16S-soil-ash-Bangladesh, Here we investigated in large scale field trials across two geographic regions and two seasons, if domestic hearth ash can be used as a fertilizer for paddy rice cultivation, how geographic, season and application of household ash to soil impact on rice yield, and grain quality (accumulation of As, Cd, alongside nutrient elements) and rhizosphere soil microbial composition. The study was conducted in 9 homesteads each for two geographic regions (Madhupur & Barind tract), over two seasons (wet &dry). In each season, the following 3 treatments were applied: 1=control (conventional NKPS), 2= Ash (ash to supply all required P plus urea and K), 3 =control plus ash (1 t ash per ha plus conventional NPKS). At the end of each season, grain yield, mineral elements in grain (ICP-MS) and rhizosphere soil microbial community (16S rRNA amplicon sequencing, Illumina) were assessed and at the end of the overall experiment the overall impact on mineral elements in soil (XRF) e

AbstractBackgroundIn Bangladesh most agronomic biomass (straw, husk, dried dung) is burnt for domestic cooking use, supplemented by scavenged arboreal detritus (leaves, twigs, branches). This means that soils are continually stripped of mineral nutrients contained in that biomass and a loss of carbon (C) substrate to drive microbial activity, with most fields cropped 2-3 times per year. Recycling of household ash as fertilizer has potential to sustainably improve overall soil fertility and stimulate microbial function. Rhizosphere soil microbial communities play a role in plant productivity, nutrient uptake and accumulation of toxic elements (As, Cd) in rice grain. Here we investigated in large scale field trials across two geographic regions and two seasons, if domestic hearth ash can be used as a fertilizer for paddy rice cultivation, how geographic, season and application of household ash to soil impact on rice yield, and grain quality (accumulation of As, Cd, alongside nutrient elements) and rhizosphere soil microbial composition. The study was conducted in 9 homesteads each for two geographic regions (Madhupur & Barind tract), over two seasons (wet &dry). In each season, the following 3 treatments were applied: 1=control (conventional NKPS), 2= Ash (ash to supply all required P plus urea and K), 3 =control plus ash (1 t ash per ha plus conventional NPKS). At the end of each season, grain yield, mineral elements in grain (ICP-MS) and rhizosphere soil microbial community (16S rRNA amplicon sequencing, Illumina) were assessed and at the end of the overall experiment the overall impact on mineral elements in soil (XRF) evaluated.ResultsCompared to conventional NPKS, household biomass ash addition boosted rice yield by circa. 20%, for both regions, repeated over wet and dry season and increased rice grain Zn in the Barind region, but did not effect amount of carcinogenic inorganic arsenic (iAs), dimenthyl arsenic acid (DMA), cadmium (Cd) in rice grain and had no impact on soil elements measured at the end of the experiment. PERMANOVA analysis identified a significant region and season effect on microbial communities, but no treatment effect. Further to that, abundance of certain abundant microbial genera showed significant positive correlation (Spearman, P<0.05) with accumulation of rice grain elements. For example grain Cd, Zn correlated with abundance of Marmoricola, Nocardioles, Pseudolabrys in the Barind and grain Rb with abundance of Geobacter, Methylocystis in the Madhupur region. Furthermore grain Cd, Mn, P correlated with abundance of Anaerolineaceae, methanogenic archaea in wet and grain iAs, DMA with abundance of Rhodobacter in the dry season. ConclusionsThis study illustrates that use of household biomass ash can reduce the requirement for expensive chemical fertiliser application, whilst at the same time increasing rice yield, with potential role in zinc (Zn) nutrition, making farming in Bangladesh more sustainable and productive. Further to that this study provides novel insight with respect to the combined impact of geographic, season, and rhizosphere soil microbes on accumulation of elements in rice grain in Barind (Cd, Zn) versus Madhupur (Rb) region, and in wet (Cd, Mn, P) versus dry (iAs, DMA) season.