Long term use of different organic fertilizer types and impact on phosphorus leaching

Phosphorus (P) is an essential nutrient for all living organisms. P is present in every living cell, and no other element can replace it in its vital role in several physiological and biochemical processes. However, its supply in the earth s crust is limited. P is of most concern because of the rate of exploitation of this non-renewable resource to meet current demand. Globally, recycling processes gain in interest to reduce the required amount of mined P.Many agricultural soils around the globe, mainly in tropical regions, are P deficient. However, in many agricultural regions such as Northwestern Europe, several states in the United States of America, the Baltic sea region and several provinces in China, P accumulation took place in the past decades, due to high doses of P fertilization. These are due to (i) the availability of cheap mineral P fertilizers and/or (ii) the large livestock, fed with large amounts of imported feed. These feeds contain large amounts of P, transferred inefficiently by animals to animal products and largely transferred to animal manure, that is mainly applied on the agricultural fields nearby. P is being sorbed to the soil by reactive clay particles, Ca, Al and Fe (hydr)oxides, organic matter and carbonates and is therefore quite immobile in the soil. However, all soils have a finite capacity to retain P and continued application of fertilizers will ultimately reach the environmental limit for safe storage of P. The amount of P lost to the environment with non-point leaching, will be determined by the sorbed amount of P and the P retention capabilities of the soil. This implies that P leaching is mainly determined by the total P fertilization. However in several studies based on long term field trials, it was observed that with the addition of organic amendments to the soil, soil P intensity and P leaching were increased, compared to mineral fertilizers at the same P input level. This means that the eventual P leaching will also be determined by the type of fertilizer and his chemical composition.In Flanders, many intensively managed agricultural soils suffer from decreasing soil organic carbon (SOC) levels, but have also extremely elevated P contents (P-AL >> 180 mg/kg dry soil). One of the strategies to maintain the SOC levels, is growing catch crops during autumn, and incorporating the produced biomass in early spring. Incorporation of catch crops in early spring, can however induce P mineralization, before the next crop is installed and starts taking up P from the soil solution. We hypothesized that in excessively P containing soils thiese catch crop residues increase the P leaching losses. Another strategy is adding organic amendments to the soil by applying a wide variety of organic fertilizers such as animal slurries, farmyard manure, several types of compost, processed digestate products, etc. However, the chemical and organic matter composition of these organic fertilizers is very different, which has an important influence on the potential to increase the SOC level. Furthermore, it is not known which influence these differences have on P leaching. This study was conducted to investigate which organic fertilizers have the highest potential to increase or at least maintain the SOC level without any further increase in P leaching.We investigated whether P leaching was increased by winter/early spring incorporation of catch crop residues from white mustard (Sinapis alba L.), Italian ryegrass (Lolium multiflorum L.), black oats (Avena strigosa L.) and a mixture of perennial ryegrass/white clover (Lolium perenne L./Trifolium repens L.). The incorporation of the catch crop residues was imitated by mixing a sample of the soil where the catch crop was grown, with a plant sample at a dose equal to the biomass crop yield of the catch crop in the field trial and in the state the plant tissue was in early spring. By conducting a leaching experiment with these mixtures, the influence of the incorporated catch crop residue on the P leaching could be compared with the fallow soil. Incorporation of white mustard, Italian ryegrass and perennial ryegrass/white clover crop residues, resulted in an approximately 40% decrease of P concentrations in the leachate, compared to the fallow soil and the soil with incorporation of black oats. We indicated that Italian ryegrass and perennial ryegrass/white clover incorporation reduced the P leaching by P immobilization processes. In contrast, decomposition of the white mustard and black oats was small. Little or no P was mineralized by these catch crop residues. The crop residues of black oats contained however 5 times more soluble P compared to white mustard crop residues. P in the black oats was eventually leaked out of the plant tissue during the leaching experiment, leading to P concentrations in the leachates, comparable to those of the fallow soil. We conclude that incorporation of the studied catch crops do not increase P leaching. Repeating this experiment with more types of catch crops and at different growth stages (and therefore different in composition and biodegradability) will help to understand better the effects of decomposition of plant residues on P leaching.In order to investigate the influence of organic amendments on SOC levels, soil P intensity and P leaching on the long term, two long term fertilizer field trials were intensively sampled during this study. The first field trial at Melle, Belgium (Ghent University,° 2005, silt loam) was sampled to compare the influences of the long term application of 3 different types of plant-based composts, dairy farmyard manure and cattle slurry with the long term application of mineral fertilizer (NPK) and a non-fertilized soil. The second field trial at Feucherolles, France (INRA France,°1998, silt loam) was sampled to compare 2 different types of plant-based composts and dairy farmyard manure with mineral N fertilizer (no P fertilization). In the field trial at Melle, applications of dairy farmyard manure and plant-based composts could enhance the SOC levels to 1.21-1.32%, compared to 1.03% for the mineral fertilized soil. In the field trial at Feucherolles, applications of dairy farmyard manure and plant-based composts had comparable effects on the SOC level, which increased to 1.30-1.58%, compared to 1.05% in the mineral N fertilized soils. In both field trials, the soil P intensity was however significantly increased in the soils with farmyard manure applications, compared to the mineral fertilized soils. In contrast, applications of compost at the field trial in Melle did not increase the soil P intensity, measured as 0.01 M CaCl2 extractable P (P-CaCl2) and hot water extractable P (HWP), compared to a non-fertilized soil. Similarly in the field trial at Feucherolles, the repeated application of composts based on plant material resulted in a comparable soil P intensity compared to the mineral N fertilized soil with no P input. Soil samples from both field trials were also brought to the laboratory to conduct leaching experiments. These experiments revealed that P concentrations in the leachates from dairy farmyard manure amended soils, were also significantly increased, compared to compost and mineral fertilized soils. In the field trial at Feucherolles, the total P concentration in the leachates per unit of P fertilized since the beginning of the experiment was 1.5 to 3 times increased for farmyard manure amended soils, compared to the compost amended and mineral fertilized soils.Since P-CaCl2 is easily influenced by environmental conditions, it was checked whether the increased soil P intensity levels and P concentrations in the leachates from the farmyard manure amended soils were increased the whole season. From 8th September 2012 to 12th October 2013, P-CaCl2 and HWP were monitored in all treatments of the field trial in Melle. The seasonal fluctuations in P-CaCl2 and HWP were similar for all treatments and could be explained by seasonal changes in pH-H2O, temperature, precipitation and P uptake by crops. P-CaCl2 and HWP were throughout the whole season significantly increased in the soil with addition of dairy farmyard manure, compared to all other treatments. This proves that the increased soil P intensity was not a random phenomenon.In a sorption experiment with radioactive labelled 33PO4, the orthophosphate distribution coefficient as estimator of the soil orthophosphate sorption strength was determined in both field trials. The P concentrations in the leachates of the leaching experiments were strongly negatively correlated to the soil orthophosphate sorption strength, which means that the adsorption of orthophosphate is affected by the organic fertilizer type, rather than a difference in organic P mobility between the organic fertilizers. The long term application of farmyard manure decreased the orthophosphate adsorption strength of the soil, where long term amendments of composts based on plant-based tended to have no or even an increasing effect on the soil orthophosphate adsorption strength.Both compost and farmyard manure will release organic acids in the soil that can chelate P sorption sites and compete strongly with orthophosphate on these P sorption sites (Fe and Al (hydr)oxides). In addition, organic C in organic fertilizer amendments forms stable complexes with P and enhances P retention in organic fertilizer amended soils. Since compost is a more decomposed and stable product than farmyard manure, we speculated that the release of organic acids from compost is smaller than from farmyard manure. Furthermore, more and more stable P containing organic C complexes are formed during composting of plant-based. We hypothesize that P amended with compost is retained in compost particles and is less soluble, whereas P and organic acids are rapidly released by farmyard manure. Based on our results, the differences in soil P sorption are less likely to be a pH-effect. We also found no evidence for Ca-P forming in or induced by plant-based composts.A third fertilization trial (Ghent University, °2010, silt loam) was sampled (i) to compare the effects of several processed digestate products with mineral fertilizers, VFG compost and animal manure, and (ii) to compare the effects of zero P fertilization, with continued yearly mineral P fertilization at 37 kg P/ha, on soil P intensity (P-CaCl2 and HWP), desorbable P stocks (P-AL) and P leaching (P concentrations in leachates). Substitution of mineral P fertilization by the solid fraction of mechanical separation of digestate from anaerobic digestion of plant material, increased both the soil P availability (P-CaCl2) and P leaching (P concentrations in leachates) by approximately 20%, compared to mineral P fertilization at an equal P fertilization rate of 37 kg P/ha.year. Similarly to dairy farmyard manure, the composition of this processed digestate product influenced clearly the properties of the soil, to retain P. Reduction to zero P fertilization significantly reduced the P concentrations in soil leachates from 0.43 mg P/L to 0.30 mg P/L, without any further effects on crop yield and P export.A pooled dataset was compiled with the data of the three field trials above and the data of two additional long term fertilizer field trials, conducted in silt loam soils in Melle (ILVO and Ghent University) to compile prediction models for P concentrations in soil leachates based on soil parameters. We observed that such a model is preferably based on soil P availability parameters P-CaCl2 or HWP. Although the P-CaCl2 based model had the highest model efficiency, P-CaCl2 fluctuates throughout the season. This means that P-CaCl2 can only predict the P leaching short after the soil sampling, or that the parameters that induce the seasonal trends in P-CaCl2 such as pH-H2O, need to be included in the model.The pooled dataset was also used to investigate whether farmyard manure, mineral fertilizers, cattle slurry and composts based on vegetal debris have a different effect on the soil P intensity. Based on this dataset, the soil P intensity was not determined by the fertilizer type, but however by the soil P content (P-AL and total P content of the soil). As this dataset contains soils with a large range of P contents, this could be expected. The eventual amount of P that becomes available in the soil solution will be determined by the soil P content. However, within one field, with the same P fertilizer history and P content, the capacity to retain P in the soil will be dependent on the fertilizer type. This is supported by the effect of fertilizers, that was observed in the long term fertilizer field trials separately. Although soil A with a larger soil P content than soil B, will result in a larger soil P intensity, the application of dairy farmyard manure will increase the soil P intensity and P concentrations in soil leachates in both soils. Based on this study, compost based on vegetal debris is a better option than farmyard manure to enhance SOC levels in (historical) excessively P fertilized soils. In contrast to farmyard manure, composts enhance the SOC levels without an increase in P leaching losses, compared to the reference situation. The underlying mechanism is however not yet fully understood and should be subject of further research. We suggest that future research should focus on the properties (straw/manure ratio, C/P ratio, biodegradability, organic acid content, biochemical composition, product stability, Ca content, pH, ) of farmyard manure, but also other organic fertilizers, that have an impact on soil P intensity and P leaching.nrpages: 262status: publishe

Prediction of P-concentrations in soil leachates: results of 6 long-term field trials on soils with a high P-load

We tested if a single soil P capacity test allows for a reliable forecast of P leaching from agricultural soils with a high P load. In regions with intensively managed arable soils, the soil P content has been dramatically increased by overfertilization with significant P leaching losses as a result. As a consequence, in order to control the P losses, P fertilization has been legally restricted. In several EU28 countries, the ammonium lactate extraction method (P-AL) is used as a soil test for P fertilizer advice, but sometimes also to determine the allowed P fertilizer dose to reduce leaching losses. We hypothesize that P-AL as an estimator of soil P capacity should be combined with 0.01M CaCl2 extractable P (P-CaCl2) and/or hot water extractable P (HWP), both estimators of the soil P intensity, to predict P leaching losses in soils with a high P load.Six long term field trials with a high P load (P-AL: 123 to 375mgPkg−1) on silt loam soils with a specific history of organic and inorganic fertilizer application were sampled for soil analysis and to conduct leaching experiments in the laboratory. P concentrations in the leachates served as a proxy for P leaching. Five field trials were used for model calibration and a sixth one for model validation. Two models, either with P-CaCl2 or with HWP as independent variables, have proven to be suited to distinguish soils with low and high risk for P leaching. In the range of P-AL in this study, P-AL proved to be a non-significant factor and was therefore not retained in either of the models. We conclude that for soils with large soil P stocks (high P-AL concentrations), both P-CaCl2 and HWP are suitable to detect the ones with a higher risk of P leaching losses. We suggest a threshold value for P-CaCl2 and HWP to be used in combination with P-AL, to select those soils where further P fertilization restrictions or other measures to reduce P leaching losses are needed most urgently. This threshold value however depends on what is considered as an acceptable P concentration in the leaching water of the tillage layer.status: publishe

Short-term effects of cover crops and tillage methods on soil physical properties and maize growth in a sandy loam soil

Soil compaction is a serious threat to agricultural production because of an expanding agricultural mechanization. Conservation tillage and use of pioneer plants can be an environmentally solution to alleviate the adverse effects of soil compaction. Root penetration into compacted soil of two winter cover crops with different rooting patterns, i.e. tap-rooted white mustard (Sinapis alba L.), and fibrous-rooted winter rye (Secale cereal L.), and of maize (Zea mays L.) in the consecutive growing season was assessed. Additionally, the effects of two spring tillage methods were evaluated, i.e. strip tillage and intensive tillage (by mouldboard ploughing). Winter rye showed significantly higher root penetration than white mustard in the top 15 cm, while an opposite trend was observed at 20-45 cm depth. After one season, maize root penetration was significantly greater following white mustard than winter rye at 30-40 cm depth. Strip tillage, like intensive tillage, could sufficiently loosen soil for adequate maize growth even though maize root distribution was restricted to tilled rows in contrast with intensive tillage. In conclusion, white mustard already showed positive short-term effects on maize growth, whereas strip tillage did not negatively affect it. Combining both is a viable option to reduce the negative impact of soil compaction on maize growth

Invited: Colloids Mediate Phosphate Leaching in Agricultural Soil: Observations and CD-MUSIC Modelling.

Phosphate (PO4) leaching through the soil profile is a pathway by which waterbodies are enriched with phosphorus (P) in agricutural areas. Colloidal-mediated PO4 leaching has been revealed before but it is unclear which factors contribute. Here, 123 columns, prepared from 40 different agricultural soils in Flanders (Belgium) and Feucherolles (France), were leached with artificial rainwater under unsaturated condition. Steady state P leachate concentrations ([P]) ranged from 0.001 to 0.235 mM P, out of which 113 exceeded 0.0045 mM P, i.e. the Flemish environmental limit for surface waters. The iron concentrations ([Fe]) in the leachates ranged from below detection limit to 1.4 mM. Moreover, aluminium concentrations ([Al]) in the filtrates correlated strongly with [Fe]. Both [Fe] and [Al] sharply increased with decreasing calcium concentrations ([Ca]), with largest concentrations below 1 mM Ca. The leachate [P] correlated remarkably strong with [Fe + Al] (r = +0.68 on log-log relationship) for soils with low P saturation (i.e. POx / 0.5(FeOx+AlOx) < 0.30, as measured in a soil oxalate extract). Multisite surface complexation modelling, with the CD-MUSIC model, predicted PO4 leaching by including effects of organic matter anions and Ca on PO4 sorption to particulate Fe- and Al(oxy)hydroxides and to colloids, with leachate Fe and Al as proxies for ferrihydrite colloids. The inclusion of the colloids improved predicted PO4 leaching (RMSE of the 10log transformed [P] = 0.47). The fraction of predicted colloid-bound PO4 increased with increasing [Fe + Al] (p < 0.001), yielding about a doubling of PO4 mobility at 0.3 mM [Fe + Al]. Up to 96 % of PO4, leached at steady state, was modelled to be colloid-bound. This study shows that high solution Ca, rather than high pH constraints colloidal PO4 transport.status: publishe

Investigation on the control of phosphate leaching by sorption and colloidal transport: Column studies and multi-surface complexation modelling

© 2018 Elsevier Ltd Surface complexation modelling (SCM) is a powerful tool to estimate speciation and fate of solutes in soil, provided sufficient model validation. This study aims to describe phosphate (PO4) leaching with SCM. The leachate phosphorus concentrations ([P]) of 120 unsaturated columns of contrasting agricultural soils were measured and modelled. Leachate [P] ranged 0.7–240 μM. Leachate [P] increased as the ratio of P to iron and aluminium ([Formula presented]) in acid oxalate soil extracts increased and as leachate Fe and Al concentrations ([Al + Fe]) increased. SCM was used to describe PO4 sorption to ferrihydrite (CD-MUSIC model). This yielded adequate description of leachate [P] (RMSElog10 = 0.39), but only when reactive PO4 was described from isotopically exchangeable PO4, when organic matter was included as the main competing adsorbate and when mobile colloidal ferrihydrite was included. The model reveals that colloidal PO4 transport enhanced leachate PO4 concentrations up to a factor 50 at small soil P content and small calcium (Ca2+) concentration in solution, as a large Ca2+ concentration enhances colloidal stability. This modelling approach explained that long-term application of organic fertilisers with higher Ca content reduced P leaching, likely due to the effect of Ca2+ on colloidal stability. A two-parameter empirical Langmuir model, based on soil Fe and Al oxyhydroxides, fitted data better than any SCM, suggesting that the empirical model might be advocated for application at large scale. This study revealed the power of SCM to better understand colloidal transport of P in soil.status: publishe

Renewable P sources: P use efficiency of digestate, processed animal manure, compost, biochar and struvite

International audienc

P availability and P leaching after reducing the mineral P fertilization and the use of digestate products as new organic fertilizers in a 4-year field trial with high P status

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The long term use of farmyard manure and compost: Effects on P availability, orthophosphate sorption strength and P leaching

This study was set up to identify the role of dairy farmyard manure and green waste or farm compost used as a source of stable organic matter on soil P availability and P leaching. We sampled two long term field trials (8 and 16 years) on silt loam soil, with continuous amendment of dairy farmyard manure (FYM) and 6 types of organic waste (VFG, BIO), municipal solid waste (MSW), sludge (GWS) or organic farm waste (CMC1, CMC2) composts. Soil P availability was measured as 0.01 M CaCl2 extractable P (P-CaCl2) and hot water extractable P (HWP) and fresh subsamples were used to conduct a leaching experiment in unsaturated conditions in the laboratory. Since the P fertilization history was not equal among the treatments, P leaching concentrations (TP) were standardized with the total P content of the soil (Ptot). P-CaCl2, HWP and the P leaching experiment revealed that in long term farmyard manure amended soils, more P becomes available and is susceptible to leaching than in long term VFG, BIO, MSW, CMC1 and CMC2 compost amended soils. We observed a seasonal trend in P-CaCl2 with minimum and maximum at end of winter (February) and mid-summer (July), respectively. Although this trend was independent of the fertilizer type amended on the soil, the P-CaCl2 significantly increased for farmyard manure amended soil, compared to compost amended soil at any time during the sampling period of >1 year. A sorption experiment with radiolabelled orthophosphoric acid (33PO4) revealed that increased soil P availability and P leaching are related to a decrease in orthophosphate sorption in farmyard manure amended soils, which was not observed in compost amended soils. It is concluded that farmyard manure derived P is more available and more prone to leaching compared to compost derived P due to differences in PO4 sorption.publisher: Elsevier articletitle: The long term use of farmyard manure and compost: Effects on P availability, orthophosphate sorption strength and P leaching journaltitle: Agriculture, Ecosystems & Environment articlelink: http://dx.doi.org/10.1016/j.agee.2015.09.009 content_type: article copyright: Copyright © 2015 Elsevier B.V. All rights reserved.status: publishe