Nitrification of [formula omitted]-ammonium sulphate and crop recovery of [formula omitted]-labelled ammonium nitrates injected in bands

Abstract

The influence of fertiliser incorporation and band injection on immobilisation and nitrification of ammonium-nitrogen (N) was investigated in a bare soil field experiment. Total and inorganic forms of 15 N in the 0–20 cm soil layer were measured on days 0, 7 and 16 after ( 15 NH 4) 2 SO 4 application in framed micro-plots. Injection of the nitrogen fertiliser in a concentrated band reduced immobilisation, leaving more of the applied fertiliser-N available to plants. Band injection also reduced the nitrification rate from 2.7 to 1.8 kg N ha −1 per day and thus reduced the risk of N leaching losses until depletion of the soil inorganic N pool by crop uptake. In a parallel field experiment, crop 15 N recovery of inorganic N forms was studied in framed micro-plots. Bands of 15 NH 4 15 NO 3 , 15 NH 4 14 NO 3 or 14 NH 4 15 NO 3 solutions were injected parallel to a single row of spring wheat at early tillering. The injection depth as well as the band distance from the crop row was 5 cm. Root damage by injector tine was simulated using a knife. In addition, a treatment without root cut-off was included for the 15 NH 4 15 NO 3 application to study effects of injector-tine-caused root damage on 15 N uptake. The crop 15 N recovery was calculated on eight sampling dates during the elongation phase; a sigmoid growth function was fitted for each of the four treatments and uptake parameters were estimated. The crop uptake of banded nitrogen occurred within 4 weeks after application and the average maximum crop 15 N recovery of 65% was not significantly affected by the treatments. Maximum 15 N uptake rate varied within 5.6–8.2 kg N ha −1 per day. Simulation of an injector tine by root cut-off delayed the start of 15 N uptake by 2–3 days, and reduced the maximum uptake rate by 2.6 kg N ha −1 per day. Differences between the ammonium- and nitrate-derived 15 N uptake courses were not significant. In contrast to findings for broadspread N-fertilisers, the crop uptake of ammonium-N and nitrate-N may be considered as similar after band injection of the fertiliser.