Mineralisation and nitrification of biuret and urea nitrogen in two New Zealand forest soils

Abstract

Context Biuret has potential to improve tree growth when applied at high rates as a slow-release nitrogen (N) fertiliser. However, there is little comparative research into the transformation of biuret and urea-N in forest soils. Aims This study comparatively investigated the mineralisation, nitrification and immobilisation of biuret and urea-N in two forest soils (a sandy loam soil and a silt loam soil) to further evaluate the suitability of biuret as a slow-release N source. Methods A 112-day long soil C and N mineralisation incubation study was conducted following application of 0, 4.08, 40.8 and 408 mg N kg−1 soil of biuret (referred to as control, B4, B41 and B408) and urea (referred to as control, U4, U41 and U408). CO2-C, microbial biomass C and N, NH4+-N and NO3−-N were measured at six times (on Days 2, 7, 14, 28, 56 and 112) to quantify net mineralisation and nitrification. Key results In both soils, biuret (especially in B408) was slowly mineralised with a steady increase in soil NH4+-N while urea was readily hydrolysed with a sharp increase and subsequently considerable decrease in soil NH4+-N. B408 had less nitrification than U408 in both soils, especially during the first 56 days. Conclusions Due to the lower mineralisation, nitrification and greater immobilisation, more biuret-N remained in the soils compared to urea-N. Biuret could be used as a potential slow-release N fertiliser in forest soils. Implications The research findings could have important implications for future biuret fertiliser development for plantation forests.