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 - , , , ) 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 and Cl - were significantly affected by crop cycle, salinity and urine interactions ( p < 0.05) whereas the effect of urine fertilizer on extractable and 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.