Impact of poultry manure and rock phosphate amendment on C allocation in the rhizosphere of ryegrass plants

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Chemical characterization of poultry manure compost and soil

Chemical analyses of PM and soil samples were carried out according to the methodology described by Sadzawka et al. (2006). pH was determined in H2O with a 1:2.5 PM sample:
water solution ratio. Total C and nitrogen (N) were determined by dry combustion using a CHN auto-analyzer (CHN NA 1500, Carlo Erba). No carbonate was present in the soil; therefore, soil C is considered to be exclusively organic. Basic exchangeable cations (Ca, Mg, Na and K) were extracted with 1 M ammonium acetate (pH 7) and determined by atomic absorption spectrophotometry (AAS). Determination of Al and Fe present in the -humus complex (Alpyro and Fepyro) were determined by extraction with 0.1 M sodium pyrophosphate diphosphate (pH 10) and amorphous Al and Fe (Alox and Feox) were determined by extraction with 0.2 M ammonium oxalate pH 3.0 (van Reeuwijk, 2002). Al and Fe in pyrophosphate and oxalate extracts were measured by atomic absorption (UNICAM, 969 AA spectrometer) at 309 and 248 nm, respectively.

Phosphorus concentration and fractionation

Total P of PM and soil was determined in extracts by alkaline digestion with sodium hypobromite (NaBrO) (Dick and Tabatabai, 1977). Plant available P was extracted with sodium bicarbonate (0.5 M NaHCO3 at pH 8.50) (Olsen and Sommers, 1982).
The nature of P in PM and soil was determined by sequential extraction using a scheme based on that proposed by Hedley et al. (1982). Briefly, to quantify readily available P, 1 g of sample was extracted with 25 mL of deionized H2O. The samples were shaken during 16 h and then centrifuged at 5000g for 20 min. The soil solution was filtered and stored at 4 °C. The remaining sample was extracted, as described above, with sodium bicarbonate (0.5 M NaHCO3 at pH 8.5), followed by sodium hydroxide (0.1 M NaOH) and hydrochloric acid (1 M HCl) to extract P of decreasing lability. In all extracts, inorganic P was measured directly by colorimetry (Murphy and Riley, 1962), total P was measured by NaBrO digestion (Dick and Tabatabai, 1977), and organic P was calculated as the difference between total and inorganic P.

Soil particle size distribution

Aggregates of soil samples were metered out directly into a beaker with distilled water and the particle-size distribution was measured by the laser diffraction technique. Additionally, aggregate size of PM and soil samples was analyzed by scanning electron microscope (Variable Pressure Scanning electron microscope VP-SEM), with transmission module STEM SU-3500 (Hitachi-Japan). The details regarding applied voltage, magnification used and the scale of the images were implanted on the photographs.

Statistical analysis

Normality and homogeneity of variance were determined before analyses. Statistical differences of means (95% significance level) were analyzed using two ways analyses of variance (two-way ANOVA) with the aov function followed by Tukey test using p-value of 0.05. We identified significant differences among treatments in each soil and differences among soils in same treatment. The magnitude of correlations among soil available P, total C and the particle size distribution with Al and Fe forms parameters were tested by Pearson correlation coefficient. No statistical test was made with the percent of soil P proportion because these results were calculated with values already processed in ANOVAs. Principal component analysis (PCA) was performed using the package Factoextra; we consider the soil P fractions, total carbon concentration, particle size distribution and Al, Fe forms. Statistical testing was done using the statistical program R Foundation for Statistical Computing Version 1.1.456 (R Development Core Team 2009-2018 RStudio, Inc); effects were deemed significant at P < 0.05.

Chemical characterization of PM added to pasture soils

Sequential fractionation showed that composted PM was constituted similarly of organic P and inorganic P forms, representing 51 and 44% of total P, containing a 4.9% as residual P form. The P in PM was distributed as follows 18.5% in H2O, 26.4% in NaHCO3, 32.0% in NaOH, and 18.0% in the HCl extractable fraction (table 4). Additionally, PM had a high contribution of NaHCO3 extractable organic P.
Figure 6. Images scanning electron microscope (SEM) in composted poultry manure amendment showing its morphological structure. Magnification of 300x (left) and 500x (right).
The morphology of PM was heterogenous, being composed of different compounds (animal waste and straw) (Fig. 5). The scanning electron microscopy images showed the porous structure of this amendment and straw residues.

Soil chemical characterization and aggregation of Andisols under pasture amended with PM

The chemical characterization of the soil varied between the control, and the PM application group are shown in Table 5. Soil pH, and total C increased significantly in Huifquenco (p<0.001; p=0.003) and Santa Teresa (p=0.002; p<0.001) for PM amended soil as compared to the control. SOM (p<0.001) and Total N (p<0.001) content was significantly higher only for the Santa Teresa PM amended soil (9.8 g kg-1), as compared to the control (5.3 g kg-1).
Olsen P concentration was increased significantly (p<0.001) for all soils amended with PM, as compared with the controls. The highest increase was obtained for Santa Teresa Farm being 12-fold higher than the control. The pyrophosphate and oxalate-extractable Al concentrations were higher than both extractable Fe concentrations (Table 5).

Synergistic and Antagonistic Effects of Poultry Manure and Phosphate Rock on Soil P Availability, Ryegrass Production, and P Uptake

To maintain grassland productivity and limit resource depletion, scarce mineral P (phosphorus) fertilizers must be replaced by alternative P sources. The effect of these amendments on plant growth may depend on physicochemical soil parameters, in particular pH. The objective of this study was to investigate the effect of soil pH on biomass production, P use efficiency, and soil P forms after P amendment application (100 mg kg−1 P) using poultry manure compost (PM), rock phosphate (RP), and their combination (PMRP). We performed a growth chamber experiment with ryegrass plants (Lolium perenne) grown on two soil types with contrasting pH under controlled conditions for 7 weeks. Chemical P fractions, biomass production, and P concentrations were measured to calculate plant uptake and P use efficiency. We found a strong synergistic effect on the available soil P, while antagonistic effects were observed for ryegrass production and P uptake. We conclude that although the combination of PM and RP has positive effects in terms of soil P availability, the combined effects of the mixture must be taken into account and further evaluated for different soil types and grassland plants to maximize synergistic effects and to minimize antagonistic ones.
Fertilization of grasslands with mineral phosphorus (P) fertilizer is a common practice in many regions of the world to maintain productivity, especially on soils with high P retention (Redel et al., 2016; Rumpel et al., 2015; Velásquez et al., 2016a). In order to reduce the use of scarce phosphate rock (RP), alternative P fertilizers need to be found (Cordell et al., 2009; Reijnders, 2014). In this context, poultry manure, an abundant organic waste material from the growing broiler industry (FAO, 2018a), is known for its high P content (Pagliari and Laboski, 2012). Its transformation through composting into organic amendments, and their subsequent application in grassland systems may be a promising strategy (Calabi-Floody et al., 2018; Redding et al., 2016) to reduce the use of mineral fertilizers. Several studies showed that plant nutrient uptake and the biomass of several plants could be significantly increased using poultry manure compost (PM) (Evers, 2002; Pederson et al., 2002). The application of PM led to changes in soil P forms and phosphatase activity (Waldrip et al., 2011). However, despite its positive effects on plant nutrient availability and biomass production, the application of PM may lead to the simultaneous introduction of contaminants (Foust et al., 2018) and could also lead to a loss of P to waterways following long term application.
Therefore, nowadays, the use of PM in combination with RP has been considered as good practice to limit the use of both materials without compromising plant requirements (Song et al., 2017). However, the fertilizer value of both substrates may depend on the soil reaction. For example, RP efficiency may be limited in soils with high pH due to its low dissolution rate (Zapata and Roy, 2004), while in soils with acid pH, RP may lead to further acidification (Rajan et al., 1991). The efficiency of PMRP mixture for increasing wheat and chili yield and P uptake has already been demonstrated for acid and alkaline soils (Abbasi et al., 2015, 2013). However, no study has been carried out to investigate quantitatively the synergetic or antagonistic effects of the combined application of both materials.
In this study, we carried out a growth chamber experiment to investigate the effect of the combined use of PM and RP as compared to their application as a single amendment in soils with similar properties, but contrasting in pH. The objective of the study was to determine the effect of PM application, alone or combined with RP, on ryegrass biomass production, P use efficiency, and soil P availability in an acid and an alkaline soil. We hypothesized that the soils’ and plants’ response to the combined use of PM and RP in terms of biomass production and P use efficiency may depend on the soil reaction and that the mixture will have additional effects as compared to the use of PM and RP as a single amendment. Moreover, we hypothesized that the combined use of PM and RP will ameliorate P availability and biomass production as compared to their use as a single amendment.

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Table of contents :

Chapter I. General introduction 
1.1 General introduction
1.2 Phosphorus status of pasture ecosystems
1.3 Phosphorus cycling in pasture soils
1.3.1. Soil phosphorus forms
1.3.2. Phosphorus inputs and outputs
1.4. Plant available phosphorus in pasture soils and its uptake by plants
1.5. Managements practices to improve soil phosphorus availability
1.5.1. Mowing, grazing, and stocking density
1.5.2. Pasture plant species
1.5.3. Animal manure input as fertilization management
1.6. Conclusion and perspectives
2 Hypothesis
CHAPTER II. “Soil available P on southern Chilean pastures under composted poultry manure is regulated by soil organic carbon, and iron and aluminum complexes”
2.1 Introduction
2.2 Material and methods
2.2.1 Study farms and soil sampling
2.2.2. Chemical characterization of poultry manure compost and soil
2.2.3. Phosphorus concentration and fractionation
2.2.4. Soil particle size distribution
2.2.5. Statistical analysis
2.3 Results
2.3.1. Chemical characterization of PM added to pasture soils
2.3.2. Soil chemical characterization and soil particle size distribution on Andisols under pastures amended with PM
2.3.3. Soil phosphorus distribution of Andisols under pastures amended with PM
2.3.4. Relationship between soil parameters and soil particle size
2.4 Discussion
2.5 Conclusions
CHAPTER III. “Synergistic and Antagonistic effect of poultry manure and phosphate rock on soil P availability, ryegrass production, and P uptake”
3.1 Introduction
3.2 Materials and methods
3.2.1. Materials
3.2.2. Growth chamber experiment
3.2.3. Soil analyses
3.2.4. Biomass analyses
3.2.5. Synergistic and antagonistic effect of mixture
3.2.6. Statistical analysis
3.3 Results
3.3.1. Total soil C, N and P concentration
3.3.2. Soil phosphorus forms
3.3.3. Microbial biomass P
3.3.4. Shoot and root biomass production
3.3.5. Shoot and root concentrations and uptake
3.3.6. Relationship between soil parameters and plant parameters
3.3.7. Synergistic and antagonistic effect between PM and RP on soil
plant parameters
3.4 Discussion
3.4.1. Impact of organic and inorganic P amendments on C, N, and P stoichiometry and microbial biomass P
3.4.2. Impact of organic and inorganic P amendments on nutrient uptake and biomass production and soil P forms
3.4.3. Synergistic and antagonistic effect of the combined application of PM and RP
3.5 Conclusions
CHAPTER IV. “Impact of poultry manure and rock phosphate amendment on C allocation in the rhizosphere of ryegrass plants”
4.1 Introduction
4.2 Materials and Methods
4.2.1. Materials
4.2.2. Growth chamber experiment
4.2.3. Microbial biomass C
4.2.4. Soil organic matter density fractionation
4.2.5. Sources of soil organic carbon
4.2.6. Statistical analysis
4.3 Results
4.3.1. Microbial biomass C
4.3.2. Plant-derived C, poultry manure compost- derived carbon, and native rhizosphere soil C
4.3.3. Total C and N derived from plant and poultry manure compost input and their distribution in SOM fractions
4.4.4. Relationship between parameters
4.4 Discussion
4.4.1. Effect of amendments on soil C and N status
4.4.2. Effect of amendments on C transfer from plant to soil
4.5 Conclusions
Chapter V. “General discussion and concluding remarks” 
5.1 General discussion
5.2 Concluding remarks and future directions

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