Soil chemical and microbiological properties in hay production systems: residual effects of contrasting N fertilization of swine lagoon effluent versus ammonium nitrate

This study characterized soil chemical and microbiological properties in hay production systems that received from 0 to 600 kg plant-available N (PAN) ha⁻¹ year⁻¹ from either swine lagoon effluent (SLE) or ammonium nitrate (AN) from 1999 to 2001. The forage systems contained plots planted with bermudagrass (Cynodon dactylon L.) or endophyte-free tall fescue (Festuca arundinaceae Schreb.). In March 2004, the plots were sampled for measurements of a suite of soil chemical and microbiological properties. Nitrogen fertilization rates were significantly correlated with soil pH and K₂SO₄-extractable soil C but not with total soil C, soil C/N ratio, electrical conductivity, or Mehlich-3-extractable nutrients. Soil supplied with SLE had significantly lower Mehlich-3-extractable nutrients than the soil supplied with AN. Two indicators of soil N-supplying capacity (potentially mineralizable N and amino sugar N) varied with plant species and the type of N fertilizer. However, they generally peaked at an application rate of 200 or 400 kg PAN ha⁻¹ year⁻¹. Soil microbial biomass C also peaked at an application rate of 200 or 400 kg PAN ha⁻¹ year⁻¹. Nitrification potential was significantly higher in soil supplied with AN than in the unfertilized control but was similar between SLE-fertilized and unfertilized soils. Our results indicated that an application rate as high as 600 kg PAN ha⁻¹ year⁻¹ did not benefit soil microbial biomass, microbial activity, and N transformation processes in these forage systems.     

The non-recoverable phosphorus following sorption onto a Brazilian Ultisol

Phosphorus (P) immobilization in soil involves geochemical (e.g., sorption, precipitation, and diffusion) and microbiological (microbial uptake) processes. Using a Brazilian Ultisol, relative contributions of both processes to the total immobilization of applied P over 14 days were investigated. The P immobilized by microbes as interpreted by microbial suppression (achieved by mercury sterilization) was 17, 50, 54, and 56% (of the total immobilized P) on days 3, 7, 10, and 14 after fertilization, respectively. In the short-term (1 to 3 days), microbes played less of a role than did the physical effect of shaking the soil, but became the major factor by days 7 to 14. Geochemical process that might be considered short-term ageing caused only 13–16% of the total immobilization in the same time period above. Calculations supported the interpretation that measurable diffusion occurred across water films on the soil particles.     

<Emphasis Type="Italic">Achromobacter insolitus</Emphasis> and <Emphasis Type="Italic">Zoogloea ramigera</Emphasis> associated with wheat plants (<Emphasis Type="Italic">Triticum aestivum</Emphasis>)

This study reports for the first time the presence of diazotrophic bacteria belonging to the genera Achromobacter and Zoogloea associated with wheat plants. These bacterial strains were identified by the analysis of 16S rDNA sequences. The bacterium IAC-AT-8 was identified as Azospirillum brasiliense, whereas isolates IAC-HT-11 and IAC-HT-12 were identified as Achromobacter insolitus and Zoogloea ramigera, respectively. A greenhouse experiment involving a non-sterilized soil was carried out with the aim to study the endophytic feature of these strains. After 40 days from inoculation, all the strains were in the inner of roots, but they were not detected in soil. In order to assess the location inside wheat plants, an experiment was conducted under axenic conditions. Fifteen days after inoculation, preparations of inoculated plants were observed by the scanning electron microscope, using the cryofracture technique, and by the transmission electron microscope. It was observed that all isolates were present on the external part of the roots and in the inner part at the elongation region, in cortex cells, but not in the endodermis or in the vascular bundle region. No colonizing bacterial cells were observed in wheat leaves.     

Experimental snowpack reduction alters organic matter and net N mineralization potential of soil macroaggregates in a northern hardwood forest

Climate change is predicted to reduce or delay annual wintertime snow pack formation in the forests of the northeastern US. Any delay in snowpack formation could increase soil freezing in winter and, thereby, alter soil characteristics and processes. We examined the hypothesis that delayed snowpack would disrupt soil structure and change organic matter bioavailability in an experimental snow removal study at the Hubbard Brook Experimental Forest (HBEF), NH, USA. Pairs of reference and snow removal treatment plots were studied in four different sites at HBEF. Snow was removed from November–January of two winters, inducing soil freezing throughout both winters. Size class distribution and organic matter concentration and content of aggregates, and carbon and nitrogen mineralization potential of size fractions were quantified for surface mineral soils in the spring of both years immediately after snowmelt. In the first year of sampling, the only significant effect of snow removal was an increase in the smallest (<53 μm) size fraction of mineral soil. In the second year, snow removal increased organic matter concentrations of macroaggregate (250–2,000 μm) and microaggregate (53–250 μm) size fractions. This change corresponded to an increase in net N mineralization potential and the ratio of N to C mineralized in the macroaggregate fraction, but there were no effects of snow removal on C mineralization. We propose that soil freezing increases the movement of organic matter from organic to mineral soil horizons and increases the N content of mineralizable substrates in mineral soil following years with delayed snowpack formation.     

Sampling strategies and screening of chickpea (<Emphasis Type="Italic">Cicer arietinum</Emphasis> L.) germplasm for salt tolerance

Six hundred accessions of chickpea (Cicer arietinum L.) landraces and its wild relatives from 28 different countries, available at Australian Temperate and Field Crops Collection (ATFCC) were screened for tolerance to salt under greenhouse conditions using three sampling strategies; (1) random sampling of 200 accessions from different countries, (2) restricted random sampling of 200 accessions from geographical regions with salinity problems and high diversity (Middle East and West & South Asia) and (3) as for strategy 1 but with a reduced representation of accessions from the geographical regions used in strategy 2. Degree of salt tolerance was based on necrosis scores and shoot biomass reduction relative to unstressed controls at harvest after subjecting stressed plants to salt treatment from 21 to 42 days after sowing. There was a wide variation in salinity tolerance determined by both measures. For sampling strategies 1, 2 and 3 respectively; 24, 28 and 14% of accessions were salt tolerant. Accessions from the middle east and south Asian (regions with salinity problem, a long history of chickpea cultivation and high diversity) gave a higher probability (P < 0.01) of getting salt tolerant accessions.     

Classification of Peruvian highland maize races using plant traits

The maize of Latin America, with its enormous diversity, has played an important role in the development of modern maize cultivars of the American continent. Peruvian highland maize shows a high degree of variation stemming from its history of cultivation by Andean farmers. Multivariate statistical methods for classifying accessions have become powerful tools for classifying genetic resources conservation and the formation of core subsets. This study has two objectives: (1) to use a numerical classification strategy for classifying eight Peruvian highland races of maize based on six vegetative traits evaluated in two years and (2) to compare this classification with the existing racial classification. The numerical classification maintained the main structure of the eight races, but reclassified parts of the races into new groups (Gi). The new groups are more separated and well defined with a decreasing accession within group × environment interaction. Most of the accessions from G1 are from Cusco Gigante, all of the accessions from G3 (except one) are from Confite Morocho, and all of the accessions from G7 are from Chullpi. Group G2 has four accessions from Huayleño and four accessions from Paro, whereas G4 has four accessions from Huayleño and five accessions from San Geronimo. Group G5 has accessions from four races, and G6 and G8 formed small groups with two and one accession each, respectively. These groups can be used for forming core subsets for the purpose of germplasm enhancement and assembling gene pools for further breeding.     

Physiological,morphological, chemical and genomic diversities of different origins of thyme (<Emphasis Type="Italic">Thymus vulgaris</Emphasis> L.)

For the selection of donors with valuable characteristics for breeding, 39 thyme accessions were evaluated in three years according to a staggered schedule. The criteria investigated were: winter hardiness, beginning of flowering, growth height, yield of the dry herb, content of essential oil, composition of the essential oil, DNA content of cell nuclei and number of chromosomes. The most strongly varying traits between the populations were the yield of dry herb, the content of essential oil and the content of volatile phenols with coefficients of variation (CV) between CV 40% and 50%. The largest variation within a population was detected for the yield of dry herb (CV 25–46%) and the content of essential oil (CV 17–48%). The homogeneity of the populations was different. The minimal average coefficient of variation of all traits (CV 19%) was determined in the population of the cultivar ‘Varico II’ and in a population from Lithuania. The ploidy level of T. vulgaris was diploid (2n = 30).     

Genetic diversity of ICARDA’s worldwide barley landrace collection

Twenty genic- and genomic SSR markers were used to study genetic diversity and geographical differentiation of barley from 29 countries through analysis of a worldwide collection of 304 ICARDA’s barley landraces. Of these, 19 loci were highly polymorphic in the material studied. Based on Nei-distance matrix, Principal Component Analysis (PCoA) and cluster analysis using UPGMA associated with AMOVA the data revealed countries’ grouping within regions. Three distinct germplasm pools were identified in the landraces. The first of these was from Eastern Africa (Eritrea and Ethiopia) and South America (Ecuador, Peru and Chile) suggesting that barley introduced to South America might have originated specifically from East Africa or that they share a common genetic basis for adaptation. The second was the Caucasus (Armenia and Georgia) and the third included the remaining regions of Central Asia, Near East, Northern Africa and Eastern Asia. Genetic diversity of barley subspecies (Six-rowed barley, Two-rowed barley, H. spontaneum C. Koch and H. agriocrithon Åberg) also discriminates them into three groups: cultivated barleys (Six-rowed barley and Two-rowed barley), wild barley H. spontaneum and subspecies H. agriocrithon. These results associated with parsimony analysis demonstrate that H. agriocrithon and H. spontaneum might be distinct and do not support a hybrid origin for H. agriocrithon suggesting further investigation of the basis of more intense sampling of the two subspecies H. spontaneum and H. agriocrithon.