Department of Plant Sciences

The use efficiency of fertilizer N decreased gradually during the grain production in black soil region in northeast China. Through a ten-year long experiment on wheat, corn and soybean, the evaluation on soil capacity of keeping and supplying N under three different soil management patterns using 15N have been conducted. The results showed there was no significant difference between the three management patterns in wheat removal of soil N, while the removal of fertilizer differed significantly; the residual rate of fertilizer was 12.84%,15.28% and17.51% respectively in pattern Ⅰ, pattern Ⅱ and pattern Ⅲ, and the loss rates of fertilizer in the three patterns were 57.93%, 49.49% and 42.07% respectively. Under the patternⅠmanagement, soil N removal by corn was less. There were no significant differences on the soil N removal between pattern Ⅱand pattern Ⅲ. The loss ratios were 54.19%, 46.61% and 39.94% in patternⅠ, Ⅱ and Ⅲ respectively. The order of utilizing N efficiency of soybean was pattern Ⅲ>pattern Ⅱ>pattern Ⅰ. The use efficiency of fertilizer N of wheat, corn and soybean were 29.93%, 32.01 and 26.85% respectively under the fertilization and rotation conditions (patternⅠ), 35.23%, 37.22% and 31.25% respectively under the management of fertilizer plus organic manure (Pattern Ⅱ) and 40.42%, 41.98% and 39.55% respectively under the management of intercrop of corn and sweet clover in which the sweet clover were returned to the field (Pattern Ⅲ).