Fertilizing effect of human urine and ammonium nitrate as sources of nitrogen for sorghum [Sorghum bicolor (L.) Moench] under saline conditions

Abstract

An experiment was conducted in a greenhouse to assess the influence of urine- and ammonium nitrate-N fertilization on sorghum biomass yield, shoot nutrient concentrations, and root:shoot ratio under different levels of NaCl salinity. Nitrogen applications were 90 and 180 mg N kg⁻¹ soil substrate made from a mixture of bio-waste compost, quartz sand, and silty loam soil. A NaCl solution was added to the soil substrate to achieve target EC_e of 1.3 (no salt added), 4.6, and 6.6 dS m⁻¹, imitating different levels of salinity. Sorghum was sown as a second crop after maize, and biomass was harvested 12 weeks after sowing to assess dry weight and shoot nutrient concentrations. Salinity significantly decreased biomass yield regardless of N source. At an application rate of 90 mg N kg⁻¹ substrate, biomass yield was 30% higher in plants fertilized with urine compared to ammonium nitrate regardless of salinity level. The application of 180 mg urine-N kg⁻¹ raised substrate salinity and caused a significant decrease in shoot biomass yield in NaCl-treated substrates. Correlation analyses showed a relatively weak relationship between shoot N concentration and biomass yield in urine (r = 0.34; p > 0.05) compared to ammonium nitrate (r = 0.91, p < 0.0001). At a salinity of 6.6 dS m⁻¹, nitrogen use efficiency was lower (33%) in urine compared to ammonium nitrate treatments. In conclusion, urine fertilization improves sorghum growth. However, where soil salinity is a problem (e.g. EC_e 6.6 dS m⁻¹), lower urine dosages should be considered.

Keywords:

• human urine fertilizer
• nitrogen use efficiency
• root:shoot ratio
• soil salinity and sodicity

Acknowledgments

We thank Dr. Jörn Germer for his useful comments on an earlier version of this manuscript.

Conflict of interest

No conflict of interest was reported by the authors.

Additional information

Funding

The authors are grateful for the financial support of the Katholischer Akademischer Ausländer Dienst (KAAD), Germany as well as the laboratory assistance of Frau Helene Ochott.