Effects of dicyandiamide (a nitrification inhibitor) on leaching of nitrogen and growth of cereals

Abstract

Dicyandiamide (DCD) was tested as a nitrification inhibitor with urea in 10 field experiments (ammonium nitrate was included in 2 of them) in 3 years on sites where leaching of nitrogen was a potential problem. The investigations included different rates and times of nitrogen application. At 1 site in 1982 and 2 in 1983 the soil was sampled to 30cm throughout the season. Nitrification of ammonium nitrogen was delayed by DCD (applied as a mixture with urea and supplying 10% ofthe nitrogen in the mixture) by up to 30 days compared with untreated urea and reduced the danger of nitrogen leaching. Early sampling at the 1982 site showed increased uptake of ammonium nitrogen and decreased nitrate nitrogen in wheat plants receiving DCD-treated urea compared with those receiving untreated urea. This confirmed that DCD inhibits nitrification. The only significant (P<0.05) grain yield increase from DCD was a 22% increase from an application of nitrogen at sowing on a particularly highly leaching soil. DCD significantly (P < 0.05, P < 0.01) reduced grain yield (7 and 8%) and vegetative yield (1 3 and 9%) at 2 sites. DCD increased vegetative yield by 16% at 1 site (not the same site as the grain yield increase). In 2 of 3 experiments plant dry matter production (up to 11 weeks after sowing) was significantly (P < 0.05 to P < 0.001) reduced (up to 30%) by DCD application. The final value of the use of DCD will depend on the balance between the benefit in preventing nitrogen losses by leaching at a particular site and the harm caused by suppressing early plant growth.