Effect of white clover cultivar on apparent transfer of nitrogen from clover to grass and estimation of relative turnover rates of nitrogen in roots

Abstract

The alSparent transfer of N from clover to associated grass was evaluated over a four year period both on the basis of harvested herbage and by taking account of changes in N in stubble and root (to 10 cm depth) in swards with perennial ryegrass and three different white clover cultivars differing in leaf size. The large leaved Aran transferred 15% of its nitrogen while Huia transferred 24% and the small leaved Kent Wild White transferred 34%. When changes in stubble and root N were taken into account the percentage of N transferred was calculated to be 5% less than in harvested herbage only, as the small leaved types had proportionately more N in the roots and stolons, but the large leaved type was probably more competitive towards the grass.Loss of N from clover roots from July to October was compared to that from grass roots in a grass/white clover sward continuously stocked with steers using a method which incorporated tissue turnover and 15N dilution techniques. Less than 1 mg N m -2 d -i was lost from the grass roots. In contrast 8 mg m -2 d -l were estimated to be lost from clover roots while 12 mg N m -2 d -l were assimilated.It is concluded that clover cultivar and competitive ability on grass have to be taken into account together with the relationship between N turnover in roots and N available for grass growth when modelling N transfer in grass/clover associations.

Nutrient relations in calcareous grassland under elevated CO 2

“…Wilson et al 1933;Masterson and Sherwood 1978;Finn and Brun 1982;Murphy 1986;Overdieck and Reining 1986a, b;Norby 1987;Ta et al 1987;Vogel and Curtis 1995;Zanetti et al 1996). In the long term, legume stimulation together with transfer of legume N to non-N 2 -®xing species via legume litter decomposition, exudation and mycorrhizal hyphal interconnections between legumes and non-legumes also increases overall plant productivity (Rao and Giller 1993;Farnham and George 1993;Seresinhe et al 1994;Laidlaw et al 1996). However, all these experiments were carried out under fertile, horticultural or agronomic conditions not representative for natural plant communities where other nutrients such as P may limit legume growth.…”

The role of arbuscular mycorrhizal fungi in the transfer of nutrients between white clover and perennial ryegrass

“…Although there was no indication from Experiment 3 of the root systems, by microscopy or from the autoradiographs that hyphal links had been involved in the transfer, it is possible that AMF external hyphae may have translocated 14 C from the donor plants and released it into the rhizosphere of the receivers. Alternatively, roots may have released carbon compounds during growth (Barber and Martin, 1976;Martin, 1977) and white clover roots turn over much faster than those of grass (Laidlaw et al, 1996). Therefore the 14 C in grass roots may have resulted from uptake of some of this released carbon.…”

“…Inoculum comprised heavily mycorrhizal root fragments and adhering soil from grass/white clover plots in an experiment already described (Laidlaw et al, 1996). The inoculum was mixed thoroughly with the sterilised soil/sand mixture in the appropriate treatments and a pad of infected roots was also inserted below the roots of transplanted seedlings.…”

“…It is generally acknowledged that in grass/white clover associations turnover of N in roots, nodules and stolons is the major source of transferable N (Laidlaw et al, 1996) but the evidence for hyphae-mediated transfer of N between legumes and grass is con¯icting (Haystead et al, 1988;Barea et al, 1989;Frey and Schuepp, 1993;Ikram et al, 1994).…”

Estimación de la fijación de nitrógeno en una vega de Tierra del Fuego por el método de la diferencia de nitrógeno

“…Otros reportes de niveles de fijación de N en leguminosas forrajeras por diferentes métodos de medición se encuentran en los rangos; 18-61 kg N ha -1 (Farnham & George, 1994) y 20 -90 kg N ha -1 (Heichel et al 1981) para Lotus corniculatus; para Trifolium repens en mezcla con gramíneas 30 -52 kg N ha -1 (Laidlaw et al 1990); 20 -53 kg N ha -1 (Laidlaw et al 1996) y 15 kg N ha -1 (Moller Hansen et al 2002) y para Medicago sativa 68 -72 kg N ha -1 (West & Wedin, 1985). Si se compara la cantidad promedio de N fijado por el trébol (98,7 kg N ha -1 ) con los fertilizantes salitre (16%N) y urea (46%N), se puede estimar que el aporte anual de N al sistema podría ser equivalente a 610 kg de salitre o 212 kg de urea por hectárea.…”