Simulating the effects of human urine on phenology and some cultivar coefficients of Cowpea (Vigna unguicalata L. Walp) using the DSSAT-CROPGRO model

Abstract

The DSSAT-CROPGRO model was used to characterize phenology and cultivar coefficients of cowpea treated with diluted human urine (equivalent to 60 kg-N/ha), simulated under ten irrigation schedules for a 5 year production period in Juba County of Central Equatoria State, South Sudan.  Two treatments (T₀) without urine and (T₁) with human urine dilution during the growing season of 2016 were used and, 5-years model simulations on the grain number/m², LAI, canopy height (m) and pod number/m² compared. Irrigation schedules were carried out once the volumetric soil moisture content measured using the Theta Soil Moisture Probe was close to 15%. Results showed that cultivar coefficients EM-LF, FL-LF and FL-SH for both T₁ and Y2015 (calibrant) were on average 6-8 days shorter than under T₁. Also, the SIZLF under T₁ was about 8-17% greater than under both T₀ and calibrant Y2015 indicating the significance of diluted human urine on cowpea cultivar coefficients and phenology. The model also gave good agreement between observed and simulated growth parameters with low RMSE of the pod nr/m² at 17 for T₀, and 37.5 for T₁, the RMSE for grain nr/m² was 360 kg for T₁, and 347 kg for T₀, whereas the RMSE of LAI showed no significant difference. The d-indices in estimating LAI and canopy height were generally low and showed the largest errors than for pod nr/m² and grain nr/m². The results showed that the model satisfactorily simulated and underscored the significance of diluted human urine on both phenology and cultivar coefficients of cowpea.