Enhanced nutrient use efficiencies from liquid manure by positioned injection in maize cropping in northwest Germany

• Manure injection below maize seeds improves nutrient availability during early growth.
• Adding a nitrification inhibitor obviates the need for mineral starter fertilizer.
• The resulting reduction of N- and P-input is beneficial for the environment.

Maize (Zea mays L.), the dominating crop in northwestern Germany usually receives mineral nitrogen (N) and phosphorous (P) fertilizer side dressed (MSD) at planting as a starter to ensure proper early-growth development, on top on a usually nutrient demand covering manure application. Recently developed injection techniques, along with auto-guidance systems allow liquid manure injection below the maize seeds in a separate operation. Thus, the need for starter fertilizer might be obviated.Field trials were conducted on seven sites in northwestern Germany to compare liquid manure broadcast application versus injection at recommended rate with and without addition of a nitrification inhibitor in 2013. Several treatments were tested with and without MSD (23–10 kg N–P ha−1). In 2014, the trials were adapted to a proper two-factorial setup with additional reduced manure application rate treatments. Biomass accumulation and nitrogen uptake were assessed at V8 growing stage and at harvest.Compared to broadcast application with MSD, liquid manure injection without MSD showed retarded early-growth, but equal yield and N uptake at harvest in both years. Adding a nitrification inhibitor to injected liquid manure led to equal early-growth and yield, but significantly increased N uptake by 7% in 2013 and 6% in 2014, respectively. Regarding the proper performance of reduced rate injection treatments, the increase in N use efficiency is even more noticeable. The reduction of P input did not influence early growth and yield. P use efficiency from manure is higher when manure is injected prior to planting.These results indicate that liquid manure injection might reduce N and P surpluses in maize growing and therefore benefit farmers and environment.