Synergism between feremycorrhizal symbiosis and free-living diazotrophs leads to improved growth and nutrition of wheat under nitrogen deficiency conditions

A controlled-environment study was conducted to explore possible synergistic interactions between the feremycorrhizal (FM) fungus Austroboletus occidentalis and soil free-living N2-fixing bacteria (diazotrophs). Wheat (Triticum aestivum) plants were grown under N deficiency conditions in a field soil without adding microbial inoculum (control: only containing soil indigenous microbes), or inoculated with a consortium containing four free-living diazotroph isolates (diazotrophs treatment), A. occidentalis inoculum (FM treatment), or both diazotrophs and A. occidentalis inoculums (dual treatment). After 7 weeks of growth, significantly greater shoot biomass was observed in plants inoculated with diazotrophs (by 25%), A. occidentalis (by 101%), and combined inoculums (by 106%), compared to the non-inoculated control treatment. All inoculated plants also had higher shoot nutrient contents (including N, P, K, Mg, Zn, Cu, and Mn) than the control treatment. Compared to the control and diazotrophs treatments, significantly greater shoot N content was observed in the FM treatment (i.e., synergism between the FM fungus and soil indigenous diazotrophs). Dually inoculated plants had the highest content of nutrients in shoots (e.g., N, P, K, S, Mg, Zn, Cu, and Mn) and soil total N (13–24% higher than the other treatments), i.e., synergism between the FM fungus and added diazotrophs. Root colonization by soil indigenous arbuscular mycorrhizal fungi declined in all inoculated plants compared to control. Non-metric multidimensional scaling (NMDS) analysis of the bacterial 16S rRNA gene amplicons revealed that the FM fungus modified the soil microbiome. Our in vitro study indicated that A. occidentalis could not grow on substrates containing lignocellulosic materials or sucrose, but grew on media supplemented with hexoses such as glucose and fructose, indicating that the FM fungus has limited saprotrophic capacity similar to ectomycorrhizal fungi. The results revealed synergistic interactions between A. occidentalis and soil free-living diazotrophs, indicating a potential to boost microbial N2 fixation for non-legume crops

Mapping Meaning : Critical Cartographies for Participatory Water Management in Taita Hills, Kenya

Participation of local people is often neglected in natural resource management, which leads to failure to understand the social aspects and historical construction of environmental problems. Participatory mapping can enhance the communication of local spatial knowledge for management processes and challenge the official maps and other spatial representations produced by state authorities and scientists. In this study, we analyze what kind of social meanings can be revealed through a multimethod participatory mapping process focusing on water resources in Taita Hills, Kenya. The participatory mapping clearly complicates the simplified image of the physical science mappings, typically depicting natural water supply, by addressing the impacts of contamination, inadequate infrastructure, poverty, distance to the sources, and restrictions in their uses on people's access to water. Moreover, this shared exercise is able to trigger discussion on issues that cannot always be localized but still contribute to place making. Local historical accounts reveal the social and political drivers of the current water-related problems, making explicit the political ecology dynamics in the area.Peer reviewe

Effect of long-term plant biomass management on phosphatase-producing bacterial populations in soils under temperate grassland

Organic forms of phosphorus (P) account for over half of the total P present in most soils and make a significant contribution to P cycling and plant nutrition through the actions of various plant and microbial phosphatase enzymes. However, not much is known about the bacterial communities harbouring phosphatase genes, either in composition, abundance, or transcriptional activity. Thus a grassland trial was selected that was undergoing long-term management of plant biomass removal/retention. Treatment plots were sampled after 22 years to examine the impact of prolonged nutrient depletion on bacterial communities helping to mediate organic P turnover. Total bacteria, total fungi, alkaline phosphatase (phoD) and the three classes (A, B, C) of non-specific acid phosphatases (NSAPs) were quantified and amplicons of the phoD and NSAP genes were sequenced. Of the genes quantified, class B (CBAP) genes were positively impacted by biomass removal (p < 0.01). Phosphatase gene transcripts generally appeared to increase in the biomass removed plots, but perhaps only weakly differentiated at this one time point. In the removed plots, we identified the class A (CAAP) community as the most significantly differentiated (p < 0.05). This difference was found strongly at the level of the operational taxonomic unit, indicating that changes in composition are reflective of the biomass management. Several key differentiating bacteria were found, many of which shared a closest known identity to Stenotrophomonas spp. Further, Mantel tests also revealed strong associations of NSAP communities CAAP and CCAP to measures of soil biogeochemistry. The findings of this study further support the importance of microbial mediated P cycling and in the contribution of under-studied P cycling enzymes such as bacterial acid phosphatases

Impacts of long-term plant biomass management on soil phosphorus under temperate grassland

Aims: We assessed and quantified the cumulative impact of 20 years of biomass management on the nature and bioavailability of soil phosphorus (P) accumulated from antecedent fertiliser inputs. Methods: Soil (0–2.5, 2.5–5, 5–10 cm) and plant samples were taken from replicate plots in a grassland field experiment maintained for 20 years under contrasting plant biomass regimen- biomass retained or removed after mowing. Analyses included dry matter production and P uptake, root biomass, total soil carbon (C), total nitrogen (N), total P, soil P fractionation, and ³¹P NMR spectroscopy. Results: Contemporary plant production and P uptake were over 2-fold higher for the biomass retained compared with the biomass removed regimes. Soil C, total P, soluble and labile forms of inorganic and organic soil P were significantly higher under biomass retention than removal. Conclusions: Reserves of soluble and labile inorganic P in soil were significantly depleted in response to continued long-term removal of P in plant biomass compared to retention. However, this was only sufficient to sustain plant production at half the level observed for the biomass retention after 20 years, which was partly attributed to limited mobilisation of organic P in response to P removal

Investigating the relationships between soil acidity and phosphorus fractions in high country farmland of New Zealand's South Island

Soil fertility remains a limitation to pasture production in the South Island high country of New Zealand, despite a strong history of aerial superphosphate fertiliser applications. This may in part be due to the acidic nature of these soils. This study of extensively farmed high country soils (n = 19) aimed to investigate the current status of soil fertility, and to quantify the effects soil acidity and exchangeable aluminium (Al) have on the accumulation of phosphorus (P) in these soils. To a depth of 7.5 cm, mean soil pHH₂O across these soils was 5.2 ± 0.1, and exchangeable Al concentrations increased exponentially as pH decreased (R² = 0.87), exceeding 3 mg kg¯¹ at pHH₂O ≤ 5.1. Sulfur (S) concentrations were highly deficient for pasture production in these high country soils, with sulfate S (SO₄−S) and organic S (Org-S) only exceeding 10 mg kg-1 at 6 and 3 out of the 19 sites, respectively. Total soil P concentrations, measured by Hedley fractionation, ranged from 587 to 1570 mg P kg¯¹ but only 7.2 ± 0.5% of this P was plant-available P (20.1-152 mg P kg¯¹). The greatest concentrations of P that these soils contained were in the moderately-labile organic P fraction (176-730 mg P kg¯¹), which may have the potential to become available due to organic matter mineralisation following liming. However, using Pearson's correlations and principal component analysis, no strong correlations between the quantities or proportions of P contained in each P fraction were found due to the acidity or concentrations of exchangeable Al in these soils. This suggests that liming these soils is unlikely to result in substantial increases in plant P availability from the mineralisation of P in non-labile soil P fractions

Effects of long-term irrigation on soil phosphorus under temperate grazed pasture

The effect of 62 years of different irrigation regimes on the amounts, forms and distribution of phosphorus (P) in the soil profile to 100 cm under grazed pasture was determined. Irrigation treatments included nil irrigation (base average rainfall of 740 mm year¯¹; control), together with flood irrigation applied when gravimetric moisture (GM) in the topsoil decreased below 10 or 20% (i.e. rainfall +260 mm year¯¹ of supplemental irrigation [irrigation10%GM] and rainfall +770 mm year¯¹ [irrigation20%GM], respectively). Phosphorus fertilizer in the form of single superphosphate was applied annually at the rate of 23 kg P ha¯¹ to all treatments. Total soil profile P was smallest under the large rate of irrigation (5054 kg P ha¯¹) compared with the small rate (5908 kg P ha¯¹) and the control (6423 kg P ha¯¹), which was attributed mainly to changes in inorganic P. These data indicated that markedly more P was removed, transferred or lost under irrigation. Substantial increases in pasture production and animal grazing capacity occurred in response to irrigation, which in turn resulted in increased removal and transfer of P in animal products, animal excreta (stock camp transfer and irrigation outwash) and by leaching. Thus, combined annual removal of P in animal products, internal dung transfer and loss in irrigation outwash were directly related to irrigation frequency and increased from 8 to 18.6 kg P ha¯¹ for the irrigation10%GM and irrigation20%GM treatments, respectively. Highlights: Examined effect of 62 years of irrigation on phosphorus in the soil profile to 100 cm. Phosphorus fertilizer was applied annually at the same rate to all treatments. Total soil profile P decreased with irrigation and was smallest under the large rate of irrigation. P removal and transfer or loss increased with irrigation frequency

Plant biomass management impacts on short-term soil phosphorus dynamics in a temperate grassland

The objective of this study was to quantify the combined effects of long-term plant biomass retention/removal and environmental conditions on soil microbial biomass phosphorus (P), bioavailable P, and acid phosphomonoesterase activity. Topsoil samples (0–2.5 and 2.5–5 cm) were collected from replicate field-based plots that had been maintained under contrasting plant biomass retention and removal regime for 21 years. Samples were collected on 14 occasions over a 17-month period and assessed for microbial P, bioavailable P, and phosphomonoesterase activity. All P measurements were consistently and significantly higher under plant biomass retention compared with biomass removal. Temporal variations in microbial P and phosphomonoesterase activity were evident in top soil (0–2.5 cm) and were driven by environmental conditions, mainly soil moisture, rainfall, and potential evapotranspiration, while bioavailable P had no temporal variation. Detailed analysis of microbial P data for the top 2.5-cm soil depth revealed that annual P flux through this pool was two times greater under biomass retention (10.3 kg P ha⁻¹ year⁻¹) compared with plant biomass removal (5.0 kg P ha⁻¹ year⁻¹). Similar and consistent trends were observed in soil from 2.5- to 5-cm sampling depth; however, differences were not significant. The findings of this study confirm the importance of the microbial biomass in determining the bioavailability of P in temperate grassland systems

Mass balance assessment of phosphorus dynamics in a fertilizer trial with 57 years of superphosphate application under irrigated grazed pasture

Improving the efficiency of phosphorus (P) use is a major challenge for agricultural production and sustainability. Using a combination of new and historic data, a mass balance approach was employed to construct and discuss a comprehensive P budget under temperate irrigated grazed pasture that had received different inputs of superphosphate fertilizer for 57 years [nil (Control), 188 kg ha⁻¹ (188PA) and 376 kg ha⁻¹ (376PA)]. Most (97–99%) of the applied P was accounted for in soil storage, plant residues, removal in animal products, excretal transfers, losses via irrigation outwash, rainfall runoff and leaching in the soil–plant–animal system. Management of soil available P that exceed the critical level (17–22 mg L⁻¹) for optimal pasture production can result in low P balance efficiency and excessive soil legacy P in the soil profile (0–1 m). Results of this study revealed that accumulation of P in soil and plants (68–80%), P losses by irrigation outwash (8–11%), and excretal transfers to stock camps (6–12%) were important factors that determined applied P use efficiency. These findings highlight the need to apply appropriate quantities of P fertilizer to maintain optimal soil P fertility, plant growth, and animal production, together with enhanced utilization of accumulated soil P and reduced P transfer in drainage

Fate of phosphorus applied to soil in pig slurry under cropping in southern Brazil

Strongly weathered soils (such as Oxisols), are inherently phosphorus (P) limiting and highly P-sorptive thus requiring continued P inputs for productive agriculture. Constant P inputs result in accumulation of soil P with increasing risk of eutrophication of waterways. The state of Santa Catarina is the largest pork producer in Brazil. Production is concentrated in confined systems, with large generation of nutrient rich waste, commonly utilised as fertiliser. The objective of this work was to investigate and quantify the impact of long-term P inputs in pig slurry to a high P-sorbing Oxisol under cropping in southern Brazil. Fifteen years of pig-slurry addition resulted in P accumulation and vertical movement down the soil profile in proportion to application rates, but significant effects were confined to the 0–20 cm soil layer. Phosphorus accumulated mainly in inorganic forms. Slurry input rates of 25, 50, 100, and 200 m 3 ha −1 y −1 resulted in accumulations of 25, 57, 106, and 159 kg P ha −1 y −1 (0–40 cm), of which only 8, 10, 23, and 28 kg P ha −1 y −1 were organic P forms. Mass balance showed that between 62 and 94% of the P inputs in slurry were accounted for in grain exports (7–35%), soil storage (58–83%), minimal amounts were estimated in crop residues ( < 1%), while the remainder (6–38%) was presumed to have been lost in drainage by overland flow

The fate of pig slurry phosphorus applied to a sandy loam soil under no-till cropping in southern Brazil

Repeated phosphorus (P) inputs can lead to the accumulation of surplus P in soil with enhanced potential risk of transfer and accelerated eutrophication of aquatic environments. Intensive pork production in Rio Grande do Sul in southern Brazil results in the generation of large quantities of P-rich waste in the form of pig slurry, which is used to fertilise crops. The aim of this study was to assess and quantify the impact of repeated application of pig slurry P over 8 years (2000–2007) on the fate of P in a sandy loam soil maintained under a mixed cropping regime. In a replicated field trial, pig slurry was applied at three rates (20, 40, and 80 m³ ha¯¹), which resulted in cumulative P inputs over the 8-year period of 628, 1256, and 2511 kg P ha¯¹. Slurry inputs of 20, 40, and 80 m³ ha¯¹ resulted in the accumulation of 368, 936, and 2039 kg P ha¯¹ in soil to 60 cm, respectively. A combination of soil storage (59–81 %), crop removal (7–14 %), and total P transfer in surface runoff (5–15 %) accounted for most of the P applied in pig slurry over 8 years. Our results highlight the potential environmental impacts of runoff P losses in long-term waste-amended and intensively managed subtropical coarse-textured soils. Measures to minimise soil erosion and P transfers from land to water bodies are of utmost importance