Man-made carbon-14 in deep Pacific waters: transport by biological skeletal material

Calcareous particles present in Pacific waters at depths of 50 to 3500 meters were collected by filtering seawater through spongin matrix. The specific activity of carbon-14 could be measured in two of these collections from depths of 2300 and 3500 meters. The ratios of carbon-14 to carbon-12 correspond to values observed in surface waters in recent years as a result of the addition of manmade carbon-14, thus indicating that the calcareous particles resulted from recent biological productivity. The results are related to the mean settling rates and the sizes and dissolution rates of biogenic calcareous particles in transit through a seawater column.     

Nitrogen fertilization of wheat residue affecting nitrous oxide and methane emission from a central Ohio Luvisol

Fertilization of wheat (Triticum aestivum, L.) residue applied to degraded soils has shown promise as an option to restoring soil organic C (SOC) stocks, but the impact of the practice on N2O and CH4 emissions is not clear. It was hypothesized that, in addition to the mulch-induced soil wetness conditions favorable for N2O and CH4 formation, emission of these gases will be stimulated due to increased availability of mineral N and interference of NH4⁺ with CH4 oxidation in soils. During the period February–November 2000, fluxes of N2O and CH4 were monitored in a plant-free central Ohio Crosby soil (fine, mixed, mesic Aeric Ochraqualf) amended for 4 years with wheat straw (bare, 0; low, 8 Mg ha^–1 year^–1; and high, 16 Mg ha^–1 year^–1) without and with N fertilization (244 kg N ha^–1). The average annual N2O fluxes were 1.1 kg N2O-N ha^–1 in the unfertilized and 4.1 kg N2O-N ha^–1 in the fertilized treatments. Annual N2O emission (Y, mg N2O-N m^–2) was strongly correlated to the maximum daily flux (X, mg N2O-N m^–2 day^–1; Y=48.3X−58.1, R²=0.85, P<0.001) recorded on experimental plots. These flux maxima occurred at spring thaw in the unfertilized, and 6–30 days after fertilization in the fertilized treatments. Net CH4 uptakes were measured on some occasions; overall, however, all the treatments were net CH4 emitters with annual rates of 3.6, 4.9 and 5.1 kg CH4-C ha^–1 in the bare, low and high residue treatments, respectively. No significant effect of fertilization and mulch rate on CH4 fluxes was found, but temperature and landscape position appeared as strong controllers. Regardless of treatments, the highest CH4-emitting plots were located in a minor depressional area at the experimental site. A comparison of SOC gain and N2O and CH4 emission expressed as CO2-equivalents indicates that the residue treatments have a net CO2-mitigating effect, but since C sequestration rates are expected to decrease with time, that positive effect will likely vanish after 7 and 12 more years in the fertilized and unfertilized residue treatments, respectively.     

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.