IPI International Potash Institute
IPI International Potash Institute

Research Findings: e-ifc No. 39, December 2014

Experimental setup at Jamia Hamdard University. Photo by S. Umar.

Managing Nitrate Accumulation in Forage Sorghum by Potassium Fertilization

Khanum Al Akbari, W.M.(1), and S. Umar(1)(1a)
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(1)Jamia Hamdard University, Hamdard Nagar, New Delhi, India
(1a)Corresponding author: S. Umar

Abstract

Excessive nitrogenous fertilization or environmental stress due to drought, cold, frost, hail, leads to nitrate (NO3-) accumulation in forages. Elevated nitrate levels are a major concern because they can be detrimental to animal health and have caused several mass cattle-death incidents. A pot culture experiment was conducted under greenhouse conditions to screen 16 genotypes of sorghum (S. bicolor L.) for leaf nitrate reductase activity (NRA) and, hence, also potential nitrate accumulation. Marked differences in NRA and nitrate concentrations were observed among the genotypes, many of which accumulated nitrate to very high concentrations. From this screening experiment a high nitrate reductase (HNR) genotype and a low nitrate reductase (LNR) genotype viz. POP-52 (V9) and EB-15 (V7), respectively, were selected to study the effect of potassium (K) application on NRA and nitrate accumulation. The two sorghum genotypes were grown in specially designed PVC drums and the plants supplied with increasing levels of K, supplied as KCl at rates of 0, 30, 60 and 120 mg K2O kg-1 soil. Measurements made for leaf NRA and nitrate concentration at 30 and 60 days after sowing (DAS). Regardless of K treatment, NRA values increased from the 30 to the 60 day harvest and, correspondingly, nitrate concentrations decreased. At both harvests, K treatment up to 60 mg K2O kg-1 soil, (K60) increased leaf NRA and depressed leaf nitrate accumulation. An approximately three-fold decrease in nitrate concentration was observed in the K60 treatment in both genotypes from 30 to 60 DAS. Leaves of the 60 day old (K60) treated plants, V9, the genotype with the higher NRA (9.916 μmol NO2-1 h-1 g-1 fresh wt.), showed the lower nitrate accumulation (816.6 mg kg-1 fresh wt) and vice versa with the V7, the genotype with the lower NRA (5.018 μmol NO2-1 h-1 g-1 fresh wt.), which showed the higher nitrate accumulation (2691.8 mg kg-1 fresh wt.). K application also substantially lowered the nitrate concentration in the leachate indicating that K is effective in mitigating nitrate pollution in plants and soil. The results emphasize the importance of K in increasing nitrogen use efficiency (NUE) and of balanced fertilization in combating detrimental effects of nitrate on human beings, animals and the environment.

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