Soil chemical and fertilizer influences on soluble and medium-sized colloidal phosphorus in agricultural soils

Colloid-facilitated transport can be important for preferential transfer of phosphorus (P) through the soil profile to groundwater and may in part explain elevated P concentrations in surface water during baseflow and particularly high flow conditions. To investigate the potential for colloidal P (P_coll) mobilisation in soils, this study assessed the role of soil chemical properties and P fertilizer type on medium-sized soil P_coll (200-450 nm) and its association with soil solution soluble bioavailable P (<450 nm). Hillslope soils from three agricultural catchments were sampled and untreated and treated (cattle slurry and synthetic fertilizer) subsamples were incubated. Soil supernatants were analysed for P and soil Water Dispersible Colloids (WDC) were extracted for analysis of P and P-binding materials. Soils physicochemical properties including degree of P saturation (DPS) and P sorption properties were determined. Results indicated that medium-sized P_coll was mostly unreactive P associated to some extent to amorphous forms of Fe. Medium-sized P_coll concentrations correlated negatively with soil maximum P sorption capacity and soluble P concentrations increased with increasing DPS. In soil with low sorption properties, cattle slurry increased soluble P concentrations by 0.008-0.013 mg l^-1 and DPS but did not influence medium-sized P_coll. Synthetic fertilizer increased medium-sized reactive P_coll by 0.011 mg l^-1 (0.088 mg kg^-1 soil) and DPS in a soil with lower DPS whereas it decreased it by 0.005 mg l^-1 (0.040 mg kg^-1 soil) in a soil with higher DPS. Additional soil parameters (M3-Fe, M3-Al, M3-P, and DPS) should be included in soil testing, especially in Cambisol/Podzol soils, to identify critical areas where risks of P_coll mobilisation are important. Further research should include the roles of finer colloidal and nanoparticulate (<200 nm) soil P fractions and soluble P to inform understanding of plant uptake and assess environmental risk.

Data on initial leaf P concentrations and final dry matter yields of silage maize in response to row-injected cattle slurry

This article displays a dataset obtained in a field trial conducted in 2016 on a sandy loam and a coarse sandy soil, Denmark. Leaf phosphorus (P) and nitrogen (N) concentrations at the five-leaf stage (V5) and final dry matter (DM) yields of silage maize were determined in response to seven treatments with placed slurry below the maize row. Two row-injection methods combined with slurry acidification or addition of a nitrification inhibitor were tested. Furthermore final crop P uptake and P surplus at field level were determined. This dataset can be used to assess the effect of placed slurry with or without slurry acidification and addition of a nitrification inhibitor on silage maize yields and to enhance our knowledge on maize P uptake and P surpluses at field level. In turn this can support the design of appropriate row-injection machinery of slurry. The data supplied in this article is related to the research article entitled "Row-injected cattle slurry can replace mineral P starter fertiliser and reduce P surpluses without compromising final yields of silage maize" [1], where results from 2017 and 2018 are presented and discussed. The trials in 2016, 2017 and 2018 were conducted on the same study sites. The experimental design in 2017 and 2018 was a full-factorial design and did also include reference treatments with evenly injected slurry, whereas these reference treatments were not included in the present article.

Optimizing farmyard manure and cattle slurry applications for intensively managed grasslands based on UK-DNDC model simulations

Fertilizer applications can enhance soil fertility, pasture growth and thereby increase production. Nitrogen fertilizer has, however, been identified as a significant source of nitrous oxide (N₂O) emissions from agriculture if not used correctly and can thereby increase the environmental damage costs associated with agricultural production. The optimum use of organic fertilizers requires an improved understanding of nutrient cycles and their controls. Against this context, the objective of this research was to evaluate the scope for reducing N₂O emissions from grassland using a number of manure management practices including more frequent applications of smaller doses and different methods of application. We used a modified UK-DNDC model and N₂O emissions from grasslands at Pwllpeiran (PW), UK during the calibration period in autumn, were 1.35 kg N/ha/y (cattle slurry) and 0.95 kg N/ha/y (farmyard manure), and 2.31 kg N/ha/y (cattle slurry) and 1.08 kg N/ha/y (farmyard manure) during validation period in spring, compared to 1.43 kg N/ha/y (cattle slurry) and 0.29 kg N/ha/y (farmyard manure) during spring at North Wyke (NW), UK. The modelling results suggested that the time period between fertilizing and sampling (TPFA), rainfall and the daily average air temperature are key factors for N₂O emissions. Also, the emission factor (EF) varies spatio-temporally (0-2%) compared to uniform 1% EF assumption of IPCC. Predicted N₂O emissions were positively and linearly (R² ≈ 1) related with N loadings under all scenarios. During the scenario analysis, the use of high frequency, low dose fertilizer applications compared to a single one off application was predicted to reduce N₂O peak fluxes and overall emissions for cattle slurry during the autumn and spring seasons at the PW and NW experimental sites by 17% and 15%, respectively. These results demonstrated that an optimized application regime using outputs from the modelling approach is a promising tool for supporting environmentally-friendly precision agriculture.

Concentration of trace metals in winter wheat and spring barley as a result of digestate, cattle slurry, and mineral fertilizer application

Concentration of trace metals (TMs) is one of the most crucial factors determining the quality of cereal grains. The aim of this study was to evaluate the effect of digestate, manure, and NPK fertilization on TM concentration in grains and straw of two cereal crops-winter wheat (WW) and spring barley (SB)-and TM transfer from soil to plants. The experiment was carried out between 2012 and 2016. Every year, the same treatment was used on each plot: control (without fertilization), digestate, digestate + straw, cattle slurry, and mineral NPK fertilization. In general, fertilization increased the concentration of TMs that belong to the micronutrient group (Zn, Cu, Fe), particularly after application of digestate and cattle slurry. At the same time, fertilization, regardless of the fertilizer type, led to an increase in Cd concentration in the grain of WW in comparison with the control. Despite the increase in Cd and micronutrient content as a result of fertilization, the concentration of elements remained below the applicable standards. Among TMs, only Pb content exceeded the European Union limits. The increased concentration of Pb was, however, an effect of other factors, rather than fertilization. The results clearly indicated that the biogas digestate from anaerobic codigestion of cattle slurry and agricultural residue could be utilized as fertilizer in agricultural applications without a risk of contaminating the food chain with TMs.

Gaseous emissions and modification of slurry composition during storage and after field application: Effect of slurry additives and mechanical separation

The aim of the study was to evaluate the impact of slurry treatment by additives (EU200^® (EU200), Bio-buster^® (BB), JASS^® and sulphuric acid (H₂SO₄)) and mechanical separation on the physical-chemical characteristics, gaseous emissions (NH₃, CH₄, CO₂ and N₂O) during anaerobic storage at ∼20 °C (experiment 1) and NH₃ losses after field application (experiment 2). The treatments studied in experiment 1 were: whole slurry (WS), WS+H₂SO₄ to a pH of 6.0, WS+EU200 and WS+BB. Treatments for experiment 2 were: WS, slurry liquid fraction (LF), composted solid fraction (CSF), LFs treated with BB (LFB), JASS^® (LFJ), H₂SO₄ to a pH of 5.5 (LFA) and soil only (control). The results showed an inhibition of the degradation of organic materials (cellulose, hemicellulose, dry matter organic matter and total carbon) in the WS+H₂SO₄ relative to the WS. When compared to the WS, the WS+H₂SO₄ increased electrical conductivity, ammonium (NH₄⁺) and sulphur (S) concentrations whilst reducing slurry pH after storage. The WS+H₂SO₄ reduced NH₃ volatilization by 69% relative to the WS but had no effect on emissions of CH₄, CO₂ and N₂O during storage. Biological additive treatments (WS+EU200 and WS+BB) had no impact on slurry characteristics and gaseous emissions relative to the WS during storage. After field application, the cumulative NH₃ lost in the LF was almost 50% lower than the WS. The losses in the LFA were reduced by 92% relative to the LF. The LFB and LFJ had no impact on NH₃ losses relative to the LF. A significant effect of treatment on NH₄⁺ concentration was found at the top soil layer (0-5 cm) after NH₃ measurements with higher concentrations in the LF treatments relative to the WS. Overall, the use of the above biological additives to decrease pollutant gases and to modify slurry characteristics are questionable. Reducing slurry dry matter through mechanical separation can mitigate NH₃ losses after field application. Slurry acidification can increase the fertilizer value (NH₄⁺ and S) of slurry whilst mitigating the environmental impacts through a decrease in NH₃ losses during storage and after application.

paratuberculosis (MAP) to grassland soil and its effect on the relationship between MAP and free-living amoeba

Slurry from dairy farms is commonly used to fertilize crops and pastures. This mixture of manure, urine and water can harbor multiple microbial pathogens among which Mycobacterium avium subsp. paratuberculosis (MAP) is a major concern. Persistence of MAP in soil and infection of soil Acanthamoeba was evaluated by culture, real-time IS900 PCR, and by staining of amoeba with acid-fast and vital stains comparing soils irrigated with MAP-spiked or control dairy farm slurry. MAP DNA was detected in soil for the 8 month study duration. MAP was detected by PCR from more soil samples for plots receiving MAP-spiked slurry (n=61/66) than from soils receiving control slurry (n=10/66 samples). Vital stains verified that intracellular MAP in amoeba was viable. More MAP was found in amoeba at the end of the study than immediately after slurry application. There was no relationship between MAP presence in soil and in amoeba over time. Infection of amoeba by MAP provides a protected niche for the persistence and even possibly the replication of MAP in soils. As others have suggested, MAP-infected amoeba may act like a "Trojan horse" providing a means for persistence in soils and potentially a source of infection for grazing animals.