Measurement of biological dinitrogen fixation in grassland: Comparison of the enriched 15N dilution and the natural 15N abundance methods at different nitrogen application rates and defoliation frequencies

Abstract

A plant mixture of white clover (Trifolium repens L.), red clover (Trifolium pratense L.), and ryegrass (Lolium perenne L.) was established in the spring of 1991 under a cover-crop of barley. Treatments were two levels of nitrogen (400 and 20 kg N ha -l) and two cutting intensities (3 and 6 cuts per season). Fixation of atmospheric derived nitrogen was estimated by two 15N dilution methods, one based on application of 15N to the soil, the other utilising small differences in natural abundance of 15N.Both methods showed that application of 400 kg N ha-1 significantly reduced dinitrogen fixation, while cutting frequency had no effect. Atmospheric derived nitrogen constituted between 50 and 64% of harvested clover nitrogen in the high-N treatment, while between 73% and 96% of the harvested clover nitrogen was derived from the atmosphere in the low-N treatment. The amounts of fixed dinitrogen varied between 31-72 kg N ha -1 and 118-161 kg N ha -1 in the high-N and low-N treatment, respectively. The highest values for biological dinitrogen fixation were estimated by the enriched 15N dilution method.Estimates of transfer of atmospheric derived nitrogen from clover to grass obtained by the natural 15N abundance method were consistently higher than those obtained by the enriched lSN dilution method. Neither mineral nitrogen application nor defoliation frequency affected transfer of atmospheric derived nitrogen from clover to grass.Isotopic fractionation of 14N and 15N (B value) was estimated by comparing results for nitrogen fixation obtained by the enriched 15N dilution and the natural 15N abundance method, respectively. B was on average +1.20, which was in agreement with a B value determined by growing white clover in a nitrogen free media.

Farm nitrogen balances in six European landscapes as an indicator for nitrogen losses and basis for improved management

“…4). Based on Høgh-Jensen and Schjørring (1994) and Heij and Erisman (1997), i7 was simply estimated at 100 kg N ha −1 yr −1 for field peas, lupines and faba beans, 150 kg N ha −1 yr −1 for alfalfa and grass/clover ley fields with more than 25 % clover, and 20 kg N ha −1 yr −1 for other grass/clover fields with a lower clover content. This is discussed in Sect.…”

Sustainable bioethanol production combining biorefinery principles using combined raw materials from wheat undersown with clover-grass

“…Different crop production options are possible like (a) wheat straw from the traditional sole cropping cultivation with clover-grass biomass collected from a separate field as compared to (b) the present practise where clover-grass is undersown in winter wheat in order to enhance the stability of the agroecosystems lowering the need for fossil fuel based fertilizers and agricultural chemicals [12,18]. In the present study the intercrop of glucose concept used was though as a one-year option for a traditional rotation system, but obviously when the clover-grass pasture is established it can be harvested several times over 2-3 subsequent years producing a high quality biomass with very limited use of fossil inputs [11]. The basic idea is that the clover-grass is subjected to a wet separation process resulting in a juice and a pulp fraction in order to utilize the fructan and free sugars (Fig.…”

“…Undersowing and intercropping (or mixed cropping) involves growing two or more crop species on the same field lowering the need for fossil fuel based fertilizers and agrochemicals by manipulating plant interactions in time and space [7,8,11]. It is a traditional practice and very common before the ''fossilisation'' of agriculture.…”

“…Clover (Trifolium repens)-grass (Lolium perenne) pastures are important in many low-input agroecosystems due to: (a) their use, either fresh or as silage, as feed with (b) high dry matter (DM) yields ([10 t ha -1 year -1 ) in unfertilised pastures with up to 95% of the nitrogen (N) being supplied by the N 2 fixing clover [11], (c) their roots and stubble contain 60-110 kg N ha -1 reducing fertilizer requirements for the succeeding crops [7], and (d) improve ground cover [18] securing efficient uptake of available nutrients [8,12].…”

“…An advantage of intercropping cropping strategies, defined as the growing of two or more species simultaneously on the same area of land, is that the choice of intercrop species and the final composition between components can be designed [7,8,11] to produce an almost complete medium for the microbial fermentation containing all essential nutrients, especially N when including leguminous species, whereby addition of e.g. urea and other fossil based fermentation nutrients can be reduced.…”