ABSTRACTThe Green Revolution of agriculture was in part driven by application of synthetic mineral fertilizers, largely supplanting organic manure as a source of the major nutrients nitrogen, phosphorous and potassium (NPK). Though enhancing crop production and global food security, fertilizers have contributed to soil acidification, eutrophication of water bodies, and greenhouse gas emissions. Organic agriculture, employing manures or composts, has been proposed as a way of mitigating these undesirable effects. Of particular interest is the effect of fertilizer regime on soil microbes, which are key to nutrient cycling, plant health and soil structure. Meta-analyses of experimental studies indicate that mineral fertilizer increases soil microbial biomass over unfertilized controls, and that organic fertilizers increase microbial biomass and activity over mineral fertilizers. However, the effect of fertilizers on soil microbial diversity remains poorly understood. Since biological diversity is an important determinant of ecosystem function and a fundamental metric in community ecology, the effects of fertilizer regimes on soil microbial diversity are of theoretical and applied interest. Here, we conduct a meta-analysis of 31 studies reporting microbial diversity metrics in mineral fertilized (NPK), organically fertilized (ORG) and unfertilized control (CON) soils. Of these studies, 26 reported taxonomic diversity derived from sequencing, gradient gel electrophoresis, RFLP, or dilution plate assay. Functional diversity, derived from Biolog Ecoplate™ measures of carbon substrate metabolism, was reported in 8 studies, with 3 studies reporting both diversity metrics. We found that functional diversity was on average 2.6 % greater in NPK compared with CON, 6.8 % greater in ORG vs CON and 3.6 % greater in ORG vs NPK. Prokaryote taxonomic diversity was not significantly different between NPK and CON, 4.2 % greater in ORG vs CON and 4.6 % greater in ORG vs. NPK. Fungal taxonomic diversity was not significantly different between NPK or ORG vs CON, but 5.4 % lower between ORG and NPK. There was very high residual heterogeneity in all meta-analyses of soil diversity, suggesting that a large amount of further research with detailed analysis of soil properties is required to fully understand the influence of fertilizer regimes on microbial diversity and ecosystem function.
Ascorbic acid content in leaves of Nightshade (Solanum spp.) and spider plant (Cleome gynandra) varieties grown under different fertilizer regimes in Western Kenya
