TY  - THES
TY  - BOOK
T1  - Use of charcoal and sago (metroxylon sagu rottb.) bark ash to increase phosphorus availability in low pH soils for sorghum [sorghum bicolor (L.) moecnh} production
A1  - Prisca Divra Johan,
LA  - English
UL  - http://discoverylib.upm.edu.my/discovery/Record/601198
AB  - Phosphorus (P) is one of the essential elements for plant growth and development. However, the amount of soil-available P in the humid tropic mineral acid soils is often below plant requirements. Limited availability of P is related to the fixation reaction and this reaction is pH dependent. In acid soils, the predominance of aluminium (Al) and iron (Fe) oxides or hydroxides reduce the solubility of soil inorganic P through fixation on positively charged surfaces. In alkaline soils, P readily reacts with calcium (Ca) to form sparingly soluble calcium phosphates. Hence, a large proportion of applied P may become chemically bound, whereas only a small fraction of soil P remains in the soil solution and available for plant uptake. To date, limited research has attempted to unravel the use of charcoal with the incorporation of sago (Metroxylon sagu) bark ash to reduce P fixation in acid soils. It was hypothesized that combined application of charcoal and sago bark ash will enhance P availability in acid soils through increasing soil pH. The objectives of this study were to: (i) determine the effects of amending Egypt rock phosphate (ERP) with charcoal and sago bark ash on P availability; (ii) determine the influence of charcoal and sago bark ash on P leaching; and (iii) improve dry matter production, P uptake, and P recovery efficiency of sorghum cultivated on an acid soil following co-application of charcoal and sago bark ash.
A series of experiments were conducted at Universiti Putra Malaysia, Bintulu Sarawak Campus, Malaysia, comprise incubation, leaching, pot, pH buffering capacity, and sorption studies to evaluate the potential of the combined use of these amendments to unlock P fixation in acid soils. Laboratory incubation and leaching studies were carried out for 90 and 30 days, respectively. Charcoal and sago bark ash rates were varied by 25, 50, 75, and 100% of the recommended rate, whereas ERP rate was fixed at 100% of the recommendation rate in all treatments except for soil alone. Promising treatments from incubation study was
selected and further evaluated in pot trial. Sorghum was chosen as the test crop because of its sensitivity, which can reflect nutrient recovery, uptake, and efficiency and rapid response towards nutrient deficiency. pH buffering capacity and sorption studies were performed to verify the findings in incubation and leaching studies. Soil total P was extracted using the aqua regia method, soil available P was determined using the Mehlich 1 method, and inorganic P was fractionated using the sequential extraction method based on its relative solubility. Other selected soil chemical properties were determined using standard procedures.The incubation study results indicated that application of charcoal and sago bark ash to the soil increased soil pH and at the same time, they reduced exchangeable acidity, Al3+, and Fe2+. The findings suggest that the alkalinity of sago bark ash and the high affinity of charcoal for Al and Fe ions might have impeded these acidic ions from undergoing hydrolysis to produce more H+ because a complete one mole of Al3+ hydrolysis produces three moles of H+. Additionally, amending acidic soils with these amendments positively enhanced the availability of potassium (K), calcium (Ca), magnesium (Mg), and sodium (Na). Although there was no significant improvement in soil available P with or without charcoal and sago bark ash, the application of these amendments altered inorganic P fractions in the soil. Calcium-bound phosphorus (Ca-P) was more pronounced compared with aluminium-bound phosphorus (Al-P) and iron-bound phosphorus (Fe-P) for the soil with ERP, charcoal, and sago bark ash. In the leaching study, it was noticed that as the rate of sago bark ash decreased, the pH of leachate decreased, suggesting that unlike charcoal, the sago bark ash has significant impact on the alkalinity of leachate. Similar to an incubation study, soil exchangeable acidity, Al3+, and H+ reduced significantly following co-application of charcoal and sago bark ash with ERP. Also, the addition of charcoal to soils demonstrated positive effects on reducing P loss because charcoal has the ability to capture and hold P solution. Besides, the study demonstrated that without the presence of plant, sago bark ash has the potential to release P into the water continuously and gradually compared with charcoal.
The findings of the pot trial revealed that dry matter production, P uptake, and P recovery efficiency of sorghum increased when sago bark ash was single applied or co-applied with charcoal to the soil. The low contributions of soil with charcoal alone on the aforementioned properties could be because of its slow decomposition rate. However, in comparison to the existing practice, amending soil with charcoal alone demonstrated better outcomes. Furthermore, the addition of ERP transformed the dominance inorganic P fractions in the soil from Fe-P to Ca-P. The higher Ca-P content in the ERP treatments suggests that the undissolved rock phosphates dissolved slowly with time. The increase in loosely soluble phosphorus (Sol-P) for the treatments with charcoal and sago bark ash compared with soil alone and ERP alone is partly related to the readily soluble P released by the charcoal and sago bark ash through mineralization and dissolution, respectively.The increase in the pH buffering capacity of the combination of charcoal, sago bark ash, and soil suggests that the base cations released from the sago bark ash were mainly because of the dissolution of carbonate and the release of exchangeable base cations adsorbed on negative charge sites from the dissociation of the oxygen-containing functional groups on the charcoal. In the P sorption study, the results suggest that the combined use of charcoal and sago bark ash decreased P adsorption and increased P desorption relative to untreated soils. Organic matter in the charcoal reduces P sorption by providing more negatively charged surfaces, thus increasing anion repulsion. Besides increasing the amount of P adsorbed in the soil, the use of the sago bark ash increased the amount of P desorbed because the primary reaction between sago bark ash and soils is an acid neutralization reaction.
Overall, the use of 75% charcoal with 75% sago bark ash, 75% charcoal with 50% sago bark ash, and 50% charcoal with 75% sago bark ash was found to be more effective in improving P availability in acid soils. It is believed that the long-term application of charcoal and sago bark ash can positively change the physical and chemical properties of soils. These improvements do not only reduce P fixation in acid soils, but they also promote effective utilization of nutrients through timely release of nutrients for maximum sorghum production. A field trial to consolidate the findings of this work is recommended.
OP  - 186
CN  - FSPH 2022 11
KW  - Soils.
KW  - Acid soils.
KW  - Sago.
ER  -