Carbon stock assessment and soil carbon management in agricultural land‐uses in Thailand

The organic carbon pool in agricultural land‐uses is capable of enhancing agricultural sustainability and serving as a potential sink of atmospheric carbon dioxide. A study was carried out to estimate and map carbon stock of different agricultural land‐uses in a sub‐watershed of Thailand and to assess the land‐use sustainability with respect to carbon management. A quadrat sampling methodology was adopted to estimate the biomass and its carbon content of 11 different land‐uses in the study area. Existing soil data were used to calculate the soil carbon. GIS was used for integrating biomass carbon, soil carbon and carbon stock mapping. Roth carbon model was used to project the soil carbon of present land‐uses in the coming 10 years and based on which the sustainability of land‐uses was predicted. The total carbon stock of agricultural land‐uses was estimated to be 20·5 Tg, of which 41·49 per cent was biomass carbon and 58·51 per cent was soil carbon. Among the land‐uses, para rubber had the highest average biomass C (136·34 Mg C ha⁻¹) while paddy had the lowest (7·08 Mg C ha⁻¹). About four‐fifths of agricultural land‐uses in the watershed are sustainable in maintaining the desired level of soil carbon in coming 10 years while one‐fifths are unstable. Such information on carbon stock could be valuable to develop viable land‐use options for agricultural sustainability and carbon sequestration. Copyright © 2007 John Wiley & Sons, Ltd.     

The effects of cultivation methods and water regimes on root systems of drought-tolerant (RD6) and drought-sensitive (RD10) rice varieties of Thailand

In this study, we have attempted to investigate the effect of different water-saving cultivation techniques on root systems of two Thai rice varieties. The variables were two rice varieties (RD6 and RD10), two cultivation methods (dry direct seeding [DS] and transplanting [TP]) and two soil moisture regimes (field capacity [FC] and 50% FC). RD6 variety had higher root number, root length and root length density compared with RD10 under TP method at FC. Higher root number was observed for TP than dry DS method under FC at flowering stage with 543 and 415 roots plant^–1 for RD6 and 392 and 362 roots plant^–1 for RD10 cultivated under TP and dry DS methods, respectively. Root dry matter (DM) was the highest for RD6 cultivated through dry DS method compared with TP method at FC for both tillering and flowering stages. RD6 variety resulted in 25% and 50% higher root DM at FC for dry DS than TP at tillering and flowering stages, respectively. The performance of RD10 was poor under 50% FC and dry DS method. With proper selection of variety, dry DS method could be a better alternative for sustainable rice cultivation under water-limited environments.     

Eradication of virulent footrot from sheep and goats in an endemic area of Nepal and an evaluation of specific vaccination

Programmes based on the identification and treatment of cases and the culling of animals refractory to treatment had failed to eradicate virulent footrot from two districts in the western region of Nepal. From 1993 to 1996 vaccination against two endemic virulent strains of Dichelobacter nodosus was tested for its potential to contribute to the eradication of footrot from the region. Only sheep and goats which had been free of signs of footrot at three inspections at monthly intervals before their annual migration to alpine pastures were eligible for inclusion. From November 1992, the treatment of cases identified during inspections included the injection of specific vaccine. Successfully treated cases migrated with their flocks but were excluded from the vaccine trial. Non-responding cases were culled. Forty combined flocks of sheep and goats (approximately 9500 animals) were used initially to compare three vaccination regimens. Eleven flocks (sheep and goats) were treated with two doses of specific vaccine (group A), nine (sheep and goats) were treated with commercial vaccine followed by specific vaccine (group B) and 10 (sheep and goats) were treated with two doses of commercial vaccine (group C) in March to April 1993 before the annual migration; 10 flocks (sheep and goats) remained unvaccinated (group D). Only sheep and goats free of signs of footrot were allowed to migrate. Nevertheless, virulent footrot recurred in many flocks three months later. However, its prevalence was significantly lower in group A than in the other three groups combined. Groups A, B and C then received the specific vaccine before their migrations in 1994 to 1996; group D remained unvaccinated. The annual programme of inspection and identification and treatment of cases continued for seven years, but the vaccinations ceased after four years. There was no recurrence of virulent footrot after November 1993. After the first season the virulent strains of D nodosus used in the specific vaccine could no longer be isolated, although antigenically distinct, benign strains of the organism persisted in cases of benign footrot.     

Bamboo resources of Sikkim Himalaya: diversity,distribution and utilization

We recorded 8 genera and over 30 species of bamboo in Sikkim of the reported 23 genera and 125 species in India. Thirty percent of bamboo species were recorded in tropical forests(0–900 m), 40% of species in sub-tropical forests(900–1,800 m), 17% of species in temperate forests(1,800–2,700 m), 9% of species in sub-alpine forests(2,700–3,500 m) and 4% of species in alpine vegetation(3,500–4,500 m). Bamboo is used for various purposes and its versatility qualifies it to be a multiple-use alternative to timber, food for villagers and for tribal in particular. Bamboo is also equally important to Red Panda(Ailurus fulgens), the state animal of Sikkim. We develop a list of bamboos occurring in Sikkim with their vernacular names, distributions and uses in the Himalayan state. However, more extensive study is required to fully describe the bamboo diversity of the Himalayan state.     

Distribution of glyphosate-resistant and glyphosate-susceptible hairy fleabane (Conyza bonariensis) in central California and their phenological development

Glyphosate-resistant (GR) hairy fleabane was first documented in California in 2007. A preliminary study comparing plants from this population to a glyphosate-susceptible (GS) population determined that they developed more rapidly than the GS plants. However, it was not known if this was a general characteristic of all GR populations. Therefore, seeds of hairy fleabane were collected from 122 locations in central California. Plants from each location were grown and tested for resistance using a shikimate enzyme assay. Seeds from 90 locations germinated of which 27 % were determined as GR, 21 % as GS, and 52 % as intermediate/mixed. Plants from five GR and five GS populations, as determined by the assay, were randomly selected for comparisons and were grown in 2010/2011. Time taken by each plant to reach key phenological stages was recorded and converted into growing degree day (GDD) using a base temperature of 4.2 °C. The biomass of each plant was recorded at seed set. The five GR and GS plants had similar phenological development rates and biomass. Therefore, the differences previously identified between the two populations were not present in the additionally tested populations. The phenological development was hence described by a common GDD model with the plants requiring 374, 711, 970, 1289, and 1551 GDD, to reach the rosette, bolting, first bud, first flower, and first seed stages, respectively. This study shows widespread distribution of GR hairy fleabane in central California, provides useful information on biology of this weed for management, and suggests possible label changes to herbicide manufacturers.     

Characterization of natural orchardgrass (Dactylis glomerata L.) populations of the Thrace Region of Turkey based on ploidy and DNA polymorphisms

Determining the ploidy and geneticdiversity of a germplasm is necessarybefore initiating breeding or geneticstudies. This study was conducted tocharacterize the ploidy level of 57 naturalpopulations of orchardgrass (Dactylisglomerata L.) collected from the ranges ofThrace region of Turkey and the diversityamong populations based on RAPD (RandomAmplified Polymorphic DNA) markers. Flowcytometry was used to determine nuclear DNAcontent (pg 2C^-1 = DNA content of adiploid somatic nucleus) of 6 plants foreach population. Nuclear DNA contents werecorrelated to ploidy level with root tipchromosome counts on selected plants. Onthe basis of this study, mean nuclear DNAcontent of orchardgrass was determined as9.57 ± 0.33 (with 95% confidenceinterval) while all the plants used inchromosome counting were determined to betetraploid, with 2n = 28 mitoticchromosomes, suggesting that diploidorchardgrass plants are likely very rare orabsent in ranges of Thrace region ofTurkey. In the RAPD assay, over 40polymorphic fragments were generated whichallowed some populations to bedistinguished from the rest by uniquemarkers. A cluster analysis was performedusing Nei's (1972) genetic distance indexwith an unweighted pair group method witharitmetic mean (UPGMA). The clusteranalysis indicated that there is a highlevel of gene flow among naturalorchardgrass populations and thereforegenes distributed quite homogeneouslythrough out the region. The results of thisstudy can be useful in the development ofDactylis germ plasm collectionstrategies in Thrace region for breedingpurpose.