Abstract
Forages tend to accumulate elevated levels of nitrate when fields are heavily fertilized with nitrogenous fertilizers or are environmentally stressed due to drought, cold, frost, hail, etc. Elevated levels of nitrate have detrimental effects on animal health and are regarded as a causative factor for several mass cattle-death incidents. It was observed that nitrate concentration in Sorghum bicolor L. obtained from local fields of Uttar Pradesh (Ghaziabad and Meerut) and Haryana (Gurgaon and Faridabad) exceeded the safe limit (2500 mg of nitrate kg-1 of fresh wt.) in a significant number of samples (31.7%) studied. Given this, the investigation was conducted in earthen pots to determine nitrate contents in 16 genotypes of S. bicolor L. A significant difference in nitrate content was observed among genotypes, many of which accumulated nitrate to toxic levels. POP-52 (V9), a high nitrate reductase (HNR) genotype and EB-15 (V7), a low nitrate reductase (LNR) genotype of sorghum were selected to study the effect of potassium (K) application on nitrate accumulation in specially designed PVC-drums. The minimum nitrate concentration (V9= 816.6 mg/kg fresh wt. and V7= 2691.8 mg/kg fresh wt.), coupled with maximum NR activity (V9= 9.916 μmol NO2 –1 h–1 g–1 fresh wt. and V7= 5.018 μmol NO2 –1 h–1 g–1 fresh wt.) were observed in 60 day old K60 treated plants. K application reduced the nitrate concentration by 35.24% in V9 and by 25.54% in V7 genotypes by increasing nitrate reductase (NR) activity by 86.23 % in V9 and lesser increase of 32.07% in V7 genotype of sorghum at 30 days. A two- fold (approx.) decrease in nitrate concentration was observed at K60 in both genotypes from 30 to 60-days-after-sowing. K application also reduced considerably the nitrate in the leachate indicating that K is effective in mitigating nitrate pollution in plants and soil. The data emphasizes the importance of K in increasing the nitrogen use efficiency and of balanced fertilization in combating the nitrate-related implications on human beings, animals and environment.
Highlights
Agricultural development relies largely on the production and consumption of fertilizers; addition of fertilizers does not ensure the enhanced crop production
The samples from Gurgaon and Faridabad were lower in nitrate concentrations, though all of them were not safe for consumption as some of them exceeded the safe limit
The findings of our study showed a negative relationship between nitrate reductase (NR) activity and nitrate concentration in leaves (Figure 4)
Summary
Agricultural development relies largely on the production and consumption of fertilizers; addition of fertilizers does not ensure the enhanced crop production. Inefficient use of available N leads to accumulation of nitrate in plants that causes toxicity to animals, which feed on them. Due to excessive N fertilization, leads to eutrophication of freshwater bodies [12,13] and the marine ecosystems [14,15]. Nitrate (NO3-) accumulation in plant tissue is usually observed during drought, long periods of cloudy or cool weather, or following a heavy fertilization with manures and nitrogen-containing fertilizers and due to herbicide applications [16]. Nitrates are converted to nitrites and to nitrosamines that result in gastric cancer and other diseases in the consumers [17]. Methemoglobinemia is another adverse effect of nitrate poisoning [18,19]
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