Crop residue interactions with fertilizer rate enhances volatilization loss and reduces nitrogen use efficiency in irrigated maize and potato

Ammonia (NH3) fluxes and their soil-related factors were quantified in irrigated maize and potato fields by two split-plot experiments with and without crop residue (CR) together with four fertilizer N rates: N zero (control), farmers’ N (FP), recommended N (RD) and 25% above RD (1.25 RD). CR application together with RD increased NH3 fluxes in maize by 8% in comparison to RD without CR. The NH3 emission factor in maize ranged from 29% in the farmers’ practice (FP-without CR) to 34% in 1.25 RD coupled with CR. Yield-scaled NH3 fluxes increased with N fertilizer application rate. Nitrogen use efficiency (NUE) in maize was 53% higher in FP without CR than in other treatment combinations. In potato, CR coupled with FP reduced NH3 fluxes by 23%. Crop residue and N fertilization rate interaction were significant for NUE, where 1.25 RD without CR increased NUE by 19% when compared with FP-without CR. Stepwise multiple linear regressions showed that mineral N and pH explained 95% of the variances of NH3 fluxes. NH3 fluxes in maize are a significant N loss pathway which is driven mainly by fertilizer N rate, soil mineral N and pH.