Nitrogen mineralization and efficiency from co-applied animal manures and mineral fertilizer in sweetpotato under humid tropical conditions

• Isonitrogenous sole or co-applied mineral and animal manures incorporation studied.
• Co-applied mineral N and animal manures improved soil N mineralization potential.
• Co-application significantly improved N use efficiency in sweetpotato crop.

Frequently nitrogen (N) deficiency limits productivity in subsistence sweetpotato (Ipomoea batatas (L) Lam.) production systems of humid tropical Papua New Guinea (PNG). It was envisaged to adopt a sub-optimal dose of 50 kg N ha−1 through either locally available animal manures (poultry manure and goat manure) or mineral N fertilizer to improve immediate productivity of subsistence sweetpotato crop. The study involved an incubation experiment to quantify N mineralization in relation to the crop response and efficiency of N fertilization options in field experiments. Co-application of mineral N fertilizer 25 kg N ha−1 along with poultry manure 25 kg N ha−1 produced the highest cumulative mineral N (20.8 mg N kg−1) in 90 days of incubation, followed closely by sole mineral N fertilizer 50 kg N ha−1 and lowest mineral N (18.0 mg N kg−1) release was in sole application of goat manure 50 kg N ha−1. N mineralization data fitted well to parabolic model and revealed most increase in potentially mineralizable N pool (NA) in soils receiving co-application of mineral N and animal manures followed by mineral N 50 kg ha−1 and least improvement was in sole animal manures application. Mineral N fertilizer 25 kg N ha−1 plus poultry manure 25 kg N ha−1 produced significantly (p < 0.05) greater total tuber yields than control in 2011 and 2013 due to improved N uptake and N use efficiency. Present study, substantiates the appropriateness of promoting small dose of N at 50 kg N ha−1 in the subsistence sweetpotato production systems of PNG. Co-application of animal manures 25 kg N ha−1 with mineral N fertilizer 25 kg N ha−1 assembles best option by improving potentially mineralizable N in the soil and enhancing efficiency of applied N.