Acid Oxisol Research Articles

Soil microbial biomass in Amazonian soils: Evaluation of methods and estimates of pool sizes

The suitability of the fumigation-incubation (FI), fumigation-extraction (FE) (with specific k-factor determined by 14C-labelling) and substrate induced respiration (SIR) methods to obtain measures of the microbial biomass in forest soils from the Amazonian basin was examined. Several representitive topsoil (0–10 cm) samples were studied. A reasonable estimate of microbial biomass C in two acid Oxisols (pH <4.5) with a high clay content was obtained by the FI method, provided no correction was applied for basal CO 2 respiration. However, on two Ultisols and one Alfisol more consistent estimates of microbial C were obtained by the FI method, where correction for basal respiration was obtained using the respiration of non-fumigated (NF) soils between 0–10 d, or fumigated (F) soils between 10–20 d. Estimates of microbial C by the FE method did not differ significantly from those obtained by the FI method when calculated using a specifically-determined k-factor of 0.26 to convert the extractable-C flush to microbial biomass C. In the Ultisols and the Alfisol, the SIR method gave similar estimates of microbial C to those obtained by the FI and FE methods, but in both Oxisols microbial C was underestimated when a standard conversion factor was applied. Possibly the SIR assay was adversely affected by a high proportion of dormant organisms and a slow gaseous release of respired CO 2 from these heavy clay soils. When estimated using the FE method, microbial C was in the range 890–1100 μg C g −1 soil in the Oxisols, 340–470 μg C g −1 soil in the Ultisols and around 580 μg C g −1 soil in the Alfisol. Microbial C comprised 3–4% of the total soil organic C and microbial N 4–7% of total N. Microbial C-to-N ratios averaged 6.9 ± 0.8. Although the FI method can be used on these Amazonian soils, the FE method is more convenient and generally appears suitable for estimating both microbial C and N in the same extract. The SIR method is not recommened for use with Oxisols.

Comparative effects of green manure and lime on the growth of sweet corn and chemical properties of an acid Oxisol in western Samoa

Abstract Liming values of calcium carbonate (CaCO3) and cowpea green manure were evaluated on an acid Oxisol (Typic Acrorthox, Togitogiga series), based on seed yield and tissue composition of sweet corn (Zea mays), and soil chemical properties. Application rates were 0, 5, and 10 Mg/ha for CaCO3 and 0, 7.5, and 15 Mg/ha for the green manure, factorially arranged. Treatments with commercial NPK fertilizers were included for comparison. Growth and yield of sweet corn showed that soil acidity can be corrected by either lime or green manure additions. Both lime and manure raised soil pH and (modified Truog) extractable phosphorus (P), which were partially responsible for yield increases. Green manuring significantly increased plant P and potassium (K) concentrations, which explain why the manure was more effective than lime in increasing corn yield. Ear leaves sampled at tasseling required at least 0.25% P and 2.4% K to attain >90% of the maximum seed yield.

A comparison of methods used for the extraction of K in soils of the Western Cape

A number of common soil extractants, mainly those used for soil P, were used to extract K from a range of widely differing soils which occur in the Western Cape; the objective being to evaluate the simultaneous determination of P and K availability. Soil samples were taken mainly from the upper horizons of 110 profiles representing the dominant soil forms occurring in this region. The soils varied from highly weathered, deep, well-drained acid Oxisols (Hutton form) to younger less developed duplex Alfisols (Swartland, Glenrosa and Kroonstad forms) and deep sandy Inceptisols (Fernwood form). The soils exhibited a wide range of values of clay content, CEC, pH and exchangeable K. Seven soil P extraction methods (Bray No. 1, Bray No. 2, citric acid 1%, Olsen, ISFEI (Na), Ambic and Mehlich No. 3) were compared with two K extraction methods, (0.5M NH4CI and M NH4OAc). All the methods gave K indices which were significantly correlated with one another (r> 0.9). The extractants containing NH/were better correlated with one another than with the other extractants. Significant linear relationships were obtained with all the methods between extractable K and soil K-values determined using the NH4OAc method over a range of values from < 10 mg kg−1 to over 300 mg kg−1. Apart from the results of the Bray No. 1 and ISFEI methods, which exhibited lower extractability, all R2 values were greater than 0.9. It appears that any of the methods used for extracting soil P are suitable for assessing the K status of the soils of this region.

Effects of lime and gypsum on clay dispersion and infiltration in samples of a Brazilian Oxisol

Samples of the surface layer of an acid Oxisol were treated with various amounts of CaCO 3 (lime) or with CaSO 4 (gypsum) and incubated in the laboratory to study possible effects on clay dispersion and infiltration. The treatments consisted of incorporation of gypsum and lime or superficial application of lime. Infiltration rates were determined with a rainfall simulator and clay dispersion by measuring clay concentration in runoff. Effects of treatments with lime or gypsum were similar in some respects but different in others. Incorporating lime increased clay dispersion and reduced infiltration rates significantly. Incorporating gypsum, in contrast, increased clay dispersion and reduced infiltration slightly as compared with the control. Highly significant correlations were found between pH and both clay dispersion and infiltration rates, as well as between clay dispersion and infiltration rates. The relationship between increased clay dispersion and lower infiltration rates was linear. Application of lime to surfaces of soil samples reduced clay dispersion less than did incorporation. Covering the samples with wheat straw reduced clay dispersion and maintained high infiltration rates. On the whole, effects from additions of gypsum were more favorable than those of lime. The more favorable results suggest further tests through field trials.

Potassium Uptake and Recovery by an Upland Rice‐Soybean Rotation on an Oxisol

AbstractA major limitation to improved crop growth on many acid Oxisols is low K availability. A field experiment was conducted in West Sumatra to study the effects of K fertilization of an oxisol under three levels of lime (0.375, 2.25 an 5 t ha−1) on K accumulation of a yearly upland rice (Oryza sativa L.)‐soybean (Glycine max L. Merr.) rotation where all above‐ground residue was removed. Six K treatments supplied 0 to 240 kg K ha−1 to each crop and lime treatment. Potassium fertilization increased grain yields of rice and soybean and K content of grain and stover of both crops. With both crops a large proportion of the K was present in the stover. Liming had no effect on K accumulation Of rice grain; an inconsistent effect on K accumulation in rice straw; and significantly increased the K content of soybean grain and stover. Upland rice was very efficient in utilizing K applied to that crop as well as residual soil K from previous fertilization. When K rate was greater than 100 kg ha−1 per crop appreciable amounts of K could not be accounted for indicating that the K was lost by leaching. Increases in exchangeable K with K fertilization only occurred in the 0‐ to 30‐cm depth.

Mineral element concentrations of sorghum genotypes grown on tropical acid soil

Abstract Sorghum [Sorghum bicoior (L.) Moench] genotypes show large differences in dry matter and yield when grown on many tropical acid soils. The objective of this study was to determine differences in mineral element concentrations in sorghum genotypes grown on an acid oxisol limed with 2 and 6 Mg dolomitic limestone ha‐1 in Colombia, South America. Fifty genotypes showed differences in dry matter yield and concentrations of P, K, Ca, Mg, S, Si, Al, Mn, Cu, and Zn. Liming did not change low, high, and mean leaf concentrations of P, K, Mg, S, and Cu for the genotypes. Concentrations of Al, Mn, and Fe in the genotypes were higher in leaves of plants grown at 2 (pH 4.5 and 62% AT saturation) than at 6 Mg lime ha‐1 (pH 4.8 and 34% Al saturation). At the 6 Mg ha‐1 lime rate, leaf concentrations of Ca and Si increased. Silicon may have reduced the effects of toxic Al, and possibly toxic Fe. Genotypes showed sufficient variability in mineral element concentrations that selection for improved values of these traits appears feasible.

Leaf position and genotype differences for mineral element concentrations in sorghum grown on tropical acid soil1

Abstract Mineral element deficiencies and toxicities are common problems associated with sorghum [Sorghum bicolor (L.) Moench] production on acid soils. To better understand some of the mineral element problems and the analysis of plant tissue of sorghum plants grown on acid soils, four sorghum genotypes were grown on an acid Oxisol at Carimagua, Colombia limed with dolomite at 2 and 6 Mg ha‐1. Samples for mineral element analyses were obtained from leaves at different positions on the four genotypes. Concentrations of P and Mg were highest in the flag leaf (Leaf No. 1) and decreased as the position on the plant declined from the top of the plant for plants grown at 2 Mg lime ha‐1. Similar decreases in P, Mg, K, and Zn concentrations occurred in plants grown with 6 Mg lime ha‐1. Concentrations of Ca, S, Si, Mn, Fe, Cu, and Al increased as leaf position declined from the flag leaf for plants grown at 2 and 6 Mg lime ha‐1. The higher lime supply enhanced Ca and reduced Mn and Fe concentrations in leaves. Di...

The evaluation under grazing of legumes associated with Andropogon gayanus in a tropical savannah environment on the central plateau of Brazil

SUMMARYThe persistence and productivity under grazing of seven accessions of Stylosanthes macrocephala, Zornia latifolia and Zornia brasiliensis in combination with Andropogon gayanus (cv. Planaltina) were investigated in small plots at two stocking rates on a low fertility, acid oxisol in the tropical savannah of the centre-west region of Brazil.Two new accessions of S. macrocephala CIAT 2039 (CPAC 1033) and CIAT 2053 (CPAC 1034) were more productive and persistent than the control cultivar Pioneiro. After 4 years there were no differences in dry-matter yield between the two accessions. No anthracnose (Colletotrichum gloeosporioides) problems were noted in these accessions. Animals refused to graze Z. brasiliensis accessions at any time during the trial. Stocking rate effects became pronounced over time and legume contents were highest in the treatment grazed at 3·0 animals/ha. The advantages of the small-plot grazing method used in the experiment are discussed.

Effects of Phosphorus, Calcium, and Hup− and Hup+ Rhizobia on Pigeon Pea Yields in an Infertile Tropical Soil1

AbstractPigeon peas [Cajanus cajan(L.) Millsp. var. 64‐28] were grown in the Republic of Panama in an infertile acid Oxisol (Bayano) in both greenhouse and field studies to determine if yield parameters could be increased by addition of P, Ca, and Rhizobium. In the greenhouse, P additions to the Bayano soil increased shoot and nocule weights, acetylene reduction activity, and hydrogen evolution, but neither inoculation with Rhizobiumnor Ca additions had any effect on yields or N2fixing characteristics. Similar results were observed from field trials in the Bayano soil, where grain yields and plant N content were not increased after inoculation with Rhizobiumstrains P170 or P168, which were hydrogenase positive and negative, respectively. Strain P170 was a poor competitor with indigenous rhizobia as noted by the low recovery of antibiotic resistant rhizobia from nodules, while P168 was a superior competitor as noted by its recovery from nodules and by the higher production of H2from nodules than from the uninoculated control. Grain yields in the Bayano soil were considerably lower (245 kg ha−1) in the absence of Ca and P and were increased progressively with P additions of 45, 90, 182, and 363 kg ha−1. Addition of CaCO3(909 kg ha−1) and P (90 kg ha−1) gave grain yields (1407 kg ha−1) comparable to the highest P level (1320 kg ha−1) without additional Ca. With modest addition of Ca and P, pigeon peas in a less fertile acid soil could produce yields comparable to those in a more fertile and less acid soil.

The persistence of tropical grass-legume associations under grazing in Brazil

SummaryThe persistence under a close intermittent grazing regime of eight accessions of Stylosanthes guianensis, Stylosanthes macrocephala and Stylosanthes capitata in combination with Andropogon gayanus (cv. Planaltina) and Brachiaria decumbens (cv. Basilisk) was evaluated in small plots on a low fertility acid oxisol in the tropical savannah region of Brazil. Five accessions persisted for four seasons with both grasses, although legume yields were lower in the B. decumbens associations.S. macrocephala CIAT 1582 (CPAC 139), S. capitata CIAT 1019 (CPAC 704) and CIAT 1097 (CPAC 706) were the most productive accessions at the end of the experiment. The three accessions S. guianensis cv. Cook, S. capitata CIAT 1315 (CPAC 707) and CIAT 1405 (CPAC 846), which failed to persist, were destroyed by anthracnose (Colletotrichum gloeosporioides). This disease remains the primary factor limiting the use of Stylosanthes in the region. The value of small-plot grazing experiments is briefly discussed.

Direct use of low grade phosphate rock from Brazil as fertilizer

The response of plant dry matter to addition of a low grade Brazillian (Patos) phosphate rock was increased by mycorrhizal inoculation (strain E3) ofStylosanthes guianensis andDesmodium intortum, but less so by inoculation ofCenchrus ciliaris andPaspalum plicatulum. The effect was related partly to the extent of root development. In the presence of a nitrification inhibitor the utilisation of Potos rock phosphate by Paspalum was higher with NH4+-N than with NO3-N. This effect was attributed to acidification which in turn was related to the organic anion content of the plants. The results indicate the potential for improving the utilization of the low grade phosphate rock on an acid oxisol by mycorrhizal inoculation of herbage legumes and by soil acidification when growing grasses.

Título en español

Se diseñó un sistema, utilizando tubos de material plástico, para estudiar el uso de la técnica de riego por goteo y del suministro de abonos en un Oxisol muy intemperizado, lixiviado, de fertilidad relativamente baja y ácido. Se utilizó el pimiento como cosecha indicadora. Todas las parcelas recibieron una aplicación inicial a voleo, de un abono 10-4.4-8.3 a razón de 80 kg/ha. Se utilizó un diseño de bloques completos aleatorios con cuatro tratamientos y seis repeticiones. Los tratamientos fueron como sigue: 1. N y K inyectados en el sistema de riego por goteo, P aplicado en franjas; 2. N, P y K aplicado en franjas; 3. N, P y K a voleo; y 4. Testigo-sin N, P, K fuera del aplicado inicialmente a voleo en todas las parcelas. En todos los tratamientos, excepto el control, se aplicaron 56.8 g/planta de un abono 10-10-10 y todos recibieron riego por goteo. Se hicieron dos siembras: una en la temporada de sequía y otra en la lluviosa. Los rendimientos de pimiento fueron significativamente diferentes entre todos los tratamientos en la temporada de sequía. En la temporada lluviosa las diferencias en rendimiento no fueron significativas entre el tratamiento en que se inyectó N y K en el sistema de riego y el tratamiento en que se aplicaron estos nutrimentos en franjas. Sin embargo, se obtuvieron rendimientos significativamente más altos con estos dos tratamientos que con el que se aplicó el abono a voleo. Estos tres tratamientos fueron superiores al testigo. El sistema de riego por goteo parece ser un método prometedor para el uso y suministro de agua y nutrimentos en los Oxisols de las regiones tropicales.

Fertilizer Management with Drip Irrigation in an Oxisol1

AbstractOxisols are the dominant soils of the continental shields in the tropics under permanently moist and alternately wet and dry climates. Oxisols have a low cation exchange capacity, high permeability, but low available waterholding capacity. Some have a low pH, which can cause Al3* toxicity to many crops. Together with erratic rainfall patterns, special management methods of soil‐water and plant nutrients for Oxisols are yet to be carefully studied. The relatively recent development of combined high frequency irrigation and fertilizer techniques, “drip fertilization,” may be one of the solutions for intensive production of food crops on Oxisols.A drip irrigation system using porous plastic tubing was designed for a field experiment to study the feasibility and operational techniques of drip irrigation and fertilization management in a highly weathered, acid Oxisol (Coto clay). Green pepper (Capsicum annuum L.), ‘Blanco del Pais’ was the test crop. A randomized, completeblock design was chosen to compare different fertilization techniques. In addition to the check plot, the three other treatments were: fertigation (drip irrigation and drip application of N and K, banded P); drip irrigation with banded N, P, and K; and drip irrigation with broadcast N, P, and K. All treatments, except the control plot, received a total amount of fertilizer equal to 56.8 g of 10‐10‐10 commercially available fertilizer per plant and all treatments were uniformly drip irrigated according to pan evaporation data.Different moisture profiles during the wet (June‐November) and dry (December‐May) seasons were observed. Nutrient movement profiles suggested that the distribution of fertilizer under drip irrigation depended on the method of fertilizer placement. Root development patterns indicated that more than half of the root system (dry weight) was developed in the 5 to 15 cm layer. More fibrous roots were developed toward the porous drip tubing which supplied moisture and nutrients. Yield were significantly different among all treatments during the dry season and the fertigation, broadcast, and control during the wet season. Yields from broadcast fertilizer treatments were 15.8% lower than from fertigation, and 12.3% lower than from banded fertilizer. The results of this research indicates drip fertigation can be a promising alternative to currently used water‐nutrient management methods for Oxisols in the wet‐dry tropics.

Evaluation of Cassava Germplasm for Productivity1

A yield evaluation in single‐row plots were made in Colombia of approximately 1,900 accessions of cassava (Manihot esculenta Crantz), collected throughout Latin America and 4,700 hybrid lines from crosses within the same germplasm. Superior genotypes were selected on the basis of harvest index (proportion of root weight to total plant weight) and root yield in single‐row plots and then evaluated in replicated yield trials under diverse environments. With a rainfall of less than 800 mm well distributed throughout the year on a fertile soil, root dry‐matter yield of 21 metric ton/ha/year (average of top 10 genotypes) was obtained without irrigation or fertilization. Yields of 12 metric ton/ha/year dry matter were obtained without irrigation in a climate with a 5 monthd ry season. Yields of 8 metric ton/ha/year dry matter were obtained on acid oxisols of the tropical savanna, with a moderatef ertilizer application. Several genotypes showedc onsistently superior performanceo ver the wide range of environments, and their yields exceeded those of correspondinglo cal strains by 50 to 150%. These results confirm that cassava is an efficient carbohydrate producer adapted to a wide range of environments, is tolerant of drought and acid soils, and offers a great opportunity for genetic improvement. Present farm yields of 3 to 5 metric ton/ha/year (dry matter) could be increased to 10 to 15 ton/ha/year through simple selection and improved cultural practices. Largescale carbohydratep roductioni n tropical savanna o xisols is possible by planting improved cassava genotypes.

ROOT RESPONSES OF THREE GRAMINEAE SPECIES TO SOIL ACIDITY IN AN OXISOL AND AN ULTISOL

Sorghum roots were highly sensitive to soil solution Al present in acid Ultisols and Oxisols. Corn roots were moderately sensitive and stargrass roots were tolerant. Representative acid soils from the humid region of Puerto Rico contained less soil solution Al than did several selected from the southeastern United States at the same pH level. This confirms the observation that critical soil pH range tends to be lower in soils of Puerto Rico than in those of the southeastern United States. Soil solution Al concentration can be calculated satisfactorily from soil pH and EC of the saturated paste extract using an equation developed from the data presented.