The effects of the substitution of polyacrylamide for activated carbon in the sodium bicarbonate extraction of soils for available inorganic phosphorus

Non-Peer Reviewe

Residual phosphate studies

Non-Peer ReviewedData on yield and P uptake by flax and wheat is presented from the first year of an eight year residual phosphate (P) study located on the Kernen Farm of the University of Saskatchewan. Comparison of seed-placed (0, 5, 10, 20, and 40 kg P ha-1) and broadcast P (0, 40, 80, 160, and 320 kg P ha-1) treatments showed that there was a yield response to both types of P fertilizer application with maximum yields being obtained in wheat by either 40 kg P ha-1 seed-placed or by broadcast P application of 80 to 160 kg P ha-1, and in flax by 5-10 kg P ha-1 side-banded or 80 kg P ha-1 broadcast. Laboratory studies related the prediction of fertilizer P response from seed-placed treatments to broadcast treatments by use of P sorption and P extraction techniques. P sorption isotherms were run on over 300 soil samples taken from the 0-15 cm layer of cultivated fields representing the majority of the cultivated soil associations in Saskatchewan. This data would suggest that rates of P broadcast should be four to eight times higher than recommended seed-placed or side-banded rates in the same Soil Zone with the same available P content

Broadcast and residual P versus annual seed-placed P

Non-Peer ReviewedThe yield and nutrient uptake effects of single broadcast P treatments, annual seed-placed P treatments and their combination, were studied over five years. Maximum yield was attained from a combination of moderate levels of seed-placed and broadcast P applications. Moderate broadcast treatments (40 kg P/ha) alone produced a five-year average yield which closely approached the yield from large annual seed-placed treatments ( 20 kg P/ha/year), while larger residual treatments exceeded it. The Zn concentration in plants on plots receiving 160 kg P/ha was significantly reduced and approached levels considered deficient. After the production of five wheat crops on plots which received the broadcast application of 160 kg P/ha, the distribution of the remaining fertilizer residues among various soil P fractions was: resin-P, 35 %; NaOH-P, 30-40 %; NaHCO3-P, 15 %; HCl-P, 0-5 %; H2SO4-P, 5 %; aggregate-protected P, 5 %. Half the fertilizer residues remained in plant available forms (resin-P, NaHCO3-P)

Recent work on copper and molybdenum in pastures and soils in Saskatchewan

Non-Peer Reviewe

Management effects on phosphorus transformation and implications for soil test recommendations

Non-Peer ReviewedCrop rotations and fertilizer application on long-term rotation plots at Lethbridge and Breton have dramatically affected most soil phosphorus (P) fractions. At the Lethbridge site, soil cultivation has reduced organic P (Po) levels as a result of mineralization. This has caused a significant increase in resin extractable inorganic P (Pi; most biologically available), sodium bicarbonate extractable Pi (sorbed to soil surfaces), and sodium hydroxide extractable Pi (more strongly bound to Al and Fe compounds) levels. In non-fertilized treatments, continuous wheat (CW) resulted in greater P draw-down of all labile P fractions than in wheat-wheat-fallow (WWF) and wheat-fallow (WF) rotations. The addition of P fertilizer has significantly increased Resin-Pi, Bicarb-Pi and NaOH-Pi fractions. The addition of N fertilizer has resulted in increased Bicarb-Po and NaOH-Po levels in the CW, WF, and WWF rotations. At the Breton site, continuously cropped treatments, which had not received fertilizer, resulted in greater P draw-down of all P fractions except Residual-F. Addition of fertilizer had a significant effect on all P fractions (except NaOH-Po). The added Pin the fertilizer treatments positively affected the Pi fractions and the N in the fertilizer treatment positively affected the Po fractions. Bicarb-Po levels were found to be negatively· affected by soil pH. Finally, cropping without using phosphate fertilizer has resulted in a 30 to 41 % decline in Total-P in the Breton plots. A growth chamber study was conducted to compare four routine soil test P methods with plant uptake of P. Wheat and canola were each grown in eight soils from the Lethbridge and Breton plots with different pedogenic, crop rotation and fertilizer histories. Results of the study confirm that one calibration curve to predict fertilizer P requirements for a wide range of soils and crops is virtually impossible. Future soil tests will combine a chemical extractant with a computer model prediction of Po mineralization. Much more information is needed on root rhizosphere dynamics

Phosphorus transformations and availability under cropping and fertilization assessed by isotopic exchange

International audienc

The pathogen Neisseria meningitidis requires oxygen, but supplements growth by denitrification. Nitrite, nitric oxide and oxygen control respiratory flux at genetic and metabolic levels

The human pathogen Neisseria meningitidis is the major causative agent of bacterial meningitis. The organism is usually treated as a strict aerobe and is cultured under fully aerobic conditions in the laboratory. We demonstrate here that although N. meningitidis fails to grow under strictly anaerobic conditions, under oxygen limitation the bacterium expresses a denitrification pathway (reduction of nitrite to nitrous oxide via nitric oxide) and that this pathway supplements growth. The expression of the gene aniA, which encodes nitrite reductase, is regulated by oxygen depletion and nitrite availability via transcriptional regulator FNR and two-component sensor-regulator NarQ/NarP respectively. Completion of the two-step denitrification pathway requires nitric oxide (NO) reduction, which proceeds after NO has accumulated during batch growth under oxygen-limited conditions. During periods of NO accumulation both nitrite and NO reduction are observed aerobically, indicating N. meningitidis can act as an aerobic denitrifier. However, under steady-state conditions in which NO is maintained at a low concentration, oxygen respiration is favoured over denitrification. NO inhibits oxidase activity in N. meningitidis with an apparent Ki NO = 380 nM measured in intact cells. The high respiratory flux to nitrite after microaerobic growth and the finding that accumulation of the denitrification intermediate NO inhibits oxygen respiration support the view that denitrification is a pathway of major importance in N. meningitidis