No abstract

Monitoring soil phosphorus (P) changes under continuous cropping over decades is an important agronomic and environmental issue. The aim was to determine soil P dynamics in the plough layer as a function of cumulative P budgets (Bcum) across extended cropping periods (7, 12, and 17 yr) for four rates of mineral P fertilization. This field experiment was established in 1975 on a slightly alkaline, sandy loamy soil (luvic Arenosol). Soil P was assessed by three P tests: the concentration of P ions in solution (Cp), Olsen (P Ol ), and Mehlich-3 P (P M3 ). Annual P budget was calculated as P applied minus P exported by the grain. The Bcum values were the sum of annual P budgets. Bcum, Cp, P Ol , and P M3 values were significantly influenced by cropping periods and P rates. The nine combinations (3 periods · 3 soil P tests) of P dynamics versus Bcum were described by linear regressions. For each soil P test, all means fell on the same regression line for the three cropping periods indicating that the P transformation rates were similar for positive and negative P budgets. Relationships depended on soil test P but did not vary for cropping periods. For this specific soil, we calculated that a change in P budget of 100 kg ⁄ ha would change Cp, P Ol , and P M3 by 0.11 mg ⁄ L, 3.3 mg ⁄ kg, and 14 mg ⁄ kg, respectively. Although this result needs to be confirmed and extended to other soil types, we conclude that a single year of soil sampling after a decade of experimentation would be sufficient to establish the relationship between soil P status and P budgets.

No abstract

No abstract

(1 and 160 kg N ha (1 every 2 yr and were enriched or not with 2 g of soybean residues. Under controlled conditions, the cores were subjected to various FTC treatments, with each cycle consisting of 5 d of freezing and 5 d of thawing. The water-extractable P (Pw) and Mehlich-3 extractable P (P M3 ) contents were higher in soil samples collected in the spring compared with those collected the previous fall. After one and three FTC, Pw values averaged 17.4 mg kg(1 in NT and 7.5 mg kg (1 in CT and were not influenced by the addition of soybean residues. At the end of the sixth FTC, the Pw content of soil cores collected in NT increased up to 25.9 mg kg(1 with the addition of residues but decreased in the absence of residues. The effects of freezing and thawing on soil cores with crop residues occurred at the end of the sixth FTC, where P M3 in the NT ' residues treatment increased twofold, reaching 100 mg P kg (1 . These results confirm that both Pw and P M3 in NT can be enhanced by increasing the number of FTC.

No abstract

No abstract

No abstract