Effect of NaCl-Induced Salinity and Human Urine Fertilization on Substrate Chemical Properties

Abstract

We evaluated the effect of NaCl-induced salinity and successive urine fertilization on changes in cultivation substrate chemical properties in a greenhouse study. The substrate was composed of an equal volume ratio mixture of bio-waste compost, quartz sand and silty loam soil. Salinity was imitated by adding NaCl solutions to a known substrate weight achieving three target salinity treatments of EC e 1.3 (S0-no NaCl), 4.6 (S1) and 7.6 (S2) dS•m −1. Cultivation substrate had been cropped with two cycles of maize (Zea mays L.) (crop cycles I and II) and fertilized with human urine at N amounts of 0 (U0-no urine), 180 (U1) and 360 (U2) mg•kg −1 substrate in the first cycle and half of the urine-N dosages in cycle II. Substrate samples collected at the end of each cycle were analyzed for pH KCl , EC e , exchangeable and water extractable cations (Na + , K + , Ca 2+ , Mg 2+), cation exchange capacity, water extractable anions (Cl − , 3 NO − , 2 4 SO − , 4 PO 3−) and exchangeable sodium percentage (ESP). Exchangeable Na + , K + and Ca 2+ were significantly (p < 0.05) affected by salinity x urine interaction. EC e significantly increased by 7.3, 5.3 and 7.6 dS•m −1 in the S0, S1 and S2 treatments following an increase in urine from U0 to U2. In the S0 treatment, ESP increased in the order U0 < U1 < U2. Extractable 3 NO − and Cl − were significantly affected by crop cycle, salinity and urine interactions (p < 0.05) whereas the effect of urine fertilizer on extractable 2 4 SO − and 4 PO 3− depended on crop cycle alone. There was a tendency towards increasing soil sodicity with mounting urine fertilization. The level of NaCl salinity and the amount of urine applied are important determinants of substrate chemical properties. Adoption of appropriate management techniques to avoid salinity/sodicity build up should be included in urine fertilization planning.

Fate of nitrogen and phosphorus from source-separated human urine in a calcareous soil

“…However, crops under the U3 treatment did not take up more sodium than under the other treatments (Table 3S, Supplementary data), and the soil salinity was still below the spinach salt tolerance threshold established at 9.4 dS m −1 by Ferreira et al (2018); so, it is unlikely that the spinach crops underwent a saline stress. Other studies on urine fertilization confirm that critical values of soil conductivity are only observed when urine is applied in excess (up to 13 dS m −1 with 800 kgN ha −1 ) (Boh and Sauerborn 2014;Mnkeni et al 2008;Neina 2013) and that the crop response depends on its salt tolerance threshold (Mnkeni et al 2008). Nevertheless, the effects of urine fertilization on soil salinity have not been investigated so far for longer than one or two cropping seasons.…”

“…Thus, it could represent a complete fertilizing solution even though the bioavailability of urine micronutrients has not been well documented (Olivia et al 2015). Yet, the high concentrations in Na + , Cl − and SO 4 2− could also cause soluble salt accumulation in soils (Boh and Sauerborn 2014;Mnkeni et al 2008;Shingiro et al 2019).…”

Fate of nitrogen and phosphorus from source-separated human urine in a calcareous soil

“…Yet, the high concentration in Na + , Cl − and SO 4 2− could also cause salt accumulation in soils. A few studies (Boh and Sauerborn, 2014;Mnkeni et al, 2008;Shingiro et al, 2019) have reported an increase in soil conductivity after urine application, suggesting that urine fertilisation can cause the build-up of soluble salt concentrations in soils.…”