Measurement of total nitrogen and assimilable nitrogen in grape juice to assess vine nitrogen status

Abstract

<p style="text-align: justify;">Five indicators of vine nitrogen status were compared for their accuracy to differentiate two levels of nitrogen fertilization (0 and 45 kg N / ha) : petiole total nitrogen content, leaf blade color intensity measured by a device called “N-tester”, grape juice total nitrogen content, grape juice assimilable nitrogen content and grape juice ammonium content. Differences in must total nitrogen content and must assimilable nitrogen content were highly significant between fertilization levels. They can be considered as two powerful tools to assess vine nitrogen status. Levels of must total nitrogen content and must assimilable nitrogen content were highly correlated.</p><p style="text-align: justify;">Mineralizing must in order to measure its total nitrogen content is difficult, mainly because of the presence of large amounts of sugar. This operation can take more than 12 hours and it can fail because of caramelization and the appearance of foam. We propose mineralizing must by means of microwave. Complete mineralization was obtained in only one hour. No foam or caramelization was observed on any of the samples mineralized.</p><p style="text-align: justify;">Vine nitrogen uptake is likely to vary to a considerable extend with soil parameters, even if no nitrogen fertilization is applied. Figuring among those parameters are: soil organic matter content, organic matter C/N ratio and soil organic matter turnover. The latter depends mainly on soil temperature, soil aeration, soil pH and soil moisture content. Differences in vine nitrogen status depending on the soil type were clearly evidenced by measuring must total nitrogen and must assimilable nitrogen at ripeness. Limited nitrogen uptake, as a result of particular soil conditions, can limit vine vigor and be a quality enhancing factor in red grape production. This emphasizes the role of moderate environmental stress in the production of high quality potential grapes.</p>

Anthocyanin composition of grapes from three different soil types in cv. Tempranillo A.O.C. Rioja vineyards

“…In 2016, YAN values were higher in TC than in FH samples, but the same in PP samples, while in 2017 they were highest in FH, followed by TC, and lowest in PP samples (Table ). These results were in agreement with the observation that the vine nitrogen status was highly correlated with the ammonia and must nitrogen status and with the soil N‐NO 3 − content …”

“…In 2016, YAN values were higher in TC than in FH samples, but the same in PP samples, while in 2017 they were highest in FH, followed by TC, and lowest in PP samples ( Table 2). These results were in agreement with the observation that the vine nitrogen status was highly correlated with the ammonia and must nitrogen status 59 and with the soil N-NO 3 − content. 50 Only grapes from FH soil in 2017 and TC soil in 2016 presented values of the must nitrogen compounds (YAN, which corresponds mainly to the sum of the ammonium and primary free amino acids) higher than 140 mg N L -1 , which is commonly recommended to ensure that musts avoid stuck/sluggish alcoholic fermentation that can lead to the formation of undesirable haze and/or thiols in the resulting wines, 60 while only the must from PP samples in 2017 yielded values of YAN below 90 mg N L -1 , which indicates that these musts would need supplementation before the start of alcoholic fermentation.…”

Soil type and soil preparation influence vine development and grape composition through its impact on vine water and nitrogen status

“…Each sample was composed of 60 berries taken randomly on 20 adjacent vines. Berries were weighted, pressed, and analyzed for δ 13 C in order to determine vine water status [5] and Yeast Available Nitrogen (YAN) to determine vine nitrogen status [6]. Reducing Sugars, Total Acitidy (TA), Malate (MAL) and pH were assessed through classical methods.…”

“…Vine water status was assessed by means of stem water potential measurements (SWP, three measurements over the season) and δ 13 C. Only the results from the last SWP measurement (9 September 2016), when water deficits were most intense, are presented. Vine nitrogen status was assessed over the whole 7 ha section through N-tester measurements over a grid of 142 locations at two dates, at bloom and at veraison [6]. Only vine nitrogen status at veraison is presented.…”

Rootstock and vineyard floor management influence on ‘Cabernet Sauvignon’ grape yeast assimilable nitrogen (YAN)

“…All samples contained YAN below 90 mg N/l or kg, which indicates that these juices would need supplementation before the start of alcoholic fermentation. It is also possible that the vines need nitrogen fertilisation as juice nitrogen status and ammonia have been highly correlated with vine nitrogen status (Van Leeuwen et al, 2000).…”