Early effects of surface liming on soil P biochemistry and dynamics in extensive grassland

Liming effects on soil phosphorus (P) availability via biological P cycling are not clear. We conducted an 18-month field experiment on a long-term (60 years +) permanent fertilized grassland in a relatively dry environment. The aim was to examine the impact of liming on P biochemical processes and dynamics. Lime was applied at the beginning of the experiment to produce a soil pH range of 5.4–7.0, with no fertilizer P treatments. Soil sampling was conducted throughout the experimentation period at 0–75 mm. All soils were analysed for moisture content, pH, Olsen P, resin P, exchangeable aluminium (Al), microbial biomass P (MBP) and enzyme activities. At the final sampling, the soil samples were analysed for total C, total N and anaerobic mineralizable N (AMN). A sequential P fractionation was conducted for 0–30 mm depth samples. Liming effects on soil pH and P processes were limited to the surface 30 mm only, where labile inorganic P (Pᵢ) fraction increased by 42% at pH 7.0 compared to pH 5.4, while labile and moderately labile organic P (Pₒ) decreased by 33% and 25%, respectively. Strong positive relationships were found between microbial P and: soil pH, labile Pᵢ, total C and AMN. Absolute activities of acid and alkaline phosphomonoesterases were not affected by liming. However, their specific activity decreased by 47% and 28%, respectively at pH 7.0 compared to pH 5.4. Absolute enzyme activity of phosphodiesterase correlated strongly and positively with labile Pᵢ. Our findings demonstrate that liming enhances plant P availability under field conditions in long-term fertilized extensive grassland. However, the effects are limited to near-surface depths in the soil

Biowastes promote essential oil production on degraded soils

Biowastes (wastes of biological origin) can improve soil fertility but may render the land unsuitable for food production because they introduce contaminants, including heavy metals, pathogens and xenobiotics. We investigated whether sewage waste (pond sludge from Kaikoura and anaerobically-digested biosolids from Christchurch) and Dairy Shed Effluent (DSE) could improve degraded soils for the production of essential oils (EOs). We grew lavender (Lavandula angustifolia Mill.), rosemary (Rosmarinus officinalis L.) and thyme (Thymus vulgaris L.) in two greenhouse experiments in Lismore stony silt loam soil (LSL) amended with pond sludge or biosolids (500–4500 kg N ha⁻¹ equiv.) or DSE (200 kg N ha⁻¹ equiv.). Pond sludge application (2800 kg N ha⁻¹ equiv.) increased the biomass of L. angustifolia and T. vulgaris by 60 % and 62 %, respectively. Christchurch biosolids application up to 1500 kg N ha⁻¹ equiv. to L. angustifolia and R. officinalis increased the biomass of both plant species by up to 86 % and 80 %, respectively. The effect of treatments on EO concentration was insignificant in most cases except for DSE (200 kg N ha⁻¹ equiv.) and Christchurch biosolids at rates >1500 kg N ha⁻¹ equiv., which decreased the EO concentrations in R. officinalis and L. angustifolia. This decrease in EO concentration offset some of the increase in EO production resulting from the increased biomass of the biowaste-amended plants. The ideal EO production increase occurred when Christchurch biosolids were applied at 1500 kg N ha⁻¹ equiv. The benefits of biowaste additions to degraded soils are greater than would occur if they were added to high-fertility soils. Heavy metal concentrations in all treatments were below food safety standards. Biowastes could rebuild degraded soils and produce valuable EOs, thereby reducing the economic and environmental costs of biowaste disposal, while improving soil fertility and generating revenue from otherwise underproductive land

The effect of lignite on nitrogen mobility in a low-fertility soil amended with biosolids and urea

© 2015 Elsevier B.V. Lignite has been proposed as a soil amendment that reduces nitrate (NO₃⁻) leaching from soil. Our objective was to determine the effect of lignite on nitrogen (N) fluxes from soil amended with biosolids or urea. The effect of lignite on plant yield and elemental composition was also determined. Batch sorption and column leaching experiments were followed by a lysimeter trial where a low fertility soil was amended with biosolids (400kgN/ha equivalent) and urea (200kgN/ha equivalent). Treatments were replicated three times, with and without lignite addition (20t/ha equivalent). Lignite did not reduce NO₃⁻ leaching from soils amended with either biosolids or urea. While lignite decreased NO₃⁻ leaching from an unamended soil, the magnitude of this effect was not significant in an agricultural context. Furthermore, lignite increased cumulative N₂O production from soils receiving urea by 90%. Lignite lessened the beneficial growth effects of adding biosolids or urea to soil. Further work could investigate whether coating urea granules with lignite may produce meaningful environmental benefits