to adapt the amounts to the content of mineralised nitrogen in the soil (Nmin). Target values for Nmin demand under Swedish conditions have been established experimentally for yields of at least 60 tons per hectare.
Target values for five dates during the season are available, but growers do not accept the requirement for so many soil analyses.
During most years, the main nitrogen supply is given before sowing and in the middle of June.
We therefore recommend growers to make soil analyses on these two dates and to supply nitrogen according to the appropriate target values.
If the weather conditions indicate a large risk for leaching, growers may make additional analyses and give an extra nitrogen dose according to the target values.
This will only rarely be necessary, but may be decisive for the yield in these cases.
According to experimental data, this fertilisation strategy ensures a high yield even in rainy years and in years with low mineralisation.
During years with normal weather conditions, the strategy results in a lower level of nitrogen fertilisation.
Authors
U. Gertsson, I. Björklund
Keywords
Allium cepa, mineralisation, split application, yield
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