In order to avoid excessive nitrogen (N) fertilisation, it is advisable to monitor the N supply of the plant during the growing season. This work evaluates the results of the plant SAP nitrate test and the relative chlorophyll content (SPAD value) measurements for the characterisation of N supply provided to spring oat.

A small-plot field experiment was set up with Lota spring oat (Avena sativa L.) on calcareous chernozem soil in the Exhibition Garden of University of Debrecen. Ammonium nitrate was applied in the following rates: 0, 30, 60 and 90 kg ha-1 N in three replicates.

During the growing season, measurements were performed at tilling (BBCH 31) and boot stages (BBCH 45). Nitrate SAP tests were carried out on an average sample of 10 plants per plot. Measurements of relative chlorophyll content were performed on five plants per plot. The average of five measurements was taken per leaf. At harvest, grain yield, thousand-grain weight, oat height were measured and yield index was determined.

Based on ours results it was found that 60 kg ha-1 N treatment was proved to be optimal with a yield of 3.54 t ha-1.

At tilling, nitrate SAP values for the whole plant increased as a result of N treatments (580, 887, 1040, 3033 mg nitrate dm-3). The relative standard deviation of the measurements was 17% in most cases. At the boot stage, SAP nitrate values measured on the leaves and from the lower part of the stem increased due to the applied N doses, but in some cases a very high relative variance (30–40%) was observed after the same N treatment.

SPAD values increased significantly at tilling and at boot stages with increasing N doses: at tilling 41.3; 45.5; 48.9; 58.5, at boot stage: 47.8, 52.4; 53.5; 58.5 were measured with increasing of nitrogen doses, and the maximum relative standard deviation values related to the replicates was 11.6%.

Based on the obtained data, it was found that the SAP nitrate data measured at tilling and SPAD data measured at the tilling and boot stages are suitable for determining the critical values for adequate N supply. The critical value for SAP nitrate related to proper N supply is 650 ppm (mg nitrate dm-3) at tilling, the SPAD critical values were 43 at tilling and 48 at boot stage.

Keywords: SAP nitrate, SPAD, relative chlorophyll, oat