ISHS Acta Horticulturae 563: International Conference on Environmental Problems Associated with Nitrogen Fertilisation of Field Grown Vegetable Crops
15N FERTILIZER USE EFFICIENCY BY SPINACH GROWN UNDER PORTUGUESE FIELD CONDITIONS |
| Authors: | C. Carranca, A. Soares da Silva, M. Fernandes, J. Varela |
| Keywords: | Blades, cultivars, Ndff, nitrate, N rates, 15N recovery, petioles, roots |
| Abstract:
Maximum nitrate (NO3-) levels in spinach leaves as proposed by the EU (1993) are 2500 mg kg-1 in fresh product for direct consumption, and 2000 mg kg-1 in fresh product for processing. In Switzerland, the maximum NO3- level allowed in vegetables is 3500 mg kg-1 in fresh product. Although not proven, it seems that excess NO3- in the leaves may cause methemoglobinaemia, particularly in pregnancy and babies. The main objective of this study was to evaluate the N fertilizer use efficiency by two cultivars of Spinacea oleracea L. A split-plot randomized block experiment with four N levels (30, 60, 90 and 120 kg N ha-1) and four replicates was carried out in 1995 on an anthropogenic soil in west Portugal. Microplots (1.2 m2) were fertilized with 30 kg N ha-1 of 15NH415NO3 with 4.8 atom % 15N excess, as basal dressing. The remaining N was applied as topdressing, thirty days after sowing, in the form of 15NH415NO3 with 4.8 atom % 15N excess. N treatment did not significantly affect yields and N uptake by the plants, except for total N in the petioles, which accumulated four times as much as in the blades, and exported N in the roots. Nitrate content was lower than the EU (1993) recommended level for spinach. Percent N in the blades derived from the fertilizer was significantly affected by the treatment, with higher values for 90 and 120 kg N ha-1. Most N in the crop (82.5%) came from the soil and irrigation water. Recovered 15N in the crop did not vary significantly with the treatment and indicates very low fertilizer N use efficiency (17.5%). Cultivars differed significantly in yields and exported N, with ‘Space’ (F1) giving a significantly higher yield (29 t ha-1), but 15N recovery in the crops did not vary significantly between cultivars. | |
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