Poultry litter increased irrigated cotton N uptake with limited improvement on 15N-labelled urea recovery over one season

Limited field research has investigated the impact of poultry litter (PL) on urea-nitrogen (N) recovery in irrigated cropping systems. This study investigated the effect of PL (nil or 15t ha(-1)) on the fate of N-15-labelled urea at different rates (0, 50, 150, and 300 kg N ha(-1)) and changes in soil N mineralisation-immobilisation dynamics on an irrigated cotton farm. Our study highlighted multiple soil and plant N benefits from the use of PL, while limited improvements were seen on fertiliser N-15 plant uptake and recovery. Total N-15 recoveries were some of the highest observed for Australian cotton studies (61.0-92.3%) and PL increased overall plant N uptake (398-421 kg ha(-1)) compared to urea-only treatments (325-370 kg ha(-1)). Poultry litter stimulated soil NH4-N and NO3-N release at the start of the season then immobilised soil NO3-N for the remainder, which helped to retain residual N-15-urea (12% N-15 recovery) in the soil surface after harvest. Despite high total N-15-fertiliser recoveries, the crop sourced most of its N (67.1-92.6%) from existing soil and PL reserves rather than current-season urea, potentially due to high native soil N supply rates and urea immobilisation in the microbial pool. These results confirm the lack of N rate response on yield observed in this study and commonly seen in other cotton farm studies. We suggest future research to follow post-harvest soil N into consecutive growing seasons to determine how to best manage integrated PL-urea applications to preserve soil N and improve fertiliser-N use efficiency.

Automated summary

Limited research has been done on the impact of poultry litter on urea-nitrogen recovery in irrigated cropping systems. This study found that poultry litter had multiple benefits on soil and plant nitrogen, but did not significantly improve fertilizer uptake and recovery. The use of poultry litter increased total nitrogen recovery and plant uptake compared to urea-only treatments. However, most of the nitrogen in the crop came from soil and litter reserves, rather than current-season urea.