Browsing by Subject "Holzasche"

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Human urine as a crop fertilizer under saline conditions
(2013) Boh, Michael Yongha; Sauerborn, Joachim
Soil salinity and nutrients deficiency are jointly responsible for low agricultural production in many parts of the world. With a still growing world population and a continuing pressure on arable land, there is need to increase the productivity of salt affected soils. It is known that the application of N fertilizer can mitigate the deleterious effects of salinity on crop growth but this beneficial effect depends on the source of nitrogen and the extent of soil salinity. Whereas commercial inorganic fertilizers are expensive and often inaccessible to poor farmers especially in developing countries, human urine is an alternative low-cost fertilizer which, if collected and used, can replace up to 20% of current world fertilizer consumption. Its efficacy to increase crop productivity has been validated in scientific experiments. However, the high concentration of soluble salts (especially Na and Cl) in urine may impose a restriction on its use under saline and/or sodic conditions. The research presented in this thesis investigates the extent to which urine can be used as a fertilizer under saline/sodic conditions. It compares the effect of urine and ammonium nitrate-N sources on nutrients accumulation and growth of maize and sorghum plants in NaCl-saline substrate under controlled environmental conditions. Additionally, the effect of urine fertilization on changes in substrate chemical composition was investigated. Due to the high content of K, Ca and Mg in wood ash which can improve the soil cationic balance in salt affected soils, it was further investigated whether or not supplemental wood ash application can enhance salt- and Na-tolerance of urine-fertilized maize plants. Regardless of NaCl salinity treatment, no significant difference in investigated growth factors (height, leaf area and shoot biomass accumulation) of maize plants was measured when N was supplied at 180 mg kg-1 cultivation substrate as urine or ammonium nitrate. Meanwhile, urine treated maize plants produced comparatively less shoot biomass following the application of 380 mg N kg-1 of cultivation substrate and at NaCl salinities of 4.6 and 7.6 dS m-1. As expected, sorghum plants were more tolerant to salinity than maize and produced more biomass under urine than ammonium nitrate fertilization. Though there was a positive relationship between biomass yield and tissue nitrogen concentration regardless of salinity treatment level, this relationship was stronger for ammonium nitrate than urine treatments. Ca and Mg concentration in the tissue of urine-fed maize and sorghum plants was higher than those treated with ammonium nitrate which can be explained by the inherent content of these nutrients in urine. However, there was no direct relationship with biomass yield of maize plants of either nutrient. Additionally, urine fertilization significantly increased substrate salinity by 2 to 3-fold. Substrate sodium concentration and a tendency towards mounting sodicity with an increase in urine fertilization were also observed. At a NaCl-salinity of ECe 4.2 dS m-1, the application of wood ash (150 mg kg-1 soil) alone or in combination with 75 mg urine-N kg-1 soil fostered Na and salinity tolerance of maize which can be explained by the dilution effect of K and Ca supplied through wood ash. However, at a higher urine-N dosage (150 mg kg-1 soil) with or without wood ash enrichment growth inhibition occurred indicating that the tolerance threshold had been exceeded assumingly due to urine-induced increase in Na and salinity. It was demonstrated that urine can substitute ammonium nitrate as a source of nitrogen for maize and sorghum and can be considered for fertilization if salinity does not exceed ECe 4.0 dS m-1. Due to urine-induced increase in salinity and Na concentration in the growing medium, regular monitoring for salt build up and the use of salt-tolerant crop varieties should be included in urine fertilizer planning. It was further demonstrated that supplemental wood ash enhances Na and salinity tolerance and where necessary should be incorporated in urine-fertilizer programs.