Phosphorus leaching from loamy sand and clay loam topsoils after application of pig slurry

Inorganic phosphorous availability and mobility in a manufactured soil

Manufactured soils, created by combining various organic and inorganic waste materials and byproducts, may be tailored to specific applications, providing an alternative to the extraction of natural soils. It is important for them to be capable of supporting plant growth without the need for significant management or fertiliser applications, the over-application of which can have adverse environmental effects. We examined the dynamics of phosphorus (P) transformations within a manufactured soil and the implications for nutrient cycling. A freshly prepared manufactured soil (32.5 % composted green waste, 32.5 % composted bark, 25 % horticultural grit, and 10 % lignite clay) was studied over one year in temperature and moisture controlled mesocosms. Leachate was collected to achieve high-resolution monitoring of leached phosphate concentrations. Initially, leached dissolved inorganic phosphorus (DIP) concentrations were low (0.02 ± 0.01 mg P L-1), before increasing by 160 μg P L-1 d-1 over the first 42 days to 5.57 ± 1.23 mg P L-1. After reaching a maximum concentration, DIP concentrations remained relatively consistent, varying by only 1.67 mg P L-1 until day 270. The increase in leached DIP was likely driven by soil organic matter mineralisation and the cleavage of carbon‑phosphorus bonds by the soil microbes to satisfy carbon demand with mineralogical influences, such as a decrease in apatite content, also contributing. Sorption and desorption from soil particles were the processes behind the P loss from the soil, which was followed by slow diffusion and eventual loss via leaching. The fertiliser application on phosphate dynamics resulted in increased DIP leaching. P concentrations observed in the manufactured soil were within the range considered sufficient to support plant growth. However, the mean leached phosphorus concentrations were higher than reported eutrophication thresholds suggesting that these soils may pose a risk to surface waters in their current form.

Shallow groundwater table fluctuations promote the accumulation and loss of phosphorus from surface soil to deeper soil in croplands around plateau lakes in Southwest China

The continuous excessive application of phosphorus (P) fertilizers in intensive agricultural production leads to a large accumulation of P in surface soils, increasing the risk of soil P loss by runoff and leaching. However, there are few studies on the accumulation and loss of P from surface soil to deep soil profiles driven by shallow groundwater table (SGT) fluctuations. This study used the intensive cropland around 7 plateau lakes in Yunnan Province as an example and conducted in situ monitoring of P storage in the soil profile and SGT during the rainy season (RS) and dry season (DS) as well as simulation experiments on soil P loss. The aim was to study the spatiotemporal variation in P accumulation in the soil profile of cropland driven by SGT fluctuations in the RS and DS and estimate the P loss in the soil profile driven by SGT fluctuations. The results showed that fluctuations in the SGT promoted P accumulation from the surface soil to deeper soil. The proportions of P stored in various forms in the 30-60 cm and 60-100 cm soil layers in the RS were greater than those in the DS, while the average proportion in the 0-30 cm soil layer in the DS was as high as 48%. Compared with those in the DS, the maximum decreases in the proportion of P stored as TP and Olsen-P in the 0-100 cm soil layer in the RS were 16% and 58%, respectively, due to the rise in the SGT (SGT <30 cm), while the soil TP storage decreased by only 1% when the SGT was maintained at 60-100 cm. The critical thresholds for soil Olsen-P and TP gradually decreased with increasing soil depth, and the risk of P loss in deeper soil increased. The loss of soil P was increased by fluctuations in the SGT. Based on the cropland area around the 7 plateau lakes, P storage, and SGT fluctuations, the average loss intensity and loss amount of TP in the 0-100 cm soil layer around the 7 plateau lakes were estimated to be 25 kg/ha and 56 t, respectively. Therefore, reducing exogenous P inputs, improving soil endogenous P utilization efficiency and maintaining deep soil P retention are the basic strategies for preventing and controlling P accumulation and loss in deep soil caused by SGT fluctuations.

Soil Fertility and Phosphorus Leaching in Irrigated Calcareous Soils of the Mediterranean Region

To ensure soil quality and soil health, it is necessary to improve fertilization practices while minimizing environmental impacts. The aim of this study was to record the state of the art on soil fertility related to fertilization management (organic and/or mineral) and to detect environmental challenges in highly productive fields. A soil survey was set up in a new irrigated area (c. 20 years old), in the north-eastern part of Spain, which is mainly devoted to double annual crop rotations of cereals and maize. The area also supports an important animal rearing activity. The survey covered 733 ha of calcareous soils, owned by 35 farmers. At each farm, fertilization management was recorded, and soil was analyzed for nutrients and heavy metals. Multivariate analyses were performed. Total N, P, Cu and Zn, and available P, Cu, Zn and Mn soil concentrations were associated to the use of organic amendments. Heavy metals concentrations were below established thresholds. Available P (Olsen-P) was identified as an indicator of the previously adopted fertilization management and of the potential of P leaching towards deeper soil layers. Regression analyses were performed. A displacement of available P from the uppermost layer (0-0.3 m) occurs in the breakpoint of 86 mg P kg-1 soil. Preventative actions might be established from 53 mg P kg-1 soil due to the slowdown in P immobilization. Our results reinforce the importance of setting up P threshold soil levels for best practices of fertilization, as a basis for sustainable agriculture intensification.

Impacts of soil, climate, and phenology on retention of dissolved agricultural nutrients by permanent-cover buffers

Nutrient losses from farms affects environmental and human health, but retention by riparian buffers can vary by nutrient identity, flow path, soil texture, seasonality, and buffer width. On conventional farms with corn, we test the relationships between levels of dissolved nitrogen (N) and phosphorus (P) in downslope surface-water, and flow paths relating to porewater in soils (to 40 cm deep), groundwater of the saturated zone (to 2.5 m deep), soil nutrient pools, and changes in plant biomass and tissue quality by season. We found that the major drivers of surface-water nutrients were multi-factor and nutrient-specific, variously relating to soil, climate, vegetation uptake, and tiling on clay soils. N retention was best explained by soil type, with 10 times more surface-water N in the sand versus clay setting, despite identical fertilization rates on corn. P retention was best explained by precipitation and time of year. Vegetation uptake was strongest for shallow-soil porewater, and was greatest in buffers where root biomass was 20 times greater by weight. We were unable to detect any impact of vegetative uptake on groundwater nutrients. Overall, peak nutrient inputs to surface-water were in early summer, fall, and winter - all times when plant uptake is low. Buffers appear to be a necessary component of nutrient capture on farms, but insufficient unless partnered with measures that reduce nutrient flows at times when plants are inactive.

Effects of Phosphorus Fertilizer Application Rates on Colloidal Phosphorus Leaching in Purple Soil in Southwest China

Phosphorus (P) lost via leaching from agricultural land is of major concern for water resource managers worldwide, and colloidal phosphorus (CP) may have a high contribution, since it is an important mobile form of P in soil and subsurface drainage. The objective of this study is to relate P fertilization application rates to CP leaching. To eliminate the influence of climate and facilitate the accurate measurement of P contents in different soil layers, we established soil columns to investigate the impacts of fertilizer application rates and timing on P leaching. Therefore, a soil column leaching experiment was undertaken with different P fertilization application rates (0, 20, 40, 100, 200, and 400 mg kg−1) for purple soil in southwest China. P application rates had significant effects on CP and dissolved phosphorus concentrations in the top soils (p < 0.05) (e.g., 0–10 cm in this study), and they further increased P leaching loss by 24–375%. CP was the dominant P form and contributed 31–61% to total phosphorus in the leachate. The concentration of different P forms in leachates decreased significantly over time, and the risk of P leaching loss was greater within two weeks after P application (p < 0.05). The advisable range of P application rate is recommended to be 0–450 kg ha−1 for agricultural practice, and it is also recommended to keep P fertilizer in the soil for more than two weeks. Some countermeasures, related to application rates and timing, should be taken to minimize the buildup of P in the field and reduce the risk of P leaching.

Soil slope and texture as factors of phosphorus exportation from pasture areas receiving pig slurry

Phosphorus (P) loss from agricultural areas to waterbodies is a worldwide concern. However, the effect of soil source and transport factors, such as clay (C) content and slope (S), on the magnitude of the P transport in Brazilian subtropical soils is still understudied. The objectives of this study were i) to quantify the loss of P fractions by runoff in areas receiving pig slurry application and with variations in S and C content; ii) propose an environmental critical limit model of P (P-threshold) for Brazilian subtropical soils. Thus, two series of experiments were conducted from 2016 to 2018, one under a Nitisol with 642 g kg^-1 of C and another under a Cambisol with 225 g kg^-1 of C. The treatments were four P rates (0, 56, 112 and 224 kg P ha^-1 year^-1) superficially applied as pig slurry, on Tifton (Cynodon sp) pasture, and three S (10, 20 and 30% in the Nitisol and 15, 25 and 35% in Cambisol). P losses increased in both soils as the S and P rates rose. The Nitisol showed P losses three times higher than the Cambisol. Soil S above 25% promotes P losses at a rate three times higher than in soil below this limit. Therefore, we propose a P-threshold model for Mehlich-1 extractable P levels for Brazilian subtropical soils as: "P-threshold = (42.287 + C) - (0.230 S + 0.0123 C S)" in soils with a S ≤ 25% and "P-threshold = (42.287 + C) - (-0.437 S + 0.039 C S)" in soils with a S >25%, where both C and S are shown in percentage. The soil clay content and slope are aggravating factors to the P transfer process, thus must be considered in suitable models to predict the P losses risk.

Impacts of Cover Crops and Crop Residues on Phosphorus Losses in Cold Climates: A Review

The use of cover crops and crop residues is a common strategy to mitigate sediment and nutrient losses from land to water. In cold climates, elevated dissolved P losses can occur associated with freeze-thaw of plant materials. Here, we review the impacts of cover crops and crop residues on dissolved P and total P loss in cold climates across ∼41 studies, exploring linkages between water-extractable P (WEP) in plant materials and P loss in surface runoff and subsurface drainage. Water-extractable P concentrations are influenced by plant type and freezing regimes. For example, WEP was greater in brassica cover crops than in non-brassicas, and increased with repeated freeze-thaw cycles. However, total P losses in surface runoff and subsurface drainage from cropped fields under cold climates were much lower than plant WEP, owing to retention of 45 to >99% of released P by soil. In cold climatic regions, cover crops and crop residues generally prevented soil erosion and loss of particle-bound P during nongrowing seasons in erodible landscapes but tended to elevate dissolved P loss in nonerodible soils. Their impact on total P loss was inconsistent across studies and complicated by soil, climate, and management factors. More research is needed to understand interactions between these factors and plant type that influence P loss, and to improve the assessment of crop contributions to P loss in field settings in cold climates. Further, tradeoffs between P loss and the control of sediment loss and N leaching by plants should be acknowledged.

Arundo donax L. can substitute traditional energy crops for more efficient, environmentally-friendly production of biogas: A Life Cycle Assessment approach

Maize silage contributes to biogas production in Lombardy Region (400 anaerobic digestion plants) employing 47,000 Ha (Production Model - PM1). Reducing the area devoted to this energy crop is a goal to free soil for food production. Double cropping (PM2) and Arundo donax L. (PM3) have been proposed and tested to measure the impacts for the three Production Models by Life Cycle Assessment (LCA). The impact category related to Climate Change remained stable for PM2 while it decreased by 17% for Arundo donax L. (PM3) in comparison with PM1. Impact categories related to nutrient management (acidification, particulate matter eutrophication) showed an increase in the range of 3-5% for PM2 in comparison with PM1, while Arundo donax L. allowed the same impact categories to be reduced by 31%, 24%, 17% and 33%, respectively.

Solid Cattle Manure Less Prone to Phosphorus Loss in Tile Drainage Water

Forms (e.g., liquid and solid) of manure influence the risk of P loss after land application. The objective of this study was to investigate the effects of P-based application of various forms of cattle manure (liquid, LCM; or solid, SCM) or inorganic P as triple superphosphate (IP) on soil P losses in tile drainage water. A 4-yr field experiment was conducted in a clay loam soil with a corn ( L.)-soybean [ (L.) Merr.] rotation in the Lake Erie basin. Over the 4 yr, the dissolved reactive P (DRP) flow-weighted mean concentration (FWMC) in tile drainage water was greater under SCM fertilization than under either IP or LCM fertilization. Despite its lower value on an annual basis, DRP FWMC rose dramatically immediately after LCM application. However, the differences in DRP FWMC did not result in detectable differences in DRP loads. Regarding particulate P and total P losses during the 4 yr, they were 68 and 47%, respectively, lower in the soils amended with SCM than in those with IP, whereas both values were similar between IP and LCM treatments. Overall, the P contained in solid cattle manure was less prone to P loss after land application. Accordingly, the present results can provide a basis for manure storage and application of best management practices designed to reduce P losses and improve crop growth.

Regional analysis of groundwater phosphate concentrations under acidic sandy soils: Edaphic factors and water table strongly mediate the soil P-groundwater P relation

Historic long-term P application to sandy soils in NW-Europe has resulted in abundant sorption, saturation and eventually leaching of P from soil to the groundwater. Although many studies recognize the control of site-specific factors like soil texture and phosphate saturation degree (PSD), the regional-scaled relevance of effects exerted by single factors controlling P leaching is unclear. Very large observational datasets of soil and groundwater P content are furthermore required to reveal indirect controls of soil traits through mediating soil variables. We explored co-variation of phreatic groundwater orthophosphate (o-P) concentration and soil factors in sandy soils in Flanders, Belgium. Correlation analyses were complemented with an exploratory model derived using 'path analysis'. Data of oxalate-extractable Al, Fe, P and pH_KCl, phosphate sorption capacity (PSC) and PSD in three depth layers (0-30, 30-60, 60-90 cm), topsoil SOC, % clay and groundwater depth (fluctuation) were interpolated to predict soil properties on exact locations of a very extensive net of groundwater monitoring wells. The mean PSD was only poorly correlated to groundwater o-P concentration, indicating the overriding control of other factors in the transport of P to the groundwater. A significant (P < 0.01) positive non-linear relationship was found between groundwater o-P concentrations and pH_KCl for all depth layers. Likewise, lower SOC% (P < 0.01) and shallower groundwater level (MHL or MLL) corresponded (P < 0.01) with higher o-P concentrations. Groundwater o-P unexpectedly correlated positively to clay% and path analysis indicated this to be an indirect effect of the groundwater level. Path analysis furthermore indicated an important indirect control of pH on groundwater o-P concentrations and a considerable direct effect of P_{ox, 0-90}, Al_{ox, 0-90} and MHL. The fact that groundwater o-P concentration was stronger controlled by soil pH and groundwater table depth than by PSD indicates the likely oversimplification of the latter index to measure the long-term potential risk of P leaching. Accounting for controls on leaching not included in PSD via an alternative index, however, seems problematic as in Flanders for example groundwater o-P turned out to be higher in finer textured soils or soils with higher pedogenic Fe content, probably because of their lower pedogenic Al content and higher soil pH. Path analysis of extensive soil and groundwater datasets seems a viable way to identify prime local determinants of soil P leaching and could be further on used for 'ground-truthing' more complex P-migration simulation models.

Assessment risk of phosphorus leaching from calcareous soils using soil test phosphorus

Accurate estimation of phosphorus (P) leaching is important because excess P may reduce surface and ground water quality. Little attention has been paid to estimate P leaching from soil tests in calcareous soils. The relation between different soil tests P (STP), P sorption index (PSI) and degree of P saturation (DPS) and leaching of P were examined for assessing the risk of P loss from calcareous soils. Columns leaching repacked with native soils were leached with either distilled water or 10 mM CaCl₂ solutions, separately. Four leaching events were performed at four days, and 28.7 mm of distilled water or 10 mM CaCl₂ solutions was applied at each leaching events. Compared with distilled water, CaCl₂ had a small ability to solubilize P from soils. Concentration of P in leachate in both leaching solutions was exceeding 0.1 mg l^-1 associated with eutrophication. Cumulative P leached P was ranged from 0.17 to 18.59 mg P kg^-1 and 0.21-8.16 mg P kg^-1, when distilled water and 10 mM CaCl₂ solutions were applied, respectively and it was higher in sandy clay loam soils compared with clay soils. Among evaluated environmental soil P tests, P_CaCl2-3h (P extracted by 10 mM CaCl₂ for 3 h), P_CaCl2-1h (P extracted by 10 mM CaCl₂ for 1 h) were more accurate than other soil P tests for predicting P concentration in the leachates in both leaching solutions and accounting for 83% and 72% of variation of P concentration, respectively. The water extractable P (WEP) (r = 0.771) and Olsen-P (P_Ols)(r = 0.739) were significantly related to the leached P concentration using distilled water solution in a split line model, with a change point of 27.4 mg P kg^-1 and 61.5 mg P kg^-1, respectively. Various DPS were calculated and related to the leached P concentration. Based on P extracted by Mehlich-3 (P_M3) and HCl (P_HCl) and PSI, the change point of the relationship between leached P concentration and DPS_M3-3 (P_M3(P_M3+PSI)×100) and DPS_HCl-2 (P_HCl(P_HCl+PSI)×100) for both leaching solutions was approximately the same, thus a mean value of 49% for DPS_M3-3 and 73% for DPS_HCl-2 was obtained. Soils were grouped into four categories of increasing P leaching potential based on WEP, P_Ols, and DPS_M3-3. The results indicated that 8.00%-25.50% of the soil grouped in no risk category whereas 8.00%-13.70% of the soils fell into the high risk category.

Can Organic Materials Reduce Excess Nutrient Leaching from Manure-Rich Paddock Soils?

Horse paddocks have been identified as a significant contributor of animal waste nutrients to natural waters; thus, modified paddock management is needed. Because chemical amendments pose a health risk to horses, an alternative for reducing nutrient translocation from manure is to add available organic residues to the soil. To examine the feasibility of outdoor use of organic materials to reduce nutrient losses from paddock soils, three commonly available organic materials (peat, wheat straw, and wood chips) were tested for their nutrient retention capacities in batch experiments followed by leaching experiments in an in-house lysimeter station using artificial rainfall. Results showed that the grounded peat and wood chips retained some phosphorus (P), whereas grounded wheat straw released P to the solution. In leaching experiments, peat reduced nitrogen (N) losses by 40% but increased P and carbon (C) losses severalfold. Wheat straw was ineffective in reducing P, N, or C losses and in some cases increased the losses. Wood chips effectively reduced P and C losses, by 70 and 40%, respectively, but not N losses. It was concluded that, among the three organic materials, only the wood chips can be used outdoors to reduce nutrient losses from paddock soils.

Turnover and losses of phosphorus in Swedish agricultural soils: long-term changes, leaching trends, and mitigation measures

Transport of phosphorus (P) from agricultural fields to water bodies deteriorates water quality and causes eutrophication. To reduce P losses and optimize P use efficiency by crops, better knowledge is needed of P turnover in soil and the efficiency of best management practices (BMPs). In this review, we examined these issues using results from 10 Swedish long-term soil fertility trials and various studies on subsurface losses of P. The fertility trials are more than 50 years old and consist of two cropping systems with farmyard manure and mineral fertilizer. One major finding was that replacement of P removed by crops with fertilizer P was not sufficient to maintain soil P concentrations, determined with acid ammonium lactate extraction. The BMPs for reducing P leaching losses reviewed here included catch crops, constructed wetlands, structure liming of clay soils, and various manure application strategies. None of the eight catch crops tested reduced P leaching significantly, whereas total P loads were reduced by 36% by wetland installation, by 39 to 55% by structure liming (tested at two sites), and by 50% by incorporation of pig slurry into a clay soil instead of surface application. Trend analysis of P monitoring data since the 1980s for a number of small Swedish catchments in which various BMPs have been implemented showed no clear pattern, and both upward and downward trends were observed. However, other factors, such as weather conditions and soil type, have profound effects on P losses, which can mask the effects of BMPs.

Past, present, and future use of phosphorus in Chinese agriculture and its influence on phosphorus losses

Large inputs of phosphorus (P) in chemical fertilizers and feed supplements since 1978 have improved soil P status in arable land in China, but have also created challenges by increasing P concentrations in manure and exacerbating water quality degradation. Arable land in China can be divided into five management zones based on soil P chemistry, with 15-92 % of arable land having lower P status than the agronomic optimum and 0.3-7.2 % having severe risks of P leaching losses. A scenario analysis of soil P budget and agronomic P demand during 2011-2030 highlighted the great pressure China faces in sustainable P management and the need for drastic changes in current practices. This includes new policies to reduce P supplementation of feed and improved P use efficiency by livestock and programs to expand the adoption of appropriate fertilization, soil conservation, and drainage management practices to minimize P losses.

Are horse paddocks threatening water quality through excess loading of nutrients?

The Baltic Sea is one of the most eutrophied water bodies in northern Europe and more than 50% of its total anthropogenic waterborne phosphorus (P) and nitrogen (N) loads derive from agricultural sources. Sweden is the second largest contributor of waterborne N and the third largest contributor of waterborne P to the Baltic Sea. Horse farms now occupy almost 10% of Swedish agricultural land, but are not well investigated with regard to their environmental impact. In this study, potential P, N and carbon (C) leaching losses were measured from two representative horse paddock topsoils (0-20 cm; a clay and a loamy sand) following simulated rainfall events in the laboratory. Results showed that the leachate concentrations and net release of P, N and dissolved organic C (DOC) from paddock topsoils were highest in feeding and excretion areas and considerably higher from the loamy sand than the clay paddock topsoil. Leaching losses of dissolved reactive P (DRP) were significantly (p < 0.05) correlated with concentrations of water-soluble P and ammonium acetate lactate-extractable P (P-AL) in the soil, while leaching losses of dissolved organic P and total organic N were significantly correlated with DOC concentration in leachate. Leaching loads of P and N from paddock topsoils greatly exceeded average figures for Swedish agricultural topsoils. It was concluded that: i) horse paddocks pose a potential threat to water quality via leaching of excess P and N, ii) feeding and excretion areas are potential hotspots for highly enhanced leaching losses, and iii) paddocks established on sandy soils are particularly susceptible to high N leaching losses.

Impact of slurry management strategies on potential leaching of nutrients and pathogens in a sandy soil amended with cattle slurry

For farmers, management of cattle slurry (CS) is now a priority, in order to improve the fertilizer value of the slurry and simultaneously minimize its environmental impact. Several slurry pre-treatments and soil application methods to minimize ammonia emissions are now available to farmers, but the impact of such management strategies on groundwater is still unclear. A laboratory experiment was performed over 24 days in controlled conditions, with undisturbed soil columns (sandy soil) in PVC pipes (30 cm high and 5.7 cm in diameter). The treatments considered (4 replicates) were: a control with no amendment (CTR), injection of whole CS (WSI), and surface application of: whole CS (WSS), acidified (pH 5.5) whole CS (AWSS), the liquid fraction obtained by centrifugation of CS (LFS), and acidified (pH 5.5) liquid fraction (ALFS). An amount of CS equivalent to 240 kg N ha(-1) was applied in all treatments. The first leaching event was performed 72 h after application of the treatments and then leaching events were performed weekly to give a total of four irrigation events (IEs). All the leachates obtained were analyzed for mineral and organic nitrogen, electrical conductivity (EC), pH, total carbon, and phosphorus. Total coliforms and Escherichia coli were also quantified in the leachates obtained in the first IE. The results show that both acidification and separation had significant effects on the composition of the leachates: higher NO3(-) concentrations were observed for the LFS and ALFS relative to all the other treatments, throughout the experiment, and lower NO3(-) concentrations were observed for acidified relative to non-acidified treatments at IE2. Acidification of both the LF and WS led to higher NH4(+) concentrations as well as an increase of EC for treatment ALFS relative to the control, in the first IE, and lower pH values in the AWSS. Furthermore, the E. coli and total coliform concentrations in AWSS, LFS, and ALFS were significantly higher than in WSI or WSS. In conclusion, none of the strategies generally used to minimize ammonia emissions impact positively on leaching potential relative to the traditional surface application of CS. Furthermore, some treatments, such as separation, might increase significantly the risk of leaching.