Treating farm dairy effluent with poly-ferric sulphate dramatically reduces phosphorus and E. coli leaching through subsurface drains—A physical drainage model study

Land application of farm dairy effluent (FDE) may lead to water contamination, by contaminants such as phosphorus (P) and E. coli. A new FDE treatment technology using poly-ferric sulphate (PFS) has been developed to recycle wastewater in FDE for washing the farmyard. A physical drainage model study was conducted to investigate the effect of treating FDE with PFS on phosphorus and E. coli leaching through model subsurface drains. Dissolved reactive phosphorus (DRP) and total phosphorus (TP) leaching losses from untreated effluent (FDE) averaged 3.48 kg P ha⁻¹ and 11.44 kg P ha⁻¹, respectively. The application of PFS-treated effluent (TE) resulted in significantly lower DRP and TP leaching losses at 0.24 kg P ha⁻¹ and 4.52 kg P ha⁻¹ for fresh TE and 0.27 kg P ha⁻¹ and 6.31 kg P ha⁻¹ for TE stored for 3 weeks before application (TE-S). Cumulative DRP lost to drainage water from the TE and TE-S treatments was 93.1% and 92.2% lower than that from the FDE treatments. Compared with the FDE treatment, there was a 98.27% and 99.99% reduction in E. coli in the drainage water from the TE and TE-S treatments. Plant biomass and P uptake were not affected by the effluent treatments. These results indicate that land application of PFS-treated effluent, fresh or stored, on drained pasture soils can produce significant environmental benefits by reducing the concentration and amount of P and E. coli in the drainage water, without adversely impacting plant growth.     

A new method to treat farm dairy effluent to produce clarified water for recycling and to reduce environmental risks from the land application of effluent

Purpose

There is increasing public concern about the amount of fresh water used on New Zealand dairy farms and the adverse impacts that farm dairy effluent (FDE) has on the environment. FDE mainly consists of fresh water (99%) with a small amount of solid material (1%). There is an opportunity to treat FDE to remove the colloidal solid material and recycle the water to wash the farm yard.

Materials and methods

A new method of treating FDE has been developed. The method uses a coagulant to flocculate and settle the colloidal particles in the FDE and thus produce the clarified water for recycling. The research and development programme involved three stages: (i) standard laboratory jar tests to establish the amount of coagulant required to treat the FDE, (ii) large tank tests to confirm the effectiveness of the coagulant at a larger scale and (iii) construction and testing of two pilot plants. A pasture field trial was conducted to test the effect of the clarified water and treated effluent on plant production.

Results and discussion

The new method of treating FDE was highly successful in removing the colloidal material and producing clarified water that can be recycled to wash the farm yard. The average turbidity of the clarified water from the first pilot plant was 52 nephelometric turbidity units (NTU) (a 97% reduction in NTU compared to the original FDE) and the average Escherichia coli concentration was 9 cfu per 100 mL (a 99.99% reduction compared to the original untreated FDE). The average total-phosphorus (P) concentration of the clarified water was 1.8 g m^?3 (94% reduction), dissolved reactive phosphorus (DRP) was <?0.1 g m^?3 (99% reduction) and total nitrogen (N) was reduced by >?70% (from 200 to 61 g m^?3). The average turbidity of the clarified water from the second pilot plant was <?20 NTU (a 99.5% reduction). There was no adverse impact from the land application of the clarified water or the treated FDE on plant growth.

Conclusions

A new method for treating farm dairy effluent was successfully developed that produced clarified water that could be recycled to wash the farm yard and had a lower potential risk of environmental impacts when applied to land than untreated FDE. Land application of the clarified water or the treated FDE had no adverse impact on plant growth.

     

Nitrous oxide emissions from dairy farm effluent applied to a New Zealand pasture soil

A field experiment on permanent ryegrass–white clover pasture at AgResearch's Ruakura dairy farm near Hamilton, New Zealand quantified nitrous oxide (N₂O) emissions from different types of dairy effluent applied to soil at three seasons and evaluated the potential of dicyandiamide (DCD) (a nitrification inhibitor) to decrease gaseous N₂O emissions. Fresh or stored manure and farm dairy effluent (FDE; from dairy shed washings), with or without DCD (10 kg/ha), were applied at approximately 100 kg N/ha to plots on a well‐drained soil on volcanic parent material. A field chamber technique was used to measure N₂O emissions. Application of manure or FDE, both in fresh and stored forms, to pasture generally increased N₂O emissions. Overall N₂O emission factors (EF) varied between 0.01% and 1.87%, depending on application season and effluent type. EFs in spring and autumn were greater than those in summer (P < 0.05). Among the effluents, N₂O EFs were largest from fresh FDE (1.65%) during the spring measurement period, stored manure (1.87%) during the autumn and stored FDE (0.25%) during the summer. DCD was effective in decreasing N₂O EFs from fresh FDE, fresh manure, stored FDE and stored manure by 40–80%, 69–76%, 24–84% and 60–70%, respectively. DCD reduced N₂O emissions during the spring and autumn seasons more effectively than in the summer season.     

Use of nitrogen process inhibitors for reducing gaseous nitrogen losses from land-applied farm effluents

Applications of dairy farm effluents to land may lead to ammonia (NH₃) volatilization and nitrous oxide (N₂O) emissions. Nitrogen (N) transformation process inhibitors, such as urease inhibitors (UIs) and nitrification inhibitors (NIs), have been used to reduce NH₃ and N₂O losses derived from agricultural N sources. The objective of this study was to examine the effects of amending dairy effluents with UI (N-(n-butyl) thiophosphoric triamide (NBTPT)) and NI (dicyandiamide (DCD)) on NH₃ and N₂O emissions. Treatments included either fresh or stored manure and either fresh or stored farm dairy effluent (FDE), with and without NBTPT (0.25 g kg^?1 N) or DCD (10 kg ha^?1), applied to a pasture on a free-draining volcanic parent material soil. The nutrient loading rate of FDE and manure, which had different dry matter contents (about 2 and 11 %, respectively) was 100 kg N ha^?1. Application of manure and FDE led to NH₃ volatilization (15, 1, 17 and 0.4 % of applied N in fresh manure, fresh FDE, stored manure and stored FDE, respectively). With UI (NBTPT), NH₃ volatilization from fresh manure was significantly (P?<?0.05) decreased to 8 % from 15 % of applied N, but the UI did not significantly reduce NH₃ volatilization from fresh FDE. The N₂O emission factors (amount of N₂O–N emitted as a percentage of applied N) for fresh manure, fresh FDE and stored FDE were 0.13?±?0.02, 0.14?±?0.03 and 0.03?±?0.01 %, respectively. The NI (DCD) was effective in decreasing N₂O emissions from stored FDE, fresh FDE and fresh manure by 90, 51 and 46 % (P?<?0.05), respectively. All types of effluent increased pasture production over the first 21 days after application (P?<?0.05). The addition of DCD resulted in an increase in pasture production at first harvest on day 21 (P?<?0.05). This study illustrates that UIs and NIs can be effective in mitigating NH₃ and N₂O emissions from land-applied dairy effluents.     

Impact of biochar coated with magnesium (hydr)oxide on phosphorus leaching from organic and mineral soils

Purpose

Recent research suggests that Swedish organic arable soils have been under-recognized as a potential source of phosphorus (P) loading to water bodies. The aim of this study was to compare P losses through leaching from organic and high-fertility mineral soils. In addition, the effectiveness of a magnesium-salt-coated biochar applied below the topsoil as a mitigation strategy for reducing P losses was evaluated.

Materials and methods

Phosphorus leaching was measured from four medium- to high-P arable soils, two Typic Haplosaprists (organic 1 and 2), a Typic Hapludalf (sand), and an unclassified loam textured soil (loam), in a 17-month field study utilizing 90-cm-long lysimeters. A magnesium-salt-coated biochar was produced and characterized using X-ray powder diffraction (XPD), scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), and X-ray adsorption (XANES) spectroscopy, and its phosphate adsorption capacity was determined at laboratory scale. It was also applied as a 3-cm layer, 27 cm below the soil surface of the same lysimeters and examined as a mitigation measure to reduce P leaching.

Results and discussion

Total-P loads from the 17-month, unamended lysimeters were in the order of organic 2 (1.2 kg ha^?1)?>?organic 1 (1.0 kg ha^?1)?>?sand (0.3 kg ha^?1)?>?loam (0.2 kg ha^?1). Macropore flow, humic matter competition for sorption sites, and fewer sorption sites likely caused higher P losses from the organic soils. Analysis by XRD and SEM revealed magnesium was primarily deposited as periclase (MgO) on the biochar surface but hydrated to brucite (Mg(OH)₂) in water. The Langmuir maximum adsorption capacity (Q_max) of the coated biochar was 65.4 mg P g^?1. Lysimeters produced mixed results, with a 74% (P?<?0.05), 51% (NS), and 30% (NS) reduction in phosphate-P from the organic 1, organic 2, and sand, respectively, while P leaching increased by 230% (NS) from the loam.

Conclusions

The findings of this study indicate that P leached from organic arable soils can be greater than from mineral soils, and therefore, these organic soils require further investigation into reducing their P losses. Metal-enriched biochar, applied as an adsorptive layer below the topsoil, has the potential to reduce P losses from medium- to high-P organic soils but appear to be less useful in mineral soils.

     

Effects of form of effluent,season and urease inhibitor on ammonia volatilization from dairy farm effluent applied to pasture

Purpose

With land application of farm effluents from cows during housing or milking as an accepted practice, there are increasing concerns over its effect on nitrogen (N) loss through ammonia (NH₃) volatilization. Understanding the relative extent and seasonal variation of NH₃ volatilization from dairy effluent is important for the development of management practices for reducing NH₃ losses. The objectives of this study were to determine potential NH₃ losses from application of different types of dairy effluent (including both liquid farm dairy effluent (FDE) and semi-solid dairy farm manure) to a pasture soil during several contrasting seasons and to evaluate the potential of the urease inhibitor (UI)—N-(n-butyl) thiophosphoric triamide (NBTPT, commercially named Agrotain^®) to reduce gaseous NH₃ losses.

Material and methods

Field plot trials were conducted in New Zealand on an established grazed pasture consisting of a mixed perennial ryegrass (Lolium perenne L.)/white clover (Trifolium repens L.) sward. An enclosure method, with continuous air flow, was used to compare the effects of treatments on potential NH₃ volatilization losses from plots on a free-draining volcanic parent material soil which received either 0 (control) or 100 kg N ha^?1 as FDE or manure (about 2 and 15 % of dry matter (DM) contents in FDE or manure, respectively) with or without NBTPT (0.25 g NBTPT kg^?1 effluent N). The experiment was conducted in the spring of 2012 and summer and autumn of 2013.

Results and discussion

Results showed that application of manure and FDE, both in fresh and stored forms, potentially led to NH₃ volatilization, ranging from 0.6 to 19 % of applied N. Difference in NH₃ losses depended on the season and effluent type. Higher NH₃ volatilization was observed from both fresh and stored manure, compared to fresh and stored FDE. The difference was mainly due to solid contents. The losses of NH₃ were closely related to NH₄ ⁺-N content in the two types of manure. However, there was no relationship between NH₃ losses and NH₄ ⁺-N content in either type of FDE. There was no consistent seasonal pattern, although lower NH₃ losses from fresh FDE and stored FDE applied in spring compared to summer were observed. Potential NH₃ losses from application of fresh FDE or manure were significantly (P?<?0.05) reduced by 27 to 58 % when NBTPT was added, but the UI did not significantly reduce potential NH₃ volatilization from stored FDE or manure.

Conclusions

This study demonstrated that NH₃ losses from application of FDE were lower than from manure and that UIs can be effective in mitigating NH₃ emissions from land application of fresh FDE and manure. Additionally, reducing the application of FDE in summer can also potentially reduce NH₃ volatilization from pasture soil.     

Manure management practices applied to a seven‐course rotation on a sandy soil: effects on nitrate leaching

This experiment tested whether it was possible to incorporate broiler litter (BL) or cattle farmyard manure (FYM) into a 7‐yr arable rotation on a sandy soil without causing an increase in nitrate‐nitrogen (NO₃‐N) leaching. Four manure treatments (with adjusted fertilizer inputs), varying in frequency and timing of application, were imposed on the rotation and compared with a control that received inorganic fertilizer according to recommended rates. Over seven winters, the annual average NO₃‐N leached from the inorganic fertilizer treatment (control) was 39 kg/ha in 183 mm drainage. Total manure N loadings over the period of the experiment ranged between 557 and 1719 kg/ha (80–246 kg/ha/yr) for the four treatments. Three of the four manure treatments significantly increased NO₃‐N leaching over the rotation (P < 0.001). Annual applications of FYM (1719 kg/ha manure N or 246 kg/ha/yr) increased NO₃‐N leaching by 39%. We hypothesize that this was due to increased mineralization of the organic N accumulating from repeated FYM applications. BL applied each year (1526 kg/ha manure N or 218 kg N/ha/yr) increased NO₃‐N leaching by 52% above the control; BL applied 5 of 7 yr (972 kg/ha manure N or 139 kg N/ha/yr on average) and including inadvisable autumn applications increased leaching by 50%. BL applied in late winter or early spring every 2–3 yr (557 kg/ha manure N or 80 kg N/ha/yr on average) resulted in NO₃‐N leaching similar to the control. This suggests that to avoid additional NO₃‐N leaching from manure use in an arable rotation, manure should not be applied every year and autumn applications should be avoided; there are real challenges where manure is used on an annual basis.     

Coupled effects of biochar use and farming practice on physical properties of a salt-affected soil with wheat–maize rotation

Purpose

Being carbon-rich and porous, biochar has the potential to improve soil physical properties, so does conventional farming practice. Here, a field trial was conducted to investigate the combined effects of biochar use and farming practice on the physical properties of a salt-affected compact soil for wheat–maize rotation in the Yellow River Delta region.

Materials and methods

Salix fragilis L. was used as feedstock to produce biochar in the field via aerobic carbonization at an average temperature of 502 °C, terminated by a water mist spray, for use as a soil amendment at 0, 1, 2, and 4 g kg^?1 doses (CK, T1, T2, and T3, respectively). Farming practices included rotary tillage/straw returning for wheat sowing, spring irrigation, no-tillage seeding of maize, and autumn irrigation. Both cutting ring and composite samples of the soil were collected at four stages of wheat–maize rotation (22, 238, 321, and 382 d after the benchmark date of land preparation for wheat sowing) for the determination of soil properties by established methods.

Results and discussion

Rotary tillage/straw returning reduced soil bulk density (BD) from 1.48 to 1.27 g cm^?3 (CK) and 1.14 g cm^?3 (T3) and increased saturated hydraulic conductivity (Ks) from 0.05?×?10^?5 to 0.75?× 10^?5 cm s^?1 (CK) and 1.25?× 10^?5 cm s^?1 (T3). This tillage effect on BD and Ks gradually disappeared due to the disturbance from the subsequent farming practice. Biochar use lessened the disturbance. At maize harvest, BD was 1.47 (CK) vs. 1.34 g cm^?3 (T3), and Ks was 0.06?×?10^?5 (CK) vs. 0.28?×?10^?5 cm s^?1(T3); in comparison with CK, T3 increased Na⁺ leaching by 65%, Cl^? leaching by 98%, organic carbon content by 40.3%, and water-stable aggregates (0.25–2 mm) by 38%, indicating an improvement in soil properties.

Conclusions

Biochar use and rotary tillage improved soil physical properties (BD, Ks) and favored soil aeration, water filtration, and salt leaching, which further helped the accumulation of soil organic carbon, the formation of water-stable aggregates, and the amelioration of salt-affected compact soil.

     

Nitrogen Leaching of Two Forest Ecosystems in a Karst Watershed

Karst watersheds are a major source of drinking water in the European Alps. These watersheds exhibit quick response times and low residence times, which might make karst aquifers more vulnerable to elevated nitrogen (N) deposition than non-karst watersheds. We summarize 13 years of monitoring NO ₃ ^? , NH ₄ ⁺ , and total N in two forest ecosystems, a Norway spruce (Picea abies (L.) Karst.) forest on Cambisols/Stagnosols (IP I) and a mixed beech (Fagus sylvatica L.) spruce forest on Leptosols (IP II). N fluxes are calculated by multiplying concentrations, measured in biweekly intervals, with hydrological fluxes predicted from a hydrological model. The total N deposition in the throughfall amounts to 26.8 and 21.1 kg/ha/year in IP I and IP II, respectively, which is high compared to depositions found in other European forest ecosystems. While the shallow Leptosols at IP II accumulated on average 9.2 kg/ha/year of N between 1999 and 2006, the N budgets of the Cambisols/Stagnosols at IP I were equaled over the study period but show high inter-annual variation. Between 1999 and 2006, on average, 9 kg/ha/year of DON and 20 kg/ha/year of DIN were output with seepage water of IP I but only 4.5 kg/ha/year of DON and 7.7 kg/ha/year of DIN at IP II. Despite high DIN leaching, neither IP I nor IP II showed further signs of N saturation in their organic layer C/N ratios, N mineralization, or leaf N content. The N budget over all years was dominated by a few extreme output events. Nitrate leaching rates at both forest ecosystems correlated the most with years of above average snow accumulation (but only for IP I this correlation is statistically significant). Both snow melt and total annual precipitation were most important drivers of DON leaching. IP I and IP II showed comparable temporal patterns of both concentrations and flux rates but exhibited differences in magnitudes: DON, NO ₃ ^? , and NH ₄ ⁺ inputs peak in spring, NH ₄ ⁺ showed an additional peak in autumn; the bulk of the annual NO ₃ ^? and DON output occurred in spring; DON, NO ₃ ^? , and NH ₄ ⁺ output rates during winter months were low. The high DIN leaching at IP I was related to snow cover effects on N mineralization and soil hydrology. From the year 2004 onwards, disproportional NO ₃ ^? leaching occurred at both plots. This was possibly caused by the exceptionally dry year 2003 and a small-scale bark beetle infestation (at IP I), in addition to snow cover effects. This study shows that both forest ecosystems at Zöbelboden are still N limited. N leaching pulses, particularly during spring, dictate not only annual but also the long-term N budgets. The overall magnitude of N leaching to the karst aquifer differs substantially between forest and soil types, which are found in close proximity in the karstified areas of the Northern Limestone Alps in Austria.     

Residue retention mitigated short-term adverse effect of clear-cutting on soil carbon and nitrogen dynamics in subtropical Australia

Purpose

This study aimed to investigate the benefits of retaining harvest residues on the dynamics of soil C and N pools following clear-cut harvesting of a slash pine plantation in South East Queensland of subtropical Australia.

Materials and methods

Immediately following clear-cut harvesting, macro-plots (10?×?10 m) were established on a section of the plantation in a randomised complete block design with four blocks and three treatments: (1) residue removal (RR₀), (2) single level of residue retention (RR₁) and (3) double level of residue retention (RR₂). Soils were sampled at 0, 6, 12, 18 and 24 months following clear-cutting and analysed for total C and N, microbial biomass C (MBC) and N (MBN), hot water–extractable organic C (HWEOC), hot water–extractable organic N (HWEON), NH₄⁺–N and NO_x^?–N.

Results and discussion

The study showed that although soil total C decreased in the first 12 months following clear-cutting, harvest residue retention increased soil total C and N by 45% (p?<?0.001) and 32% (p?<?0.001), respectively, over the 12–24 months. NH₄⁺–N, HWEOC, HWEON and MBC showed initial surges in the first 6 months irrespective of residue management, which declined after the 6th month. However, residue retention significantly increased HWEOC and HWEON over the 12–24 months (p?<?0.001).

Conclusions

This study demonstrated that harvest residue retention during the inter-rotation period can minimise large changes in C and nutrient pools, and can even increase soil C and nutrient pools for the next plantation rotation.

     

Soil and nutrients losses under different crop covers in vertisols of Central India

Purpose

Accelerated erosion removes fertile top soil along with nutrients through runoff and sediments, eventually affecting crop productivity and land degradation. However, scanty information is available on soil and nutrient losses under different crop covers in a vertisol of Central India. Thus, a field experiment was conducted for 4 years (2010–2013) to study the effect of different crop cover combinations on soil and nutrient losses through runoff in a vertisol.

Materials and methods

Very limited information is available on runoff, soil, and nutrient losses under different vegetative covers in a rainfed vertisol. Thus, the hypothesis of the study was to evaluate if different crop cover combinations would have greater impact on reducing soil and nutrient losses compared to control plots in a vertisol.

This experiment consisted of seven treatment combinations of crop covers namely soybean (Glycine max) (CC₁), maize (Zea mays) (CC₂), pigeon pea (Cajanus cajan) (CC₃), soybean (Glycine max)?+?maize (Zea mays) ??1:1 (CC₄), soybean (Glycine ma x))?+?pigeon pea (Cajanus cajan) ?2:1 (CC₅), maize (Zea mays)?+?pigeon pea (Cajanus cajan) ??1:1 (CC₆), and cultivated fallow (CC₇). The plot size was 10?×?5 m with 1% slope, and runoff and soil loss were measured using multi-slot devisor. All treatments were arranged in a randomized block design with three replications.

Results and discussion

Results demonstrated that the runoff and soil loss were significantly (p?<?0.05) higher (289 mm and 3.92 Mg ha^?1) under cultivated fallow than those in cropped plots. Among various crop covers, sole pigeon pea (CC₃) recorded significantly higher runoff and soil loss (257 mm and 3.16 Mg ha^?1) followed by that under sole maize (CC₂) (235 mm and 2.85 Mg ha^?1) and the intercrops were in the order of maize?+?pigeon pea (211 mm and 2.47 Mg ha^?1) followed by soybean?+?maize (202 mm and 2.38 Mg ha^?1), and soybean?+?pigeon pea (195 mm and 2.15 Mg ha^?1). The lowest runoff and soil loss were recorded under soybean sole crop (194 mm and 2.27 Mg ha^?1). The data on nutrient losses indicated that the highest losses of soil organic carbon (SOC) (25.83 kg ha^?1), total nitrogen (N), phosphorus (P), and potassium (K) (7.76, 0.96, 32.5 kg ha^?1) were recorded in cultivated fallow (CC₇) as compared to those from sole and intercrop treatments. However, sole soybean and its intercrops recorded the minimum losses of SOC and total N, P, and K, whereas the maximum losses of nutrients were recorded under pigeon pea (CC₃). The system productivity in terms of soybean grain equivalent yield (SGEY) was higher (p?<?0.05) from maize?+?pigeon pea (3358 kg ha^?1) followed by that for soybean?+?pigeon pea (2191 kg ha^?1) as compared to sole soybean. Therefore, maize?+?pigeon pea (1:1) intercropping is the promising option in reducing runoff, soil-nutrient losses, and enhancing crop productivity in the hot sub-humid eco-region.

Conclusions

Study results highlight the need for maintenance of suitable vegetative cover as of great significance to diffusing the erosive energy of heavy rains and also safe guarding the soil resource from degradation by water erosion in vertisols.

     

Interactive influence of livestock grazing and manipulated rainfall on soil properties in a humid tropical savanna

Purpose

The effect of uncontrolled grazing and unpredictable rainfall pattern on future changes in soil properties and processes of savanna ecosystems is poorly understood. This study investigated how rainfall amount at a gradient of 50%, 100%, and 150% would influence soil bulk density (ρ), volumetric water content (θ_v), carbon (C), and nitrogen (N) contents in grazed (G) and ungrazed (U) areas.

Materials and methods

Rainfall was manipulated by 50% reduction (simulating drought—50%) and 50% increase (simulating abundance—150%) from the ambient (100%) in both G and U areas. Plots were named by combining the first letter of the area followed by rainfall amount, i.e., G150%. Samples for soil ρ, C, and N analysis were extracted using soil corer (8 cm diameter and 10 cm height). Real-time θ_v was measured using 5TE soil probes (20 cm depth). The EA2400CHNS/O and EA2410 analyzers were used to estimate soil C and N contents respectively.

Results and discussion

The interaction between grazing and rainfall manipulation increased θ_v and C but decreased N with no effect on ρ and C:N ratio. Rainfall reduction (50%) strongly affected most soil properties compared to an increase (150%). The highest (1.241?±?0.10 g cm^?3) and lowest (1.099?±?0.05 g cm^?3) ρ were in the G50% and U150% plots respectively. Soil θ_v decreased by 34.0% (grazed) and 25.8% (ungrazed) due to drought after rainfall cessation. Soil ρ increased with grazing due to trampling effect, therefore reducing infiltration of rainwater and soil moisture availability. Consequently, soil C content (11.45%) and C:N ratio (24.68%) decreased, whereas N increased (7.8%) in the grazed plots due to reduced C input and decomposition rate.

Conclusions

The combined effect of grazing and rainfall variability will likely increase soil θ_v, thereby enhancing C and N input. Grazing during drought will induce water stress that will destabilize soil C and N contents therefore affecting other soil properties. Such changes are important in predicting the response of soil properties to extreme rainfall pattern and uncontrolled livestock grazing that currently characterize most savanna ecosystems.

     

Toxicity of imidacloprid to the earthworm Eisenia andrei and collembolan Folsomia candida in three contrasting tropical soils

Purpose

Imidacloprid is a widely used seed dressing insecticide in Brazil. However, the effects of this pesticide on non-target organisms such as soil fauna still present some knowledge gaps in tropical soils. This study aimed to assess the toxicity and risk of imidacloprid to earthworms Eisenia andrei and collembolans Folsomia candida in three contrasting Brazilian tropical soils.

Materials and methods

Acute and chronic toxicity assays were performed in the laboratory with both species in a tropical artificial soil (TAS) and in two natural soils (Oxisol and Entisol), at room temperature of 25 °C. The ecological risk was calculated for each species and soil by using the toxicity exposure ratio (TER) and hazard quotient (HQ) approaches.

Results and discussion

Acute toxicity for collembolans and earthworms was higher in Entisol (LC₅₀?=?4.68 and 0.55 mg kg^?1, respectively) when compared with TAS (LC₅₀?=?10.8 and 9.18 mg kg^?1, respectively) and Oxisol (LC_{50collembolans}?=?25.1 mg kg^?1). Chronic toxicity for collembolans was similar in TAS and Oxisol (EC_{50 TAS}?=?0.80 mg kg^?1; EC_{50 OXISOL}?=?0.83 mg kg^?1), whereas higher toxicity was observed in Entisol (EC₅₀?=?0.09 mg kg^?1). In chronic assays with earthworms, imidacloprid was also more toxic in Entisol (EC₅₀?=?0.21 mg kg^?1) when compared to TAS (EC₅₀?=?1.89 mg kg^?1). TER and HQ values indicated a significant risk of exposure of the species to imidacloprid in all soils tested, and the risk in Entisol was at least six times higher than in Oxisol or TAS.

Conclusions

The toxicity and risk of imidacloprid varied significantly between tropical soils, being the species exposure to this pesticide particularly hazardous in very sandy natural soils such as Entisol.

     

Turbulent mixing accelerates PAH desorption due to fragmentation of sediment particle aggregates

Purpose

Stripping contaminants from sediments with granular activated carbon (GAC) is a promising remediation technique in which the effectiveness depends on the rate of contaminant extraction from the sediment by the GAC. The purpose of the present study was to investigate the effect of mixing intensity on the short-term extraction rate of polycyclic aromatic hydrocarbons (PAHs) from contaminated sediment.

Materials and methods

PAH desorption from sediment at a wide range of rotational speeds (min^?1; rotations per minute (rpm)) was monitored by uptake in Tenax polymeric resins using a completely mixed batch reactor. Desorption data were interpreted using a radial diffusion model. Desorption parameters obtained with the radial diffusion model were correlated with particle size measurements and interpreted mechanistically.

Results and discussion

Fast desorption rate constants, D _e /r ², with D _e the effective diffusion coefficient and r the particle radius, ranged from 3.7 × 10^?3 to 1.1 × 10^?1 day^?1 (PHE) and 6 × 10^?6 to 1.9 × 10^?4 day^?1 (CHR), respectively, and increased with the intensity of mixing. The D _e /r ² values would correspond to D _e ranges of 1.8 × 10^?14–1.2 × 10^?16 m² × day^?1 and 1.8 × 10^?12–3.7 × 10^?15 m² × day^?1, assuming fast desorption from the measured smallest particle size (9 μm) classes at 200 and 600 rpm, respectively.

Conclusions

Desorption of PAHs was significantly accelerated by a reduction of particle aggregate size caused by shear forces that were induced by mixing. The effective intra-particle diffusion coefficients, D _e , were larger at higher mixing rates.

     

Effect of plantain on nitrous oxide emissions and soil nitrification rate in pasture soil under a simulated urine patch in Canterbury,New Zealand

Purpose

The aim of this research was to quantify the effect of plantain (Plantago lanceolata L.) on soil nitrification rate, functional gene abundance of soil ammonia oxidisers, and the concomitant effect on nitrous oxide emissions from urine patches in a shallow, free-draining soil in Canterbury during late autumn/winter season.

Materials and methods

Urine was collected from dairy cows grazing either ryegrass/white clover (RGWC), 30% plantain (P30) mixed in with RGWC or 100% plantain (P100) pasture, and applied at two rates (700 or 450 kg N ha^?1) to intact soil blocks growing either RGWC, P30 or P100 pasture.

Results and discussion

Results showed that increased plantain content reduced N-concentration in urine from 7.2 in RGWC urine to 4.5 and 3.7 g N L^?1 in P30 and P100 urine, respectively. Total N₂O emissions and emission factors (EF₃) from urine-treated pastures were low, <?2 kg N ha^?1 and <?0.22%, respectively. Urine application at the lower urine N-loading rate of 450 kg N ha^?1 (i.e. representative of that in a P30 urine patch) resulted in 30% lower N₂O emissions (P?<?0.01) and 35% lower soil nitrate concentrations (P?<?0.001) compared to those at the higher urine loading rate of 700 kg N ha^?1 (i.e. representative of that in a RGWC urine patch). Increasing plantain content in the pasture sward from 0 to 30% and 100% with urine N applied at the same loading rate did not reduce N₂O emissions or nitrification compared to the standard ryegrass-white clover pasture. Cow urine derived from the different pasture diets had no effect on N₂O emissions, N transformation or ammonia-oxidiser abundance in soil compared to the RGWC urine applied at the same rate.

Conclusions

The main effect of plantain in this study appears to be related to the reduction in urine N-loading rate, rather than factors related to urine properties or plantain-soil interactions.

     

Impact of soil organic matter on calcium carbonate equilibrium and forms of Pb in water extracts from Kastanozem complex

Purpose

Accounting for ionic strength and ion association, the degree of calculated supersaturation with CaCO₃ of gleyic solonetz and molic solonetz soil solution is high. The purpose of the research was to reveal the effect of the water-dissolved organic matter (DOM) on the calcium carbonate equilibrium (CCE) in soil solution, to create a thermodynamic model of carbonate association and complexation with DOM and heavy metals (HMs), and to correct the principal of soil management.

Materials and methods

Object of research—Kastanozem complex of the dry steppe, Rostov Oblast, Russia. The water extraction of soluble salts was made at the water-to soil-ratio 5:1 and analyzed using standard methods. DOM content was determined by Strosser (J Agrobiol 27:49–60, 2010). The soil solution macro-ion equilibrium composition was calculated using ION-2 program (Endovitsky et al. 2009). DOM role in soil solution supersaturation with СаСО₃ was assessed, comparing C content in real solution and in identical artificial solution prepared without organic matter. Taking into account the ion association, the molar fractions of free and bound HM ion were calculated using microelement association coefficient, k_as(ME). The soil liquid-phase saturation with CaCO₃ was characterized by the ratio of the real solubility product (S) to the thermodynamic solubility product (S⁰): К?=?S/S⁰.

Results and discussion

The soil solution supersaturation with CaCO₃ was characterized by the product of analytical concentrations (S), equilibrium concentrations [accounting ion activity (S^I), ion association (S^II), ion association and complexation (S^III)], and the thermodynamic solubility product (S⁰). To evaluate the role of DOM in soil solution supersaturation with CaCO₃, the initial pure Ca (HCO₃)₂ solution series was prepared. The humic and fulvic acids from the illuvial horizon of gleyic solonetz with concentrations of 20 mg C L^?1 and 120 mg C L^?1 decreased the CaCO₃ precipitation compared with initial soil solution. The release of CaCO₃ from soil water extracts containing water-soluble organic matter was 1.2–1.9 times less compared with identical artificial solution not containing organic matter. The HM binding by carbonates is proportional to the DOM content.

Conclusions

In molic solonetz and gleyic solonetz, the neutralization of the soda should be assessed by the soil solution supersaturation with CaCO₃. To calculate the degree of HM passivation in soil solution containing DOM, the coefficient of soil solution oversaturation with CaCO₃ is proposed. For reducing soil organic matter and DOM mobility and loss from soil, as well as for Pb passivation, intra-soil mechanical processing, intra-soil waste management, and intra-soil watering are proposed.

     

Phosphorus desorption from calcareous soils with different initial Olsen-P levels and relation to phosphate fractions

Purpose

Calcareous soils are characterized by high pH and phosphorus (P) fixation capacity. Increasing application of P fertilizer recently has significantly improved soil P concentration, especially available P (Olsen-P) and inorganic phosphate (P_i) fractions. However, there are few data available on the ability of soils with different initial Olsen-P levels to continuously supply P (i.e., P desorption capacity) to crops without additional P fertilization and on which P_i fraction exerts the greatest influence on P desorption capacity.

Materials and methods

Five soils with different initial Olsen-P levels (0.5, 14.3, 38.4, 55.4, 72.3 mg kg^?1, hereafter refer as OP1, OP2, OP3, OP4, and OP5) but similar other soil properties were selected to evaluate the capacity of P desorption and its relationship with P_i fractions. Soil P was sequentially extracted once daily for 16 consecutive days using Olsen solution.

Results and discussion

The content and proportions of dicalcium phosphate fraction (Ca₂-P), octacalcium phosphate fraction (Ca₈-P), aluminum phosphorus fraction (Al-P), and iron phosphorus fraction (Fe-P) in P_i increased significantly with the increase of initial Olsen-P (P?<?0.01). Applied P fertilizer was mostly stored as Ca₈-P in the soil. Soil P desorbed reached an equilibrium after 16 extractions for all soils, and P desorption capacity (12–358 mg kg^?1) showed a significant linear relationship with initial Olsen-P (P?<?0.01), with an increase of 4.2 mg kg^?1 desorbed P per 1 mg kg^?1 increase of initial Olsen-P. Ca₂-P exerted the conclusive effect on P desorption in the first four extractions, but Ca₈-P played a more important role in the 16 extractions.

Conclusions

Ca₈-P was the greatest potential pool for P desorption after Ca₂-P was depleted. P desorption capacity was significantly linearly related to initial Olsen-P (P?<?0.01). Different fertilizer use strategies were developed based on P desorption capacity for soils with different initial Olsen-P levels. The present study provided basic data on how to reduce effectively the application amount of chemical P fertilizer.

     

Soil organic carbon storage and quality are impacted by corn cob biochar application on a tropical sandy loam

Purpose

Humic substances, which are integral components of total organic carbon (TOC), influence soil quality. The study aimed to investigate whether humic and non-humic fractions exhibit early, consistent, and measurable changes and affect TOC sensitivity and storage in a tropical sandy loam soils amended with corn cob biochar.

Materials and methods

There were four treatments with four replicates established in a randomized complete block design. Composite soil samples were taken from plots without biochar (CT), from plots incorporated with 15 t biochar ha^?1 (BC-15), and 30 t biochar ha^?1 without or with phosphate fertilizer (BC-30 and BC-30+P). The TOC, and humin, humic acid (HA), and fulvic acid (HA) fractions of soil organic carbon were determined for each treatment. The optical densities (400–700 nm) were measured on the soil-free extracts by spectrophotometry; the densities measured at 465 and 665 nm were used to calculate the E₄₆₅/E₆₆₅ ratios.

Results and discussion

The BC-30 and BC-30+P plots recorded the highest TOC, humin, humic acid (HA), and fulvic acid (FA) contents with respect to the lowest in the CT. The total exchangeable carbon stratification was significantly higher in all the biochar-treated plots relative to the CT. Spectral analysis showed higher values of E₄₆₅/E₆₆₅ (5.02 and 5.15) in the CT and BC-15-treated soils, respectively, compared with the BC-30 and BC-30+P-amended soils with E₄₆₅/E₆₆₅ ratios of 2.76 and 2.98, respectively.

Conclusions

Corn cob biochar applied to a tropical sandy loam:

? increased the concentrations of HA and FA and led to increased stratification of TOC, with a stronger effect on HA compared with FA;

? significantly lowered E₄₆₅/E₆₆₅ at the high biochar application rate of 30 t ha^?1, implying the dominance of high molecular weight humic acid-like substances, and increased degree of aromaticity of the TOC.

     

Optimum plant stand and nutrient doses for summer groundnut under check basin irrigation and drip fertigation in light black soils of peninsular Western India

Abstract

A field experiment was conducted at Research Farm of ICAR-Directorate of Groundnut Research, Junagadh for consecutive three summer seasons of 2013, 2014, and 2015 with the objectives of identifying optimum plant density and nutrient doses under check basin irrigation and drip fertigation for higher productivity and net returns. The treatments were; three plant densities viz., 3,33,333 plants/ha (100% of recommended plant density; P1); 4,16,666 plants/ha (125% of recommended plant density; P2), and 4,99,999 plants/ha (150% of recommended plant density;P3) in main plots, and three nutrient doses viz., 18.75–37.5–22.5 NPK kg ha^?1 (75% of recommended nutrient dose; F1), 25-50-30 NPK kg ha^?1 (100% of recommended nutrient dose; F2), and 31.25–62.5–37.5 NPK kg ha^?1 (125% of recommended nutrient dose; F3) in sub-plots, and replicated thrice. The same sets of treatments were tested under both check basin irrigation and drip fertigation. The data were analyzed using split plot design. Pod yield, haulm yield, and net returns were significantly higher with P3 as compared to P1 under check basin irrigation but only haulm yield was found significantly higher with P3 under drip fertigation. Under check basin irrigation, NH₄–N, NO₃–N, and available P and K in soil were found in the order P1?>?P2?>?P3 (p?<?0.05) while in case of drip fertigation, differences were significant only for available K which was significantly higher in P1 over both P2 and P3. Under check basin irrigation, F2 i.e., application of 100 percent of recommended nutrient doses, being at par with F3, significantly improved pod yield, haulm yield and net returns over that with F1 however, differences were not significant under drip fertigation. NH₄–N, NO₃–N and available P and K in soil under both the irrigation systems were in the order F3?>?F2?>?F1 (p?<?0.05).     

RETRACTED ARTICLE: The bioremediation of metolachlor in soil using Rhodospirillum rubrum after wastewater treatment

Purpose

Reliable and effective techniques for removing contaminants from soil are highly desirable. However, metolachlor residue bioremediation and soil fertility improvement by Rhodospirillum rubrum (R. rubrum) in effluent after wastewater treatment have not yet been investigated. The aims of this study were to investigate the feasibility of bioremediation of metolachlor residues in soil and soil fertility improvement by R. rubrum in effluent and to explain the mechanism that R. rubrum in effluent was induced to express the regulatory gene.

Materials and methods

Soybean processing wastewater was obtained from Harbin Soybean Products Machining Factory. Soil samples were the surface soil (0–30 cm) from campus (1.77 g/kg total N, 4.15 g/kg total P, 1.58 g/kg total K, 17 g/kg SOM, 0.07 g/kg SMBC). Cytochrome P450 monooxygenase regulatory gene, MAPKKKs gene, was measured by RT-PCR.

Results and discussion

Compared to control treatment, metolachlor was removed efficiently and soil fertility was remediated by effluent containing R. rubrum. The removal in concentrations reached 2.97 mg/L (99%). Soil organic matter (SOM) and SMBC were enhanced 42 times. Molecular analysis revealed that metolachlor induced cpm gene expression to synthesize cytochrome P450 monooxygenase through activating MAPKKKs gene in MAPK signal transduction pathway.

Conclusions

Bioremediation of metolachlor in soil and improvement of soil fertility using R. rubrum in effluent were feasible. Metolachlor, as environmental pressure, induced cpm gene expression to synthesize cytochrome P450 monooxygenase and to remove metolachlor through activating MAPKKKs, MAPKKs, MAPKs genes in MAPK signal transduction pathway.