Nitrogen fixation by irrigated lucerne during the first three years after establishment

Nodulation, N2 fixation (estimated by 15N natural abundance methods) and dry matter production were studied in a lucerne (Medicago sativa) crop managed for hay production at Ginninderra Experiment Station, A.C .T. Measurements were taken in the year of establishment and during two subsequent growing seasons. There were three treatments: (1) no inoculation and no annual fertilizer applied, (2) initial inoculation and superphosphate applied annually, (3) no inoculation, superphosphate applied annually and ammonium sulfate periodically. Before planting and after each growth season, soil was analysed for extractable mineral nitrogen, total nitrogen and the 15N natural abundance of this nitrogen, to the depth explored by lucerne roots. Before planting, no appropriate root-nodule bacteria (Rhizobium meliloti) were detected in the soil and initially plants were nodulated only in the inoculated treatment. Thereafter nodulation increased on the other treatments. Eight months after sowing there were no differences between treatments in numbers of R. meliloti g-l soil or in nodulation. In the third growing season, almost 30 kg ha-1 (dry wt) of nodules were recovered to a depth of 25 cm. These nodules were primarily located on fine, ephemeral roots and many appeared to be renewed after cutting of the lucerne. In the year of establishment, dry matter yields (0% moisture) totalled 3 to 4 t ha-1 in three hay cuts. In succeeding years, total yields were in the range 10 to 13 t ha-1 in four or five cuts per season. Nitrogen removed in the harvested lucerne reached 340 to 410 kg N ha-lyr-l in the second and third years and between 65 and 96% of this N arose from N2 fixation, depending on the method of calculation used. Poorer dry matter production and N2 fixation in treatment 1 in the third growing season was attributed to an insufficient supply of available phosphorus. Fixed N removed in Lucerne hay from treatment 2 totalled at least 640 kg N ha-1 in the three years of the experiment. Also, there were substantial increases in soil nitrogen due to lucerne growth. Although soil compaction made the quantification difficult, at the end of the experiment it was estimated that there was at least an extra 800 kg N ha-1 in the total soil nitrogen under lucerne compared to strips of Phalaris aquatica grown between the lucerne plots. It was concluded that lucerne contributed at least the same amount of fixed nitrogen to the soil as was being removed in the harvested hay.

[1]  D. M. Lilley,et al.  Effects of surface application of lime and superphosphate to acid soils on growth and N2 fixation by subterranean clover in mixed pasture swards , 1995 .

[2]  N. Smith,et al.  Contribution to the N status of soil by free-living N2-fixing bacteria in a lucerne stand , 1995 .

[3]  R. Dalal,et al.  Estimates of Nitrogen Fixations by Legumes in Alternate Cropping Systems at Warra, Queensland, using Enriched -15N Dilution and Natural 15N Abundance Techniques , 1995 .

[4]  P. Saffigna,et al.  Nitrogen fixation in chickpea. II: Comparison of 15N enrichment and 15N natural abundance methods for estimating nitrogen fixation , 1995 .

[5]  M. Bell,et al.  The N2-fixing capacity of peanut cultivars with differing assimilate partitioning characteristics , 1994 .

[6]  J. Pate,et al.  Potential precision of the δ15N natural abundance method in field estimates of nitrogen fixation by crop and pasture legumes in south-west Australia , 1994 .

[7]  G. Roberts,et al.  Biological nitrogen fixation. , 1993, Annual review of nutrition.

[8]  J. Raven,et al.  The use of natural abundance of nitrogen isotopes in plant physiology and ecology , 1992 .

[9]  R. W. Sheard,et al.  In situ labeling of legume residues with a foliar application of a 15N‐enriched urea solution , 1991 .

[10]  P. A. Taylor,et al.  Factors Contributing to Reduced Productivity of Subterranean Clover (Trifolium subterraneum L.) Pastures on Acidic Soils , 1990 .

[11]  J. Brockwell,et al.  Effects of available soil N and rates of inoculation on nitrogen fixation by irrigated soybeans and evaluation of δ15N methods for measurement , 1989 .

[12]  Chris Smith,et al.  Fate of urea nitrogen applied to irrigated wheat at heading , 1989 .

[13]  S. Danso,et al.  Dinitrogen Fixation Measurements in Alfalfa‐Ryegrass Swards Using Nitrogen‐15 and Influence of the Reference Crop , 1988 .

[14]  M. P. Russelle,et al.  Nitrogen Transfer from Forage Legumes to Grass in a Systematic Planting Design1 , 1987 .

[15]  J. Evans,et al.  Nitrogen fixation and accretion of soil nitrogen by field-grown lupins (Lupinus angustifolius) , 1987 .

[16]  R. Gault,et al.  Differences in natural abundance of 15N in the extractable mineral nitrogen of cropped and fallowed surface soils , 1987 .

[17]  G. Shearer,et al.  N2-Fixation in Field Settings: Estimations Based on Natural 15N Abundance , 1986 .

[18]  J. Simpson,et al.  Field evaluation of 15N techniques for estimating nitrogen fixation in legume-grass associations , 1985 .

[19]  D. K. Barnes,et al.  N 2 Fixation, and N and Dry Matter Partitioning During a 4‐Year Alfalfa Stand 1 , 1984, Crop Science.

[20]  R. French,et al.  The annual legume pasture in cereal—Ley farming systems of southern Australia: A review , 1983 .

[21]  F. Bergersen,et al.  An evaluation of 15N methods for estimating nitrogen fixation in a subterranean clover-perennial ryegrass sward , 1983 .

[22]  W. H. Paulson,et al.  Legume and Mineral N Effects on Crop Yields in Several Crop Sequences in the Upper Mississippi Valley1 , 1981 .

[23]  I. Holford.  Changes in nitrogen and organic carbon of wheat growing soils after various periods of grazed lucerne, extended fallowing and continuous wheat , 1981 .

[24]  I. Holford.  Effects of duration of grazed lucerne on long-term yields and nitrogen uptake of subsequent wheat , 1980 .

[25]  P. Cocks,et al.  From wild plants to pasture cultivars: annual medics and subterranean clover in Southern Australia. , 1980 .

[26]  K. Norrish,et al.  Plant analyses by X‐ray spectrometry I—Low atomic number elements, sodium to calcium , 1977 .

[27]  J. Brockwell,et al.  Nodulation studies on chickpea (Cicer arietinum) , 1977 .

[28]  J. Simpson.  Transfer of nitrogen from three pasture legumes under periodic defoliation in a field environment , 1976 .

[29]  J. Simpson,et al.  Effects of management on soil fertility under pasture. 1. Influence of experimental grazing and fertilizer systems on growth, composition and nutrient status of the pasture , 1974 .

[30]  J. Brockwell.  Accuracy of a Plant-Infection Technique for Counting Populations of Rhizobium trifolii. , 1963, Applied microbiology.

[31]  R. H. Bray,et al.  DETERMINATION OF TOTAL, ORGANIC, AND AVAILABLE FORMS OF PHOSPHORUS IN SOILS , 1945 .