Carbon dioxide emissions after application of tillage systems for a dark red latosol in southern Brazil

Soil tillage may influence CO₂ emissions in agricultural systems. Agricultural soils are managed in several ways in Brazil, ranging from no tillage to intensive land preparation. The objective of this study was to determine the effect of common soil tillage treatments (disk harrow, reversible disk plow, rotary tiller and chisel plow tillage systems) on the intermediate CO₂ emissions of a dark red latosol, located in southern Brazil. Different tillage systems produced significant differences in the CO₂ emissions, and the results indicate that the chisel plow produced the highest soil carbon loss during the 15 days period after tillage treatments were performed. Emissions to the atmosphere increased as much as 74 g CO₂ m⁻², at the end of a 2-week period, in the plot where the chisel plow treatment was applied, in comparison to the non-disturbed plot. The results indicate that the total increase on the intermediate term soil CO₂ emissions due to tillage treatments in southern Brazil is comparable to that reported for the more humid and cooler regions.     

Influence of storage on soil microbial biomass estimated by three biochemical procedures

The effects of 28 and 56 days' storage at 25°, 4° and ?20°C on the microbial biomass content of four soils from tussock grasslands were studied by three biochemical procedures. Two of the procedures involved measurement of CO₂ and mineral-N (Min-N) production by chloroform-fumigated and unfumigated soil, and consequent estimation of biomass C and Min-N flush respectively. In the third, adenosine 5'-triphosphate (ATP) content was determined.Patterns of CO₂ production were often influenced by storage treatment. The use of fixed incubation periods for estimating the CO₂ flush of fumigated soil and the steady rate of CO₂ production by unfumigated soil did, however, give biomass C estimates that were generally similar to those calculated from individually determined incubation periods for each treatment and soil.Biomass C values could change significantly at all storage temperatures, but generally least at ?20°C. Storage at ?20°C was also the most suitable for retaining ATP contents, whereas 4°C was best for values of Min-N flush. Values of Min-N flush after storage of soil at ?20°C decreased significantly in two of the soils but increased in another. No storage temperature was thus satisfactory for all three indices of microbial biomass. Generally, however, 4°C was adequate for short periods, and 25°C the least suitable.     

Ionic composition of acid lakes in relation to airborne inputs and watershed characteristics

Present acid forming emissions to the atmosphere have the potential to alter significantly the chemistry of rain, snow, and surface water of weakly buffered lakes in the Upper Midwest. Average precipitation pH from field measurements during 1979–1983 declined from west to east from 4.8, 4.6, and 4.3 along a cross-section of sites in Minnesota, Wisconsin, and Michigan respectively where 990 lake and stream sampling sites were studied. Measurements of weakly buffered lakes show a parallel decline in lake water pH with the lowest values measured, 5.1, 4.6 and 4.4, respectively in the same regions. Correspondingly, the percentage of lakes sampled with little or no acid neutralizing capacity (ANC) was found to increase from 0 to 4 and 13%, respectively. The geographic patterns in ionic composition of airborne acids and bases, and the resultant surface water concentrations are compared. The acid forming capacity (AFC) from airborne inputs is calculated using mass balance and in-lake processes. Stoichiometric acid-base reactions are used to balance the observed chemical differences between airborne inputs and surface water composition considering nitrification, denitrification, other oxidation-reduction reactions, and the evaporation concentration process. Microbial activity in surface water can result in a net decrease in ionic strength from the conversion of most of the ammonium and nitrate to neutral compounds and biomass, but only a partial reduction of about 20% of the sulfate inputs to weakly buffered lakes. The resulting AFC of airborne inputs are calculated to range from 30 to 60, 50 to 90, and 80 to 130 μeq H+L-l, respectively, in northeastern Minnesota-Ontario, northcentral Wisconsin and northern Michigan-Ontario. The differences in AFC of airborne inputs from west to east, and differences in in-lake processes explain the observed acidity of weakly buffered lakes across the region.     

A characterization of the detroit wintertime aerosol

The physical characterization of winter-time aerosol in the Detroit area studied over a 7-week period (January–March, 1983) is presented. Total suspended particle levels (<15 μm) were 56 ± 29 μg m^?3, with 66% of the material in the fine (<2.5 μm) particle fraction. Coarse and fine particle masses were reasonably correlated, indicating that local sources, not long-range transport, influenced winter-time aerosol at the site. Mobile sources were responsible for a marked diurnal variation in the nuclei mode particle count and accounted for about 10% of the submicron aerosol mass. Decreases in submicron aerosol concentrations during precipitation appear to be associated with advection of clean air into the area during frontal passage rather than to precipitation scavenging.     

Growth response of field-grown Siratro (Macroptilium atropurpureum Urb.) and Aeschynomene american L. to inoculation with selected vesicular-arbuscular mycorrhizal fungi

Summary The effect of inoculation with a selected isolate of Glomus etunicatum Becker and Gerdemann and one of G. intraradices Schenck and Smith on the growth and nutrient content of Macroptilium atropurpureum Urb. cv. Siratro and Aeschynomene americana L., at applied P levels of 10, 30, 60, and 120 kg ha^-1, was studied under field conditions. At all P levels and for all harvests, the shoot dry mass of Siratro and A. americana were greater for the plants inoculated with the vesicular-arbuscular mycorrhizal (VAM) fungi than the control plants. Differences between the VAM fungus-inoculated and the control plants were most marked between 30 and 90 kg ha^-1 of applied P and diminished at 120 kg ha^-1. At the first harvest of Siratro, the plants inoculated with G. etunicatum had a greater shoot dry mass than those inoculated with G. intraradices, for all levels of applied P. However, for subsequent harvest of Siratro and for the one harvest of A. americana the response of shoot dry mass to the two VAM fungi was equivocal. Fungal inoculation gave at least a 30% saving in the amount of P fertilizer required (40 kg ha^-1) for the maximum yield. The plants inoculated with VAM fungi had a greater tissue concentration and total content of P and N than the control plants at low and intermediate levels of applied P. The percentage of root colonized by VAM fungi for the inoculated plants of the two legumes increased linearly with P additions up to 60 kg ha^-1. The conclusion is that under amended (limed and fertilized) soil conditions, inoculation with selected VAM fungi can improve the establishement and growth of forage legumes in fields that contain ineffective populations of native VAM fungi.     

Net fluxes of mineral nutrients,water, and carbohydrate influenced by manganese in root and shoot of Cucumis sativus L. 1

An experiment was conducted with cucumber (Cueumis sativus L., cv. Sumter) plants in the vegetative phase of growth to determine effects of manganese deficiency (0.2 μM Mn) and toxicity (182 μM Mn) on fluxes of several mineral nutrients, water, and carbohydrate in the root and shoot, beginning 43 d after germination. Plants were sampled every three days from 34 to 58 d after germination. First and second derivatives of regression equations were used to estimate fluxes and study source/sink phenomena of dry weight (DW), fresh weight (FW), H₂O, Cu, Fe, Mn, Zn, N, P, and K in root and shoot tissues.

With Mn sufficiency (1.8 μM Mn), both root and shoot acted as sinks for of each of the 10 dependent variables through 58 d. In contrast, Mn deficiency caused net loss of K and N from the root beginning at 53 and 56 d, respectively, and net loss of P and Fe from the shoot beginning at 57 and 58 d, respectively. With Mn toxicity, net loss of Cu, N, and K from the root began at 46, 46, and 51 d, respectively, and net loss of Fe from the shoot began at 55 d. Both Mn deficiency and toxicity increased the shoot:root ratio (S:R) of K and decreased the S:R of Fe, compared to Mn‐sufficiency. Manganese deficiency decreased the S:R of DW and H₂O, and Mn toxicity increased the S:R of FW, DW, H₂0, and N. Under the conditions of this experiment, acute Mn toxicity affected fluxes more severely than did Mn deficiency.     

Nitrogen and phosphorus nutritional interactions in a CO2 enriched environment

Nonnodulated soybean plants (Glycine max. [L.] Merr. ‘Lee') were supplied with nutrient solutions containing growth limiting concentrations of N or P to examine effects on N‐ and P‐uptake efficiencies (mg nutrient accumulated/gdw root) and utilization efficiencies in dry matter production (gdw²/mg nutrient). Nutritional treatments were imposed in aerial environments containing either 350 or 700 μL/L atmospheric CO₂ to determine whether the nutrient interactions were modified when growth rates were altered.

Nutrient‐stress treatments decreased growth and N‐ and P‐uptake and utilization efficiencies at 27 days after transplanting (DAT) and seed yield at maturity (98 DAT). Atmospheric CO₂ enrichment increased growth and N‐ and P‐utilization efficiencies at 27 DAT and seed yield in all nutritional treatments and did not affect N‐ and P‐uptake efficiencies at 27 DAT. Parameter responses to nutrient stress at 27 DAT were not altered by atmospheric CO₂ enrichment and vice versa. Nutrient‐stress treatments lowered the relative seed yield response to atmospheric CO₂ enrichment.

Decreased total‐N uptake by P‐stressed plants was associated with both decreased root growth and N‐uptake efficiency of the roots. Nitrogen‐utilization efficiency was also decreased by P‐stress. This response was associated with decreased plant growth as total‐N uptake and plant growth were decreased to the same extent by P stress resulting in unaltered tissue N concentrations. In contrast, decreased total P‐uptake by N‐stressed plants was associated with a restriction in root growth as P‐uptake efficiency of the roots was unaltered. This response was coupled with an increased root‐to‐shoot dry weight ratio; thus shoot and whole‐plant growth were decreased to a much greater extent than total‐P uptake which resulted in elevated P concentrations in the tissue. Therefore, P‐utilization efficiency was markedly reduced by N stress.     

Interseeded legumes with loblolly pine. I. Effect of phosphorus and legume variety on pine seedling establishment and mortality

A study was conducted to determine the effects of legume companion crops and phosphorus (P) fertilizer on the growth and survival characteristics of newly established loblolly pine (Pinus taeda L.) seedlings. At 12 months post‐establishment, there was no legume effect (P>0.05) on root lateral development or ropting depth for pine seedlings. Likewise, there was no legume effect (P>0.05) on aboveground biomass production of pine seedlings. Partridge pea (Cassia fasciculata Michx.) had a negative effect (P<0.05) on pine seedling total root biomass compared to other treatments. Pine seedlings grown with legumes allocated less resources to root development compared to pine seedlings grown alone. Pine seedlings grown alone or with cowpea [Vigna unguiculata (L.) Walp.] were subject to less mortality (P<.05) than seedlings grown with alyceclover [Alysicarpus vaginalis (L.) DC] or partridge pea. Phosphorus fertilization enhanced dry matter (DM) yield of legumes but had no effect on rooting depth of pine seedlings during the first 12 months of growth. After 12 months post‐establishment, the most pronounced effect of P fertilization was that of increased nitrogen (N) content of leaf, stem, and roots of pine seedlings. Native, annual herbaceous grass biomass in the control plots (no legume) reduced the amount of soil N to below pre‐planting levels, while soil N levels in all legume plots exceeded pre‐trial levels.     

Long-term impacts of even-aged timber management on abundance and body condition of terrestrial amphibians in Northwestern California

Conservation needs for amphibians in managed timberlands may differ based upon the species present and the timber harvesting methods employed. Clearcuts have been documented to be detrimental to amphibians but the impacts of associated silvicultural edges and alternative harvesting treatments are not well understood. The primary objective of this study was to determine if amphibian abundances and body condition differed in thinned forests and intact forests, and in clearcuts and associated silvicultural edges. We also examined which environmental attributes were important in explaining observed differences. We sampled clearcuts, silvicultural edges, and adjacent late-seral forests at 10 sites in northwestern California from October 1999 to July 2002. Clearcuts at these sites ranged in age from 6 to 25 years. Five of these forest stands were intact and five had been commercially thinned at least 10 years prior to our study. Amphibian abundances were similar in thinned and unthinned forests, but body condition of the most common species was lower in thinned forests. Abundances of amphibians were nearly twice as high in forests and at silvicultural edges than in clearcuts. Clearcutting at these sites appears to have affected amphibian numbers up to 25 years post-harvest, however, silvicultural edges were suitable habitats for amphibians. While commercial thinning did not reduce amphibian numbers, it is an intermediate treatment followed by clearcutting. Where conservation of amphibians is a concern, even-aged silvicultural systems may not provide the most appropriate method for maintaining viable populations on managed forestlands in the northwestern US.     

Tomato responses to ammonium and nitrate nutrition under controlled root‐zone pH

Tomato (Lycopersicon esculentum L. Mill. ‘Vendor') plants were grown for 21 days in flowing solution culture with N supplied as either 1.0 mM NO₃ ^‐ or 1.0 mM NH₄ ⁺. Acidity in the solutions was automatically maintained at pH 6.0. Accumulation and distribution of dry matter and total N and net photosynthetic rate were not affected by source of N. Thus, when rhizosphere acidity was controlled at pH 6.0 during uptake, either NO₃ ^‐ or NH₄ ⁺ can be used efficiently by tomato. Uptake of K⁺ and Ca²⁺ were not altered by N source, but uptake of Mg²⁺ was reduced in NH₄ ⁺‐fed plants. This indicates that uptake of Mg²⁺ was regulated at least partially by ionic balance within the plant.