R. J. Wright

Soil aluminum toxicity and plant growth

Abstract Soluble aluminum (Al) exists in a variety of forms in the soil system and is responsible for limiting plant growth in many areas of the world. Some phytotoxic forms of soluble Al have been identified in solution culture experiments, but current soil test methods do not effectively discriminate between toxic and nontoxic forms of Al. Large differences in Al tolerance exist within and among plant species. Efforts to select or breed plants for Al toxic soils have been somewhat successful, but accelerated progress will occur when plant Al tolerance mechanisms are more fully understood.

Influence of soil solution aluminum on root elongation of wheat seedlings

Wheat (Triticum aestivum L.) seedlings were grown for 4 days in an acid soil horizon treated with 10 levels each of Ca(OH)2, CaSO4 and CaCl2. The treatments resulted in a wide range of Al levels and Al speciation in soil solution. Seedling root length in the Ca(OH)2 treatments was significantly related (p<0.01) to calculated Al3+ activity in soil solution. The Al−SO4 complex in soil solution had a negligible effect on the root growth of Hart wheat, thus confirming the previously reached conclusion concerning the nonphytotoxicity of Al−SO4. The short-term seedling root growth technique used in this investigation allowed for separation of Al effects on root elongation from those on plant nutrition and should be useful for studying Al toxicity relationships in soil.

Screening wheat and other small grains for acid soil tolerance

Abstract Aluminum (Al) toxicity in acid soils is a major growth-limiting factor for cereal crops in many parts of the world. The most striking effect of high Al concentration in acid soils is stunting of the root system. Liming reduces Al toxicity in surface soils; however, cereal breeders must be prepared to develop cultivars that have tolerance to soil acidity. A 4 day root bioassay, originally used to identify Al toxics soils, was adapted to evaluate tolerance to soil acidity of cereal species and genotypes. Acid soil tolerance was related to the extent of inhibition of root elongation in an Al-toxic soil (pH 4.2) relative to root elongation in the same soil treated with lime (pH5.2). Of the entries, 18% were tolerant or moderately tolerant, and 48% were susceptible or moderately susceptible when 75 bread wheat ( Triticum aestivum L.) genotypes were tested. None of the 22 entries of durum wheat ( Triticum durum Desf.) were tolerant or moderately tolerant, indicating much lower adaptability to soil acidity than bread wheat. The following ranking of acid soil tolerance of cereal species was obtained: rye ( Secale cereale L.) #62;oats ( Avena sativa L.) #62;millet( Panicum miliaceum L.) #62;bread wheat ( Triticum aestivum L.) #62;barley ( Hordeum vulgare L.) #62;durum wheat ( Triticum durum Desf.). Variation in tolerance within the other cereal species was much lower than within bread wheat species. The root bioassay method is relatively quick, simple and inexpensive. The method can also be used to screen early-generation populations because assayed seedlings are still viable and can be transplanted for growing until harvest.

Aluminum tolerance of segregating wheat populations in acidic soil and nutrient solutions

Abstract Increased demand for wheat (Triticum aestivum L.) cultivars tolerant to acid‐soil stress has accelerated genetic research on aluminum (Al) tolerance in soil and solution media. Our objective was to characterize the genetic segregation of tolerant and susceptible plants from two populations in an Al‐toxic Porters soil (coarse‐loamy, mixed, mesic Umbric Dystrochrepts), and in nutrient solutions with 0.09, 0.18, 0.36, 0.72, and 0.90 mM Al. Rapid bioassays were applied to determine seedling responses of two Al‐tolerant (Cardinal and Becker) and two susceptible cultivars (GK Zombor and GK Kincso) and their F2 progenies. In the Al‐toxic soil, Becker/Kincso F2 and Cardinal/Zombor F2 exhibited contrasting segregation patterns but with similar heritability values (0.60 and 0.57, respectively). Higher values of root length in soil were dominant in Cardinal/Zombor F2 (degree of dominance, d = 0.98), but dominance was absent (d = 0.07) for Becker/Kincso F2. The results of the soil and nutrient‐solution exper...

Rapid bioassay of aluminum toxicity in soil

Fifty-five acid soil horizons from 19 profiles were evaluated for aluminum toxicity using root elongation as a criterion in a two-day petri dish bioassay. The method proved to be simple, efficient, and precise enough to clearly distinguish aluminum toxicity differences among horizons within and between profiles. Although toxicity patterns within profiles differed, it was common for surface horizons to be less toxic even when very acid. The R2 for correlations of relative root lengths with pH in H2O, pH in KCl, soluble and exchangeable aluminum and percent aluminum saturation were only 0.42, 0.45, 0.52, 0.66, and 0.54, respectively, which indicates the need for a bioassay. In a further use of the method, and to demonstrate its efficiency, 243 horizons from 26 profiles were screened. Approximately half of the horizons with a pH of 5.0 or below showed Al toxicity. When used by different operators, with a variety of soil and treatment parameter changes, the two-day bioassay in petri dishes gave consistent rankings of soils by degree of aluminum toxicity.

Links among Nitrification, Nitrifier Communities, and Edaphic Properties in Contrasting Soils Receiving Dairy Slurry

Soil biotic and abiotic factors strongly influence nitrogen (N) availability and increases in nitrification rates associated with the application of manure. In this study, we examine the effects of edaphic properties and a dairy (Bos taurus) slurry amendment on N availability, nitrification rates and nitrifier communities. Soils of variable texture and clay mineralogy were collected from six USDA-ARS research sites and incubated for 28 d with and without dairy slurry applied at a rate of ~300 kg N ha(-1). Periodically, subsamples were removed for analyses of 2 M KCl extractable N and nitrification potential, as well as gene copy numbers of ammonia-oxidizing bacteria (AOB) and archaea (AOA). Spearman coefficients for nitrification potentials and AOB copy number were positively correlated with total soil C, total soil N, cation exchange capacity, and clay mineralogy in treatments with and without slurry application. Our data show that the quantity and type of clay minerals present in a soil affect nitrifier populations, nitrification rates, and the release of inorganic N. Nitrogen mineralization, nitrification potentials, and edaphic properties were positively correlated with AOB gene copy numbers. On average, AOA gene copy numbers were an order of magnitude lower than those of AOB across the six soils and did not increase with slurry application. Our research suggests that the two nitrifier communities overlap but have different optimum environmental conditions for growth and activity that are partly determined by the interaction of manure-derived ammonium with soil properties.

Phosphorus sorption isotherm characteristics and availability parameters of Appalachian acidic soils

Abstract Phosphate (P) sorption isotherms have been widely used to characterize the P status and to establish fertilizer requirements of soils. Recently, mechanistic models have successfully described the nutrient uptake by plants under changing soil and plant parameters. Phosphorus sorption characteristics of eleven representative soils of the Appalachian Region of the United States were evaluated, and experimental P adsorption data were fitted to Temkin, Freundlich, and Langmuir equations to determine the relative importance of the soil parameters in P retention and supply to plant roots. The Barber and Cushman model was used to predict the effect of P fertilization on P uptake by plant. The soils of Appalachia differ considerably with respect to the retention of added P. All three isotherm equations gave good fit with the experimental data and were reliable to describe the P quantity/ intensity relationships of these soils. The following sequence of P adsorption capacity in various soils was establishe...

Characterization of physical and chemical properties of Varzea soils of Goias State of Brazil

Abstract Brazil has approximately 30 million hectares of lowland areas, known locally as “Varzea,”; distributed throughout the country. Soils in these areas have the potential to support agricultural production, but very little is known about their fertility. The current experiment was undertaken to characterize the chemical and physical properties of representative “Varzea”; soils collected at 0–20, 20–40, 40–60, and 60–80 cm depth intervals from 23 sites in Goias State of Brazil. Organic matter contents averaged 42 g/kg in the surface 20 cm of soil and should make a significant contribution to overall nutrient availability. Soil pH increased slightly with depth from a mean value of 5.2 in the surface 20 cm of soil to a mean value of 5.4 in the 60–80 cm depth interval. Several soils had exchangeable Al values ≥ 1.0 cmol Al/kg, but soil Al saturation was generally less than the 60% level frequently associated with Al toxicity. However, cereal and legume production could benefit from lime addition in many ...

The influence of acid soil factors on the growth of snapbeans in major appalachian soils

Abstract Acid soil limitations to plant growth were assessed In 55 horizons of 14 major Appalachian hill land soils. Aluminum sensitive “Romano” and Al‐tolerant “Dade” snapbeans (Phaseolus vulgaris L.) were grown for 5 weeks in limed and unlimed treatments of the 55 horizons. Shoot and root growth was depressed >20% in unlimed relative to limed treatments in approximately 2/3 of the horizons. Dade snapbeans were generally more tolerant of the acid soil conditions and had higher Ca concentrations in the shoots than Romano snapbeans. However, the sensitive‐tolerant snapbean pair could not consistently be used to identify horizons with soil Al problems. Growth of both snapbeans was generally best in A horizons and worst in E horizons. The E horizons in this study were characterized by low Ca saturation (exchangeable Ca x 100/cation exchange capacity) and high Al saturation (exchangeable Al x 100/cation exchange capacity). Exchangeable Ca, soil Ca saturation and total soil solution Ca were positively correlat...

The effect of phosphate rock dissolution on soil chemical properties and wheat seedling root elongation

Soils of the Appalachian region of the United States are acidic and deficient in P. North Carolina phosphate rock (PR), a highly substituted fluoroapatite, should be quite reactive in these soils, allowing it to serve both as a source of P and a potential ameliorant of soil acidity. An experiment was conducted to evaluate the influence of PR dissolution on soil chemical properties and wheat (Triticum aestivum cv. Hart) seedling root elongation. Ten treatments including nine rates of PR (0, 12.5, 25, 50, 100, 200, 400, 800, and 1600 mg P kg-1) and a CaCO3 (1000 mg kg-1) control were mixed with two acidic soils, moistened to a level corresponding to 33 kPa moisture tension and incubated for 30 days. Pregerminated wheat seedlings were grown for three days in the PR treated soils and the CaCO3 control. Root length was significantly (P<0.05) increased both by PR treatments and CaCO3, indicating that PR dissolution was ameliorating soil acidity. The PR treatments increased soil pH, exchangeable Ca, and soil solution Ca while lowering exchangeable Al and 0.01 M CaCl2 extractable soil Al. Root growth in PR treatments was best described by an exponential equation (P<0.01) containing 0.01 M CaCl2 extractable Al. The PR dissolution did not reduce total soil solution Al, but did release Al complexing anions into soil solution, which along with increased pH, shifted Al speciation from toxic to nontoxic forms. These results suggest that North Carolina PR should contribute to amelioration of soil acidity in acidic, low CEC soils of the Appalachian region.