Transfer of legume nitrogen to associated grass

In improved hill-peat a rapid increase in rhizosphere soil bacteria occurs following clover defoliation. The increase in bacterial-cell N is equivalent to 19% of the N released from the clover roots in the first 5 days after cutting. Subsequent ammonification of the immobilized N is dependent on the resistance of the microbial fraction to further degradation. In three fertilized hill soils examined, [¹⁵N]labelled bacterial N was mineralized quite rapidly, some 20% of the bacterial N being taken up by grass over 17 days. Under glasshouse conditions the rate of mineralization is different in the three soils examined, the peat providing a more favourable environment than brown earth for bacterial N transfer.