Nitrogen fertilization strategies to reduce the risk of nitrate leaching in open field cultivation of spinach (Spinacia oleracea L.)^#

Abstract

Background Spinach is a nitrogen (N) demanding crop with a weekly N uptake of up to 60 kg ha–1. Consequently, a high N supply is required, which can temporarily lead to high quantities of nitrate (NO3–) being at risk of leaching. Aims The objective of this study was to develop a N fertilization approach to reduce the risk of NO3– leaching in field‐grown spinach production without adversely affecting crop yield and quality at an early and late harvest stage. Methods Ten fertilization trials were conducted to compare different base fertilization rates and splits of top dressings. For top dressings, granulated fertilizers or foliar sprays were used. In a further treatment, N supply was reduced by withholding the second top dressing of 50–70 kg ha−1. Results Nitrate concentration at risk of leaching was considerably reduced by decreasing the base fertilizer rate as well as by splitting the top dressing. However, at an early harvest stage, total aboveground dry mass was reduced by, on average, 6% by these measures across all seasons. In contrast, at a later harvest stage, spinach was less affected by the fertilizer schedule. Urea foliar sprays proved to be insufficient in promoting plant growth and caused leaf necrosis. A reduced N supply led to impaired plant growth and yellowish leaves in both spring and winter. Conclusions Base N fertilization of spinach is only required in spring, but not in other seasons. Despite slight yield reduction, the top dressing should be split to reduce the risk of NO3− leaching after an early harvest.

Crop Residue Management Strategies to Reduce Nitrogen Losses during the Winter Leaching Period after Autumn Spinach Harvest

“…The authors derived a minimum N min residue of 7 kg ha −1 (0-30 cm) at a marketable yield of 25 t ha −1 . However, when spinach is harvested at an earlier stage, this leads to higher N min residues even if total N supply corresponds to plant demand [10].…”

“…Spinach (Spinacia oleracea L.), cultivated for the processing industries, is typically grown in frequent sowings and harvested from April to late October [10]. The crop is typically grown on sandy soils because this facilitates specific field management and reduces the impact of variable weather conditions on yield [4,5,11].…”

“…On the other hand, soil N mineralization is still high in autumn because of relatively high soil temperatures, potentially leading to high soil mineral N (N min ) concentrations at harvest [17]. Therefore, depending on the actual harvest stage, 50-100 kg NO 3 − -N ha −1 (0-30 cm) typically remains in the soil at the harvest of autumn-grown spinach [10,18].…”

Fate of nitrogen and phosphorus from source-separated human urine in a calcareous soil

“…On July 5th, the above-ground biomass was collected and dried for biomass and nutrient content analysis. Spinach was chosen because of its relatively high N requirements (170 kgN.ha − 1 under optimal growth conditions) (Frerichs et al, 2022) and short growing cycle. Irrigation was conducted with sprinklers located above the tanks and controlled with tensiometers placed at 15 cm depth in the soil to maintain soil moisture around eld capacity.…”

Fate of nitrogen and phosphorus from source-separated human urine in a calcareous soil

“…On July 5 th , the above-ground biomass was collected and dried for biomass and nutrient content analysis. Spinach was chosen because of its relatively high N requirements (170 kgN ha −1 under optimal growth conditions) (Frerichs et al 2022) and short growing cycle. Irrigation was conducted with sprinklers located above the tanks and controlled with tensiometers placed at 15-cm depth in the soil to maintain soil moisture around field capacity.…”