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 (T 0) without urine and (T 1) 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 T 0 and Y2015 (calibrant) were on average 6-8 days shorter than under T 1. Also, the SIZLF under T 1 was about 8-17% greater than under both T 0 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 T 0 , and 37.5 for T 1 , the RMSE for grain nr/m 2 was 360 kg for T 1 , and 347 kg for T 0 , 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.

Using the DSSAT-CROPGRO model to simulate gross margin and N-leaching of cowpea fertigated with human urine

“…Such a high N on the four-fold N (uptake) by T 1 than under T 0 , would suggest the significance of fertigation as well as the role of N in enhancing cowpea nodulation, which in turn must have facilitated increase in N (uptake) . Although cowpea plants symbiotically fix atmospheric nitrogen, the additional application of 60 kg ha -1 of organic nitrogen fertilizer enhanced a three-fold N (uptake) and so positively affected cowpea phenology and yield significantly (Lomeling and Huria, 2019). The findings of (Xia et al, 2017) showed that low concentrations of nitrogen (<50 mg/L) added to soybean plants tended to increase nodulation while higher concentrations (>50 mg/L) had an inhibitory effect.…”

“…The CROPGRO model satisfactorily simulated the positive effect of human urine on cowpea yield. This positive effect is particularly attributable to the role of macro-and micro elements contained in the urine (Lomeling and Huria, 2019).…”