CONTRIBUTION FROM STOLONS AND ROOTS TO ESTIMATES OF THE TOTAL AMOUNT OF N-2 FIXED BY WHITE CLOVER (TRIFOLIUM-REPENS L.)

Growth and N-accumulation rates in leaves, stolons and roots of indivi dual white clover plants were studied in three experiments using two m ethods. In a growth chamber experiment, the relative differences betwe en tissues were found to be almost constant For a wide range of clover plant sizes. The stolen dry matter (DM) production was 56% and the ro ot DM production 40% of the DM production in leaves. The N yield of st olons was 30% while N yield in roots was 34% of N yield in leaves. The effect of N application on these relations was investigated in a glas shouse experiment. Application of N reduced the root:shoot N ratio fro m 0.50 to 0.28, whereas the stolen + root:leaf N ratio (i.e. for above vs. below cutting-height tissues) was only reduced from 0.97 to 0.80. In a field trial with two contrasting N regimes, growth and N accumul ation were measured on individual clover plants. Dinitrogen fixation w as estimated by N-15 isotope dilution based on analysis of leaves-only or by including stolons. Using leaves-only did nor affect the calcula tion of percentage of clover N derived from N-2 fixation (% Ndfa) sinc e the N-15 enrichment was found to be uniform in all parts of the clov er. A correction factor of 1.7 to account for N in below cutting-heigh t tissue is suggested when N-2 fixation in white clover is estimated b y harvesting the leaves only. (C) 1997 Annals of Botany Company.