N. V. Hue

Correcting soil acidity of a highly weathered Ultisol with chicken manure and sewage sludge

Abstract The seriousness of soil acidity and the unavailability of “conventional”; liming materials in many developing countries necessitate a search for alternatives. With this goal in mind, the liming potential of two organic manures was investigated. The investigation was conducted in the greenhouse, using a highly weathered, acid Ultisol. Application rates were 0, 5, 10, 20, and 40 g kg‐1 for chicken manure and 20 g kg‐1 for sewage sludge. Treatments of Ca(OH)2 at 2, 4, 6, and 8 cmolckg‐1, were included for comparison. Based on growth response of Desmodium intortum, a tropical forage legume with a relatively high Ca requirement and low Al tolerance, it was demonstrated that soil acidity can be corrected by either Ca(OH)2 or organic manure additions. Both lime and manures raised soil pH and inactivated Al. In terms of pH increases, 5 and 10 g chicken manure kg‐1 were equivalent to 3.4 and 6.7 cmolckg‐1; and 20 g sludge kg‐1, equivalent to 6.5 cmolckg‐1 as Ca(OH)2. The manures also detoxified soluble Al...

Predicting compost stability

Sixteen composts consisting of 14 commercial samples, one immature yard waste compost and one raw material of mostly grass clippings were evaluated for their stability. In a three-day incubation test, the commercial composts yielded from 9 to 99 mg CO2/kg/ hr, with a mean CO2 production rate of 61 mg CO2/kg/hr. By contrast, the immature compost produced 684 mg CO2/kg/hr and the raw material, 1,433. The low CO2 production rates of the commercial composts along with dark brown color and lack of unpleasant odors in moist conditions indicated that these composts were indeed stable. We devised a quick chemical test to predict compost stability. Several compost properties were measured: (i) total (C, N and C:N), (ii) water-soluble (C, N and C:N), (iii) NaOH-soluble C, humic and fulvic acids, and optical absorbances at 465 nm (E4) and 665 nm (E6) of the NaOH-soluble fractions. Water-soluble fraction, particularly water-soluble C and the C:N ratio, best separated stable from unfinished composts. However, water-so...

Aluminum detoxification with green manures

Abstract A greenhouse experiment was conducted to evaluate “liming”; potential of different green manures. Ground leafy materials of cowpea (Vigna unguiculata), leucaena (Leucaena leucocephala) and guinea grass (Panicum maximum) were added at 0, 5, 10 and 20 g/kg to an Ultisol having a soil‐water pH 4.0, KCl‐extractable Al = 7.6 cmoLc/kg, Al saturation = 50% and soil‐solution Al = 2.2 mM. Treatments with Ca(OH)2 were established for comparison. Sesbania cochinchinensis, an Al‐sensitive tree legume, was grown for 4 weeks as a test crop. Biomass production and chemical composition of the soil indicated that (i) cowpea and leucaena were more effective than guinea grass in detoxifying Al; for example, the additions of 10 g manure per kg soil were equivalent to 1.8 cmol(OH)/kg for guinea grass, 3.4 for cowpea and 4.2 for leucaena (at least on a short‐term basis), (ii) reduction of soluble Al at increased pH as a result of manure additions was the major mechanism for Al detoxification, and (iii) complexation of...

Increasing plant‐available phosphorus in an Ultisol with a yard‐waste compost

Abstract Beneficial uses of a yard‐waste compost as a soil amendment and plant‐growth medium were evaluated on a highly weathered, acid soil (Ustic Kanhaplohumult), using corn (Zea mays L.) seedlings as a test crop. First, factors responsible for the soils infertility were identified in a greenhouse experiment consisting of five phosphorus (P) rates (0, 75, 150, 300, and 600 mg/kg) with or without 1.0 g calcium (Ca)/g (2 tons Ca/ha) as gypsum (CaSO4‐2H2O) or calcium hydroxide [Ca(OH)2]. At no or low P additions, severe growth restrictions (low dry matter production and shoot P concentration <0.10%) irrespective of the Ca amendments indicated that P deficiency was the most growth limiting factor in this tropical soil. Subsequently, P sorption isotherms were constructed for the soil, the compost, and soilxompost mixtures by equilibrating 1.0 g soil in 20 mL 0.001M calcium chloride (CaCl2) containing various P concentrations. The results showed that in the unamended state, the soil supported only 0.01 mg P/...

Nutritional Values of Some Biowastes As Soil Amendments

As a result of increased population, improved standards of living, and strict environmental laws, biowastes have been generated in huge quantities. Thus, land applications of these wastes are desirable, or even necessary, to keep the environment healthy and to conserve natural resources. Yet, the success of such uses requires knowledge of complex biochemical reactions when the wastes are applied to soils. To obtain this knowledge, we evaluated soil amendment properties, primarily nitrogen (N) mineralization/immobilization of six bio wastes when used as plant growth media. An immature yard trimmings compost, ground fresh corn stovers, a commercial peat moss, a chicken manure, and two biosolids were each mixed with a Mollisol at either 25 percent and 50 percent by volume for the plant based wastes, or at 2.5 percent and 5.0 percent by weight for the animal based wastes. Treatments with urea at 0, 70 and 210 mg N kg−1 were included for comparison. The treated soils were incubated moist for two weeks at which...

Temporal changes of selected chemical properties in three manure – Amended soils of Hawaii

Soil amendment with organic materials (crop residues animal manure, and green manure) reportedly has positive effects on soil properties, from acidity to plant-nutrient availability. To examine that hypothesis, an incubation study was conducted to assess the changes in some chemical properties of three different tropical soils (Andisol, Ultisol, and Oxisol) amended with chicken manure and green manure (Leucaena leucocephala) at the rate of 10tha(-1). The results showed that organic amendments raised soil pH and EC, regardless of the type of manure used. Manuring lowered the concentrations of Mehlich-3 extractable Ca, P, Mn and Si in all soils and decreased the concentration of Mg in the Ultisol and Oxisol. However, manure amendment led to increases in the concentrations of Mg and K in the Andisol. Organic amendments caused a decrease in KCl extractable Al. Initial soluble C levels were highest in the Oxisol (60micromolg(-1)) and lowest in the Andisol (20micromolg(-1)). The concentration of soluble C decreased exponentially with duration of incubation. Three low molecular weight organic molecules (acetic acid, catechol and oxalic acid) out of the eight tested were found in all manure-amended soils. This study quantified the release of some Al chelating organic acids, the reduction of exchangeable Al, and the changes in major plant-nutrients when organic materials were added to nutrient poor, tropical acid soils.

Response ofLeucaena leucocephala to vesicular-arbuscular mycorrhizal colonization and rock phosphate fertilization in an Oxisol

Response ofLeucaena leucocephala (Lam) de Wit to rock phosphate application and inoculation with the vesicular-arbuscular mycorrhizal (VAM) fungusGlomus aggregatum (Schenck and Smith emend Koske) was evaluated in a pot experiment. VAM colonization increased as rock phosphate application increased. Using phosphorus concentration in pinnules as an indicator of VAM activity, significant VAM activity occurred at 25 days after planting at the lower levels of rock phosphate application (0, 0.34 and 0.68 g P kg−1). The time required for significant VAM activity was shortened by 5 days at the higher P levels (1.36, 2.72 and 5.44 g P kg−1). The highest VAM activity was associated with the highest rate of rock phosphate application.Inoculation withG. aggregatum significantly increased the uptake of Cu, P and Zn and dry-matter yield at all levels of rock phosphate applied. Copper concentrations in roots of mycorrhizal Leucaena were significantly higher than that of shoots. The results indicated that Leucaena in symbiotic association with VAM fungi effectively utilized P from rock phosphate. However, high rates of rock phosphate are required to attain growth comparable to that obtained with the application of water-soluble phosphate.

A turbidimetric method for determining phosphate‐extractable sulfates in tropical soils 1

Abstract Turbidimetric methods, using Ba ions to precipitate SO4, are frequently used to determine soil sulfates extracted with phosphate solutions. These methods, as routinely performed, seriously underestimate SO4 in some soils of the tropics because phosphate is removed from the extractant by soil adsorption and because many extracts fail to yield satisfactory precipitate even if the extracting procedure is adequate. Decolorizing the extracts with carbon black, treating extracts with strong oxidizing agents, adding SO4 spikes, and seeding the extracts with BaCl2 seed‐crystals improve precision, but some extracts, especially those from soils derived from volcanic ash, do not yield reliable precipitates even though these procedures are employed. This paper presents a method that consistanlty yielded more SO4 than other turbidimetric procedures with which it was compared. The proposed method was further validated against an ion‐chromatographic method for SO4 determination. The two methods yielded virtuall...

Manganese Solubility and Phytotoxicity Affected by Soil Moisture, Oxygen Levels, and Green Manure Additions

Abstract Manganese (Mn) toxicity is common in tropical acid soils, second only to aluminum toxicity. Changes in soil pH and redox potential (Eh) caused by soil moisture conditions and organic amendments certainly affect Mn solubility and toxicity to plants grown in soils with high Mn reserves. Laboratory incubation and greenhouse experiments were conducted to quantify such effects using a high-Mn Oxisol and a moderate-Mn Mollisol from Hawaii, with soybean (Glycine max L. cv. Kahala) being a test crop. The soils were mixed with a green manure (leucaena leaf) at 0, 10, and 20 g kg−1, and were incubated at 24 ± 1°C at 80% of field water holding capacity—equilibrated with air (FC), or N2 gas (N2)—or submerged under 8 cm of water. Soil pH, Eh, and soluble Mn as measured in saturated paste extract, Mehlich-3 and hydroxylamine hydrochloride (NH2OH) solutions were periodically determined over 56 days of incubation. The submergence and N2 treatments increased soil pH towards 7.0 and decreased soil Eh from 600 mV to between 300 and 400 mV, indicating a more reducing environment, which seemed to be controlled by the MnO2-Mn2+ and/or FeOOH-Fe2+ redox couples. Green manure additions had similar effects, but to a lesser extent. Consequently, soluble soil Mn concentrations increased by 100–1000 fold relative to those of the controls (no manure, at FC). There was a marked decrease in soybean growth and a marked increase in leaf Mn concentration in the treatments of submergence and green manure additions. A 10% reduction in dry matter yield was expected when leaf Mn exceeded 200 mg kg−1, leaf Ca/Mn (weight-to-weight) <80, saturated paste Mn >0.50 mg L−1, Mehlich3 Mn >200 mg kg−1, and NH2OH Mn >1100 mg kg−1. The effects were most evident at 14–28 days after incubation.

Effects of Vermicompost Tea (Aqueous Extract) on Pak Choi Yield, Quality, and on Soil Biological Properties

This study investigated the effects of vermicompost tea (aqueous extract) on yield and chemical quality of pak choi (Brassica rapa cv Bonsai, Chinensis group) grown in three media (two soils and a peat-perlite medium) under two fertilizer regimes (compost and synthetic fertilizer). The impacts of tea application on the chemical and biological properties of the growth media were also investigated. Vermicompost teas were prepared using various extraction methods (non-aerated, aerated, aerated with additives) with 1:10 (v:v) chicken manure-based vermicompost to water dilution and applied weekly at the rate of 200 mL plant−1 for 4 weeks. Application of vermicompost tea increased plant production, total carotenoids and total glucosinolates in plant tissue. This effect was most prominent under compost fertilization. Total phenolic was lower in vermicompost tea treated plants compared to those treated with only mineral nutrient solution and the water control. Vermicompost tea improved mineral nutrient status of plants and media, and enhanced the biological activity of the media. Variability in yield and chemical quality of plants across treatments was explained largely by variability in tissue N uptake and dry matter accumulation. Dehydrogenase activity and soil respiration of vermicompost tea-treated growth media were approximately 50% higher than untreated media. This study confirmed that vermicompost tea can positively influence plant yield and quality and increase soil biological activity in multiple soil types.