Carbon budget and seasonal carbon dioxide emission from a central Ohio Luvisol as influenced by wheat residue amendment

Enhancement of soil organic carbon (SOC) stocks through mulching has been proposed, and although this practice can alter several soil properties, its impact on the temporal variability of carbon dioxide (CO₂) emission from soils has not been widely investigated. To that end, we monitored CO₂ fluxes from a central Ohio Luvisol (fine, mixed, mesic Aeric Ochraqualf) amended with wheat (Triticum aestivum L.) straw applied at rates of 0 (M0), 8 (M8) and 16 (M16) Mg dry matter ha⁻¹ per year and supplemented with fertilizer (244 kg N ha⁻¹ per year) or without. The experimental design was a randomized complete block design with three replications. The intensity of CO₂ emission was higher in the late winter (mean: 2.79 g CO₂-C m⁻² per day) and summer seasons (2.45 g CO₂-C m⁻² per day) and lowest in the autumn (1.34 g CO₂-C m⁻² per day). While no significant effect of N fertilization on CO₂ emission was detected, soil mulching had a significant effect on the seasonal variation of CO₂ fluxes. The percentage of annual CO₂ emitted during the winter and spring was similar across treatments (17–22%); however, 43% of the annual CO₂ loss in the M0 plots occurred during the summer as opposed to 26% in the mulch treatments. A close relationship (F=0.47X+4.45, R²=0.97, P<0.001) was found between annual CO₂ flux (F, Mg CO₂-C ha⁻¹) and residue-C input (X, Mg C ha⁻¹). Litter and undecomposed residue amounted to 0.32 and 0.67 Mg C ha⁻¹ per year in the M8 and M16 plots, respectively. After 4 years of straw application, SOC stocks (0–10 cm) were 19.6, 25.6 and 26.5 Mg C ha⁻¹ in the M0, M8 and M16 treatments, respectively. The results show that soil mulching has beneficial effect on SOC sequestration and strongly influence the temporal pattern of CO₂ emission from soils.     

Tillage systems and soil properties in North America

This paper reviews current knowledge on the range and extent of various tillage systems used in North America with special reference to the effects on soil properties, the erosion hazard and water quality. The increasing adoption of conservation-tillage systems since their introduction in the early 1960s follows an enhanced awareness of the increasing risks of soil erosion and non-point source pollution and the high cost of fuel with conventional tillage. Most “conventional tillage” systems encompass complete inversion tillage along with several secondary and tertiary tillage methods. In contrast, conservation-tillage systems involve streamlining various farm operations, thereby reducing the frequency and intensity of the soil manipulative operations. Reduction in tillage intensity has been accompanied by the development of rotations and cropping systems, methods of surface and internal drainage, fertilizer technology and pest management alternatives.

The status of antecedent soil physical properties is an important factor affecting the choice of tillage systems. Important soil physical properties governing the choice of tillage systems include soil wetness and anaerobiosis, soil temperature and soil structure including its susceptibility to compaction, crusting or erosion. Tillage systems affect soil physical, chemical and biological properties. Among drastic tillage-induced changes in soil properties are bulk density, infiltration rate, aggregation and aggregate size distribution, soil organic carbon and nutrient profile, microbial activity and species diversity, and the population of earthworms. Macropores and biochannels are usually more prevalent in conservation-tillage than conventional-tillage systems. Conservation tillage induces stratification of soil organic matter and related nutrients, enhances the activity of soil fauna and leads to acidification. The magnitude of these changes depends on the soil type, the cropping systems and the type of conservation tillage adopted. Soil organic carbon and nutrient stratification are generally more pronounced in coarse-textures than in clayey soils. Conservation tillage is also associated with greater biomass pool size. The latter affects the nutrient response curves of the soil. Nitrification and denitrification are other important processes affected by tillage systems.

The widespread adaption of conservation-tillage systems, although beneficial in controlling off-site sedimentation, has raised concerns about the potential for increased leaching of nutrients and pesticides to groundwater. Important pollutants associated with conservation tillage are nitrate and pesticides. Some studies have shown little effect of tillage on losses of pesticides. Conservation tillage may suppress crop yields, especially on heavy textured soil with poor internal drainage and in those prone to soil compaction caused by vehicular traffic.     

Growth and yield of paddy rice as affected by tillage and nitrogen levels

Although tropical wetlands are rapidly being developed for the needed increase in rice (Oryza sativa L.) production, knowledge is still limited concerning the optimum soil and crop management practices. A study was thus carried out to evaluate the effects of different tillage systems on the growth and yield of paddy rice, grain yield response to N applications, and weed control. Five experiments were conducted for three consecutive seasons on hydromorphic soils (loamy and sandy loamy, mixed, isohyperthermic Aeric Tropaqualfs) at the International Institute of Tropical Agriculture, Ibadan, comparing the effects of zero tillage (without dry tillage and puddling) and conventional tillage (dry tillage and puddling) at two or more N levels. In two of the above experiments the effects of either two moisture regimens or chemical versus manual weed control were also evaluated.In four experiments there were no statistically significant differences in grain yield between zero-tillage plots sprayed with paraquat and conventional-tillage plots. Only in Experiment 2 did zero-tillage (with paraquat) plots give a significantly lower yield than conventional-tillage plots (5200 versus 5580 kg ha^?1, respectively) but the difference could be explained by greater rat damage in the former. The highly significant response in grain yield to N applications in all five experiments was statistically similar under both tillage systems. The continuous flooding treatment (Experiment 1) gave better weed control and higher grain yield than the saturation moisture regime (6150 versus 5420 kg ha^?1 grain yield). In zero-tillage plots where weeds were slashed before transplanting (Experiment 2), grain yield was lower and the weed growth greater than in zero-tillage and low N level. Satisfactory weed control was obtained with paraquat and continuous flooding.     

Productivity and Cytogenetic Analysis of an Unbranched Mutant in Hyoscyamus niger L.

An unbranched mutant (Ub) with marginal arrangement of large leaves substantially altered floral and reproductive features in H. niger was isolated in M₂. It bred true for all mutant characteristics in M₂ generation. Appearance of restricted branching (Rb mutant) in some M₃ families seems 10 be a transient phase. Erect growth habit Coupled with non-overlapping leaf-disposition is useful for high crop density to obtain higher biomass field and, in turn, more crude drug production per unit area. Improvement in alkaloid content is an additional advantage augmenting its economic viability. Seed setting was, however. Poor due to pollen-polymorphism accruing from desynapsis and lack of organized alignment of chromosomes at Ml and subsequent abnormal disjunction at Al.     

Components of resistance to late leaf spot and rust among interspecific derivatives and their significance in a foliar disease resistance breeding in groundnut (Arachis hypogaea L.)

Late leaf spot (LLS) and rust cause substantial yield losses and reduce the fodder and seed quality in groundnut (Arachis hypogaea L.). Adoption of resistant cultivars by the semi-arid tropic farmers is the best option to overcome yield losses. Knowledge on components of resistance to these diseases should facilitate the development of groundnut cultivars with enhanced resistance to LLS and rust. The objectives of the experiments were to study the genetic variability and relationships among components of resistance to LLS and rust, and assess their significance in disease resistance breeding. Fifteen interspecific derivatives for LLS and 14 for rust and a susceptible control, TMV 2, were evaluated in a randomised complete block design with two or three replications under greenhouse conditions. The experiments were repeated twice. Genotypic differences were highly significant for all the traits studied. Resistance to LLS is due to longer incubation and latent periods, lesser lesions per leaf, smaller lesion diameter, lower sporulation index, and lesser leaf area damage and disease score. Selection based on components of resistance to LLS may not lead to plants with higher retained green leaf area. The remaining green leaf area on the plant should, therefore, be the major selection criteria for resistance to LLS in breeding programs. Resistance to rust is due to longer incubation and latent periods, fewer pustules per leaf, smaller pustule diameter, lower sporulation index, and lesser leaf area damage and disease score. Rust resistant components appear to work additively, therefore, selection based on resistance components together with green leaf area retained on the plant should be the basis of selecting for resistance to rust in breeding programs. ICGV 99005, 99003, 99012, and 99015 for rust and ICGV 99006, 99013, 99004, 99003, and 99001 for LLS are the better parents for use in resistance breeding programs. This revised version was published online in July 2006 with corrections to the Cover Date.     

Experimental evaluation of mass selection to improve red body colour in Fijian hybrid tilapia (Oreochromis niloticus × Oreochromis mossambicus)

Mass selection was trialed on Fijian hybrid tilapia (Oreochromis niloticus × Oreochromis mossambicus) to reduce the amount of black spots on otherwise red phenotypes. The responses of two selection intensities (low‐selection line, top 50% – L) and (high‐selection line, top 30% – H) were compared with that of a control line (no selection – C) across three generations. The relative growth performance of treatments (C, L and H) was examined in parallel in each generation to assess whether mass selection had a correlated negative effect on growth performance. The results show clearly that red phenotype can be improved significantly by applying mass selection, without affecting growth performance. We propose that black spots on an otherwise red phenotype could represent the allelic products of a second genetic locus influencing skin colour, which can be expressed in red individuals (genotype Rr) but which may be masked in black individuals (genotype rr).     

Two promoter rearrangements in a drug efflux transporter gene are responsible for the appearance and spread of multidrug resistance phenotype MDR2 in Botrytis cinerea isolates in French and German vineyards

In French and German vineyards, Botrytis cinerea isolates with multiple fungicide resistance phenotypes have been observed with increasing frequencies. Multidrug resistance (MDR) results from mutations that lead to constitutive overexpression of genes encoding drug efflux transporters. In MDR2 and MDR3 strains, overexpression of the major facilitator superfamily transporter gene mfsM2 has been found to result from a rearrangement in the mfsM2 promoter (type A), caused by insertion of a retroelement (RE)-derived sequence. Here, we report the discovery of another, similar RE-induced rearrangement of the mfsM2 promoter (type B) in a subpopulation of French MDR2 isolates. MDR2 isolates harboring either type A or type B mutations in mfsM2 show the same resistance phenotypes and similar levels of mfsM2 overexpression. RE sequences similar to those in mfsM2 were found in low copy numbers in other but not all B. cinerea strains analyzed, including non-MDR2 strains. Population genetic analyses support the hypothesis that the two rearrangement mutations have only occurred once, and are responsible for the appearance and subsequent spread of all known MDR2 and MDR3 strains in French and German wine-growing regions.     

Diurnal changes in moisture content and isothermal and thermally induced moisture fluxes under n-tillage and c-tillage in Nigeria

A study on the diurnal changes of soil moisture content and on the isothermal and thermally induced moisture fluxes was conducted on an Alfisol at the International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria, on no-tillage and conventional-tillage plots. These studies were conducted during the 1980 dry season, 9 years after initiating the tillage treatments in 1971. Three bare 5 × 5 m² plots per treatment were used to study diurnal changes in moisture content as soil dried from the initial moisture status of field capacity. The latter was attained by excessive and deep irrigation. Moisture content, moisture potential, and soil temperature were monitored three times a day (08:00, 14:00 and 18:00 h) at the depths of 0–7, 7–14 and 14–21 cm for four 7 day periods at weekly intervals. These results, along with physical characterization of the soil profile and changes in air temperature, were used to calculate isothermal, thermally induced liquid and vapor fluxes.

Results showed that there was a general increase in soil moisture content with sampling depth during the night (18:00 to 08:00 h), and a general decrease with depth during the day (08:00 to 18:00 h). The amplitude of the diurnal cycle of water content changes decreased with depth, and was superimposed on a progressive depletion in water content in the layers studied. The first layer of the conventional-tillage treatment dried to a lower water content than that of the no-tillage treatment. Partition of moisture fluxes, induced by isothermal and thermal conditions, showed that isothermal liquid flux was dominant in no-tillage, and that thermal vapor flux was very important as soil dried in conventional-tillage.

The direction of the fluxes observed (i.e. isothermal liquid flux always being positive upwards and thermal vapor flux positive during the night and negative downwards during the day) was of critical importance as the soil dried. The liquid fluxes became less important and thermal vapor and probably isothermal vapor fluxes became more important with soil moisture depletion. Vapor movement under these circumstances may have played an important role in supplying water to roots both during the day (deep roots) and night (shallow roots) depending on the magnitude of the fluxes. Vapor fluxes were higher and started earlier in conventional-tillage than in no-tillage.     

Development of non-narcotic (opiumless and alkaloid-free) opium poppy, Papaver somniferum

A mutation breeding programme using gamma rays and ethyl methane sulphonate (EMS) was carried out for genetic conversion of narcotic ‘opium poppy’ into non-narcotic ‘seed poppy’. Two families contained 31 latexless (opiumless) and 23 partial latex-bearing plants which were identified in the M² and confirmed in the M³ generations by the ‘ray-pluck’ method. Thin-layer chromatography (TLC)-densitometry of powdered capsule hulls (straw) from 22 representative plants also revealed that none of the five opium alkaloids (morphine, codeine, thebaine, papaverine and narcotine) was present in the straw. Six plants also possessed high seed yield (4.0–5.66 g/capsule vs. 3.39 g for control) and seven had a high seed oil content (50.7-53.5%). The best mutant genotype, LL-34 of the family C¹-Comb-113-2, with 5.66 g/capsule seeds containing 52.6% oil was designated as cv. ‘Sujata’. This, perhaps the world's first opiumless and alkaloid-free seed poppy cultivar, offers a cheap and permanent (fundamental) solution to the global problem of opium-linked social abuse. Simultaneously, it serves as a safe and potential food crop with protein-rich seeds and healthy unsaturated seed oil.