The fate of nitrogen and phosphorus in soil receiving 30 annual cattle manure applications

摘要

Improving nutrient management of livestock manure will benefit both agricultural production and the environment. This paper examines the fate of nitrogen and phosphorus nutrients in soil receiving 30 annual cattle manure applications under both rainfed and irrigated conditions in a semiarid climate. Solid cattle feedlot manure has been applied since 1973 in a split-plot experiment to rain-fed and irrigated well-drained Dark Brown Chemozemic clay loam at 0, 30, 60 and 90 Mg ha~(-1) yr~(-1) (wet wt) on rain-fed and 0, 60, 120 and 180 Mg ha~(-1) yr~(-1) on irrigated land under semi-arid climate conditions in Lethbridge, Alberta, Canada. The cumulative amount of manure TC, TN and TP applied between 1973 and 2003 increased with rate of manure application and the amount applied was much higher than that removed by crop uptake. Crop production used only about 12 to 33% manure N and 4% to 12% manure P applied over 30 years. Even at the recommended agronomic rate, crops only used 29% N and 10% P under rainfed and 33% N and 12% P under irrigated conditions. As a result, significant amounts of C, N and P accumulated in the soil. In addition, NO_3 accumulates in the soil profile with greater soil NO_3 content under rainfed conditions. Although soil NO_3 content was not as high, greater amounts of NO_3 have leached to the groundwater under irrigation. The residual effect of 14 years of manure application, even at the recommended agronomical rate, was long lasting. The C, N and P content in soil was still elevated even after 16 years of no manure applications. The high level of N and P content in soil could pose pollution risks as the nutrient rich soil erodes and is deposited onto nearby surface water.