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Amending growing media with biochar has the potential to sequester carbon and enhance the properties of the receiving substance. However, knowledge of the mechanisms of how biochar amends the physical properties of the material is incomplete. By combining 3D image analysis and more conventional methods, this study aimed to (1) characterise the pore structure properties of three different plant-based biochars and (2) quantify their impact on Sphagnum moss growing media physical properties. The 3D imaging showed that irrespective of the feedstock, the majority (0.80–0.94 m3 m−3) of the biochar pore volume resided in pores with diameters 2–11 μm. Biochar pore properties shared similarities due to the structure of plant tissue. The application of biochar increased the water retention of the growing media by a maximum increase of 0.06 m3 m−3 in the pore diameter range 1–8 μm. This is relevant for plant-available water and microbiological activity, which indicates the usability of the biochar amendments. From methodological point of view, the benefits of combining 3D imaging with conventional measurements and impacts of the water table continuum discontinuity between the biochar and the surrounding growing media were demonstrated. The design of biochar for optimal water retention would benefit from further studies quantifying pore structure characteristics of biochar produced from a wide range of feedstocks.

Feasibility of pyrolysing wastewater sludge for char and energy production is dependent on the usability of the produced sludge char. This study aimed to produce mechanistic information of char impacts on amended porous media by determining (1) pore structure of sludge chars with 3D image analyses and (2) their influence on water retention and shrinkage properties of three contrasting soils. The pore structure of the chars consisted of crevices and large spheres. Their water retention impacts were minor, even though the low-porous char slightly increased porosity in the amended materials in various pore-size ranges. The dominating, though small, impacts were the increase in easily drainable interpores and decrease in smallest pore sizes relevant for plant available water. The char impacts were more visible in fine-than coarse-textured soils. The chars also significantly reduced shrinkage in clay soils. The results were insensitive to sludge feedstock or char particle size. publishedVersion

Production of organic fertilizers from poultry manure may compromise availability of phosphorus (P) to plants. This study examined the effects of granulation, feather meal addition, and pyrolysis on bioavailability of P in broiler manure in a pot experiment with ryegrass and assessed whether P availability is enhanced by inoculating arbuscular mycorrhizal fungi (AMF) into soil. Granulated broiler manure gave similar plant yield and P uptake to superphosphate. Feather meal addition had a minor negative effect on P availability, whereas pyrolysis lowered the fertilization effect of broiler manure. The yield-based mineral-P equivalences were 120%, 85% and 75% during the first harvest, and 100%, 75% and 45% during one growing season for granulated unamended, granulated amended with feather meal and pyrolyzed broiler manure. Soil inoculation with AMF did not enhance P availability. Granulated poultry manure is suitable as a P fertilizer for annual crops with comparable bioavailability to mineral fertilizer P, whereas pyrolyzed poultry manure is suitable as a slow-release or storage P fertilizer in slightly acidic soils. Knowledge on P bioavailability in organic fertilizers produced with different technologies can be used for optimizing fertilization, minimizing build-up of soil P and its adverse environmental effects. (C) 2021 The Author(s). Published by Elsevier B.V.

Pyrolysis is an option for enhancing the sustainable management of broiler manure surpluses by producing a concentrated, hygienic char product with a fertilizer and soil conditioner value. In this study, the impacts of pyrolysis conducted at 350, 400 and 450 °C on total nutrient and harmful element concentrations in biochars derived from peat-bedded broiler manure were examined. Emphasis was placed on the availability of phosphorus (P). In addition, the pore structures of these biochars were explored using X-ray microtomography and image analysis. During pyrolysis, 35–50%, 40–55% and 35–45% of the original carbon, nitrogen and sulfur contents, respectively, of the feedstock biomass were lost as volatiles. Mineral elements, including P, were concentrated in the biochar. Although water-extractable P was found to be converted to less labile forms due to charring, the concentration effect and notable increase in sodium bicarbonate-extractable P rendered broiler manure biochars richer in total labile P in comparison with feedstock manure (7.1, 10.0, 11.1 and 14.8 g labile P kg−1 in feedstock and biochars produced at 350, 400 and 450 °C, respectively). The pore volume of the micrometer-scale porosity of the broiler manure biochar was comparable to that found earlier in wood-based biochars. In comparison with wood-based biochars, the pore structure of broiler manure biochars was more versatile, and the pore size distribution was wider. Consequently, part of the porosity was too large to store plant-available water, which may reduce the potential of broiler manure biochars to improve soil water storage capacity.

Refining broiler manure to nitrogen (N) fertilizer products of consistent quality and balanced nutrient content could promote agronomic exploitation of this nutrient rich resource. For ensuring the effectiveness and sustainable use of such products, their plant available N supply needs to be known. In this study, the N fertilizer value of peat bedded broiler manure as pure granules (BM) and feather meal amended granules (BM+FM) was assessed in a pot experiment with ryegrass and field experiment with onion. The pot experiment examined also the performance of pure feather meal (FM) and slow pyrolyzed broiler manure (PyrBM). As measured by mineral N fertilizer equivalence, 68%, 45%–50%, 35%–43%, and 3% of the total N in FM, BM+FM, BM and PyrBM, respectively, was available to plants during the first growing season in favorable conditions. A minor (

Addition of biochar into a soil changes its water retention properties by modifying soil textural and structural properties. In addition, internal micrometer-scale porosity that is able to directly store readily plant available water affects soil water retention properties. This study shows how precise knowledge of the internal micrometer-scale pore size distribution of biochar can deepen the understanding of the biochar-water interactions in soils. The micrometer-scale porosity of willow biochar was quantitatively and qualitatively characterized using X-ray tomography, 3D image analysis and Helium ion microscopy. The effect of biochar application on clay soil water retention was studied by conventional water retention curve approach. The results indicate that the internal pores of biochar, with sizes of at 50 and 10 μm (equivalent pore diameter), increased soil porosity and the amount of readily plant available water. After biochar addition, changes in soil porosity were detected at pore size regimes 5–10 and 25 μm, i.e. biochar pore sizes multiplied by factor 0.5. The detected pore size distribution of biochar does not predict directly (1:1 compatibility) the changes observed in the soil moisture characteristics. It is likely that biochar chemistry and pore morphology affect biochar-water interactions via e.g. surface roughness and contact angle. In addition, biochar induced changes in soil structure and texture affected soil moisture characteristics. However, the approach presented is an attractive pathway to more generalized understanding on how and why biochar internal porosity affects soil moisture characteristics. publishedVersion

Vegetated buffer zones (BZs) between arable fields and bodies of water are commonly established to reduce erosion and run-off of particle-bound nutrients. Functioning of a BZ depends on soil structure, as it is important for water infiltration. Therefore, it is vital to understand how varying management practices affect soils of BZs. We studied the structural and hydraulic properties of three differently managed BZs established in a boreal Vertic Stagnic Cambisol (clay, 51%). The three management practices for vegetation were as follows: natural with no treatment, harvested yearly and grazed by cattle. We used bulk density and macroporosity, together with a pore geometry index (air permeability per unit air-filled porosity), to describe the soil structural properties. Hydraulic properties were measured at different length scales by means of an aggregate sorptivity test, saturated hydraulic conductivity of the core samples and field-saturated hydraulic conductivity. Vegetation management markedly affected the physical properties in the top 5 cm of the soil. Properties were least favourable for infiltration at the grazed site, with the greatest bulk density, least macroporosity and hydraulic conductivity or greatest pore tortuosity. In general, spatial variation in zones with restricted and good hydraulic conductivity together with reduced aggregate sorptivity in the deeper horizons made the soil prone to preferential flow when initially dry. Prolonged wetness, on the other hand, reduced saturated hydraulic conductivity significantly, resulting in surface run-off. Harvesting was considered the best management practice due to its inherent capacity for reducing the soil nutrient content and because it has minor implications for soil physical properties.

Soil test P (STP) concentration indicates whether annual P applications can be expected to give yield increases and can also indicate an elevated risk of P mobilization and potential for P transfer to surface waters and groundwater from a particular field. Changes in STP with time thus project agronomic benefits and environmental risks of different P use strategies. To predict STP changes with time, we constructed a simple dynamic model for which the input variables are P balance and initial STP. The model parameters (soil type-specific constants) were fitted using data originating from 44 P fertilizer experiments with different P rates. Model performance was evaluated using independent data sets that either had reasonably accurate input values ( = 103) or were obtained from farmers through interviews ( = 638). The simulations were in agreement with measured STP changes for both evaluation data sets when fittings were performed separately for four main soil types (clays, silts, coarse mineral soils, and organic soils). Statistical analysis confirmed that the model captured the trends in STP (NHOAc test) with acceptable accuracy and precision, with of 0.83 and 0.66 for the data with more accurate input and for farmer interview data, respectively; the corresponding model efficiency statistics were 0.88 and 0.66. The model is not restricted to use with one soil test, as fittings for several different types of soil tests can be generated. In this study, we fitted the model for Olsen P data retrieved from the literature. Agronomic use of the model includes evaluation of P use strategies, e.g., when a certain STP level is targeted or when long-term economy of P use is calculated. In an environmental context, the model can be used to predict STP changes with time under variable P balance regimes, which is essential for realistic assessment of changes in the potential for dissolved P losses.

Water infiltration is a crucial process for functioning of vegetated buffer zones (BZ). Structure of a clayey surface soil of three differently managed BZs, i.e., 1) natural with no treatment, 2) harvested once a year and 3) grazed by cattle was investigated in this study. Soil macro pores (> 50 μm) were characterized by qualitative description and quantitative image analysis of soil thin sections in order to assess their capability to water infiltration. Less than 10% of the macro pores consisted of rounded and irregular pores smaller than 300 μm indicating root activity. Instead, macro porosity was clearly dominated by elongated pores characterized by irregularity, expressing the complexity of the pore system. This pore pattern appeared in thin sections as weak or moderate ped separation suggesting good water infiltration when initially dry. Partial accommodation of pores may result in decrease of hydraulic conductivity, as these pores tend to close upon wetting and swelling. In the grazed site a platy structure was observed due to hoof pressure, which may further impair the hydraulic properties of soil. Moisture and temperature related processes (shrink–swell, freeze–thaw, and water saturation) are thought to be conducive to the aggregation and rearrangement of soil structure around the year, resulting in a complex pore system with low intra-aggregate porosity. In addition, wet periods typical of boreal soils result in clay dispersion and formation of aggregate-related pedofeatures of dense infillings, described as fine clay intrusions.

The sorption and desorption of phosphorus (P) from eroding soil particles in land runoff are important processes contributing to agriculturally-driven eutrophication. We investigated the P-exchange properties and related chemical characteristics of contrasting European agricultural soils and sediment material eroded from them under indoor (small-scale) and outdoor (larger-scale) rainfall simulations. Quantity-intensity (Q/I) relationships revealed large variation in equilibrium P concentrations at zero net P sorption (EPC 0 ) (0-10.3 mg 1 -1 ) and instantly labile P (-Q 0, the amount of P to be desorbed to obtain a P equilibrium concentration of 0 mg 1 -1 ) (2-75 mg kg -1 ), both correlating closely with Al-bound P and the P saturation degree of Al oxides (DPS Alox ). Maximum P sorption (Q max ) (43-515 mg kg -1 ) also correlated most closely with Al ox . The indoor and outdoor rainfall simulations produced sediments with different P sorption properties: in the indoor simulation (less kinetic energy, constant slope), the sediments had larger EPC 0 values, and usually larger —Qo values, than the sediments in the outdoor simulation (greater kinetic energy, variable slopes). Furthermore, the P exchange properties of the sediments differed from those of the bulk soil depending on the enrichment of soil P-sorption components (Fe/Al oxides, clay). The outdoor simulation indicated that sites with gentle slopes produced sediments that were more enriched with Al ox , Fe ox , Mn ox and organic C than those with steeper slopes. In this study, when the bulk soil had an initial EPC 0 greater than 1.3 mg l -1 , the outdoor rainfall simulation produced sediment with smaller EPC 0 and vice versa, indicating that, depending on the P status of the bulk soil, the sediment material was acting as source or sink for P during transport. However, on the basis of their EPC 0 values, most eroding sediments might be expected to desorb, rather than adsorb, P when entering surface water.

Soil cracking is a well-known phenomenon, also seen in clay soils in the boreal climatic zone. This study was carried out to quantify soil shrinkage properties in six differently managed clay soils in Finland (Vertic Cambisols, 51% clay). Cylinder samples (100 cm(3)) were taken in spring from two depths (0-5 and 5-10 cm), then saturated with water and dried as a function of applied suction. The heights of the sample were measured after each drying step and the volume of soil was calculated assuming isotropic shrinkage. The volume loss by shrinkage at a suction of -50 kPa was 1.6-3.8% and the total shrinkage was 5.2-10.5% of the total soil volume, respectively. All shrinkage curves showed structural shrinkage which occurred in the matric potential range from saturation to around -6 kPa. The shrinkage curves were characterized by minor proportional and wide residual shrinkage zones. Eight of twelve sites showed a steeper shrinkage in the proportional shrinkage zone than the theoretical 1:1 line. Large slope values, up to 3.0, reflect the collapse of inter-aggregate pore space due to shrinkage pressure. The results indicate significant particle rearrangement and structural changes, e.g. structural collapse and changes in inter-aggregate pore space due to shrinkage pressure. Continuous water saturation and variable periods of freezing between spring and autumn are mostly responsible for soil weakness against increasing effective stress as soil dries. It is presumed that shrinkage behaviour will change substantially with increases in drying and wetting cycles.

Soil structure that favours infiltration is essential for successful functioning of vegetated buffer zones. We measured bulk density, air permeability and precompression stress in a clay soil (Vertic Cambisol) and a sandy loam (Haplic Regosol) in Finland, to identify management-related changes in the physical and mechanical properties in the surface soil of buffer zones. In addition, the impact of texture on these properties was studied at depths down to 180?200 cm. Soil cores (240 cm3) were sampled from a cultivated field, from buffer zones harvested by grazing (only in a clay soil) or by cutting and removing the vegetation, and from buffer zones covered with natural grass vegetation. The samples were equilibrated at a matric potential of -6 kPa and compressed at a normal stress range of 20-400 kPa (7 h), followed by stress removal (1 h). Generally, the clay soil was more compressible than the sandy loam. Due to trampling by cattle, the young grazed buffer zone (0-3 cm) had the largest bulk density and the smallest total porosity. For the grazed sites, reduced air permeability (2.7-5.1 × 10-5 m s-1) was found, compared with that of the buffer zone under natural vegetation (15-22 × 10-5 m s-1), indicating decreased pore continuity. Although the old grazed site was easily compressed, compared with the younger site, it showed a greater resilience capacity due to the protective cover of organic residues accumulated on the soil surface., Hydrologiselta kannalta suojavyöhykkeiden ja -kaistojen tarkoitus on pintavalunnan hillitseminen ja imeynnän eli infiltraation edistäminen. Koska maan rakenne vaikuttaa keskeisesti suojavyöhykkeiden ja -kaistojen toimintaan, tässä tutkimuksessa tarkasteltiin suojakaistojen hoitotoimenpiteistä aiheutuvia mahdollisia muutoksia maan fysikaalisiin (irtotiheys ja ilmanjohtavuus) ominaisuuksiin ja maan kokoonpuristumisominaisuuksiin. Tutkittuja hoitotoimenpiteitä olivat niitto ja niittojätteen poiskorjaaminen, laidunnus sekä alueen jättäminen luonnontilaan.Jokioisilla savimaan (Vertic Cambisol) ja Maaningalla hietamaan (Haplic Regosol) koekenttien maaprofiili tutkittiin 200 cm:n (savi) ja 180 cm:n (hieta) syvyyteen saakka, ja maanäytteet otettiin kustakin horisontista. Etenkin hietamaalla oli muokkauskerroksen alapuolella kyntöantura yhä havaittavissa 10 vuotta viljelyn lopettamisen ja suojakaistan perustamisen jälkeen. Savimaan syvemmissä, todennäköisesti märkinä läpi vuoden säilyvissä horisonteissa (90-200 cm) maan irtotiheys oli pieni (< 1,19 g cm-3) ja kokonaishuokostilavuus suuri (> 0,52 cm3 cm-3), vaikka orgaanisen hiilen pitoisuus (< 0,9 %) oli erittäin alhainen. Maan rakenne on yhä massiivinen ja hyvin heikosti kehittynyt. Suojakaistojen pintamaakerroksesta (0-3 cm) ja maaprofiilien horisonteista otetut häiriintymättömät lieriönäytteet (240 cm3) kyllästettiin ja tasapainotettiin hiekkapedillä (-6 kPa). Maan ilmanjohtavuus mitattiin ja näytteitä kuormitettiin 7 tunnin ajan pystysuoralla normaalivoimalla (20, 40, 70, 100, 200 ja 400 kPa), minkä jälkeen kuormitus vapautettiin (1 tunti). Jännitystilan ja vastaavan muodonmuutostilan välistä riippuvuutta eli maan kokoonpuristumisominaisuuksia tarkasteltiin puolilogaritmisella asteikolla toisen asteen polynomin mukaisesti sovitetun jännitys-puristumakuvaajan avulla. Maan sisäistä lujuutta eli kykyä vastustaa ulkoapäin tulevia voimia arvioitiin ns. esitiivistysasteen avulla, joka johdettiin graafisesti ns. Casagranden menetelmällä. Maaprofiilin eri horisonttien kokoonpuristuminen oli riippuvainen maalajista, ei niinkään hoitotoimenpiteistä, ja se oli huomattavasti suurempaa savimaalla kuin hietamaalla. Molemmilla maalajeilla kokoonpuristuminen väheni siirryttäessä pintamaasta pohjamaahan. Tämä voi osaltaan selittyä sillä, että veden poistuminen huokosista oli estynyt, mikä esti kokoonpuristumisen. Suojakaistojen hoitotoimenpiteistä laidunnus aiheutti epäsuotuisia muodonmuutoksia savimaan rakenteessa, mikä heijastui kaistojen heikentyneenä ilmanjohtavuutena (2,7-5,1 10-5 m s-1) luonnontilaisiin kaistoihin verrattuna (15-22 10-5 m s-1). Kauttaaltaan alhaiset esitiivistysasteet voivat osin selittyä varhaisella näytteenottoajankohdalla, jolloin maan rakenne on talven jäljiltä heikoin mahdollinen. Laiduntaminen vaikutti kuitenkin maan kokoonpuristumisominaisuuksiin. Vaikka nuoren laidunkaistan tiivistyminen oli jo tiiviimmästä alkutilanteesta johtuen vähäistä, myös puristuman kimmoinen palautuminen oli kuormituksen lakattua pientä. Vanha laidunkaista oli taas helposti tiivistyvä, mutta maan pintakerrokseen kerääntynyt orgaaninen aines lisäsi kuormituksesta aiheutuneen puristuman palautumista. Tulosten perusteella laidunnusta tulisikin välttää etenkin hiljattain perustetulla nurmella.

Water repellency (WR) delays soil wetting process, increases preferential flow and may give rise to surface runoff and consequent erosion. WR is commonly recognized in the soils of warm and temperate climates. To explore the occurrence of WR in soils in Finland, soil R index was studied on 12 sites of different soil types. The effects of soil management practice, vegetation age, soil moisture and drying temperature on WR were studied by a mini-infiltrometer with samples from depths of 0-5 and 5-10 cm. All studied sites exhibited WR (R index >1.95) at the time of sampling. WR increased as follows: sand (R = 1.8-5.0) < clay (R = 2.4-10.3) < organic (R = 7.9-undefined). At clay and sand, WR was generally higher at the soil surface and at the older sites (14 yr.), where organic matter is accumulated. Below 41 vol. % water content these mineral soils were water repellent whereas organic soil exhibited WR even at saturation. These results show that soil WR also reduces water infiltration at the prevalent field moisture regime in the soils of boreal climate. The ageing of vegetation increases WR and on the other hand, cultivation reduces or hinders the development of WR., Kun kuivaan, huokoiseen maahan tiputettu vesipisaraei imeydy välittömästi, maa on vettä hylkivää eli hydrofobista. Lämpimien ilmastoalueiden karkeilla mailla vedenhylkivyys on yleisesti havaittu ja tutkittu ominaisuus. Boreaalisella ilmastovyöhykkeellä ilmiötä on sen sijaan tutkittu vähän. Vedenhylkivyyden esiintyminen liitetään orgaaniseen ainekseen, vaikkakin on epäselvää, mitkä spesifit yhdisteet ilmiön synnyttävät. Vedenhylkivyys aiheuttaa veden imeytymisen heikkenemistä ja maan epätasaista kostumista. Nämä seikat puolestaan edistävät oiko- ja pintavirtauksien syntyä sekä eroosiota. Vedenhylkivyydelle on tyypillistä suuri ajallinen ja paikallinen vaihtelu. Tässä tutkimuksessa maan vedenhylkivyysindeksi (R) määritettiin mini-infiltrometrillä käyttäen kolmesta suomalaisesta maalajista, savesta, hiedasta ja eloperäisestä maasta, 0–5 cm:n ja 5–10 cm:n syvyydeltä otettuja näytteitä. Tulosten perusteella arvioitiin kosteuden, kasvillisuuden iän ja viljelymuodon vaikutusta vedenhylkivyyden voimakkuuteen sekä tarkasteltiin määritysmenetelmän soveltuvuutta eri maalajeihin. Tutkitut maanäytteet olivat näytteenottohetkellä vettä hylkiviä, ja ominaisuus lisääntyi maalajeittain järjestyksessä hieta < savi < eloperäinen maa. Kasvipeitteisillä alueilla veden imeytymisen maan pintaan todettiin heikentyneen hiedalla 3–4-kertaisesti ja savimaalla 4–10-kertaisesti vedenhylkivyyden takia. Näiden maalajien vedenhylkivyys lisääntyi kasvillisuuden ikääntyessä vuosittain kynnetyllä pellolla se oli vähäisintä. Lisäksi vedenhylkivyys oli suurempaa maan pinnalla kuin syvemmässä kerroksessa. Tämä lienee seurausta pinnalle kertyvästä orgaanisesta aineksesta ja sen runsastumisesta, kun maata ei kynnetä. Vedenhylkivyys lisääntyi maan kuivuessa. Kivennäismaat osoittautuivat vettä hylkiviksi, kun kosteus oli alle 41 tilavuusprosenttia. Eloperäinen maa taas oli lievästi vettä hylkivä jopa vedellä kyllästettynä. Kun määritettiin näytteiden potentiaalista vedenhylkivyyttä, savelle ja hiedalle sopivaksi kuivatuslämpötilaksi osoittautui +40 °C. Sen sijaan eloperäisen maan näytteiden esikäsittely potentiaalisen vedenhylkivyyden määrittämiseksi vaatii vielä lisätutkimuksia. Tulokset osoittavat vedenhylkivyyttä esiintyvän myös boreaalisen ilmastovyöhykkeen maalajeilla, vaikka sitä ei aiemmissa maan veden liikkeitä käsittelevissä tutkimuksissa ole otettu huomioon. Ilmiön merkitys korostuu etenkin kuivissa olosuhteissa kasvipeitteisillä alueilla.

Pore space characteristics of biochars may vary depending on the used raw material and processing technology. Pore structure has significant effects on the water retention properties of biochar amended soils. In this work, several biochars were characterized with three-dimensional imaging and image analysis. X-ray computed microtomography was used to image biochars at resolution of 1.14 $\mu$m and the obtained images were analysed for porosity, pore-size distribution, specific surface area and structural anisotropy. In addition, random walk simulations were used to relate structural anisotropy to diffusive transport. Image analysis showed that considerable part of the biochar volume consist of pores in size range relevant to hydrological processes and storage of plant available water. Porosity and pore-size distribution were found to depend on the biochar type and the structural anisotopy analysis showed that used raw material considerably affects the pore characteristics at micrometre scale. Therefore attention should be paid to raw material selection and quality in applications requiring optimized pore structure., Comment: 16 pages, 4 figures. The final publication is available at Springer via http://dx.doi.org/10.1007/s11356-017-8823-x

We applied gypsum (CaSO4×2 H2O) amendments to 100 m2 plots within two clay-textured fields, one under shallow cultivation to 10 cm depth and the other ploughed to 20 cm depth. Unamended plots and plots subjected to a CaCO3 (finely ground limestone) application served as controls. Separate soil monoliths (30 cm in diameter, 40 cm in depth) were collected for laboratory rainfall simulations from all plots 7, 19 and 31 months after the initial application of the amendments. Water passed through the monoliths during these simulations was analysed for turbidity, dissolved and particulate phosphorus (DRP and PP), nitrogen species, dissolved organic carbon (DOC), as well as dissolved Ca2+, Mg2+, K+ and S, pH, and electrical conductivity (EC). Over the three-year monitoring period, gypsum amended soils exhibited substantial decreases in turbidity (45%), PP (70%), DRP (50%) and DOC (35%) relative to control samples. The effects gradually decreased with time, and after 31 months gypsum effects on P species were detectible, but no longer statistically significant. We consider gypsum amendments as a potential tool for slowing P loss from agricultural areas with high P loss potential.