Assessment of nitrogen diagnosis methods in sunflower

Abstract

Nitrogen deficiency can severely limit sunflower (Helianthus annuus L.) grain yield and quality. Our objective was to evaluate N diagnosis methods based on: (a) preplant soil nitrate-nitrogen (NO 3 --N) test (PPSNT) and soil N mineralized in shortterm anaerobic incubation (Nan), (b) Greenness index (G I ) and the normalized difference vegetation index (NDVI) measured at 6 (V 6 ) and 12 (V 12 ) leaves, and (c) grain nitrogen concentration (N c ). Seventeen experiments were carried out between 2010 and 2019 in Argentina, evaluating nine N rates (0, 30, 40, 60, 80, 90, 120, 150, and 160 kg N ha -1 ). The G I , NDVI, N sufficiency index and relative normalized difference vegetation index (NDVIr) were determined at V 6 and V 12 growth stages. On average, yield response to N was 492 kg ha -1 and N c response was 0.25% in 9 and 11 responsive experiments, respectively. The inclusion of Nan improved the PPSNT diagnosis method. The critical N availability (PPSNT + fertilizer N) threshold was 115 kg N ha -1 for experiments with low Nan (<60 mg kg -1 ), and 90 kg N ha -1 for experiments with high Nan (>60 mg kg -1 ). The NDVIr at V 12 allowed monitoring the crop N status with a 0.95 critical threshold. The N c adequately diagnosed N deficiencies and the critical threshold was 2.26%. Also, N c was predicted from the ratio between N availability and grain yield (R 2 = .39). Our results would allow to better estimate N availability to recommend adequate N fertilizer rates for sunflower aiming to optimize grain yield and quality, and minimize the economic and environmental cost of fertilization.

Does nitrogen fertilization rate, timing, and splitting affect sunflower yield and grain quality?

“…Hernandez et al, 2021). As an example, Nan values in our study (∼60 mg kg −1 ) were greater than those observed byDiovisalvi et al (2018) (∼50 mg kg −1 ).…”

“…Along this line, at similar edaphoclimatic conditions, Tovar Hernandez et al. (2021) observed that the initial N availability (N–NO 3 − ) and N mineralization throughout the growing season were the variables that defined sunflower grain response to N. The observed yield response was lower than that reported by other authors (540–1400 kg ha −1 ) (Diovisalvi et al., 2018; Schultz et al., 2018; Wajid et al., 2012), which can be attributed to differences in the soil potentially mineralizable N between studies (Tovar Hernandez et al., 2021). As an example, Nan values in our study (∼60 mg kg −1 ) were greater than those observed by Diovisalvi et al.…”

“…Considering that WA was sufficient for the optimum development of the crop, the lack of response to N fertilization at some experiments could be mainly attributed to (i) a high initial N availability and mineralization potential (Table 1) and (ii) the yield potential at each environment (maximum attainable yield) which could be low enough to generate a limited N demand. Along this line, at similar edaphoclimatic conditions, Tovar Hernandez et al (2021) observed that the initial N availability (N-NO 3 − ) and N mineralization throughout the growing season were the variables that defined sunflower grain response to N. The observed yield response was lower than that reported by other authors (540-1400 kg ha −1 ) (Diovisalvi et al, 2018;Schultz et al, 2018;Wajid et al, 2012), which can be attributed to differences in the soil potentially mineralizable N between studies (Tovar…”