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Publication Date

1977

Description

In field experiments it has become clear that at a high level of N fertilization an N reserve can be built up in the soil-plant system which can have a residual effect on the regrowth of a grazed or mown pasture. This residual effect is most apparent when the regrowth is not fer­tilized with N. In the experiments on clay soil comparisons were made between the amounts of residual N of high-and low-N pretreat­ments. This was done by calculating the dif­ference between N application and N uptake during the pretreatment period. In the high-N pretreatments this difference was about 80 to ll0 kg N per ha higher than in the low-N pre­treatments. In the absence of new fertilizer N the residual effect of that quantity of N was found to be equivalent to 25 to 70 kg N per ha at 5 weeks of regrowth. Assuming no losses by leaching or denitrification, this meant a recovery of about 55 % in July/August, decreas­ing to about 25 % in September. When fertiliz­ing with N, the residual effect became smaller because it was obscured by the freshly applied N.

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The residual effect of fertilizer nitrogen on grassland within one growing season

In field experiments it has become clear that at a high level of N fertilization an N reserve can be built up in the soil-plant system which can have a residual effect on the regrowth of a grazed or mown pasture. This residual effect is most apparent when the regrowth is not fer­tilized with N. In the experiments on clay soil comparisons were made between the amounts of residual N of high-and low-N pretreat­ments. This was done by calculating the dif­ference between N application and N uptake during the pretreatment period. In the high-N pretreatments this difference was about 80 to ll0 kg N per ha higher than in the low-N pre­treatments. In the absence of new fertilizer N the residual effect of that quantity of N was found to be equivalent to 25 to 70 kg N per ha at 5 weeks of regrowth. Assuming no losses by leaching or denitrification, this meant a recovery of about 55 % in July/August, decreas­ing to about 25 % in September. When fertiliz­ing with N, the residual effect became smaller because it was obscured by the freshly applied N.