Nitrogen assimilation potential in relation to nitrate-N toxicity at different growth stages and N inputs in oats (<i>Avena sativa </i> L.)

Abstract

Oats (<i>Avena sativa</i> L. Fam. Poaceae) is an important cereal crop known for its use as human food as well as fodder. In situations, such as excessive fertilization, cool weather conditions, low intensity of light, younger growth stage, etc., oats accumulate more nitrates and exhibit nitrate toxicity. Here, we conducted field experiment to determine the activity of various nitrate and ammonia assimilating enzymes <i>i.e.</i> nitrate reductase (NR), nitrite reductase (NIR), glutamine synthetase (GS), glutamate dehydrogenase (GDH) and glutamate synthase (GOGAT) and nitrate-N content at different growth stages (30, 45 and 60 DAS) under different nitrogen doses (0, 50, 75 and 100 Kg N/ha) in oats. Nitrate-N is an anti-nutritional factor present in small-grain crops, and it has a direct relationship with activities of nitrate and ammonia assimilating enzymes. The nitrate-N content was maximum in 45 DAS followed by 30 DAS and was above the toxic levels (>2000 ppm). Enzyme activities increased significantly with advancement of growth stage in all varieties of oats. At 60 DAS, which is first cutting stage of multi-cut fodder oats, the activity of nitrate and ammonia assimilating enzymes was maximum which conclusively decreased nitrate-N content to safer limit (<2000 ppm). Strong positive correlation was observed between NR activity and nitrate-N content at 45 and 60 DAS. The OL-10 (766 ppm) at 60 DAS had the minimum nitrate-N content which may be due to higher activities of nitrate and ammonia assimilating enzymes at this stage. With the increased nitrogen rate, significant increase in the activities of NR, NIR, GS, GDH, GOGAT and nitrate-N content was noted. Maximum nitrate-N content was observed at 100 Kg N/ha and it was above the toxic level (>2000 ppm) at early growth stages.