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Management practices to improve soil phosphorus availability
The P bioavailability in productive grasslands is affected by several factors of managements including soils nutrients interactions (Paredes et al., 2011). Due to high phosphate fertilizer prices following phosphate rock (RP) future scarcity (Cordell et al., 2009; Reijnders, 2014), there is a research need for strategies by which P fertilizers can be used more effectively and improve their uptake efficiency by plants. Possible options to do this include the management of: pasture plant species (Cougnon et al., 2018; Klabi et al., 2018; Maltais-Landry, 2015), grazing intensity (Baron et al., 2001; Chaneton et al., 1996; Mundy et al., 2003; Neff et al., 2005; Simpson et al., 2012), cutting intensity, stocking density (Alfaro et al., 2009; Gao et al., 2016; Simpson et al., 2015), and animal manure inputs (Abdala et al., 2015; Adeli et al., 2003; Costa et al., 2014; Duan et al., 2011; Geisseler et al., 2011; Mclaughlin et al., 2004; Takeda et al., 2009; Vanden Nest et al., 2016). In grazed pasture, improving the recycling of P may be achieved through grazing management that reaches more uniform animal excreta distribution, hence, P returns to the pasture (Syers et al., 2008; Williams and Haynes, 1990).
Mowing, grazing and stocking density
Mowing trials are used to measure pasture responses to nutrients because they are much cheaper to operate than grazing trials, but in mowing trials the influence of the grazing animal through excreta return, treading and defoliation is absent (Morton and Roberts, 2001). Longterm biomass removal contribute to a less labile organic P relative to SOC attributed to enhanced mineralization of labile organic P in response to continued depletion of soil inorganic P (Boitt et al., 2017). Simpson et al. (2012) found that inorganic and organic P in the readily available fraction and the residual P were higher in soil from clippings left treatments compared with the no mowing and clippings removed treatments. Moreover, the P uptake for the clipping left was 51-54% higher than no mowing treatment. Grazing can improve soil quality over time, maintaining higher moderate and labile P pools and contributing increases on pasture yield (Costa et al., 2014). Increasing animal densities reduces the selection for palatable vegetation patches within a grazing camp, and that this can reduce the spatial heterogeneity in vegetation vigor over time (Venter et al., 2019). Also, differences in the stage of the plant before start the grazing is important to consider as nutritive value. Lawson et al. (2017), demonstrated that 3-leaf stage in tall fescue appears to be the most productive of the grazing-management plant persistence and the ability of lactating dairy cows to consume the dry matter (DM) grown efficiently.
Animal manure input as fertilization managements
Nowadays, as a consequence of the growing global population, the animal production has been increasing heavily with greatly effects on animal disposal. According to FAO (2018b) beef production in developing countries by 2027 was projected to be 21% higher, also the sheep meat consumption worldwide on a per capita basis will reach 1.8 kg retail weight equivalent (r.w.e.) by 2027, as a consequence its production will experience a higher rate of growth than that of the previous decade. Moreover, sheep and goats increased 60% from 1961-2016, while swine increased 140% and poultry had a remarkable five-fold increase. Manure applications during grazing periods have a different nutrient content which can vary widely depending on manure type (Table 2), animal physiology, species and age, composition of diets, and moisture content (Fuentes et al., 2006). The inorganic P pool of manures is large and has been reported to vary between 60 – 90%, being quite soluble and readily available to plants (Bolan et al., 2010; He and Honeycutt, 2001; Pagliari and Laboski, 2012; Sato et al., 2005). Options to increase plant-available P pool and optimize plant contribution to modify soil P cycle are the strategic use of organic-anion secreting plants or organic manures (Richardson et al., 2009). During grazing, plants received different manure inputs depending of the grazing animal type (Table 2).
Study farms and soil sampling
Soil samples were collected in the summer of 2015-2016 from 4 grazing farms located in southern Chile: Copihual (39°13’45”S, 72°12’27”W), Carilafquen (39°01’57”S, 72°03’57”W), Huifquenco (39°17’17”S, 72°14’18”W), and Santa Teresa (39°54’60”S, 72°41’30”W) (Fig. 5). All farms were located on Andisols with loamy texture formed from volcanic parent material and belong to 3 different soil series (Villarica, Cunco and Los Lagos) (CIREN, 2003). The climate in this region is temperate with rainfall ranging between 200 and 2000 mm year-1. Although land management at the farms was similar, at Copihual and Carilafquen the soils received 3 Mg ha-1 of composted PM annually for 5 years and at Huifquenco and Santa Teresa 3 Mg ha-1 of composted PM were added to soils annually for 10 years.
Table of contents :
Acknowledgements
Abbreviations
Thesis summary and outline
Table of contents
Figures index
Tables index
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
Hypothesis
General objective
Specific objectives
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”
Abstract
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”
Abstract
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
References
