Factors affecting N immobilisation/mineralisation kinetics for cellulose-, glucose- and straw-amended sandy soils

The kinetics of nitrogen immobilization/mineralization for cellulose-, glucose- and straw-amended sandy soils were investigated in a series of laboratory incubations. Three Scottish soils expected to exhibit a range of biological activity were used: aloamy sand, intensively cropped horticultural soil subject to large inputs of inorganic fertilizers and pesticides (Balmalcolm - pH 7.2, organic matter 3.3%); a sandy loam soil highly enriched with organic manures and used for organic vegetable production (Strathmiglo - pH 7.1, organic matter 7.3%); and a loamy sand soil of low fertility in a zero-grazing, low intensity organic ley-arable rotation (Aldrochty - pH 6.0, organic matter 5.0%). Incubations of soils with 1000 mg cellulose-C per kg soil at 8 °C, showed peak N immobilization of 71 6, 92 6 and 65 15 mg N per g added C for the Balmalcolm (after 34 d), Strathmiglo (after 34 d) and Aldrochty soils (after 63 d). The N remineralization by the end of the incubation (>300 d) was 0, 50 and 22 mg N per g cellulose-C in the Balmalcolm, Strathmiglo soil and Aldrochty soils, respectively. Only about 30% of the N immobilization could be explained by soil microbial biomass N accumulation (much less than expected from model simulations). The C/N ratio of theextra microbial biomass was quite wide (19). Bacterial, protozoan and nematode biomass accounted for only 18%, 0.1% and 0.5% of the extra C immobilization, respectively. These data suggest that fungal biomass growth and deposition of recalcitrant fungal metabolites are the main sinks for the N immobilized. With 1000 mg glucose-C per kg added to the Balmalcolm soil, about 75 mg N per g added C were immobilized after 6 d. Under less well aerated conditions at 15 °C, immobilization of only 10-20 mg N per gadded cellulose-C took place in 2-4 weeks, but soluble organic C increased greatly. The N remineralized after 4-6 weeks

Can macrophyte harvesting from eutrophic water close the loop on nutrient loss from agricultural land?

This work was supported by the UK Natural Environment Research Council, as part of the Recycling Biomass to Agricultural LANd: Capitalising on Eutrophication (ReBALAN:CE) project (NE/K015710/1)Eutrophication is a major water pollution issue and can lead to excessive growth of aquatic plant biomass (APB). However, the assimilation of nutrients into APB provides a significant target for their recovery and reuse, and harvesting problematic APB in impacted freshwater bodies offers a complementary approach to aquatic restoration, which could potentially deliver multiple wider ecosystem benefits. This critical review provides an assessment of opportunities and risks linked to nutrient recovery from agriculturally impacted water-bodies through the harvesting of APB for recycling and reuse as fertilisers and soil amendments. By evaluating the economic, social, environmental and health-related dimensions of this resource recovery from 'waste' process we propose a research agenda for closing the loop on nutrient transfer from land to water. We identify that environmental benefits are rarely, if ever, prioritised as essential criteria for the exploitation of resources from waste and yet this is key for addressing the current imbalance that sees environmental managers routinely undervaluing the wider environmental benefits that may accrue beyond resource recovery. The approach we advocate for the recycling of 'waste' APB nutrients is to couple the remediation of eutrophic waters with the sustainable production of feed and fertiliser, whilst providing multiple downstream benefits and minimising environmental trade-offs. This integrated 'ecosystem services approach' has the potential to holistically close the loop on agricultural nutrient loss, and thus sustainably recover finite resources such as phosphorus from waste.Publisher PDFPeer reviewe

Can macrophyte harvesting from eutrophic water close the loop on nutrient loss from agricultural land?

Eutrophication is a major water pollution issue and can lead to excessive growth of aquatic plant biomass (APB). However, the assimilation of nutrients into APB provides a significant target for their recovery and reuse, and harvesting problematic APB in impacted freshwater bodies offers a complementary approach to aquatic restoration, which could potentially deliver multiple wider ecosystem benefits. This critical review provides an assessment of opportunities and risks linked to nutrient recovery from agriculturally impacted water-bodies through the harvesting of APB for recycling and reuse as fertilisers and soil amendments. By evaluating the economic, social, environmental and health-related dimensions of this resource recovery from 'waste' process we propose a research agenda for closing the loop on nutrient transfer from land to water. We identify that environmental benefits are rarely, if ever, prioritised as essential criteria for the exploitation of resources from waste and yet this is key for addressing the current imbalance that sees environmental managers routinely undervaluing the wider environmental benefits that may accrue beyond resource recovery. The approach we advocate for the recycling of 'waste' APB nutrients is to couple the remediation of eutrophic waters with the sustainable production of feed and fertiliser, whilst providing multiple downstream benefits and minimising environmental trade-offs. This integrated 'ecosystem services approach' has the potential to holistically close the loop on agricultural nutrient loss, and thus sustainably recover finite resources such as phosphorus from waste