The Mehlich-III method used for the determination of available P in 82 Quebec soils was compared to five other chemical methods (Bray-II, Bray-I, Mehlich-II, Mehlich-I and Olsen) and to two anion exchange resin techniques (F -and HCO -3 ) In general, very good correlations were found between Mehlich-III, Bray-II and Bray-I methods on acid soils (r=0.95** and 0.98**). The Mehlich-III-P content is somewhat the same as that determined by Bray-I and corresponds approximately to 80% of Bray-II-P. The Mehlich--III extractant was found to be more reliable than Bray-II and Bray-I on very acid spodosols having high P-sorption capacity. The Bray methods, with high NH 4 F concentration, extracted strongly fixed Al-P in these soils and may overestimate the available P. In some acid soils containing apatite and in calcareous soils, the Bray-II and Mehlich-I (double acid) easily dissolved these Ca-P compounds and gave exaggerated high P values. The Mehlich-III and the other methods were less vigourous for these compounds and were

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Tran, T. S. and N'dayegamiye, A. 1995. Long-term effects of fertilizers and manure application on the forms and availability of soil phosphorus. Can. J. Soil Sci. 75: 28I,285. Long-term application of cattle manure and fertilizer can affect the forms and availability of soil phosphorus. This cumulative effect was evaluated on Le Bras silt loam (Humic Gleysol) cultivated with silage corn (Zea mays L.). In this long-term trial, treatments were arranged in a split-plot design, with dairy cattle manure applied at 0 and 20 Mg ha-1 as the main factor. The subplots consisted of six fertilizer treatments (NK, PK, NP, NPK, NPKMg and the unfertilized check). Fertilizer rates for silage corn were 150, 100, 150 and 40 kg ha-l N, P20s, KrO and Mg, respectively. The N fertllizer rate was reduced to 100 kg N ha-l in manured plots. Soil inorganic P (P,) and organic P (Po) fractions were sequentially extracted by resin, NaHCO3, NaOH, HCI and a final HrSOo we'" digestion of the residue. On average, labile P extracted by resin and NaHCO, represented lTVo of the total P (P,); moderately labile NaOH-P, and -Po more than 40Va; and stable P 36Vo.Application of manure and fertilizers increased significantly resin-, NaHCOT-, NaOH-P, and P,. However, NaOH-Po was decreased by P fertilizer application in NPK and NPKMg treatments, while long-term manure application maintained this Po pool in the soil. Stable P fractions were not affected by fertilization or by manuring. In all 6 yr ofthe study, P uptake by silage corn was significantly increased both by longterm N and P fertilizer application and also by manure incorporation. Phosphorus uptake by com was highly related to all labile and moderately labile P, fractions and P,. Long-term application of dairy manure at a rate of 2O t ha-l increased soil P, forms and maintained Po fractions.Key words: Inorganic labile P, organic P, soil-P fractionation, P uptake, silage com d6termin6es par des extractions s6quentielles avec la r6sine HCO.-, NaHCO,, NaOH, HCI et enfin le P r6siduel par la digestion dans HrSOo. En moyenne, le P labile (r6sine et NaHCOT) repr6sente environ 77Vo du P total (Pr), tandis que les formes du P mod6r6menl labile extraites par NaOH et les formes plus stables correspondent respectivement d 40 et 36Vo dtPr. L'application d long terme du fumier et des engrais min6raux a augment6 signifrcativement les teneurs des fractions P, extraites par la r6sine, NaHCOr, NaOH ainsi que les niveaux de P,. Cependant la fraction de NaOH-Po a 6t6 diminu6e significativement par I'apport de P dans les traitements NPK et NPKMg, tandis que I'application d long terme du fumier a maintenu ce pool de Po du sol. Les fractions stables du P n'ont pas 6t6 affect6es par I'application du fumier ou des engrais min6raux. Sur les six ans de l'6tude, les pr6lbvements en P du mais-ensilage ont 6t6 augment6s significativement par l'application d long terme des engrais min6raux N et P ainsi que par le fumier. Les pr6ldvements annuels en P sont reli6s 6troitement avec toutes 1es fractions de P, labiles , mod6r6me...

N' Dayegamiye, A. and Tran, T. S. 2001. Effects of green manures on soil organic matter and wheat yields and N nutrition. Can. J. Soil Sci. 81: 371-382. A field study was conducted for 5 yr (1993)(1994)(1995)(1996)(1997) to evaluate the effects of green manure residues applied to the soil in 1993 and 1995, on wheat (Triticum aestivum L.) yields and N nutrition as subsequent crop in 1994, 1996 and 1997. The effect of green manure application was also evaluated on soil microbial activity (CO 2 ), on C and N contents of whole soil and on labile (LF) and heavy fractions (HF) of organic matter (OM). The experiment was initiated on a Le Bras silt loam (Humic Gleysol). The green manures, as a main factor, were clover (Trifolium pratense L.), buckwheat (Fagapyrum esculentum L.), millet (Echinicloa crus galli L.), mustard (Brassica hirta Moench), and colza (Brassica campestris L.), and there was a control without green manure. The sub-factors consisted of four N fertilizer rates for wheat in the subsequent years at 0, 30, 60 and 90 kg N ha -1 . Broadcast application of 15 N-labelled NH 4 NO 3 was made in 90 kg N ha -1 fertilizer treatments. Two green manure applications did not influence the C and N contents of densimetric fractions of OM (LF and HF), but significantly increased those of whole soil, and microbial respiration (CO 2 ). Green manures significantly increased wheat yields and N uptake in 1994 and 1996. Levels of N derived from fertilizer (Ndff) were lower in all green manure treatments as compared to the control, which indicates that the proportion of N derived from soil and green manures (% Ndfs) was higher in these treatments. The contribution of N from green manure varied in the following order: buckwheat < clover < mustard < millet < colza. With the exception of the clover treatment (< 100%), the N recoveries from the other green manure N (NRGM) ranged from 23 to 34% and from 19 to 36 % for 1994 and 1996, respectively. Green manure application provided 15 to 24 kg N ha -1 in 1994 and from 16 to 36 kg N ha -1 in 1996 and this contribution accounted for 25 to 31% of the total wheat N uptake. Significant green manure effects on wheat yield and N nutrition were primarily due to the improvement of soil properties and to high N recoveries from the green manure. In the cold temperate climate of Québec, green manure incorporation into soil in late summer or early fall of the preceding year allowed N synchronization with wheat N needs in subsequent cropping seasons. Nitrogen fertilizer rates could be reduced after the incorporation of green manures having high yields and N contents in the previous season. (FL et FD), mais ont significativement augmenté celles du sol entier, ainsi que la respiration microbienne (CO 2 ). Les engrais verts ont aussi augmenté de facon significative les rendements et les prélèvements en N du blé en 1994 et 1996. Les quantités de l'azote derivé de l'engrais (Ndff) étaient plus faibles dans les traitements avec les engrais verts, en comparaison avec le témoin, ce qui indique que la pro...

Tran, T. S. and Tremblay, G. 2000. Recovery of 15 N-labeled fertilizer by spring bread wheat at different N rates and application times. Can. J. Soil Sci. 80: 533-539. Optimal N fertilization can improve the yield and quality of spring bread wheat in eastern Canada. This study aimed to determine the economical N rate for the production of spring bread wheat (Triticum aestivum L. 'AC Pollet') and to compare the effect of application times on the efficiency of fertilizer N use. The experiment was conducted during 2 yr on two sites of Sainte-Rosalie clay loam. The experimental treatments were arranged in a split-plot design with N rates (0, 30, 60, 90, 120, 180 kg ha -1 ) as the main plots and the application times of fertilizer N ( 15 NH 4 15 NO 3 applied at seeding and booting stages) as the subplots. Grain yield, grain protein concentration and straw N content of wheat were increased significantly with N application rates. The economic N rates were 90 and 120 kg ha -1 for 1993 and 1994, respectively. The recovery of 15 N-labeled fertilizer (%FNR) in grain and straw was higher when applied at booting stage than at seeding in both years. In 1993, FNR varied from 37.8 to 45.7% for seeding and from 62.1 to 68.4% for booting stage treatments. The respective values were 23.1 to 30.4% and 41.3 to 50.7% in 1994. At each N rate, the proportion of N derived from fertilizer (Ndff) was higher in grain than that in straw when 15 N fertilizer was applied at booting stage. The combined recovery of 15 N fertilizer (% total FNR) applied at seeding and booting, as determined by the isotopic and the difference method, was in the same range, with a mean of 49.8% and 36.2% for 1993 and 1994, respectively. Soil N supplies for wheat during the growing season were 54 and 61 kg N ha -1 in 1993 and 1994, respectively. No priming effect of added fertilizer N on the mineralization of soil N was observed.