Nitrogen fertilization is considered as an important source of atmospheric N 2 O emission. A seven site-year on-farm field experiment was conducted at Ottawa and Guelph, ON and Saint-Valentin, QC, Canada to characterize the affect of the amount and timing of N fertilizer on N 2 O emission in corn (Zea mays L.) production. Using the static chamber method, gas samples were collected for 28-days after preplant and 28-days after sidedress fertilization at the seven site-year, resulting in 14 monitoring periods. For both methods of fertilization, peak N 2 O flux and cumulative emission increased with the amount of N applied, with rates ranging from 30 to 900 lg N m À2 h À1 . Depending on N amount and time of application, cumulative emission varied from 0.05 to 2.42 kg N ha À1 , equivalent to 0.03% to 1.45% of the N fertilizer applied. Differences in N 2 O emission peaks among fertilizer treatments were clearly separated in 13 out of 14 monitoring periods. Total N 2 O emissions may have been underestimated compared with annual monitoring in 10 out of the 49 cases because the monitoring period ended before N 2 O efflux returned to the baseline level. The flux of N 2 O was negligible when soil mineral N in the 0-15 cm layer was o20 mg N kg À1 . While rainfall stimulated emission, soil temperature 415 1C was likely the driving force responsible for the higher levels of N 2 O found for sidedress than preplant application methods. However, caution must be taken when interpreting these later results as preplant fertilization may have continuously stimulated N 2 O emissions after the 28-days monitoring period, especially in situations where N 2 O effluxes have not fallen back to their baseline levels. Increasing fertilizer rates from 90 to 150 kg N ha À1 resulted in slight increases in yields, but doubled cumulative N 2 O emissions.

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Ammonia (NH3) volatilization is one of the main pathways through which applied N enters the environment undesirably. A seven site‐year on‐farm field experiment was performed for 3 yr at Ottawa, ON, and 2 yr at Guelph, ON, and Saint‐Valentin, QC, Canada. Our objectives were to (i) quantify the flux and the amount of NH3 volatilization as affected by the rate and time of N fertilizer; (ii) assess the impact of rainfall and soil temperatures on NH3 volatilization; and (iii) determine the threshold level of N fertilizer at which large NH3 volatilization losses occur. Using the static chamber method, NH3 volatilization was monitored after preplant or sidedress N application. Rate of NH3 volatilization peaked at 3 to 7 d and then dropped sharply within next 7 d before leveling off in the following weeks. The amount of NH3 volatilization increased with increasing N levels applied preplant or sidedress at all site‐years. Peak NH3 volatilization ranged from 40 to 8000 g N ha−1 d−1 after preplant fertilization and from about 100 to 2100 g N ha−1 d−1 after sidedress, resulting in NH3 losses of 0.1 to 47 kg N ha−1 and 0.6 to 20 kg N ha−1, respectively, equivalent to 0.1 to 38% and 0.3 to 13% of fertilizer‐induced emission (FIE) within 28 d after preplant or sidedress N fertilization. Our data clearly indicate that sidedress applications enable reduction in N fertilizer for economic crop yields, and may reduce losses simply due to lower total N rates.

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In this paper, a new kind of graph on a commutative ring R with identity, namely the co-maximal ideal graph is defined and studied. We use [Formula: see text] to denote this graph, with its vertices the proper ideals of R which are not contained in the Jacobson radical of R, and two vertices I1 and I2 are adjacent if and only if I1 + I2 = R. We show some properties of this graph. For example, this graph is a simple, connected graph with diameter less than or equal to three, and both the clique number and the chromatic number of the graph are equal to the number of maximal ideals of the ring R.

Precise estimation of soil nitrogen (N) supply to corn (Zea mays L.) through N mineralization plays a key role in implementing N best management practices for economic consideration and environmental sustainability. To quantify soil N availability to corn during growing seasons, a series of in situ incubation experiments using the method of polyvinyl chloride tube attached with resin bag at the bottom were conducted on two typical agricultural soils in a cool and humid region of eastern Canada. Soil filled tubes were retrieved at 10-d intervals within 2 months after planting, and at 3-to 4-week intervals thereafter until corn harvest. Ammonium and nitrate in the soil and resin part of the incubation tubes were analyzed. In general, there was minimal NH 4 + -N with ranges from 1.5 to 7.3 kg N ha -1 , which was declined in the first 30 d and fluctuated thereafter. Nitrate, the main form of mineral N, ranged from 20 to 157 kg N ha -1 . In the first 20-50 d, main portion of the NO 3 --N was in the soil and thereafter in the resin, reflecting the movement of NO 3 -in the soil, which was affected by rainfall events and amount. Total mineralized N was affected by soil total N and weather conditions: There was more total mineralized N in the soil with higher total N, and rainy weather stimulated N mineralization. The relationship between the accumulated mineral N and accumulated growing degree-days (GDD) fitted well into first order kinetic models. The accumulated mineralized soil N during corn growing season ranged from 96 to 120 kg N ha -1 , which accounted for 2-3% of soil total N. Corn plants took up 110-137 kg N ha -1 . While the mineralized N and crop uptake were in the same magnitude, a quantitative relationship between them could not be established in this study.

± ZusammenfassungThe effects of selected tillage and rotation systems on soil organic carbon and its fractions were studied on Chernozemic soils in south-western and east-central Saskatchewan. After practicing a no-till fallow unfertilized-wheat rotation for 7 years on an Orthic Brown Chernozem in southwestern Saskatchewan, total soil organic carbon (TOC) in the 0 ± 5 cm and 5 ± 10 cm layers was slightly lower than the tillage fallow-unfertilized wheat comparable treatment. However, light fraction of organic carbon (LFOC) was similar in the two treatments. Comparison of the tillage fallow-unfertilized wheat to a treatment involving conversion to a fertilized continuous cropping system for 10 years showed TOC increased slightly in the two depths and LFOC increased by 24 % and 29 % in the 0 ± 5 cm and 5 ± 10 cm layer, respectively, of the continuous cropping treatment. Microbial biomass carbon (MB-C) was increased significantly at the 5 ± 10 cm depth. After conversion of fallow-wheat to alfalfa as perennial forage for 10 years, TOC increased by 80 % and 27 %, LFOC by 245 % and 286 %, and HFOC by 63 % and 20 % at 0 ± 5 cm and 5 ± 10 cm depths, respectively, compared to the tilled cereal-fallow system. Meanwhile, water soluble organic carbon (WSOC) was not affected but MB-C increased significantly. In an Orthic Black Chernozem in east-central Saskatchewan, the depletion and restoration of organic carbon was observed when native sod was changed into cropland and then back to grassland. For example, the TOC of cropland under cereal-fallow rotation for 62 years decreased by 42 % and 33 % at 0 ± 5 cm and 5 ± 10 cm depths, respectively, compared to native sod. The LFOC decreased by 79 % and 74 % in the layers, and reductions in WSOC and MB-C were even greater. After cropland was re-seeded to grassland for 12 years, the concentration of total organic carbon was increased by 16 % and 22 % while the mass of organic carbon was the same as the cropland in the two layers. The LFOC and MB-C amounts in the grass seed-down were double that of the cropped land, but the amounts of TOC, LFOC, and MB-C in grass seed-down were still significantly lower than the native sod. Wirkung von Bodenbearbeitung und Fruchtfolge auf Fraktionen der organischen Bodensubstanz in Tschernosemen in SaskatchewanDie Wirkungen ausgewählter Bodenbearbeitungs-und Fruchtfolgesysteme auf den organischen Kohlenstoff im Boden und Fraktionen der organischen Bodensubstanzen wurden untersucht in Schwarzerdeböden im südwestlichen und östlich-zentralen Saskatchewan/Kanada. Nach einer 7-jährigen Fruchtfolge von unbearbeiteter Brache und Weizenanbau ohne Düngung auf Baunerde-Tschernosem im südwestlichen Saskatchewan war der gesamte organische Kohlenstoff (TOC) in der Schicht 0 ± 5 cm und 5 ± 10 cm geringfügig niedriger als bei einer vergleichbaren Behandlung mit bearbeiteter Brache/Weizenanbau ohne Düngung. Die leichte Fraktion der organischen Substanz (LFOC) war jedoch in beiden Schichten ähnlich. Im Vergleich zu der Fruchtfolge ªunbearbeitete Brache/Weizenanbau ohne ...

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