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Agroforestry systems deposit great amounts of plant residues on soil and this leads to high levels of soil organic matter content and has increased soil biodiversity and improved its conservation. This study compares the distribution of meso and macrofaunal communities in soil and litter under cacao agroforestry systems and in a natural forest in the southern Bahia state of Brazil. Soil and litter samples were obtained in September 2003, February 2004, and August 2004 in five cacao agroforestry systems. The systems evaluated included: cacao renewed under Erythrina sp. ( Erythrina poeppigiana) (CRE); cacao renewed under natural forest (Cabruca, CRF); an old cacao system under Erythrina sp. (OCE); an old cacao system under a natural forest system (Cabruca, OCF) and a cacao germplasm collection area (CGC). As a reference soil and litter under a natural forest (NF) was included. Organisms were collected over a 15-day period with a Berlese–Tullgren apparatus. The density and richness of total fauna varied distinctly according to sites, sampling time and material sampled (soil and litter). 16,409 of fauna were recovered from soil and litter samples and the density of total fauna was 2,094 individuals m−2 in the litter and 641 individuals m−2 in the soil. The richness was 11.8 in the litter and 7.5 in the soil. The cacao agroforestry systems adopted for growing cacao in the southern Bahia region of Brazil have beneficial effects on the soil and litter faunal communities, and such systems of cacao cultivation could be considered as a conservation system for soil fauna. The development of a litter layer resulted in higher abundance and diversity of soil fauna. [ABSTRACT FROM AUTHOR]

Phosphate rock (PR), limestone, coal combustion by-product (CCBP) high in Ca and high organic manures are potential amendments for increasing agricultural production in the acidic soils of the Appalachian region. The objective of this study was to examine effects of PR, CCBP and cellulose addition on soil microbial biomass in an acidic soil based on the measurement of soil microbial biomass P ( Pmic) and on the mineralization of organic matter. Application of PR alone or in combination with CCBP increased Pmic. The Pmic was far less when the soil received PR in combination with limestone than with PR application alone or PR in combination with CCBP. Either CCBP or limestone application alone considerably decreased Pmic in the soil due to reduced P solubility. Cellulose addition alone did not increase Pmic, but Pmic was significantly increased when the soil was amended with cellulose in combination with PR. The decomposition of added cellulose was very slow in the soil without PR amendment. However, mineralization of both native organic matter and added cellulose was enhanced by PR application. Mineralization of organic matter was less when the soil was amended with PR in combination with high rates of CCBP (> 2.5%) because PR dissolution varied inversely with amount of CCBP addition. Overall, CCBP had no detrimental effect on soil microbial biomass at low application rates, although, like limestone, CCBP at a high rate may decrease Pmic in P-deficient soils through its influence on increased soil pH and decreased P bioavailability in the soil. Application of PR to an acidic soil considerably enhanced the microbial activity, thereby promoting the cycling of carbon and other nutrients. [ABSTRACT FROM AUTHOR]

Tall fescue (Festuca arundinacea Schreb.) plants infected by the fungal endophyte Neotyphodium coenophialum (Morgan-Jones & Gams) (Glenn et al., 1996) often perform better than noninfected plants, especially in marginal resource environments. There is a lack of information about endophyte related effects on the rhizosphere of grasses. In a greenhouse experiment, four endophyte-infected (E+) tall fescue clones(DN2, DN4, DN7, DN11) and their endophyte-free (E-) forms were grownin limed (pH 6.3) Porter soil (low fertility, acidic, high aluminum and low phosphorus content, coarse-loamy mixed mesic Umbric Dystrochrept) at three soil P levels (17, 50 and 96 mg P kg-1 soil)for five months. Excluding the genotype effect, endophyte infectionsignificantly increased cumulative herbage DM yield by 8% at 17 mg Pkg-1 soil but reduced cumulative herbage DM yield by 12% at 96 mg P kg-1 soil. With increased P availability in the soil, shoot and root DM, and root/shoot ratio in E+ plants were significantly less when compared to E- plants. Endophyte infection increased specific root length at 17 and 50 mg P kg-1 soil. Atsoil P level of 17 mg P kg-1 soil, E+ plants had significantly higher P concentrations both in roots and shoots. Similar relationships were found for Mg and Ca. E+ plants had significantly higher Zn, Fe, and Al concentration in roots, and lower Mn and Al concentration in shoots when compared to E- plants. Ergot alkaloid concentration and content in shoot of E+ plants increased with increasing P availability in the soil from 17 to 50 mg P kg-1 but declined again at 96 mg P kg-1 soil. Ergot alkaloid accumulationin roots increased linearly with P availability in the soil. Results suggest that endophyte infection affects uptake of phosphorus and other mineral nutrients and may benefit tall fescue grown on P-deficient soils. Phosphorus seems also to be involved in ergot alkaloid accumulatio [ABSTRACT FROM AUTHOR]

Difference in Ni tolerance/accumulation in plant genotypes might be used to identify or develop plants for remediation of high Ni soils. Ryegrass was shown to be more sensitive to Ni toxicity and accumulated much more Ni in shoots than maize. The objectives of this study were to examine the relationship of organic acids to Ni accumulation andxylem transport of Ni in ryegrass (Lolium perenne L.) and maize (Zeamays L.). The results showed that accumulation of Ni in shoots was 5to 7 fold higher in ryegrass than in maize grown at 20 to 80 5M Ni, whereas Ni concentration in ryegrass roots was only 1 to 2 fold higher at 0.1 to 40 5M Ni and 1.5-fold lower at 80 5M Ni than that of maize roots. Xylem transport rates of Ni increased with increasing Ni supply for both species, and were about 2 to 7 times higher in ryegrass than in maize. Shoot concentrations of citric, malic, oxalic and cis-aconitic acids increased at Ni levels above 20 5M, and were about 2 to 6 times higher in ryegrass than in maize. Whereas, maize roots accumulated greater amount of malic, oxalic, and cis-aconitic acids than ryegrass roots, especially at Ni levels of 40-80 5M. The rate of Ni exudation by roots in the two species was significantly correlated with root Ni concentrations. It could be concluded that high Ni accumulation in shoots was closely related to high xylem transport rates of Ni and that the accumulation of organic acids, citric and malic acid in particular. A high root exudate rate of Ni and the enhanced accumulation of organic acids, malic acid in particular, in roots might be among the important factors which are associated with the tolerance ofcrops to toxic Ni levels. [ABSTRACT FROM AUTHOR]

Maize (Zea mays L.) is the third most important cereal grown in the world. In South and Central America, maize is mostly grown on acidic soils. On these soils, yields are limited by deficient levels of available P, Ca, and Mg, and toxic levels of Al and Mn. A greenhouse study was conducted with 22 maize genotypes originating from Africa, Europe, and North, Central, and South America on acid, dark red latosol (Typic Haplorthox) at 2%, 41%, and 64% Al saturation at correspondingpH of 5.6, 4.5, and 4.3. With increasing Al levels, the nutrient efficiency ratios (NER = mgs of dry shoot weight / mg of element in shoot) for K, Ca and Mg increased, and NER for P and Zn tended to decrease. Overall, Al-tolerant genotypes produced higher shoot and root weight and had higher NER for P, Ca Mg, and Fe at 41 % Al saturation. Genotypes used in this study showed genetic diversity for growth and NER of essential nutrients. It was concluded that selection of acid-soil-tolerant genotypes and further breeding of acid-soil-tolerant maize cultivars are feasible. [ABSTRACT FROM AUTHOR]

Soil acidity in the Great Plains of the USA can reduce forage and grain yields of winter wheat, primarily by Al toxicity. Indigenous cultivars may vary in seedling tolerance to Al toxicity, but the benefit that Al tolerance provides to forage and grain production is not welldocumented in this region. Backcrossed-derived lines of 'Chisholm' and 'Century' were selected with an additional gene from 'Atlas 66' conferring Al tolerance in solution culture. Our objective was to determine the impact of this source of Al tolerance on forage production prior to the jointing stage and subsequent grain yield. Experiments were conducted at several locations on non-limed (pH=4.5--4.7) and limed soils (pH=5.2--6. 1) in Oklahoma. Two cultivars ('TAM 105', susceptible; '2180', tolerant) with extreme differences in Al tolerance wereused as controls. In limed conditions, forage and grain production did not differ between Al-tolerant and -susceptible genotypes, indicating a neutral effect of the Atlas 66 gene in the absence of Al toxicity. Despite visual differences in early-season plant vigor in non-limed acid soil, the Al-tolerant selections did not yield greater season-long forage than their susceptible parents. At sites where Al saturation in the non-limed soil exceeded 30%, spike production at maturitywas nearly doubled in the Century background by the addition of Al tolerance, but final grain yield was not significantly improved. In the Chisholm background, grain yield was improved 50 to 74% by Al tolerance. The magnitude of the agronomic benefit of Al tolerance was highly influenced by the edaphic environment and genetic background. Acidsoils of the Great Plains appear highly variable in Al toxicity; hence, consideration of the target environment is essential to predict the potential impact of Al tolerance selected in solution culture. [ABSTRACT FROM AUTHOR]