Matoka, C: Bacterial community responses to Soil-injected li

predominant ammonium to mixed nitrogen through the availability of partial nitrate is deemed to have played a role in the alleviation of ammonium toxicity symptoms commonly associated with crops fertilized with ammonium. Though mixed nitrogen nutrition is usually reported to produce superior grain yields, none was recorded in this study. This study has provided the first molecular evidence demonstrating the occurrence of bacterial communities in CULTAN-fertilized soils contrary to the presumption that ammonium injected zones remain highly toxic and never allow any microbial inhabitation and/or any substantial activity. In addition to this, the presumed toxic zones with high ammonium concentrations and acidic pH levels supported the highest diversity of bacterial communities. This diversity shifted spatio-temporally with regard to distance from injection zones and time after the injection was performed. Analysis of ammonia monooxygenase sub-unit A (amoA) gene revealed the occurrence of ammonia oxidizing bacteria (AOB) within these same toxic zones where their functional role is thought to have mainly been nitrogen transformation, especially in non-inhibitor incorporated ammonium treatments. Despite the presence of a large bacterial diversity in the early part of the season, it decreased as the season progressed. Though temporal bacterial community shifts also occurred (30 and 60 days after fertilization) with decreasing ammonium concentration and changing pH levels. The banding pattern seemed to have been restored to the original patterns of nitrate and non-fertilized control. This suggests the occurrence of an endogenous stability of the bacterial community structure over the season. This is an indication that CULTAN fertilization effects are not permanent, but only transient. The population of ammonia oxidizing bacteria in the treatment experiencing `mixed nitrogen nutrition¿ had the highest estimates of population abundance. This illustrates that high nitrification rates per se did not support the high population occurrence, but rather supported root exudation, which could have influenced the rhizosphere by improving microbial nutritional resources and suitable niches. 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 temperate and tropical regions.