Field-grown spinach production – fertilization strategies to reduce risk of nitrate leaching

Spinach for the frozen food industry in Northwestern Germany is preferably cultivated in sandy soils to enable field management which is largely independent of weather conditions.
However, on these sites, nitrate (NO₃^–) can easily be leached and thus contaminate the groundwater.
Furthermore, short cultivation cycles (5-10 weeks) and high nitrogen (N) demand (up to 205 kg N ha^‑1 in the 0-30 cm soil layer) result in a high risk for NO₃^– leaching in spinach cultivation.
In 2018-2020 ten fertilization experiments were conducted in Borken, Germany, and spread throughout the year from spring till winter.
Total N dosage was calculated by the software N-Expert (IGZ Großbeeren, Germany) and split into a base and top dressing (standard procedure) or a base dressing and two top dressings.
The second top dressing was applied after reaching the early harvest stage.
In a third treatment the total N fertilization rate was reduced by omitting the second top dressing (50-70 kg N ha^‑1). Overall, the fresh matter yield was reduced by splitting the N dosage into three applications and even more by reducing the total N dosage.
Under reduced N supply, the foliage turned yellowish at the late harvest date.
However, this phenomenon was only observed in spring.
Total N dosage complied with the German Fertilizer Ordinance (2020). However, when spinach is harvested within an earlier stage, total N dosage can be above the calculated legal limit.
In this case the second top dressing must be omitted to meet legislation and lower the soil mineral N (N_min) residue.
As well as reduced N_min residue in an early harvest, risk of NO₃^– leaching was reduced by splitting of the total N dosage into three applications due to flatter NO₃^– peaks after fertilization.
However, nutrient availability must be ensured by precipitation or irrigation immediately after the second top dressing.

IV International Symposium on Horticulture in Europe – SHE2021

C. Frerichs, D. Daum

spinach (Spinacia oleracea L.), nitrogen fertilization, sandy soil, nitrate leaching, German Fertilizer Ordinance

https://doi.org/10.17660/ActaHortic.2021.1327.20