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 ECe 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. ECe 6.6 dS m−1), lower urine dosages should be considered.