Investigation of the interactions between soil acidity, phosphorus biochemistry and dynamics and legumes in acid grassland soils : A thesis submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy at Lincoln University

Soil acidity and associated phosphorus (P) deficiency and aluminium (Al) toxicity are major constraints to agricultural production worldwide. For instance, in New Zealand steep lands, the so-called hill and high country, many commercial legume species fail to establish and persist in these acidic, low fertility environments. This PhD research project investigated (1) the impact of phosphogypsum (PG) on soil fertility and Al speciation in the soil solution and (2) the impact of lime-induced pH elevation on P biochemistry and dynamics in the rhizosphere of lupins and under open field grassland conditions. For the first part of the investigation, two experiments were conducted, each with a specific objective; in the first experiment (Chapter 2) the objective was to compare the effects of PG amendment, soluble fertilizer, and lime on short-term lucerne yield and P and sulphur (S) uptake in two different acidic soils under controlled environment conditions. The objective of the second experiment (Chapter 3) was to examine the impact of PG on Al speciation in the porewaters of both planted and incubated (unplanted) soils using the Visual Minteq Model. These two complementary experiments revealed that (1) PG has increased P and S bioavailability and therefore improved lucerne P and S uptake and yield. However, the application of PG to low pH soils necessitates its combination with lime because it has been found that pH was the most important factor controlling the nutrition and growth of lucerne as evidenced by the large difference in the yield and P and S uptakes between PG alone and PG combined with lime. The second key result (2) was that PG reduces soil exchangeable Al and monomeric Al3+in the soil solution if applied at 1-3 t ha-1. Higher application rates could acidify the soil and displace Al from the soil exchangeable sites into the soil solution. The mechanisms by which PG reduced Al3+ activity included the immobilization process through sulphate (SO42-) and fluoride (F-) binding and via precipitation reactions. For the second part of the investigation, three experiments were conducted (Chapters 4, 5 and 6), each with a specific objective. Experiment 1 (Chapter 4) objective was to examine the effects of increasing soil pH from 5.3 to 6.0 using lime on P-related processes and dynamics in the rhizosphere of two lupins (Lupinus polyphyllus and Lupinus angustifolius) after 11 weeks of plant growth in pots under glasshouse conditions. Experiment 2 (Chapter 5) was conducted to examine the impact of soil pH increase to near-neutral (pH 6.3) using lime on (1) acid phosphatase activity and labile P (DGT-P) distribution patterns in the rhizosphere of Lupinus angustifolius grown in two contrasting acid pasture soils, using innovative imaging techniques, (2) root morphological and physiological root traits. Experiment 3 (Chapter 6) was carried out in the field to study and quantify the effects of liming on P biochemistry and fractionation during 18 months on a long-term (+60 years) permanent fertilized grassland. All three experiments investigated the same soil (Mt Grand soil), collected from Central Otago, NZ—they proved unanimously that liming increases P availability and increases the mineralization of labile and moderately labile organic P (Po) in this soil. For instance, in the field experiment, labile inorganic P (Pi) increased by 42% at pH 7.0 compared to pH 5.4, while labile and moderately labile Po decreased by 33% and 25%, respectively. It was concluded from Chapters 4 and 5 that increasing soil pH above 6.0 negatively affects Lupinus angustifolius growth and P acquisition processes such as organic anions exudation and fine root length, while Lupinus polyphyllus was unresponsive to liming. Another conclusion drawn from the field trial (Chapter 6) is that liming enhances the mobilization of the historically applied P fertilizer and promotes Po mineralization

A Phenomenological Study of Academic Retention: The Lived Experiences of Adults Who Were Retained in K-12

The purpose of this qualitative transcendental phenomenological study was to understand the lived experiences of young adults who were retained during their K-12 education and persisted to high school graduation from a southwestern Kansas school. The central research question guiding the study were: What are the lived experiences of young adults who were retained during their K-12 education and persisted to high school graduation from a southwestern Kansas school? Guiding questions were implemented to further understand the phenomenon of grade retention. The guiding questions were: How did the young adults believe their self-efficacy was influenced either positively or negatively by grade retention? How did the young adults explain their K-12 educational experiences and the adult’s future in connection with their personal grade retention? Bandura’s self-efficacy theory is the examination of one’s own belief on their own ability to achieve a self-determined level of success is based on their own life’s experiences and will serve as the theoretical framework. Bandura’s theory relates to the proposed study in the understanding of the life experiences of adults’ self-efficacy who were retained during their K-12 education. Study participants were selected through a participant recruitment survey. The study included 13 participants who were retained during their K-12 education. The data collection methods included interviews, journal entries, and a focus group of the young adults. The transcendental phenomenological reduction process was used for data analysis. This research disclosed both positive and negative outcomes to retention

Early effects of surface liming on soil P biochemistry and dynamics in extensive grassland

Liming effects on soil phosphorus (P) availability via biological P cycling are not clear. We conducted an 18-month field experiment on a long-term (60 years +) permanent fertilized grassland in a relatively dry environment. The aim was to examine the impact of liming on P biochemical processes and dynamics. Lime was applied at the beginning of the experiment to produce a soil pH range of 5.4–7.0, with no fertilizer P treatments. Soil sampling was conducted throughout the experimentation period at 0–75 mm. All soils were analysed for moisture content, pH, Olsen P, resin P, exchangeable aluminium (Al), microbial biomass P (MBP) and enzyme activities. At the final sampling, the soil samples were analysed for total C, total N and anaerobic mineralizable N (AMN). A sequential P fractionation was conducted for 0–30 mm depth samples. Liming effects on soil pH and P processes were limited to the surface 30 mm only, where labile inorganic P (Pᵢ) fraction increased by 42% at pH 7.0 compared to pH 5.4, while labile and moderately labile organic P (Pₒ) decreased by 33% and 25%, respectively. Strong positive relationships were found between microbial P and: soil pH, labile Pᵢ, total C and AMN. Absolute activities of acid and alkaline phosphomonoesterases were not affected by liming. However, their specific activity decreased by 47% and 28%, respectively at pH 7.0 compared to pH 5.4. Absolute enzyme activity of phosphodiesterase correlated strongly and positively with labile Pᵢ. Our findings demonstrate that liming enhances plant P availability under field conditions in long-term fertilized extensive grassland. However, the effects are limited to near-surface depths in the soil

Nitrogen fertilization effects on soil phosphorus dynamics under a grass-pasture system

Nitrogen (N) and phosphorus (P) are critical to pasture productivity; however, limited information is available on how the single and combined additions of N and P affect soil P fractions and seasonal changes in microbial and biochemical processes linked to P cycling under pasture systems. A two-year field trial was conducted where N (0 or 250 kg ha¯¹yr¯¹) and P (0 or 50 kg ha¯¹yr¯¹) were applied in a full factorial design to an intensively managed grass-pasture system. Changes in plant growth and nutrient uptake, soil microbial biomass P, soil phosphatase activities, and soil inorganic and organic P fractions were assessed by regular sampling. Phosphorus addition increased Olsen P and shoot P uptake but not shoot biomass compared to the control. In contrast, N addition decreased Olsen P by 23% but increased both shoot biomass and P uptake by 1.6-fold, compared to the control. Microbial biomass P was irresponsive to N and P additions. Phosphatase enzyme activity significantly increased in summer under N addition, which was linked to labile organic P mineralization. After two growing seasons, N addition alone significantly decreased readily-available inorganic P, labile inorganic P, moderately labile inorganic P, and labile organic P by 75, 19, 7, and 28%, respectively, compared to the control. On the other hand, combined N and P addition significantly decreased readily-available inorganic P, labile inorganic P, and labile organic P by 39, 26, and 28%, respectively, but had no impact on moderately labile inorganic P compared to P addition alone. The findings of this study revealed that short-term N fertilization to N-limited grass-pastures can accelerate P cycling by mobilizing labile inorganic and organic P as well as moderately labile inorganic P pools. However, N fertilization combined with P applications exceeding plant requirements cannot mobilize moderately labile inorganic P, which accumulates under high P sorbing soils

Lime-induced pH elevation influences phosphorus biochemical processes and dynamics in the rhizosphere of Lupinus polyphyllus and Lupinus angustifolius

The biochemical drivers of phosphorus (P) availability and cycling are sensitive to changes in soil pH. However, reports of lime-induced pH modification effects on P availability are (1) inconsistent, (2) focused mainly on chemical changes, and (3) often limited to the bulk soil. Using lupin as an indicator species, we aimed to evaluate the effects of lime-induced soil pH change, from 5.3 to 6.0, on biochemical processes responsible for P mobilization and dynamics in the rhizosphere of two different lupin species. Indicator species, blue lupin (Lupinus angustifolius) and Russell lupin (Lupinus polyphyllus), were grown in a P-deficient acid grassland soil without P inputs for 11 weeks in a glasshouse. The rhizosphere soils were analyzed for enzyme activity, microbial P, and carboxylates. Both bulk and rhizosphere soils were analyzed for P fractions, exchangeable aluminum (Al), and pH. Plant yields and shoot P uptake were measured. Labile inorganic P (Pi) increased in the rhizospheres of both lupin species, likely due to Pi desorption combined with labile organic P (Po) mineralization, induced by rhizosphere pH elevation after liming. Soil pH increase promoted microbial P immobilization and reduced phosphomonoesterase activity in the rhizosphere, leading to an accumulation of Po mainly as moderately labile and stable Po forms. Total carboxylate concentration (TCC) increased with soil pH increase. Variation in shoot P uptake was mostly explained by TCC. These results indicate that (1) lime application strongly affects P biochemical processes and dynamics in the rhizosphere of lupins. (2) Russell lupin utilizes less P than blue lupin and is unresponsive to liming

Impacts of phosphogypsum, soluble fertilizer and lime amendment of acid soils on the bioavailability of phosphorus and sulphur under lucerne (Medicago sativa)

Legumes play critical dual roles in grazed grassland ecosystems; providing nitrogen inputs and high-quality feed for grazing livestock. However, many species fail to persist in acidic, low fertility soils. A glasshouse study was conducted to investigate the response of lucerne (Medicago sativa) to phosphogypsum (PG), lime and soluble P + S fertilizer (PS) application to two soils. Phosphorus and sulphur were applied through either PG (0, 1, 3 and 9 t ha¯¹) or P + S fertilizer at equivalent rates to PG. Both PG and PS were applied with or without lime, which was applied at 2 t ha¯¹. Yield and nutrient uptake of the lucerne was measured, while the soil was analyzed for pH, Olsen P and exchangeable aluminum. Yield responses were significantly different between the two soils. Maximum yields and P and S uptakes were obtained under PG 9 t ha¯¹ combined with lime. Exchangeable Al decreased in both soils under 1 ha¯¹ of PG compared with the control. At the highest rate, Olsen P increased by 8 and 6 mg kg¯¹ for PG and by 6 and 11 mg kg¯¹ for PS compared with the control for Glenmore and Molesworth soils respectively. Phosphogypsum showed positive effects on P and S bioavailability

Soil pH effects on phosphorus mobilization in the rhizosphere of Lupinus angustifolius

Purpose Increasing the pH of acid soils is a well-recognized means of improving their fertility; however, the effects that plants impose on rhizosphere soils in response to this change are not well understood. This research sought to investigate changes in phosphorus (P) availability in the rhizosphere of blue lupin (Lupinus angustifolius) in response to an increase in pH. Methods Blue lupin plants were grown in rhizoboxes using two contrasting acid soils at their native pH (5.3 and 4.7) and treated with lime to increase their pH to 6.3 in a replicated trial. Measurements of localized acid phosphomonoesterase activity and P flux were made next to lateral root segments using a combination of zymography and diffusive gradient in thin films (DGT). Rhizosphere and bulk soils were tested for pH, organic anions, exchangeable aluminium (Al), labile P and phosphomonoesterase activity. Root morphological traits, root and shoot yields and shoot nutrient concentrations were also recorded. Results Profiles of DGT-P fluxes across lateral roots showed mobilization of P in the soil with the higher organic P content, and depletion in the other. The extent of acid phosphomonoesterase activity in the rhizosphere decreased with soil pH increase. Shoot P uptake was strongly correlated with fine root length and total organic anions in the rhizosphere. The proportion of thin roots decreased at pH 6.3 compared to the native pH, whereas that of thick roots increased. Conclusion Soil pH increase to 6.3 using lime negatively affects the P acquisition by blue lupin due to the reduction of organic anion exudation, fine root length and the extent of acid phosphomonoesterase activity in the rhizosphere

The relationship between soil moisture and soil water repellency persistence in hydrophobic soils

In this work, we modelled the response of soil water repellency (SWR) persistence to the decrease in moisture in drying soils, and we explored the implication of soil particle size distribution and specific surface area on the SWR severity and persistence. A new equation for the relationship between SWR persistence and soil moisture (θ) is described in this paper. The persistence of SWR was measured on ten different hydrophobic soils using water drop penetration time (WDPT) at decreasing levels of gravimetric water content. The actual repellency persistence showed a sigmoidal response to soil moisture decrease, where Rₐ(θ) = Rₚ/1 + eδ⁽θ⁻θ⁾. The suggested equation enables one to model the actual SWR persistence (Rₐ) using θ, the potential repellency (Rₚ) and two characteristic parameters related to the shape of the response curve. The two parameters are the critical soil moisture θ, where the Rₐ increase rate reaches its maximum, and the parameter δ affecting the steepness of the curve at the inflexion point of the sigmoidal curve. Data shows that both soil carbon and texture are controlling the potential SWR in New Zealand pastures

Effect of phosphogypsum application on aluminum speciation in acid pasture soils

Purpose: Legume establishment and persistence in New Zealand hill and high-country soils are largely limited by high soil acidity and associated aluminum (Al) toxicity. The present study aimed to evaluate the effect of four rates of phosphogypsum (0, 1, 3, and 9 t ha¯¹) on Al speciation in the soil solution and to examine which species are mostly impacting total dry matter (TDM) yield of lucerne. Methods: Glasshouse and incubation experiments were conducted using three acid soils with different exchangeable Al concentrations: Molesworth, Glenmore, and Lindis Peaks. The distribution of Al species was modeled using visual Minteq. Partial least square (PLS) regression was used to evaluate the relationships between Al³⁺ and other variables in the soil-soil solution system. Results: In the planted and incubated Molesworth soils, Al³⁺ and hydroxylated Al (Al–OH) fractions decreased significantly at 1 and 3 t of phosphogypsum ha−1 compared to 0 t ha¯¹. However, in the planted Glenmore and incubated Lindis Peaks soils, these two fractions remained unchanged. The contribution of variables in Al³⁺ concentration depended on the soil type. However, the loading plot of the whole soil data set (n = 62) showed that Al–OH, base saturation, soil/soil solution pHw, and exchangeable Al were the main explanatory variables for the variation in Al³⁺ concentration. The TDM yield of lucerne was better explained by Al³⁺ , Al-F, and Al-DOM than exchangeable Al. Conclusions: Reasonable amounts of phosphogypsum (1 to 3 t ha¯¹) can help to alleviate Al toxicity in acid soils (pH ≤ 5.3), but higher application rates should be avoided

Recent advances of AOPs: Promising solutions for the degradation of emerging contaminants in wastewater

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