Title: Long term use of different organic fertilizer types and impact on phosphorus leaching
Other Titles: Impact van het langetermijn bemesten met verschillende organische meststoffen op fosforuitspoeling
Authors: Vanden Nest, Thijs
Issue Date: 5-Jan-2015
Abstract: 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.
Publication status: published
KU Leuven publication type: TH
Appears in Collections:Division Soil and Water Management

Files in This Item:
File Status SizeFormat
20141213_PhD_ThijsVandenNest.3-262.pdf Published 5838KbAdobe PDFView/Open Request a copy

These files are only available to some KU Leuven Association staff members


All items in Lirias are protected by copyright, with all rights reserved.