Tropical Acid Soils Research Articles

Co-Application of Inorganic Fertilizers with Charcoal and Sago Bark Ash to Improve Soil Nitrogen Availability, Uptake, Use Efficiency, and Dry Matter Production of Sorghum Cultivated on Acid Soils

Efficient management of N fertilizers enhances crop yields and contributes to sustainable food security. Tropical acidic soils with high Al and Fe are prone to easy loss of basic cations, such as NH4+, via leaching and erosion. Appropriate soil amendments and agronomic practices minimize the loss of fertilizer nutrients, improve soil nutrient retention, and maximize their uptake by plants. This study aimed to evaluate the effects of co-applying charcoal and sago bark ash with inorganic fertilizers on N availability, uptake, use efficiency, and dry matter production of sorghum in a tropical acid soil. The results revealed that the co-application of inorganic fertilizers with charcoal and sago bark ash increased sorghum plant height, dry matter production, N uptake and N use efficiency. The soil treated with a combination of 100% of the recommended rate of charcoal and sago bark ash (C1A1) resulted in significantly higher sorghum dry matter production, N uptake, and use efficiency compared with normal fertilization (U1). The C1A1 treatment resulted in significantly lower soil available N compared with U1. The C1A1 treatment enhanced the uptake of N by the sorghum plants, resulting in less available N in the soil after the experiment. Although the effects of co-applying charcoal and sago bark ash on soil total N were not glaring, this practice increased soil pH and total C, and reduced exchangeable acidity and Al3+. A long-term field study is recommended to confirm the effects of co-applying inorganic fertilizers with charcoal and sago bark ash on sorghum productivity, economic viability, and soil nutrient residual effects.

Dynamics of ammonia volatilization from NBPT-treated urea in tropical acid soils

The urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) reduces NH3 losses from urea (UR) surface-applied to soils, but its efficacy may be lower in acidic soils. The period when urease inhibition occurs efficaciously may change with soil pH. This needs to be clarified in tropical soils which are commonly acidic. This study evaluated the effectiveness of NBPT-treated urea to delay and reduce ammonia volatilization in two soils at three pH levels. Two experiments were conducted under laboratory conditions in soils with different textures (sandy-clay and clay). The treatments consisted of three soil pH levels and two N sources (UR and UR + NBPT), with five replicates. The soil pH values were adjusted and reached values of 4.5, 5.6, and 6.4 in the sandy-clay, and 4.5, 5.4, and 6.1 in the clay soil. Ammonia volatilization was measured using glass chambers (1.5 L). In the sandy-clay soil, NH3 losses were 40-47 % of the UR-N. In the clay soil, losses were 26-32 %. The addition of NBPT to UR reduced the NH3 volatilization by 18-53 %; the inhibitor decreased the N losses under all soil pH conditions but was significantly less efficient in acidic soils (pH 4.5). The lower efficiency of the inhibitor under acidic conditions was more evident in the first few days: 50 % of the total NH3 losses occurred in less than four days in soils with pH 4.5, but in 8-11 days in soils with pH above 5.4. The rapid loss in efficiency in more acidic soils is a drawback. Using NBPT in severely acidic soils showed a relatively small advantage over untreated UR as the inhibitor did not provide extra time for fertilizer incorporation and further reduction of NH3 losses.

Biochar and NPK fertilizer co-applied with plant growth promoting bacteria (PGPB) enhanced maize grain yield and nutrient use efficiency of inorganic fertilizer

A field experiment was carried out for two consecutive years to assess the yield response of maize and the use efficiency of nitrogen, phosphorus and potassium following the application of biochar and mixed culture of Bacillus spp and Pseudomonas spp to Inorganic NPK fertilizer. Seven treatments comprising: control, inorganic NPK fertilizer at half rate (HR), inorganic NPK fertilizer at full rate (FR), inorganic NPK fertilizer (HR)+biochar (1500 kg ha -1 ), inorganic NPK fertilizer (FR) + biochar (1500 kg ha -1 ), inorganic NPK fertilizer (FR)+biochar (1500 kg ha -1 )+P + B, inorganic NPK fertilizer (HR)+biochar (1500 kg ha -1 )+P + B were laid in a randomized complete block design. Bulk density reduced only in fields amended with the treatments that included biochar. Also, soil pH increased in all plots that were co-amended with inorganic NPK and biochar. Soil organic carbon, cation exchange capacity, dehydrogenase activity and metabolic quotient significantly increased in the amended plots compared with the control. However, inorganic NPK fertilizer + biochar with mixed bacteria cultures, enhanced organic C, dehydrogenase activity and metabolic quotient compared with NPK alone or NPK + biochar. Nitrogen, phosphorus and potassium uptake and the use efficiency and yield of maize, were superior in treatments that included mixed bacteria cultures compared to the addition of NPK alone or NPK + biochar. Our study showed that the inclusion of mixed culture of bacteria in combination with biochar is a promising strategy to increase grain yield, enhance the use efficiency and reduce the rates of inorganic NPK fertilizer application recommended for cultivating maize in the coastal savannah agroecological zone of Ghana. • Arable soils in sub-Saharan Africa are characterised by aluminium toxicity and nutrient deficiency hence causing yield decline of maize. • Chemical fertilizers, although successful in supplying macro- and micro-nutrients, their use efficiency is reduced due to nitrogen leaching and phosphorus precipitation in tropical acid soils. • The co-application of biochar and microbial resources proved superior in improving the use efficiency of inorganic NPK fertilizer and maize yield compared with either inorganic NPK fertilizer alone or inorganic fertilizer + biochar.

Nitrogen-enriched biochar co-compost for the amelioration of degraded tropical soil

ABSTRACT Tropical soils are often deeply weathered and vulnerable to degradation having low pH and unfavorable Al/Fe levels, which can constrain crop production. This study aims to examine nitrogen-enriched novel biochar co-composts prepared from rice straw, maize stover, and gram residue in various mixing ratios of the biochar and their feedstock materials for the amelioration of acidic tropical soil. Three pristine biochar and six co-composts were prepared, characterized, and evaluated for improving the chemical and biological quality of the soil against a conventional lime treatment. The pH, cation exchange capacity (CEC), calcium carbonate equivalence (CCE) and nitrogen content of co-composts varied between 7.78–8.86, 25.3–30.5 cmol (p+) kg−1, 25.5–30.5%, and 0.81–1.05%, respectively. The co-compost prepared from gram residue biochar mixed with maize stover at a 1:7 dry-weight ratio showed the highest rise in soil pH and CEC, giving an identical performance with the lime treatment and significantly better effect (p < .05) than the unamended control. Agglomerates of calcite and dolomite in biochar co-composts, and surface functional groups contributed to pH neutralization and increased CEC of the amended soil. The co-composts also significantly (p < .05) increased the dehydrogenase (1.87 µg TPF g−1 soil h−1), β-glucosidase (90 µg PNP g−1 soil h−1), and leucine amino peptidase (3.22 µmol MUC g−1 soil h−1) enzyme activities in the soil, thereby improving the soil’s biological quality. The results of this study are encouraging for small-scale farmers in tropical developing countries to sustainably reutilize crop residues via biochar-based co-composting technology.

Soil Acidity Indicators for Liming in Tropical Acid Soils Cropped With Soybean Under Short- and Long-Term No-Tillage Systems

Although the movement of liming materials under no-tillage (NT) systems can intensify stratification of soil chemical properties and be deleterious to soybean growth, little is known regarding the soil acidity indicators used to predict lime requirement (LR) in Brazilian soils under NT. Thus, we hypothesize that the recommendation criteria used for predicting LR in soils under NT must be different from those adopted in soils under conventional tillage (CT), and the reference values for such liming indicators may vary according to the phase following the adoption of the NT system. The study aimed to obtain soil acidity indicators for soybean (Glycine max (L.) Merill) in tropical acid soils under no-tillage (NT) systems and their respective critical levels according to the phase of NT. Sites under NT were commercial soybean crop areas located in the Cerrado region, Brazil. Systems analyzed were NTI (NT management from 0 to 5 years&amp;mdash;initial phase), and NTTC (NT management from 5 to 20 years&amp;mdash;transition-consolidation phase). Soil samples were collected at the 0-5, 0-10, and 0-20 cm layers, and analyzed for chemical characteristics. Relationships between crop yield response of soybean to lime application and various soil acidity-related characteristics led to establishing soil acidiy indicators for liming in tropical acid soils under no tillage. Critical levels were approximately similar in both phases of NT for exchangeable Ca and Mg, and potential acidity, but varied greatly depending on the soil layer and phase of NT management for soil pHCaCl2, CECpH7.0, and base saturation. In general, for both phases of NT, the critical levels of soil acidity indicators were lowest for the 0-20 cm layer, moderate for the 0-10 cm layer, and highest for the 0-5 cm layer. Lime applied with incorporation in the NTTC phase kept the soil with chemical attributes more favorable for plant growth than when surface liming was employed in the NTI phase, which was verified by the soybean yield response. Our results indicate the differences on the soil acidity indexes between the top and bottom depths that would not have been realized in a soil sampling for conventional tillage. Hence, recommendation criteria for lime application considering distinct soil depths and NT systems will be helpful when making lime decisions. Further research should focus on the development of reliable methods for predicting LR according to the NT phase and consequently maximize soybean production under NT systems in Brazil.

Organomineral Fertilizer Is an Agronomic Efficient Alternative for Poultry Litter Phosphorus Recycling in an Acidic Ferralsol

Brazil is a large phosphate importer due to the high demand for this nutrient for grain cropping on very weathered soils. However, Brazil has an important poultry production that generates ~6.8 million m3 year−1 of organic residue containing phosphorus and other nutrients, increasing the risk of environmental harm. However, if well managed, poultry litter can be a valuable source of P for crop growth in low fertile tropic soils. This article summarizes the long-term agronomic efficiency of organomineral fertilizers in supplying P to soybean and soil P maintenance as a strategy for secondary P recycling. Three fertilizers were used as P source: organomineral based on raw poultry litter, organomineral based on composted poultry litter; and a mineral monoammonium phosphate. Five soybean crop seasons were conducted with annual P doses (20, 40, 60, and 80 kg ha−1 of P2O5) and control without P application. After five crops, one additional soybean crop season was grown without P to evaluate the residual effect. Phosphorus concentration in leaves was evaluated in the first four seasons, and soil P availability in the first, third, and fourth seasons. There was no difference in soybean grain yield, P concentration in leaves, and soil P availability as a function of the P sources in the first crop. Soybean grain yield only varied with the P rate applied after the second season, when the control had the lowest grain yield. After five crops, organomineral resulted in a slight but significant soybean yield gain compared with MAP at higher doses. Over time, the available soil P increased with the highest P dose and decreased in the control treatment. The intermediate dose of 40 kg ha−1 P2O5 was enough to keep soil P level and lead to high soybean grain yield over the time, suggesting that the rate of applied P close to the P exportation by the grains has a long-term sustainable effect even in tropical soils, where residual P stocks are used. It can be concluded that organomineral fertilizer is an efficient farm input that can be used for residue destination and nutrient recycling, especially in acid tropical soils.

Effect of Biochar on Micronutrient Availability and Uptake Into Leafy Greens in Two Urban Tropical Soils With Contrasting Soil pH

Biochars have been proposed as a novel biotechnology to increase crop yields in acidic soils due to a liming effect. However, the application of biochar to soils with a neutral soil pH is less likely to improve yield. A rise in pH typically increases the availability of macronutrients (e.g., PO43-, NO3-) but biochar is known to immobilize some elements due to a pH increase and adsorption on the biochar surface. Therefore, biochar application may reduce the uptake of important micronutrients (e.g., Cu, Fe, and Zn) into the edible portions of food crops. Before recommending indiscriminate biochar application to tropical soils, an understanding of the potentially negative impacts of biochar application to contrasting soil types should be fully appreciated to prevent unintended consequences. Our aim was to determine the impact of biochar amendment to an acidic soil and a neutral soil on micronutrient availability and uptake into leafy greens. We produced biochars from 3 different organic feedstock materials (corn cobs, rice husk and teak sawdust) and applied these in pot experiments to an acidic tropical soil (pH 4.5) and a neutral tropical soil (pH 6.9) collected from urban farms in Tamale and Kumasi, respectively, in Ghana. We grew leafy greens (Amaranthus, Corchorus, and Lettuce) and measured their growth and the uptake of Cu, Fe, and Zn, alongside supporting measurements of soil pH and micronutrient availability in the soil. We also measured water soluble Cu, Fe, and Zn in the soils amended with biochars pyrolyzed at different temperatures. The corn cobs biochar increased soil pH and considerably increased plant growth in the acidic soil from Tamale. In the neutral soil from Kumasi we found that, while corn cob biochar increased soil pH, rice husk biochar decreased soil pH. Furthermore, corn cob biochar considerably reduced plant growth in the neutral soil. The concentration of micronutrients in the edible portions of leafy greens was not greatly affected by biochar application, but the total uptake (i.e., concentration multiplied by biomass) of micronutrients into leaves was generally increased by biochar application in the acidic (Tamale) soil and application of the corn cob biochar generally decreased total uptake of micronutrients in the neutral (Kumasi) soil. Our results highlight the need for site-specific information on biochar feedstock and soil pH prior to recommending biochar application to tropical urban soils so that the benefits can be optimized and unintended consequences can be prevented.

Can silicon in glacial rock flour enhance phosphorus availability in acidic tropical soil?

Can silicon in glacial rock flour enhance phosphorus availability in acidic tropical soil?

Liming tropical high upland acid soils improves soil fertility and cardamom productivity

Increasing the productivity of Indian cardamom is revolving around both soil and forest canopy management. Maintaining tropical acid soil fertility and its productivity is the prime concern for successful cardamom cultivation under ongoing deforestation of fragmented rainforest. A field experiment with two doses each (1 and 2 kg plant-1) of burnt lime, dolomite and ground lime stone was carried out in an acidic soil. Results showed that all of the liming materials have had significant effect on correcting the soil acidity. Liming with dolomite at 2 kg plant-1 considerably improved soil chemical properties and increased the soil pH from very acidic to near neutral. Correction and improvement in the soil pH led to significantly enhance the growth and yield of cardamom. However, utmost care must be taken on the environmental implications of liming; particularly the ratio of soil Calcium and Magnesium as well as organic carbon loss and evolution of CO2.

Acidity and Aluminum Speciation in Biochar Amended Tropical Soils

ABSTRACT Soil acidification in the tropics has become a more pressing issue due to its associated aluminum (Al) phytotoxicity. The chemical reactive nature of biochar can alter Al speciation in soils. The study assessed the chemical properties and Al speciation in a Ultisol and an Oxisol amended with corn cob (CC) and rice husk (RH) biochars charred at 300, 450 and 650°C in an incubation study for 120 d. pH was determined periodically while organic carbon (OC), cation exchange capacity (CEC), exchangeable base cations, exchangeable acidity, and exchangeable Al3+ were measured at the end of the incubation period. Dissolved organic carbon (DOC) and pH were also determined in soil solution from each treatment. Throughout the incubation period CC and RH biochars significantly increased soil pH, with CC biochar showing a greater effect. Similar effects were also observed for OC, CEC, and exchangeable base cations (Ca2+, Mg2+ and K+). Soil exchangeable Al3+ and exchangeable acidity, soluble Al and Al3+ activity in soil solution decreased significantly upon biochar application; it was more significant at the 650°C. Biochars at 300–450°C exhibited a more notable increase in soil DOC. At pH ≤ 5.8, Al-DOC and free Al3+ dominated in soil solution while at pH > 5.8, Al species was mainly Al-OH ions (i.e. Al(OH)2+, Al(OH)2 +, Al(OH)3, and Al(OH)4 −). Biochars at 300–450°C promoted the large formation of Al-DOC while Al-OH ions dominated in 650°C-biochar treatments. Biochar can be used to ameliorate Al phytotoxicity in tropical acid soils, particularly at 300–450°C.

Environmental filtering controls soil biodiversity in wet tropical ecosystems

The environmental factors controlling soil biodiversity along resource gradients remain poorly understood in wet tropical ecosystems. Aboveground biodiversity is expected to be driven by changes in nutrient availability in these ecosystems, however, much less is known about the importance of nutrient availability in driving soil biodiversity. Here, we combined a cross-continental soil survey across tropical regions with a three decades' field experiment adding nitrogen (N) and phosphorus (P) (100 kg N ha−1y−1 and 100 kg P ha−1y−1) to Hawai'ian tropical forests with contrasting substrate ages (300 and 4,100,000 years) to investigate the influence of nutrient availability to explain the biodiversity of soil bacteria, fungi, protists, invertebrates and key functional genes. We found that soil biodiversity was driven by soil acidification during long-term pedogenesis and across environmental gradients, rather than by nutrient limitations. In fact, our results showed that experimental N additions caused substantial acidification in soils from Hawai'i. These declines in pH were related to large decreases in soil biodiversity from tropical ecosystems in four continents. Moreover, the microbial activity did not change in response to long-term N and P additions. We concluded that environmental filtering drives the biodiversity of multiple soil organisms, and that the acidification effects associated with N additions can further create substantial undesired net negative effects on overall soil biodiversity in naturally tropical acid soils. This knowledge is integral for the understanding and management of soil biodiversity in tropical ecosystems globally.

Soil Mineralogy and Applied Phosphate Transformation in a Toposequence of a Tropical Semi-arid Landscape: Montgomeryite [Ca2Al2(PO4)3(OH).7H2O] as the Possible Metastable Phosphate Transformation Residue

ABSTRACT The residual responses of crops to phosphate fertilizers in weathered soils depend on the mineralogy and the nature of the phosphate reaction residue formed by soil–phosphate interactions. The study examined the metastable phosphate residues formed from soil-phosphate interactions along a tropical semi-arid toposequence by solubility criteria principles after soil-phosphate incubation for 28 weeks. The powder X-ray diffraction of the sand and silt-sized particles showed the dominance of K-feldspars in association with quartz and muscovite, while the oriented clay fractions indicated a preponderance of kaolinite and illite derived from the weathering of K-feldspars that were the surviving primary silicates in the soils. Soil-phosphate incubation with 12.5 mmol P kg−1 for 28 weeks showed, by the 7th week, phosphate, , activities in apparent equilibrium with montgomeryite, Ca2Al2(PO4)3(OH).7(H2O), solubility at pH ≥ 6.0. After 28 weeks, the HPO4 2- activities were in apparent equilibrium with hydroxyapatite, Ca5(PO4)3OH at the pH range of 6.5 to 7.2. The study provides an indirect evidence of the existence of montgomeryite as the potential metastable phosphate residue of soil-phosphate reactions in these slightly acid tropical semi-arid soils, before reverting to the more stable hydroxyapatite with time.

Co-application of triple super phosphate and chicken litter biochar improves phosphorus availability of mineral tropical acid soils to reduce water pollution

Co-application of triple super phosphate and chicken litter biochar improves phosphorus availability of mineral tropical acid soils to reduce water pollution

Amending Potassic Fertilizer with Charcoal and Sago (Metroxylon sagu) Bark Ash to Improve Potassium Availability in a Tropical Acid Soil

In Ultisols and Oxisols, potassium (K) in the soil solution is leached from the rhizosphere before it interacts with soil colloids, or exchanged with other cations at the exchange sites of the soils because of the abundance of kaolinite clay minerals. These soils are highly weathered, low in organic matter, and low in pH, but high aluminium (Al) and iron (Fe) ions. Hence, K becomes unavailable for plants, and this compromises crop production and farmers’ profitability. The pH neutralizing effects of sago (Metroxylon sagu) bark ash and the ability of charcoal to chelate Al and Fe could be utilized to improve soil pH, reduce soil acidity, and improve K availability. The objective of this study was to determine the effects of amending muriate of potash (MOP) with charcoal and sago bark ash on selected soil chemical properties in a tropical acid soil (Typic Paleudults) over 90 days in a laboratory incubation. The proportions of charcoal and sago bark ash were varied at 20%, 40%, 60%, 80%, and 100%, but the MOP was fixed at 100% of the recommended rate. Selected soil chemical properties before and after incubation were determined using standard procedures. Results revealed that co-application of the soil amendments with MOP increased soil-exchangeable K compared with conventional practice. Moreover, amending the acid soil with charcoal and sago bark ash positively enhanced the availability of other base cations and soil cation exchange capacity (CEC). This was possible because the amendments increased soil pH and reduced exchangeable acidity, exchangeable Al3+, and exchangeable Fe2+. However, there was no significant improvement in water-soluble K (WSK) in the soil with or without charcoal and sago bark over the 90 days laboratory study. The findings of this study suggested that increasing soil pH could potentially improve soil K sorption capacity. Thus, the optimum rates of charcoal and sago bark ash to increase K availability were found to be 80% charcoal with 80% sago bark ash, 60% charcoal with 60% sago bark ash, and 80% charcoal with 40% sago bark ash, because these rates improved soil-exchangeable K+ and CEC significantly, besides minimizing soil-exchangeable acidity.

Acid Soils Nitrogen Leaching and Buffering Capacity Mitigation Using Charcoal and Sago Bark Ash

Soil acidity compromises agricultural output in tropical acid soils. Highly weathered tropical acidic soils are characterized by low pH, organic matter, nutrient availability, but high aluminium and iron concentration. Hence, N availability becomes a limiting factor in such soils. To this end, these leaching and pH buffering capacity studies were conducted to determine the effects of co-application of charcoal and sago bark ash on the N leaching or retention and pH buffering capacity of acid soils. The soil leaching experiment was conducted for 30 days by spraying distilled water to each container with soil such that the leachates were collected for analysis. The rate of urea used was fixed at 100% of the recommended rate. The rates of charcoal and sago bark ash were varied by 25%, 50%, 75%, and 100%, respectively, of the recommended rates. The pH buffering capacity was calculated as the negative reciprocal of the slope of the linear regression. The leaching study revealed that the combined use of charcoal, sago bark ash, and urea does not only reduce leaching of NH4+ and NO3− but the approach also improves soil pH, total C, and soil exchangeable NH4+. This effect is related to the fact that the sago bark ash deprotonates the functional groups of charcoal because of its neutralizing components such as Ca, Mg, Na, and K ions. As a result, the combined use of charcoal and sago bark ash was able to retain NH4+ in the soil. The carbonates in the sago bark ash and functional groups of charcoal improve pH buffering capacity. Thus, the combined use of charcoal and sago bark ash improved soil exchangeable NH4+, soil pH, and soil total C, but reduced exchangeable acidity and amount of NH4+ leached out from soil. This study will be further evaluated in a pot trial to confirm the results of the present findings.

Co-Application of Charcoal and Wood Ash to Improve Potassium Availability in Tropical Mineral Acid Soils

Potassium (K) is a macronutrient required by plants for energy production, enzyme activation, formation of cell wall, production of protein, and photosynthesis. However, K in the soil solution is leached from the rhizosphere before it interacts with soil colloids because of the abundance of kaolinite clay minerals in mineral acid soils such as Ultisols and Oxisols. These soils are highly weathered, low in organic matter, low in pH, but high aluminium (Al), and iron (Fe) ions. As a result, K becomes unavailable for plants, and this affects crop production and farmers’ profitability. This problem has steered the attention to the application of amendments to minimise K loss. Animal manures, plant residues, and composts applications are some of the corrective measures taken to improve the K availability in tropical acid soils. However, there is dearth of information on co-application of charcoal and wood ash as soil amendments to improve the K availability and the changes they cause to the dynamic equilibrium of K in mineral acid soils. Hence, this review discusses the dynamics, availability of K, and proposed mechanisms involved when charcoal and wood ash are used to amend tropical acid soils. The optimisation and understanding of the role of charcoal and wood ash co-application as soil amendments have potential benefits to improve the K availability and physicochemical properties of mineral acid soils.

Combined Use of Calciprill and Sodium Silicate Improves Chemical Properties of Low-pH Soil

The highly weathered, acidic tropical soils are generally less fertile because of their low pH, high exchangeable acidity, and Al, Fe, and Mn saturations. Using soil amendments to solve the aforementioned problems is essential. To this end, Calciprill and sodium silicate are worth considering because of their high neutralizing value and dissolution to suppress exchangeable acidity and Al, Fe, and Mn hydrolysis, while at the same time increasing soil pH to improve the availability of inorganic N, available P, exchangeable base cations, and Effective Cation Exchange Capacity (ECEC). An incubation study was conducted to determine the right combination of Calciprill and sodium silicate to reduce exchangeable acidity and Al and Fe hydrolysis to improve inorganic N, available P, exchangeable base cations availability, and ECEC. Bekenu series (Typic Paleudults) was incubated with a combined use of Calciprill at 80%, 90%, and 100% Ca saturations and sodium silicate at 90, 105, 120, 135, and 150 kg ha−1 for 40, 80, and 120 days, respectively. The laboratory incubation study was carried out using a Completely Randomized Design (CRD) with triplicates to determine the aforementioned treatment effects of the combined use of Calciprill and sodium silicate on soil pH, exchangeable, Al, inorganic N, available P, electrical conductivity, exchangeable cations (K, Ca, Mg, Na, Fe, and Mn), and ECEC using standard procedures. Soils with both amendments significantly increased soil inorganic N, available P, electrical conductivity, exchangeable base cations (K, Ca, Mg, and Na), and ECEC. This was because the amendments increased soil pH by suppressing exchangeable acidity. Moreover, they transformed Al, Fe, and Mn ions into insoluble compounds such as Al and Fe hydroxides and Mn oxides because of their high inherent exchangeable cations, especially Ca and Na. This suggests that the combined use of Calciprill and sodium silicate can enhance soil productivity. The most suitable combination is 7.80 g Calciprill and 9.26 g sodium silicate (C3S5) per one kilogram soil. Additionally, the findings provide fundamental information for future greenhouse and field trials to determine the effects of the suitable combination of the amendments uncovered by this present study on soil health and crop productivity.

Combined Use of Charcoal, Sago Bark Ash, and Urea Mitigate Soil Acidity and Aluminium Toxicity

Highly weathered tropical acidic soils are characterized by low pH, low organic matter, and aluminium and iron toxicity. These factors pose a challenge to achieving sustainable agriculture. The continued increase in the human population with the accompanied increasing food demand have negatively impacted the global N cycle partly because of excessive use N fertilizers particularly urea which is commonly used in agriculture. Ammonia volatilization from urea as an example, negatives the environmental quality. This study focuses on soil-N availability, pH, exchangeable acidity, Al3+, and H+ of a highly weathered acid soils (Bekenu series) through the combined use of charcoal, sago bark ash, and urea. To this end, an incubation study was conducted for 90 days through the combined use of charcoal, sago bark ash, and urea to determine if this approach could improve soil N availability and pH at the same time reducing exchangeable acidity, and Al3+, and H+ toxicity. The amount of urea used was fixed at 100% as the recommended rate. Charcoal and sago bark ash were varied by 25%, 50%, 75%, and 100%, respectively of the recommended rate. Selected soil physico-chemical properties were determined using standard procedures. This study revealed that combined use of charcoal, sago bark ash, and urea increased soil pH and base cations simultaneously the approach also reduced exchangeable acidity, exchangeable Al3+, and exchangeable H+. There were no significant differences in soil total N, exchangeable NH4+, and available NO3− for the combined use of charcoal, sago bark ash, and urea and urea alone because of the acid neutralizing effect of the amendments. Apart from the sago bark ash’s liming effect, the high affinity of the functional groups of the charcoal for Al3+ might have impeded Al3+ from undergoing hydrolysis to produce more H+ because a complete one mole of Al3+ hydrolysis produces three moles of H+. Thus, the combined use of charcoal and sago bark ash can mitigate soil acidity and aluminium toxicity, although this approach has minimal effect on-N.

Production of Organic Acids by Arbuscular Mycorrhizal Fungi and Their Contribution in the Mobilization of Phosphorus Bound to Iron Oxides.

Most plants living in tropical acid soils depend on the arbuscular mycorrhizal (AM) symbiosis for mobilizing low-accessible phosphorus (P), due to its strong bonding by iron (Fe) oxides. The roots release low-molecular-weight organic acids (LMWOAs) as a mechanism to increase soil P availability by ligand exchange or dissolution. However, little is known on the LMWOA production by AM fungi (AMF), since most studies conducted on AM plants do not discriminate on the LMWOA origin. This study aimed to determine whether AMF release significant amounts of LMWOAs to liberate P bound to Fe oxides, which is otherwise unavailable for the plant. Solanum lycopersicum L. plants mycorrhized with Rhizophagus irregularis were placed in a bicompartmental mesocosm, with P sources only accessible by AMF. Fingerprinting of LMWOAs in compartments containing free and goethite-bound orthophosphate (OP or GOE-OP) and phytic acid (PA or GOE-PA) was done. To assess P mobilization via AM symbiosis, P content, photosynthesis, and the degree of mycorrhization were determined in the plant; whereas, AM hyphae abundance was determined using lipid biomarkers. The results showing a higher shoot P content, along with a lower N:P ratio and a higher photosynthetic capacity, may be indicative of a higher photosynthetic P-use efficiency, when AM plants mobilized P from less-accessible sources. The presence of mono-, di-, and tricarboxylic LMWOAs in compartments containing OP or GOE-OP and phytic acid (PA or GOE-PA) points toward the occurrence of reductive dissolution and ligand exchange/dissolution reactions. Furthermore, hyphae grown in goethite loaded with OP and PA exhibited an increased content of unsaturated lipids, pointing to an increased membrane fluidity in order to maintain optimal hyphal functionality and facilitate the incorporation of P. Our results underpin the centrality of AM symbiosis in soil biogeochemical processes, by highlighting the ability of the AMF and accompanying microbiota in releasing significant amounts of LMWOAs to mobilize P bound to Fe oxides.

Genome-wide molecular characterization of Phosphate Transporter 1 and Phosphate Starvation Response gene families in Elaeis guineensis Jacq. and their transcriptional response under different levels of phosphate starvation

Phosphate (Pi) fertilizer is applied in huge amount due to the poor absorption of Pi by crops especially in acidic tropical soil. As the major global source of oil and fats, the mechanism of Pi transport in oil palm needs to be studied to maintain good productivity for sustainable palm oil production. Ten Elaeis guineensis Phosphate Transporter1 (EgPHT1) and three Elaeis guineensis Phosphate Starvation Response (EgPHR) genes were identified in this study. All EgPHT1 proteins contain GGDYPLSATIxSE, the signature sequence of PHT1. All EgPHR have MYB-binding domain and coiled-coil domain characteristic of PHR at their C-terminal regions and one unique SOG2 domain for EgPHR1. The expression of four of the EgPHT1 and two of the EgPHR under low Pi (LP) and Pi starvation (-P) was studied by real-time quantitative PCR (qPCR). All genes showed enhanced expression in roots at −P compared to +P but no detectable change in the leaves. The expression profile of EgPHR2 which showed significant upregulation at LP compared to +P and further increase at −P correlated with EgPHT1;4 and EgPHT1;7 that possess P1BS motif in their promoter sequences, the binding site for PHR. PHR2, as a potential early transcriptional regulator for phosphate starvation was proven to be nuclear localized by subcellular localization experiment. Altogether, this study suggests all four analyzed EgPHT1 and two EgPHR play critical role in responding to Pi deprivation in oil palm. EgPHT1;4 and EgPHT1;7 which possess the P1BS motif are potentially upregulated by EgPHR2 as an early response mechanism against phosphate starvation.