Bacterial community responses to soil-injected liquid ammonium nutrition and effect of temperature on barley (Hordeum vulgare L.) grain yield formation
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Injection of concentrated liquid ammonium nutrition into soil is an agricultural practice aimed at mitigating nitrogen losses. In Germany, it is referred to as controlled uptake long term ammonium nutrition (CULTAN) technique. Being an anion, nitrate is mobile in soil and thus is not bound to negatively charged surfaces of clay minerals or organic compounds. This may thus result in leaching and may eventually cause environmental pollution. Ammonium ions, on the other hand, may be unspecifically bound to negatively charged surfaces or even fixed in inter-layers of 2:1 clay minerals. Upon injection of liquid ammonium into soil, it remained the predominant N form accompanied by acidic pH values suggesting its stability. However, its concentration rapidly decreased 30 days after injection. Unspecifically bound ammonium liable for exchange was readily oxidized to nitrate by nitrifying bacteria. The demonstration of bacterial community occurrence within the ammonium injection-zones and the detection of ammonia monooxygenase sub-unit A (amoA) gene revealed the occurrence of ammonia oxidizing bacteria (AOB) within the depot-zones where nitrification was greatest. The suppression of nitrification through the incorporation of nitrification inhibitor (Nitrapyrin®) is clear evidence that ammonium transformation was microbialy mediated. The population of ammonia oxidizing bacteria in treatments experiencing mixed nitrogen nutrition had the highest estimates of population abundance. Bacterial community banding profiles were restored to patterns similar to those of nitrate and non-fertilized control treatments which remained same over the season, suggesting endogenous stability of bacterial community structure. This indicated that CULTAN fertilization effects are not permanent, but only transient. The study provided the first molecular evidence of bacterial community occurrence in CULTAN-fertilized soils contrary to the presumption that ammonium injected-depots never allow any microbial inhabitation and/or any substantial activity. Non-incorporation of nitrification inhibitor caused formation of high concentrations of nitrate which suggesting that CULTAN technique offers mixed nitrogen nutrition contrary to earlier assumptions that it supplies predominantly ammonium. This is the first experimental evidence of the occurrence of mixed nitrogen nutrition in CULTAN-fertilized soils. It can be generally concluded from this study that growth temperatures interact with CULTAN-injected liquid ammonium to cause a suite of growth responses such as growth duration alterations, tillering and ear formation which have a great impact on grain and biomass yields. Crop growth rate among different phenological stages influenced grain yield and yield forming-factors which significantly affected yield output. The role of temperature on microbial activity, especially the nitrification of injected liquid ammonium can not be ruled out. The possible occurrence of mixed nitrogen and crop growth durations could have also contributed to superior grain and biomass yields under low temperatures. These findings could be useful under temperate and tropical regions.Verknüpfung zu Publikationen oder weiteren Datensätzen
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Göttingen : http://www.cuvillier-verlag.de: Cuvillier; 2008