Nitrification Inhibitors for Agriculture, Health, and the Environment

This literature survey is the English version of P. Kerkhoff and J.H.G. Slangen “Nitrificatieremstoffen in Land- en Tuinbouw, Interne Mededeling 54, Vakgroep Bodemkunde en Bemestingsleer, Landbouwhogeschool, Wageningen, 99 p, 1980”, supplemented by reference to the literature of 1980 and a partly of 1981. The literature cited has been taken from sources in East and West Europe and North America.

Nitrification inhibitors in agriculture and horticulture: A literature review

Summary
• Nitrification results in poor nitrogen (N) recovery and negative environmental impacts in most agricultural systems. Some plant species release secondary metabolites from their roots that inhibit nitrification, a phenomenon known as biological nitrification inhibition (BNI). Here, we attempt to characterize BNI in sorghum (Sorghum bicolor).
• In solution culture, the effect of N nutrition and plant age was studied on BNI activity from roots. A bioluminescence assay using recombinant Nitrosomonas europaea was employed to determine the inhibitory effect of root exudates. One major active constituent was isolated by activity-guided HPLC fractionations. The structure was analysed using NMR and mass spectrometry. Properties and the 70% inhibitory concentration (IC70) of this compound were determined by in vitro assay.
• Sorghum had significant BNI capacity, releasing 20 allylthiourea units (ATU) g−1 root DW d−1. Release of BNI compounds increased with growth stage and concentration of supply. -grown plants released several-fold higher BNI compounds than -grown plants. The active constituent was identified as methyl 3-(4-hydroxyphenyl) propionate.
• BNI compound release from roots is a physiologically active process, stimulated by the presence of . Methyl 3-(4-hydroxyphenyl) propionate is the first compound purified from the root exudates of any species; this is an important step towards better understanding BNI in sorghum.

Detection, isolation and characterization of a root-exuded compound, methyl 3-(4-hydroxyphenyl) propionate, responsible for biological nitrification inhibition by sorghum (Sorghum bicolor).

The tropical pasture grass, Brachiaria humid- icola (Rendle) Schweick, produces nitrification inhib- itory compounds (termed biological nitrification inhibitors or BNIs) in its shoot and root tissues and releases BNIs from its roots. In the present study, two BNI compounds were isolated and identified from the shoot tissue of B. humidicola using activity-guided fractionation. The recombinant Nitrosomonas europaea containing luxAB genes derived from the biolumines- cent marine gram-negative bacterium Vibrio harveyi, were used to determine BNI activity. The BNI com- pounds in the shoot tissue were identified as linoleic acid (LA) and linolenic acid (LN) using authentic- chemicals obtained from ©Sigma (ED80 16.0 μ gm l −1 for both LA and LN) for verification. None of the other tested free fatty acids namely stearic acid, oleic acid, arachidonic acid, and cis-vaccenic acid showed any inhibitory effect on nitrification. Among the fatty acid methyl esters (FAME) evaluated (methyl oleate, methyl linoleate (LA-ME) and methyl linoleneate (LN-ME)), only LA-ME showed an inhibitory effect (ED80 8.0 μ gm l −1 ). The inhibitory effect of LA, LN and LA-ME in the soil was stable for 120 days at 20°C. Soil treated with LA, LN and LA-ME showed a very low accumulation of NO3 − and the maintenance of soil inorganic N in the NH4 + form. The inhibitory effect of LA-ME on soil nitrification was greater than that of LA or LN. In addition to BNI activity, both LA and LA- ME showed a suppressive effect on urea hydrolysis in soil. Both LA and LN blocked the AMO (ammonia monooxygenase) and HAO (hydroxylamino oxidoreduc- tase) enzymatic pathways in Nitrosomonas .S ince LA and LN can be produced from vegetable oils such as soybean, flax or sunflower, they have the potential for use as nitrification inhibitors in production agriculture.

Free fatty acids from the pasture grass Brachiaria humidicola and one of their methyl esters as inhibitors of nitrification

Nitrification inhibitory activity was found in root tissue extracts of Brachiaria humidicola, a tropical pasture grass. Two active inhibitory compounds were isolated by activity-guided fractionation, using recombinant Nitrosomonas europaea containing luxAB genes derived from the bioluminescent marine gram-negative bacterium Vibrio harveyi. The compounds were identified as methyl-p-coumarate and methyl ferulate, respectively. Their nitrification inhibitory properties were confirmed in chemically synthesized preparations of each. The IC50 values of chemically synthesized preparations were 19.5 and 4.4 μM, respectively. The ethyl, propyl, and butyl esters of p-coumaric and ferulic acids inhibited nitrification, whereas the free acid forms did not show inhibitory activity. Keywords: Brachiaria humidicola; nitrification inhibitor; methyl ferulate; methyl-p-coumarate

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Nitrification Inhibitors from the root tissues of Brachiaria humidicola, a tropical grass.

The literature on karanja is evaluated critically. As with any other material, there is still a vast
area of research remaining uncovered but the present
information does point out areas where seeds andoil available in a large amount in the country can
 be utilized. To mention some of the uses, the use of karanjin as a nitrification inhibitor and karanja oil as a synergist-cum-solvent for chlorinated msecti­ cides might consume considerable amounts of these materials. Similarly, karanja cake meal can be
processed and used as a cheap cattle feed. The
oil is already finding considerable use in soap making.Besides, it is a potential source of fatty acids

Pongamia glabra: constituents & uses

The manurial value of P. glabra seed-cake in India has been attributed to nitrification inhibitors. In laboratory experiments with soil samples, both seed and bark extracts inhibited the oxidation of NH4-N (NH4-N concn. approx. twice that of controls at 45 days), the effect being slightly greater with the seed extract. Dried leaves had no such effect. It is concluded that components of the alcoholic seed extract may be used to increase the efficiency of ammoniacal fertilizers

K L Sahrawat

Papers

Pongamia glabra: constituents & uses

Note on the nitrification inhibitors in the seeds, bark and leaves of Pongamia glabra Vent