Fertilizer 15N recovery in cereal crops and soil under shallow tillage

We examined the effect of tillage system on crop recovery of soil and fertilizer N. 15N-labelled ammonium nitrate was applied in the spring to small confined plots at five experimental sites where shallow tillage (ST) and mouldboard ploughing (MP) had been practised for up to 36 years. Winter wheat was grown on three sites and spring barley on the other two. Grain yields were similar under ST and MP at all sites, and total N uptake was similar under MP and ST at four of the five sites. Grain and straw recovered 59–64% of the applied 15N fertilizer except at the most sandy site where crop recovery was 37% (ST) and 44% (MP). At two sites, crop 15N recovery was lower under ST despite similar total N uptake for the two tillage systems. Recovery of 15N in crop and soil was 74–75% at the most sandy site and 86–92% at the other sites. Conversion from MP to ST tillage appeared to have little influence on the fertilizer N balance at each site.